Emerson Vilter VilTech, Руководство по эксплуатации и обслуживанию

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Control Groups
Four groups of control setpoints can be defined for use with automatic capacity control. Each setpoint group
consist of a Cut-In, Cut-Out, Control, Low Alarm, and Low Failure setpoint.
Cut-Out Setpoin t -The Viltech will stop the compressor when the suction pressure or process temperature goes
below the cut-out setpoint.
Cut-In Setpoint - The Viltech will start the compressor when the suction pressure or process temperature goes
above the cut-in setpoint.
Control Setpoint -The Viltech will change the capacity in an attempt to maintain the suction pressure or process
temperature at the control setpoint.
Low Alarm/Failure Setpoints -
These are the low suction pressure or process temperature alarm and failure
values associated with the control setpoint. In Sequenced Mode, the local setpoints are replaced by the Sequencer
low alarm and failure set-points transmitted by the master sequencer controller.
Time Proportional Control Strategy
For automatic capacity control, the amount of time between stage changes is a function of how far the Control
Parameter is from the Control Setpoint and how long the Control Parameter remains outside the Control Deadband.
A separate set of control parameters is defined for increasing or decreasing load conditions.
Control Deadband - When the difference between the Control Setpoint and the Control Parameter is less than the
deadband value capacity changes will take place. If the Control Deadband values are too small, the capacity may
increase and decrease excessively causing fluctuations in the Control Parameter. If the Control Deadband are too
large, the compressor may not hold the Control Parameter close enough to the Control Setpoint resulting in
inefficient capacity control.
Normal Bandwidth - If the difference between the Control Setpoint and the Control Parameter is between the
Control Deadband value and the Normal Bandwidth value, the Normal Stage Delay timer will be used to determine
when a stage will be added or removed.
If the difference between the Control Setpoint and the Control Parameter is greater than the Normal Bandwidth
value, the Fast Stage Delay timer will be used to determine when a stage will be added or removed. This ensures
that capacity changes will occur more quickly when the Control Parameter is far from the Control Setpoint.
If the Normal Bandwidth values are too small, the compressor will respond too quickly to small load changes and
may constantly overshoot the optimal position. If the Normal Bandwidth values are too large, the compressor will
react too slowly to load changes.
Normal Stage Delay - This is the amount of time used between stage changes when the Control Parameter is
between the Control Deadband and the Normal Bandwidth. This value should be greater than the Fast Stage Delay
time. If the Normal Stage Delay time is too small, then capacity changes will occur too often, possibly not allowing
the affects of the previous change to take effect.
Fast Stage Delay - This is the amount of time used between stage changes when the Control Parameter is outside
the Normal Bandwidth. This value should be less than the Normal Stage Delay time. If the Fast Stage Delay time is
too large, then capacity changes will not occur often enough, possibly allowing the system to exceed safe limits.