Rockwell Automation 1771-TCM TEMPERATURE CONTROL - Manual (Page 50)

Chapter
6
Publication 1771Ć6.4.5 - January 1997
Tuning the Loops
This chapter shows you how to tune a loop. This includes:
•
configuring tuning
•
auto-tuning the loops
•
viewing auto-tuning results
•
changing system response
•
fine-tuning the loops
Before a PID loop can be run in automatic control mode, the
proportional, integral, and derivative gains must be set.
Traditionally, these gains have been set manually using a trial and
error process. This manual process can be very time-consuming, and
often results in less than optimal performance.
Although you can use the manual process to set the gains, the TCM
module includes an advanced auto-tuning algorithm that is capable
of automatically determining near optimum gain values. We
recommend that you use the auto-tuning process to determine initial
gain values, which can then be adjusted manually, if necessary, to
correct any slight remaining performance problems.
During auto-tuning, the TCM module controls the loop output and
monitors the change in the measured variable in order to measure
several parameters that are characteristic of your process. Using
these parameters, the TCM module then calculates proportional,
integral, and derivative gains that will provide good automatic
control. This process can take from a few minutes to several hours,
depending on the response time of your process.
Before you begin the auto-tuning process, we recommend that you
perform several preparatory steps:
1. After configuring your module and loops, as described in
Chapters 4 and 5, operate your loops in Manual mode.
By operating the loop in Manual mode, you can verify that the
inputs and outputs are connected properly, the temperature
sensors are correctly measuring your process temperature, and the
loop output properly controls heating and/or cooling.
Introduction to Loop
Tuning
The AutoĆTuningĆProcess
Preparing to AutoĆTune
Loops