www.DaikinApplied.com 33 OM 1280-2 • MICROTECH UNIT CONTROLLER
PI Control Parameters
CAUTION
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.
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 (Figure 18).
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 making further adjustments. If you do not have
the means to graph the space performance, record the actual
measured value and setpoint for several minutes and then plot
the results using a spreadsheet to determine the correct action
to change the PI parameter.
Figure 18: Optimized PI Loop Control
Proportional Band
The proportional band, or proportional action, causes the
controlled output to change in proportion to the magnitude of
A proportional band setting that is too small (Figure 19) causes
control oscillations that go fully above and below the setpoint.
A proportional band setting that is too large (Figure 19) causes
Figure 19: Proportional Bands
In general, it is best to start with a relatively large proportional
band setting (use of default setting is recommended) 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 proportional band to a lower setting.
Integral Time
The integral time, or integral action, causes the controlled
the actual value and setpoint forms an “area under the curve”
(Figure 20). The integral action works to reduce this “area
Figure 20: Integral Time
The smaller the integral time, the faster the output ramps up or
down with small changes in the space. The smaller the integral
time, the quicker the system reacts to small changes in the
space. If the Integral Time is set too small, long oscillations
occur (Figure 20).
In general, it is best to start with a relatively large integral time
setting the factory default setting is best and adjust to smaller
values. If you want the system respond strongly to small
changes in the space, lower the integral time. If you want the
system to react weakly to small changes in the space, adjust the
integral time to a higher setting.
Too Small
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