The principle of the valve positioner: the feedback lever feedback valve opening position changes, when the electromagnetic torque generated by the input signal is equal to the torque generated by the positioner feedback system, the positioner force balance system is in a balanced state, and the positioner is in a stable state. At this time, the input signal is proportional to the valve position. When the input signal changes or the force of the medium fluid changes, the equilibrium state of the force balance system is broken, and the force of the magnetoelectric component and the force generated by the feedback loop caused by the change of the valve stem position are in an unbalanced state.

There are many types of valve positioners used in the field, including pneumatic valve positioners, electric valve positioners, valve positioners with membrane actuators, valve positioners with piston actuators, powerful balanced valve positioners, and displacement Balanced valve positioners and valve positioners are widely used. In the production process, various failures will inevitably occur. In order to ensure quality, quantity, and safety in production, it is necessary to eliminate all possible failures of the positioner in time.

To eliminate the fault of the valve positioner, it is necessary to correctly determine which part of the valve positioner, which component has a fault. There are usually two failure analysis methods as follows: One is to analyze the valve positioner link by link and element by element according to the transfer function of the valve positioner. This is not suitable for on-site maintenance, but it is very useful for the analysis of difficult problems. Effective; second, comprehensive analysis and judgment of the fault phenomenon based on the maintenance personnel, this method is most suitable for on-site maintenance.