Rockwell Automation 1769-IF4FXOF2F Compact Combination Fast Analog I/O Module - Manual (Page 24)

24 Publication 1769-UM019A-EN-P - October 2008
Chapter 2 Installation and Wiring
For example, for Belden 8761 two conductor, shielded cable and a
1769-IF4 input module:
Rc = 52.5
Ω
/1000 m
Rs = 1
Ω
Ri = 220 K
Ω
As output 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 module’s voltage outputs and cable.
Label the Terminals A removable, write-on label is provided with the module. Remove the
label from the door, mark the identification of each terminal with
permanent ink, and slide the label back into the door. Your markings
(ID tag) will be visible when the module door is closed.
Effect of Output Impedance and Cable Length on Accuracy
Length of Cable DC Resistance of the Cable Rc Accuracy Impact at the
Input Module
50 m (164 ft) 2.625
Ω
0.00284%
100 m (328 ft) 5.25
Ω
0.00523%
200 m (656 ft) 10.50
Ω
0.01%
300 m (984 ft) 15.75
Ω
0.01477%
TIP
For current outputs, source and cable impedance do not impact
system accuracy as long as the total resistance of the cable and
input impedance of the load remain within the specified
maximum limits for the module's current outputs.
% Ai 1
Vin
Vs
--------- – ⎝ ⎠
⎛ ⎞
100
×
=
Vs Vin
Rs 2 Rc
× ( )
Ri + +
[ ]
Ri
--------------------------------------------------------
Ч
=