Operation
50 UDC2300 Universal Digital Controller User Manual 4/00
4.11 Three Position Step Control Algorithm
Introduction
The Three Position Step Control algorithm allows the control of a valve (or other
actuator) with an electric motor driven by two controller output relays; one to
move the motor upscale, the other to move it downscale, without a feedback
slidewire linked to the motor shaft.
Estimated Motor Position
The Three-Position Step control algorithm provides an output display (“OT”)
which is an estimated motor position since the motor is not using any feedback.
• although this output indication is only accurate to a few percent, it is corrected
each time the controller drives the motor to one of its stops (0 % or 100 %).
• it avoids all the control problems associated with the feedback slidewire
(wear, dirt, and noise).
• when operating in this algorithm, the estimated “OT” display is shown to the
nearest percent (that is, no decimal).
Motor Position Display
Table 4-10 Procedure for Displaying 3Pstep Motor Position
Step Operation Press Result
1 Access the
Displays
DISPLAY
Until you see:
Upper Display = PV
Lower Display = OT (The estimated motor position
in %)
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