Service manual

6 – 5
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.9
• Defi nes the minimum and maximum positions for
the capacity slide. While in 1 step control these values
should be 0% for minimum and 100% for maximum.
VFD Speed:
• Defi nes the minimum and maximum speed for the
motor speed. While in 1 step control these values
should refl ect the full range of the VFD.
2 Step VFD Control:
• Enables the second step in the VFD control algorithm.
Capacity Slide Position:
• Defi nes the minimum and maximum position of the
capacity slide in the 2 step VFD control.
VFD Speed:
• Defi nes the minimum and maximum speed for the
motor in the 2 step VFD control.
P = Proportional (gain) setpoint:
• Used to adjust the motor speed action in direct
proportion to the difference between the control
setpoint and the process variable (SP - PV error).
This is a unit-less quantity and is used for coarse ad-
justment. This setpoint should be set to the lowest
value that gives adequate control system response.
Increasing the proportional setting increases the
control system’s sensitivity to small process fl uctua-
tions and the tendency to hunt.
I = Integral (reset) setpoint:
• Used to adjust the capacity control action, integrating
the error over time, to account 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
process variations. This setpoint should be set high
enough to prevent hunting but low enough to pre-
vent control system overshoot.
D = Derivative (rate) setpoint:
• Used to adjust the capacity control action, account-
ing for how fast the error is changing, positively or
negatively. A standard PID loop variable, it is not used
for our applications.
Section 6 • Compressor Control
Figure 6-5. VFD One-Step Control Method
Figure 6-6. VFD Two-Step Control Method