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Dcell & DSC version 2 Manual - Load and Force Cells, Indicators

1. read out random data using E G 1001 LKD1 gt 03123 e g 1001 LKD2 gt 11723 e g now calculate the unlock value send it to turn the lock off using e g 1001 ULCK 173 To rewrite security code you would send e g 1001 LKK1 7207 1001 LKK2 42219 1001 LKWR 3123 matching LKD1 NOTE The value sent to LKWR value must match the current LKD1 value This is to prevent accidental writes The VisualLink protocols for DCell DSC devices also provide convenience functions for performing these operations If device is a VisualLink instrument object of an appropriate type then device PerformUnlock k1 k2 k3 k4 unlocks the device where k1 k4 are the key code byte values k1 the low order byte device RewriteSecurityCode k1 k2 k3 k4 installs a new security code value where k1 k4 are the four bytes of the code 42 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 10 Additional Software Features This chapter describes a variety of features not covered elsewhere SOUT Output Selection The control ICNT can be used to make the SOUT value track any one of several different output parameters Every time a new main reading value is processed the SOUT parameter is updated to contain a copy of the current selected output reading This is important for a number of other operations as described in the following sections e Continuous output SOUT is
2. into intended parameters and variables This can be downloaded from our website http www mantracourt co uk vllitre htm A great advantage of using VisualLink is that it is protocol independent so that the same application can be used with different types of DCell DSC if required This is possible because the command set itself is the same for all devices regardless of the communications protocol used see Chapter 12 Software Command Reference for the complete list Commands are generally referred to by their mnemonic names as used in the ASCII protocol VisualLink uses these same names for the instrument properties which access the commands so this makes the property set of a DCell DSC device as a VisualLink instrument object the same for all product types Other simple ways of using the different protocols are as follows 1 The ASCII protocol only uses basic printable characters and so can be accessed with a simple terminal program like Windows HyperTerminal 2 The MODBUS protocol can be accessed via a proprietary generic MODBUS application For evaluation purposes we suggest the free shareware demo of ModScan32 from Win Tech software visit www win tech com 3 MANTRABUS needs a purpose designed program to handle full 8 bit data bytes and the proprietary checksum calculations VisualLink and VisualLink Lite provides this Common Features of All Protocols The communications protocols are all of the master slave
3. Di 63 SERH In Jo serial number high Ji Jop SIN fint Rw station numpe a oi BAUD Inte Ju baud rate seet Jo og ICNT pe Ju oumutseledt PS 0 RATE pute Rw___ reading rate see Jo Io DP byte RW digits after point 37 75 DPB byte RW digits before point 38 77 e dat E Sai Ems fa CT1 5 boet Rw __ tempco TEMPs 111 115 223 231 CTG1 5 boat RW __ tempco gain adjust_ 116 120 233 241 CTO1 5 boat RW__ tempco offset adjust_ 121 125 243 251 CGAI ffoat Rw _ fcellgain po COES West Rw fcelloffsst br o CMIN ffoat Iw eelrongemn br eg CMAX West RW__ cellrangemax bh 9 CLN byte Iw innen Jon fio CLX1 7 feat RA lin raw values Pree Wis CLK1 7 float RW lin corrections GI Gi 123 135 SGA Jost RW__ systemgain po Da SOFS West RW__ systemoffset Fi a SMIN Jost Iw system rangemin bi Dag SMAX Weoat RW__ systemrangemax FS i USR1 9 RW g p storage values 81 89 163 179 EEAD fit RW EEPROM address oo ja EEV byte RW EEPROM value 183 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 59 x read EEPROM b Dos x write EEPROM Do 205 K take snapshot 103 207 byte W unlock 104 209 i lock random data 105 6 211 213 write new lock code 107 215 int wo new lock code data 92 93 185 187 GD ebe rr bon Go el E o 60 Mantracourt Electronics Limited DCell a
4. However any tests to establish temperature corrections must always be carried out as close to normal operational conditions as possible and this includes operation at the same power supply voltage Changes in power supply voltage must also be avoided Of course the measurement may be inadequate if a nominal temperature correction is wanted i e a known calibration change per degree or if a temperature measurement is wanted for its own sake In these cases the temperature calibration can be adjusted if required see Temperature Calibration in Chapter 10 Additional Software Features The absolute accuracy of the TEMP measurement would not exceed 1 C at best due to the relatively simple sensor used Temperature accuracy problems can mostly be eliminated by fitting an external temperature sensor near to the sensor See also Fitting an External Temperature Sensor in Chapter 13 Installation Parameter Calculations and Example This is based on Method 3 above i e compensation is designed so that the measured test results will be exactly compensated at the test temperatures Suppose load tests are performed at a series of different temperatures Ti i 1 n Known loads xA xB are applied and the resulting electrical readings at each temperature are ELEC eAj eBj for each Ti Ideal offset and gain factors can then be derived for each temperature gaij xB xA eBj eAj ofsj eAj xA COFS CGAI
5. For baud rate problems see previous section You can try all 3 protocols if confused but this should be indicated by the product code on the product label if it has not been removed Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 73 If a station number is unknown it can be reset via broadcast command as long as the device is the only one on the bus If two devices on the same bus end up set to the same bus address they can no longer be commanded separately The only solution is to remove one device from the bus and connect it exclusively to a PC to change its STN Always remember that a reboot power off or RST command is needed to change settings 74 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 15 The VisualLink Application Introduction An evaluation version of VisualLink the SCADA package from Mantracourt is available with special designs constructed to communicate with the supplied DCell and DSC instruments This will enable you to test and program the instrument Limitations The evaluation version of VisualLink allows you to do everything that can be achieved with the full version except that a pop up notice will appear every minute The example designs mentioned in this manual are special designs that will not display this notice If you save one of these designs in your version of VisualLink you will no longer be able to run it without
6. The memory layout of the 4 byte floating point numbers is MSB 31 Sign bit 1 negate 30 22 Exponent 7 bit excess 127 LSB 21 0 Mantissa 23 bit fraction with implicit 1 The value of the number is thus 1 Von 2 Exponent 127 4 Mantissa Note the assumed 1 before the mantissa The exception to this is the special value 0 0 which is represented as 4 zeroes E G a floating point number of 12345 678 is represented as hex C6 40 E6 B6 This is transmitted in nibble format as hex 0C 06 04 00 OE 06 0B 06 End of Data Identifier As the protocol has no fixed length or length identifiers the last nibble of data sent to the device has its MS nibble set This indicates to the device that all data has been received amp the next 2 bytes will be checksum data ACK amp NAK Mantrabus II supports ACK amp NAK sending ACK 06h at the end of a successful operation and NAK 15h for an unknown command or failed operation These are always preceded by the station number see examples below N B Mantrabus II will not transmit a NAK for invalid checksum data but instead remains silent This is different from the behaviour of the older Mantrabus I Writing to Variables Station number and command number are followed by 8 bytes of nibble data the last having its MS bit set followed by the 2 checksum nibbles E G To write the value 100 0 Floating point 100 0 42h C8h 00h 00h to variable CGAI command nu
7. e Select the protocol appropriate to the product code e Select the station number according to the device serial number as described above If you need to use a serial port other then COM1 See Chapter 15 The VisualLink Application Now hit the Start Communications button 12 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Viewing Device Data The following main Communications Page should now appear Figure 2 6 Device Communications Page DSC amp DCell Evaluation YisualLink Dcell DSC Device Communications i Device MantraASClI2 type Serial Number 0000114823 Station Number 023 MAIN OUTPUTS WARNING FLAGS SOUT 047 4701 FLAG 2763 SO SE TEMP 12 87 Temperature range TEMPUR TEMPOR Sensor impedance EXCUR lt EXCOR Excitation off EXCSC Elec input overrange ECOMUR ECOMOR Cell value overrange CRAWUR CRAWOR Sys output overrange SYSUR SYSOR Comms receive error COMMSFAIL Power fail reboot REBOOT Restart Comms System Calibration Control Settings At the top are shown the device type serial number and current communications station number The main device output values are shown on the left The diagnostics flags are shown on the right If there is a communications problem a separate Error window will appear after a few seconds check all settings and Chapter 14 Troubleshooting for additional advice Once communications are established the screen displ
8. lt CR gt if the value 32 1 and format settings are DP 3 and DPB 5 the response string will be 00032 100 lt CR gt Action Command If the command is accepted by the device then a lt CR gt is transmitted Example A command to reset device 14 would look like 1014 RST lt CR gt the response string will be just lt CR gt Broadcast Commands If the station address in a command message is 000 this means a broadcast command All slaves act as normal on a broadcast command but do not respond Example A command to all devices on the bus to sample their inputs would look like this 1000 SNAP lt CR gt there is no response Bad Commands If any command is not understood by the device then a is transmitted followed by a lt CR gt Example A unrecognised command correctly addressed to station 173 1173 XYWR lt CR gt produces the general error response lt CR gt Continuous Output Stream When the STN is set to 999 the ASCII protocol also provides a continuous output stream facility The new SOUT value is transmitted on every result update see Chapter 10 Additional Software Features The MODBUS RTU Protocol MODBUS is a proprietary standard of Modicom Inc The full specification is quite complex including a timeout based framing strategy and polynomial CRC calculation so full details are not given here Refer to Modicom documentation Knowledge of the MODBUS protocol is therefor
9. 0 ECH RRE Two Point Calibration Calculations and Examples Values for both the Cell and System calibrations can be set up in any of the ways described under Calibration Methods in Chapter 3 Basic Setup and Calibration Examples are given here for two point calibration as this is by far the most common method Cell Calibration The scaling parameters are COFS CGAI CMIN and CMAX COFS is in nominal percent full scale from electrical calibration CGAI is in cell units per CMIN CMAX are in cell units The cell output calculation is in the absence of temperature and linearity corrections CELL ELEC COFS x CGAI If we have two electrical output ELEC readings for two known force loads we can convert the output to the required range So if test load fA gt ELEC reading cA test load fB gt ELEC reading cB then calculate the following gain value CGAI fB fA cB cA and the offset is COFS cA fA CGAI The outputs should then be CELL fA fB true force values as required System Calibration For system calibration the arrangement is very similar The parameters are SGAI SOFS SMIN and SMAX So SOFS is in cell units SGAI is in engineering units per cell unit SMIN SMAX are in engineering output units The system calculations are SRAW CELL SOFS x SGAI SYS SRAW SZ Mantracourt Electronics Limited DCell amp DSC Version 2 User Manu
10. CMAX CLN CLX1 7 CLK1 7 SGAI SOFS SMIN USR1 9 g p storage values float RW 81 89 163 179 EEAD EEV LKK1 2 RST JD Dn Du O EERD XS Du f EEWR o o K ho bpo O SNAP K Y Ro ek LKD1 2 lock random data int RO 105 6 211 213 LKWR write new lock code int WO 107 215 58 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Table Key Denotes a range e g CLK1 7 means CLK1 to CLK7 Access RW RO WO X read write read only write only execute Datatype float int byte 4 byte real 2 byte integer 1 byte integer none MB reg register number for MANTRABUS protocol MD reg start register address always odd for MODBUS protocol NOTES All Modbus accesses are in register pairs Modbus addresses are just 2 MANTRABUS 1 ICNT output index values correspond to the position in this table SOUT 0 SYS 1 Table 12 2 Commands in Alphabetic Order ASCII datatype access description Modbus name Command _ register SOUT RO selected output 9 19 SYS float RO main output 10 21 TEMP RO temperature dE SRAW ffloat RO raw system output 12 25 CELL ffloat_ RO celloutput 3 Si FLAG hn Iw ergoe 14 Ge CRAW 31 ELEC 33 ECOM 35 ERAW 37 EXC 39 FILT byte RO filter averaging 20 41 OFFS char RO offset channel flag 21 43 SZ float RW system zero 22 45 SYSN float RO snapshot result 23 47 VER bus RO __ software version Jop e SERL_fint____ RO__ serialnumberlow
11. Overview The DCell and DSC products are miniature high precision Strain gauge Converters converting a strain gauge sensor input to a digital serial output They allow multiple high precision measurements to be made over a low cost serial link Outputs can be accessed directly by PLCs or computers or connected via various types of network telephone or radio modem all without compromising accuracy Key Features Ultra miniature The DCell puck format can be fitted inside most load cell pockets and similar restricted spaces The DSC cards are similarly very small optimised for mounting as a component onto custom PCBs High precision 10ppm basic accuracy equates to 17 bit resolution with comparable stability far exceeds standard instrument performance Low power Low voltage DC supply 8 5V min typically 40mA per device including 350R strain gauge Adjustable sensitivity Configured for standard 2 5mV V full scale strain gauges as supplied A single additional resistor configures the input between 1 and 100 mV V full scale Temperature sensing and compensation Built in temperature sensor and advanced 5 point temperature compensation of measurement Linearity compensation Advanced 7 point linearity compensation Serial output Lower cost cabling improved noise immunity and longer cable runs with no accuracy penalty Device addressing allows up to 253 devices on a single bus drastically reducing cabling cost and comp
12. The following features are of importance 2 Wire RS485 Connection Baudrate Support Must support at least the rates to be used Driver enable Control Can be either hardware control line driven normally via DTR or automatic host transmitting enables driver Hardware Control requires special host software especially under Windows and the serial port hardware must be suitable VisualLink provides support for this on most PCs For Automatic Control the converter detects host transmissions It usually needs to be set to the correct baud rate and may only support certain specific baudrates Power Options Can be self powered i e from the RS232 port maybe RTS DTR or Tx data pin or require an external power supply Although a self powered converter seems attractive it will usually have a limited drive capability It will thus only drive a reasonably short bus with a few devices on it The RS232 amp RS485 bus converter Mantracourt supplies as standard is an externally powered device supporting all the DCell DSC data rates It features completely automatic data rate detection no setup switches and automatic enable control switching with opto isolation OG GND PSU must be connected to GND of the RS485 device Input Sensitivity Adjustment If your strain gauge does not deliver a 2 5mV V full scale output you may want to adjust the sensitivity of the electronics hardware and or the software gain controls If you want to te
13. The lookup table based on parameters CLXi CLKi defines an offset adjustment based on the CRAW value which is then added in to give the final CELL output So linearity correction is applied after any temperature compensation The parameters involved are CLN sets the number of linearisation points from 2 up to 7 CLX1 7 raw input CRAW value points CLK1 7 output CELL adjustments to apply at these points They are used like this e The number of calibration points is set by CLN from 2 up to 7 e Raw input value points are set by CLX1 CLX2 CLX7 or up to the number set by CLN These must be arranged in order of increasing input value e The output corrections at these points are set by CLK1 CLK2 CLK7 e Corrections are specified in thousandths of a cell unit so a CLKi of 1 0 actually adds 0 001 to the CELL output Internal Calculation This uses the same basic interpolated table lookup method as for temperature compensation First a working table index i is derived from the current raw input CRAW x as follows n number of points used as set by CLN When x lt CLX1 then i 1 When x gt CLXn 1 then i n 1 Otherwise i is chosen so that CLXj lt x lt CLX 1 The resulting interpolated adjustment value is then calculated as ofs CLKj CLKj 4 CLKj x x CLXj CLXi 1 CLXj Then the compensated cell value is calculated as CELL CRAW 10 x ofs 34 Mantracourt Elect
14. User Manual Issue 1 3 Table 12 2 Commands in Alphabetic Order 59 Chapter 13 Installation eegegiekue eege ENEE EE ONSE Kee EENS 61 BetoreJnstallston 2000 61 Physical MOUMUMG EE 61 Electrical Protector Tee EeceEek e eh teeta bee terse ae a ee et el vn ad oa 61 Moisture Protection serrana u e A RE E N E E E E T ENTA 61 Soldering Methods cccccccesssssceesssseeeecsseeeeeesseeeeeecseeaeeeesceeeeeecsesaeeeeeceeeeeeseeesaeecescesaeeeseseeeeesseaaeeseseeeeess 62 Power Supply HReouirements Snn En Ennn EE nnnn nenna ennnen nEn nn ennnen 62 Identifying Sensor End Connections tta nrt ttt trett trna r EEEn E ranner nnn nE EEEren 62 Figure 13 1 DCell Input Connections ceccccceeccceecceeeececeeeeeeeeseeeeeseeeecaeeeseeeeeeaeeeeeeeecaeeesceeseneeesseeeees 62 Figure 13 2 DSC Input Connections cccccceececeeeeeeeeceeeeeeeeeeeeeeecaeeeseeeeeceeeesesaeeeceeeecaeeeecaeeseeeeeseeeeeeees 63 Identifying Bus End Connections esssesssesssessetestressrsstnsttnetnnnstnnsttntttnnstnntttatttnrttnnstnnsnnnetnnnnnn nnn nnnnn ne 63 Figure 13 3 DCell Bus Connechons ttnt Ennntn ttnn EEn nE nnr En Ennn Emeen 63 Figure 13 4 DSC4 RS485 Versions Bus Connections cc ccceececeeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeseeeeeseeeeees 63 Figure 13 5 DSC2 RS232 Bus Connections ceccccesceceeeceeeeceeeeeeeeeceeeeeeneececeeeeceeeeceeeeeecaeeseneeeseeeseees 64 Sensor Cabling and Grounding Requirements sssesssesseeseitett
15. be stored for the device itself the load cell and the installed system characteristics Electrical The Electrical calibration produces corrected electrical readings from the internal measurements This is factory set by Mantracourt during the production process There are effectively three electrical calibrations one for each output rate setting The main outputs from this are e ELEC is the raw electrical output in full scale units e TEMP is a device temperature measurement in C There are also two flags ECOMUR and ECOMOR not shown on the diagram which indicate an input electrical under or over range The electrical calibration is not covered in detail here because it normally never changes after manufacture and is not controlled by communications parameters A fuller account is given in Electrical Calibration in Chapter 10 Additional Software Features 24 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Cell The Cell calibration converts the raw electrical output into a cell force reading This can be used by an OEM sensor manufacturer to provide a standard calibrated output in force units which could be based on either typical or device specific calibration data This stage also includes the temperature and linearity corrections not covered here The outputs from this are CELL is a load cell force reading in Force units e g KN CRAWUR and CRAWOR
16. limit values set in output units The units and functions of the main scaling controls can thus be summarised as Cell Calibration COFS fs ELEC value offset ELEC value giving CELL 0 CGAI force fs CELL ELEC gain factor CMIN force Minimum value for CRAW CMAX force Maximum value for CRAW System Calibration SOFS force CELL value offset CELL value giving SRAW 0 SGAI eng force SYS CELL gain factor SMIN eng Minimum value for SRAW SMAX eng Maximum value for SRAW SZ eng SRAW value offset SRAW value giving SYS 0 where fs is per cent full scale force is force units and eng is engineering units Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 25 The SOUT Main Output Value The main output value SOUT is normally an identical copy of the final system output SYS In fact however SOUT can be selected to track any of a whole group of different output parameters Details for this are given in SOUT Output in Chapter 10 Additional Software Features A Complete Picture of Readings Processing For completeness the following diagram shows a total overview of the calibration processes Figure 5 2 Readings Processing Full Electrical Outputs Cell Calibration System Calibration CTOXx CTXx COFS gt 1 CTGx CTx WH CMIN SIS CLKx CLXx KC The detailed operation of the Cell calibration stage a
17. output value but generally at longer intervals If some warnings are active i e FLAG is non zero then the host tries to cancel the warnings found by writing FLAG 0 The host then notes whether the error then either remains i e couldn t be cancelled or if it disappears or if it re occurs within a short time and will take action accordingly The warning flags are generally latched indicators of transient error events By resetting the register the host both signals that it has seen the warning and readies the system to detect any re occurrence i e it resets the latch What the host should actually do with warnings depends on the type and the application Sometimes a complete log is kept sometimes no checking at all is needed Often some warnings can be ignored unless they recur within a short time Warning flags survive power down i e they are backed up in non volatile EEPROM storage Though useful this means that repeatedly cancelling errors which then shortly recur can wear out the device non volatile storage see WARNING Finite Non Volatile Memory Life in Chapter 3 Basic Setup and Calibration The flags EXCSC and OLDVAL are exceptions to the above scheme These are both set and unset by the device software and are not stored in EEPROM See below for more details Meaning and Operation of Flags The various bits in the FLAG value are as follows Bit Value TI Description Name O o Excitation under range a
18. serial number This is decoded as serno 65536 SERH SERL The VisualLink DCell DSC protocols include a convenience Serial Number property that automatically does this The nine parameters USR1 9 are read write real values These can be freely used for non volatile storage of customer information such as OEM serial numbers or calibration dates Software Reset The RST command forces a device reset equivalent as near as possible to power cycling The reset action may take up to about a second to take effect followed by the normal start up pause another 1 2 seconds 46 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The VisualLink protocols RST property imposes a 3 second application delay to avoid communications failure during a reset operation The command is mostly used when a device reboot is required to changes to certain parameters take effect such as STN and BAUD Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 47 Chapter 11 Communication Protocols This chapter gives details of communication protocols and bus connections There are effectively three layers to DCell DSC communications 1 Internally all devices support the same command set as described in Chapter 12 Software Command Reference 2 Command accesses are coded into actual byte sequences according to a communications protocol Several different protocols are availab
19. 5104000126 Supply mg UNIEN Geet ae Z MANTRACOURT ww A TSO Z Tel 44 0 1395 232020 W i a Sen Fax 44 0 1395 233190 GND Serial Number Exc Manufactured In the UK CE 99 1 DLCPKASC ASCII output DLCPKMAN MANTRABUS output DLCPKMOD MODBUS output For a DSC card the Product Code is one of the following 6 types DSC4AS RS485 output card with ASCII protocol DSC4MA RS485 output card with MANTRABUS protocol DSC4MB RS485 output card with MODBUS protocol DSC2AS RS232 output card with ASCII protocol DSC2MA RS232 output card with MANTRABUS protocol DSC2MB RS232 output card with MODBUS protocol NOTE For evaluation purposes the electrical output standard RS485 or RS232 is not important Your kit should contain the correct equipment to connect the device to a PC The product code should match your original order The serial number of the device is also shown The station number of a new DCell DSC device is set up to have the same last 2 digits as its serial number E G 817752 gives station 52 while 103800 gives station 100 N B this is only the factory set value and its value changed by a previous user Make a note of both the protocol and station number now The communications application needs to be told both the protocol to use and the station number to communicate with Connecting Up The Evaluation Kit For RS485 Connect the PC using the 9 way D Type to the RS232 RS485 converter Plug the cable provided in
20. 517 153 Date 15 01 04 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 79 80 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3
21. 7 2077 0 120721 0 00114510 and SMAX SMIN 1 10 NOTE The usual method for weighing systems is to make point 1 the unloaded state which should read zero and point 2 with a known test weight on which should read the value in required units of the test weight This approach is simpler because you can remove the offset first as explained in the previous section Method 4 Multi point Calibration Test For ultimate accuracy to a whole series of point measurements may be taken to determine the best linear scaling of input output Effectively a best line through the data is then chosen and the calibration is set up to follow the line Testing of this sort is also used to establish linearity corrections and similar tests at different temperatures are used to set up temperature compensation see Chapter 6 Temperature Compensation and Chapter 7 Linearity Compensation Changing Device Communications Settings This section explains the other most commonly used settings those used to control device communications The device bus standard and protocol type are specified by the product code and fixed during manufacture However the communications station number bus address and baudrate are programmable via communications parameters Care is needed when changing these to avoid losing communications with the device so this section demonstrates how to do this correctly If you lose all communications with the dev
22. 7 Linearity Compensation This chapter describes the Linearity Compensation features and how to use them Purpose and Method of Linearisation Load cell sensor outputs are never precisely proportional to the input applied load If the graph of the measurement output against the true value shows slight deviations from the ideal straight line then slight errors remain even when the basic calibration offset and gain is as good as possible Linearity compensation adjusts the raw measurement by a small amount that is calculated as a function of the raw measurement value itself Ideally this will adjust the output response for any given input load by exactly the right amount to place the final result onto the ideal straight line The DCell DSC non linearity compensation uses a single lookup table similar to those used for temperature compensation see previous chapter This provides a linearly interpolated compensating value with up to 7 control points which is then added to the output result Generally linearisation is a finer level of compensation than temperature compensation It should only be applied after the basic Cell calibration and temperature compensation if any have been set up Although the tests are generally simpler than testing over temperature the accuracy requirement is often greater See below for notes of possible difficulties to be avoided Control Parameters Refer to Figure 5 2 Readings Processing Full
23. 8 7735 so SRAW 498 7735 0 487495 x 1 003580010 0 5006987 The remaining errors are due to rounding the parameters to 7 figures Internal parameter storage is only accurate to about 7 figures so errors of about this size can be expected in practice 28 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 6 Temperature Compensation This chapter explains how to use the Temperature Compensation facilities to compensate for changes in the measurement with ambient temperature Purpose and Method of Temperature Compensation Most measurement methods are affected by changes in temperature and uncompensated load cells are especially sensitive having a large overall temperature coefficient Temperature compensation adjusts the measured value in a way that depends on a temperature measurement so that ideally the output does not depend on the current temperature In practice it is usual to refer to a calibration reference temperature The ideal output value is then what the reading would have been if made at the reference temperature The DCell DSC temperature compensation facilities make adjustments to the Cell calibration parameters i e gain and offset which depend on temperature according to a digitally programmed curve These adjustments are automatically applied based on the current device temperature measurement With some care this can remove the need for the usual e
24. 98 We choose these precise test points as our linearisation reference points so CLN 5 CLX1 0 0010 CLX2 100 44 CLX3 200 57 CLX4 349 75 CLX5 449 98 Note that these are the raw reading values not the known true values Now calculate all the residual errors and set up the correction factors CLK1 10 x x1 c1 1000x 000 00 0 0010 1 0 CLK2 10 x x2 c2 1000x 100 13 100 44 310 0 CLK3 10 x x3 c3 1000x 199 72 200 57 850 0 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 35 Note on the Example If you graph the errors from the above example the results look like this 0 4 0 2 0 0 2 0 4 0 6 0 8 1 This doesn t show any very definite linear trend so the calibration is okay However there is a big jump between points 3 and 4 which might be worth a more detailed investigation Some important features of the error curve could have been missed by the test 36 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 8 Self Diagnostics This chapter describes the use of the in built self diagnostics All the self diagnostics rely on the FLAG parameter which is a 16 bit integer register in which different bits of the value represent different diagnostic warnings Monitoring Warning Flags The flags are normally used something like this FLAG is read at regular intervals by the host like the main
25. AUD parameter is a read write byte value specifying a standard communications baudrate according to the following table baud rate 2400 4800 9600 19200 38400 bps BAUD can only take the values shown above If set lt 1 or gt 5 the baud rate defaults to 9600 Warning When changing this setting it is possible to lose communication with the device As well as keeping track of the correct baudrate it is also essential in this case to be sure that your hardware supports the rate you are changing to The evaluation kit supports all possible DCell DSC baudrate settings When changing baudrates you should not see any noticeable difference except maybe slight changes in responsiveness when changing parameter values However if you design your own communications applications with VisualLink or otherwise higher baudrates will allow faster readout rates etc Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 21 Lowering the baudrate is generally only needed where very long cable runs are used to improve communications reliability To change the baudrate follow a similar sequence to changing the STN value First set BAUD to the new value Now hit the RST button to reboot needed to make the device start using the new value Wait for the VisualLink Errors window to appear Return to the startup page by hitting the Restart Comms button Clear the errors and close the Error
26. DCell amp DSC Miniature Hi Precision Strain Gauge Converters Version 2 Converts a strain gauge sensor input to a digital serial output www mantracourt co uk User Manual Instructions Contents Chapter TIntroductonn siiiscscscccccae ege EEN ege ENEE eege NEE EE 4 OVeEV EW sni rn E EEN SEENEN 4 Key Features icici 4 areri e e i deaa e ea eege de Sege eeh Andes d er Ea dd etara daiat 4 ee IR le A The Product Range EE 5 leen RR WEE 5 Additional DSC Variants Available eseneseneeeneeseeesensstnteenntssnsstnsrtnnntrnsstnsrtnntnnnnnntnntnnnnnnntnnatnnnnnnnnn nenna 6 Some Application Examples ccsccccceeseeceeeeececeeeeaeeeceaeeecaaeeeeeneceeaeeeeceeeeseeeeeeeesscaeeeecaeeeeeeeseeeseeeeeeees 6 Chapter 2 Getting Started with the Evaluation Kit ccccccseceeseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeaeseseeeseaeeseeeeeeenes 8 The Evaluation EE 8 Dee ect sit EE A AE E SA ee EE 8 Figure 2 1 Evaluation Kits for the DCell amp DC 8 Other Things you Will need 8 Checking the Device Protocol Type and Station Number 9 Connecting Up The Evaluation Kit For RGAgn ennenen 9 Figure 2 2 DCell RS485 Versions Evaluation Kit Communication 10 Figure 2 3 DSC4 RS485 Versions Evaluation Kit COnnectionS c ccccceecceeeeeceeeeseeeeeeeeeeereeeeeeeeeees 10 Connecting Up The Evaluation Kit For Rn 10 Figure 2 4 DSC2 RS232 Versions Evaluation Kit COnnectionS ccccceeeeceeeeceeeeeseeeeeeeees
27. Excitation over range 2 4 Temperature under range TEMP TEMPUR 3 8 Temperature over range EM TEMPOR _ 4 Ip Strain gauge input under range ECOMUR 5 Strain gauge input over range ECOMOR 4 Cell under range CRAW CRAWUR 0 AIN gt NIO 6 EE 12 System over range SRAW SYSOR 2048 unused reserved EE 12 4096 unused reserved 8192 Stale output value 14 16384 Excitation Short circuit cell currently off EXCSC AIN NOTE The mnemonic names are used by convenience properties in VisualLink but are otherwise for reference only the flags can only be accessed via the FLAG parameter Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 37 The various warning flags have the following meanings The EXCSC and EXCUR EXCOR warnings are triggered by measurements of the bridge excitation voltage EXCOR is set when the excitation measures high sensor open circuit EXCUR is set when the excitation measures low sensor short circuit EXCSC is set while excitation is turned off to reduce over currents but this flag is self resetting See Cell Excitation Management below TEMPUR and TEMPOR indicate temperature under and over range The temperature minimum and maximum settings are part of the temperature calibration fixed at 50 0 and 90 0 C ECOMUR and ECOMOR are the basic electrical output range warnings These are tripped when the elect
28. S seiersen arar ae est fa Bete eee eee etter ed Gael 48 Choice of Bus Formats EEA E ete i ao eh hee eeh tad eT cede pee ahd 48 The RS232 Bus Standard 2 ccccccceccccceeccceenceceseeeeeeceeeeaeeecaeeesaaeeceaceeseaeeeseaeeesaaeeesaeeeseaeeceaeeeesseeteneeeteneees 49 The RS485 Bus Standard cccccccceccceesceeeeeeeeeeeececeneeeceeeceeeeesaeeeeeaesecaeeesaeeseaeeseeeeseeeeeeseeeeaeeeesseeeseeeess 49 Communications Protocols ccccescceeecceeeceeeeeeeceeeeeeceeeeeaeeeceeeesecaeeeaeeseaaeseeaaesecaaeeseaeeseaeeseeeeeeeeeeseeeeeees 49 Choosing a ProtOCol EE 49 Communications Software for the Different Protocols ccc cceeeceeeeeeeceeeeeceeeeeeseeeeceseeeseseeetneeeeeneeeeas 50 Common Features of All Protocols 2 cccccceeeeeeeceececeeeeaeeeeeacecceaeeeseneeeseeeeseaeeeeceeeseaeeeseeeeeeeeesseeees 50 Data Type Conversions and Rounding ccccccssseceeseseseeeecsseeeeeseseeeeeeccsueeeeecceeeeeessseeeeesseneeeeeestieeeeeses 51 TNEASCIMPROLOCOl 4c EE ge eetexcs EAEE A E E E ee ty veg EE 51 The MODBUS RTU PYrotocol orestis eere ne ra aaae aea e Aae aih A areata ne Eea ed adare ee ate Etk ai 53 The M ntrabus M Protocols e ne e a aa abe a a EI E EE E E ETE EE 56 Chapter 12 Software Command Reference ccccecceseeceeseeeeseneeeseeeeeseeeeseneeeeaeeeeeneeeeeneeeseeeeeeeeseeeseeeneneeeees 58 Table 12 1 Commands in Access Order 58 2 Mantracourt Electronics Limited DCell amp DSC Version 2
29. SOFS values to be used E G a10 tonne load cell has a calibration sheet specifying 2 19053mV V full scale output and 0 01573mV V output offset SOFS is set to the input offset in of 2 5mV V which is 0 01573 2 5 100 0 629200 SGAI is set to 10 100 2 5 2 19053 0 114128 SMAX and SMIN can be set to 10 0 and 0 1 if negative loads are not expected in this case NOTE Methods 1 and 2 require no load tests This means that systematic installation errors cannot be removed such as cells not being mounted exactly vertical The accuracy is also limited by the DCell DSC electrical calibration accuracy which is about 0 2 The remaining methods require testing with known loads but are therefore inherently more reliable in practice as they can remove unexpected complicating factors relating to installation Method 3 Two Point Calibration Method This is a simple in system calibration procedure and probably the commonest method in practice as in the previous example Two known loads are applied to the system and reading results noted then calibration parameters are set to provide exactly correct readings for these two conditions 18 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 E G a 10KN 1 tonne load cell has a CELL reading of 0 120721 with no load and 87 2077 with a known 100Kg test weight To calibrate this to read in a 1 0 to 1 0 tonne range set SOFS 0 120721 SGAI 0 1 8
30. TR Line Hi F You should never need to change any of the other settings When finished hit OK to confirm and close the window If message boxes indicate that instruments cannot reside on the same serial ports just press OK accept Note that the next time you use the design the communications will revert to the defaults COM1 and 9600 baud Evaluation Version Limitation Without a full licence VisualLink will display a pop up message about registration once a minute while in run mode The designs provided have been specially processed to remove this restriction but in any device you save to disk this limitation will reappear Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 to 77 Chapter 16 Specifications Table 16 1 Technical Specifications D Cell is nominally set for 2 5mV V sensitivity Parameter Min Typical Max Units Strain Gauge Excitation System 4 Wire Strain Gauge Excitation Voltage Strain Gauge Drive Capability 320 Strain Gauge Sensitivity Internal Resolution Output Resolution 1Hz readings 10Hz readings 100Hz readings Signal Filter a o S em mw ry its 5 147 mw Dynamic recursive type Non Linearity before Linearization 0 0005 0 001 FSD Offset Temperature coefficient before compensation 0 0005 0 001 Gain Temperature coefficient before compensation 0 001 0 003 DC 0 002 0 005 Offset long ter
31. Tj 1 Ti The compensated cell value is then calculated as CELL ELEC COFS 10 xcto x 1 0 10 xctg x CGAI Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 29 How to Set Up a Temperature Compensation There are a number of ways of setting up a temperature compensation curve The best possible compensation for a given piece of physical hardware can only be achieved by performing detailed experiments on that particular unit to characterise the measurement output at a variety of different stable temperatures in the required operating range The cost time expertise and equipment needed to do this can be considerable The basic choice of methods thus depends on trading off ideal accuracy against the expense of the calibration procedure Method 1 Apply a simple linear drift correction i e for known constant gain and offset changes per degree by specifying zero correction at the calibration temperature and appropriately adjusted correction values at extreme temperatures above and below this This can be used when the measurement or sensor has known temperature coefficients Method 2 Where the temperature characteristics of the measurement are known but not linear a similar scheme to Method 1 can be used with a multi point table defining an approximation to the known ideal temperature curves of offset and gain variations NOTE Both of the above methods are based on known charact
32. To defeat locking you need either the device specific release code or a valid code key pair Such information will only be released to authorised suppliers 40 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Lock Calculation Details The lock operations are summarised in the following diagram Figure 9 2 Lock Operations SECRET security code cell release code y write only all other data normal commands open untried SECRET ist keycode 7 LOCK command reboot A AG set S not shut calculation open shut lock SECRET T unlock A mmm attempt key code unlock P calculation read only random data The components of this system are as follows e The security code key and random data all consist of sequences of four bytes e The random data bytes are accessed as a pair of read only integer parameters LKD1 2 Each contains 2 bytes of the four byte sequence like SERL and SERH The lower byte of the LKD1 value is the first data byte These are the only values that can be read back before the device is unlocked They are rewritten randomly on every reboot e The security code is stored in the EEPROM It is written to by first writing the two integer parameters LKK1 LKK2 and then sending the LKD1 value as a check to the command LKWR The lower byte of the LKK1 value is the first code byte e The internal key code is derived from the s
33. Versions Cable Data Converter 4 Cable to data converter right serial port standard 9 pin straight through cable not null modem type with Tx Rx crossed 5 Power connected to data converter 6 Data converter baudrate setting if not Evaluation Kit type DIL switches for this may be essential for automatic enable switching 7 Data converter enable switching if not Evaluation Kit type If done by control line check the serial port connects this correctly If by transmission detect how is baudrate set Evaluation Board or Device 8 Power reaches the device 9 RS485 connections the right way round with comms idle B should be a few tenths of a volt higher than A 10 Device settings correct station number baudrate How do you know these are correct A substitute device is very useful here 11 Device protocol double check product label 12 Device running okay devices take 20 30mA supply current without sensor attached 30 50 with device should produce 4 5V AC across sensor end EXC connections Bad Readings The cause can be either hardware or software related 72 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Software 1 Check the ELEC reading first and ensure it is correct This figure is the RAW input and is not affected by the user configurable calibration settings 2 If ELEC looks correct check the calibration settings step by step Consider resetting all the calibrat
34. ace items with known good alternatives This also applies to cables power supplies devices etc No Communications The majority of problems involve a failure to communicate as there are a fair number of optional settings that must be set the same at both ends of the link For this reason any communications application should always check command responses and flag a problem when there these responses are not activated Possible problems can be categorised according to where in the chain of communication the problem may be The typical chain runs as follows PC software port connection baudrate station number protocol PC serial port working Serial lead to converter RS232 RS485 data converter power supply PC port wiring transmit enable baudrate setting Bus wiring Device wiring station number baudrate protocol working A quick checklist elaborates on these requirements in the case that you are using the VisualLink evaluation software other software may have different requirements at the PC end Check that PC End 1 PC software settings right serial port baudrate and protocol standard data setup is 1 start bit 1 stop bit no flow control 2 PC serial port okay check with other serial device e g wire 2 PCs together with Hyperterminal running on both RS232 Versions RS232 Evaluation Cable 3 Evaluation Kit cable on right serial port end without power supply wires connects to PC RS485
35. al warnings operate Bear in mind the following possible problems 1 REBOOT or COMMSFAIL may indicate intermittent connections 2 Where ECOMUR OR or EXCUR EXCOR are triggered suspect input wiring 3 Various range errors CRAWUR OR SRAWUR OR are also likely to be set if the excitation was interrupted EXCUR OR 4 For DSC cards EXCUR OR may also be due to bad excitation sense connections 5 For range errors check the associated limit parameters CMIN MAX SMIN MAX 6 Problems are likely if any calibration MIN MAX parameters are set the wrong side of zero i e MIN gt 0 or MAX lt 0 Problems with bus baud rate There are a number of special difficulties to be considered here e Systems with very long cabling may not work with higher baud rates e When using an RS232 RS485 converter it may be necessary to change some converter settings when changing baud rate Some baud rates may not be supported by some converters e Always remember you need to reboot devices before the change takes effect e Abus with two devices talking at different baud rates may become unusable So always change all at once by powering down or issuing a broadcast reset command RST Difficult problems can always be overcome if necessary by isolating individual devices and trying the different baud rates in turn This deals with all possible problems as long as your hardware can deliver all the supported baud rates Recovering a Jost DCell DSC
36. al Issue 1 3 27 If we have two cell output CELL readings for two known test loads we can convert the output to the required range So if testload xA gt CELL reading cA testload xB gt CELL reading cB then we calculate the following gain value SGAI xB xA cB cA and then the offset SOFS cA xA SGAI The outputs should now be SRAW XA xB true load values as required Example A 2500Kgf load cell installation is to be calibrated by means of test weights The cell calibration gives an output in Kgf ranging 0 2000 A system calibration is required to give an output reading in the range 0 1 0 tonnes Calculations Take readings with two known applied loads such as For test load of xA 99 88Kg CELL reading cA 100 0112 For test load of xB 500 07Kg 3 CELL reading cB 498 7735 Calculate gain value In this case put SGAI xB xA cB cA 0 50007 0 09988 498 7735 100 0112 0 001003580 1 003580010 Calculate offset value In this case SOFS cA xA SGAI 100 0112 0 09988 1 003580 10 0 487495 Set SMIN SMAX to include the expected output range say SMAX 1 0 and SMIN 0 1 to allow for small negative loads Check Putting the values back into the equation results for the two test loads should then be For x 99 88Kg CELL 100 0112 so SRAW 100 0112 0 487495 x 1 0035800 10 0 0998799 For x 500 07Kg CELL 49
37. amp DSC Version 2 User Manual Issue 1 3 Chapter 9 Device Locking This chapter describes the security locking scheme All devices contain a lock that prevents unauthorised usage This is not intended as a data security feature but to insure DCell DSC resellers against being undercut by third party resellers In order to access a device s data outputs it must first be in an unlocked state This is achieved by programming it to either disable locking completely or to release the lock when a specific coded command is received The locking scheme has the following general features e A device can be tied exclusively to supplied software and vice versa e Access requires knowledge of a secret security code unique to the supplier e All communications are normal uncoded data including the unlock operation e The lock can be completely disabled when required by programming in a separate secret code number Lock Operation The device lock is always in one of the states shown Figure 9 1 Lock States and Transitions SECRET security code cell release code y write only all other data normal commands open untried SECRET W Gg User keycode S LOCK command calculation EE set not shut open shut R lock SECRET unlock E key code attempt unlock calculation read only random data The behaviour in the different states can be summarised as follows e W
38. ansitions cccccceeccceesceeeeeeeeeeeeeeeeeeeeecaeeeeaeeeeeaeeeeeaeeeeaeeeeeaeessneeesseeseaas 39 Ways of Using the Locke 40 Purpose of the Security Gcheme nenne Ennn nn 40 Lock Calculation WE EE 41 Figure 9 2 Lock Operations Eer i iae e E eiTe E EAE e E aE EE aT NEG 41 Lock Commands Examples cccsscccccsssceeeeeeseceecsseeeeeecseeeeeecsaeeeessceneeeeecssaaeeessceeeeeeeesaseeesseeeeessseeaaeeseees 42 Chapter 10 Additional Software Features ccccccsecceseeceeseeeeeeeeeeseneeeseeeeeeneeeeaeeeeeeeeeseneeeeeeeeeeeeeeeeseeeneneeeees 43 SOUT Output Selection c 04 4 202k e nen dies diners digesta cence a siege stat a ESEE a E e 43 Output Update Tracking 2 5 sae 8 ete EES 43 Reading Snapshots gereest eRe eh eee Al Ae Ae ee ee ee A e a 43 Output Format Control ASCII ONLY 44 Continuous Output ASCII ON 44 EERSTEN ees et 44 Electrical ee EE 44 Figure 10 1 Electrical Calibration Process 45 Dynamic Filtering DEE 45 Temperature Cahbraton nen erE Arrn EEE EEEE E EEEE EE EEEE EEEE EEEE EE EEEE EErEE 46 Informational Parameters EE 46 Software Resets deed aer ea eE SEE TE Aa E pacer 46 Chapter 11 Communication Protocols cccceceeeeeeeeeeeeeseeeeeeneeeseeeeeeaeeeeeneeeseeeeeeeeeeeenesesesaeeeseeeseeeeeneeeeeees 48 Bus Standards fe2 2 Ee EE heen alee ce ae hs lel seed ege ad ed eevee alata Mae ate EES 48 G tter Ketter eege Lea ae ata te ee E 48 Communications Flow Confro ne 48 Communications EOT
39. are connected in parallel to the communications and power supply wire pairs as shown in the following diagrams Figure 13 11 RS485 Bus Connections for Multiple DCells Station 1 Station 2 Station N max 128 e 7 GND A RS 485 K Device B Connections 68 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Figure 13 12 RS485 Bus Connections for Multiple DSC4 RS485 Versions Station 1 Station 2 Station N max 128 ew WI Bus Connections GND A RS 485 Se Device B Key Requirements e The main bus cable must be terminated at either end e Where the bus does not go directly to each attached device each stub cable connecting to the bus should have just one device on it e Stub branches should be kept as short as possible less than 10m at most e The stub cables should be grounded at each device and the main cable grounded at the data converter end None of these should connect e Stubs are not terminated Bus Layout and Termination The ideal bus is a single length of cable terminated at either end Each end connects to a communicating device while other devices are connected as near as possible directly to the main bus as it passes them i e not on long side branches The bus must be terminated at both ends to avoid reflections This is done by
40. are two flags indicating under or over range for the force measurement System The System calibration converts the Cell output into a final output value in the required engineering units This is normally be set up by a systems installer or end user to provide whatever kind of output is needed independently of device specific information in the Cell calibration Making this split allows in service replacement without re calibration The outputs from this are e SRAW is a re scaled and offset adjusted output e SYS is the final output value after removing a final user output offset value SZ from SRAW e SRAWUR and SRAWOR are output warning limit flags In practice SRAW and SYS can be used to represent something like gross and nett values Results Value Scaling Both the Cell and System calibrations are simply linear rescaling calculations i e they apply a gain and offset In both cases four parameters define the scaling offset and min and max limit values These calculations are applied in the following way Output input OFS x GAI Output min output MAX Output max output MIN In addition if the value exceeds either limit one of two dedicated error flags is set The control parameters thus have the following characteristics e OFS is the input value that gives zero output set in input units e GAI is the multiplying factor set in output units per input unit e MAX and MIN are output
41. atching flag value EXCOR is set when the excitation measures high so that the apparent bridge impedance is considerably greater than 1kOhm This can mean that the sensor or wires are broken open circuit EXCUR is set when the excitation measures low so that the apparent bridge impedance is considerably less than 350ohm This normally means a short circuit For a DSC only with 6 wire cell connection it may also be due to a wiring failure Whenever EXCUR is triggered the device also sets the EXCSC flag and turns off the bridge excitation in order to protect itself against a possible overcurrent About every 10 seconds EXCSC is cancelled and the excitation turned back on again in case the problem has cleared itself If the excitation still measures low after a few milliseconds EXCSC will be set and the excitation turned off again Otherwise normal operation resumes with EXCSC cancelled but the EXCUR warning will remain set until cancelled by the host When the excitation is turned off of course some readings may be invalid usually near zero This can be important if the data are being logged as a continuous stream To ensure good readings it will probably be necessary to reject all data up to a few readings around and especially after the time EXCSC is reported Also note that EXCSC will always be clear for a short period every few seconds even if the apparent short circuit persists 38 Mantracourt Electronics Limited DCell
42. ate the end of the message Summary e A command message begins with followed by a 3 digit station address then a and finishes with a lt CR gt e The and lt CR gt only appear at the beginning and end of commands respectively e From the to the final lt CR gt is the command instruction of read write or execute type e All instructions begin with an alphanumeric command identifier of up to 4 characters and end with a non alphanumeric which may be the final lt CR gt Slave Response Message Formats Each slave monitors the bus for command messages It responds to any message that is addressed to it by sending a response message To be accepted by a slave device a message must start with T the correct 3 digit slave address and and end with lt CR gt with no intervening extra The slave will then always respond There are three possible types of response acknowledge ACK acknowledge with data for a read and not acknowledge NAK ACK is a single lt CR gt character This confirms an execute or write command ACK with data is a decimal number followed by lt CR gt This confirms a read and returns the data value NAK is an lt CR gt sequence The device rejected the command There are several possible reasons for a NAK response Command identifier not recognised Badly formatted command Missing command identifier unrecognised access code character or unexpec
43. ays current information values read from the DCell DSC device e The SOUT value is the main device output this is probably currently near zero as there is no input connected e The TEMP value is the internal temperature measurement reading this will probably be changing slowly as the device warms up The application refreshes these two displays at a reasonably fast rate about 3 times a second while the other data is read less frequently every 1 or 2 seconds On the right the FLAG value shows the device diagnostic warning flags Individual bits of this 16 bit parameter register represent specific warning conditions This value is generally zero in normal use but at present will have at least bits 15 and 1 set value 32768 2 32770 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 13 The application also displays the current bit settings as individual indicators Bits 15 and 1 are shown as the REBOOT and EXCOR flag indicators REBOOT means the device has been reset usually powered down EXCOR means the excitation measurement is above a warning high limit EXCitation Over Range This is a sensor high impedance warning i e the input gauge is broken or disconnected If you now hit the Clear All button next to the FLAG value the REBOOT warning and any others should clear but the EXCOR flag will remain set assuming that there is still no load cell conne
44. ccording to a specific protocol All devices on a bus must use the same protocol to avoid confusion The protocol specifies the structure and meaning of data exchanged and how access is controlled so as to avoid collisions The various DCell DSC variants support a variety of different protocols allowing integration with various other types of devices on a network Choosing a Protocol The current choices are ASCII printable characters easy to drive direct output to printers displays MODBUS RTU binary industry standard inter compatible with other devices such as PCBs MANTRABUS II efficient binary protocol checksums give better security than ASCII Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 49 NOTE In a VisualLink communications application a DCell DSC is represented by an object with a property for each available command As VisualLink supports all the DCell DSC protocols this is a convenient way of designing portable protocol independent applications Communications Software for the Different Protocols To access a DCell DSC you will need a communications application running on your PC or PLC in addition to the appropriate hardware connections The simplest approach for initial experiments is to use the VisualLink evaluation application A purchased version of VisualLink can be used for more much more complex control and monitoring applications VisualLink Lite can be used providing a window
45. ce during changes in temperature 4 The relationship between internal device temperature and that at the sensor is complicated by the fact that the device itself emits heat in use See Temperature Measurement Accuracy These problems can be addressed as follows 1 No real solution 2 Should be adequately repeatable if random noise is acceptable The temperature measurement is typically not that stable anyway due to fluctuating cooling conditions 3 Do not rely on large temperature compensation factors where temperature may change quickly Or use external temperature sensor bonded to the input sensor see next section 30 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 4 Always operate with a fixed stable power supply voltage Temperature Measurement Accuracy The TEMP reading is a taken from a sensor within the DCell DSC device With a DCell placed directly in the sensor pocket it will measure as near as practical the sensor temperature A DSC should at least be mounted close to the sensor and preferably in good thermal contact The TEMP reading can be expected to track that at the sensor but with an offset The offset is due to the device itself giving off heat i e the internal temperature is always above the ambient temperature it finds itself in Luckily the temperature compensation process only needs a reasonably repeatable measurement which relates to actual conditions at the sensor
46. cell sensor Figure 13 7 DSC Input Cabling Arrangement Load Cell Case Strain P Gauge SS 4 Rg Key Requirements The load cell cable should be a triple twisted pair with independent screens with the three pairs used for the EXC SNS and SIG signal pairs The cable should be as short as possible up to 5 meters for a low capacitance cable when connected to a 350 ohm bridge For specified performance the load cell must be grounded to the CH pin using a separate conductor not via the load cell cable screen This should be a solid wire at least 16 0 2 again as short as possible and at most 2m The cable screen must be grounded at the cell end and not at the DSC end Communications Cabling and Grounding Requirements To achieve full performance specifications and conform to environmental approvals it is important to follow the wiring procedures outlined in this section DCell Power and Communications Wiring The following diagram illustrates how to connect a puck to the communications and power supply bus cable Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 65 Figure 13 8 DCell Bus End Arrangement 2 x Twisted Pair KE P N Q 8 E No Connection Key Requirements The cable must enter the load cell via an EMC cable gland which connects the cable screen to the load cell body The cable must be a twin twisted pair with independent scree
47. connecting a 120 Ohm resistor between the A and B lines Loading In addition to reflections each connected device places a load on the bus According to the RS485 standard a maximum of 32 standard load devices can be simultaneously connected The DCell DSC devices are each one quarter standard load so a maximum of 128 devices may be connected at once to a single length of bus It is possible to increase this with bus repeaters but the bi directional nature of RS485 means it is usually simpler to add extra communications ports at the host driving completely separate busses Grounding The RS485 standard does not specify any particular ground connection If two external devices are both externally grounded i e not floating the grounds must be within the bus common mode range 7 volts to connect safely and communicate Beyond this an isolating converter may be needed Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 69 2 Wire amp 4 Wire Connections DCell DSC devices only use 2 wire RS485 connections A 2 wire RS485 connection uses the same pair for transmit and receive so the master has no special rights to the bus and only the rules of the protocol used prevent two devices transmitting at once RS232 amp RS485 Bus Converters Typical DCell DSC applications use a PC or PLC host connecting via an RS232 port This then requires an RS232 to RS485 bus converter to communicate with the bus
48. cted and the FLAG value will be 2 Now you have successfully established communications with your evaluation device future chapters concentrate on specific feature areas 14 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 3 Basic Setup and Calibration This chapter explains the most common setup and maintenance operations for operating DCell DSC devices This includes initial calibration and communications settings Connecting a Load Cell You can now connect a strain gauge bridge load cell or simulator to the DCell DSC A suitable strain gauge should have an impedance of 350 1000ohms and at least for now a nominal output of around 2 5mV V NOTE You can t just simulate a cell input with a small voltage This is because DCell DSC devices use an AC bridge excitation so the input is an AC signal changing in phase with the excitation Note the following 1 If using the DCell or a 4 wire strain gauge then ensure LK1 amp LK2 are fitted Connections to Sen amp Sen will not be made 2 The cable length from strain gauge to evaluation PCB should be as short as possible and not exceed 3 meters 3 The screen should be connected to the body of the load cell and terminated at CHASS Figure 3 1 Evaluation Board Sensor Connections LK1 O Evaluation 6 wire DSC only Board 6 wire DSC only OJ LK2 Once you have connected the load c
49. d Rate and Station Number Controls 2 cc ccccecceeeseeeeeeeeeeeeeeeeeeeeseeeeeeaeeseaeeeceeeeeeaeeeeeaeeeeseeeeseeeeees 21 Chapter 4 Summary of Software Features ccccccceesseceeseeeeeeneeeseeeeeeeeeeseeeeeeaeeeeeeeeeeeeeseseeseeeeeeeseseeeneneeeees 23 Chapter 5 Readings Processing and Calibration ccccccssssccssssseeeeeesseeeeeessseeeeeeesssaeeeesssaeeeeeessssaeeeensaaees 24 Main Reading Calculations ccccccecccecescceeeeeeeeeeeeeeeeeeeeeaeeceaeceeeaeeeeaeeeeaeeseaeesesaeeeeaaeeecaeeesceeeeenetesereeeaes 24 Figure 5 1 Readings Processing Main Features 24 Results Value SCaling due eege eA eee Ape cde et ay dent Meets 25 The SOUT Main Output Value 2 0 2 ccecccceecceesceecececesceeceeceeeceeeecaeeeeeeeeeceeeeesaeeeecaeeeseaeeeseeeeccaeeeeeeeeseeeeeeeess 26 A Complete Picture of Readings Processing ccccssssseceesesseeecessseeeeeccseeeeecssaseeeesceeeeeesseesueeeeseeeteeesseeaes 26 Figure 5 2 Readings Processing Fu 26 Calibration Parameters Summary and Detaults tnne etn rraren nnne e ennnen nnen 26 Two Point Calibration Calculations and Exvamples rennene ne 27 Chapter 6 Temperature Compensation ccccscceseeeeeeeeeeceeeeeeneeeeeeeeeeeeeseneeeeaeeeeeeeeeeeeeeesesaeeeseeeeeseeeneeaeeees 29 Purpose and Method of Temperature Compensation cccesccceeeeeeeeeeeeeeeeeeeeeeeeeeaeeeeeeeseceeeeeneeeeenseeeees 29 Control Parameters 2 2 2 6s542 sehss ead deelcecstied i eee
50. ded is nominally 8 5 to 15V DC but any possible droop or ripple must be included The devices contain brown out detection which may trigger if the supply voltage at the device drops below the 8 5 volts A single device consumes typically 35mA with a 350Q gauge connected except RS232 output units which use about 10mA more An installation should therefore assume at least 50mA per unit and allow for extra current being taken at power on though supply voltage can safely drop temporarily and for possible voltage drops in long cables Any power supply ripple should be below 30mV and supply arrangements should provide current limiting for fault conditions see Electrical Protection above Identifying Sensor End Connections Figure 13 1 DCell Input Connections a 62 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Figure 13 2 DSC Input Connections EXC 0 SEN O o pn O d Ke SIG O E RG SEN O EXC O em T a EXTT No Strain gauge bridge connections are as follows e EXC positive negative excitation supply e SNS DSC ONLY positive negative excitation sense e SIG positive negative output signal Other Connections e Resistor RG and track cut TC are used to adjust the mV V sensitivity see Input Sensitivity Adjustment below e Connections T and track cut EXTT are used to connect an external temperature sensing device see Fitting an External Temperature Senso
51. device in turn Less frequently the host also checks the devices warning flags Other occasional activities may use other commands In this situation the permanently stored control parameters for calibration and communications setup are normally set up in the initial installation process and then never or rarely touched WARNING Finite Non Volatile Memory Life The DCell and DSC use EEPROM type memory as the storage for non volatile controls i e all the settings that are retained even when powered down The device EEPROM itself is specified for 100 000 write cycles for any one storage location Therefore When automatic procedures may write to stored control parameters it is important to make sure this does not happen too frequently So you should not for example on a regular basis adjust an offset calibration parameter to zero the output value However it is reasonable to use this if the zeroing process is initiated by the operator and won t normally be used repeatedly For the same reason automatically cancelling warning flags must also be implemented with caution It is okay as long as you are not getting an error recurring repeatedly and resetting it every few seconds Setting a Precise Calibration NOTE the full calibration facilities are considerably more complex than the basic calculations described here See Chapter 5 Readings Processing and Calibration for fuller details In order to get correct m
52. e 1 Set RATE to the new value 2 Hit the RST button to reboot the device 3 Wait for 3 seconds for the reset procedure to complete and measure cycle to start The value displays will freeze for 2 3 seconds as VisualLink interrupts communications for a while whenever a device is rebooted to avoid spurious errors when the device does not respond With RATE set to 1 you should be able to see the SOUT update rate slow to once a second and the noise level should also noticeably decrease 20 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 With RATE 2 you won t see any difference in rate because VisualLink can t display the results much quicker than 10 a second but increased noise can be seen All the main reading output values are updated at this rate See Figure 5 1 Readings Processing for an overview of readings processing Baud Rate and Station Number Controls Station Number STN The STN parameter controls the station number which specifies the device address for bus communications As supplied devices have the station number set according to the device serial number as described previously in Checking the Device Protocol Type and Station Number To change the station number of your device 1 First set STN to a suitable new value making sure that no other device of the same number is also connected 2 Now hit the RST button to reboot needed before the device begi
53. e 1 3 Error codes Only three Modbus error codes are supported which are used as follows 01 Illegal Function request for function other than 3 16 02 Illegal Data Address attempt to read an unsupported register address 03 Illegal Data Value attempt to write a read only parameter or message too long for buffer valid messages have a known maximum length Write Command Example Write value 1 23 represents as hex 3F9D70A4 to registers 57 58 on slave 4 by sending hex 04 station address 10 function code 00 38 start reg hi lo NB h38 56 addresses register 57 00 02 quantity 2 registers 04 byte count 4 70 A4 first lower register 17 value hi lo 3F 9D second upper register 18 value hi lo 6B AB checksum hi lo A correct response would then be hex 04 station address 10 info copied from command 00 38 00 02 co 50 checksum hi lo Read Command Example Read a value from registers 13 14 on slave 52 by sending hex 34 station address 03 function code 00 OC start reg hi lo NB h14 20 addresses register 21 00 02 quantity 2 registers 01 AD checksum hi lo A correct response with a value 55 2317 hex C25CED51 would then be hex 34 station response 03 function 04 byte count ED 51C25C data AA D4 checksum hi lo Execute Command Example Execute command 101 on slave 17 by sending hex 11 station address 10 function code 00 64 start addr h64 100 register 101 00 02 quant
54. e Eer E ee E EE EE Eia a ENEE EENS 29 Ju Ree HE TEE 29 How to Set Up a Temperature Compensation ssessssessteesteestestt tet tnetntrtnnnnnnrnettnntnnnnnnnennnn rnrn ennenen 30 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 1 Potential ele EE 20 Temperature Measurement ACcuracy eeeeececeeeeenneeeeeeeeeeeseeeaaeeeeeeaaeeeeeeeeaaeeeeesaaeeeeeeeeaaeeeeesaaeeeeneeeeeeseeaaes 31 Parameter Calculations and Example nnn nn ennnen 31 Chapter 7 Linearity Compensation jis iicccsssscccececcssecesiescceetcececdecececsecevcecescdiecetentessidesesecsesueressatedesatcessaterecseeaa 34 Purpose and Method of Linearisation cc ccccescceeeeeeeeeceeeeeeeeeeeeeeeeeeeeeeaeesesaeesesaeeecaaeeseeeeseaeeseseeesereeeeees 34 Control Parameters 2 2 c cfnci eevee isd le EE dip Rap dete ee des cathe arene A aE e T i AoE 34 Ju Bee HE TEE 34 How to Set Up Linearity Compensation cccccccceeeeeeeeeeceeeeeeeeeeaeeceeeeecaeesesaeeseeaeeesaaeescaeeeeeeeeeceetessreseees 35 Parameter Calculations and Example nn nnr ennnen 35 Ghapter S Self DiaQnoSti s csiii 3cc s65 cc ra a aa Eege Eed Seege 37 Monitoring Warning Flas absent e aa tein See REESEN SE eigen atime dies 37 Meaning and Operation Of Flag ttt EnEEnnttnntt rnnt EEnE Ennn En Ennen EEEn meenen 37 Cell Excitation Management 38 Chapter 9 Device tockipg 22eedebeber ege geegent eara auaa dotsa e 39 Ree ele ee RE 39 Figure 9 1 Lock States and Tr
55. e assumed Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 53 The MODBUS protocol is a partial implementation of the RTU binary form of the MODBUS standard sufficient to allow DCell DSC units to coexist on a serial bus with other MODBUS compliant devices NOTE Third party applications for MODBUS communications are readily available e g ModScan from Win Tech software www win tech com who offer a free trial version Modbus Messages All messages and responses are formatted and checksummed according to the normal RTU rules The slave number is the device station number Slave 0 may also be used for broadcast writes The device command set is mapped into the MODBUS Output or Holding Registers Parameters read or write are mapped onto a pair of registers containing a 4 byte floating point value Action commands are implemented as dummy parameters Writing activates the command and reading returns a dummy value with no action Only two valid message function codes are supported Function 03 Read Holding Registers to read a register pair Function 16 Preset Multiple Registers to write a register pair The start address must always be a valid parameter address which is always an odd number see below The only permitted data length is 2 registers i e 4 bytes Registers can not be read or written singularly in larger groups or using other addresses i e eve
56. e coefficient before compensation 0 0005 0 001 C Gain Temperature coefficient before compensation r ll eee a C 0 002 0 005 Offset long term drift 0 0005 0 001 month Gain long term drift SS 0 005 month Common mode imbalance offset 0o01 GES Common mode imbalance gain oo Een Temperature resolution 0 1 C max 5 mA Power Supply current LL 28 IL o Im Power Supply ripple a es ee A Output Data terminal RS232 485 Data transmission rate EEE EEE Output cable length speed dependant 1000 m Operating temperature range 40 85 C e Storage temperature 40 Humidity o0 Housing PCB with metal shield case if required Connectors Input 6 pins Connectors Output 6 pins including dc power Environmental protection IP40 PCB Dimensions L x W x H 87 4mm x 20mm x 8 5mm Notes Italics figures in brackets refer to the low cost version For reporting of excitation open circuit Able to drive up to 10K Ohms but will continually report excitation open circuit Power amp Communications Connections For a 350R Bridge a cable length of 5 meters will give no more than 80ppm gain shift By setting of the gain resistor a OM ISO 9001 REGISTERED FIRM In the interests of continued product development Mantracourt Electronics Limited reserves the right to alter product specifications without prior notice MANUFACTURED IN THE UK Doc No ME3000ML1D Code No
57. e format Response to command 1 Byte 1 Station number 2 9 SYS 10 17 TEMP 18 25 SRAW 26 33 CELL 34 41 FLAG 42 49 VER 50 57 SERL 58 65 SERH 66 73 STN 74 81 BAUD 82 89 RATE 90 97 DP 98 105 DPB 106 113 SGN 114 121 SOFS 122 129 SMIN 130 137 SMAX 138 145 SHST 146 147 XOR Checksum Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 57 Chapter 12 Software Command Reference This chapter contains tables of all DCell DSC commands with brief details of each Table 12 1 Commands in Access Order ASCII name datatype access MBreg MD reg SOUT float RO B M SYS float eo Ho D TEMP float RO Mm D SRAW float RO f2 D CELL float RO N3 SI FLAG error flags int RW 14 29 CRAW float RO 15 31 6 O ba o oO 216 z RIL g2 IO SIS Els ro cio Las EN O ELEC float 1 33 RO 17 35 ECOM unfiltered ELEC float ERAW raw reading fot RO m B7 O EXC raw excitation ffo RO mg B9 FILT filter averaging byte RO l0 A OFFS offsetchannel flag ener RO D WB SZ system zero float SYSN snapshotresutt float RO D W VER software version Joe RO B80 SERH serial number high int RO 32 65 STN station number int RW 33 67 BAUD baud rate select byte RW 34 69 ICNT RATE DP DPB CTN CT1 5 CTG1 5 CTO1 5 tempco offset adjust float RW 121 125 243 251 CGAI cell gain float RW 40 81 COFS cell offset float RW 41 83 CMIN cell range min float RW 44 89
58. easurement values from a device you need to establish precise values for the calibration controls This generally depends on the combined performance of the measuring device load cell and often the mechanical system it is installed in Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 17 Once you have worked out correct values for SGAI and SOFS these values are simply written into the parameters as shown above This then gives precise readings in the required output units The SMIN and SMAX controls are then set to the expected normal range of the output value One of the advantages of digital calibration is that the results of changing the calibration are always precisely known Je you can calculate exactly what results you will get with a particular change to the calibration setup there is no cut and try needed If you have a load cell connected and a suitable test weight you can calibrate the cell in the simplest way as follows 1 Run up the VisualLink DCell DSC Evaluation Design Application and select the System Calibration page as above 2 Set SGAI back to the default 1 0 SOFS to 0 0 and SMIN SMAX to 100 0 3 Remove all load so the inputs see s the desired zero calibration point and allow to settle 4 Note the CELL reading value and copy this into SOFS SOUT should then read zero 5 Apply your test weight and allow to settle ideally this would be about full range for be
59. ecurity code by a secret algorithm e The cell release code is a special value unique to each device Setting the security code to this value disables the lock e The ULCK command requires an unlock value as its argument This must match the value calculated by the device from its security key code and the random data If the wrong value is sent the device becomes completely locked and can then only be reset Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 41 The unlock value itself is a single byte calculated as follows a bit jumbling routine unsigned char Scramble Bits unsigned char data int i bit rotate rotate data amp 7 extract lower 3 bits MOD 8 for i 0 i lt rotate i and rotate by this many if data gt 128 data 2 data 128 else data 2 data 1 return data the main calculation unsigned char Unlock Value unsigned char data 4 unsigned char key 4 int i unlock unlock 0 for i 0 i lt 4 i do for each of 4 bytes unlock key i XOR with one byte of key unlock Scramble Bits unlock jumble up unlock data i XOR with one byte of data unlock Scramble Bits unlock jumble up return unlock Lock Commands Examples To unlock a device the command sequence looks like this note examples are described using ASCII protocol commands
60. ed to the DSC CH pin and should not be connected to the bus cable screen or the sensor cable Suitable Cable Types DCell DSC4 RS485 Versions RS485 Bus Cable Requires e 2 x twisted pair with independent screens e Characteristic impedance 50 150 ohms e Core to core and core to screen capacitance below 300pF m A suitable type is BICC Brand Rex BE56723 also equivalent to Belden type 8723 In the UK this is available from Farnell part number 148 539 DSC Sensor Cable and DSC2 RS232 Versions RS232 Cable Both of these require 3 x twisted pair version otherwise similar to the above A suitable type is BICC Brand Rex PD3003 also equivalent to Belden type 8777 In the UK this is available from Farnell part number 148 540 Warning Special Problems with Portable Computers Many portables use double insulated power supplies with no ground connection and in this case a considerable voltage can appear on the port pins chassis when the PC is powered off the mains When such a system hosts a DCell DSC bus the whole arrangement may be connected to the mains ground only via the external power supply or the ground connections to the data converter or the DCell DSC units Electrical damage due to the brief presence of high voltages can easily occur when such a system is connected up Permanent harm can easily be done to the PC serial port the data converter and or DCell DSC devices This is not simply a theoretical risk We have seen
61. eeeeeeeeeeeees 11 Installing RE UE 11 Running the VisualLink Evaluation Application ccceseeeeeccecceeeeeeeeeeeceaeaaeeeeeeeeeeeeseseceeenssaeeeeeeeeesseeeees 11 Figure 2 5 Communication amp Parameter Test Page 12 KEIER Re EE 13 Figure 2 6 Device Communications Page 13 Chapter 3 Basic Setup and Calibration ccc cccsseceeeeeceeseeeeeeeeeeeeeeeeeneeeeeneeeeaeeeessaesesaeesesaeeeseaeeeneeeeseeeeees 15 Connecting a Load Cell 15 Figure 3 1 Evaluation Board Sensor Connections sseessesssssssrsrtrsrrsettesrirntntnttntttnetnnnttnnsrnernn ntete nt 15 Adjusting the System Calibration cccccccceecceeeeeeeeeeeeeeeeeeeseeeseeeeeecaeeeceaeeecaeeceaaeeecacesseaeeeseaeeeceeeseeeeeneees 15 Figure 3 2 System Calibration Page cc ccsscccceeceecenceeeeeeeeeeneeeeeeeeeceseeeceeceeaeeseeaeeecaeeeseaeeseeeeeseaeeeeees 16 Device Communications ce cccccecceeeeeeeeeeeeeeeeeeecaeecesaeeeeaeeseaeeesaaeeseaaeeseaaesecaeeeeaeeesaeeseaeeeeceeeeseeeeeeeeeeees 17 WARNING Finite Non Volatile Memory Life ccccccccsssseeeecseeeeesssseeeeeeseeeeeeeseesseeeseceeeeeeessaaeeeeeeeeeeess 17 se tting a Precise Calibration SEA ge iert 17 Calibration Methods issii beens ase ENNER EEN E EEN EENS 18 Changing Device Communications Settings ccccccccccsssssseeecssseeeecessnseeeeecseeeeeeesesseeeeeseeeeeesssnsaeeescaeeeess 19 Figure 3 3 Control Settings Page 20 Output Rate Control EE 20 Bau
62. ell you should see believable output values on the main reading SOUT indicator that change with the input level between about 100 0 and 100 0 The readings are scaled in percent full scale i e it reads 100 0 for a 2 5mV V input If you hit the Clear All Flags button the EXCOR warning flag should now clear and the FLAG value will just be zero Adjusting the System Calibration The values obtained so far are simple electrical readings in full scale where 100 is the basic 2 5mV V output level These are produced by the device electrical calibration which is factory fixed to within about 0 2 accuracy This inbuilt calibration cannot be changed however the device also contains separate user adjustable calibration controls These allow you to rescale the output value to read in units of your choice and to calibrate precisely to your load cell system hardware for much more precise results To see this from the main Communications page hit the System Calibration button Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 15 The following page should now appear Figure 3 2 System Calibration Page DSC amp DCell Evaluation E O x 23 7087 0 0264 2 0 1 2000 00095 500 00024 WI l E aAroe e The boxes labelled SOFS SGAI SMIN and SMAX show the current values of control parameters stored in the device To change a
63. ent physical form for mounting standalone or on a board The DSC is also available with an RS232 output External connections are via header pins which can plug into connectors or be soldered to wires or into a host PCB Which Device To Use It is important to select the correct product for your application e First choose DCell or DSC based on your physical installation needs e Choose the communications protocol depending on performance integration requirements e the RS232 output option may be simpler if your system only uses a single DSC card Common Features Both physical formats offer identical control and near identical measurement performance Both are available in all three output protocols MODBUS ASCII or MANTRABUS Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 5 Differences DCell puck has a 4 wire gauge connection for mounting very close to the sensor The DSC card has a 6 wire gauge connection allowing a short cable run Only the DSC card is currently available with the RS232 output option Special Aspects To Consider The DCell fits neatly into a strain gauge pocket The DSC lends itself to PCB mounting The RS485 output version must be used for multiple devices on the same bus Additional DSC Variants Available A separate DSC variant is available with CANbus output using a CANOpen compliant protocol A DSC variant with 3 bits of digital i o is available for simple control interfaci
64. er Help Getting Started The on line help for VisualLink Help VisualLink zl Tutorial Adding an Instrument sl Tutorial Object Manipulation A brief animated tutorial about manipulating objects A VisualLink Application A brief animated tutorial about adding an instrument The VisualLink application The following window should appear Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 11 Figure 2 5 Communication amp Parameter Test Page EN DSC amp DCell Evaluation VisualLink Please connect the Dcell DSC device to serial pot COM1 as directed in the manual Select the Device Type and Station Number of your device and press the Start Communications button when ready Select the device type MantradSCll2 e Click to start comms Start Communications Select station number bn d SE of device to communicate with Last 2 digits of instrument serial number unless digits are 00 in which case station number is 100 NOTE This design has been specially created to not require a protection key If you save this design after editing it will require a runtime key to run without warning messages The type drop down selects the protocol to communicate with The station number selects the correct device on the bus Use the selection controls to make appropriate selections from the data you noted down in the earlier section Checking the Device Protocol Type and Station Number
65. er bn d SS of device to communicate with Last 2 digits of instrument serial number unless digits are 00 in which case station number is 100 NOTE This design has been specially created to not require a protection key If you save this design after editing it will require a runtime key to run without warning messages Select the instrument type from the drop down menu amp the station number If you have changed the serial number and lost track of it s setting click on the Scan button and VisualLink will search from 1 to 253 producing a list of found devices This may take some time When you are happy with your selection and the instrument is connected to COM click the Start Communications button This will now attempt communications with the instrument see Device Communications in Chapter 3 Basic Setup and Calibration 76 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The layout has been designed to use the COM1 serial port at 9600 baud If these settings are not appropriate you can change them via the following pop up window that appears when you hit the Change Comms Settings button Figure 15 3 Instrument Settings Window xi Q MantraASCll 2 D Cell v2 Name Station No E D r Serial Port Settings Pott D d Baudrate asco m Handshaking T RATS CTS TT 2Wire RTS J DIR DSR on off m Line Control M ATS Line Hi V D
66. eristics which could come from datasheets This is fairly easy but also brings into question the actual accuracy of the TEMP measurement see Temperature Measurement Accuracy below The remaining methods assume some calibration testing Method 3 Do a series of measurements at different temperatures and install the appropriate correction values to give exactly correct results at those same temperatures i e calculate ideal gain and offset corrections at the tested temperatures This method is the most common Method 4 Use a set of test results to plan a best correction curve not necessarily perfect at test temperatures but slightly better overall NOTES All of these methods can be applied either to data from individual devices or to an average correction for a particular type of sensor hardware During testing temperatures should be measured using the internal TEMP measurement as this is the measurement used to do the corrections For in system tests the environment of the DCell DSC must always be as near as possible to the exact conditions of the eventual in system use Potential Problems It is worth always bearing in mind some unavoidable limitations of the compensation scheme 1 Equipment physical characteristics may drift over time 2 The internal temperature measurement may drift over time 3 The temperature measurement will experience a time lag in tracking the actual temperature of the measuring devi
67. fer quite a lot in the available types of error and acknowledgements The distinction between different access types is also protocol dependent in that some use a dummy read or write command for execute access E G the following are example commands of the ASCII protocol 1001 BAUD is to read the value of the BAUD parameter 1001 CLX3 3 74 is a write to the CLX3 parameter 1001 SNAP is to execute the SNAP action N B all these are addressed to station number 1 only Slave Addressing and Broadcast Every slave device on the bus is identified by a unique address value known variously as its station number node id etc depending on the protocol Each command message contains an address specifying to which slave device it is directed A slave will ignore all communications that are not addressed to it All the protocols also define a special address value normally 0 which is reserved for broadcast commands which all slaves act on No response is allowed to broadcast commands as multiple replies would collide with one another E G 037 BAUD is an ASCIIl protocol command asking station 37 for its BAUD value 1000 SNAP is an ASCIll protocol broadcast command telling all devices to sample their data Parameters Parameters are the values used for all control settings and output values They have an associated storage type byte integer or real value and may be either read write read only or write o
68. form to a very tight specification without the use of any trimming components High Reliability Load Sensing A road bridge has a dedicated load monitoring and active control computer system System calibration adjustments are only established during construction so sensors must be replaceable without recalibration Each load monitoring point has a digital load cell fitted with calibration values set during construction Self diagnostics aid detection of failures When a failed load cell is replaced it will produce identical force measurements The old load cell set up data values are programmed into the separate user level calibration store in the unit to produce an identically performing replacement Remote radio weigher A variety of lifting machines in a loading yard can be used with a weighing link to display weight in tonnes on a remote hand held readout A heavy duty strain gauge load link is fitted with a battery powered radio modem and DCell The independent handheld display unit communicates with the DCell over a transparent radio link providing a simple LCD readout and tare button operation 6 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Load balance monitor A lorry loading weighpoint monitors left right load balance and sounds a warning if loading is too uneven for safety A drive on weighing platform is provided with load cells at each of four corners Each cell is wired to a DSC unit and t
69. g Designs Click on the Design Examples item within the VisualLink program group to open the examples folder Within this the file DSC amp DCell evaluation is the DCell DSC evaluation software You can select and run DSC amp DCell evaluation by using any one of the following methods e Double click on the design file This will launch VisualLink and load and run the design with no access to the editor e Right click on the design file and select Run from the pop up menu This will perform the same Run Edit action as above e Right click on the design file and select Edit from the pop up menu This will launch VisualLink Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 75 and load the design in edit mode You can then experiment with editing the design To run press gt on the Toolbar e Launch VisualLink and open the design file using the Open button on the Tool Window To run press p button on the Toolbar DCell DSC Evaluation Application Notes This is the first screen you will see in the Evaluation Figure 15 1 Communication amp Parameter Test Page Yi DSC amp DCell Evaluation VisualLink Please connect the Dcell DSC device to serial pot COM1 as directed in the manual Select the Device Type and Station Number of your device and press the Start Communications button when ready Select the device type MantradSCll2 Click to start comms Start Communications Select station numb
70. gaij as described in Two Point Calibration Calculations and Examples in Chapter 5 Readings Processing and Calibration note that this is easier if you put COFS 0 to start with Choosing one of the Tj say Tk as the most usual operation temperature the reference we then use the gain and offset for that temperature as the basic Cell gain and offset parameters CGAI gaik COFS ofsk The lookup tables are then set up to contain the ppm differences from these centre values CTN n CTj Tj CTGj 10 x gaij CGAI 1 CTO 10 x ofs COFS Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 31 last factor is 10 because 100 0 full scale gives 1ppm f s 0 0001 NOTES 1 The Tj values are temperatures as measured by the device i e TEMP values The actual temperatures are not important 2 The calculation yields exact results except for rounding errors at all the calibration points ei ei at the appropriate temperatures 3 For the centre temperature T the correction values disappear i e CTGK CTO 0 This is less wasteful than it appears as the calculation needs to be told the temperature that the basic gain and offset apply at 4 Any subsequent calibration changes to CGAI and COFS will probably not require the table values to change unless the change is fairly large Example Suppose electrical readings are taken with two k
71. hen the device is rebooted it is in the OPEN or UNTRIED state depending on whether locking is currently disabled or enabled controlled by lock security code parameter e Inthe lock open state the device behaves as normal e Inthe lock untried state no data can be read from the device but parameter writes and action commands including the unlock command are permitted e Inthe lock shut state all access is forbidden The only way out of the shut state is to reset the device e When the lock is open it can still be deliberately permanently shut by sending a bad unlock value Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 39 Ways of Using the Lock Locking is controlled by setting the stored security code in each device to enable use in one of two ways refer also to Figure 9 2 Lock Operations Locking Disabled The security code is set to the cell release code This disables locking allowing access to the full set of commands As the security code cannot be read out and the release code is different for each device this information can be restricted as required Devices are supplied in this state which can be reinstated at any time simply by rewriting the security code Mantracourt will only reveal a Cell s release code to the original supplier Locking Active In this case the security code is set to a supplier code issued to authorised supp
72. hese are cabled to a 3 party LCD display and control unit producing a complete turnkey system A digital I O card is wired to the same bus to control the warning alarm Application software running on the control unit provides a left right balance readout with a graphical tipping display and a total weight indication The balance indication is calculated by comparing the different corner readings If it exceeds a programmed limit a command to the I O card turns the relay on Total weight is calculated by summing the individual results mathematically Automatic re zeroing occurs when the total is near zero for more than a few seconds A control button enables a set up mode for recalibration protected by operator password which displays individual readings and total Corner compensation can be checked by observing the changing total as a weight is moved around Simple button presses control two point recalibration for any cell Weighing subsystem for process control Several strain gauge loads are monitored as part of a larger data acquisition monitoring system based around a high speed Profibus network The load measurements occur in groups of physically related signals which relate to specific area modules along with a number of other measurements and control outputs The strain gauges are wired to DSC cards controlled and interrogated via MODBUS protocol commands on an RS485 bus The DSCs and other 3 party MODBUS compliant devices w
73. hich govern the area module are all connected to a single RS485 spur The devices in each area module spur are controlled from the main Profibus backbone using an off the shelf bus gateway unit Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 2 Getting Started with the Evaluation Kit This chapter explains how to connect up a DCell D or the first time and how to get It working For simplicity this chapter is based on the standard DCell DSC Evaluation Kit which contains everything needed to communicate with a puck or card from your PC It is advised that first time users wishing to familiarise themselves with the product use Mantracourt s Evaluation Kit This provides a low cost easy way to get started If you do not have an Evaluation Kit the instructions in this chapter mostly still apply but you will need to wire up the device and possible bus converter and have some means of communicating with it See Communications Protocols in Chapter 11 Communication as appropriate to the protocol type See also Chapter 13 Installation for details on wiring up the device The Evaluation Kit Contents e An Evaluation PCB which comprises of A7 Way Screw Connector for the Strain Gauge A 4 Way Screw Connector for Power amp RS485 Comms A 9 Way D Type for Direct RS232 Connection to PC Link Headers for 4 Wire Strain Gauge Option DCell Link Headers for RS232 or RS485 Comms Selection Terminat
74. ice see Chapter 14 Troubleshooting to solve the problem The section also shows you how to adjust the device output rate and how this affects the output readings From the main Device Communications page in the VisualLink evaluation application hit the Control Settings button The following page should now appear Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 19 Figure 3 3 Control Settings Page DSC amp DCell Evaluation YisualLink Serial Number 0000114823 Golf 27 4702 ELAG 32 68 Clear Flags Device reset command reboot RST Output rate O0 10Hz N B requires T to take effect Bus station number N B requires RST to take effect Comms baudrate Change Comms Settings 00 5 38400 N B requires Restart Comms Main Comms Page The SOUT and FLAG info are shown here for reference only The RATE STN and BAUD settings control output rate station number and comms baudrate The RST button sends a device reboot command This is needed for changes to RATE STN and BAUD to take effect Output Rate Control The RATE parameter is used to select the output update rate according to the following table of values RATE value 0 1 2 update rate readings per second The normal rate is 10Hz RATE 0 The other settings give a different speed accuracy trade off Invalid RATE values are treated as if it was set to 0 To change the output rat
75. ifying the DCellTrandT TrackCut nnt 71 Chapter 14 Troubleshooting Eve ass eccveswsacueivsassecasesssbcedivnawedveussouvedessavanssuvesececeebusuaeevesdenssuid 72 No Gooler eeh as EES 72 arale ele e Te GE 72 Unexpected Warning FAO El e r biediecetensclocpecuucectnetsgtcdnedubectetenedecbidve suds a a a a aa aaea a E aa 73 Problems with bus baud rate eee eecescceeeeeeeceeeeeeeeceeeesaaeeeeeeesaeaeesaaaeaeeeeesueaeeseaaeeeeseeaaaaeeseeneeeeeeneneeeeeeees 73 Recovering a Jost DCelitDpc rn nnrnneeieennennarnne ener nnr renar enererernnre rener m nennen 73 Chapter 15 The VisualLink Application ccccccsssseeceesssneeeenssceeeseesssneeeeensaaeeeseessnaeeeeeeseeesenssneaseessaaeas 75 Figure 15 1 Communication amp Parameter Test Page 76 Figure 15 3 Instrument Settings Window c cccceccceeseeeeeeeeeceeeeceeeeseeaeeeaeesesaeeecaeeseaeeesneeseeeeeeneeeeaes 77 Chapter 16 o oT eeo g FAA E E ere EE EE EE E 78 Table 16 1 Technical Specifications cccccscceessssececsesnseeeecsceeeeeecsseeeeeeeseceeeesessaeeeesceeeeeeeseaeeseseaeeess 78 Table 16 2 DSC Technical Specifications cccccceeccceeeceeeeeeeeeeeeeeeceeeeeceeesecaeeeceaeeeeeeeeecneeeeseeeeseeeeneees 79 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 3 Chapter 1 Introduction This chapter provides an introduction to DCell DSC products describing the product range main features and application possibilities
76. increased settling time Programmable Output Modes Output rate control enables speed accuracy trade off ASCII output version provides decimal format control and continuous output mode for dumb terminal output Unique Device Identifier Every unit carries a unique serial number tag readable over the communications link Communications Locking A private key locking scheme can restrict device access to the suppliers own software giving suppliers or systems integrators control over 3 party re supply Communications Error Detection An interruption of normal communications due to drop outs or noise is detected as badly formatted receive data which triggers a diagnostic warning flag External Temperature Sensing The internal temperature sensor can be replaced with an external device in contact with the sensor for improved accuracy especially tracking changing temperature conditions Software Reset A special communications command forces a device reboot as a failsafe to ensure correct operation The Product Range Devices are available in two physical formats The DCell puck products consist of a Digital Strain gauge Signal Conditioner with RS485 bus output in an ultra miniature cylindrical puck format This is suitable for installation in very small spaces including load cell pockets External connections are made by wiring to solder pads The DSC card products are very similar to the DCell but in a differ
77. ing resistor for RS485 An Evaluation DCell or DSC of your choice A CD ROM containing VisualLink Evaluation Software A 9 to 25 Way D Type Adaptor for the PC Comms Port A 9 Way D Type Extension Lead e For RS485 ONLY an RS232 to RS485 converter and connecting cable e For RS232 ONLY a power connection cable See the following diagram Figure 2 1 Evaluation Kits for the DCell amp DSC Evaluation Kit for the RS485 with the DCell Evaluation Kit for the RS232 with the DSC Other Things you will need e A regulated power supply capable of providing 10 15V at 100mA 10v is minimum requirement for RS485 converter e APC running Windows 95 or above with a spare RS232 communications port and 35Mb free disk space 8 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 and ideally e A strain gauge load cell or simulator 350 1000 ohms impedance NOTE the devices use ac excitation so a dc mV source will not work Checking the Device Protocol Type and Station Number Before running the communications application you should check both the protocol to use and the device station number The product label shows the product code which determines the protocol and its serial number which determines initial station number Example DCell label Example DSC label Product Code Product Code Serial Number DLCPKMAN MANTRACOURT C E Manufactured in the UK ME ELECTRONICS LIMITED Ie DSC4AS sin
78. ion controls to default values see Calibration Parameters Summary and Defaults in Chapter 5 Readings Processing and Calibration This should make SOUT ELEC at all times Hardware 3 Excitation problems should be obvious from the flags value If the input appears to device to be shorted the device only applies excitation briefly every 10secs or so This can look like a disconnected sensor results read near zero all the time Check excitation voltage 4V AC With DSC cards broken missing excitation sense connections will cause similar problems 4 Genuine hardware problems usual show up as total failure i e no reading always unchanging usually near zero sometimes always full scale Check wiring take voltage level readings and again if possible use a known good device and set up 5 Check the sensor is connected properly and has some resistance across excitation wires and around 350 Ohms across output wires when disconnected from device 6 Check for damaged DCell DSC device by replacement Unexpected Warning Flags Remember that all ordinary warning flags i e not EXCSC OLDVAL must be explicitly reset they do not clear themselves when a problem is resolved If a flag cannot be cleared the cause must be persistent i e it keeps happening again This can be immediate regular every few seconds or irregular occasional See Chapter 6 Temperature Compensation Self Diagnosis for precise details of how the individu
79. itional Software Features Software Reset A reboot command is also used to implement communications settings changes See Software Reset in Chapter 10 Additional Software Features Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 23 Chapter 5 Readings Processing and Calibration This chapter gives a complete account of the calibration controls and processing of input readings except for the linearity and temperature compensation processes which have their own chapters later on Main Reading Calculations The following figure shows a simplified view of the whole of the readings processing calculations omitting the compensation calculations see Figure 5 2 for the complete version Figure 5 1 Readings Processing Main Features Electrical Outputs Cell Calibration System Calibration CRAWUR gt lt SMIN SRAWUR CRAWOR SRAWOR E cmax h SMAX gt SRAW C 4 SZ This chain of calculations is performed on every input reading The named values shown in the boxes are all output parameters which can be read back over the comms link These calculations are updated continually at the update rate set by the RATE control see Output Rate Control in Chapter 3 Basic Setup and Calibration The diagram shows three separate calibration stages called the Electrical Cell and System This allows independent calibrations to
80. ity 2 registers 04 byte count 00 00 00 00 data value irrelevant AO B4 checksum hi lo The acknowledge response is then hex 11 station response 10 info copied from command 00 64 00 02 02 87 checksum hi lo Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 55 The Mantrabus II Protocol Mantrabus II is a 2 wire system where data is transmitted amp received over a common pair of wires For this reason the framing character must not be sent in a reply from the responding DCell The protocol ensures this does not occur by splitting byte data into nibbles with the exception of the framing character amp station number Framing Character The framing character for Mantrabus II is FEh this being different from the older Mantrabus I FFh to allow the two protocols to be mixed on one bus Checksum Both Host amp Device send their EXOR checksum of all data sent excluding framing character in nibble format the MS nibble being first E G EXOR Checksum of data is A7h Checksum characters sent 0Ah 07h Data Transfer Data is both sent and received as 4 bytes split into 8 nibbles following the station number plus two nibbles of checksum Floating Point Data Format All data sent amp received in Mantrabus II is in the IEEE floating point format this being a 4 byte floating point number The byte containing the sign amp exponent is sent first with the LS byte of the mantissa being last
81. ldered directly to the pads on the top and bottom of the puck Care must be taken to electrically insulate the connection pads from the surrounding metal DSC is normally installed in a protective enclosure such as a metal box The pins can be plugged into standard 0 1 pitch PCB header sockets or soldered directly into a host board or to connecting wires It can be mounted either way up Unwanted pins projecting on one side may be cropped off For extra vibration resistance the three mounting holes provided can be used If not required the protruding end with the single hole can be cut off to make the board smaller Electrical Protection No additional electrical screening is normally needed Electrostatic protection is sufficient for installation purposes only Devices are protected up to 25V against reverse polarity supply shorting of communications lines to power supply and shorting of sensor inputs No over current protection is provided in case of faults so the supply arrangements should ensure adequate power limiting or fusing Moisture Protection Both DCell and DSC must only be operated in a dry environment as moisture can dramatically degrade the measurement performance DCell Will normally be sealed into a load cell pocket While flexible silicone sealant can be used to completely embed the unit this is not adequate moisture protection in itself Mantracourt Electronics Limited DCell amp DSC Version 2 Use
82. le 3 Serial communications are carried out over a bus which operates according to the usual RS232 or RS485 standards The bus standard and protocol type are fixed for a given device during production The communications baudrate and station number the bus address are configured for each device by the ordinary control parameters STN and BAUD see Baud Rate and Station Number Controls in Chapter 2 Getting Started with the Evaluation Kit Bus Standards Serial Data Format Serial data formatting is the same for all the protocols and is fixed to e one start bit e one stop bit e 8 data bits e no parity Communications Flow Control Bus flow control is managed as part of the protocol managed differently by each No hardware or software flow control signals are to be used for any of the bus standards Communications Errors Serial data which does not conform to the expected format causes a serial framing error to be registered which sets the COMMSFAIL flag see Chapter 8 Self Diagnostics What this actually means is that following a starting 1 to 0 transition a stop 1 bit was not seen in the expected place This is obviously baudrate dependent the commonest cause being data transmitted at a lower baudrate than the unit was configured for Choice of Bus Formats Essentially the RS232 bus is only suitable where the application will only ever need a single DCell DSC device The only real advantage of RS232 outp
83. lectrical compensation components altogether Control Parameters The temperature compensation parameters define a pair of lookup tables that contain adjustments to the cell calibration gain and offset over temperature The parameters concerned are the following CTN number of temperature table points CT1 CT5 C indicated TEMP value at table point CTO1 CTO5 ppm fs ELEC offset x10 adjustment at table point CTG1 CTG5 ppm cell gain x10 adjustment at table point They work like this e The number of temperature calibration points is set by CTN from 2 up to 5 e The temperature values are set by CT1 CT2 CT5 or to the number set by CTN These must be arranged in order of increasing temperature The gain adjustments at these temperatures are set by CTG1 CTG2 CTG5 The offset adjustments at these temperatures are set by CTO1 CTO2 CTO5 Gain adjustments are specified in parts per million ppm Offset adjustments are specified in parts per million full scale or 0 0001 Internal Calculation A working table index i is derived from the current measured temperature T as follows n number of points used as set by CTN When T lt T1 then i 1 When T gt Tn 1 then i n 1 Otherwise i is chosen so that Tj lt T lt Tj 1 The resulting current gain and offset adjustment values are then ctg CTGj CTGj 4 CTG x T Ti Tj 1 Ti cto CTO CTOj 4 CTO x T Ti
84. lexity Two way communications allow in situ re calibration multiple outputs and diagnostics No separate measuring instruments needed Digital calibration Completely drift free adjustable in system and or in situ via standard communications link Two independent calibration stages for load cell and system specific adjustments Programmable compensation for non linearity and temperature corrections Calibration data is also transferable between devices for in service replacement Self diagnostics Continuous monitoring for faults such as strain overload over under temperature broken sensors or unexpected power failure All fault warnings are retained on power fail Multiple output options Choice of 2 communications standards RS232 or RS485 Choice of 3 different protocols ASCII MODBUS or MANTRABUS for ease of integration All variants provide identical features and performance Special Facilities Output Capture Synchronisation A single command instructs all devices on a bus to sample their inputs simultaneously for synchronised data capture Output Tare Value 4 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 An internal control allows removal of an arbitrary output offset enabling independent readings of net and gross measurement values Cell Excitation Sensing For increased accuracy and sensor malfunction detection Dynamic Filtering Gives higher accuracy on stable inputs without
85. liers by Mantracourt The device must then be specifically unlocked for use after every device reboot i e following powerdown or a reset command To unlock the device for use the user first reads back some data which is randomly produced on reboot and then issues an unlock command passing an unlock value calculated using this random data Calculating the unlock value requires the matching supplier key issued by Mantracourt with the supplier code This prevents anyone from reusing a device by setting an unauthorised security code they will need the appropriate key value as well Purpose of the Security Scheme It is fairly easy to gain access to any device simply by using the supplier s approved software to access it and then reconnecting the device to communicate with something else It is also possible to get in by trying random unlock values The unlock value is only one byte so this will usually succeed in around 1 200 tries However this is not practical as a general get around as the device must also be repeatedly reset taking around 2 3 seconds per attempt In view of this the scheme does not attempt to make unlocking hard Instead it makes it hard to determine the unlock key This is done by making the unique release code device specific using random data in the calculation making the security code write only and deriving the unlock key from the security code by a secret algorithm
86. ll calibration is wrong and should be redone The table points must always cover more or less the whole range of output values to be used because corrections are extrapolated outward beyond the first and last points It is always worthwhile including more test points than will be used in the correction table because this gives confidence that no regions of rapidly changing error have been missed Tests should be done both with steadily increasing and decreasing load values as hysteresis effects for load cells are often of a similar size to non linearities Parameter Calculations and Example Based on the simple method outlined above we suppose that we have obtained test results for a series of precisely known load values test loads Xj give readings of CRAW Cj for i 1 n Then calculate the errors that need to be removed at these points Ej Xj Cj Now just enter these values into the correction table remembering to scale the errors CLN n CLX X CLKj 1000 e Ej Example Suppose we have a load cell and Cell calibration giving a result in the range 0 500 KgF The following test results were obtained using a series of known test loads For test load of x1 0Kg CELL reading c1 0 0010 For test load of x2 100 13Kg CELL reading c2 100 44 For test load of x3 199 72Kg CELL reading c3 200 57 For test load of x4 349 97Kg CELL reading c4 349 75 For test load of x5 450 03Kg CELL reading c5 449
87. m drift 0 0005 0 001 month Gain long term drift month Common mode imbalance offset 0o01 F D Common mode imbalance gain 0o01 F D Temperature resolution ees ae en Temperature accuracy ee S EE max Power Supply current as a5 E E Ai i Power Supply ripple BEER Output Data terminal RS485 Data transmission rate Output cable length speed dependant Operating temperature range Storage temperature Humidity Housing PCB Dimensions 1000 m 85 C Black nylon sleeve Diameter 20 7mm Height 12mm ojo Notes Italics figures in brackets refer to the low cost version report excitation open circuit By setting of the gain resistor kk For reporting of excitation open circuit Able to drive up to 10K Ohms but will continually 78 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Table 16 2 DSC Technical Specifications DSC Conditioner is nominally set for 2 5mV V sensitivity Parameter Min Typical Max Units Strain Gauge Excitation System Strain Gauge Excitation Voltage LJ 45 VA Strain Gauge Drive Capability 320 1200 m Strain Gauge Cable length see note SS Power amp Communications Strain Gauge Sensitivity 1 2 5 20 mV V Output Resolution 1Hz readings 190 Bits 10Hz readings ml LB T0OHZ readings 5 4 its Signal Filter Dynamic recursive Non Linearity before Linearization 0 0005 0 001 FSD Offset Temperatur
88. mber 40 at station 20 send the following FEh 14h 28h 04h 02h OCh 08h 00h 00h 00h 80h OBh OEh DATA EXOR CS Frame Station Cmd MS bit char number number of last Byte set the response is then 14h 06h i e station number ACK 56 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Reading of Variables To read an individual variable the command number is sent with the MS bit set i e no data following E G To read CGA command number 40 from station number 20 send the following FEh 14h A8h OBh 0Ch EXOR CS Frame Station Cmd with char number MS bit set of last byte Assuming the value was 12345 678 coded as C640E6B6h representing 1 2 12345 678 8192 the response will be 14h OCh 06h 04h 00h OEh 06h OBh 06h 01h OFh DATA EXOR CS Station number Action Commands These are transmitted like read commands i e no data sent The response is as for write commands E G To reset station 3 command 100 send the following FEh 03h E4h DER 07h EXOR CS Frame Station Cmd with char number MS bit set The response is then 03h 06h Dump Commands Mantrabus II supports commands 1 data dump and 2 read display similar to the older Mantrabus I Command 2 is treated exactly like a read command for the SYS value command 10 Command 1 returns a set of data outputs in the normal nibbl
89. mount of common mode rejection this improves performance over longer distances 2 It uses driver enable disable controls to allow the same wires to be shared between several devices This enables multidrop operation The RS485 standard is a two wire bus For good noise immunity the two wires are normally twisted together and shielded There is no defined ground connection All attached devices load the A and B lines so as to normally pull the grounds of floating devices to within a few volts of each other The common mode tolerance effectively about 7 Volts then allows communications without any further grounding provision An RS485 bus of any length also behaves like a transmission line and so must be terminated to avoid reflections This is done by connecting a 120 Ohm resistor between the A and B lines at each end of the bus The RS485 standard is specified for operation up to 4000 feet 1200 metres at any rate below 9600 baud and proportionately less at higher rates However this assumes an ideal straight cable run with termination at both ends In practice a bus with many devices along its length can fall short of this especially if any connected devices are on long stubs leading off the main bus This may mean that the bus has to run at a slower speed than expected for reliable communications For practical details see RS485 Bus in Chapter 13 Installation Communications Protocols All communications take place a
90. mp DSC Version 2 User Manual Issue 1 3 Chapter 13 Installation This chapter gives detailed information on integrating DCell and DSC devices into a production system including mounting protection adjustments wiring and electrical requirements Before Installation Carefully remove the DCell DSC device from its shipment box Check that the device is complete and undamaged Check the Product Type Code on the product label is that which you ordered The DCell DSC can operated in any industrial environment providing the following limits are not exceeded Operating Temperature 40 C to 80 C Humidity 95 non condensing Storage temperature 40 C to 80 C For precise details of environmental approvals see Chapter 16 Specifications It is advisable to follow the following installation practice where possible e Minimise vibration Do not mount next to strong electrical or magnetic fields transformers power cables Ensure easy access to the module Install electrical protection device as the unit is not internally fused Always ensure the package is secure and protected Physical Mounting DCell is normally sealed in the pocket of the load cell which provides mechanical and moisture protection and electrical screening The case is a flexible nylon sheath which can be secured with a suitable flexible adhesive An ordinary silicone sealant works well Rigid glues or cements are not suitable Connecting wires are so
91. mp DSC Version 2 User Manual Issue 1 3 45 The dynamic filter produces the basic ELEC result by passing the evenly sampled ECOM value through a low pass filter with a variable amount of averaging With a static input this averages the input over a fairly large number of readings smoothing the signal value to significantly improve noise performance When the input changes however the filter responds to the increased rate of change by reducing its averaging time constant to better track the change The FILT parameter shows the current time constant setting This is 1 after a sharp step change and increases up to a fixed maximum depending on RATE while the input is steady This approach produces a better trade off between steady state output noise and response to input changes However the output noise on ELEC and all subsequent values increases during an input level change and for some time after it takes time for the filter time constant to ramp up again The filter settings are optimised for each rate setting assuming a relatively clean input signal However dynamic filtering is inherently sensitive to noise Extra noise on the input can thus have a disproportionate effect on the output reading noise something like a square law Temperature Calibration While the basic Electrical calibration stage is factory set and not suitable for adjustment by the user the TEMP calibration can be modified if needed This might be
92. n numbered registers cannot be addressed directly Parameter Addresses All MODBUS parameter addresses are derived from the equivalent MANTRABUS register number by a simple times 2 plus 1 calculation For example the FLAG parameter is Mantrabus register 14 so this occupies MODBUS holding registers 29 and 30 because 2x14 1 29 See the command table in Chapter 12 Software Command Reference for the starting register numbers Parameter Values All exchanged values read and write parameters are in the standard IEEE 4 byte floating point format The 32 bits of the number are distributed as follows MSB 31 Sign bit 1 negate 30 22 Exponent 7 bit excess 127 LSB 21 0 Mantissa 23 bit fraction with implicit 1 The value of the number is thus 1 sin 2 Exponent 127 4 Mantissa Note the assumed 1 before the mantissa The exception to this is the special value 0 0 which is represented as 4 zeroes E G a floating point number of 12345 678 is represented as hex C6 40 E6 B6 These 32 bits are mapped onto a register pair in the following way The lower register holds bits 15 0 and the upper register bits 31 16 These values are coded according to normal Modbus conventions so the actual byte sequence in a read write message is thus Rihi Rik Ri R210 which in terms of bits is rather oddly 15 8 7 0 31 24 23 16 54 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issu
93. necessary if a more precise temperature reading value is required or the measured temperature doesn t track the sensor temperature well enough to perform a desired nominal temperature compensation The temperature calibration is an adjustable linear rescaling and limiting process similar to those for the Cell and System reading calibrations There are no communications parameters provided to access this but the controls are stored with the other control settings in the non volatile memory EEPROM and can be accessed via the EEPROM read write commands These values are formatted as IEEE 4 byte floating point values as described for the MANTRABUS protocol see The Mantrabus Jl Protocol in Chapter 11 Communication They are stored from the LSB at the lowest address to the exponent byte at the highest NOTE These storage addresses may change between software releases These addresses are valid for Version 2 As with any use of the temperature measurement any tests must be done using the exact intended operating conditions including power supply voltage for any useful accuracy see Temperature Measurement Accuracy in Chapter 6 Temperature Compensation for more details Informational Parameters The VER parameter read only byte returns a value identifying the software release number coded as 256 major release minor release E G current version 2 2 returns VER 514 SERL and SERH are read only integer parameters returning the device
94. ng These variants are sufficiently different to require their own manuals Future Planned Versions DCell puck form with RS232 output DCell puck form with CANbus output Ethernet connection Radio connection Contact Mantracourt for latest details Some Application Examples Simple Distributed Measurement Pressure loads are taken at a number of keys points in a manufacturing process distributed over a large area Each pressure sensor contains a DCell unit and all the sensors are connected by a single cable carrying power and RS485 communications A central PC allows continuous display monitoring and logging of all values from a central control room This displays a control panel and current display window and logs information to an Excel spreadsheet for future analysis Further monitoring checks and displayed information can easily be added when required to the system where up to 253 nodes can be installed Low cost dedicated weighing station A basic load cell weighing pad device has a cable leading to a wall mounted weight display Digital Load Cell Load cell products are offered with a high precision digital communications option A DCell is fitted into the gauge pocket of each load cell in manufacture During product testing each unit undergoes a combined load test and temperature cycle Each unit is then programmed with individually calculated gain offset linearity and temperature compensation tables All units per
95. nly Output or result values are mostly read only Configurable parameters are held in non volatile storage so control settings are retained permanently even when power is removed E G SYS is the main system output value It is a read only real floating point value E G BAUD controls the serial communications rate It is a read write byte value Data Type Conversions and Rounding Type Conversion Depending on the protocol an integer byte parameter may need to be converted to or from a floating point representation for reading or writing The rules are as follows For reading integer and byte parameters are treated as unsigned and never read negative i e read value ranges are 0 to 65535 0 and 0 to 255 0 For writing values written to integer and byte parameters are truncated to the nearest integer and negative or positive values are acceptable NOTE Floating point data is not always exact even when reading integral data E G could get 3 999974 instead of 4 E G for a byte write 240 240 1 and 239 66 are all the same value Rounding Although rounding is applied when writing to integral values data read from a device is not rounded off The ASCII Protocol The ASCII protocol uses only printable characters and carriage return lt CR gt which allows a dumb terminal device or a PC programme like Hyper Terminal to interrogate the device Host Command Message Format The basic command request st
96. nown loads xA 99 88Kg xB 500 07Kg at different three temperatures giving the following ELEC values at T1 15 3 C ELEC readings are eA1 14 25537 eB41 70 18944 at T2 20 7 C ELEC readings are eA2 14 31633 eB2 70 50611 at T3 35 2 C ELEC readings are eA3 14 40616 eB3 71 00749 at T4 51 9 C ELEC readings are eAg 14 39212 eB4 71 05322 Calculations applying the formulae for gain and offset values then gives gai41 xB xA eB1 eA1 7 154673 ofs4 eA41 xA gai4 0 295263 gai2 xB xA eB2 eA2 7 122114 ofs2 eA2 xA gai2 0 292404 gai3 xB xA eB3 eA3 7 070329 ofs3 eA3 xA gai3 0 279519 gai4 xB xA eB4 eA4 7 062870 ofs4 eA4 xA gai4 0 250560 taking T2 20 7 C as normal operating temperature we then set CGAI gai2 7 122114 COFS ofs2 0 292404 the temperature correction tables are then set relative to this as follows CTN 4 CT1 T14 15 3 CT2 T2 20 7 CT3 T3 35 2 CT4 T3 51 9 CTG1 10 x gaiq CGAI 1 4571 536 CTG2 10 x gai2 CGAI 1 0 CTG3 10 x gai3 CGAI 1 7271 015 CTG4 10 x gai4 CGAI 1 8318 317 CTO1 10 x ofs4 COFS 028 5900 CTO2 10 x ofs2 COFS 0 CTO3 10 x ofs3 COFS 128 850 32 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 33 Chapter
97. ns with one pair used for the communications and the other for the power wires The cable screen must be grounded to the CH pad of the DCell and not at the host end DSC4 RS485 Versions Power and Communications Wiring The following diagram illustrates how to connect a DSC4 card to the communications and power supply bus cable Figure 13 9 DSC4 RS458 Versions Bus End Arrangement 2 x Twisted Pair No Connection Key Requirements The cable should be a twin twisted pair with independent screens with one pair used for the communications and the other for the power wires The cable screen must be grounded to the CH pin at the DSC end and not at the host end Any further metal housing should also be grounded to the DSC CH pin and should not be connected to the bus cable screen or the sensor cable DSC2 RS232 Versions RS232 output Power and Communications Wiring The following diagram illustrates how to connect a DSC2 card to the communications and power supply bus cable 66 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Figure 13 10 DSC2 RS232 Versions Bus End Arrangement 3 x Twisted Pair Key Requirements The cable should be a triple twisted pair with independent screens Each of the Rx Tx and VIN wires is paired with a VIN wire The cable screen must be grounded to the CH pin at the DSC end and not at the host end Any further metal housing should also be ground
98. ns to use the new value Wait for a VisualLink Errors window to appear because it is no longer getting responses to commands addressed to the old number Return to the startup page by hitting the Restart Comms button Clear the errors and close the Errors window Select the new Station Number in the dropdown list Hit Start Communications button again You should now find you can talk to the device again oO NOOR To connect multiple devices on the same bus it is first vital to set all the station numbers to different values This is because if two devices with the same station number are connected to the same bus it is not possible to talk to them individually So in particular you cannot correct the problem by changing the station number of one of them If a bus connects to two devices with the same station number the only solution is to remove one of them and connect it to a one to one link to reprogram it NOTES e The valid range of STN depends on the protocol but it is always at least 1 253 e All the protocol types have a bus address type device identifier which is known as the station number for MANTRABUS address for ASCII and node id for MODBUS e The valid ranges for different protocols are 1 253 for MANTRABUS 1 999 for ASCII and 1 255 for MODBUS e Inall cases if STN is set outside the valid range it behaves as if set to a default of 1 Baudrate Control BAUD The B
99. ntracourt s own rapid development software platform for PC SCADA applications It provides communications drivers for the DCell DSC products amongst many others An evaluation copy is provided on CD ROM with the DCell DSC Evaluation Kit Uninstall any previous versions of VisualLink before proceeding Install the VisualLink demonstration application by inserting the CD in the CD ROM drive This should start the AutoRun process unless this is disabled on your computer If the install program does not start of its own accord run SETUP EXE on the CD by selecting Run from the Start Menu and then entering D SETUP where D is the drive letter of your CD ROM drive The install program provides step by step instructions The software will install into a folder called VisualLink inside the Program Files folder You may change this destination if required After installation you may be asked to restart the computer This should be done before proceeding with communications For further information refer to Chapter 15 The VisualLink Application Running the VisualLink Evaluation Application Having installed VisualLink you can now run the special evaluation application which the rest of this chapter is based around From the windows Start button select Programs then Visual Link select Design Examples This opens a folder double click on DSC A DCell Evaluation vid Design Examples Will open the design example fold
100. on To increase sensitivity TC is left in place so that the fitted Rg appears in parallel this gives better temperature stability It s value should then be Rg 1 0 025 0 01 required mV V Two effects should be noted 1 The purpose of increasing sensitivity is to reduce reading noise which governs the effective resolution Using software gain alone obviously gives reduced performance 2 The sensitivity should however not be set greater than typically 1mV V Beyond this input noise usually dominates and no extra benefit can be achieved Fitting an External Temperature Sensor An external temperature sensing diode can be fitted in place of the one on board by cutting the link EXTT and wiring the sensor anode cathode to pads T and T Figure 13 14 Identifying the DCell T and T Track Cut Contact your supplier for suitable devices and further information The sensor itself is a small surface mount device approximately 0603 resistor size It will need to be secured in good thermal contact with the sensor typically with adhesive See Temperature Measurement Accuracy in Chapter 6 Temperature Compensation for more details of when this might be useful Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 71 Chapter 14 Troubleshooting This chapter gives a quick guide to problem solving for DCell DSC devices Bear in mind that the quickest way to pin down problems is to usually repl
101. ould be to adjust the Temperature Calibration see Figure 10 1 Electrical Calibration Process EEAD is a read write integer holding an EEPROM address 0 495 EEV is a read write byte value holding the read write value EERD EEWR are action commands triggering a read write operation To read a byte set EEAD to the address execute EERD and read the result from EEV To write set EEAD to the address write the value required to EEV and execute EEWR There are 496 bytes of EEPROM data which can be addressed After use EEAD is always reset to 65535 for safety an invalid address which prevents a write Electrical Calibration The Electrical calibration stage is the initial phase of results processing responsible for producing the basic TEMP and ELEC value outputs This contains factory set calibration information which should never need to be changed and therefore has no control parameters Details are included here for explanation only as none of these facilities can be adjusted 44 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The operation of the Electrical Calibration is illustrated by the following diagram Figure 10 1 Electrical Calibration Process Raw Results Electrical Calibration Electrical Outputs Temp Cal Settings Temperature _ se gt LTEMP EE gt TEMPUR E eet eee gt TEMPOR Excitation _ EXC Reading ERAW Elec Cal Setting
102. ous output mode The SOUT value is continually broadcast at the output rate or as fast as possible if limited by communications speed The output is switched on and off by sending the standard ASCII XON XOFF control bytes ctrl Q 0x11 and ctrl S 0x13 This feature is intended for output to a single simple serial display devices and printers It has certain special limitations as follows e lItcan only be used in one to one operation i e only one unit on a bus as otherwise collisions can occur e On a RS485 bus it is not always easy to switch off as the stop instruction must be transmitted when the device itself is not transmitting If the output rate is limited by communications speed then output is virtually continuous and may be impossible to stop N B this does not apply to RS232 which has separate transmit and receive connections e The operation does not start automatically i e an initial Ctr Q must be sent This means that if there is for instance a brief power interruption output will stop To avoid possible problems continuous output operation is only enabled when the station number STN is set to the special value of 999 EEPROM Controls The special commands EEAD EEV EEWR EERD are provided for accessing the built in non volatile storage EEPROM This is potentially dangerous as all non volatile settings are stored in the EEPROM At present the only expected end user use of these commands w
103. r Manual Issue 1 3 61 If required the entire unit can be embedded in a potting compound A two part epoxy compound can be used but bubbles and gaps must be avoided to prevent mechanical stresses which could break the device compound can be injected into the outer sheath with a syringe The compound used must be specified for electrical use and have sufficient thermal conductivity to cope with the heat given off up to 1W on a 15V supply DSC no additional electrical screening is required but moisture and or mechanical protection is often required Any simple box or enclosure can be used If metal the enclosure should be earthed to the CH connection see Communications Cabling and Grounding Requirements below Soldering Methods Take care soldering cables to the pads Use a temperature controlled soldering iron set toa maximum 330 C for no longer than 2 seconds per pad Excessive heat or increased soldering time may result in damage to the PCB NOTES 1 Solder with water soluble flux should not be used even low residue as this can leave a surface film which attracts atmospheric moisture degrading measurement performance VAS 2 DCell units are especially easily damaged by poor soldering due to the use of thin flexible circuit boards Overheating or applying any pressure to a pad can de solder components on the other side of the board or cause the pad itself to become detached Power Supply Requirements The power supply nee
104. r below Identifying Bus End Connections Figure 13 3 DCell Bus Connections Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 63 Figure 13 5 DSC2 RS232 Bus Connections VIN are the DC power supply and return connections A and B are RS485 communications connections RX and Tx are RS232 communications connections GND is a communications ground connection not DCell use VIN CH is the chassis ground used for shielding and earthing only Sensor Cabling and Grounding Requirements To achieve full performance specifications and conform to environmental approvals it is important to follow the wiring procedures outlined in this section DCell Sensor Wiring The following diagram illustrates how to wire up a puck to a strain gauge Figure 13 6 DCell Input Wiring Arrangement Load Cell Case Strain 64 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Key Requirements All the load cell wires should be kept as short as feasible at most 10cm The EXC wires should be twisted together also the SIG pair and the two pairs kept apart It is also recommended to secure the wires from moving due to shock or vibration The CH pad must be grounded to the load cell body For specified performance this should be less than 10cm of at least 16 0 2 solid wire DSC Sensor Cabling The following diagram illustrates how to connect a DSC card to the load
105. resietttntttnttnntttnntnnnttrnsttnstnnnnnnnnnnnrnnn ennet 64 DGell Sensor Wiring EE 64 Figure 13 6 DCell Input Wiring Arrangement 64 Figure 13 7 DSC Input Cabling Arrangement 65 Communications Cabling and Grounding Requirement cccscccceecceeeeceeeeeeeeeeeeeseseeeeeeeeseeeseneetees 65 Figure 13 8 DCell Bus End Arrangement 66 Figure 13 9 DSC4 RS458 Versions Bus End Arrangement 66 e CN 66 Figure 13 10 DSC2 RS232 Versions Bus End Arrangement 67 Suitable Cable ype 2 2 5 e 2 hades sn eebe ee glee eege lege Neuer 67 Warning Special Problems with Portable Computers t 67 To Avoid These broblemme 2320ege SEENEN NENNEN caves ict Ed E SEENEN 67 RS232 TEE TEE 68 RS485 BusiPayout eier BEE 68 Figure 13 11 RS485 Bus Connections for Multiple DCells cceecceeeeeceeceeeeeeeeeeeeeeeeeeeeeeeeeeseieeeeees 68 Figure 13 12 RS485 Bus Connections for Multiple DSC4 RS485 Versions 69 RS232 amp RS485 BUS Converters 2 0 2 cecccceeeeeceeeeceeeceeeeeeeeeeeeeeeaaeeceaeeseaaeeseaeesesaeeseeaeeecaaeeseeeeseaeesesaeesseereees 70 Input Sensitivity Adjustments lt 200 cece cee pete ier aae a eCall eater eel Gas babel rides 70 Figure 13 13 Identifying the DCell Rg Resistor ecccceecccceeseceeeceeeeeeeeeeeeeceeeeeeeeeeeecaeeeseeeeeeneeeseeeeeeees 70 Fitting an External Temperature Sensor ccceccccesceceeeeeeeeceeeeecececeeececeeeeseeeeeecaeeeccaeesecaeeeeseeeeseeeeseeeeeees 71 Figure 13 14 Ident
106. rical reading and the temperature measurement are described in Electrical Calibration and Temperature Calibration in Chapter 10 Additional Software Features Input Filtering The input Electrical calibration processing involves a dynamic filtering technique explained in Chapter 10 Additional Software Features Result Snapshot Multiple inputs can be sampled simultaneously with a single bus command See Reading Snapshot in Chapter 10 Additional Software Features Continuous Output ASCII protocol only Devices can be made to transmit continuously for output on slave display See Continuous Output in Chapter 10 Additional Software Features Output Formatting ASCII protocol only The decimal formatting of the output value is adjustable See Output Format Control in Chapter 10 Additional Software Features Output Tracking A flag mechanism allows every output result to be sampled once and once only See Output Update Tracking in Chapter 10 Additional Software Features Output Selection The main output can be switched between different internal values See SOUT Output Selection in Chapter 10 Additional Software Features Information Parameters The device serial number and software version can be read back over the communications See Informational Parameters in Chapter 10 Additional Software Features EEPROM access Special commands to access internal storage are used to adjust the factory calibration See EEPROM Controls in Chapter 10 Add
107. rical reading goes outside fixed 120 limits This indicates a possible overload of the input circuitry i e the input is too big to measure The tested value ECOM is an unfiltered precursor of ELEC CRAWUR and CRAWOR are the cell output range warnings These are tripped when the cell value goes outside programmable limits CMIN or CMAX The tested value CRAW is the cell output prior to linearity compensation SYSUR and SYSOR are the system output range warnings These are triggered if the SYS value goes outside the SMIN or SMAX limits COMMSFAIL indicates that a serial communications framing error was detected which indicates that improperly formatted data was detected on the bus If this occurs 3 times in 100 output times this causes a communications reset See Communications Errors in Chapter 11 Communication OLDVAL indicates that the value SOUT used for various special purposes has not been updated since last read This flag is not reset by the host in the usual way See Output Update Tracking in Chapter 10 Additional Software Features REBOOT is set whenever the DCell DSC is reset The possible causes are power loss the RST command or a software watchdog timeout should never happen Cell Excitation Management The EXCSC and EXCUR EXCOR warnings are triggered by measurements of the bridge excitation voltage EXCUR EXCOR are reset in the usual way by host action only but EXCSC is a self resetting warning indication not a normal l
108. ronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 How to Set Up Linearity Compensation A linearity correction can be set up either from sensor specification calibration data or more commonly from in system testing results Assuming we do not have any prior information on linearity errors the usual approach is to do a series of controlled tests with accurately known test loads Just as with temperature compensation it is possible to obtain a detailed graph of linearity error and then choose a best fit piecewise linear curve for the compensation table However it is generally good enough and much simpler to simply test at several different points and then apply an exact correction at those points If the error curve is reasonably smooth this should give exact results at the test points and reasonably accurate values in between NOTES Linearisation tests should only be done after the cell calibration is set because the correction values are dependent on the cell calibration Similarly linearisation testing should only be done at the calibration reference temperature or after temperature compensation is installed to avoid temperature effects from distorting the results The linearisation tests should not reveal any significant remaining linear trend in the errors If errors do appear to lie on a definite line this could drastically reduce the accuracy of the correction If this does happen it shows that the ce
109. ructure is shown in the following example illustrating the message 1001 SGAI 123 456 lt CR gt meaning write 123 456 to parameter SGAI on station 1 Framing Station Separator Command Access End of Character Address Identifier Code frame jp 001 LI SGA CO 99 9999 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 51 An explanation of each field is as follows e Framing character A character is used to signal the start of a new message This character is only ever transmitted by the host for framing purposes e Station Address A 3 digit ASCII decimal number 0 999 determining which slave device s the command is intended for All 3 digits must be sent Address 000 is reserved for broadcast addressing e Separator Always present As no checksum or message verification technique is used slaves use this as an extra check on message validity e Command Identifier Up to 4 alpha numeric characters case insensitive giving the name of the required command e Access Code Defines what sort of response is expected means write data is expected to follow 9 means the host is expecting to receive read data back lt CR gt i e nothing more before end means the command is an action type execute e Data An ASCII decimal formatted number can include 0 9 7 and spaces This field can have a maximum length of 15 characters e End of frame A lt CR gt is always present to indic
110. s gt ECOMOR Filter Settings EE FILT In the same way as Figure 5 2 Readings Processing Full this diagram shows the initial phase of results processing The basic internal reading processes result in the following initial outputs ERAW is the basic reading value OFFS is set to 1 0 indicating a reading on the offset main channel readings near to zero are read on a separate channel for noise reasons EXC is the excitation voltage measurement TEMP is the temperature reading All of these except TEMP are debug only values The other outputs are of no particular use to the ordinary user as their values may depend on the selected output rate and may change between software releases In the next stage of calculation ERAW is divided by EXC to give a corrected reading value This value is adjusted by stored calibration constants and block averaged depending on output rate setting to give rise to ECOM the first guaranteed calibrated output value The electrical limit values fixed at about 120 are also applied here which are connected to the ECOMUR and ECOMOR flags Finally ECOM is dynamically filtered to give the main Electrical Output ELEC as described in the next section ECOM can safely be used if an unfiltered electrical output value is needed Dynamic Filtering See also previous section including Figure 10 1 Electrical Calibration Process Mantracourt Electronics Limited DCell a
111. s shown above as follows e The raw ELEC input is rescaled by the Cell controls and temperature compensated based on current TEMP value to give the CRAW value e CRAW is then linearity compensated to give the final CELL output NOTES 1 Temperature compensation is integrated with the basic cell scaling calculations so there is no uncompensated cell output value available 2 The cell range limits CMIN and CMAX are applied to the CRAW result not the linearised value 3 The system range limits are applied to SRAW not SYS so the range errors SYSUR and SYSOR are independent of the SZ setting This more complete picture is used for the discussion of the compensation facilities in the following chapters Calibration Parameters Summary and Defaults The various control parameters are listed for each stage This also includes the compensation parameters not covered in this chapter but shown in Figure 5 2 Readings Processing Full The default values shown set the device back to its nominal default calibration full scale output 26 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Cell Control Defaults Command Action Default Values COFS sf basiccelloffset_ 100 O CTG1 5 gain adjusts 0 0 0 0 0 CLX1 7 linearity raw value points 0 0 100 0 0 0 System Control Defaults Command Action Default Values Default Values SOFS SMIN raw min limit 50
112. s window Hit the Change Comms Settings button A new popup window appears Select the new VisualLink communications baudrate with the popup menu controls Hit Ok to confirm and hide the window Hit Start Communications button again You should now find you can talk to the device again SEET 22 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Chapter 4 Summary of Software Features This chapter gives a complete overview of all the software functions Each item has only a brief description here consult the references for detailed information User Calibrations The devices have sophisticated digital calibrations which can be adjusted via communications See Chapter 5 Readings Processing and Calibration Diagnostic Warnings Checks are continually made on correct operation and warning flags record any problems found See Chapter 6 Self Diagnostics Temperature Compensation An internal temperature measurement can be used to correct for sensor drifts with temperature See Chapter 6 Temperature Compensation Linearity Compensation Corrections can be applied to correct for non linearities in the input measurement See Chapter 7 Linearity Compensation Communications Lock A security scheme enables a supplier to ensure that devices they sell can only be used with their software and vice versa See Chapter 9 Device Locking Factory Calibration The calculations for the basic elect
113. setting just click in the relevant box and enter the new value The new value is sent to the device immediately This application page shows how the SOUT output is produced from the basic CELL reading value by the following steps 1 The input is the CELL reading value 2 This then has SOFS the system offset subtracted from it 3 The result of this is multiplied by SGAI the system gain 4 After applying GAIN the result is limited to the range SMIN SMAX system minimum to system maximum 5 This gives the new SOUT output value The system over range flags are also shown SYSUR SYSOR system under range over range If the scaled result was bigger than SMAX or smaller than SMIN then the SYSOR or SYSUR flag is set NOTE SMIN amp SMAX also clamp the output SOUT to exceeded value Try changing the SOFS and SGAI parameters to different values The SOFS parameter is used to remove the cell output offset E G If CELL reads 0 1253 when the load cell is unloaded set SOFS 0 1253 to make SOUT 0 with no load The SGAI parameter scales the results so changing the output units E G if you have a 2 5mV V output 5 tonne load cell then the CELL output should be 100 for a nominal 5 tonne load So setting SGAI 0 05 causes the cell to read approximately in 16 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 tonnes Note that when you change SGAI you change the output units so SMIN and SMAX ma
114. several converters and some DCell devices destroyed in this way Also note that this kind of damage may often not be immediately obvious appearing as erratic operation rather than outright failure To Avoid These Problems 1 Any portable should be separately grounded e g via the converter supply before connecting it to the mains supply or to a DCell DSC bus Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 67 2 We always recommend the use of externally powered rather than port powered data converters see below for details of suitable converters RS232 Bus Layout Essentially the only limitation here is on the cable length As described in The RS232 Bus Standard in Chapter 11 Communication this is supposedly up to 15m independent of baudrate This is not a very realistic figure for typical modern hardware For genuine RS232 compatible hardware the length might be at least twice this at 9600 baud and perhaps more at lower speeds However some PCs have serial ports that are not truly RS232 hardware compatible and may not have sufficient drive for specified operation In these cases the port will probably still be usable with a short enough cable It would be far safer though to replace the suspect hardware with something more suitable RS485 Bus Layout See also the general discussion of RS485 characteristics The RS485 Bus Standard in Chapter 11 Communication Multiple devices
115. st accuracy over the measurement range 6 Take the known weight of your test weight in the required engineering units and divide by the current SOUT value i e calculate weight SOUT Put this value into SGAI 7 Set SMIN and SMAX to an appropriate output value range SOUT should now show the value of the test weight as required The next section briefly reviews different methods of establishing the calibration values Calibration Methods There are a number of ways of establishing the correct control values Method 1 Nominal data sheet performance values This is the simplest method where the given nominal mV V sensor output is used to calculate an approximate value for SGAI as described in the above example E G a 50 KN i e approx 5 tonne load cell has nominal sensitivity of 2 2mV V full scale The standard DCell DSC sensitivity is 2 5mV V giving an output value of 100 so to get 50 0 for an input of 2 2mV V we set SGAI to 50 100 2 5 2 2 0 568182 N B 6 figures is a suitable accuracy to work to It is also useful to set SMIN SMAX 50 0 to show when the input goes out of the normal range because the electrical signal will now never exceed the normal range Method 2 Device Standard Calibration Values With some load cells you may have a manufacturer s calibration document This gives precise cell output gain and offset specifications for the individual cell These values can be used to set the SGAI and
116. st with an input of more than 2 5mV V you will have to adjust the hardware sensitivity to avoid saturating the input If it is less you can correct in software alone but increasing sensitivity will generally improve accuracy To adjust the mV V of a DCell or DSC an extra resistor Rg is fitted across the pads RG as shown above in Figure 13 13 Identifying the DCell Rg Resistor Rg resistor l l l l D Identifying Sensor End Connections The link across TC can be cut to disconnect the internal 100R gain resistor This is needed for lowering the sensitivity 70 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The resistor is 0805 size surface mount chip A 0 1 15ppm resistor must be used to maintain performance Reducing Sensitivity To accommodate a maximum sensor output larger than 2 5mV V it is necessary to reduce the electrical sensitivity of the input circuitry To decrease sensitivity the link TC is cut and the value of the resistor fitted in kQ should be Rg required mV V x 40 where S is the required sensitivity in mV V Increasing Sensitivity When the full scale output is smaller than 2 5 mV V it may be desired to increase sensitivity However it is often possible instead to compensate partly or entirely in software by increasing a software gain control CGAI or SGAI see Main Reading Calculations in Chapter 5 Readings Processing and Calibrati
117. ted character somewhere else Access attempted not supported by this command NOTES e From receipt of the host s terminating lt CR gt to a response from the device if any will be at most 50mS After this it can be assumed there is no response e There is no value checking A slave can not NAK a command because a write data value is unsuitable in some way only if write access itself is disallowed For the Ack with data i e a successful read command the returned value consists of printable ASCII characters finishing with a lt CR gt formatted according to the DP and DPB settings as follows 52 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Write Command If the command is accepted by the device then a lt CR gt is transmitted There is no error checking on the data received by the device Example A command to set the BAUD parameter to 3 on station 1 could look like this 1001 BAUD 3 lt CR gt assuming a device with STN 1 is present it will respond with lt CR gt Read Command Returns the requested value specified by the command The returned value is formatted according to the DP and DPB values The response consists of a sign character DPB decimal digits before a decimal point DP digits after the point and a terminating lt CR gt The length of the response is thus fixed at DP DPB 3 characters Example A command to read the SOUT output could look like this 1001 SOUT
118. the data fast enough Reading Snapshot The action command SNAP samples the selected output by copying SOUT to the special result parameter SYSN The main use of this is where a number of different inputs need to be sampled at the same instant Normally multiple readings are staggered in time because of the need to read back results from separate devices in sequence By broadcasting a SNAP command at the required time all devices on the bus will sample their inputs within a few milliseconds The resulting values can then be read back in the normal way from all the devices SYSN parameters Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 43 Output Format Control ASCII ONLY The parameters DP and DPB are used to control the formatting of floating point values in the ASCII protocol DP controls the number of decimal places after the point and DPB controls the number of decimal places before the point Values of 1 8 are appropriate in both cases All output values are then transmitted in this same format As values are limited to a normal 4 byte accuracy about 7 digits it may sometimes be necessary to alter the formatting for best accuracy in reading writing values E G if DP 5 and DPB 2 the value 1 257 is output as 01 25700 Changes to DP and DPB only take effect when the device is rebooted as for BAUD and STN Continuous Output ASCII ONLY For the ASCII protocol only there is a continu
119. the notice being displayed Save it to another filename if you want to retain the original designs Hardware Requirements Recommended minimum PC specification e Pentium 200 with Windows 95 or better e Mouse e 64MB RAM e CDROM e 45MB hard disk space A lower specified PC will still run the software but speed will be reduced Installing the Software Uninstall any previous versions of VisualLink before proceeding Placing the CD in the CD ROM drive should start Auto Install If not run SETUP EXE from the CD drive by selecting Run from the Start Menu and typing D SETUP where D is the drive letter of your CD ROM drive The software will install into a folder called Visua Link inside the Program Files folder You may change this destination if required After installation you may be asked to restart the computer This should be done before proceeding with communications Once installation is complete a new item will be placed in the Programs section of your Start Menu called VisualLink This will contain the following items see below Design Examples ge Help Getting Started ge Help VisualLink The on line help for VisualLink Will open the design example folder 1 Tutorial Adding an Instrument A brief animated tutorial about adding an instrument l Tutorial Object Manipulation Z Visuallink Application A brief animated tutorial about manipulating objects The VisualLink application Runnin
120. the value that is transmitted e Snapshot SOUT is the result latched into SYSN by a SNAP command e Result update the OLDVAL flag is reset only when SOUT is read In order to choose the selected output result ICNT is set to an indexing value The following values are currently supported see Figure 5 2 Readings Processing Full and Figure 10 1 Electrical Calibration Process for details of these parameters SRAW System output before SZ Gross value Cell force output 400 FLAG faultdiagnostics_ 5 LCB cell output before linearisation 6 ELEC rawelectrical reading ek 8 RAW rawinputvaluebefore 9 EXC sf excitation measure _ _ Y dynamic filter me constant 11 OFFS input channel in use 1 Mi to zero 13 SYSN_ Smapshotvalue _ _ _ _ The usual default setting is ICNT 0 which makes SOUT SYS New devices are always shipped with this setting Output Update Tracking The OLDVAL flag is cleared every time new reading values are produced and set when the SOUT output value is read This allows sampling each result exactly once SOUT is read and possibly other results and then the host waits polling the FLAG value until OLDVAL is cleared to indicate a new output is ready This scheme works as long as the communications speed is fast enough to keep up With faster update rates and slower baud rates it may not be possible to read out
121. to the converter and connect the other end to the 4 way screw connector on the PCB using the colour codes indicated on the PCB ident Ensure LK4 amp LK5 are set to pins 1 amp 2 Fit LK3 which terminates the RS485 comms Connect the power cable to your power supply which has been set to deliver between 10 amp 15 volts then switch on Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 9 Figure 2 2 DCell RS485 Versions Evaluation Kit Communications Connecting Up The Evaluation Kit For RS232 Connect the supplied power cable Red amp Black twisted to the 4 way screw noting the colours indicated on the PCB Connect the 9 way D Type extension lead to the J1 of the evaluation board marked RS232 and the other end to the comms port of the PC Ensure LK4 amp LK5 are set to pins 3 amp 2 again see PCB indent for the markings of these links Now connect power cable to your power supply which has been set to deliver between 10 amp 15 volts and switch on 10 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 Figure 2 4 DSC2 RS232 Versions Evaluation Kit Connections Note that if your PC serial port has a 25 way serial port connector you should use the 9 to 25 way D type adaptor provided to connect to the evaluation hardware Installing VisualLink The DCell DSC evaluation communications application is written for the VisualLink environment VisualLink is Ma
122. type A central host device normally a PC or PLC acts as a bus master in control of all communications Communications consist of the master transmitting command messages addressed to particular DCell DSC slave devices The target slave may then transmit a response message back to the master Because there is only one bus master and slaves never initiate communications the master is in control of all communications This enables multidrop operation i e a single master can control any number of slave devices at a time In practice the master usually polls the attached slaves interrogating them in a fixed rotation Command Types A single command sent to a device can instruct it to read from or write to an internal parameter value or to execute a Control Action The device responds by returning data for a parameter read or a simple acknowledge for write or action Precise details depend on the protocol in use Each command message contains the following information 1 The intended slave address or broadcast 2 The command to access 3 The access type one of read write execute 4 for write accesses only the write value The command response will then be one of the following three types 1 An error indication 2 Asimple acknowledge 3 A read data value implicit acknowledge 50 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The various protocols dif
123. ut is that no data converter is required to connect the device to a PC The RS485 bus is the simplest and most flexible choice from the wiring point of view It enables multi drop operation and much longer cable lengths However it usually requires a bus converter which must be chosen to suit the equipment in use 48 Mantracourt Electronics Limited DCell amp DSC Version 2 User Manual Issue 1 3 The RS232 Bus Standard RS232 has separate dedicated transmit Tx and receive RX wires Each wire is permanently driven by the sending end with no transmit enable disable controls so RS232 is only suitable for one to one communications The connection is basically 3 wire in that the Tx and RX signals are related to a common ground potential For DCell DSC connections this ground is shared with the power return VIN 3 It is therefore especially important for RS232 devices to connect the earth at the device end to avoid noise from communications degrading the reading accuracy The RS232 standard specifies operation over line lengths of 15M 50 ft or less more or less independent of baudrate The drive capability of RS232 compatible hardware varies a great deal but most exceed this comfortably at least at the baudrates used by DCell DSC devices The RS485 Bus Standard RS485 differs from RS232 in two important respects 1 It uses differential signalling on pairs of signal wires With small voltage detection thresholds and a large a
124. y also need to be adjusted E G if in the previous example you wanted an output in Kg you would set SGAI 5 0 But the valid output range will then be 5000 Kg so you also need to set SMIN 5000 and SMAX 5000 as well otherwise the output will still be limited to 100 The boxes show the current values of parameters in your device The applications page reads data from the device to display the values and allows you to enter new values which are then sent back to the device It thus acts as a window on the data within the device you are currently communicating with To return to the previous page just hit the Main Comms Page button Device Communications Most interactions with DCell DSC devices actually involve reading and writing parameter values e Device outputs are read from read only parameters e Control values such as the calibration controls above are read write parameters e Some fixed values such as device serial number are also read only However some commands can simply cause a one off action to be performed e g the SNAP command takes a snapshot sample of the current output value see in Chapter 10 Additional Software Features and the RST command causes a device reboot see Changing Device Communications Settings below The commonest use of DCell DSC devices in an overall system involves several devices on one bus with a host controller reading the main output value from each

Dcell & DSC version 2 Manual - Load and Force Cells, Indicators

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Dcell &amp; DSC version 2 Manual - Load and Force Cells, Indicators

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Dcell & DSC version 2 Manual - Load and Force Cells, Indicators