Campbell Scientific AM16/32A Multiplexer - Manual (Page 7)

AM16/32A Relay Analog Multiplexer
1. Function
The primary function of the AM16/32A 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 AM16/32A is positioned
between the sensors and the datalogger. The AM16/32A is a replacement for
CSI’s AM16/32 model. Mechanical relays in the AM16/32A 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 AM16/32A’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 AM16/32A
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 Sections 6.1,
6.2, and 6.6).
Up to 32 single-ended sensors that require excitation. Example: some half
bridges (see Section 6.3.1).
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 and 6.4).
In conjunction with a second AM16/32A, up to 16 six-wire full bridges
(Section 6.5).
1.1 Typical Applications
The AM16/32A is intended for use in applications where the number of
required sensors exceeds the number of datalogger input channels. Most
commonly, the AM16/32A 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 (i.e., those that require
only intermittent sampling). It is also possible to multiplex sensors of
different, but compatible, types (e.g., thermocouples and soil moisture blocks,
see Section 6.7.1).
1