3. 1 INTRODUCTION
Pneumatic actuator for linear motion with power supply: a) schematic; b) energy flow
scheme; c) two-port representation. 1: AC motor, 2: air compressor, 3: pressure-relief valve, 4:
air filter with water trap, 5: air storage (accumulator), 6: 4/3 proportional valve, electrical
solenoid actuation, spring return, 7: double-rod cylinder; 8: diaphragm drive with spring return
4. CONTD..
Pneumatic actuators consist of an airflow valve and an actuating
device transforms the pneumatic energy into mechanical energy.
The valve is connected to the pneumatic pressure line manipulates
the pressurized air flow to the actuating device.
The valves are either proportional-acting valves or switching
valves.
Proportional acting valves allow a continuous manipulation of the
airflow either electrically by two solenoids or pneumatically with
one air flow modulator and return spring.
Switching valves are electromagnetic devices and operate with
PWM at high frequencies to generate actuator position.
5. 2 FAULTS OF PNEUMATIC VALVES
Faults of pneumatic valves may arise in the
air supply
air supply line
piston or diaphragm actuators
valve stem sealing and
plug–seat combination
Cross-sectional view of a
pneumatic valve with an
electro-pneumatic position
controller
6. Typical faults of pneumatic flow valves and fault-detection
coverage in dependence on instrumentation- x:yes, 0: no
7. 2.1 MODELS OF PNEUMATIC VALVES
The parameters for the chamber pressure are time-variant and depend
on the motion and the position of the diaphragm.
8. The dynamics of the mechanical part of the valve, the diaphragm, the
valve stem and the plug are governed by the balance of forces:
where mv :mass of the stem and connected parts,
cs : spring constant,
dv ,fc :coefficients of the viscous and dry friction of the
stuffing box and guidance
Fext: external forces, mainly the force through the flowing
fluid
9. RESULTS
Sensor
Fault on
intake
air flow
Sensor
Fault on
Manifold
pressure
Fault in
Manifold
Due to air
leak
10. CONCLUSIONS
• The fault detection strategy is designed for
three
important faults as from manufacturer point of
view.
• Observed that after initial transient effect the
performance of each residual is effective.
11. REFERENCES
1. J. A. F. Vinsonneaut, D. N. Shieldst, K. J. Bumhamt. Improved SI
engine modeling techniques with application to fault detection .
Pages 719-724, Proceedings of 2002 IEEE international Conference
on Control Applications, September 18-20.2002 Glasgow, U.K.
1. R. Iserman. Fault Diagnosis Systems An introduction from fault
detection to fault tolerance, Chapter 11 Fault detection with state
observers and state estimation, Springer, Berlin.
1. Graham C. Goodwin, Stefan F. Graebe, Mario E. Salgado,
Control system design, Chapter V Advanced SISO control,
Prentice Hall, New Jersey 1990.
1. K.P. Mohandas. Modern control engineering, Sanguine
Technical
Publishers. Bengaluru. 2006.
