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22 PCI-1710/1710HG User's Manual
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 kΩ, 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 calculat-
ing process.
r
a
r
b
ExternalInternal