Campbell Scientific AM16/32B Relay Multiplexer - Manual (Page 11)

AM16/32B Relay Multiplexer
1. Function
The primary function of the AM16/32B Multiplexer is to increase the number
of sensors that can be measured by a CR1000, CR3000, CR800, CR850,
CR23X, CR10(X), 21X, or CR7 datalogger. The AM16/32B is positioned
between the sensors and the datalogger. The AM16/32B is a replacement for
Campbell Scientific’s AM16/32A model. The hardware is the same as the
AM16/32A model. The AM16/32B adds a mode to address an individual
relay. Mechanical relays in the AM16/32B connect each of the sensor
channels in turn to a common output destined for the datalogger. The user
program advances the multiplexer through the sensor channels making
measurements and storing data.
A slide switch located on the AM16/32B’s top panel selects one of two modes
of operation. In “2x32” mode the multiplexer can scan 32 sensor input
channels, each with two lines. In “4x16” mode it can scan 16 input channels
with four lines a piece. The datalogger program is written according to the
selected mode and the sensors to be measured.
The maximum number of sensors that can be multiplexed by an AM16/32B
depends primarily on the type(s) of sensors to be scanned. The following
guidelines assume identical sensors:
Up to 32 single-ended or differential analog sensors that do not require
excitation. For example: pyranometers and thermocouples (see Section 6.1,
Single-Ended Analog Measurement without Sensor Excitation, Section 6.2,
Differential Analog Measurement without Sensor Excitation, and Section 6.6,
Thermocouple Measurement).
Up to 32 single-ended sensors that require excitation. Example: some half
bridges (see Section 6.3.1, Half Bridge Measurement with Completion Resistor
at Datalogger).
Up to 16 single-ended or differential sensors that require excitation. Examples:
full bridges and four-wire half bridge with measured excitation (see Section
6.3.3, Four Wire Half Bridge, and Section 6.4, Full Bridge Measurements).
In conjunction with a second AM16/32B, up to 16 six-wire full bridges
(Section 6.5, Full Bridges with Excitation Compensation).
1.1 Typical Applications
The AM16/32B is intended for use in applications where the number of
required sensors exceeds the number of datalogger input channels. Most
commonly, the AM16/32B is used to multiplex analog sensor signals, although
it can also be used to multiplex switched excitations, continuous analog
outputs, or even certain pulse counting measurements (those that require only
intermittent sampling). It is also possible to multiplex sensors of different, but
compatible, types (for example, thermocouples and soil moisture blocks, see
Section 6.7.1, Mixed Sensor Example: Soil Moisture Blocks and
Thermocouples).
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