AM25T Solid State Multiplexer Revision: 1/10 C o p y r i g h t © 1 9 9 5 - 2 0 1 0 C a m p b e l l S c i e n t i f i c , I n c .
Warranty and Assistance The AM25T SOLID STATE MULTIPLEXER is warranted by CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and workmanship under normal use and service for twelve (12) months from date of shipment unless specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
AM25T Solid State Multiplexer Table of Contents PDF viewers note: These page numbers refer to the printed version of this document. Use the Adobe Acrobat® bookmarks tab for links to specific sections. 1. General .........................................................................1 1.1 AM25T Specifications..............................................................................1 1.2 Physical Description .................................................................................2 1.
AM25T Solid State Multiplexer Table of Contents Figures 1. AM25T Thermocouple Multiplexer........................................................... 3 2. External Battery Connections .................................................................... 6 3. Differential Measurement of Type T Thermocouple ................................. 7 4. Differential Voltage Measurement............................................................. 7 A-1. Single-Ended Measurement of a Type T Thermocouple ................
AM25T Solid State Multiplexer 1. General The AM25T Multiplexer increases the number of channels for measuring thermocouples or voltage sensors with Campbell Scientific dataloggers. The AM25T is positioned between the sensors and the datalogger. The datalogger controls the AM25T's solid state relays, sequentially connecting each sensor to the datalogger.
AM25T Solid State Multiplexer OPERATING TEMPERATURE Standard: -40°C to +85°C RTD accuracy ±0.4°C OPERATING HUMIDITY Noncondensing: 0 to 95% DIMENSIONS Length: Width: Depth: 23.6 cm (9.3”) 5.10 cm (2.0") 13.2 cm (5.2”) WEIGHT 0.91 kg (2.0 lbs) 3.6 kg (8.
AM25T Solid State Multiplexer The terminal strips that run the length of the AM25T are for sensor connections. All inputs are protected by spark gaps. All terminals accept stripped and tinned lead wires up to 1.5 mm (0.059 inches) in diameter. A strain-relief flange is located between the input terminals.
AM25T Solid State Multiplexer Ground (GND) Each differential input channel has a ground terminal located next to it. The ground terminal is common with the power ground and the ground lug on the base. Connect the sensor shields to the ground terminals ( ). Always tie the datalogger and multiplexer to a common earth ground via the grounding lug. Analog Ground (AG) The analog ground (AG) terminal is the ground reference for the AM25T reference temperature measurement.
AM25T Solid State Multiplexer U-bolts are used to attach the enclosures to a 1.25" NPT pipe. The enclosure may also be lag-bolted to a wall or similar flat surface. Fasten the AM25T to the enclosure backplate. Securely fasten the leads to the strain relief flange running between the AM25T terminal strips and install the cover to reduce temperature gradients during thermocouple measurements. 3.
AM25T Solid State Multiplexer AM25T FIGURE 2. External Battery Connections 4. Sensor to AM25T Wiring This section and the examples describe differential voltage measurements of thermocouples. It is possible to make single-ended measurements with the AM25T, however they are more likely to have problems (Appendix A). Shield wires are connected to the ground terminal next to the measurement channel and left unattached at the sensor. 4.
AM25T Solid State Multiplexer FIGURE 3. Differential Measurement of Type T Thermocouple 4.2 Differential Analog Measurements Connect one differential sensor to a differential AM25T input channel. Connect the sensor shields to the ground terminals next to the input channel. Up to 25 differential sensors may be measured by one differential channel on the datalogger (Figure 4). FIGURE 4. Differential Voltage Measurement 4.3 Mixed Sensor Types Different sensors may be mixed on the AM25T.
AM25T Solid State Multiplexer 5. General Measurement Considerations Cables have additional capacitance that increases the time required for a signal to settle its true value. To reduce settling time, Campbell Scientific recommends use of Teflon, polyethylene, or polypropylene insulation around individual conductors. Do not use PVC as conductor insulation. PVC may be used as a cable jacket.
AM25T Solid State Multiplexer is greater than 1, the Dest parameter must be a variable array. If 0 is entered, the only measurement that is made is the reference temperature measurement. Range: The Range parameter is the expected voltage range of the input from the sensor. An alphanumeric or the numeric code can be entered. The range code options depend on the datalogger used.
AM25T Solid State Multiplexer ClkPort: The ClkPort argument is the control port that will be used to clock the AM25T. One clock port may be used with several AM25Ts. A numeric code is entered for this argument: Code 1 2 3 4 5 6 7 8 Description Control Port 1 Control Port 2 Control Port 3 Control Port 4 Control Port 5 Control Port 6 Control Port 7 Control Port 8 ResPort: The ResPort argument is the control port that will be used to enable and reset the AM25T. Each AM25T must have a unique Reset port.
AM25T Solid State Multiplexer Mult, Offset: The Mult and Offset parameters are each a constant, variable, array, or expression by which to scale the results of the measurement. With a multiplier (mult) of 1 and an offset of 0, the output is in degrees Celsius. NOTE The AM25T instruction must NOT be placed in a conditional statement when running in pipeline mode. 6.1.1 Example CRBasic Programs Both CRBasic example programs are written for CR1000 dataloggers.
AM25T Solid State Multiplexer ‘Main Program BeginProg Scan (1,Sec,0,0) AM25T (TC(),25,mV2_5C,1,1,TypeT,Tref,5,4,Vx1,True,0,250,1.0,0) CallTable Dat15sec CallTable Dat5min NextScan EndProg 6.1.1.2 CR1000 Example Program 2 In this example, one AM25T instruction is used to measure the on-board PRT, and another AM25T instruction is used to measure ten type T thermocouples. Table 6-2 provides the wiring for the example. TABLE 6-2.
AM25T Solid State Multiplexer 'Only the Reference Temperature is measured and stored in RTemp_C. 'To do this, enter 0 for the REP value AM25T(RTemp_C,0,mV2_5C,1,1,TypeT,RTemp_C,2,1,1,True,0,250,1,0) 'Ten Type T (copper-constantan) are measured on the AM25T. 'Thermocouple measurements are stored in the Temp_C() variable AM25T(Temp_C(1),10,mV2_5C,1,1,TypeT,RTemp_C,2,1,0,True,0,_60Hz,1,0) 'Call Data Tables and Store Data CallTable(Table1) NextScan EndProg 6.
AM25T Solid State Multiplexer TABLE 6-3. RTD Excitation Voltage and Measurement Range for AM25T Multiplexers Prior to Serial Number 1839 Datalogger 21X CR10(X) CR7 Temperature Range -40 to 85°C -24 to 65°C -40 to 85°C -11 to 52°C -40 to 85°C Excitation voltage 250 mV 350 mV 350 mV 250 mV 350 mV Vs Range ± 5 mV ± 5 mV ± 7.5 mV ± 2.5 mV ± 15 mV Vx Range ± 500 mV ± 500 mV ± 2500 mV ± 250 mV ± 500 mV 6.2.
AM25T Solid State Multiplexer 03: Full Bridge (P6) ;Measure the output of the reference temp. full bridge 1: 1 Reps 2: 23 25 mV 60 Hz Rejection Range ;See Table 6-1 for older AM25T multiplexers 3: 1 DIFF Channel 4: 1 Excite all reps w/Exchan 1 5: 1200 mV Excitation ;See Table 6-1 for older AM25T multiplexers 6: 1 Loc [ RefTemp_C ] 7: -0.001 Mult 8: 0.09707 Offset 04: BR Transform Rf[X/(1-X)] (P59) 1: 1 Reps 2: 1 Loc [ RefTemp_C ] 3: 10.
AM25T Solid State Multiplexer Example 4. CR10(X) Program for Measuring 25 Type T Thermocouples with the Differential Thermocouple Instruction and Long Lead Length Compensation on the RTD Measurement *Table 1 Program 01: 10 Execution Interval (seconds) 01: Set Port(s) (P20) ;Configure Control Ports for 1 millisecond pulse 1: 9999 C8..C5 = nc/nc/nc/nc 2: 9933 C4..C1 = nc/nc/1ms/1ms 02: Do (P86) 1: 42 Set Port 2 High ;Turn On AM25T 03: Full Bridge (P6) ;Measure the output of the reference temp.
AM25T Solid State Multiplexer 09: BR Transform Rf[X/(1-X)] (P59) 1: 1 Reps 2: 1 Loc [ RefTemp_C ] 3: 10.025 Multiplier (Rf) ;Calculate RTD resistance R/R0 10: Temperature RTD (P16) ;Calculate reference temperature 1: 1 Reps 2: 1 R/R0 Loc [ RefTemp_C ] 3: 1 Loc [ RefTemp_C ] 4: 1.0 Mult 5: 0.
AM25T Solid State Multiplexer 6.2.2 Example CR23X Program The CR23X uses Instruction 134 for measuring thermocouples or voltages with the AM25T. Example 5 is a portion of a datalogger program that uses the instruction to measure 25 type T thermocouples. Instruction 134 automatically compensates for long lead lengths. TABLE 6-5.
Appendix A. Single-Ended Measurements Single-ended measurements with the AM25T are not recommended. This is not due to any problem with the AM25T. Single-ended measurements have some problems that differential measurements avoid. The problems with single-ended measurements are: • • Reduced noise rejection. Ground reference and Ground Loops. A differential voltage measurement measures the voltage difference between two inputs. Current is not allowed to flow through either input.
Appendix A. Single-Ended Measurements A.1.1 Thermocouple Measurements Wire the high side of each thermocouple into an input terminal. The low side of each thermocouple is wired into the adjacent ground terminal (Figure A-1). FIGURE A-1. Single-ended Measurement of a Type T Thermocouple Example A-1.
Appendix A. Single-Ended Measurements 05: Temperature RTD (P16) ;Calculate reference temperature 1: 1 Reps 2: 1 R/R0 Loc [ RefTemp_C ] 3: 1 Loc [ RefTemp_C ] 4: 1.0 Mult 5: 0.
Appendix A. Single-Ended Measurements 03: BR Transform Rf[X/(1-X)] (P59) 1: 1 Reps 2: 1 Loc [ RefTemp_C ] 3: 10.025 Multiplier (Rf) ;Calculate RTD resistance R/R0 04: Temperature RTD (P16) ;Calculate reference temperature 1: 1 Reps 2: 1 R/R0 Loc [ RefTemp_C ] 3: 1 Loc [ RefTemp_C ] 4: 1.0 Mult 5: 0.
Appendix A. Single-Ended Measurements FIGURE A-2. Single-Ended Measurement A.2 Indexing with Loops When a multiplexer is measured with a measurement instruction within a loop, the input locations in which to store measurements must be indexed to the loop counter so the measurement is stored in the next input location each pass through the loop. When more than one repetition is used on the measurement instruction, as in examples A-1 and A-2, Instruction 90 is used to set the increment of the loop index.
Appendix A. Single-Ended Measurements instruction has one repetition. If the instruction has two repetitions, then every other Input Location will be over written. This effect is illustrated in Table A2. The program fragment in Example A-4 generated this effect. NOTE The multiplexer control instructions are not included in the example program fragment. TABLE A-2.
Appendix A. Single-Ended Measurements Example A-4. Measuring Single Ended Thermocouples with the Input Location Indexed and no Step Loop Index 01: Beginning of Loop (P87) 1: 0 Delay 2: 6Loop Count 02: Thermocouple Temp (SE) (P13) 1: 2 Reps 2: 21 2.5 mV 60 Hz Rejection Range 3: 1 SE Channel 4: 1 Type T (Copper-Constantan) 5: 1 Ref Temp (Deg. C) Loc [ RefTemp ] 6: 18-Loc [ TC_1 ] 7: 1.0 Mult 8: 0.0 Offset 03: End (P95) Example A-5.
Appendix A.
Appendix B. Differences Between the AM25T, AM416, and the AM32 The AM25T differs from Campbell Scientific's AM416 and AM32 multiplexers in the following ways: 1. The AM25T cannot be used to multiplex power and is not suitable for bridge measurements because of the high impedance of the solid state relays. 2. The AM25T switches 25 sets of 2 lines at time, (HI and LO) (2 x 25), unlike the AM416 which switches 16 sets of 4 lines at a time (4 x 16). The AM32 switches 32 sets of 2 lines at a time (2 x 32).
Appendix B.
Campbell Scientific Companies Campbell Scientific, Inc. (CSI) 815 West 1800 North Logan, Utah 84321 UNITED STATES www.campbellsci.com • info@campbellsci.com Campbell Scientific Africa Pty. Ltd. (CSAf) PO Box 2450 Somerset West 7129 SOUTH AFRICA www.csafrica.co.za • cleroux@csafrica.co.za Campbell Scientific Australia Pty. Ltd. (CSA) PO Box 444 Thuringowa Central QLD 4812 AUSTRALIA www.campbellsci.com.au • info@campbellsci.com.au Campbell Scientific do Brazil Ltda.
