Valve signature
Valve signature is the result of plotting the amount of control valve travel in response to positioner output air pressure following a ramp input signal. Through the execution of this test, the following indicators of the control valve’s performance are obtained, and its soundness can be determined from that information.
Air circuit diagnosis
If oil, moisture, or other foreign substances enter the instrumentation equipment air due to an equipment failure, they often accumulate in the positioner and can cause it to malfunction. The air circuit diagnostics provide a diagnostic algorithm for detecting the progression of the accumulation of foreign substances through a tendency comparison of the relationship between the control signal and nozzle back pressure in the positioner. The positioner identifies trends caused by accumulation of foreign substances in the nozzle flapper and clogging of the seat area and informs the user when to perform maintenance on the air circuits.
Force-balance diagnosis
Control valves function with a balance between the unbalance force generated by the fluid pressure, valve seating force, frictional force generated by gland packings, spring force of the actuator, and operation thrust force generated by the output air pressure from the positioner and the actuator diaphragm.
Force-balance diagnosis provides an online algorithm for diagnosing whether these forces are properly balanced for control valve actuation.
There are two types of force-balance diagnosis: output air pressure validity diagnosis (Po Validity) and maximum frictional force diagnosis (Max. Friction).
Spring
Operation thrust force by
the positioner output air pressure
Frictional force
Valve seating force Unbalance force
Improved stick-slip diagnosis
The phenomenon of alternating stick and slip of the valve stem due to an increase in sliding resistance arising in a control valve is called stick-slip. Stick- slip diagnosis is Azbil’s own unique control-valve diagnostic algorithm for detecting this phenomenon online.
In addition to the stick-slip diagnostic algorithm which was implemented in the 300 Series, the 700 Series provides exception handling of non-stationary operation data and a gradual threshold setting function, both of which increase the usefulness of this diagnostic algorithm.
Of course, all diagnostic algorithms and checking functions implemented in the 300 Series have been inherited by the 700 Series.
- Seating force (valve