Heating circuits for detection of localized overheating

Details Heating circuits for detection of localized overheating Heating circuits for detection of localized overheating

1978-08-14

1980-05-27

Reynolds, B. A.

Electric heating

Heating devices

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

219492, 219505, 219508, 219212, H05B 102

Patent

active

042052238

ABSTRACT:
A heating circuit comprises input terminals for connection to an AC supply, an elongate heating conductor and a switch connected in series between the input terminals, a switch control operative to close the switch to cause AC current to flow from the supply through the heating conductor, an elongate sensor conductor spaced from the heating conductor, and a temperature sensitive element disposed between the heating and sensor conductors and responsive to over-heating at any position along the length of the heating conductor to drop substantially in impedance at that position to connect the sensor conductor to the potential of the heating conductor at that position. The heating circuit further comprises a voltage detector to cause the control, while the control is operative to close the switch, to periodically open the switch so that the heating conductor is at substantially the same potential along its length, and a sensor to sense the potential on the sensor conductor during each periodic opening of the switch and responsive to the potential being such as to indicate that there is an overheat at any position along the length of the heating conductor to prevent subsequent re-closure of the switch. Periodically switching off the switch and sensing the potential on the sensor conductor at that time enables reliable detection of localized overheating at any position along the length of the heating conductor, because due to the heating conductor not passing heating current there is no voltage drop along its length.

REFERENCES:
patent: 2831099 (1958-04-01), Crowley
patent: 3789190 (1974-01-01), Orosy et al.
patent: 3814899 (1974-06-01), Gordon, Jr. et al.
patent: 3920955 (1975-11-01), Nakata

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