Process control system
First Claim
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1. Apparatus comprising:
- a first control valve means for manipulating the flow of a fluid;
means for establishing a first signal representative of the desired position of said first control valve means;
means for establishing a second signal representative of the actual position (P) of said first control valve means;
a velocity controller for comparing said first signal and said second signal and for establishing a third signal which is representative of any change (Δ
P) which must be made in the position of said first control valve means in order for said first signal to remain substantially equal to said second signal;
a position controller which requires a velocity set point;
means for establishing a fourth signal which is representative of the position set point (An) generated by said position controller in response to said velocity set point;
means for establishing a fifth signal which is representative of a driving force limit (R);
means for establishing a sixth signal representative of the value of said fourth signal one time period earlier (An-1);
means for calculating said velocity set point (Δ
A) for said position controller in response to said second signal, said third signal, said fifth signal and said sixth signal, wherein said velocity set point is represented by ##EQU2## means for supplying said first signal to said position controller, wherein said position controller compares said first signal and said fourth signal to establish a seventh signal which is representative of the driving force which must be applied to said first control valve means; and
means for manipulating said first control valve means in response to said seventh signal.
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Abstract
A variable limit is utilized to prevent a position controller which requires a velocity set point signal from overdriving a stuck control valve. Control based on a comparison of the actual position to desired position is utilized unless the valve is stuck. If the valve is stuck, the variable limit controls the velocity set point provided to the position controller until such time as the valve becomes unstuck.
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Citations
8 Claims
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1. Apparatus comprising:
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a first control valve means for manipulating the flow of a fluid; means for establishing a first signal representative of the desired position of said first control valve means; means for establishing a second signal representative of the actual position (P) of said first control valve means; a velocity controller for comparing said first signal and said second signal and for establishing a third signal which is representative of any change (Δ
P) which must be made in the position of said first control valve means in order for said first signal to remain substantially equal to said second signal;a position controller which requires a velocity set point; means for establishing a fourth signal which is representative of the position set point (An) generated by said position controller in response to said velocity set point; means for establishing a fifth signal which is representative of a driving force limit (R); means for establishing a sixth signal representative of the value of said fourth signal one time period earlier (An-1); means for calculating said velocity set point (Δ
A) for said position controller in response to said second signal, said third signal, said fifth signal and said sixth signal, wherein said velocity set point is represented by ##EQU2## means for supplying said first signal to said position controller, wherein said position controller compares said first signal and said fourth signal to establish a seventh signal which is representative of the driving force which must be applied to said first control valve means; andmeans for manipulating said first control valve means in response to said seventh signal. - View Dependent Claims (2, 3, 4)
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5. A method for controlling the position of a first control valve in response to the output signal from a position controller which requires a velocity set point signal, said method comprising the steps of:
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establishing a first signal representative of the desired position of said first control valve means; establishing a second signal representative of the actual position (P) of said first control valve means; comparing said first signal and said second signal and establishing a third signal which is representative of any change (Δ
P) which must be made in the position of said first control valve means in order for said first signal to remain substantially equal to said second signal;establishing a fourth signal which is representative of the position set point (An) generated by said position controller in response to said velocity set point; establishing a fifth signal which is representative of a driving force limit (R); establishing a sixth signal representative of the value of said fourth signal one time period earlier (An-1); calculating said velocity set point (Δ
A) for said position controller in response to said second signal, said third signal, said fifth signal and said sixth signal, wherein said velocity set point is represented by ##EQU3## supplying said first signal to said position controller, wherein said position controller compares said first signal and said fourth signal to establish a seventh signal which is representative of the driving force which must be applied to said first control valve means; andmanipulating said first control valve means in response to said seventh signal. - View Dependent Claims (6, 7, 8)
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Specification