Motorized Valve Control; Motorized Valve With Feedback; Motorized Valve Control Without - ABB COMMANDER 1900 Series Programming Manual

...4 CONTROL CONFIGURATION LEVEL

4.2 Motorized Valve Control

Information.
This page is not displayed if position proportioning or boundless control is not enabled on either of the controllers.
• Motorized valve control with or without feedback – position-proportioning (with feedback) or boundless (without
feedback).
• Ratio and bias settings – can be applied to adjust the range of valve travel (position-proportioning only).
• Deadband setting – adjustable to minimize hunting of the motorized valve.
4.2.1 Motorized Valve with Feedback (Position-Proportioning) – Fig. 4.3
P.I.D. Output
100
80
50
20
0
4.2.2 Motorized Valve Control without Feedback (Boundless) – Fig. 4.4
A 'boundless' process controller provides an output that is effectively the time derivative of the required regulator position, i.e. the
controller signals the regulator, not where to go to (position derivative), but in which direction to travel and how far to move, by a
series of integral action pulses. Thus, the controller does not need to know the absolute regulator position and is unaffected when
the regulator reaches the upper or lower limit, as determined by the regulator's limit switches (giving rise to the term 'boundless').
In this system, the final regulator must act as an integrator, integrating both the raise and lower pulses in direction and duration
so that the final position of the regulator reproduces the required 2 or 3 term control function, and must remain stationary
indefinitely in the absence of raise or lower commands.
When a deviation from set point is introduced the regulator is driven, for a length of time equivalent to the proportional step. The
regulator is then driven by integral action pulses until the deviation is within the deadband setting.
+
Control
Deviation
–
Raise
Lower
34
Ratio Bias
Ratio Setting Bias Setting
(0.01 to 10.00) (within Eng. range)
0%
1.00
0%
0.50
–25%
Fig. 4.3 Position-Proportioning Schematic Diagram
Integral Action
Proportional
Step
Fig. 4.4 Boundless Control Action
Valve Travel
Limits
100% Valve
Open
Valve
0%
Closed
Pulses
Proportional Integral Action
Step
Desired Valve Position
Valve Travel Valve Travel
Limits Limits
75%
50%
25%
Time
Proportional
Step
Time
Pulses
0%