Emerson Vission 20/20 Operation And Service Manual page 56

Section 6 • Compressor Control
Liquid Inj. Setpoint 1:
• Setpoint at which the liquid solenoid will activate if in
solenoid control or if the setting for the control vari-
able for the PID is in liquid motorized value control.
Liquid Inj. Setpoint 2:
• Not yet available
Oil Sep. Temp. Override:
• Defi nes the temperature the oil must reach before the
liquid injection solenoid is allowed to be activated.
P = Proportional (Gain):
• Used to adjust the positioning valve in direct propor-
tion to the difference between the control setpoint
and the discharge temperature (SetPt - DT = error).
The proportional term is a unit-less quantity and is
used for coarse adjustment. This setpoint should be
set to the lowest value that gives adequate response
to the control system. Increasing the proportional
setting increases the control system's sensitivity to
small discharge temperature fl uctuations and the
tendency to hunt.
I = Integral (reset):
• This parameter integrates the error over time, to ac-
count for a small error that has persisted for a long
time. This quantity is used for fi ne adjustment. This
setpoint is used to smooth out discharge tempera-
ture variations. This setpoint should be set high
enough to prevent hunting but not too high or it will
cause control system overshoot.
D = Derivative (rate):
• This parameter accounts for how fast the error is
changing, positively or negatively.
Minimum Valve Open %:
• When enabled, this is the valve position used when-
ever the control variable drops below Liquid inj.
Setpoint 1. Use only if the compressor is tripping off
for low oil temperature due to large overshoots and
all other tuning methods have failed.
Avg. with Oil Manifold Temperature:
• When enabled, averages the Oil manifold tempera-
ture and the discharge temperature. This creates
a more stable control variable and should result in
more stable control.
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Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0