AM416 RELAY MULTIPLEXER INSTRUCTION MANUAL REVISION: 2/96 COPYRIGHT (c) 1987-1996 CAMPBELL SCIENTIFIC, INC.
WARRANTY AND ASSISTANCE The AM416 RELAY 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.
AM416 RELAY MULTIPLEXER MANUAL TABLE OF CONTENTS PAGE 1. 1.1 1.2 FUNCTION Typical Applications ................................................................................................................... 1 Compatibility .............................................................................................................................. 1 2. PHYSICAL DESCRIPTION .................................................................................................... 1 3.
11. 12. 13. 14. 15. 16. 17. Potentiometer Hook-up and Measurement ............................................................................. 12 Four Wire Half Bridge Hook-up and Measurement ................................................................. 13 Differential Measurement with Sensor Excitation .................................................................... 13 Full Bridge Measurement with Excitation Compensation ........................................................
CAUTIONARY NOTES The AM416 is not designed to multiplex power. Its intended function is to switch low level analog signals. Switched current in excess of 30 mA will degrade contacts and render them unsuitable for future low level analog measurements. Customers who need to switch power are directed to CSI's A6REL-12 or A21REL-12 relays. Adjacent AM416 channels may be shorted together for up to 5 ms during the clocking procedure. Users should consider this when assigning AM416 input channels.
AM416 RELAY MULTIPLEXER 1. FUNCTION The primary function of the AM416 Multiplexer is to increase the number of sensors that may be scanned by Campbell's CR10(X), 21X and CR7 dataloggers. The AM416 is positioned between the sensors and the datalogger; mechanical relays are used to switch the desired sensor signal(s) through the system. Most commonly, users will multiplex signals from analog sensors into single-ended or differential datalogger channels.
AM416 RELAY MULTIPLEXER Wires from sensors and datalogger are connected to the gray terminal strips. The set of four terminals located near the strain-relief flange are the connections for datalogger control of the AM416 (Section 4.1). The terminal strips that run the length of the AM416 are for measurement connections (Section 4.2). The sensor inputs are not spark gapped. All terminals accept stripped and tinned lead wires up to 1.5 mm in diameter.
AM416 RELAY MULTIPLEXER 3. AM416 SPECIFICATIONS POWER*: unregulated 12 VDC (9.6 V to 16 V) - See Figure 4 for implications of low power to relay actuation CURRENT DRAIN: Quiescent: < 100 uA Active: 17 mA (typical) RESET*: a continuous signal of 3.5VDC < voltage < 16 VDC holds AM416 in an active state (i.e. a clock pulse can trigger a scan advance). A signal voltage of < 0.9VDC deactivates the AM416 (clock pulse will not trigger a scan advance; AM416 is also reset). CLOCK*: on the transition from <1.
AM416 RELAY MULTIPLEXER FIGURE 2. Hook-up Diagrams for Datalogger - AM416 Connections CR10(X) Hook-up 21X Hook-up CR7 Hook-up The 21X or CR7 (with a 725 Card) can be used to connect 12VDC supply and ground to the AM416. One control port is used for reset, and one switched excitation channel is used for clock. If switched excitations are unavailable, a control port may be used to provide clock pulses to the multiplexer. 4.1.1 RESET Reset (RES) controls activation of the multiplexer. A voltage (3.
AM416 RELAY MULTIPLEXER voltage level must fall below 1.5VDC then exceed 3.5VDC to clock. Pulse width must be at least 5 ms. An additional delay is required before the measurement to ensure adequate time for the relay to close. In the 21X and CR7 dataloggers, a switched excitation is generally used to clock the multiplexer (Instruction 22 - 5,000 mV excitation). If no switched excitation channels are available it is possible to clock using control ports. See Section 5.1 for additional details.
AM416 RELAY MULTIPLEXER FIGURE 4. Actuation Time of Relays vs. Temperature (oC) and Battery Voltage. 4.2 THE MEASUREMENT TERMINALS The terminals that run the length of the AM416 are dedicated to the connection of sensors to the datalogger (Figure 1). The 16 groups of 4terminal inputs allow attachment of stripped and tinned sensor leads. The terminals marked COM allow attachment of the common signal leads that carry the sensor's signal between multiplexer and datalogger.
AM416 RELAY MULTIPLEXER (3) Clock/Delay - With the CR10(X), the clock line is connected to a control port. Instruction 86 with the pulse port command (71- 78), sets the clock line high for 10 ms. Instruction 22 is used to delay an additional 10 ms. When controlled by the 21X or CR7, the clock line may be connected to either an excitation or a control port. Connection to an excitation port is preferred because only one instruction (22) is required to send the clock pulse.
AM416 RELAY MULTIPLEXER EXAMPLE PROGRAMS - GENERALIZED PROGRAM LOOPS FOR THE CR10(X), 21X AND CR7. 21X SAMPLE PROGRAM * 1 Table 1 Programs 01: 60 Sec. Execution Interval CR7 SAMPLE PROGRAM * 1 Table 1 Programs 01: 60 Sec. Execution Interval CR10(X) SAMPLE PROGRAM * 1 Table 1 Programs 01: 60 Sec. Execution Interval ACTIVATES MULTIPLEXER 01: P20 Set Port 01: 1 Set high 02: 1 Port Number ACTIVATES MULTIPLEXER 01: P20 Set Port 01: 1 Set high 02: 1 EX Card 03: 1 Port No.
AM416 RELAY MULTIPLEXER FIGURE 7. Wiring Diagram for Strain Gages and Potentiometers (8) Additional Loops - Additional loops may be used if sensors that require different measurement instructions are connected to the same multiplexer. In this instance, like sensors are assigned to sequential input SETS. Each group of sensors is measured in a separate loop (steps 2 through 7, Figure 4).
AM416 RELAY MULTIPLEXER BEGINNING OF POTENTIOMETER MEASUREMENT LOOP 06: P87 Beginning of Loop 01: 0 Delay 02: 6 Loop Count 07: 01: P90 2 CLOCK PULSE 08: P22 01: 1 02: 1 03: 1 04: 5000 Step Loop Index (Extended) Step Excitation with Delay EX Chan Delay w/EX (units=.01sec) Delay after EX (units=.01sec) mV Excitation POTENTIOMETER MEASUREMENT INSTRUCTION 09: P4 Excite,Delay,Volt(SE) 01: 2 Reps 02: 5 5000 mV slow Range 03: 1 IN Chan 04: 2 Excite all reps w/EXchan 2 05: 1 Delay (units .
AM416 RELAY MULTIPLEXER FIGURE 8. Single-ended Measurement Without Excitation FIGURE 9. Differential Measurement Without Excitation 6.2 DIFFERENTIAL ANALOG MEASUREMENT WITHOUT SENSOR EXCITATION Sensor to Multiplexer wiring - Up to two differential sensors that don't require excitation may be connected to one input SET. Sensor shields are routed through shield terminals. Multiplexer to Datalogger wiring - A pair of COM terminals (e.g.
AM416 RELAY MULTIPLEXER FIGURE 10. Half Bridge (Modified 107 Temperature Probe) Hook-up and Measurement. FIGURE 11. Potentiometer Hook-up and Measurement 6.3.2 POTENTIOMETER MEASUREMENT Sensor to Multiplexer wiring - up to two potentiometers may be connected to one input SET. Excitation and ground leads may be common; signal leads must be routed separately (Figure 11).
AM416 RELAY MULTIPLEXER FIGURE 12. Four Wire Half Bridge Hook-up and Measurement FIGURE 13. Differential Measurement with Sensor Excitation 6.4 FULL BRIDGE MEASUREMENTS Sensor to Multiplexer wiring - Excitation, ground, and the two signal leads may be connected to one input SET (Figure 13). Multiplexer to Datalogger wiring - COM terminals are connected to a datalogger excitation channel, a differential analog input channel, and analog ground.
AM416 RELAY MULTIPLEXER FIGURE 14. Full Bridge Measurement with Excitation Compensation 6.6 THERMOCOUPLE MEASUREMENT The datalogger manuals contain thorough discussions of thermocouple measurement and error analysis. These topics will not be covered here. 6.6.1 MEASUREMENT CONSIDERATIONS Reference Junction - As shown in Figure 15 and 16, two reference junction configurations are possible: reference at the datalogger or reference at the AM416.
AM416 RELAY MULTIPLEXER FIGURE 15. Differential Thermocouple Measurement with Reference Junction at the Datalogger. FIGURE 16. Differential Thermocouple Measurement with Reference Junction at the AM416. If a mix of TC's and other sensor types are multiplexed through the AM416, it is generally best to locate the reference junction on the AM416, as shown in Figure 16. AM416 Reference - An external reference, usually a thermistor, may be located at the AM416, as shown in Figure 16.
AM416 RELAY MULTIPLEXER 6.6.2 SINGLE-ENDED THERMOCOUPLE MEASUREMENT 6.6.3 DIFFERENTIAL THERMOCOUPLE MEASUREMENT In single-ended thermocouple measurement, the following precautions must be taken to ensure accurate measurement: Sensor to Multiplexer wiring - up to two thermocouples per input SET. 1. Only shielded thermocouple wire should be used; the sensor shields should be tied to datalogger earth ground through the multiplexer shield terminals. 2.
AM416 RELAY MULTIPLEXER EXAMPLE PROGRAM - THERMOCOUPLE AND SOIL BLOCK MEASUREMENT (PROGRAM IS FOR CR10(X) - 33 LOCATIONS ALLOCATED TO INPUT STORAGE) * 01: 1 60 Table 1 Programs Sec.
AM416 RELAY MULTIPLEXER 7. GENERAL MEASUREMENT CONSIDERATIONS 1. Long lead lengths - long lead lengths contribute to the formation of induced and capacitive voltages within the sensor and AM416 lead wires. To minimize this phenomenon, CSI recommends use of Teflon, polyethylene, or polypropylene insulation around individual conductors. Do not use PVC insulation as conductor insulation, although it may be used as a cable jacket.
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APPENDIX A.
APPENDIX B. DIFFERENCES BETWEEN THE AM416 AND THE AM32 The AM416 differs from Campbell Scientific's AM32 multiplexer in the following ways: 1. The AM416 switches sixteen sets of four lines at a time (4 x 16). The AM32 switches thirty-two sets of two lines at a time (2 x 32). 2. The AM416 is packaged in an aluminum case that should decrease temperature gradients across the multiplexer terminal strips. 4. The AM416 contains terminals and circuitry for sensor shield wires.
