Campbell AVW1 Specifications download pdf (Page 16)

AM16/32B Relay Analog Multiplexer

on average system current drains (e.g. logger, multiplexer, other peripherals

and sensors) at the expected ambient temperatures.

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 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 AM16/32B, 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 supply for the

AM16/32B (Figure 5).

AM16/32B

FIGURE 5. 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 AM16/32B 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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Campbell AVW1 Specifications Page 16