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Chapter 3
– 26 –PCI-1712/1712L User’s Manual
Advantech Co., Ltd.
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Figure 3-4: Differential input channel connection - floating signal
source
However, this connection has the disadvantage of loading the source
down with the series combination (sum) of the two resistors. For r
a
and
r
b,
for example, if the input impedance r
s
is 1 kΩ, and each of the two
resistors is 100 kW, then the resistors load down the signal source with
200 kΩ (100 kΩ + 100 kΩ), resulting in a –0.5% gain error. The following
gives a simplified representation of the circuit and calculating process.