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Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.8.5153
As mentioned in the above paragraph, the distance of
the process variable from the control setpoint deter-
mines the size of the pulse used to move the capacity
slide. This is called the proportional band and is set by
the Proportional Setpoint. When the process variable is
outside the proportional band, the slide will move in the
direction of the error continuously. Increasing the size
of the proportional band can help slow the compres-
sors reaction by varying loads if desired, see Figure 6-2.
Proportional Band & Setpoint.
The Dead Band Setpoint defi nes area around the control
setpoint where the algorithm stops adjusting the capac-
ity slide. This area is a percentage of the proportional
band. By default the proportional band is set to 4 Psig
and the dead band is set to 10% of 4 Psig. Making the
dead band +/- 0.4 Psig of the control setpoint. Once the
process variable is within the dead band, the algorithm
considers the compressor to be on setpoint. If the op-
erator wishes the compressor to operate closer, the set-
point can be set to a smaller percentage. However this
will result in the capacity slide excessively moving to
maintain the setpoint and could over heat the actuator
or shorten the actuators operational life.
Auto-Cycle
The auto-cycle setpoints defi ne the control points in
which the compressor will automatically cycle on and off
when the compressor has been placed into “Auto” run
mode. These setpoints can be “enabled” or “disabled”
using the check box. A delay can be entered to momen-
tarily delay the start or stop from immediately occurring
when the setpoint is met. If a compressor shutdown is
desired on a suction pressure drop and a manual reset
is required, set the OFF value below the Low Suction
Pressure safety trip value. This will shut down the com-
pressor and a Reset will be required to restart it.
Section 6 • Compressor Control
Figure 6-2. Proportional Band & Setpoint