Rockwell Automation 1766-L32xxx MicroLogix 1400 Programmable Controllers Installation Instructions - Manual (Page 27)

MicroLogix 1400 Programmable Controllers 27
Publication 1766-IN001C-EN-P - October 2009
Minimizing Electrical Noise on Analog Channels
Inputs on analog channels employ digital high-frequency filters that significantly reduce the
effects of electrical noise on input signals. However, because of the variety of applications and
environments where analog controllers are installed and operated, it is impossible to ensure
that all environmental noise will be removed by the input filters.
Several specific steps can be taken to help reduce the effects of environmental noise on
analog signals:
• Install the MicroLogix 1400 system in a properly rated (NEMA) enclosure. Make sure
that the MicroLogix 1400 system is properly grounded.
• Use Belden cable #8761 for wiring the analog channels, making sure that the drain
wire and foil shield are properly earth grounded, (see Grounding Your Analog Cable
on page 27 for more information).
• Route the Belden cable separately from any AC wiring. Additional noise immunity can
be obtained by routing the cables in grounded conduit.
Grounding Your Analog Cable
Use shielded communication cable
(Belden #8761). The Belden cable
has two signal wires (black and
clear), one drain wire, and a foil
shield. The drain wire and foil
shield must be grounded at one
end of the cable.
IMPORTANT Do not ground the drain wire and foil shield at both ends of the cable.
Foil Shield
Black Wire
Drain Wire
Clear Wire
Insulation
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