Watlow CLS200 - Manual (Page 79)

CLS200 Series User’s Guide Chapter 3: Using the CLS200
Doc.# 0600-3050-2000 Watlow Anafaze 63
It must be safe to operate the thermal system, and the ap-
proximate desired operating temperature (setpoint) must
be known.
The technician or engineer performing the autotune should
know how to use the controller front panel or MMI software
interface (e.g., AnaWin or Anasoft) to do the following:
1. Select a loop to operate and monitor.
2. Set a loop’s setpoint.
3. Change a loop’s control status ( MAN, TUNE, AUTO).
4. Read and change the controller’s global and loop setup
parameters.
Background
Autotuning is performed at the maximum allowed output.
If you have set an output limit, autotuning occurs at that
value. Otherwise, the control output is set to 100% during
the autotune. Only the heat output (output 1) of a loop may
be autotuned.
The PID constants are calculated according to process’s re-
sponse to the output. The loop need not reach or cross set-
point to successfully determine the PID parameters. While
autotuning the controller looks at the delay between when
power is applied and when the system responds in order to
determine the proportional band (PB). The controller then
looks for the slope of the rising temperature to become con-
stant in order to determine the integral term (TI). The de-
rivative term (TD) is derived mathematically from the TI.
When the controller has finished autotuning, the loop’s
control status switches to
AUTO. If the process reaches 75%
of the setpoint or the autotuning time exceeds ten minutes,
the controller switches to
AUTO and applies the PID con-
stants it has calculated up to that point.
The Watlow Anafaze autotune is started at ambient tem-
perature or at a temperature above ambient. However, the
temperature must be stable and there must be sufficient
time for the controller to determine the new PID parame-
ters.
Performing an Autotune
NOTE! A loop must be stable at a temperature well
below the setpoint in order to successfully
autotune. The controller will not complete
tuning if the temperature exceeds 75% of set-
point before the new parameters are found.
The following procedure explains how to autotune a loop:
1. Select the single loop display of the loop to be tuned.