MICROPROCESSOR-BASED CONTROL AND DIAGNOSTIC SYSTEM FOR MOTOR OPERATED VALVES

摘要

A microprocessor (32) periodically tests the status of the stem (40) of the motor operated valve (22), and turns off the valve's motor (24) if certain predefined criteria for the valve stem position and the valve stem load are satisfied. A position sensor (46) provides a valve stem position signal and a predicted stem position signal is computed. The current and predicted positions are compared with a preselected target position. A stem load sensor (48) provides a current valve stem load signal, a predicted stem load is computed and the current and predicted loads are compared with a preselected maximum desirable stem load. When the control system is being used to fully open and fully close a gate valve, the control logic can use either a predicted position criterion or a predicted stem load criterion to determine when to turn off the valve motor (24). When the control system is being used with a flow control valve, the use of a predicted position criterion minimizes overshoot problems which would cause the motor (24) to be reversed one or more times while moving to a target position. A motor load sensor (70) allows periodic measuring of the actual load on the motor (24). The motor is turned off if the measured motor load exceeds any one of a plurality of preselected maximum motor load values for a corresponding predicted period of time.