Ward & Goldstone Limited

Salplex Limited

Michael J Hampshire

Norman J Poole

John Parkes

Jonathan H Williamson

A switching circuit has a solid state power switch (9) which is either a PNP or NPN transistor or a VMOS p- or n-channel device. Three individual sensing circuits (2, 3, 4) are set to indicate whether a predetermined operating characteristic of the switch (9) is greater or less than a given threshold value and thus to indicate if a fault is present in the switch (9) or the load (L) it supplies. Digital logic circuit means comprising three logic circuits (5, 6, 8) produce two digital signals from the output signals of the sensing circuits respectively indicating if a fault exists and if it is a serious fault or not. A circuit (7) comprising gating means disables the switch (9) in the event of a serious fault and a delay circuit (33, 34) is provided associated with the logic circuit means to prevent current surges due to short circuit faults being confused with normal operating current surges in switch on.

Switching circuit

A multiplex information handling system for a vehicle has a number of transmitters and receivers all interconnected by a common power bus and signal bus. The transmitters transmit signals along the signal bus representing the operational state of control equipment or equipment controlled by that equipment and the receivers respond to and act on such signals to, for example, authorize the display of information received or the initiation of a control function. System management and supervision is provided, such that, where the transmission of certain signal states is made dependent upon the state of other signals in the system, this dependence can be overridden, for example, for vehicle servicing. Supervision also provides for certain urgent signals to be given priority over other signals.

Multiplex information handling system

A multiplex information handling system comprises a series of electronic processing units each comprising a receiver and a transmitter and each having an electronic address in binary form. The units are joined by a coaxial cable which in operation carries power along the cable sheath and information signals in binary form along the central core. Each unit controls the operational state of various items of equipment, for example of a vehicle, and receives and transmits signals controlling and representing those states. All units receive all transmitted signals, the correct signal being directed to the correct item of equipment by producing the correct unit address at the head of each information signal. The transmitters transmit repeatedly and sequentially, all transmitters being inhibited from transmitting except the transmitter transmitting at the time. The information concerning the operational states of the various items of equipment is therefor continually updated.

An open ended can has a piezoelectric crystal attached to its closed end face and contains within it the battery supply and circuitry operative to cause the can to resonate. The can is attached at its open end to a back board through a ring of closed cell foamed synthetic plastics material to form a waterproof enclosure for battery and circuitry. The circuitry is based on one or more CMOS integrated circuits having gates or inverters connected to form one or more oscillators and one of the oscillator pulses the crystal through a transistor power amplifier and step up transformer. That oscillator may be adjusted off the resonant frequency to reduce the output or a feedback path provided to lock the oscillator onto a resonant frequency.

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Liversedge, United Kingdom

Michael J Hampshire