System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin
52
Note: Both of the following methods for determining an I-C setting require you to install, set up, and operate the
control loop in your controlled system under a variety of typical load conditions and observe the response
to load changes and different I-C settings.
Testing the Slowest to Fastest Time Integral to Determine I-C Setting
One method of determining the best I-C setting for a control loop is to observe the controlled system’s operation at
the slowest time integral (I-C setting of 1) and then increase the I-C setting one step at a time to determine the best
setting.
To determine the best I-C setting for an analog output by testing slowest to fastest time integral:
1. Set up the System 450 control loop for proportional-only control (I-C setting of 0 [zero]), power the controlled
system under typical or steady load conditions, and allow the system to stabilize at a control point somewhere
in the proportional band between the Setpoint and End Point values.
2. After the controlled system has stabilized at a control point, set the integration constant to the slowest time
integral (I-C setting of 1) and observe the control point to see if it stabilizes closer to the selected Setpoint.
• If the control point overshoots Setpoint, go to Step 3.
• If the control point stabilizes closer to Setpoint but does not overshoot Setpoint, set the integration constant
to the next (faster) time integral and then observe the control point to see if it stabilizes closer to the
selected Setpoint.
If the control point does not overshoot Setpoint at new I-C setting, continue to increase the setting and
observe the system until the control point overshoots Setpoint, then go to Step 3.
3. When the control point overshoots Setpoint, continue to observe the control point:
• If the control point drifts past Setpoint, reverses, and then drifts back towards Setpoint and stabilizes at or
near Setpoint, go to Step 4.
• If the control point drives significantly beyond Setpoints, then reverses quickly, drives back past Setpoint,
and continues oscillating significantly above and below Setpoint, reset the I-C setting to the previous
(slower) time integral and go to Step 4.
4. When the control point stabilizes near Setpoint or drifts slightly above and below Setpoint, operate the control
loop under a variety of load conditions, including the maximum load condition:
• If the control point drives past Setpoint and begins to oscillate significantly above and below Setpoint, reset
the I-C setting to the previous (slower) time integral and repeat Step 3.
• If the control point drifts to or past Setpoint and stabilizes near Setpoint, the current I-C setting for your
control loop is correct.
Continue to observe the controlled system until you are sure that the system control point stabilizes somewhere
near Setpoint and does not oscillate under all load conditions.
Using the Response Time to a Step Change to Determine the I-C Setting
Another method for determining the best I-C setting for a System 450 control loop is to temporarily create a step
change that shifts the proportional band in your controlled system away from the original or desired proportional
band. To do so, measure the (first response) time it takes for your controlled system to drive to and stabilize at the
shifted control point. Then shift (step change) the proportional band back to original and measure the (second
response) time that it takes to return to the original control point.
You need a digital voltmeter set to VDC to perform this procedure.
To determine the best I-C setting for a control loop using the response time to a step change:
1. Set up the System 450 analog output for proportional-only control (I-C setting of 0 [zero]), power your
controlled system on, operate the system under steady load conditions, and allow the control loop to stabilize
at a control point within the proportional band between the selected Setpoint and End Point values.
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