Positive temperature coefficient transition sensor

Details Positive temperature coefficient transition sensor Positive temperature coefficient transition sensor

1993-12-15

1996-02-20

Paschall, Mark H.

Electric heating

Heating devices

With power supply and voltage or current regulation or...

219506, 219505, 219481, H05B 102

Patent

active

054931010

ABSTRACT:
A transition sensor is responsive to transition of a positive temperature coefficient resistive element from a nominal low resistance state to a protective high resistance state. A positive temperature coefficient (PTC) element is placed in a power distribution circuit between a power source and a load. Excessive load current in the event of a high current fault heats the PTC element to a threshold temperature at which the PTC element transitions into a protective state of high resistance, limiting current flow to the load. The LED of an optoisolator is coupled in parallel with the PTC element, preferably with a resistor in series with the LED. Under nominal current conditions the voltage across the LED is less than its forward bias voltage. During a high current fault, the LED becomes forward biased and switches on the optoisolator phototransistor to operate an alerting device such as an audible alarm and/or a light. A relay can be coupled to the phototransistor for decoupling the load and the PTC element from the power source, and preferably is arranged to latch in the protective position when tripped. The invention is applicable to direct current or alternating current and single or multi-phase applications. Optocouplers with reversed polarity LEDs are used for alternating current, one pair for each phase, with the optocoupler phototransistors coupled in parallel to operate the alerting device and/or relay.

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patent: 5064997 (1991-11-01), Fang et al.
PTC Application Notes, Keystone Carbon Company Bulletin T-929, pp. 34-42.
PCT/SE91/00076, Feb. 4, 1991, Hansson et al.
PCT/SE91/00375, May 28, 1991, Hasson et al.

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