A-B 1746-OX8 module Rockwell SLC 8 digital output control

Switching the barrel control

For some applications, even though the loops are independent with

no thermal conduction between zones, barrel control might provide

better performance than non–barrel control. If a loop has any of these

characteristics, you might want to use barrel control if the:

• time constant is greater than 10 - 30 seconds

• loop has a problem of overshooting the setpoint

• loop output is saturating (CV is at 100%) for a significant duration

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.

Barrel Control

Select barrel control for multiple–zone applications in which there is

thermal conduction between the zones. Injection molding and

extrusion are good example applications because they use multiple

heater bands (zones) mounted on one thermal conductor (the metal

barrel). The barrel conducts heat between different zones. If you

select barrel control, also select between inner and outer zones (word

1, bit 13 for channel 1). A barrel loop is autotuned as the temperature

rises from a cold start to a temperature setpoint during startup.

Non–barrel control

Select non–barrel control for applications with independent loops and

no thermal conduction between zones. If you select non–barrel

control, the inner/outer zone selection doesn’t apply.

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

TC Break Control

Word 4 or O:e.8 for Channel1

If a loop input circuit becomes open (open wire) the loop can not

measure temperature. In automatic mode, the lack of temperature

feedback makes it impossible to control the temperature. To guard

against this condition, the BTM module provides TC break detection.

When a break is detected, the module responds in one of these ways:

• disables the loop

• forces CV to this (TC Break Control) value (word 4 for loop 1)

• forces the CV to the manual %–output value (O:e.8 for loop 1)

Once the thermocouple break has been repaired you must disable the

loop and then re-enable it (through the input image table O:e.0/0 loop 1).

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