Publication 1769-UM002B-EN-P - July 2005
2-14
Installation and Wiring
For example, for Belden 8761 two conductor, shielded cable and a 1769-IF4
input module:
Rc = 16
Ω
/1000 ft
Rs = 15
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 output
module and cable.
Table 2.3 Effect of Output Impedance and Cable Length on Accuracy
Length of Cable (m)
dc resistance of the cable
Rc (
Ω
)
Accuracy impact at the
input module
50
2.625
0.00919%
100
5.25
0.01157%
200
10.50
0.01634%
300
15.75
0.02111%
TIP
In a current loop system, source and cable impedance do
not impact system accuracy.
%
Ai
1
Vin
Vs
---------
∠
⎝
⎠
⎛
⎞
100
×
=
Vs
Vin
Rs
2
Rc
×
(
)
Ri
+
+
[
]
Ri
-------------------------------------------------------
×
=
Summary of Contents for Allen-Bradley 1769-IF4
Page 1: ...CompactI OAnalog Modules 1769 IF4 IF8 OF2 OF8C and OF8V User Manual ...
Page 4: ...Publication 1769 UM002B EN P July 2005 Summary of Changes 2 Notes ...
Page 10: ...Publication 1769 UM002B EN P July 2005 Table of Contents vi ...
Page 14: ...Publication 1769 UM002B EN P July 2005 4 Notes ...
Page 183: ......
