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VAPOR-LOGIC
®
VERSION 6 INSTALLATION AND OPERATION MANUAL
PID SETUP TIPS
A large PID band (10% to 20%) yields tighter and more stable control with
longer response times. A small PID band produces quicker response times, but
control may become unstable if the RH regularly goes outside the band.
As a rule, start with a PID band of 10%. When the humidifier is operating at
steady state, make sure the RH does not go outside the PID band. The intent of
the PID band is to quickly get the RH into a controllable range. To increase or
decrease the effect of the proportional term on system performance, adjust the
proportional gain (Kp).
However, for the majority of systems, the factory default setting of 80 is
sufficient. Generally speaking, a large integral gain (Ki) quickens the system
response but may cause it to oscillate and become unstable. A small integral
gain yields tighter, more stable control at the expense of a long response time.
These principles can be applied in the following examples: If a system
eventually reaches the desired RH level but takes a long time to do so without
overshooting the set point, faster response can be achieved by increasing the
integral gain. If the measured RH oscillates above and below the set point
numerous times before finally reaching set point, decrease the integral gain.
Typically, if a large adjustment is made to the integral gain, better response
is achieved by decreasing the magnitude of the change. Then, modify the
proportional gain slightly in the same direction the integral gain was changed.
RH history data, available for download from the Diagnostics menu, can aid
when doing PID loop tuning.
PID tuning
OPERATION
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