Service manual

6 – 10
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.9
position is below the “Slide %” setpoint. The operator
can choose between “N.O.” or “N.C.”. This setpoint
is not available for Economizer Port 2, so Economizer
Port 2 follows the setpoint of Economizer Port 1.
Active:
• Check box to enable the digital output. There is no
check box for enabling Economizer Port 2 digital
output. Economizer Port 2 digital output is enabled
when Compressor type selected from confi guration
screen is “VSM7” and Economizer Port 1 digital out-
put is enabled.
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:
• Defi 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 defi ned in the proportional control sec-
tion to a percent duty cycle.
Soft load %:
• Defi 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
defi 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 specifi 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:
• Defi 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.
Section 6 • Compressor Control