Rockwell Automation 1771-TCM TEMPERATURE CONTROL - Manual (Page 51)

6–2 Tuning the Loops
Publication 1771Ć6.4.5 - January 1997
2. Once you are satisfied that your loop is operating properly in
Manual mode, use the Manual Tuning screen to set the
proportional gain to 1, leaving the integral and derivative gains
at 0.
This configures the loop for straight proportional control.
3. Place the loop in Automatic mode.
With a proportional gain of 1, the loop output should be directly
proportional to the deviation between the measured variable and
the setpoint.
4. When you are satisfied the loop is operating properly in this
mode, you can proceed with the auto-tuning process described in
the following sections.
Important: You must allow the equipment to cool down
before you begin the autotune process or your
results will be invalid.
There are several tuning parameters that you can configure to tailor
the auto-tuning process to suit particular applications:
aggressiveness, disturbance size, and system response.
•
Aggressiveness
The aggressiveness setting affects how the module controls the
loop during start-up in barrel control mode. Start-up is the period
between the time the loop is placed in Automatic control at a low
initial temperature, and the time it first nears the setpoint.
This setting can range from 0 to 100. A setting of 0 minimizes
the chance of overshoot during start-up, but increases the time
needed to reach the setpoint. A setting of 100 minimizes start-up
time, but will result in the temperature overshooting the setpoint
during start-up.
This setting does not affect the quality of the control once the
start-up period has passed. During an ideal start-up, the
temperature should rise steeply toward the setpoint. As the
temperature nears the setpoint, the rate of climb should gradually
level off until the temperature reaches the setpoint. If the
temperature drops for a while after the initial climb before slowly
climbing toward the setpoint, you should increase the
aggressiveness.
•
Disturbance Size (non-barrel loops only)
Disturbance size is the percentage of the step change made in the
output during auto-tuning of non-barrel loops. The disturbance
size setting can range from 0.00 to 100.00. (Note: A setting of
0.00 is equivalent to a setting of 100.00.)
Tuning Parameters