OM WGS-5
WGS 130A to 190A
59
Unit Capacity Overrides
Unit capacity limits override the automatic slide control when the chiller is in COOL mode
only. The active capacity limit as well as the estimated unit capacity will be calculated in the
unit controller and sent to all circuits.
If the unit capacity is greater than the active capacity limit, then no circuit will increase slide
position. If the unit capacity is greater than the active limit plus 1%, the circuits will unload
until the unit capacity is less than 1% greater than the active limit.
Pumpdown
When a circuit reaches a condition where the compressor needs to shut down normally, a
pumpdown will be performed. The slide target will automatically go to 0 while pumping
down, and the compressor will run until the pumpdown pressure has been reached, or the
pumpdown time has been exceeded.
Service Pumpdown
If the option for a service pumpdown is enabled, then on the next pumpdown the pressure
setpoint will be 5 psi. The circuit will pumpdown to this pressure and shut off. When the
compressor has completed the service pumpdown, the setpoint is reset to No.
Slide Positioning
Slide Position Indicator
Each compressor estimates its slide load percentage from the present value of the slide
position indicator. The percentage is based on the 4-20mA signal from the slide load
indicator. A percentage value of 0 corresponds to approximately a 4mA signal, a percentage
value of 100 corresponds to approximately a 20mA signal.
Slide Calibration Procedure
Slide Position is a relative capacity adjustment from 0.0%(Min load) to 100.0%(Max Load).
There are two MicroTech readings that apply to the indicator, Slide Target and Slide
Position. It is important to understand the difference between these. The
Slide Target
is
the value in which the controller uses to display the calculated prediction of slide position,
this value represents the destination or goal of pulsing the load and unload solenoid coils.
The slide target is used for direction of control for all load and unload operations, including
alarm limit events. When putting a circuit in Manual mode, the slide target is the value that
you will be adjusting. The controller will load or unload the chiller to match, with in about
3%, the target entered with the current slide position value. The second value is the
Slide
Position (Pos)
this is the slide position value which is the 4-20mA reading received from
the position indicator. These values can be viewed at the circuit controller on screen
“VIEW CIR STATUS (1)”.
A slide target of 0.0% is fully unloaded and the unload solenoid will be constantly
energized. A slide target of 100.0% means that the chiller is at full load and the load
solenoid is continually energized. The chiller will regulate the slide position to infinite
steps between 0% and 100% by pulsing the appropriate solenoid. Facing the discharge end
of the compressor, looking along the left side, the solenoid coil on the top is for load (oil
vent) and the solenoid coil on the side is for unload (oil feed). During normal operation, the
controller makes decisions to move the Slide target, the calculated value, and pulses the
proper solenoid in order to keep the actual and the target position with in a few percent.
Содержание WGS130AA: WGS140AW
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