Pi Control Parameters; Proportional Band - Daikin MicroTech II Operation And Maintenance Manual

OM 752-4

PI Control Parameters

Associated with each PI loop is a set of two adjustable parameters: Proportional Band and
Integral Time. When the unit ventilator is properly sized for the space, the factory settings
for these parameters provides the best and most robust control action (see
If field problems arise, first ensure these parameters are set back to the factory default
settings. If adjustment is required, only make small adjustments to one parameter at a
time. After each adjustment, allow enough time for the system to stabilize before mak-
ing further adjustments. If you do not have the means to graph the space performance,
record the actual measured value and set point for several minutes and then plot the
results using a spreadsheet to determine the correct action to change the PI parameter.
Adjusting PI parameters can cause erratic unit operation, and potentially damage the equipment.
PI control parameters should only be adjusted by trained personnel having a complete understanding of
how these parameters affect system operation. Generally these parameters do not need to be adjusted
from the factory default settings.
Figure 19: Optimized PI loop control

Proportional Band

The proportional band, or proportional action, causes the controlled output to changes
in proportion to the magnitude of the difference between the sensor value and set point.
A proportional band setting that is too small (see
that go fully above and below the set point.
Figure 20: Proportional bands
Too Small
A proportional band setting that is too large (see
the actual measured oscillation center and the set point. A small offset is not necessar-
ily a problem since most systems have a small "natural" offset and the integral function
automatically works to eliminate or reduce this effect.
In general, it is best to start with a relatively large proportional band setting (the factory
default setting is best) and adjust to smaller values.
If you want the system to respond strongly to small changes in the space, adjust the
proportional band to a higher setting.
If you want the system to react weakly to small changes in the space, adjust the pro-
portional band to a higher setting.
CAUTION
Figure
Figure
30
d o
esCrIptIon of peratIon
Figure 19).
20) causes control oscillations
Too Large
20) causes an offset between
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