Campbell Scientific AM16/32A Multiplexer - Manual (Page 14)

AM16/32A Relay Analog Multiplexer
The average power required to operate an AM16/32A 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 AM16/32A would be about ((.030 Sec/chan x
32 chan)/60 Sec) 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 Sec/chan x 32 chan)/2 Sec) 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 AM16/32A, 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 supply for the
AM16/32A (Figure 4).
FIGURE 4. Power and Ground Connections for External Power Supply.
Low supply voltage and high ambient temperatures affect the actuation time of
the multiplexer relays (Figure 2). 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 AM16/32A are dedicated to the connection of
sensors to the multiplexer (Figure 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.
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