Motor control system including motor protector and remote sensor for controlling motor operation

Claim 2

A control for an electric motor the operation of which motor affects the value of at least one variable parameter of a system at a distance remote from said motor, said control comprising: a thermostatic motor protector including a temperature-sensitive switch for selectively interrupting the flow of current from an electric power source to said motor, said protector including a heater in heat exchange relationship with said switch for effecting operation thereof, said heater being adapted to effect operation of said temperature-sensitive switch in response to overloading of said motor and in response to predetermined changes in the variable parameter in the remote system, a thermistor having a resistance which varies in response to changes in the value of said parameter, said thermistor being disposed at a location remote from said motor, and in thermal communication with the variable parameter; and means interconnecting said heater and said thermistor for varying the energization of said heater as a function of the value of the variable parameter to effect deenergization of the motor when the value of the parameter crosses a predetermined threshold.

Claim 3

A control as set forth in claim 1 wherein said thermistor and said heater are connected in series across said electric power source.

Claim 4

A control as set forth in claim 2 wherein said thermistor has a negative temperature coefficient of resistivity.

Claim 5

A control as set forth in claim 3 wherein said thermistor has a transition temperature above which the resistance of said thermistor decreases relatively abruptly.

Claim 6

A control as set forth in claim 1 wherein said protector further includes a second heater, said second heater being in heat exchange relationship with said switch and connected in series with said motor for operating said switch when said motor draws an overload current.

Claim 7

A control as set forth in claim 5 wherein said first heater and said thermistor are connected in series across said second heater whereby the sensitivity of said thermistor to variations in the value of said parameter varies as a function of the current drawn by said motor.

Claim 8

A control as set forth in claim 1 wherein said heater is connected in series with said motor for operating said switch to deenergize said motor when said motor draws an overload current.

Claim 9

A control as set forth in claim 7 wherein said thermistor is connected across said heater.

Claim 10

A control as set forth in claim 8 wherein said thermistor has a positive temperature coefficient of resistivity.

Claim 11

A control as set forth in claim 9 wherein said thermistor has a transition temperature above which the resistance of said thermistor increases relatively abruptly.

Claim 12

A control as set forth in claim 1 wherein said switch comprises a snap-acting bimetal disc.

Claim 13

A control for an electric motor the operation of which motor affects the value of at least one variable parameter of a system at a distance remote from said motor, said control comprising: a thermistor having a resistance which varies in response to changes in the value of said parameter, said thermistor beinG disposed at a location remote from said motor; and a thermostatic motor protector including a single temperature-sensitive switch for selectively interrupting the flow of current from an electric power source to said motor in response to overloading of the motor and in response to changes in the resistance of said remote thermistor, said protector including a first heater in heat exchange relationship with said switch and connected in series with said motor for operating said switch when said motor draws an overload current and a second heater electrically coupled to said remote thermistor the energization of said second heater being controlled by the resistance of said remote thermistor, said second heater also being in heat exchange relationship with said switch for effecting operation of said switch in response to predetermined variations in the parameter to effect deenergization of the motor when the value of said parameter crosses a predetermined threshold.

Claim 14

A control for an electric motor the operation of which motor affects the value of at least one variable parameter of a system at a distance remote from said motor, said control comprising: a thermistor having a resistance which varies in response to changes in the value of said parameter, said thermistor beinG disposed at a location remote from said motor; and a thermostatic motor protector including a single temperature-sensitive switch for selectively interrupting the flow of current from an electric power source to said motor in response to overloading of the motor and in response to changes in the resistance of said remote thermistor, said protector including a first heater in heat exchange relationship with said switch and connected in series with said motor for operating said switch when said motor draws an overload current and a second heater electrically coupled to said remote thermistor the energization of said second heater being controlled by the resistance of said remote thermistor, said second heater also being in heat exchange relationship with said switch for effecting operation of said switch in response to predetermined variations in the parameter to effect deenergization of the motor when the value of said parameter crosses a predetermined threshold.

Claim 15

A control as set forth in claim 12 wherein said thermistor and said second heater are connected in series across said source.

Claim 16

A control for a three-phase electric motor having three windings, the operation of which motor affects the value of at least one variable parameter of a system at a distance from said motor, said control comprising: a thermistor having a resistance which varies in response to changes in the value of said parameter; and a thermostatic motor protector including three heaters each respectively connected in series with one of said windings and temperature-sensitive switching means in heat exchange relationship with said heaters for interrupting the flow of current from an electric power source to said windings, said protector including also a fourth heater the energization of which is controlled by the resistance of said thermistor said fourth heater also being in heat exchange relationship with said switch whereby said motor is deenergized if the value of said parameter crosses a predetermined threshold.

Claim 17

A control for a three-phase electric motor having three windings, the operation of which motor affects the value of at least one variable parameter of a system at a distance from said motor, said control comprising: a thermistor having a resistance which varies in response to changes in the value of said parameter; and a thermostatic motor protector including three heaters each respectively connected in series with one of said windings and temperature-sensitive switching means in heat exchange relationship with said heaters for interrupting the flow of current from an electric power source to said windings, said protector including also a fourth heater the energization of which is controlled by the resistance of said thermistor said fourth heater also being in heat exchange relationship with said switch whereby said motor is deenergized if the value of said parameter crosses a predetermined threshold.

Claim 18

A control as set forth in claim 14 wherein said switching means connects said windings to a neutral terminal and wherein said thermistor and said fourth heater are connected in series across one of said windings.