초록 ▼

A motor overload protection system (OL) that has a speed of operation fast enough so that it will always trip before the power switch (MC) has had time to operate if the turn-on control means (ON) is operated under overload conditions. In one version, modules (OL1,OL2) are provided having PTC thermi

A motor overload protection system (OL) that has a speed of operation fast enough so that it will always trip before the power switch (MC) has had time to operate if the turn-on control means (ON) is operated under overload conditions. In one version, modules (OL1,OL2) are provided having PTC thermistor sensors (PTC1,PTC2) bonded to resistance heaters (H1,H2) connected in the motor power circuit (L1,L2,L3), these sensors being supplied from a current source (CT) and being effective to shunt current to a protective trip device (TR) upon occurrence of an overload condition, there being an ambient temperature compensating PTC themistor (PTC3) in series in the sensor circuit (OLC). In another version, a thermal mass (TM) is preheated above ambient temperature by an ambient temperature compensating PTC thermistor (ATC) operated above its switching temperature level and a sensor PTC thermistor (ST) and a heater (HT) are also thermally coupled to the thermal mass (TM) with a bias resistor (R1) connected to the sensor thermistor (ST) to provide a step voltage output (OUT) on overload. The heater may be a PTC thermistor (HT) having a higher switching temperature for self-shutoff on higher than usual overload or may be a resistance heater (H3) with a PTC thermistor (TP) in series therewith for self-shutoff.

대표청구항 ▼

A modular thermistor overload protection system comprising: a power circuit including an electrical power supply source and a load device; switching means operable to connect said load device to said source and to disconnect said load device therefrom thereby to selectively energize or deenergize sa

A modular thermistor overload protection system comprising: a power circuit including an electrical power supply source and a load device; switching means operable to connect said load device to said source and to disconnect said load device therefrom thereby to selectively energize or deenergize said load device; control means for operating said switching means; and protective means operable to sense an overload trip current in said power circuit and trip said switching means so as to cause said switching means to disconnect said load device from said source comprising: trip means for directly tripping said switching means without delay; a thermistor sensor in circuit with said trip means and having a switching temperature level at which its resistance abruptly changes; a control circuit for applying an electrical bias to said thermistor sensor; heater means responsive to an overload trip current in said power circuit for heating said thermistor sensor to its switching temperature level whereby its abrupt change in resistance causes direct operation of said trip means; and the speed of operation of said protective means being fast enough due to said direct operation of said trip means so that said trip means will always trip before said switching means has had time to operate long enough to apply enough power to cause motor energization if said control means is operated to apply power under overload conditions.