Gardner Denver XMX Series, Installation Instruction

Page: 13 / 34

GARDNER DENVER
Model XMX Demand Expander
Page 13
©Copyright 2005-2013
Gardner Denver Corporation
Version 4.10
P: (Proportional Gain – 0.1 to 2550)
Proportional only control basically recognizes the
magnitude and direction of the error between the Process Variable (PV) and the Setpoint (SP). It
responds rapidly to setpoint changes or disturbances but always results in a steady state error or
offset between PV and SP. Too much proportional action will result in oscillations.
I: (Integral - 0.1 to 255)
- Integral action looks error between PV and SP and integrates it over
time so that the output continues to change until the error is eliminated. Offset is eliminated and
the loop responds quicker at the expense of higher overshoots and longer settling time.
D: (Derivative – 0.1 – 2.55) -
Derivative action outputs a signal based on the rate of change of
the error between PV and SP. It can be useful in processes with long time constants such as
temperature control. Too much derivative can make loops unstable. Use with caution.
Expander Alarm Below Setpoint (P4)
is an offset subtracted from the Demand Expander
setpoint (if provided) and will activate an alarm should the pressure on the demand side of the
expander fall below the Demand Expander setpoint by the value entered in this field.
Suggested PID Setpoints: P =200.0 - I = 0.1 - D = 0.00
Operation:
Once set-up and placed into service, the XMX will provide a constant demand side air pressure
to the facility regardless of flow requirements. It is not unusual to accumulate an excessive
amount of water at the discharge header and the use of an automatic trap is again highly
recommended. Should the controller fail for any reason, or should power fail to the controller, the
valve will fail opened, providing the necessary volume of air to the system under uncontrolled
conditions.
If any set-point changes are desired or the system is not as stable as desired, refer to section
PID Tuning to re-tune the controller.