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.

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.

Abstract: A circuit for the protection the contacts of a switch device such as a reed switch when used in a control circuit. The protection circuit isolates the switch contacts from the load it is controlling by establishing parallel electrical current paths between two inputs. Two such parallel paths provide for a symmetrical bi-directional current flow within the protection circuit. Each parallel path contains a controlled switching device which conducts the current in the respective parallel path when the input polarity is in a given direction. The controlled switching device may be controlled from a polarity sensing in the primary branch which contains the switch device. A single parallel path between inputs can be used to provide polarized DC operation. Diodes in the primary path containing the switch device provide for polarity sensing for control of the controlled switch devices in the parallel paths.