Installation guide

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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 speaking, 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. The RH graph on the
reports menu, which displays the effect modifying PID gain values
has on system response, can aid in PID loop tuning. The RH graph
feature is explained in the reports section on Page 80.
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Kp = Proportional gain factor
Ki = Integral gain factor
Kd = Derivative gain factor
VL3_IOM.pdf 73 11/19/2009 9:11:15 AM