Campbell Scientific AM16/32B Relay Multiplexer - Manual (Page 39)

AM16/32B Relay Analog Multiplexer
analog ground. Up to sixteen full bridges may be multiplexed through the
AM16/32B.
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 AM16/32B, but bypass the AM16/32B 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 excitation channel. Alternatively, the
excitation an ground leads can be multiplexed through an additional
AM16/32B a owing the sensors to be excited one at a time (FIGURE 6-7). In
ultiplexer are
e multiplexer to
“8x16”.
D, EVEN
in the
d AM16/32B.
reset and clocked by the same control ports and/or
excitation channels to simplify programming.
d
ll
this case the 12V, GND, CLK, and RES lines of the second m
wired in parallel with those of the first, effectively widening th
Multiplexer to Datalogger Wiring — Four leads from the COM OD
terminals connect to two sequential differential analog channels
datalogger. Excitation and ground are multiplexed by the secon
Both multiplexers can be
"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 E E VX
H H H H
L L L L
H H H H
L L L L
G
ensation FIGURE 6-7. Full bridge measurement with excitation comp
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