Noninvasive ultrasonic proximity detector for a fluid actuated cylinder

Abstract

The invention provides a generally noninvasive device and method for detecting a reciprocative piston located within a cylinder bore. An ultrasonic transducer mounted on the outside of the cylinder wall selectively generates an ultrasonic transmission signal directed through the cylinder. The transducer then receives any desired ultrasonic signal produced by propagation of the ultrasonic transmission signal. Control circuitry processes electrical signals produced on the ultrasonic transducer by the propagated ultrasonic signal to indicate presence or absence of the piston. In presently preferred embodiments, the control circuitry determines whether the piston is present by comparing a signal level in the received ultrasonic signal during a sample time window in which the desired signal may be expected with a predetermined threshold level. To perform this function, electrical signals produced on the transducer by the propagated ultrasonic signal are first passed to an amplifier having a selected gain. An output of the amplifier is then fed to an detector circuit which produces an detection level signal which may be representative of energy present in the received ultrasonic signal during the sample time window. Comparator means then perform the comparison of the detection signal with the threshold. In many embodiments, it is generally desirable to utilize two piston sensors respectively located to indicate presence of the piston at limits of its reciprocative stroke. For greatest flexibility, some presently preferred embodiments of the device are capable after being initially activated to identify with which cylinder model, from a plurality of such models, the detector is being used. In this way, the device can automatically set certain operating parameters to optimize signal-to-noise ratio. The device may also incorporate light emitting diodes or other indicators to alert the user of current operating conditions.