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1. CNTRL CHNL Select control monitor chnl RESET MONIT CHNL Confirm monitor ENT 3 CU CONST Sensor type selection RESET 2 FE CONST RESET 1 CR ALUMEL ENT OF 0 Defaults for true ENT SG 4 0800 reference junction ENT VTC 90 Finished Note that in the case of monitor channel only the compensated reference junction mode is available F HARDWARE DESCRIPTION reference drawing REAR VIEW OF PARTS In this section we describe the internal composition of the instrument s hardware at the level of boards It is essentially intended as a guide for the following Hardware Calibration section THE SYSTEM IS COMPOSED OF THE FOLLOWING BOARDS VY POWER SUPPLY board provides the DC voltages of 5 and 15 for the whole unit Note that every voltage output has a separate fuse Y CPU board with EPROM RAM and EEPROM memory Occasionally new application software may become available This resides and is distributed in an EPROM chip There are two EPROM chips mounted on the board one on top of the other piggyback arrangement Since the two 24 pin chips have all the pins but one in common the lower one has a 24 pin socket soldered to it EPROM exchange consists of dissoldering the conductor connected to the single non shared pin 20 taking the upper EPROM out of the socket replacing it with the new one be STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 26 of 26
2. 5 2400 6 4800 7 9600 W is the word length code 1 7 3 8 bits 0 2 are illegal Use 8 bits code 3 only when parity is None code 0 S is the stop bits code O illegal 1 1 2 1 5 3 2 bits P is the parity code O None 1 0Odd 2 illegal 3 Even The default code set up after a Tabula Rasa is 1844 corresponding to 9600 Baud No parity 8 data bits 1 stop bit 1 2 USING THE RS232 INTERFACE The serial interface can operate in two different modes The user specific mode is used to emulate other VT controller communication protocols or to implement a user defined protocol Please contact Stelar for further information on the availability of such modes The generic mode is always active provided that the serial board is available It simply associates certain input characters with the keyboard and ignores all others When a character is received through the serial input the system first tests whether it belongs to the keyboard image set If so it proceeds as though the corresponding key were pressed otherwise the character is ignored The keyboard is also active on the first come first served basis Two special input characters are reserved as serial output enable and disable commands When the output is enabled the controller echoes through the RS232 everything that appears on the display In this way one can remotely control the unit and execute all the procedures described in this manual The generic mode keyboard image
3. PROPORTIONAL TERM COEFFICIENT It is expressed as the percentage of output power for one degree of deviation from the set point Recommended values 0 5 2 Proportional or 10000 ON OFF Admissible values any non negative number INTEGRAL TERM COEFFICIENT It is also intended as the percentage of output power per one degree variation of the deviation integral Recommended values 0 5 2 Admissible values any non negative number DERIVATIVE TERM COEFFICIENT Percentage of output power for one degree variation between two consecutive measurements It is used to damp excessively fast temperature variations and therefore decrease overshoots damping Recommended values 0 2 5 Admissible values any nonnegative number SET POINT APPROACH FACTOR In most VT controllers whenever the set point changes the new value is immediately presented to the control algorithm The VTC91 however changes the operative value of the set point gradually starting at the current temperature and terminating at the desired set point In each control cycle the difference between the final and the operative set point values is reduced by the factor SF The setting SF 0 corresponds to the traditional behaviour Recommended values 90 97 Admissible values 0 999 FILTER PREDICTOR FACTOR FOR THE MAIN SIGNAL INPUT For FP gt 1 a linear predictive action is introduced This may dramatically increase stability in highly dynamic thermal sys
4. careful to orient it the same way as the lower one and to leave its pin 20 free and connection to its pin 20 V AD_16_BIT board is a 16 bit single slope Analog to Digital converter with a sampling rate of over 200 Hz Three trimmers P1 P2 and P3 are available for the calibration of scale offset and voltage reference respectively see the Hardware Calibration section VY 4CH_DAC is a four channel Digital to Analog converter board Two channels are used to generate the reference voltages for the Evaporator Power Driver and Heater Power Driver boards The offsets of these reference sources can be corrected by the trimmers P2 and P3 respectively see the Hardware Calibration section VY The VT INPUT board implements the analog multiplexer between the different measuring channels and the hardware interlocks Trimmers P1 e P2 permit to adjust the thresholds of the safety interlocks for the evaporator and the heater respectively see the Hardware Calibration section VY RS_232 is an optional interface with a host computer VY TC ADAPTER board containing two TC transducers AD595 with electronic reference junction compensation used for TC1 and TC2 inputs and one precision OP amp transducer used with TC3 and TC REF inputs In order to minimize transducer drifts room temperature dependence all active parts are placed in a thermostated oven Y VTCON board this board implements all interlocks alarm and control signals between the u
5. characters are VTC key RS232 character ASCII code Digits 0 9 0 9 48 57 45 Frm 46 Cal Prg P 80 Enter Print 59 STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User Manual Pag 33 of 33 Reset R 82 Adv A 65 Echo display 63 The pin out of the RS232 connector at the rear panel of the VTC is listed in the following table Signal VTC Cannon25 Cable PC Cannon 25 female male female male GND 7 7 Gnd RTS 4 high gt 8 DCD DTR 20 hndshk gt 5 CTS and 6 DSR Rx 3 lt 2 Tx Tx 2 gt 3 Rx DCD 8 rxenbl lt 8 DCD CTS 5 hndshk lt 20 DTR Note On the VTC side the DSR data set ready input signal pin 6 is NOT used The table also indicates an example of a VTC PC connecting cable based on the following assumptions The presence of an active VTC and of the connecting cable is signalled to the HOST by asserting its DCD Data Carrier Detect line The same signal returns to the VTC through the cable and enables its own DCD line The VTC signals its readiness to receive DTR output by asserting the CTS Clear to Send and DSR Data Set Ready lines The Host may test any of these lines before sending characters to the VTC The VTC tests its own CTS Clear to Sent input before transmitting a character The HOST controls that line through its DTR Data Terminal Ready output If desired the HOST may do the same through its RTS Request to Send
6. voltage At some point you will either reach the end of the trimmer range low evaporator resistance or else the voltage will stop increasing because of saturation high evaporator resistance In any case set the trimmer just below the maximum voltage limit CALIBRATION OF THE HEATER SAFETY THRESHOLD The heater assembly contains a safety thermocouple A hardware interlock connected with this TC detects a SAFETY TC HOT condition It is essentially used to prevent overheating of the heater assembly in case of missing gas flow e g due to a disconnected tube The purpose of this calibration is to set the safety TC threshold to a reasonable value There are two alternative ways to calibrate the threshold a Make sure that interlocks are off the lamp INTERLOCK on the front panel must not be lighted Disconnect the heater Open the left rear panel Find out from standard tables the thermocouple voltage corresponding to the desired safety threshold You will need to know the type of thermocouple employed Using an external voltage source apply the above voltage to across pins 3 and 6 of the HEATER connector Using a screwdriver turn trimmer P2 on the VT_INPUT board until locating the position around which the interlock lamp on the front panel switches on and off b Put the safety thermocouple at the desired threshold temperature Open the left rear panel Using a screwdriver turn trimmer P2 on the VT_INPUT bo
7. wrong Recommended values 20 100 Admissible values positive integers LOWER SET POINT LIMIT IN DEGREES CENTIGRADE It may be desirable for safety reasons to make it impossible to introduce not even by a mistype an unreasonable value of the set point For this reason two set point limits low and high can be specified by the user Admissible values any number UPPER SET POINT LIMIT IN DEGREES CENTIGRADE See LL for more details Admissible values any value higher than LL LOWER SAFETY LIMIT IN DEGREES CENTIGRADE For major safety the user may specify two safety interlock limits LS low and HS high If for any reason the control channel temperature exceeds US or drops below LS both output power channels are disabled and a proper message is displayed either TEMP TOO LOW or TEMP TOO HIGH Recommended values LL 20 Admissible values lt LL UPPER SAFETY LIMITS IN DEGREES CENTIGRADE See LS for more details Recommended values UL 20 Admissible values gt UL EVAPORATOR OUTPUT POWER IN OF FULL RANGE Apart from specifying the power applied to the nitrogen boil off resistors in the liquid nitrogen evaporator this parameter is used as a flag whether the evaporator is actually used EV gt 0 or whether an external carrier gas flow is being applied Admissible values 0 100 CARRIER GAS FLOW LEVEL This parameter is meaningful only if EV gt 0 Since the gas flow regulator is manual FL serves only as a
8. 09 page 09 page 10 page 11 page 12 page 13 page 13 page 15 page 15 page 16 page 16 page 20 page 21 page 21 page 22 page 24 page 25 page 27 page 29 page 29 page 30 page 30 page 32 page 32 page 32 Stelar VTC User manual page 2 of 2 STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 3 of 3 A GENERAL DESCRIPTION The following manual describes the STELAR Variable Temperature Controller VTC91 It is intended as a general guidance for the operator It corresponds closely to the actual unit in terms of hardware configuration software structure and performance Any deviations regard optional accessories which are described as installed but which need not be ordered and therefore may be missing in the delivered equipment STELAR claims the right to implement without warning additional options modifications and improvements resulting from the ongoing development of the product This manual therefore corresponds to the minimum performance of a fully equipped unit The product conforms to the security norms of most countries in particular the EEC and USA regulations Mains voltage is only applied to the mains switch with its incorporated fuse and to the primary of the mains transformer It is nowhere accessible to a naked human hand Voltages at any other point do not exceed 30 V DC Shorting and interconnecting any input or output lines in any way can not c
9. heater into its place usually a probe or cavity dewar and connect it to HEATER socket on the rear panel c Connect the flowmeter inlet AIR IN located on the right rear panel to a supply of dry compressed air or nitrogen 1 2 Atm If a compressor is used as a supply insert suitable filters between the compressor and the instrument to prevent dust accumulation and water condensation d Connect the flowmeter outlet A R OUT on the right rear panel to the carrier gas inlet at the thermostated device usually a probe or cavity dewar with a spherical joint e Set a correct flow level on the flowmeter regulator carrier gas flow is a important control parameter Note Use flexible tubing of about 4 5 mm internal diameter and about 6 mm of external diameter for the air inlet and outlet connections The unit is now ready and you can run the control program See the Standard Operations section for further details During temperature control several safety interlocks may be tripped if for any reason a pathological condition occurs Whenever an interlock is tripped the interlock light on the front panel switches ON and output power channels are automatically disabled If no gas flow is detected by the flowmeter while the control program is operative an interlock is tripped and the error message MISSING AIR is displayed This interlock is ignored and no message occurs if you are using a liquid nitrogen evaporator If the safety ther
10. no integral action neutralization Recommended values 5 20 Admissible values any non negative number PREDICTIVE INTEGRAL APPROACH DAMPING When this term is absent value zero the integral term is quite inefficient to damp any small oscillation around the set point In order to damp these oscillations the integral term build up must be interrupted no increment if the signal derivative indicates than using the current value of integral the set point is to be reached anyway in less than IA steps Setting IA very large any value above about 100 will have the same effect is equivalent to interrupting the integral term build up whenever an excursion cycle reaches a maximum zero derivative It is very efficient in quenching oscillations but may lead to sluggish behaviour during an overdamped approach phase Recommended values 20 80 Admissible values any non negative number MAXIMUM OUTPUT POWER IN OF FULL RANGE MP may be used as a Safety precaution in those situation where you know a priori that only a fraction of the output power will be needed Admissible values 0 100 MAXIMUM OUTPUT POWER STEP IN OF RANGE The output power may not change by more than MS in a single control cycle Putting MS very low e g 0 25 makes the approach phase rather slow but reduces the overshoot Putting MS 100 its effect is completely eliminated Values of at least 10 are required in high dynamics systems if fast action with minimum
11. properly pre cooled operation at and below room temperature If liquid nitrogen evaporator is used make sure that it is connected and that the liquid nitrogen level is high enough to submerge the heating resistor STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 12 of 12 ii The controller is properly configured This means that the correct sensor type and reference type for the control channel must be set Moreover a satisfactory operation requires a proper set of control algorithm parameters Different set ups require somewhat different parameters in order to optimize the controller performance Proper values of the parameters are usually found empirically and stored in the non volatile memory In fact several different sets parameter tables can be stored subsequently any one of them can be selected see the Load Parameters procedure in the Special Operations section The control parameters include CP proportional coefficient Cl integral coefficient CD derivative coefficient SF FP IB IA set point approach factor filter predictor factor integral action band integral approach damping factor MP maximum heater output power MS maximum step in output power NR averaging number in regulation LL set point low limit UL set point high limit LS safety low limit US safety high limit EV evaporator power level or EV 0 for no evapora
12. 7035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 11 of 11 D 2 TEMPERATURE MONITORING PROGRAM 0 Program 0 is the default program recalled automatically after the reset interval provided you do not press any key during lt can be also entered by pressing the ENT PRT key or the 0 key for Program 0 during the reset interval Once running Program 0 will start displaying the control channel temperature in degrees Centigrade The displayed temperature will be correct only if the control channel sensor has been correctly configured sensor type reference type reference temperature For further details see Reference and Channel Configuration in the Special Operations Section During monitoring the sensor integrity is being continuously tested If the sensor breaks down or becomes disconnected the interlock light comes ON and the message BROKEN SENSOR appears repetitively until the condition ceases If a second monitor channel is also implemented and its sensor is operative and properly configured its reading will automatically appear on the display Should the sensor break down or be disconnected this reading will simply disappear without any message If the optional printer is mounted pressing the key ENT PRT during monitoring will result in a printer copy of the current display By default the monitoring routine displays the temperature with two decimal digits Pressing the keys 0 1 2
13. ATION 12 GND INST The AD 16 BIT board has a hardware failure 13 RIF TARA The AD 16 BIT board has a hardware failure H 3 SOFTWARE PROBLEMS AND FULL RE PROGRAMMING If upon switching ON or upon a CPU reset the message DIRECTORY KO appears than the EEPROM memory has been corrupted In this case you must reprogram it from scratch For full re programming proceed as follows VTC User Comment CPU RESET DIRECTORY KO If anything else happens proceed TABULA RASA as described on next page STOP PRGO gt ENT Directory program introduction 0 gt 84 Introduce initialization code VALUE 2645 for LH71 display If you have the LH2012 display use 2644 If your CPU clock is 2 5MHz use 2635 or 2634 respectively 7 gt 12 Initialization command 8 gt 19 Return command 9 gt STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 31 of 31 1 End of directory program NUMBER OF REG 640 Number of directory register if EPROM is only 2Kbye set 145 ENT 33 is minimum NUMBER OF REG 640 ENT DAC TYPE 0 1 0 Standard 12bit DACs 1 for 16bit ENT VR FACTOR 1 Voltage scale down ratio 2 for high temperature INPUT board ENT VTC 90 CAL PRG Enter SPECIAL PROCEDURES PARAMETERS ENT Now modify any parameters according to Paragraph E 3 At this point everything should be working again correctly It might also happen that upon switching on the following se
14. ESSORIES 15 column thermal printer serial RS232 interface parallel interface Xt or XY plotter interface Digital plotter interface Acoustic visual alarms Special application firmware Programming kit Pt100 sensors and sensors for pressure pH humidity etc C 1 CONNECTING THE THERMOCOUPLES a Insert the control thermocouple into whatever device is to be controlled NMR probe EPR cavity etc b Plug the control TIC into the rear panel connector TC 1 if you want to use the internal compensation of reference junction Plug the control TC into the rear panel connector TC 3 if you want to use an external reference thermocouple In this case plug the reference TC into the adjacent TC REF connector c If you want to use it plug the optional monitor thermocouple into the rear panel connector TC 2 A disconnected or misconnected control thermocouple trips an interlock and causes the error message BROKEN SENSOR to be displayed The program also tests whether the monitor channel is available and uses it only if installed In those situation where the monitor TC is required e g in the monitor sensor calibration routine its absence will be indicated by the message MISSING SENSOR STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 8 of 8 C 2 OPERATING ABOVE ROOM TEMPERATURE a Connect the control thermocouple as described above b Insert the
15. Stelar VTC User manual zom CONTENTS GENERAL DESCRIPTION A 1 Introduction A 2 Front panel description A 3 Rear panel description SPECIFICATIONS INSTALLATION C 1 Connecting the thermocouples C 2 Operating above room temperature C 3 Operating below above room temperature without evaporator C 4 Using the liquid nitrogen evaporator STANDARD OPERATION D 1 Starting up D 2 Temperature monitoring Program 0 D 3 Temperature control Program 1 page 11 D 3 1 Temperature control without evaporator D 3 2 Temperature control with evaporator D 3 3 Temperature control operative phase D 4 Power generator with temperature monitor Program 2 page 14 SPECIAL OPERATIONS E 1 Special operation Information E 2 Special operation Setting Reference Temperature E 3 Special operation Control Parameters Editing E 4 Special operation Copy a Parameters Table E 5 Special operation Join a Parameters Table E 6 Special operation Sensor Calibration E 7 Special operation Set Point Calibration E 8 Special operation Channel Configuration HARDWARE DESCRIPTION HARDWARE CALIBRATION TROUBLESHOOTING H 1 Hardware problems H 2 List of error messages H 3 Software problems and full re programming H 4 Fuses SERIAL RS232 INTERFACE 1 1 RS232 configuration 1 2 Using the RS232 interface STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it page 1 of 1 page 03 page 03 page 05 page 06 page 06 page 07 page 08 page 08 page
16. always higher than the precision of the unit when used as a simple measuring device We call the difference between the two quantities loop noise Ideally the loop noise should be zero but that would require a noiseless sensor and an absolutely perfect control algorithm Unfortunately it is impossible to rigid controller specifications unless the thermal load is also defined since this part of the loop has a crucial effect on the controller performance Changing a thermal load requires a change in the control algorithm parameters there is no and never will be fixed configuration universal controller On devices controlled by analog circuitry the re configuration consists in changing the settings of switches and variable resistors On digital devices such as ours it consists in editing the values of a number of digital parameters a much more versatile approach In principle it is possible to envisage a device which could learn from experience and refine the control parameters our unit does not behave in that way but it could implement such algorithms should they become available in the future without any hardware modification The control algorithm uses a set of control parameters stored in a non volatile memory these permit performance optimization for practically any type of thermal load Negligible overshoot control stability better than 0 1 and locking within 3 minutes are characteristic for most situations The device can me
17. ameters are likely to be somewhat different than at 1500 As a consequence The instrument therefore permits to create and edit distinctly numbered control parameters tables Using the special operation JOIN PARAMETERS see below any one of the existing tables may be selected as the active one The EDIT PARAMETERS procedure permits to check and or modify the parameters in the active table A duplicate of the current active table can be made by means of the special operation COPY PARAMETERS These three procedures allow a simple but effective management of the stored control parameter tables c Upon exit from the editing procedure the presumably modified table will be stored in the non volatile memory The currently active table is automatically recalled upon switching on or resetting the instrument ensuring a continuity between consecutive intervals of use STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 17 of 17 THE CONTROL PARAMETERS EDITING PROCEDURE For each system parameter its acronym and its current value are displayed Press ENT PRT to confirm the current value or input a new one When the list of parameters is exhausted the system save them this can take a few seconds and resets If you have the optional printer a list of all parameters will be generated THE FOLLOWING PARAMETERS ARE CURRENTLY SUPPORTED Cl CD SF FP
18. and any other activity is suspended Moreover in the case of background monitoring the reaction to pressing a key may occur only after a noticeable delay up to 2 seconds since all internal cycles must be terminated before the current task interruption In some cases the unit will present queries to the operator A query is a string followed by a question mark and a blinking cursors You can answer it either YES by pressing the ENT key or NO by pressing the RST key STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 10 of 10 Whenever a prompter string without any question mark appears the unit requires a numeric input Numerical values may be entered in any format just press the appropriate keys After pressing the first key the display will clear and indicate 0 Press the key if you want to change the sign Then press the digit keys and the eventual decimal point followed by decimal digits After at least one significant digit has been input pressing the key will start input of an optional exponent Upon a syntax error or upon pressing intentionally the RST key the message REPEAT will appear and you can restart again Once the desired number has been properly composed on display it is entered by pressing the ENT PRT key Pressing simultaneously the keys 1 2 and 3 will cause a reset of the unit equivalent to switching off and on again This
19. anual page 6 of 6 A 3 REAR PANEL DESCRIPTION SEE DRAWING The rear panels left and right contain the following devices RIGHT PANEL Carrier gas inlet and outlet for the gas flowmeter Mains connector with an incorporated slow blow fuse holder Cooling fan LEFT PANEL Connector TC1 for the compensated control thermocouple Connector TC2 for the compensated monitor thermocouple Connectors TC3 and REF for the differential arrangement with a control thermocouple TC3 and a true reference junction thermocouple REF RESET CPU reset push button HEATER 7 pin connector for the heater assembly including also a safety TC input EVAPORATOR 7 pin connector for the evaporator assembly including also a safety TC input ALARM An optional connector for external alarm device RS232 An optional communication connector B SPECIFICATIONS DIMENSIONS Table top version W54 x H18 x L35 cm Rack mounted version 19 x 3units x 35cm WEIGHT 8 kg MAINS 220Vac 50Hz 3A optional 115Vac 60Hz 6A GAS FLOW REGULATION manual 0 300 nl h or 0 1 5 nm3 h CONTROL OUTPUT POWER max 120W 30V 0 4A CONTROL OUTPUT RESOLUTION 11 bit 2048 steps EVAPORATOR OUTPUT POWER max 120W 30V 0 4A EVAPORATOR OUTPUT RESOLUTION 11 bit 2048 steps ADC ultralinear 16 bit 5msec CPU Z80 2 5MHz 16K ROM 8K RAM 8K EEPROM AUTOMATIC SELF CALIBRATION of the ADC converter SENSOR CHANNELS Control channel with two o
20. ard i e the ratio between the output current and the reference voltage voltage generated by the 4CH_DAC board The proper setting depends upon the resistance of the evaporator load If the evaporator is supplied by Stelar the calibration will be already done otherwise you will have to do it yourself in order not to downgrade the unit s performance Note Best power performance is achieved with 8 Ohm evaporator resistors Values from 4 to 16 Ohm are acceptable even though they will not permit to exploit the full range of the power driver a Open the left rear panel left and connect with care a DC voltmeter across the evaporator resistor pins 1 2 and 4 5 of the EVAPORATOR connector b Calibrate the evaporator current offset zero current Run Program 2 see the Standard operations section Select the evaporator and set POWER 0 STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 28 of 28 Using a screwdriver turn trimmer P2 on 4CH_DAC board until your voltmeter indicates 0 volt on the heating resistor Reset the instrument c Calibrate maximum evaporator current make sure the evaporator rod is immersed in liquid nitrogen Re enter Program 2 Select the evaporator and set POWER 100 Using a screwdriver turn trimmer P1 on the EVAPORATOR POWER DRIVER board until you see same voltage variation Now keep turning P1 in the direction of increasing
21. ard until locating the position around which the interlock lamp on the front panel switches on and off CALIBRATION OF THE EVAPORATOR SAFETY THRESHOLD The evaporator assembly contains a safety thermocouple A hardware interlock connected with this TC detects a MISSING N2 condition It is essentially used to prevent operation if all liquid nitrogen has been boiled off and the heater is no longer immersed The purpose of this calibration is to set the safety TC threshold to a reasonable value There are two alternative ways to calibrate the threshold a Make sure that interlocks are off the lamp INTERLOCK on the front panel must not be lighted Disconnect the evaporator Open the left rear panel Find out from standard tables the thermocouple voltage corresponding to the desired safety threshold You will need to know the type of thermocouple employed Stelar uses STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 29 of 29 normally Copper constantan TC s but other manufactures of the heater assembly may use different types Using an external voltage source apply the above voltage to across pins 3 and 6 of the EVAPORATOR connector Using a screwdriver turn trimmer P1 on the VT_INPUT board until locating the position around which the interlock lamp on the front panel switches on and off b Put the safety thermocouple at the desired threshold tempe
22. ause harm to the operator It actually should not damage the instrument either even though we will not guarantee that in written The product comes normally with a 12 month warranty Most service if needed can be done by simple exchange of its plug in printed circuit boards More complicated problems may require shipping the unit to factory In such a case please take great care of its packaging STELAR can not take over the responsibility for any damage caused by transport DISCLAIMER Since our VTC controllers are general purpose devices and STELAR cannot foresee all the uses to which they will be put we disclaim responsibility for any kind of damage to persons or property which might occur concurrently with their use A 1 INTRODUCTION VTC91 is a self contained digital temperature controller optionally usable also to control other experimental conditions or process variables It has two power outputs one for the temperature controlling device usually a wire resistor inserted into a gas flow and one for an auxiliary load such as a liquid nitrogen evaporator Both outputs are digitally controlled high precision amperostats controlling the output currents They are physically identical any apparent differences are due only to the way they are employed by the instrument s software Apart from the power output modules the control hardware and firmware and the sensors the unit contains also a gas flow regulator as well as a n
23. calibration and the instrument re configuration after a serious system breakdown Just follow the instructions without much bothering about the underlying reasons for what you are doing Whenever an anomalous behaviour occurs first switch OFF the unit and then switch it ON again This will reset all the interlocks If the message VTC 90 does not appear switch OFF the unit and then switch it ON keeping RESET key pressed and proceed for full re programming see paragraph H 3 STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 30 of 30 H 2 LIST OF ERROR MESSAGES 1 BROKEN SENSOR Control TC not connected or broken 2 MISSING SENSOR Monitor TC not connected or broken 3 MISSING AIR The flowmeter doesn t detect any gas flow 4 MISSING N2 The evaporator safety TC is too hot See HARDWARE CALIBRATION 5 SAFETY TC HOT The heater safety TC is too hot see HARDWARE CALIBRATION 6 TEMP TOO HIGH Verify parameter US see CONTROL PARAMETERS EDITING 7 TEMP TOO LOW Verify parameter LS see CONTROL PARAMETERS EDITING 8 MISSING TABLE TSpecified parameters table doesn t exist see section E 4 9 DIR KO Stored parameters are corrupted you must reprogram the unit see TROUBLESHOOTING SOFTWARE PROBLEMS 10 GND TARA The A D converter must be calibrated see HARDWARE CALIBRATION 11 RIF TARA The A D converter must be calibrated see HARDWARE CALIBR
24. e necessary Each actual reading is the mean value of a programmable number of single measurements This permits to increase considerably the already high basic resolution and suppress the sensor and transducer noise During each reading the instrument executes a self calibration cycle consisting of measuring the sensor voltage as well as the apparent ground and an reference voltage diode This implies signal multiplexing and digital evaluation but it eliminates almost all electronic circuitry imperfections such as offsets and drifts of operational amplifiers room temperature dependence of resistor and capacitor values power supply variations etc The result is a long term reproducibility better then 0 1 Apart from the resolution sensitivity and reproducibility of temperature measurements one is often interested also in their absolute precision The three parameters are in fact almost independent of each other A measuring device can for example excel in any two of them while performing badly with respect to the other one The basic absolute precision of our controllers is not particularly high We rely on the performance of the commercially available transducers such as the AD595 and thermocouples Since both belong to the 0 1 category the inherent absolute precision is about 2 However the unusually high sensitivity and reproducibility of the instrument makes it possible to calibrate it in terms of temperature and reach c
25. e the Standard Operations section for further details Like in the previous cases several safety interlocks may be tripped during the temperature control An interlock occurs if the safety thermocouple in the evaporator assembly detects a temperature higher then the threshold set by the trimmer P2 of the VT INPUT board In this case the error message MISSING N is displayed The threshold is factory set to 0 C Refer to the Hardware Calibration section for the setting this threshold D STANDARD OPERATION The unit is quite easy to use due to the presence of the alphanumeric display which permits a menu based interaction with the operator There are a few points you should remember Whenever a blinking cursor a large black box character appears on the display the unit is explicitly waiting for a keyboard input and any other activity is stopped Should any of the two output power channels be active it will be turned off if no key has been pressed for more than about 35 seconds If the cursor is not present the unit is operating but still keeps an eye on the keyboard background keyboard monitoring By pressing one of the keys you can interrupt the current task To do so you should know the effect of each key as described in this manual it may differ according to the current operating phase Keep in mind that the system always reacts to a key only after it has been released if you keep a key pressed the software cycles in a loop
26. et the instrument by pressing RST Keep in mind that if you select the control channel the calibration will regard only the currently configured reference junction mode Once the channel has been chosen the query ONE POINT will appear Press ENT PRT to confirm one point calibration or RST to execute the two point calibration 1 ONE POINT SENSOR CALIBRATION Inthis case the message MEASURE will appear Prepare your calibration device iced water bath or whatever set up the sensor and press any key The instrument will start monitoring the sensor temperature When you see that it stabilized press ENT PRT you can also press RST to reset the instrument with nothing done Atthis point the last measured value is memorized and the prompter TRUE VALUE will appear Input the correct temperature of the sensor The message WAIT will appear and remain on display for some time about 1 minute after that the instrument will reset itself and the calibration is done 1 TWO POINT SENSOR CALIBRATION STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 22 of 22 In this case the message 1ST MEASURE will appear Prepare your first point calibration device e g iced water bath set up the sensor and press any key The instrument will start monitoring the sensor temperature When you see that it stabilized press ENT PRT you can also pre
27. function is hard wired and independent of software It is also equivalent to pressing the RESET button at the back of the instrument D 1 STARTING UP A Switch ON the instrument or reset it either by pressing the RESET button located at the rear panel or by pressing simultaneously the keys 1 2 and 3 B The text VTC 90 appears and remains on display for about 5 seconds unless you press one of the following keys we will refer to this interval as the reset interval ENT PRT will immediately terminate the 5 seconds wait and enter the temperature monitoring routine 0 1 2 enter Program 0 1 2 if implemented CAL PRG will invoke the SPECIAL PROCEDURES menu RST followed by CAL PRG will ask whether to switch over to the TD MATE operating system see the TROUBLE SHOOTING section Should anything else happen please consult the TROUBLESHOOTING Section of this manual DURING THE RESET INTERVAL THE MOST FREQUENTLY USED ACTIONS ARE Press nothing Temperature monitoring starts within 5 seconds Press ENT PRT Temperature monitoring starts immediately Once you are within the temperature monitoring routine Press CAL PRG to enter the temperature control routine We will now describe in detail the following programs gt gt Program 0 Temperature monitoring gt gt Program 1 Temperature control gt gt Program 2 Power generator with temperature monitor gt gt Special Procedures STELAR s r l via E Fermi 4 2
28. l Alumel thermocouple Default transducer offset and gain Operator input Consequent VTC actions CNTRL CHNL Select control monitor chnl ENT COMPENSATED Select compensation mode RESET 3 CU CONST Select sensor type RESET 2 FE CONST RESET 1 CR ALUMEL ENT OF 0 Defaults for true ENT SG 4 0800 reference junction ENT VTC 90 Finished Note If the differential transducer for true reference junction arrangement is not implemented on your unit and you erroneously configure the control channel as though it were available the unit will signal BROKEN SENSOR as soon as you enter the monitoring or controller routine In this case the only thing to do is to reset and re configurate the channel reference mode to make it compatible with the hardware Example C Control channel Reference junction compensation STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 25 of 25 Copper Constantan thermocouple Offset and gain taken from a previous calibration Operator input Consequent VTC actions CNTRL CHNL Select control monitor chnl ENT COMPENSATED Select compensation mode ENT 3 CU CONST Select sensor type ENT OF 0 0109 Override the defaults 0 0157 an example ENT SG 4 0439 4 0207 an example ENT VTC 90 Finished Example D Monitor channel Chromel Alumel thermocouple Default transducer offset and gain Operator input Consequent VTC actions
29. libration using independent measurements of the sample temperature as a function of the set point We have found such calibration curves to be quite linear over a wide range of temperatures provided that STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 23 of 23 other conditions are maintained constant in particular the carrier gas flow and in NMR the decoupler power In practice you will have to measure the sample temperature during the temperature control This can be done for example by inserting the monitor channel thermocouple directly into a sample phantom However you can also use any other thermometric device or even any temperature dependent characteristic of the sample e g in NMR you can find out the actual sample temperature from the spectra of a suitable substance such as ethyl or methyl alcohol You will need one pair of set point true sample temperature for a one point calibration and two such pairs possibly close to the limits of the interval of interest for a two point calibration The one point calibration corrects only the calibration curve offset at the specific temperature However whenever there is a significant difference the scale of the calibration curve is also significant We therefore recommend to use always the two point calibration procedure There are two ways to execute the set point calibration It can be done outside the cont
30. mocouple in the heater assembly detects a temperature higher then the threshold set by the trimmer P1 of the VT INPUT board an interlock occurs and the error message SAFETY TC HOT is displayed The threshold is factory set to 250 C Refer to the Hardware Calibration section for more details on setting this safety interlock C 3 OPERATING BELOW ABOVE ROOM TEMPERATURE WITHOUT EVAPORATOR It is possible to increase the range of available temperatures by precooling the carrier gas This is usually done by using a spiral or serpentine heat exchanger made of a suitable metal tubing copper stainless steel brass and immersed in a suitable cold bath The baths used more often are liquid nitrogen dry ice acetone mixture and electrically refrigerated ethylenglycol The connections are identical to the preceding case except that the heat exchanger is inserted between the flowmeter outlet at the instrument and the carrier gas inlet at the thermostated device probe or cavity dewar It is also recommendable to reduce refrigeration loss in the section between the heat exchanger and the thermostated device According to the specific temperature range this is done either by a spongy plastic cobimentation or by a transfer dewar WARNING BE CAREFUL NOT TO INVERT THE ORDER AND COOL THE GAS BEFORE PASSING THROUGH THE FLOWMETER Once connected the operation as well as interlocks are identical to the preceding case The only difference is an extended lo
31. morize a number of distinct parameter tables in order to make it easy to switch between different loads and or operating conditions e g high low temperature region Since the control is carried out in terms of power rather than current or voltage it is efficient even when the difference between the control gas temperature and the set point is quite small e g 2 Other salient feature is the high resolution control of the output power channels 2048 steps These features are normally not found in commercial VT controllers A 2 FRONT PANEL DESCRIPTION SEE DRAWING The front panel contains the following devices 16 character LCD alphanumeric display 16 key keyboard with the following keys Digits 0 1 2 3 4 5 6 7 8 9 Special keys RST CAL PRG FRM ENT PRT Paper advance ADV effective only with the optional printer LED Light Emitting Diodes indicators Power supply Indicates that the instrument is ON Heater Indicates that the heater output is enabled Evaporator Indicates that the evaporator output is enabled Interlock Indicates that an interlock has been tripped Interlocks are internal safety protection whose task it is to stop erogating power to heater and or evaporator if anything goes wrong Gas flowmeter manual regulator with an interlock switch 15 column thermal printer optional STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User m
32. mpensated reference junction mode an RST otherwise In the first case you have finished and the instrument will reset In the second case the query REFERENCE TC will appear If you press RST no there will be a reset with nothing done If you confirm the mode by pressing ENT PRT however the prompter RT rrr tttt will appear where rrr tttt is the currently set reference junction temperature You may either confirm it by pressing ENT PRT or else input a new value RT indicates the temperature in C of the reference junction bath You can use any suitable reference bath such as melting ice RT 0 boiling water RT 100 freely evaporating liquid nitrogen melting gold etc E 3 SPECIAL OPERATION CONTROL PARAMETERS EDITING This option permits to check and or edit the currently active control parameters table Before proceeding you should take into account the following facts a Control parameters include all numeric parameters pertinent for the temperature control operation On the other hand they do not include numeric parameters pertinent to simple temperature measurements such as sensor configuration and calibration data b The control parameters may differ from case to case according to the carrier gas for example external room temperature or precooled source or nitrogen from a liquid nitrogen evaporator and according to the particular thermal load e g a probehead and the desired temperature range at 100 O the par
33. n is used to check current configuration data such as the active control parameters table configuration of sensors etc It does not require any input and does not modify any of the displayed parameters there are other ways to modify some of them The info items are displayed one by one in the format consisting of a short name acronym followed by the current value You must hit any key to proceed to the next one The following items are displayed VRSN Firmware version number in the format YYMM R where YYMM V where YY denotes the year MM month and R the revision number TBL Currently active control parameters table There may be several parameter tables stored in the non volatile memory Each table may correspond to a different thermal load and or different range of temperature The distinction between using or not using the optional evaporator is also stored in the table For more details see CONTROL PARAMETERS section REF Type of reference employed in the control channel 0 indicates the compensated reference junction while 1 denotes a true reference TC CSNS Control sensor type The currently implemented sensor types are 0 millivoltmeter using any transducer 1 Cromel Alumel 2 Iron Constantan 3 Copper Constantan RT Reference temperature This item will appear only if REF 1 true reference junction and indicates the temperature in C of the reference junction bath RT can be changed by means of the special operations op
34. nit and the VT_INPUT board VY HEATER POWER DRIVER supplies the heater resistor with a DC current proportional to a reference voltage signal generated by the 4CH_DAC_BOARD The ratio between the output current and the reference voltage can by set by trimmer P1 see the Hardware Calibration section VY EVAPORATOR POWER DRIVER supplies the evaporator resistor with a DC current proportional to a reference voltage signal generated by the 4CH_DAC_BOARD The ratio between the output current and the reference voltage can by set by the trimmer P1 of the latter board see the Hardware Calibration section STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 27 of 27 G HARDWARE CALIBRATION Before delivery all necessary calibrations are made in factory so you do not need to do them at installation Before making any hardware calibration please read the section Hardware Description and refer to drawing REAR VIEW OF PARTS HEATER POWER CALIBRATION The purpose of the calibration is to achieve maximum power transfer by properly changing the transconductance of the HEATER POWER DRIVER board i e the ratio between the output current and the reference voltage voltage generated by the 4CH_DAC board The proper setting depends upon the resistance of the heater wire If the heater is supplied by Stelar the heater will be already calibrated otherwise you will have to do it yourself in o
35. nternationally standardized data are approximations to the idealized physical temperature appearing in thermodynamical formulae The goal of the national and international standardization organizations is to keep the approximation as good as possible Periodically corrections are made and the decreasing magnitude of such corrections provides a measure of confidence for the standardized values For the temperature ranges of different TC types the estimated confidence level is currently about 0 05 During temperature control a feedback loop is established which includes the thermostated object thermal load the sensor the controller active element and the power source For STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 5 of 5 any controller there are two distinct operating phases the transition to a new set point locking phase and the stationary behavior at set point the locked loop phase The two phases give rise to two distinct sets of performance criteria For most practical purposes the locking phase is characterized by settling time and overshoot The most important parameters of the locked loop phase parameters are the mean square deviation from the set point stability the oscillatory components spectrum the transient response to small variations in the thermal load rigidity etc In particular the mean square deviation from the set point is
36. onsiderably better absolute precision performance Resident software makes it possible to execute a guided one point or two point calibration of any of the implemented sensors Once calibrated the absolute precision of the instrument becomes comparable to its inherent reproducibility a warning it is difficult to find guaranteed temperature references the simple freezing and boiling water baths become unsuitable for precision levels of 0 1 or below The calibration of a sensor consists of a digital correction of the corresponding transducer offset and gain It has nothing to do with the linearization of the sensor which will be discussed in the next paragraph Sensor linearization is made digitally using polynomial fits to the standard thermocouple tables as listed by the International Electrochemical Commission IEC publications n 584 1 and 584 2 for thermocouples and 751 for platinum wire thermometers These data represent the most recent basis for international standardization of temperature measurements and serve as a source for almost all national standards such as DIN British Standard UNI CTI 7938 and 7937 etc The tabulated data were interpolated by polynomials and or rational of a sufficiently high degree to achieve maximum deviation smaller than 0 05 Since all calculations are carried out internally with full 10 decimal digits precision errors due to truncation and rounding are negligible Users should keep in mind that the i
37. or 3 however you can set the display format to the corresponding number of decimal digits In any case the displayed values are properly rounded The display repetition time and the noise averaging efficiency depends upon the parameter NM number of measurements per reading during monitoring see the PARAMETERS EDITING section for further details The control and monitor channels sensor types and the control channel reference mode depend upon the current sensor configuration see the Sensor Configuration section The displayed readings are automatically adjusted according to current sensor calibration parameters see the Sensor Calibration section The monitoring will proceed until interrupted from the keyboard by pressing either the RST or the CAL PRG key In the first case the system will be reset and the power up procedure will restart In the second case the temperature controller program Program 1 is entered D 3 TEMPERATURE CONTROL PROGRAM 1 There are two ways to enter the temperature controller program 1 Enter the temperature monitoring routine and then press CAL PRG 2 Press 1 for Program 1 during the reset interval Before entering the temperature control program check that i All external parts of the system are functioning properly This means in particular If liquid nitrogen evaporator is not used the carrier gas must be flowing through the system operation above room temperature and if required is being
38. ou have input an admissible value admissible values range from 1 to 6 the message WAIT will appear and subsequently two different things may happen 1 The message ERR REG will appear if there is not enough reserved non volatile memory for the specified table number In this case reset the instrument you will find its configuration unchanged as though nothing happened You may try again with a lower table number usually space for at least 5 tables is reserved 2 The message WAIT disappears after a few seconds and the instrument resets itself automatically In this case the operation succeeded Moreover the new table has been automatically JOINED so that it is now the active one and you can if you wish proceed to editing its parameters Warning The COPY PARAMETERS procedure does not test whether the specified table already contains valid parameters lf so they are replaced by the new ones without any warning Note It is allowed to copy a parameters table into itself no harm results but of course nothing useful is done is this case STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 21 of 21 E 5 SPECIAL OPERATION JOIN A PARAMETERS TABLE This option permits to join or in other words to activate a desired parameters table The operation is extremely simple First the instrument displays the message LD TAB n where n is the number of the cur
39. output SAMPLE MONITOR PROGRAM FOR THE STELAR VTC DEFINT I N Use integers starting I N SCREEN 0 WIDTH 80 80 columns text screen LOCATE 1 1 1 Display cursor at all times CR CHR 13 Carriage Return character KEYS arpARP 0123456789 Set of allowed characters OPEN COM1 9600 N 8 1 AS 1 Open communication device Parameters correspond to the VTC code 1844 GETKEY C INPUT 1 Get a keyboard character I INSTR KEYS C Is it one of the VTC set IF 1 0 THEN GOTO GETKEY If not sending it would be useless IF lt 3 THEN C MID KEYS 1 3 1 Convert abc into ABC PRINT C Display it PRINT 1 C Send it to the VTC IF C lt gt THEN GOTO GETKEY Is an answer expected PRINT TAB 40 Yes tabulate to column 40 RESPONO TO TIMER Reset time out count RESPON I LOC 1 Is there a received character IF THEN If yes STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User Manual IS INPUTS 1 1 PRINT I IF IS CR THEN GOTO GETKEY f GOTO RESPONO ELSE A TIMER TO f IF A lt 3 THEN GOTO RESPON f GOTO GETKEY END IF Pag 34 of 34 Read it Display it CR terminates the answer Not done reset time out repeat If not Test time out If OK wait otherwise return to txmit transmit R to reset the VTC STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User Man
40. overshoot is required Experience shows that apparently paradoxically in such systems reducing the value of MS to an intermediate level 1 5 often increases the overshoot Recommended values 5 100 or 0 05 0 5 Admissible values any positive number AVERAGING NUMBER FOR TEMPERATURE CONTROL REGULATION NR specifies the number of elementary measurements which are to be averaged before the result is displayed measurements per reading Each elementary measurement requires about 15m sec including self calibration and has a nominal precision better than 0 01 C Increasing NR increases the nominal precision proportionally to the square root of NR but at the same time slows down the regulation cycle repetition rate and thus increases the undesired phase lag see the description of FP Recommended values 4 20 Admissible values positive integers STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 19 of 19 NM LL UL LS US EV FL SO AVERAGING NUMBER FOR TEMPERATURE MONITORING This parameter is similar to NR described above but applies to any temperature readings outside the temperature control routine In this case the software overhead less time consuming and substantially larger numbers can be used while maintaining a reasonable reading refresh time Note that due to the averaging the first measurement after a drastic change in conditions may be
41. perating modes compensated reference junction and true reference TC junction optional Monitor channel with compensated TC junction optional SENSORS Thermocouples types J K T Temperature measurement specifications Range 270 to 400 C for type T Cu Const 200 to 300 C for J K to be extended Reproducibility gt lt 0 1 C Resolution lt 01 C Temperature control specifications typical values exact specifications depend upon the controlled system Range from 160 to 180 C aye lt o STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 7 of 7 CONTROL ALGORITHM generalized PID with input filter predictor integral action band second derivative damping integral look ahead damping output step limit etc SPECIAL FIRMWARE FEATURES Separate calibration of each sensor channel amp mode Independent Set Point calibration Amperostat operating modes etc see the manual SAFETY INTERLOCKS BROKEN TC Interrupted thermocouple circuit TEMP TOO HIGH Main sensor temp exceeds a soft limit or a safety TC temp exceeds a hard limit MISSING FLOW Missing flow of the carrier gas MISSING N2 No liquid nitrogen in the evaporator A hard wired interlock will trip should the CPU fail Self testing capabilities automatic ADC calibration tests and EEPROM data tests programs as well as control parameters OPTIONAL ACC
42. r RST to ignore it For further details on the set point calibration see the Special Operations section D 4 POWER GENERATOR WITH TEMPERATURE MONITOR PROGRAM 2 This program can be entered only by pressing the key 2 during the reset interval It displays the query POWER SOURCE press RST no for immediate reset or ENT PRT yes for confirmation In the latter case Program 2 permits to set any one or both output channels to any value intended as a percentage of the full power range The set up dialog is the following Instrument Operator HEATER RST no or ENT PRT yes if yes POWER Any desired value 0 100 EVAPORATOR RST no or ENT PRT yes if yes POWER Any desired value 0 100 The instrument then enables the specified power channel s calculates and sets the current s corresponding to the specified power level s and proceeds to monitoring of the control channel and if mounted the monitor channel temperature s just as in Program 0 Once in operation you can press any of the following keys RST Resets the instrument 0 1 2 3 Change number of displayed decimal digits The formula used to set the currents is I set SQR I max Power 100 where l max is the maximum available current it can be trimmed separately for each channel as described in the Hardware Troubleshooting and Calibration section Once set the current is kept strictly constant by the circuitry independently of any load resistivity
43. rature Open the left rear panel Using a screwdriver turn trimmer P1 on the VT_INPUT board until locating the position around which the interlock lamp on the front panel switches on and off CALIBRATION OF THE 16 BIT ADC The A D converter needs to be calibrated only when the error message GND TARA or REF TARA is displayed In such a situation proceed as follows VTC Display Press Comment GND TARA or RIF TARA ENT Enter the diagnostic program GAIN 0 ENT Selects Gain setting MPX 0 ENT Selects Input Multiplexer OG OM 32768 RST The number 32768 is only an example it represents the ADC count for input 0 A 027 B 210 The numbers A and B are two calibration parameters for ADC Open the left rear panel Use the trimmers P1 and P2 of the ADC_16_BIT board to set the numbers A and B to about 0 000 For a satisfactory calibration A and B should fall within 010 and 010 If the calibration is impossible or if either A or B becomes overflow the ADC board has a hardware failure H TROUBLESHOOTING The controller being based on the Stelar TD MATE Transducer Mate operating system is in principle a user programmable general purpose acquisition computer To exploit this feature you need the optional TD MATE programming kit and manual H 1 HARDWARE PROBLEMS However a number of special tasks can be carried out without any special knowledge of the TD MATE programming capabilities These include in particular the ADC
44. rder not to downgrade the unit s performance Note Best power performance is achieved with 8 Ohm heater resistors Values from 4 to 16 Ohm are acceptable even though they will not permit to exploit the full range of the power driver a Open the left rear panel left and connect with care a DC voltmeter across the heater resistor pins 1 2 and 4 5 of the HEATER connector b Calibrate the heater current offset zero current Run Program 2 see the Standard operations section Select the heater and set POWER 0 Using a screwdriver turn trimmer P4 on 4CH_DAC board until your voltmeter indicates 0 volt on the heating resistor Reset the instrument c Calibrate maximum heater current make sure the heating resistance is immersed in a strong current of a carrier gas Re enter Program 2 Select the heater and set POWER 100 Using a screwdriver turn trimmer P1 on the HEATER POWER DRIVER board until you see same voltage variation across the heater Now keep turning P1 in the direction of increasing voltage At some point you will either reach the end of the trimmer range low heater resistance or else the voltage will stop increasing because of saturation high heater resistance In any case set the trimmer just below the maximum voltage limit EVAPORATOR POWER CALIBRATION The purpose of the calibration is to achieve maximum power transfer by properly changing the transconductance of the EVAPORATOR POWER DRIVER bo
45. reminder about the flow level that should be set by the operator and for which the parameters table has been presumably optimized Admissible values any number SET POINT OFFSET This parameter is normally set up by the set point calibration routine and should not be changed manually unless there are good reasons for it lts default value is O by entering a zero you can in fact cancel the effect of a set point calibration For more details see the Set Point Calibration section Admissible values any number STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 20 of 20 SS SET POINT SCALE This parameter is normally set up by the set point calibration routine and should not be changed manually unless there are good reasons for it lts default value is 1 by entering 1 0 you can in fact cancel the effect of a set point calibration For more details see the Set Point Calibration section Admissible values any positive number E 4 SPECIAL OPERATION COPY A PARAMETERS TABLE For the purposes explained above the instrument permits to create and edit distinctly numbered control parameters tables The COPY PARAMETERS procedure creates a copy of the currently active table It displays the message SV TAB n where n is the number of the currently active table At this point you must input the number of the table into which the current parameters should be written Once y
46. rently active table At this point you must input the number of the table which you want to join If the table exists the instrument will make it active and reset itself Otherwise a message MISSING TABLE will appear pressing any key leads to a reset with the original configuration left intact E 6 SPECIAL OPERATION SENSOR CALIBRATION The sensor calibration procedure permits to correct the offset and gain of the sensor transducer combination STC in any channel Three pairs of parameters are in fact maintained one for the monitor channel and two for the control channel where the two reference modes compensated true reference TC are considered as distinct distinct hardware is in fact used The sensor calibration as opposed to the set point calibration see below regards the static performance of the instrument when used as a thermometer ts purpose is to make the measured temperature correspond as closely as possible to the actual temperature at the tip of the sensor One point and two point calibrations are possible the one point calibration corrects only the voltage offset of the STC while the two point calibration corrects also the gain factor As soon as you enter into the Sensor Calibration routine the query CNTRL CHNL will appear Press ENT PRT if you want to calibrate the control channel or RST if not In the latter case the query 2MONIT CHNL will appear Confirm the monitor channel calibration by pressing ENT PRT or res
47. ries of messages might occur DIR KO followed by TABULA RASA In this case press ENT PRT for confirmation the system will arrive automatically to the point where the message PRGO gt appears see above From this point on the re programming proceeds as described above VTC User Comment STELAR PRODUCT RST Press RST before display changes PROGRAM 0S907 The version number may differ TESTS RST PROGRAMMING ENT ACCESS CODE 2 Input the last secret access code Units are delivered with A C 0 NEW FILE If NEW FILE does not occur the A C was wrong RST Not a new file ERASE FILE RST No file erasure MODIFY REG RST Not a register modification FILE DUPLIC RST Not a file duplication TABULA RASA ENT Clear all EEPROM memory TABULA RASA forced TABULA RASA ENT Confirmation STOP PRGO gt From this point you proceed as described above STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 32 of 32 H 4 FUSES MAINS 2A HEATER POWER DRIVER 6 3 A slow blow EVAPORATOR POWER DRIVER 6 3 A slow blow POWER SUPPLY BOARD 1 5 A for 5 15 15 1 1 RS232 CONFIGURATION The configuration procedure is invoked through the SPECIAL OPERATIONS menu see Chapter E Once invoked it prompts the operator for a configuration code constructed as follows Code 256 B 16 W 4 S P where B is the baud rate code 0 110 1 150 2 300 3 600 4 1200
48. rol program or even during the temperature control The latter possibility invoked by pressing the digit 9 key see Program 1 is sometimes very handy Just keep in mind that the power outputs are kept at a constant level but no active temperature control is being done while the calibration is in progress Therefore you should enter the routine only after reaching a steady state Whatever is the mode to invoke it the routine will first present the query ONE POINT Press ENT PRT to confirm the one point calibration modality or RST to negate it In the latter case the query TWO POINTS will be displayed and you may confirm it as usual by pressing the ENT PRT key At this point if you press RST the system will reset with nothing done 1 ONE POINT SP CALIBRATION In this case the message SET VALUE will appear Input the set point value used during the measurement The message TRUE VALUE will appear Input the measured sample temperature The instrument will reset and the calibration is done 1 TWO POINT CALIBRATION In this case the message SET T1 will appear Input the set point value used during the first measurement The message TRUE VALUE will appear Input the corresponding measured sample temperature The message SET T2 will now appear Input the set point value used during the second measurement The message TRUE VALUE will appear Input the corresponding measured
49. sample temperature The instrument will reset and the calibration is done The parameter modified by the Set Point Calibration routine are SO set point offset and SS set point scale within the currently active control parameters table Thus each control parameters table may have a distinct calibration setting E 8 SPECIAL OPERATION CHANNEL CONFIGURATION STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 24 of 24 If you change a sensor with a different type you must also change the corresponding sensor code Similarly if you change the reference junction mode compensated true reference TC the system must be properly re configured All this is done using the Channel Configuration option This option also permits to set reset the sensor calibration parameters offset and gain The procedure is self explanatory in the sense that it guides the operator with proper queries and prompters We will illustrate it by a few examples Example A Control channel Reference junction compensation Copper Constantan thermocouple Default offset and gain Operator input Consequent VTC actions CNTRL CHNL Select control monitor chnl ENT COMPENSATED Select compensation mode ENT 3 CU CONST Select sensor type ENT OF 0 0109 Defaults for compensated ENT SG 4 0439 reference junction ENT VTC 90 Finished Example B Control channel True reference junction Chrome
50. ss RST to reset the instrument with nothing done Atthis point the last measured value is memorized and the prompter TRUE VALUE will appear Input the correct temperature of the sensor The message WAIT will appear and remain on display for some time about 1 minute The message 2ND MEASURE will appear Prepare your second point calibration device e g boiling water bath set up the sensor and press any key The instrument will start monitoring the sensor temperature When you see that it stabilized press ENT PRT you can also press RST to reset the instrument with nothing done Atthis point the last measured value is memorized and the prompter TRUE VALUE will appear Input the correct temperature of the sensor The message WAIT will appear and remain on display for some time about 1 minute after that the instrument will reset itself and the calibration is done When the calibration is finished you can use the INFORMATION option to check the variations in scale and or offset caused by the calibration You can also void any calibration by restoring the default scale and offset of the transducer using the CHANNEL CONFIGURATION option E 7 SPECIAL OPERATION SET POINT CALIBRATION The set point calibration procedure permits to apply a linear correction of the sample temperature as opposed to the control channel sensor temperature In any practical control set up there is a fundamental problem
51. tems since it tends to compensate the phase lag between the control action power output and its effect sensor temperature With most thermal loads the phase lag is quite large and causes most of the temperature control problems Putting FP 1 the input values are left unchanged For FP lt 1 a filtering action analogous to a one pole RC filter is introduced For example if the control cycle time is 1 sec and FP 0 1 the result is identical to applying an RC filter with time constant of 10 sec to the input This will reduce system noise but on the other hand increase the deleterious phase lag described above STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 18 of 18 MP MS NR Recommended values 1 0 1 5 Admissible values gt 0 01 INTEGRAL ACTION BAND The integral term increment is given by the following formula Cl D 1 D IB 42 where D is the measured deviation from the set point For values of D substantially smaller than IB this is approximately equal to CI D With increasing D a maximum of D 2 is reached for D IB and then a rather fast decrease occurs we speak about integral action neutralization It prevents the integral term from becoming excessively large before the set point is reached a situation which would lead to a large overshoot For example if IB 10 and D 30 then the increment is only 3 rather than the 30 one would expect with
52. ter power level in of full range If the control parameters are reasonable the system will reach the set point and then stabilize in terms of both the temperature and the output power The following keys are operative in this phase RST Emulates a full reset of the instrument CAL PRG Input a new set point value while maintaining the output channel s power FRM When the monitor channel is available toggles the display format between the two case listed below Case 1 CCC C SSS S pp Case 2 ccc c mmm m C where CCC C is the control channel temperature SSS S is the set point temperature mmm m is the monitor channel temperature pp is the heater power level C is the letter C indicating we are in Control Input a new gas flow if EV 0 or evaporator if EV lt gt 0 power level while maintaining the output power channel s active ENT PRT If you have the optional printer pressing ENT PRT will result in a printer copy of the current display STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 14 of 14 0 1 2 3 Set display to 0 1 2 or 3 decimal digits precision Note If the precision is more than 1 decimal digits the display items indicated above as pp and R are not displayed for lack of space 9 Calibrate the set point while maintaining the output power level s The system will first display the query S P CALIB Press ENT PRT to confirm it o
53. tion REFERENCE T see below CSCL The scale calibration coefficient for the control channel sensor It is normally set by the two point sensor calibration procedure It can also be set manually within the sensor configuration procedure Its default value is 4 0439 for the compensated reference mode and 4 08 for the true reference junction mode COFF The offset calibration coefficient for the control channel sensor It is normally set by the one or two point sensor calibration procedure It can also be set manually within STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 16 of 16 the sensor configuration procedure lts default value is 0109 for the compensated reference junction mode and 0 for the true reference junction MSNS Monitor sensor type analogous to CSNS MSCALE The scale calibration coefficient for the control monitor sensor analogous to CSCALE MOFF The offset calibration coefficient for the control monitor sensor analogous to COFFS E 2 SPECIAL OPERATION REFERENCE JUNCTION PARAMETERS This option regards only the control channel lt is used to change the reference junction mode without having to go through the full channel configuration routine In the case of a true reference junction TC it also allows to set the actual reference junction temperature The system will first display the query COMPENSATED Press ENT PRT if you want to confirm the co
54. tor FL carrier gas flow level SO set point offset SS set point scale D 3 1 TEMPERATURE CONTROL WITHOUT EVAPORATOR EV 0 If the current configuration parameters are set for use without evaporator the following things will happen when the temperature control program is entered i The system will display the last used value of the carrier gas flow You should either confirm it by pressing ENT PRT or else introduce a new value In the latter case the message WAIT will appear for a few seconds while the system is memorizing the new configuration In any case adjust the gas flow regulator to make the actual flow correspond to the value entered from the keyboard Warning Carrier gas flow has a direct impact on the controller performance Drastic variations in the flow level may require re adjustment of other control algorithm parameters ii iii The heater light switches ON and there is an audible click as the heater power output is enabled Even though the heater is enabled however the heater output current is set to zero for safety reasons The system will display the current sample temperature and wait for the introduction of the set point the display prompter may look like 24 6 SET _ where 24 6 is the current sample temperature and the cursor is flashing Enter the desired set point value comprised within the set point range limits STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it w
55. ual Pag 35 of 35 PARAMETERS TABLE date NOTE intekenen aaa GP sen luces CD enten SP nnn BP ate IB nt WA ian MP cios MS n NR aa narneenme NM inner AA OE users Ln UB ias Ear Past Dai atte PARAMETERS TABLE date NOTEsii aa OP pencas Clinicas GD asen OP oireeni FP srate IB arseen tii MP insane MS it micas NR sad NM oetan Eat A ademende EA Ue rana EM erica Pesca OD oe SO asis PARAMETERS TABLE date NOTE EE CP santen Cl brian CD san SP urnen PP ents amen VA rent MPa MS sten NR aar NM einser A WE sutra pated Sac AA EN raare A SO nin AN PARAMETERS TABLE date NOTE EN RER OE A RE A NS OP a Olen CB ere SF andes AE WB ne ds PA anderen MIP esn MS nanne NR uren NM saatn Elcano UE vna EA US is EV nanasan Ps SO sa SO poto PARAMETERS TABLE date OZ OP dadas Olsene OD oras Eds rat AS EE Mistica MS isis NES icenretctinnans Nros EE nennen UL enten ES san WS caras EM num PE antennes SO pas SS aanmeren STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it
56. umber of safety interlocks At least one sensor channel is always implemented we will refer to it as the control channel An optional sensor channel normally used as an independent monitor is also foreseen we will call it the monitor channel The sensors are normally thermocouples types J K T but platinum wire sensors PT100 are also compatible with the input circuitry provided the choice is made upon order In the case of a thermocouple sensor the control channel can be set for two different operating modes depending upon the desired reference joint compensated reference joint using the Analog Devices transducer AD595 or optionally a true reference joint using a reference thermocouple kept at a well defined reference temperature ice water bath liquid nitrogen bath etc In both cases the STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 4 of 4 implemented transducers are thermostated in order to eliminate any residual effect of the room temperature variations The high resolution sensitivity and reproducibility of the temperature measurements is also due to the following factors The resolution of an ultralinear true 16 bit analog to digital converter permitting to detect temperature variations of the order of 0 010 while still covering the whole range of temperatures physically compatible with any sensor Thus no range switches and similar devices ar
57. variations the amperostat function unless the maximum voltage specification is exceeded by applying an excessively resistive load voltage output saturation There is no problem with low resistivity loads the output may be shorted without any problem and any variation in the current E SPECIAL OPERATIONS In order to enter the Special Operations menu press CAL PRG during the reset interval A series of queries will be displayed each corresponding to a special routine option You can select any option by pressing the ENT PRT key yes in response to the respective query STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 15 of 15 Vice versa you can skip any option by pressing the RST key no If none of the selected options has been selected the unit will return to the reset interval THE SPECIAL OPERATIONS MENU INCLUDES INFORMATION Display info about the current set up REFERENCE Set the reference junction parameters CNTRL PARAM Edit control algorithm parameters COPY PARAM Copy current control parameters table JOIN PARAM Join another control parameters table SNSR CALIB Calibrate one of the available sensors S P CALIB Calibrate the Set Point CHNL CONFIG Configurate a sensor channel RS232 CODE Configurate the serial interface We will now describe the individual options in detail E 1 SPECIAL OPERATION INFORMATION This optio
58. wer limit of controllable temperatures However at set STELAR s r l via E Fermi 4 27035 Mede PV Italy info stelar it www stelar it Stelar VTC User manual page 9 of 9 points above room temperature the instrument will have to apply more power to the heater lt may happen that the upper limit of the accessible temperature interval will become too low for your application due to insufficient maximum heater power In this case you must either try to increase the maximum output power see the Hardware Calibration section or to renounce covering the whole temperature range with a single set up Usually there is enough output power to cover about 200 C interval C 4 USING THE LIQUID NITROGEN EVAPORATOR The liquid nitrogen evaporator is probably the best solution for prolonged operations at low and very low temperatures even though temperatures close to or above room temperature are normally also accessible in this set up The connections are made as follows Insert the control thermocouple as described above Connect the evaporator cable to the EVAPORATOR socket on the left rear panel Fill the evaporator dewar with liquid nitrogen Immerse the evaporator rod slowly and wait a while until it reaches thermal equilibrium Secure the evaporator rod with the clamping ring Connect the dewar transfer line between the evaporator and the thermostated device 0Q00U0y The unit is now ready and you can run the control program Se
59. what is actually controlled is the temperature of the tip of the sensor rather than that of the sample The difference can be made small if proper precautions are taken but it is never zero Usually it is much larger than both the precision of the instrument and the inherent stability of the control loop In other words the controlled temperature may be very stable but at the same time quite incorrect In arrangements characterized by severe geometrical constraints and conflicts with other devices examples NMR probeheads or EPR cavities the difference can easily reach several degrees When using room temperature carrier gas it is always negative ie the sample temperature is lower than the set point When the carrier gas temperature is below the room temperature however the difference may be both positive and negative lt decreases with increasing carrier gas flow however differences inferior to 10C are difficult to obtain The carrier gas flow values required to reduce the difference below a tolerable level are often severely exaggerated from other points of view temperature stability heater power heat transfer efficiency carrier gas consumption etc In many techniques there are additional other sources of discrepancy A typical example is the heat generated directly inside an NMR sample tube by dielectric losses when high power RF irradiation decoupler is used The only practical solution to this problem is an empirical ca
60. ww stelar it Stelar VTC User manual page 13 of 13 Please proceed now to the section Temperature Control Operative Phase D 3 2 TEMPERATURE CONTROL WITH EVAPORATOR EV gt 0 If the current configuration parameters are set for evaporator the following things will happen upon entry into the temperature control program i The system will display the last value of the evaporator channel output power in of full range You should either confirm it by pressing ENT PRT or else introduce a new non zero value In the latter case the message WAIT will appear for a few seconds while the system is memorizing the new configuration Warning Evaporator power level has a direct impact on the controller performance Drastic variations in the flow level may require re adjustment of other control parameters ii The heater and evaporator lights switch on and there is an audible click as the two power outputs are enabled However only the evaporator output is actually powered the heater output currents is set to zero for safety reasons iii The system will display the current sample temperature and wait for the introduction of the set point just like in the previous case see lc D 3 3 TEMPERATURE CONTROL OPERATIVE PHASE The instrument now proceeds to the actual control consisting of correction cycles repeated about once a second In each cycle three numbers appear on the display the actual temperature the set point and the hea

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