MIL-HDBK-1003/3
(3) Controllers for other variables, such as
relative humidity and static pressure, shall have their
proportional mode constants set initially in a similar manner for
an achievable output range proportional to the transmitter span.
b)
Step 2.
This step shall consist of the following:
(1) Set the controller temperature setpoint at any
achievable temperature. Observe the controller output and
transmitter input.
(2) If the transmitter input continuously
oscillates above and below the setpoint without settling at a
fixed value, or if such oscillation increases, the proportional
mode constant is too small.
(3) If
the proportional mode constant is too
small, increase it in
steps until the transmitter input indicates
stable control at any
temperature, if the controller output is
not at either extreme
of the output range.
(4) If the temperature control point slowly drifts
toward or away from the controller setpoint, the proportional
mode constant is too large. Decrease its setting in steps until
oscillations occur as described in the preceding paragraphs, and
then increase the setting until stable control occurs.
(5) Introduce a step change in controller
setpoint. This should cause the controller to overshoot the
setpoint slightly, with each subsequent overshoot peak value
decreasing by a factor of two-thirds until stable control is
achieved at, above, or below the setpoint.
(6) Increase the integral mode constant setting in
small steps, and introduce setpoint changes until control point
and controller setpoint coincide at stable control. This should
happen consistently after a setpoint change within a short time,
such as 5 to 10 minutes.
c)
Step 3.
This step shall consist of the following:
(1) Unless the HVAC process variable changes
rapidly, the derivative mode constant setting can remain at zero.
This is usually the case for most HVAC applications.
(2) If derivative control is needed, gradually
increase the derivative mode constant.
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