Abstract: The invention provides an apparatus and method to confirm or deny the presence of an object within the scan area of an ultrasonic sensing system by requiring that any object be identified on at least two consecutive scans of the sensing system and using scan energy patterns which occur at irregular repetition times to selectively reject spurious direct or reflected signals present in the area. A generator of predetermined pattern burst of ultrasonic energy is arranged to produce one such burst of ultrasonic energy and a timing signal is coupled thereto so as to apply timing signals to cause production of the bursts. The timing signal source produces timing signals only according to a varying pattern whereby separation between adjacent signals meet certain present parameters. The energy patterns are applied to a transmitter which applies them to a scan area whereby the echo or returned energy from an object in the scan area is received and stored.

Abstract: A fail-safe sensor system to provide a positive indication of the proper operation of a sensor system by accounting for the return signals from an active zone and a monitor zone beyond. Search signals, provided by a transducer operating in the transmit mode, are transmitted within an active zone within which objects to be detected are expected to be located. Unreturned search signals are permitted to travel beyond the active zone into a monitor zone beyond and objects in such monitor zone cause return signals which are also employed. A counter feed from a free running clock source is permitted to run up a count whose predetermined limit represents the estimated maximum time period during which a sensor system should operate without contacting an object. Return signals, whether from objects in the active zone or the monitor zone, reset the counter back to zero.

Abstract: An intrinsically safe or an explosion proof pilot light having a cluster of light emitting diodes arranged in a pattern and visible through a lense cap located in a hazardous area. The pilot light has terminals connected through a rectifying bridge and a current regulator to the diodes to optimize the light output of the diodes and make the pilot light insensitive to the polarity or variations in the voltage of the A.C. or D.C. electrical supply to the pilot light and limiting the current to the diodes to a constant value in event one or more of the diodes is destroyed or shorted. A pair of printed circuit boards are spaced by a plurality of conductive supports with one of the boards mounted on a base of the pilot light and carrying the rectifier and current limiting components which are connected to the terminals. The other printed circuit board provides a support for the diodes and has a printed circuit thereon, portions of which provide a reflective surface for light emitted by the diodes.