Using The Response Time To A Step Change To Determine The I-C Setting - Johnson Controls Penn System 450 Series Technical Bulletin

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.
2. Connect a digital volt-meter across the analog output terminals to measure
VDC signal strength changes. Measure and record the signal strength voltage
at this (original) stable control point.
3. Change the Setpoint and End Point values to shift (step change) the
proportional band 25% away from the original proportional band; the VDC
signal rises (or drops) immediately and significantly in response to the
proportional band shift. Begin timing the response (to the first step change) at
this voltage rise (or drop).
58 System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin