The operator can use the built-in data memory to record the data measured by the torque sensor at each action of the valve . These data can be used to monitor the status of the valve operation, to indicate if the valve needs servicing, and to use the data to diagnose the valve.
The following data can be diagnosed for the valve:
1. Valve seal or packing friction
2. The friction torque of valve stem and valve bearing
3 seat friction
4. Friction in valve operation
5. The dynamic force of the spool
6. Valve stem thread friction
7. Stem position
Most of the above data exist in all types of valves, but the focus is different. For example: For butterfly valves, the friction in the operation of the valve is negligible, but the force value for the plug valve is very large. Different valves have different torque running curves. For example, for wedge-type sluice rice, the opening and closing moments are very large. In other strokes, there are only filler friction and thread friction. When closed, the hydrostatic pressure acts on the sluice. Seat friction, the final wedge effect quickly increases the torque until it is closed. Therefore, according to the change of the torque curve can predict the failure that will occur, and can provide valuable information for predictive maintenance.
The automatic control of the process control system often encounters this kind of oscillation phenomenon in the electric actuator. The oscillation frequency is also high. Due to the existence of such an oscillation phenomenon, it is easy to cause a malfunction of the magnetic amplifier. In addition, since the electric actuator is often operated in an oscillating state, the service life of the mechanism is seriously affected. The automatic control of the process control system often encounters this kind of oscillation phenomenon in the electric actuator. The oscillation frequency is also high. Due to the existence of such an oscillation phenomenon, it is easy to cause a malfunction of the magnetic amplifier. In addition, since the electric actuator is often operated in an oscillating state, the service life of the mechanism is seriously affected. Therefore, this oscillation should be eliminated in the regulating system to ensure the normal operation of the regulating system.
There are many causes of the valve position oscillation of the actuator. The design, installation, commissioning, and operation experience are used to explain the causes of the actuator oscillation and how to eliminate it.
(1) The feedback of the small-loop oscillation of the valve position of the electric actuator is mainly caused by the following two aspects.
a Since the insensitivity zone Î”g of the magnetic amplifier is too small, the magnetic amplifier is too sensitive, so that the small loop of the actuator cannot be stabilized and the oscillation is produced.
b When the actuator loses its braking effect and causes idle walking, it also causes the actuator to oscillate.
In view of the above causes of the actuator oscillation, the magnetic amplifier is not sensitive to â–³g too small to cause oscillation. According to the experience in operation, the small loop oscillation can be eliminated when the insensitivity zone Î”g of the magnetic amplifier is adjusted to Â±120-140 Î¼A. For the actuator to lose the brakes, the cause of the loss of the brakes should be found out.
(2) Oscillation of the actuator due to signal source fluctuations. In the design of the system, the damper link can be added to the circuit, and mechanical buffering devices can also be added to the piping. Use mechanical damping to reduce the fluctuation of the output signal of the transmitter and eliminate the oscillation of the mechanism.
(3) The oscillation of the system is caused by improper tuning of the adjustment system parameters, causing the actuator to oscillate.
The tuning of the regulator's parameters is not suitable and will cause the system to generate different levels of oscillation. For a single-sleep sleep adjustment system, system oscillations may occur when the proportional band is too small, the integration time is too short, and the derivative time and differential gain are too large. For the common problems of multi-loop systems and single-loop systems, there are still mutual influences of the production of loops, and the resonance between the loops is caused by improper setting of parameters.
For the oscillation caused by the actuators caused by the above reasons, these parameters may be reasonably selected in the system's overall timing, so that the loop must maintain the required stability margin.
(4) The actuator oscillates due to an over-regulation of the regulator due to a too steep valve flow rate or a small opening of the valve. When the flow rate of the regulating valve is too steep, only a slight deviation of the gas station will be adjusted to make the medium to be regulated. This often leads to excessive adjustment and causes the system to oscillate. Since the characteristics of the regulating valve are limited by the process conditions and are more difficult to modify, the proportion of the adjustment can be appropriately increased to improve the adjustment quality.
(5) The play and clearance of the coupling of the actuator due to the linkage and the adjustment of the valve gate. All couplings should be manufactured with a three-level accuracy.