Rockwell Automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Module - Manual (Page 23)

Publication 1769-UM019A-EN-P - October 2008 23
Installation and Wiring Chapter 2
As input source impedance (Rs) and/or resistance (DC) of the cable
(Rc) get larger, system accuracy decreases. If you determine that the
inaccuracy error is significant, implementing the following equation in
the control program can compensate for the added inaccuracy error
due to the impedance of the source and cable.
Voltage Output Accuracy
Where:
Rc = DC resistance of the cable (each conductor)
depending on cable length
Rs = Source impedance (1
Ω
)
Ri = Impedance of the voltage input
Vs = Voltage at the output of 1769-IF4FXOF2F module
Vin = Measured potential at the module input
%Ai = Percent added inaccuracy in a voltage-based
system due to source and cable impedance
TIP
For current signals, source and cable impedance do not impact
system accuracy.
Vs Vin
Rs 2 Rc
× ( )
Ri + +
[ ]
Ri
--------------------------------------------------------
×
=
V in Vs
Ri
Rc
Rc Rs
+
-
Vin
Ri Vs
×
[ ]
Rs 2 Rc
× ( )
Ri + + [ ]
-------------------------------------------------------- =