Campbell Scientific AM16/32A Multiplexer - Manual (Page 33)

AM16/32A Relay Analog Multiplexer
A problem with making full bridge measurements with this
configuration is that the resistance of the lead wire and multiplexer
relays can cause a voltage drop, reducing the excitation at the bridge.
The following section describes a configuration that compensates for
this by measuring the excitation at the bridge.
6.5 Full Bridges with Excitation Compensation
Sensor to Multiplexer wiring – With panel switch set to ”4x16” mode
you are 2 lines short for a six wire measurement. One solution is to
multiplex the four signal wires through the AM16/32A, but bypass the
AM16/32A with excitation and ground wires. This means that the
sensors will be excited in parallel which causes a higher current drain,
possibly enough to exceed the current available from the datalogger's
citation and ground leads can
be multiplexed through an additional AM16/32A allowing the sensors
to be excited one at a time (Figure 16). In this case the 12V, GND,
second multiplexer are wired in parallel
ctively widening the multiplexer to “8x16”.
to two sequential differential analog
excitation channel. Alternatively, the ex
CLK, and RES lines of the
with those of the first, effe
Multiplexer to Datalogger wiring - Four leads from the COM ODD,
EVEN terminals connect
channels in the datalogger. Excitation and ground are multiplexed by
the second AM16/32A. Both multiplexers can be reset and clocked
by the same control ports and/or excitation channels to simplify
programming.
"4 X 16" Mode
COM H (ODD)
COM L
COM H (EVEN)
COM L
ODD H
ODD L
EVEN H
EVEN L
SENSOR SHIELDS COM
"4 X 16" Mode
COM H (ODD)
COM L
ODD H
ODD L
/
0
CR23X/
CR800/
CR850/
CR1000
21X/
CR7 CR10(X)
CR3000/
CR5000
AG
EX
H H H H
L L L L
H H H H
L L L L
E E VX
G
FIGURE 16. Full B ridge Measurement with Excitation Compensation
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