Control block layout – Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal User Manual

Page 352

Chapter 26
PID Instruction

26–8

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Control (control block word 0, bit 2) – Reverse, the default condition,
corresponds to E=SP–PV. Forward corresponds to E=PV–SP. Direct
acting (E=PV–SP) will cause the output CV to increase when the input
PV is larger than the setpoint SP (for example, a cooling application).
Reverse acting (E=SP–PV) will cause the output CV to increase when the
input PV is smaller than the setpoint SP (for example, a heating
application).

The following display shows typical values entered for these parameters:

ZOOM on PID –(PID)– 3/3 2.0.0.0.*
NAME: PROP INTEGRAL DERIVATIVE
LOOP UPDATE: 50 [X10ms]
SET PT MIN: –100 SET PT MAX: 1000
MODE: TIMED OUT LIMIT: YES
CONTROL: REVERSE
ENTER LOOP UPDATE: 50
NEXT PG PREV PG ACCEPT

Press

[F5]

, ACCEPT, to complete the entry of parameters. If you must

change any of the parameters, you can run through the entry sequence again
before you press ACCEPT.

The control block length is fixed at 23 words and should be programmed as
an integer file. PID instruction flags (word 0) and other parameters are
located as shown on the following page.

Control Block Layout