Watlow PPC-2000 - Manual (Page 117)

PPC-2000 User’s Guide Chapter 3: Operating with AnaWin 3
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 93
Autotuning
Autotuning is a process by which a controller determines the
correct PID parameters for optimum control.
Prerequisites
Before autotuning the controller, it must be installed with
control and sensor circuitry and the thermal load in place. It
must be safe to operate the thermal system, and the
approximate desired operating temperature (set point) must be
known.
The technician or engineer performing the autotune should
know how to use HMI software interface (e.g. AnaWin3) to
perform the following:
• Set a channel’s set point
• Change a channel’s control mode (manual, tune, auto)
• Read and change the controller’s parameters
Background
Autotuning is performed at the maximum allowed output. If
you have set a limit, autotuning occurs at that value.
Otherwise, the control output is set to 100% during the
autotune. Only the heat output of a channel may be autotuned.
The PID constants are calculated according to process’s
response to the output. The channel 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 integral term (Heat/Cool Integral). The controller
also looks for the slope of the rising temperature to become
constant in order to determine the proportional band (Heat/Cool
Prop Band). The derivative term (Heat/Cool Derivative) is derived
mathematically from the integral term.
When the controller has finished autotuning, the channel’s
control mode switches to Auto. If the process reaches 80% of the
set point or the autotuning time exceeds ten minutes, the
controller switches to Auto and applies the PID constants it has
calculated up to that point. If the tune can not get good data,
the controller returns to its previous control state (i.e., manual
mode) and leaves the PID parameters unchanged.
The Watlow Anafaze autotune is started at ambient
temperature 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 parameters.