David C Squiers

US Patent:

40756742, Feb 21, 1978

Filed:

Dec 5, 1975

Appl. No.:

5/637912

Inventors:

David J. Squiers - Attleboro Falls MA
Robert E. Obenhaus - South Easton MA

Assignee:

Texas Instruments Incorporated - Dallas TX

International Classification:

H02H 504

US Classification:

361 27

Abstract:

The disclosure relates to a protection system for electric motors and the like wherein a plurality of condition responsive PTC impedances are utilized in a bridge circuit to sense predetermined changes in the condition being sensed and proceed to interrupt current flow to a motor or the like being protected. The protection circuit is capable of sensing short circuits or impedances below a predetermined minimum across the sensors to thereby provide an alarm condition also. On the occurrence of the alarm condition, a lockout circuit is energized to prevent application of power to the motor, etc. until after power has been removed from the entire electric circuit and then reapplied thereto. The protection circuit of the present disclosure is also capable of either automatic or manual reset. There is also provided a pop-up flag and remote overload light which can be operated upon sensing of an alarm condition.