A-B 1746-OBP8 module Rockwell SLC 8 digital output control

Wiring considerations

Follow the guidelines below when planning your system wiring.

• To limit the pickup of electrical noise, keep thermocouple and

millivolt signal wires away from power and load lines.

• For high immunity to electrical noise, use Alpha 5121 (shielded,

twisted pair) or equivalent wire for millivolt sensors; or use

shielded, twisted pair thermocouple extension lead wire

specified by the thermocouple manufacturer. Using the incorrect

type of thermocouple extension wire or not following the

correct polarity may cause invalid readings. See IEEE Std. 518,

Section 6.4.2.7 or contact your sensor manufacturer for additional details.

• When trimming cable leads, minimize the length of unshielded wires.

• Ground the shield drain wire at only one end of the cable. The preferred location is at the I/O chassis ground (See Figure 2.4).

• For maximum noise reduction, use 3/8 inch braid wire to

connect cable shields to the nearest I/O chassis mounting bolt.

Then connect the I/O chassis to earth ground (See Figure 2.4).

These connections are a requirement regardless of cable type.

• Tighten terminal screws. Excessive tightening can strip the screw.

• The open–circuit detector generates approximately 20 nano–

amperes into the thermocouple cable. A total lead resistance of

25 ohms (12.5 one–way) will produce 0.5 mV of error.

• Follow system grounding and wiring guidelines found in your

SLC 500 Modular Hardware Installation and Operation Manual,

publication 1747–6.2.

Output response

When the slot for this module is disabled, configuration words in the

SLC processor’s output image table are held in their last state and not

transferred to the module. When the slot is re–enabled, output image

table words are transferred to the module during the subsequent scan.

Installing and Wiring

This document gives you information about:

• avoiding electrostatic damage

• compliance with European Union directive

• determining the module’s chassis power requirement

• planning for sufficient enclosure depth

• choosing a module slot in a local I/O chassis

• installing the module

• wiring the module

Installing the Module

Follow this procedure:

ATTENTION

!

Never install, remove, or wire modules with power applied to the chassis or devices wired to the module.

1. Align the circuit board of the thermocouple module with the card guides located at the top and bottom of the chassis.

2. Slide the module into the chassis until both top and bottom retaining clips are secured. 

Apply firm even pressure on the module to attach it to its backplane connector.

Never force the module into the slot.

3. Cover unused slots with the card slot filler, catalog number 1746–N2.

4. To remove, press the releases at the top and bottom of the module, and slide the module out of the chassis slot.

Module Addressing

When you enter the module ID in processor configuration (off-line),

the processor automatically reserves the required number of I/O

image table words. In the figure below, that section of the I/O image

table is designated by “slot e”. Its location in the I/O image table is

determined by the module’s slot location “e” in the I/O chassis. Slot

location “e” is a required addressing unit when referring to the

module in ladder logic. For the sample program’s data table layout

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