Emerson Vilter Vission 20/20, Руководство по эксплуатации и обслуживанию

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6 – 2
Section 6 • Compressor Control
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
Figure 6-2. Compressor Control Screen - Process Temperature Control
the larger the corrective pulse will be. The duration of
the pulse is limited by the Pulse Time Setpoint. By de-
fault the maximum pulse time is the same as the inter-
val time. This means that the pulse time can be 100% of
the interval time given a near continuous movement of
the capacity slide. Adjusting these setpoints can be use-
ful in slowing down the reaction time of the compressor
if large thermal time contents are present in the refrig-
eration cycle. As mentioned in the above paragraph, the
distance of the process variable from the control set-
point determines 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 vari-
able 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 6-4.
The Deadband Setpoint defines the area around the con -
trol setpoint where the algorithm stops adjusting the
capacity slide. This area is a percentage of the propor-
tional band. By default the proportional band is set to 4
Psig and the deadband is set to 10% of 4 Psig. Making
the de/- 0.4 Psig of the control setpoint. Once
the process variable is within the deadband, the algo-
rithm considers the compressor to be on setpoint. If the
operator wishes the compressor to operate closer, the
setpoint 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 actuator’s operational life.
Auto-Cycle
The auto-cycle setpoints define the control points in
which the compressor will automatically cycle on and
off when placed into “Auto” run mode. These setpoints
can be “enabled” or “disabled” using the check box. A
delay can be entered to momentarily 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 compressor and a Reset will be