B&B Electronics PCI-1711 - Manual - Manual (Page 36)

Chapter 3
– 28 – PCI-1710 series User’s Manual Advantech Co., Ltd.
www.advantech.com
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 kW, and each of the two
resistors is 100 kW, then the resistors load down the signal source with
200 k
Ω
(100 k
Ω
+ 100 k
Ω
), resulting in a -0.5% gain error. The following
gives a simplified representation of the circuit and calculating process.