Electrothermal wire responsive miniature precision current sensor

An overcurrent protection system for an electrical supply circuit comprising:

• a housing comprising a base and a cover;
• a first pair of electrical terminals mounted on said base;
• an electrical resistance wire element;
• means connecting and supporting said resistance wire element on said terminals within said housing so as to conduct the supply current of an electrical supply connected to said first pair of terminals;
• a substrate mounted on said connecting and supporting means;
• an ambient temperature sensing diode mounted on said substrate;
• a hot temperature sensing diode mounted to said resistance wire element for sensing the temperature thereof proportional to the current flowing therein;
• second and third pairs of terminals mounted on said base and means connecting said diodes respectively thereto;
• an electronic circuit connected to said second and third pairs of terminals for providing a differential signal proportional to the temperature of said resistance wire element above ambient temperature;
• and means responsive to said differential signal when said supply current rises to the overload value for providing a trip signal.

An electrothermal current sensor for low amperage overload trip service comprising:

• a resistance wire sensor element connected in a low amperage electric power supply line for heating in proportion to electric current flow therethrough;
• said resistance wire sensor element being composed of an alloy having a response time for heating that provides a built-in delay to spurious transients that might occur on the power supply line;
• said wire sensor element being operable to control the current ranges within which said wire effectively produces heat in proportion to given currents therein by varying the wire diameter or the wire length;
• said wire sensor element being equally effective for heating in proportion to D.C. current or RMS A.C. current;
• said wire sensor element providing a back-up current limiting fusible link function in the event currents well in excess of the sensing range in magnitude and duration occur in said power supply line and fusing of said wire sensor element causing the current to be interrupted;
• a housing comprising a header;
• said resistance wire sensor element connected at its ends to a pair of terminals mounted on said header and being substantially M-shaped;
• a substrate mounted between said terminals within said housing;
• an ambient temperature sensing solid state diode mounted on said substrate;
• a heat sensing solid state diode mounted at substantially the midpoint of said resistance wire sensor element;
• and said ambient temperature diode and said heat sensing diode being connected to pairs of terminals supported on said header.