Johnson Controls FRICK QUANTUM HD, Операция

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QUANTUM™ HD COMPRESSOR CONTROL PANEL
OPERATION
090.040-O (MAR 12)
Page 119
reacts. If the PI output shows too much oscilla-
tion, increasing the Proportional Band will cause
the control to react slower, which will dampen
this oscillation. If the PI reacts too slowly, then
decreasing the Proportional Band will make the
control react faster.
Proportional Only Control - There will be cer-
tain applications in which only proportional con-
trol is required for good performance. When this
is the case, the Integration Time can simply be
set to zero, and the Proportional Band set to a
desired value.
Some advantages of only using Proportional
control are that it is generally more stable than
Proportional and Integral control, and its function
is easier to understand. A disadvantage of only
using Proportional control is that the Control In-
put usually will settle into a spot somewhere in
the Proportional Band, and will not move to the
Control Setpoint. For instance, from the example
shown above, if the Proportional Output aver-
ages 80%, then the Control Input will remain at
108° F and will not go to 100° F. This may be
acceptable in some applications. In certain other
cases the setpoint can be offset to move the
Control Input to the point it needs to be.
Integration Time - The Integral calculation in
PI control uses past performance to calculate
a value for the PI output. It does this by incre-
mentally, over time, adding a small value to the
PI output to move the Control Input toward the
Control Setpoint. Eventually, the Integral com-
ponent of the PI output will equal the average PI
output value as Control Input gets to the Control
Setpoint, and the Proportional component goes
to 0%. When combined with the Integral calcula-
tion, the Proportional component can be nega-
tive and its range becomes -100% to +100%.
If the Control Input moves above or below the
Control Setpoint, the Proportional control will
prevent it from moving too far, and the Integral
control will move it back to the setpoint.
Once the Proportional Band is set, start with a
large Integration Time (180 seconds). Here again,
you want to fi nd the range of Integration Time
that gives you reasonably fast performance,
without too much overshoot, and without too
much oscillation. If the Control Input repeat-
edly overshoots the Control Setpoint, or oscil-
lates too much, increasing the Integration Time
will slow the control. If the Control Input moves
too slowly toward the Control Setpoint, decreas-
ing the Integration Time will cause the control to
react faster.