AM25T Solid State Multiplexer Revision: 2/06 C o p y r i g h t © 1 9 9 5 - 2 0 0 6 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 − 95% DIMENSIONS Length: Width: Depth: 30.5 cm (12.0”) 5.10 cm (2.0") 15.3 cm (6.0”) WEIGHT 0.91 kg (2.0 lbs) 2.7 kg (6.0 lbs); Shipping EXPANDABILITY (nominal)** 4 AM25Ts 6 AM25Ts 4 AM25Ts 6 AM25Ts 7 AM25Ts per CR1000 per CR23X per CR10(X) per 21X per CR7 725 Card MAXIMUM CABLE LENGTH Multiplexers can be located up to 305 m (1000 ft) from the datalogger.
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 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. With long lead lengths, a delay within the measurement instruction will allow the capacitance of the lead wires to discharge before the measurement is made. Consult the Measurement Section of your datalogger manual for more information. 6.
AM25T Solid State Multiplexer Input locations within the measurement loops must be indexed (--), see Instruction 87 in the datalogger manual. To index a location, using Edlog ver 6.0 or greater, move the cursor to the Input location label and press “F4”. To index a location with the datalogger keyboard, press the “C” key when entering the location number and before the “A” key is pressed. TABLE 6-1.
AM25T Solid State Multiplexer 04: 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 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.
AM25T Solid State Multiplexer 03: Full Bridge (P6) ;Measure the output of the reference temp.
AM25T Solid State Multiplexer 12: Beginning of Loop (P87) 1: 0 Delay 2: 25 Loop Count ;Loop through thermocouple channels 13: Do (P86) 1: 71 ;Clock the AM25T twice Pulse Port 1 14: Do (P86) 1: 71 Pulse Port 1 15: Thermocouple Temp (DIFF) (P14) ;Measure the connected thermocouple 1: 1 Reps 2: 21 2.5 mV 60 Hz Rejection Range 3: 1 DIFF Channel 4: 1 Type T (Copper-Constantan) 5: 1 Ref Temp (Deg. C) Loc [ RefTemp_C ] 6: 2-Loc [ TC_1 ] 7: 1.0 Mult 8: 0.
AM25T Solid State Multiplexer Example 3. 21X Program for Measuring 25 Type T Thermocouples or Voltage Sensors Using a Differential Instruction *Table 1 Program 01: 10 Execution Interval (seconds) 01: Do (P86) 1: 42 ;Turn On AM25T Set Port 2 High 02: Full Bridge (P6) ;Measure the output of the reference temp.
AM25T Solid State Multiplexer 10: Thermocouple Temp (DIFF) (P14) ;Measure the connected thermocouple 1: 1 Reps 2: 1 5 mV Slow Range 3: 1 DIFF Channel 4: 1 Type T (Copper-Constantan) 5: 1 Ref Temp (Deg. C) Loc [ RefTemp_C ] 6: 2-Loc [ TC_1 ] 7: 1.0 Mult 8: 0.0 Offset 11: End (P95) ;End of loop 12: Do (P86) 1: 52 Set Port 2 Low ;Turn off AM25T Example 4.
AM25T Solid State Multiplexer 06: Z=X/Y (P38) 1: 27 X Loc [ Vs_______ ] 2: 28 Y Loc [ Vx ] 3: 1 Z Loc [ RefTemp_C ] ;Calculate Vs/Vx 07: Z=X*F (P37) 1: 1 X Loc [ RefTemp_C ] 2: -0.001 F 3: 1 Z Loc [ RefTemp_C ] 08: Z=X+F (P34) 1: 1 X Loc [ RefTemp_C ] 2: .09707 F 3: 1 Z Loc [ RefTemp_C ] 09: BR Transform Rf[X/(1-X)] (P59) 1: 1 Reps 2: 1 Loc [ RefTemp_C ] 3: 10.
AM25T Solid State Multiplexer 18: Thermocouple Temp (DIFF) (P14) ;Measure the connected thermocouple 1: 1 Reps 2: 1 5 mV Slow Range 3: 1 DIFF Channel 4: 1 Type T (Copper-Constantan) 5: 1 Ref Temp (Deg. C) Loc [ RefTemp_C ] 6: 2-Loc [ TC_1 ] 7: 1.0 Mult 8: 0.0 Offset 19: End (P95) 20: Do (P86) 1: 52 ;End loop ;Turn off AM25T Set Port 2 Low 6.3 Example CR23X Program The CR23X has a special instruction for measuring thermocouples or voltages with the AM25T.
AM25T Solid State Multiplexer Example 5. CR23X Program for Measuring 25 Type T Thermocouples ;{CR23X} ; *Table 1 Program 01: 1 Execution Interval (seconds) 01: AM25TMultiplexer (P134) 1: 25 Reps 2: 21 10 mV, 60 Hz Reject, Slow Range 3: 1 AM25T Channel 4: 1 DIFF Channel 5: 21 Exchan 1, 60 Hz Reject 6: 1 Clock Control 7: 2 Reset Control 8: 1 Type T (Copper-Constantan) 9: 1 Ref Temp (Deg. C) Loc [ RefTemp ] 10: 2 Loc [ TC_1 ] 11: 1.0 Mult 12: 0.0 Offset 6.
AM25T Solid State Multiplexer The AM25T instruction has the following parameters: Dest: The Dest parameter is a variable in which to store the results of the measurement. Reps: The Reps parameter is the number of times the measurement should be made. Measurements are made on consecutive channels. If the Reps parameter 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.
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. TABLE 6-5. Wiring for CR1000 Program Example Function +12V Power Power and Shield Ground Clock Reset RTD Excitation Common High Common Low AM25T 12 V Gnd CLK RES EX HI LO CR1000 12 V Gnd C5 C4 EX1 1H 1L Example 6.
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. Single-Ended Measurements This is a blank page.
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. Differences Between the AM25T, AM416, and the AM32 This is a blank page.
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