Campbell Scientific AM16/32B AM16/32B Relay Multiplexer - Page 20
Measurement Terminals
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AM16/32B Relay Multiplexer The average power required to operate an AM16/32B depends on the percentage of time it is active per time period. For example, if a CR10X makes differential measurements on 32 thermocouples every minute, the average current drain due to the AM16/32B would be about ((.030 s/chan x 32 chan)/ 60 s) x 6 mA = 0.1 mA. Under the same conditions, a 2-second execution interval rate increases the average system current drain to about ((.030 s/chan x 32 chan)/2 s) x 6 mA = 2.9 mA. At a minimum, the power supply must be able to sustain the system between site visits anticipating the worst environmental extremes. If a 21X power supply is used to power the AM16/32B, all low-level analog measurements (thermocouples, pyranometers, thermopiles, etc.) must be made differentially. Differential measurements are required because slight ground potentials are created along the 21X analog terminal strip when the 12V supply is used to power peripherals. This limitation reduces the number of available analog input channels and may mandate the use of an external power supply for the AM16/32B (FIGURE 4-3). AM16/32B FIGURE 4-3. Power and ground connections for external power supply Low supply voltage and high ambient temperatures affect the actuation time of the multiplexer relays (FIGURE 3-1). If your program does not allow the relay contacts sufficient time to close before a measurement is started, the result will be inaccurate or overranged values. 4.2 Measurement Terminals Most of the terminals on the AM16/32B are dedicated to the connection of sensors to the multiplexer (FIGURE 2-1). Depending on the panel switch selection ("4x16" or "2x32" mode), the sensor input terminals are organized into 16 groups (blue letters) of 4 sensor inputs or 32 groups (white letters) of 2 sensor inputs. The terminals accept solid or tinned, stripped sensor leads. The four COM terminals marked ODD H, L and EVEN H, L located by the mode switch provide for attachment of the common signal leads that carry multiplexed sensor signals to the datalogger. 10