This work was done as a part of my thesis

1. Compensation of Control
valve stiction
Supervised by
Dr. Dr. M.A.A. Shoukat Choudhury
Professor
Department of Chemical Engineering
BUET
Prepared by
Md. Habibur Rahman
Std. ID- 0902016

2. Outline of presentation
Background Of Study
Objective Of Study
Available Compensation methods
Development of a new stiction compensation model
 Comparison of Different Models
Experimental evaluation
Conclusions And Recommendations

3. Background of Study
Automation of modern plants
Control loop performance
Stiction as a process nonlinearity

4. Stiction in
Control valve

5. Stiction in Control valve(cont’d)

6. Objectives
The overall objectives of our study are:
 Study different Compensation techniques
 Development of a new technique
 Evaluation of the performance of new method

7. Available Compensation Methods
Knocker method
CR method
Two move method
Adaptive control method

8. Proposed Model
Controlle
r
Valve
input
Process

9. Simulation Diagram

10. Proposed Model Mechanism
1800 1900 2000 2100 2200 2300 2400
-4
-3
-2
-1
0
1
2
3
4
Time(s)
CompensatorOutput
ControllerOutput
StemPosition
Setpoint
Compensator Output
Set Point
Stem Position
Controller Output
A B

11. Comparison of different models
Models
Knocker model
CR model
Adaptive model
Proposed model
Parameters
 Process variable
 Stem Position
 Impact on valve reversals

12. 0 200 400 600 800 1000 1200 1400 1600
-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
Comparison(cont’d)
Knocker Model

13. Comparison(cont’d)
CR Model
0 200 400 600 800 1000 1200 1400 1600
-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV

14. 0 200 400 600 800 1000 1200 1400 1600
-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
Comparison(cont’d)
Adaptive Model

15. Comparison(cont’d)
0 200 400 600 800 1000 1200 1400 1600
-8
-6
-4
-2
0
2
4
6
8
PV Vs. Time
Time(s)
PV
Proposed Model

16. Parameter Knocker CR Adaptive Proposed
Initial
variance(PV)
6.00 6.00 6.00 6.00
Final
Variance(PV)
1.148 1.074 0.32 0.27
Variance Ratio 0.1913 0.1790 0.0533 0.045
%Reduction in
Variance
80.86 82.1 94.66 95.5
Analysis of Process variable variance
Comparison(cont’d)

17. Comparison(cont’d)
Analysis of Valve reversals
11 11
18
6
0
2
4
6
8
10
12
14
16
18
20
Knocker CR Adaptive Proposed
NoofValvereversals
Model
No of Valve reversals vs. Process model

18. Comparison(cont’d)
Analysis of Stem Position of valve
0.571
0.535
0.321
0.214
0
0.1
0.2
0.3
0.4
0.5
0.6
Knocker CR Adaptive Proposed
StempositionAmplitudeRatio
Model
Stem position Amplitude Ratio vs.Model

19. Comparison(cont’d)
Summary of comparison Analysis
The Proposed model is beneficial over other models in
the following manners:
Reduction of oscillations in process
Reduction of valve movement
Good set point tracking and disturbance rejection.
Avoidance of excessive control action.

20. Experimental Evaluation

21. 0 1000 2000 3000 4000 5000 6000
-5
0
5
10
15
20
25
30
35
40
45
Time(s)
ProcessVariable(PV)
Process Variable(PV) vs. Time
Experimental Evaluation(cont’d)

22. Experimental Evaluation(cont’d)
143
23
0
20
40
60
80
100
120
140
160
PV variance(Initial) PV variance(Final)
ProcessVariablevariance
Condition
Process Variable varance

23. Conclusions
A new model for stiction compensation is developed
Comparison of different models are done
Performance test of the proposed model is evaluated
experimentally

24.  Experimental work to compare with other models
 Correlation of model parameter with different
processes
Recommendations

25. Any Question?