Protective method and circuit arrangement for appliance incorpor

Details Protective method and circuit arrangement for appliance incorpor Protective method and circuit arrangement for appliance incorpor

1982-01-07

1984-01-03

Paschall, M. H.

Electric heating

Heating devices

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

219492, 219517, 219544, 361 42, 338238, H05B 102

Patent

active

044244398

ABSTRACT:
A protective control arrangement for heating units of the type comprising the concentric assembly of a resistance heating element embedded in an insulating material and enclosed within a metallic sheath for limiting the propagation of a rupture in the sheath resulting from an arc at a discontinuity in the heating element along a substantial portion of the length of the sheath. The control arrangement of the illustrative embodiment includes a power control triac operatively connected to the heating element for selectively coupling the heating element to an external power supply. A preprogrammed microprocessor operatively connected to the gate terminal of triac is effective to periodically interrupt power to the heating element by opening the switch means for interrupt periods of predetermined duration. The time between successive ones of these interrupt periods is determined such that extinction of any arc which may develop at a discontinuity in the heating element occurs before any resultant separation can propagate along a substantial portion of the sheath; and the duration of each of these interrupt periods is at least approximately equal to the nominal recovery time for the insulating material required to allow the insulating material to return from its relatively low resistance molten and plasma state to its relatively high resistance state. By periodically interrupting energization of the heating unit in this manner, any arc which occurs is extinguished by the next occurring interrupt period.

REFERENCES:
patent: 3789190 (1974-01-01), Orosy et al.
patent: 3881085 (1975-04-01), Traister
patent: 4109134 (1978-08-01), Van Herten
patent: 4219857 (1980-08-01), Haraldsson et al.

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