Emerson Vission 20/20 Operation And Service Manual Download

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Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0

Section 6

•

Compressor Control

Volume Slide Position Offset

These setpoints offer the ability to alter the Volume po-
sition table to take advantage of potential energy sav-
ings. Since the volume position is a function of the ca-
pacity position, the offset to the volume is based on the
position of the capacity slide. The volume offset can be
applied to the entire capacity slide range or just a por-
tion using the Capacity Range minimum and maximum
setpoints.

Volume Slide Adjustment %:
• The value in percentage of the volume slide offset.
Capacity Range:
• De

nes the range that the volume position slide off-

set will be applied.

Soft Load

This setpoint is used to slow the loading of the compres-
sor. In some refrigeration systems, a loading compres-
sor can have dramatic effects on the system parameters.
This setpoint allows an operator to reduce the continu-
ous load pulse as de

ned in the proportional control sec-

tion to a percent duty cycle.
Soft load %:
• De

nes the duty cycle of the continuous load pulse.

At 100%, the continuous pulse will truly be continu-
ous. At 50%, the continuous pulse would be reduced
to half time on and half time off in the time interval
de

ned in the proportional control section.

Load Anticipating

The purpose of the load anticipating algorithm is to re-
duce the amount of overshoot of the capacity slide posi-
tion while the compressor attempts to meet the control
setpoint. This advanced feature of the Vission 20/20
closely monitors the rate of change of the process vari-
able and compares it to the control setpoint. If the pro-
cess variable is changing in the direction of the control
setpoint at the speci

ed rate or greater, then the normal

command to move the capacity slide is interrupted. The
rate is calculated between time intervals set in the pro-
portional control section of this screen.

Enable Load Anticipation Algorithm:
• Allows the operator to choose if the load anticipation

algorithm runs.

Rate Dead Band:
• De

nes the rate at which the capacity slide move-

ment will be interrupted. This value is an absolute val-
ue of the process variable. For example, the default
value is 0.25. If the control mode is suction pressure,
then this value is 0.25 Psig or if process temperature
is the control mode then the value would be 0.25°F.

Oil Control

These setpoints determine how the Vission 20/20 will
manage the oil of the compressor, see Figure 6-11.

Oil Pump Press Restart Ratio:
• The on and off setpoints de

ne when the oil pump

will cycle on and off if the oil pump is selected to cycle
from the con

guration screen.

Oil Separator Heater Temp:
• When the oil temperature falls below this setpoint

the oil heater will turn on. Note, there is a 5°F differen-
tial associated with this setpoint. For example, when
set at 100°F, the heater will turn on at 95°F and off at
105°F.

Liquid Injection

The setpoints in this section are to control the behavior
of the liquid refrigerant injected into the compressor for
oil cooling purposes. The liquid injection solenoid con-
trol is based off of discharge temperature whether the
compressor uses just an injection solenoid or a motor-
ized valve in conjunction with the solenoid.
Liquid Injection Solenoid Control ONLY
• When using only the liquid injection solenoid, the so-

lenoid is activated once the value of discharge tem-
perature meets or exceeds the value of “Liquid inj.
Setpoint 1” and the value of oil separator tempera-
ture meets or exceeds the value of “Oil Sep. Temp.
Override”. The injection solenoid will deactivate if
either of setpoints are not met. This will prevent situ-
ations where the discharge temperature may rise
quickly, but the oil temperature is still very cold. By
preventing the liquid injection solenoid from turning
on at this point, the oil separator will not be subjected
to additional liquid refrigerant, that would cool the oil
even further.

Liquid Injection Control using a 4-20ma motorized valve:
• When a motorized valve is used to control the amount