Mannesmann Aktiengesellschaft

Thomas Karte

Wolfgang Backe

Alexander Kleist

Heiko Kresse

A method and apparatus for detecting displacement of valve rod movement in electropneumatic position regulators, by generating a high-frequency electromagnetic alternating field by exciting a high-frequency oscillation within an LC oscillating circuit in an inductive sensor, damping the high-frequency oscillation as a function of displacement via an electrically conductive body moved along by the valve rod, demodulating the oscillator signal and feeding the demodulated signal to a microcomputer without amplification for evaluation of the displacement-dependent damping of the oscillation amplitude, measuring the temperature within the inductive sensor, correlating the temperature with the measured oscillation amplitude in the microcomputer, and determining a corrected displacement signal from the correlation.

Method and device for detecting displacement of valve rod movement in an

A device for operating a servo drive having a positioning element controlled by a pressure medium. The device includes an electrical control unit generating a control signal based upon the position of the positioning element, a pre-control system connected to receive the control signal through an electrical control path and a main control system controlled by the pre-control system to operate the servo drive by moving the positioning element. A switching element is positioned between the electrical control unit and the pre-control system and opens the electrical control path prohibiting the transmission of the control signal upon detecting operation malfunction. Upon opening of the control path, the pre-control system acts to switch the main control system into a deventilation mode and said positioning element is moved into a predetermined 'fail safe' position deventilating the positioning volume of the drive.

Servo drive operated by a pressure medium

An apparatus and process for monitoring conditions of a control valve including a valve element operated by a drive controlled by a position controller. A spindle extends into a valve chamber through a dynamic seal and connects the valve element to the drive. The condition of the seal is monitored by measuring start-up time, stopping time and distance travelled. The start-up time relates to the time between application of control current to the position controller and sensing movement of the valve element. The stopping time relates to the interval between application of a second control current to the position controller and sensing the valve element has stopped. The distance travelled relates to distance the valve clement travels during the stopping time. A time difference is determined by subtracting the stopping from the starting time and is calibrated to a seal coefficient of friction. The distance travelled is also calibrated to a seal coefficient of friction. These two coefficients of friction are compared whereby a discrepancy indicates a change in air pressure has occurred during valve operation. These measurements are taken prior to and cyclically during valve operation. The coefficient of friction obtained during valve operation is compared with the coefficient of friction obtained prior to valve operation to indicate a change in the condition of the seal. If a change in air pressure occurred during valve operation, the coefficient of friction obtained by calibrating the travel distance is compared with the coefficient of friction obtained prior to valve operation.

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Lemgo, Germany

Thomas Karte