MICROLINK 305x Analogue Inputs User Manual
Contents
1. inputs to measure voltage just as in a 3050 You must connect the compensation input for that channel to 0 V although you don t need to make a connection to the current terminal of that channel 7 13 Microlink 3000 Hardware User Manual o constant current D subtract Figure 7 8 Connections for 4 Wire RTDs _ _ constant current subtract Figure 7 9 Connections for 4 Wire Compensated RTDs 7 14 Multi Channel Analogue Inputs Table 7 4 3051 Resistance Measurement Pin Connections for Left Hand 37 Way D Plug Wiring View 15V Auxiliary Current 7 Current 6 Current 5 Current 4 Current 3 Current 2 Current 1 Current 0 Input 7 Input 6 Input 5 Input 4 Input 3 Input 2 Input 1 Input 0 Please read the Connection Notes on the previous pages before making your connections 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 ov 15V Auxiliary Comp 7 Comp 6 Comp 5 Comp 4 Comp 3 Comp 2 Comp 1 Comp 0 Input 7 Input 6 Input 5 Input 4 Input 3 Input 2 Input 1 Input 0 7 15 Microlink 3000 Hardware User Manual Table 7 5 3051 Resistance Measurement Pin Connections for Right Hand 37 Way D Plug Wiring View 19 OV 15 V 37 18 15V unused 36 17 unused Current 152. The 3051 is essentially a 3050 with additional features to permit the measurement of resistance rather than voltage It is therefore appropriate for the monitoring of temperatures using Resistance Temperature Devices RTDs or Pt100 or thermistors Other variable resistance transducers can also be monitored with the 3051 The inputs accept up to 16 resistance devices in 2 3 or 4 wire form Each channel has and inputs to measure voltage across the resistors plus a current source and compensation amplifier You can choose whether or not to use the resistance option on the 3051 If the current source is not connected and the compensation input is earthed then the 3051 behaves as a 3050 measuring voltage 7 2 1 Connection Notes The 3051 is a variant of the 3050 module All the comments made in the 3050 connection notes apply to this module You should read the 3050 notes first especially if you intend to use the 3051 to measure voltage signals The 3051 uses 4 connections per channel to measure resistance The connections for channels 0 7 are on the left hand connector whilst 8 15 are on the right hand connector 7 2 2 Lead Arrangements 2 Wire In this configuration lead resistance is an additive error but can be tolerated in those applications which do not require high absolute accuracy Figure 7 2 2 Wire RTD Arrangement 7 8 Multi Channel Analogue Inputs 3 Wire This is probably the most widely used configuration T
3. 35 16 Comp 15 Current 14 34 15 Comp 14 Current 13 33 14 Comp 13 Current 12 32 13 Comp 12 Current 11 31 12 Comp 11 Current 10 30 11 Comp 10 Current 9 29 10 Comp 9 Current 8 28 9 Comp 8 Input 15 27 8 Input 15 Input 14 26 7 Input 14 Input 13 25 6 Input 13 Input 12 24 5 Input 12 Input 11 23 4 Input 11 Input 10 22 3 Input 10 Input 9 21 2 Input 9 Input 8 20 4 Input 8 Please read the Connection Notes on the previous pages before making your connections 7 16 Multi Channel Analogue Inputs 7 3 3055 Low Thermal Reed Relay Input The 3055 is essentially a 3050 with the input signal multiplexers replaced by low thermal offset reed relays The relays are specified to introduce offsets of less than 1 microvolt into the input signals This compares with about ten microvolts for the semiconductor multiplexers of 3050 The major use of such low level capability is in high resolution thermocouple measurement Because of this the standard 3055 is configured for such measurements Input Configuration All the inputs are differential This means that the amplifier measures the difference between the positive and negative inputs The inputs are fitted with thermocouple break circuitry This consists of a 1 MQ resistor tying the negative input to 0 V plus a 1 MQ resistor tying the positive input to a voltage of about 300 millivolts When a thermocouple is connected a current of about 1
4. compensation amplifier is not used so its input is tied to earth 3 Wire The constant current flows through the RTD to earth causing error voltage drops in the resistances of the B and C leads Only negligible current flows down the A lead Thus the instrumentation amplifier measures the voltage across the RTD plus the voltage developed in the B lead while the compensation amplifier measures the voltage developed in the C lead The subtraction then produces the RTD voltage assuming the lead resistances are equal 7 11 Microlink 3000 Hardware User Manual constant current subtract Figure 7 6 Connections for 2 Wire RTDs gt constant current subtract Figure 7 7 Connections for 3 Wire RTDs 7 12 Multi Channel Analogue Inputs 4 Wire The constant current flows down the D and C leads Only a negligible current flows in the B and A leads so the instrumentation amplifier directly measures the RTD voltage The compensation amplifier is not used and is connected to earth 4 Wire Compensated The constant current flows through all leads The instrumentation amplifier measures the voltage drop across the RTD and the drops in the leads to A and B The compensation amplifier measures the voltage in the C and D leads The subtraction leaves the RTD voltage drop assuming the lead resistances to be equal Voltage Measurement You can use the and
5. 10 bridge imbalance Microlink 3000 Hardware User Manual 7 4 4 3053 Specifications Accuracy for 50 Hz signal Settling time for channel switching Other specifications as 3050 7 4 5 3054 Specifications Number of channels Number of auxiliary channels Other specifications as 3050 7 4 6 3055 Specifications Relay thermal offset Relay switching time Other specifications as 3050 0 5 200 msec 1 uV 1 msec 7 20
6. 20 Volts beyond the power supply This means 35 V if the Microlink is switched on 20 V if it is switched off When a voltage above the power supply is applied to the unit its protection mechanism comes into action and this draws some current from the signal source This effect can be a problem when the Microlink is switched off It now draws current from any signal If this is a problem the current can be limited by series resistors These could be conveniently housed on the 3900 Screw Terminal module Such resistors will also protect the unit from much higher voltages There is of course a price to pay for such resistors This is higher noise slower maximum multiplex rates and dc errors caused by the amplifier input currents flowing through the resistors Unconnected Inputs You can leave unused inputs unconnected however if you attempt to read from unconnected inputs do not expect to get 0 V They could be any value If another connected channel has recently been read the unconnected input will return a similar value This is not crosstalk It occurs because the input capacitance of the amplifier is charged to the 7 4 Multi Channel Analogue Inputs voltage of the previous channel and has little incentive to change when connected to an open circuit High Impedance Signals A similar effect to that described above can occur with high impedance signal sources When the source is selected it must supply current to charge the amplif
7. 5 Input 14 34 15 Input 14 Input 13 33 14 Input 13 Input 12 30 13 Input 12 Input 11 31 12 Input 11 Input 10 30 11 Input 10 Input 9 29 10 Input 9 Input 8 28 9 Input 8 Input 7 27 8 Input 7 Input 6 26 7 Input 6 Input 5 25 6 Input 5 Input 4 24 5 Input 4 Input 3 23 4 Input 3 Input 2 22 3 Input 2 Input 1 21 2 Input 1 Input 0 20 4 Input 0 Please read the Connection Notes on the previous pages before making your connections 7 6 Multi Channel Analogue Inputs Table 7 2 3054 32 Analogue Inputs Pin Connections for Right Hand 37 Way D Plug Wiring View 15 V unused Input 31 Input 30 Input 29 Input 28 Input 27 Input 26 Input 25 Input 24 Input 23 Input 22 Input 21 Input 20 Input 19 Input 18 Input 17 Input 16 Please read the Connection Notes on the previous pages before making your connections 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 OV 15V unused Input 31 Input 30 Input 29 Input 28 Input 27 Input 26 Input 25 Input 24 Input 23 Input 22 Input 21 Input 20 Input 19 Input 18 Input 17 Input 16 7 7 Microlink 3000 Hardware User Manual 7 2 3051 Resistance Measurement
8. 50 nanoamperes flows through it This produces negligible error with a normal low impedance thermocouple If the thermocouple should become open circuit then a maximum temperature reading will be obtained If you wish to use the unit for non thermocouple measurements then it may be advisable to disable all or part of this circuitry You can remove R5 from the 3055B board to disable this facility You may also wish to remove R4 which provides the zero reference Input Voltage Range These units will operate correctly with input voltages in the range 12 V The inputs will reject voltages that are common to both positive and negative inputs These common mode voltages could be as big as 10 V The amplifier must be capable of handling both the common mode voltage and the amplified signal The maximum permissible common mode voltage for any given input signal is defined by the following formula 12 Vem Vaitt G 2 Microlink 3000 Hardware User Manual where Vom is the common mode voltage Vgiff is the differential voltage between the 2 inputs G is the input amplifier gain 1 for voltage ranges 10 5 2 10 for voltage ranges 1 0 5 0 2 100 for voltage ranges 0 1 0 05 0 02 0 01 Maximum Input Voltage The inputs are protected to 35V for continuous voltages Transient voltages much higher than this will cause no damage Since all relays are off when the unit is switched off it will not load its inputs Connections Two rows
9. 53 exactly like a 3050 The 3054 is similar to the 3050 but provides 32 differential analogue inputs instead of 16 It has only 1 auxiliary channel so thermocouples for example could only be connected to the left hand connector i e to channels 0 15 B E J K N R S and T type thermocouples are supported 7 1 1 Connection Notes Although these modules have various functional capabilities they share a common input configuration Differential Inputs All the inputs are differential This means that the amplifier measures the difference between its positive and negative inputs It is important to remember that the voltages at both inputs must be within the amplifier operating range A classic error is to connect a battery between positive and negative inputs with no other connection Although the difference between the inputs is well defined the actual voltage at each input could be anything Connecting one end of the battery to Microlink O V either direct or via a resistor would solve the problem 7 2 Multi Channel Analogue Inputs 0 V pin 19 Floating Signal Channel input Source MICROLINK Earthed Signal Channel input Source MICROLINK ait Figure 7 1 For floating signals you need to connect one end of the signal to the 0 V input on pin 19 Since the OV of the Microlink is itself connected to mains earth when making your connections you sho
10. MICROLINK 305x Analogue Inputs User Manual Biodata Limited Manual Code M3000 3 2 Issue Date December 1998 Information in this document is subject to change without notice Updates are listed on our web site at http Awww microlink co uk techsupp html Biodata Limited 1990 2005 10 Stocks Street Manchester M8 8QG Tel 0161 834 6688 Fax 0161 833 2190 Email sales microlink co uk http www microlink co uk Multi Channel Analogue Inputs Multi Channel Analogue Inputs The 305x range provides analogue input to the computer There are facilities for voltage inputs with resistance bridge and rms options An auxiliary channel is provided which is reserved for special inputs such as cold junction measurement The input signals are conditioned by the 305x module and then passed to a 304x module which digitises the signal 7 1 Microlink 3000 Hardware User Manual 7 1 3050 2 3 4 Analogue Inputs The 3050 accepts up to 16 differential voltage inputs The 3052 enables strain gauge measurements to be placed under computer control Sixteen strain gauge bridges can be monitored by any one module It can accept full half or quarter bridge configurations with programmable gain and balance The 3053 is equivalent to a 3050 with an rms converter to convert analogue voltage signals to their root mean squares The readings will therefore always be positive voltages You can disable the rms option and use the 30
11. he resistance of 1 lead is measured and used to perform a compensation for the resistances in the other leads to the RTD Figure 7 3 3 Wire RTD Arrangement 4 Wire This is the configuration that gives the most accurate measurement The measuring current is applied via 2 of the leads and the voltage drop across the RTD is measured with a high input impedance device using the other 2 leads Figure 7 4 4 Wire RTD Arrangement 7 9 Microlink 3000 Hardware User Manual 4 Wire Compensated In this configuration the resistance across the dummy leads is measured and used as compensation gt _o Figure 7 5 4 Wire Compensated RTD Arrangement 7 10 Multi Channel Analogue Inputs 7 2 3 3051 Measurement Techniques The 3051 can cope with any of the above lead arrangements for up to eight RTD devices It uses the following technique to measure resistance 1 A programmable constant current source of 1 mA 2 A high input impedance instrumentation amplifier for measuring the voltage drop across the RTD 3 A compensation amplifier for measuring lead resistance which can then be subtracted from the measured RTD resistance Figures 7 6 to 7 9 show how the RTD devices are connected to the measuring circuit for each of the different lead arrangements 2 Wire With the two wire arrangement the constant current flows through the RTD to earth The voltage across the RTD is measured by the instrumentation amplifier The
12. ier input capacitance A high impedance signal source may take some time to do this so slowing the maximum multiplex rate Auxiliary Input This input has all the facilities of the other sixteen It can indeed be used as a 17th input if required In Windmill software it is reserved for measuring cold junction temperatures with thermocouples or excitation voltage in bridge circuits If you are using a 3902 thermocouple input card or a 3904 bridge input card the auxiliary input is automatically connected as required by the software Use with 3902 3903 Thermocouple Input Units When used with these units the auxiliary input is automatically connected to the cold junction sensor This is an RTD with 1 milliampere flowing through it Its resistance is thus 1 ohm per measured millivolt If inputs are unconnected the thermocouple break detection circuitry will cause them to read positive full scale Use with 3904 Bridge Input Unit When used with this unit the auxiliary input automatically measures the excitation voltage connected to the 3904 On a 3052 module this voltage is used to produce the programmable balance function This means that the bridge remains balanced even if your excitation voltage changes 7 5 Microlink 3000 Hardware User Manual Table 7 1 3050 2 3 4 Analogue Inputs Pin Connections for Left Hand 37 Way D Plug Wiring View 19 OV 15V 37 18 15V Auxiliary 36 17 Auxiliary Input 15 39 16 Input 1
13. of 18 screw terminals provide the input connections The isothermal plate on which they are fitted is engraved with channel numbers 0 to 15 positive and negative The top 2 terminals of each row are connected to 0 V Auxiliary Input The 3056 is fitted with a cold junction sensor This is the circuitry at the front of the screw terminals It consists of an 0 01 100 ohm RTD excited by a 1 milliampere constant current Its resistance is thus 1 ohm per measured millivolt Multi Channel Analogue Inputs 7 4 305x Specifications 7 4 1 3050 Specifications Number of inputs Type of measurement Input Multiplexer On resistance Switch off leakage Analogue voltage range Max safe input voltage Power supply ON Power supply OFF Break before make delay Crosstalk Input impedance Amplifier Offset voltage drift gain 100 Input bias current Common mode rejection Common mode range Frequency response Settling time to 0 01 Relative accuracy of gain ranges Initial accuracy of gain and offset Input noise voltage 7 4 2 3051 Specifications Current sources Accuracy 10 100 pA Accuracy 1000 pA Other specifications as 3050 7 4 3 3052 Specifications Max balance range Other specifications as 3050 16 1 auxiliary voltage cold junction 400 Q lt 2 nA 11 15V 35 V 20 V 1 usec 75 dB 100 MQ 1 uV OC 30 nA 105 dB gain 1000 10 V 50 kHz 15 usec 0 02 1 LSB 2 uV rms 10 100 1000 pA 0 2 0 02
14. uld follow this policy e f your signal source is floating ie has no reference to mains earth then you must provide a reference by connecting one end of it to Microlink 0 V either direct or via a resistor The resistor could have any value up to several MQ However large values could cause 50 Hz problems if your signal source has much leakage to earth e lf your signal source is itself earthed then you should connect only positive and negative inputs You should make no connection to Microlink earth To use a differential input in single ended mode short one of the signal wires usually the input directly to ground 7 3 Microlink 3000 Hardware User Manual Input Voltage Range The 305x modules will operate correctly with input voltages in the range 11 V The inputs will reject voltages that are common to both positive and negative inputs These common mode voltages could be as big as 10 V The amplifier must be capable of handling both the common mode voltage and the amplified signal The maximum permissible common mode voltage for any given input signal is defined by the following formula 11 Vem Vaitf x G 2 where Vom is the common mode voltage Vgitt is the differential voltage between the 2 inputs G is the input amplifier gain 1 for voltage ranges 10 5 2 10 for voltage ranges 1 0 5 0 2 100 for voltage ranges 0 1 0 05 0 02 0 01 Maximum Input Voltage The input multiplexers are protected to
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