Micromod MOD: Modcell 2050R Users Guide - Manual (Page 206)

IB-23C650
POSITION PROPORTIONING CONTROL
Reasonable values for Position Proportioning Deadband and Preact can be
determined using the following procedure.
1. Perform the valve calibration in the BASE CFG MENU.
2. In the TUNE MENU, set the controller gain to 0.1, Reset to OFF. and
Preact to 0. Due to the very slow control action with these settings,
valve position can now be read by switching to Auto and quickly
observing the output display. (With position proportioning output in use,
the controller shows valve position in the numerical output display in
Auto mode, and controller output in that display in Manual mode).
3. Set Position Proportioning Deadband to 5 - 10% to eliminate its effect
from the measurement.
4. Put the controller in Manual and ramp the output (holding the button
down continuously) all the way to 100% and back to 0%. This
guarantees acquisition of maximum valve speed.
5. Ramp the output up and down 20 to 30% (or more) several times, each
time noting the percent overshoot of the valve position relative to the
controller output. Set the Position Proportioning Preact to the average of
these values.
6. Repeat step 4 and confirm that the overshoot is now near zero. Adjust
the Preact value as necessary.
7. Set the Position Proportioning Deadband to 0.1% and ramp the output
up and down to observe performance. Pay particular attention to very
small output changes once a position has been reached. Increase
deadband as necessary to eliminate “hunting”. This setting will vary
with the valve and application.
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