Rockwell Automation 1790D-NOV2/TNOV2 CompactBlock LDX Analog Modules - Manual (Page 28)

Publication 1790-UM001A-EN-P - March 2002
2-12 Installation and Wiring
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 load
1,000
Ω
10,000
Ω
100,000
Ω
1 0.0525 0.0605% 0.00605% 0.000605%
10 0.525 0.155% 0.0155% 0.00155%
50 2.625 0.575% 0.0575% 0.00575%
100 5.25 1.1% 0.11% 0.011%
TIP
In a current loop system, source and cable
impedance do not impact system accuracy.
V
s
= V
load
x
[R
s
+ (2 x R
c
) + R
load
[R
load
]