US Patent 9037281 Method and apparatus for condition monitoring of valve

In the method and apparatus of the invention, the process point is taken into account when the condition and performance of a control valve are monitored. In the condition monitoring of the valve, process measurements are used in addition to measurements inside the valve in such a manner that the process measurements identify the operating point at which the valve operates, and the measurements inside the valve are observed at these operating points to detect changes and to determine the condition of the valve. According to an aspect of the invention, the variables representing the operating point of an industrial process are considered when changes in the friction load of the valve and/or the load factor of the actuator are observed.