Liebert iCOM Microprocessor TM-10098 - Manual (Page 11)

iCOM
Controls Training and Service Manual
A suggested tuning procedure is as follows:
1. Initially adjust the integral and derivative settings to 0% / degree-min
and 0% / degree / min..
2. Starting with 20% / degree, adjust the proportional setting in small
increments (10% steps) until the control sustains a constant hunting
action (the temperature swings are approximately the same amplitude
from one peak to the next).
3. Note the time in minutes between peaks of adjacent temperature
swings and the amplitude of the temperature swing (degrees above the
set point).
4. Adjust the proportional control setting to about l/2 the value obtained in
Step 2.
5. Adjust the integral setting to a value calculated by the following
equation: approximate room load (in % full load) time between
peaks x peak amplitude x 4.
Note: If calculation results in a value of less than 1%, then set the
integral to 1%.
6. Adjust the derivative to a value calculated by the following equation:
time between peaks x 5%.
The above tuning procedure is only an approximation for an initial set of
adjustments and are based on the "average" room characteristics. Your particular
settings may need to be further adjusted for optimum PID control performance.
Some suggestions for additional tuning are as follows:
• If cooling output overshoot is occurring on load changes, decrease
the proportional setting or the derivative setting.
• If system hunting occurs with constant room load, decrease the
integral setting.
• If the control responds too slowly, resulting in large temperature
excursions on a load change, increase the proportional setting or
the derivative setting.
• If a constant temperature deviation exists between the
temperature and set point, increase the integral setting.
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