Campbell Scientific 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules - Manual (Page 37)

4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules (TIM)
R
2
= 1K Ω
R
1
= 1K Ω
R
D
R
S
Gau
ge
R
L
R
L
R
L
+ -
FIGURE 4.4-2. Shunting remotely across active gauge
R
L
represents the line resistances. R
D
is the resistor in the arm next to the active
gage which has a resistance equal to the nominal resistance of the Strain gauge
and is referred to as the Dummy Resistor. R
s
is the Shunt resistor. This setup
is the classical method for shunting a 3-wire ¼ bridge strain circuit.
4.4.2.1.2 Three Wire Gage Circuit with Shunt across the Dummy Resistor
Shunting across the active gauge is frequently impractical due to inaccessibility
or protective coatings across the gage and leads, which precludes getting an
electrical contact across the gauge. For these types of applications it is more
convenient to place a shunt resistor across the Wheatstone bridge arm that
holds the dummy resistor, R
D
. Figure 4.4-3 shows a 3-wire ¼ Bridge strain
circuit for shunting across the dummy resistor.
R
2
= 1K Ω
R
2
= 1K Ω
R
S
R
D
R
L
R
L
R
L
A
ct
ive
Gauge
FIGURE 4.4-3. Circuit for shunting across dummy resistor
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