Pumpdown Control - Emerson VILTER MicroVission Operation And Service Manual

Section 5 • Compressor Control
• This quantity is used for fine adjustment, and this
setpoint is used to smooth out process variations.
• This setpoint should be set high enough to prevent
hunting but low enough to prevent control system
overshoot.
D = Derivative (rate) setpoint:
• Used to adjust the load control action, account-
ing for how fast the error is changing, positively or
negatively. It´s a standard PID loop variable, and it
is not used for our applications.
Interval:
• This setpoint defines the time interval for calcula-
tion of Integral Error.
Figure 5-13. Compressor Control Screen – Pumpdown Control
5 – 14

Pumpdown Control

The Pumpdown Control defines a method of "pumping"
down a chiller, which is to draw off refrigerant from it.
This feature can be enabled or disabled from this page,
see Figure 5-13. If Pumpdown is enabled, this feature
will only function when the compressor is running in lo-
cal Auto Mode and Control Mode Configured is Suction
Pressure.
If the Pumpdown Operation is running, then;
• The
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Auto-cycle functionality
Pumpdown mode will cause the compressor to
cycle off via the Pumpdown Stop Pressure set-
point. Normally, the Pumpdown Stop Pressure
setpoint will be set lower than the Auto-cycle
Stop setpoint. Therefore, as the suction pressure
is pulled down, the compressor is prevented from
shutting down prematurely via the Auto-cycle
Stop setpoint by automatically ignoring the Auto-
cycle feature.
is ignored.