Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 55)

Wiring Your Controller
2–21
Minimizing Electrical Noise on Analog Controllers
Inputs on analog 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 operating,
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 1000 system in a properly rated (i.e., NEMA) enclosure.
Make sure that the MicroLogix 1000 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 at one end of the cable.
•
route the Belden cable separate from any other wiring. Additional noise
immunity can be obtained by routing the cables in grounded conduit.
A system may malfunction due to a change in the operating environment after a
period of time. We recommend periodically checking system operation, particularly
when new machinery or other noise sources are installed near the MicroLogix 1000
system.
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. Do not earth ground the drain
wire and foil shield at both ends of the cable.
Foil Shield
Black Wire
Drain Wire
Clear Wire
Insulation