Testing The Slowest To Fastest Time Integral To Determine I-C Setting - Johnson Controls Penn System 450 Series Technical Bulletin

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 on under typical/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.
System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin 57