Campbell Scientific AM416 Multiplexer - Manual (Page 17)

AM416 RELAY MULTIPLEXER
11
FIGURE 8. Single-ended Measurement Without Excitation
FIGURE 9. Differential Measurement Without Excitation
6.2 DIFFERENTIAL ANALOG MEASUREMENT
WITHOUT SENSOR EXCITATION
Sensor to Multiplexer wiring - Up to two
differential sensors that don't require excitation
may be connected to one input SET. Sensor
shields are routed through shield terminals.
Multiplexer to Datalogger wiring - A pair of
COM terminals (e.g. COM H1 and COM L1) is
connected to a differential analog input at the
datalogger. Up to 32 differential sensors may
be measured by two differential datalogger
channels in this way.
6.3 HALF BRIDGE MEASUREMENTS
Measurements of this type may be subdivided
into three categories based on completion
resistance and the presence or absence of
measured excitation. If the sensor's completion
resistor(s) are installed at the datalogger panel
(e.g. a CSI 107 probe modified for multiplexer
use), then three probes per SET may be excited
and measured (Figure 10). However, if the
circuit is completed within the sensor (e.g.
potentiometers), then excitation, wiper signal,
and ground must be multiplexed. Because
excitation and ground may be multiplexed in
common, up to two sensors per SET may be
measured (Figure 11). If measured excitation is
required (i.e. four wire half-bridge), then only
one sensor per SET may be measured (Figure
12).
6.3.1 HALF BRIDGE MEASUREMENT WITH
COMPLETION RESISTOR(S) AT
DATALOGGER
Sensor to Multiplexer wiring - up to three half
bridges may be connected to one input SET,
provided that the sensor's completion resistors
are located at the datalogger (Figure 10).
Multiplexer to Datalogger wiring - Signal lines
from the multiplexer COM terminals are input
into three consecutive single-ended analog
input channels. A precision completion resistor
ties the analog input channel to analog ground
in the CR10(X) or to datalogger ground in the
21X or CR7.