A-BMicroLogix 1000 Programmable Controllers

the load device. This reduces arcing and damage of the output contacts. (High transients can 

cause arcing that occurs when switching off an inductive device.)

If you connect a micro controller triac output to control an inductive load, we recommend 

that you use varistors to suppress noise. Choose a varistor that is appropriate for the 

application. The suppressors we recommend for triac outputs when switching 120V ac 

inductive loads are a Harris MOV, part number V175 LA10A, or an Allen-Bradley MOV, 

catalog number 599-K04 or 599-KA04. Consult the varistor manufacturer's data sheet when 

selecting a varistor for your application.

For inductive dc load devices, a diode is suitable. A 1N4004 diode is acceptable for most 

applications. A surge suppressor can also be used. See the table on page 18 for 

recommended suppressors.

Surge Suppression for Inductive ac Load Device

Minimizing Electrical Noise on Analog Controllers

Inputs on analog controllers 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 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.

• route the Belden cable separate 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. Do not ground 

the drain wire and foil shield at 

both ends of the cable.

Specifications

Environmental Specifications (all MicroLogix controllers)

Description Specification

Operating Temperature 0°C to +55°C (+32°F to +131°F) for horizontal mounting

0°C to +40°C (+32°F to +104°F) for vertical mounting(1