West Control Solutions ProVU 4 - Manual (Page 74)

ProVU4 Controller, Profiler & Recorder/Controller - Product Manual
59407, Issue 1 – March 2008 Manual Tuning Page 73
P
Input Span
T
6
11 Manually Tuning Controllers
Single Control Tuning (PID with Primary Output only)
This technique balances the need to reach setpoint quickly, with the wish to limit setpoint
overshoot at start-up or during process changes. It determines values for the Primary
Proportional Band and the Integral and Derivative time constants that allow the PID control
algorithm to give acceptable results in most applications that use a single control device.
CAUTION:
This technique is suitable only for processes that are not harmed by large
fluctuations in the process variable.
1. Check that the Setpoint Upper Limit and Setpoint Lower Limit are set to safe levels for
your process. Adjust if required.
2. Set the Setpoint to the normal operating value for the process (or to a lower value if
overshoots beyond this value might cause damage).
3. Select On-Off control (i.e. set the Primary Proportional Band to zero).
4. Switch on the process. The process variable will oscillate about the setpoint. Record the
Peak-to-Peak variation (P) of the first cycle (i.e. the difference between the highest value
of the first overshoot and the lowest value of the first undershoot), and the time period of
the oscillation (T) in minutes. See the example diagram below - Manually Tuning PID.
5. Calculate the PID control parameters using the formula below. P.Pb is the Primary
Proportional Band, Int.T is the Integral Time Constant, and Der.T is the Derivative Time
Constant. The Input Span is the difference between Scale Range Lower Limit and Scale
Range Upper Limit:
P.Pb = x 100
Int.T = T minutes
Der.T = minutes
Figure 47. Manually Tuning PID
Time
Process Variable