D8 Series User’s Guide
Chapter 4: Operation and Setup
72
Table 4.7
– Scaling Values
PARAMETER
VALUE
Input range high
65 GPM
Input high signal
95.0%
Input range low
3 GPM
Input low signal
10.0%
Autotuning
Autotuning is a process by which a controller calculates the correct PID parameters for optimum
control. Only the heat output of a loop may be autotuned.
How Does Autotuning Work?
Autotuning is performed at the maximum allowed output. If an output limit has been set, then
autotuning occurs at that value. Otherwise, the control output is set to 100 percent.
The PID constants are calculated according to process response to the output. The loop need not
reach or cross the set point to successfully determine the PID parameters.
The controller looks at the delay between when power is applied and when the system responds
and uses this information to determine the proportional band. The controller then looks for the
slope of the rising temperature to become constant to determine the integral term. The controller
mathematically derives the derivative term from the integral term.
When the controller finishes autotuning a loop, it switches the loop to automatic mode. If the
process reaches 80 percent of the set point or the autotuning time exceeds 30 minutes, the
controller switches the loop to automatic mode and applies the PID constants it has calculated up to
that point.
Autotuning 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.
Prerequisites
Before autotuning, the controller 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 the controller keypad
or HMI software interface to do the following:
• Select a loop.
• Change the set point.
• Change the control mode (manual, automatic, off or tune).
• Read and change the setup parameters.
Содержание Controller Series D8
Страница 1: ...D8 Series User s Guide...
Страница 152: ...D8 Series User s Guide Chapter 7 Troubleshooting and Reconfiguring 152...
Страница 178: ...D8 Series User s Guide 178 Declaration of Conformity...