Rockwell Automation 1790D-NOV2/TNOV2 CompactBlock LDX Analog Modules - Manual (Page 25)

Publication 1790-UM001A-EN-P - March 2002
Installation and Wiring 2-9
Effect of Transducer/Sensor and Cable Length Impedance on
Voltage Input Accuracy
For voltage inputs, the length of the cable used between the
transducer/sensor and the module can affect the accuracy of the data
provided by the module.
Where:
Rc = DC resistance of the cable (each conductor) depending on
cable length
Rs = Source impedance of analog transducer/sensor output
Ri = Impedance of the voltage input (500K
Ω
for
1790D-N4VO/TN4VO)
Vs = Voltage source (voltage at the transducer/sensor input
device)
Vin = Measured potential at the module input
%Ai = Percent added inaccuracy in a voltage-based system due
to source and cable impedance.
V in
Vs
Ri
Rc
Rc Rs
+
-
Vin
Ri Vs
× [ ]
Rs 2 Rc
× ( )
Ri + +
[ ]
------------------------------------------------------- =