Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 100)

Publication 900-UM007D-EN-E - January 2011
3-30 Configuration & Basic Operation
Determining PID Constants
(AT, ST, Manual Setup) AT (Auto-Tuning)
Figure 3.55
Overview
When you configure the controller to execute Auto-Tuning, the optimum PID
constants for the current set point during program execution are
automatically configured by the controller forcibly changing the manipulated
variable (MV) to calculate the characteristics (called the limit cycle method) of
the control target.
Either 40% AT or 100% AT can be selected depending on the width of MV
variation in the limit cycle. In the AT Execute/Cancel parameter, specify
at-2 (100% AT) or at-1 (40% AT). To cancel AT, specify off (AT cancel).
• Only 100% AT can be executed for heating and cooling control.
• AT cannot be executed when control has stopped or during ON/OFF
control.
• The results of AT are reflected in the Proportional Band (P), Integral Time
(I), and Derivative Time (D) parameters in the Adjustment function group.
The result of a controller AT cycle can be viewed/monitored from the
Proportional Band (P), Integral Time (I), and Derivative Time (D) parameters
in the Adjustment function group.
Figure 3.56 — PID
AT Description and Display Consideration
AT (Auto-Tuning) is started when you configure either at-2 (100%) or
at-1 (40% AT).During execution of AT, the No. 1 display for the AT
Execute/Cancel parameter blinks (refer to Figure 3.57). When AT ends, the
AT Execute/Cancel parameter turns OFF, and the No. 1 display stops
blinking.
Figure 3.57 — AT Execute/Cancel Parameter
Adjustment Level
i
233
C p
(0
d
40
Proportional
Band Integral
Time Derivative
Time
at
off
at
on
AT Execute/Cancel
No. 1 display