Robertshaw Controls Company

Dennis E Newell

Hugh J Tyler

Method and apparatus for monitoring a plurality of thermal parameters and the pressure related work load of a motor-compressor unit utilized in a heat pump system and providing protection for the motor-compressor by turning off the system for time periods dependent upon which parameter caused the system to be turned off.

Method and apparatus for heat pump system protection

A motor control circuit for controlling the operation of a motor having main running-speed windings and also start-up windings includes a fixed time delay circuit to energize the main windings after a time delay following energization of the startup windings. In addition a lock-out circuit is provided to prevent re-start of the circuit following a particular fault condition.

Motor control circuit

A control circuit for a motor usable in a refrigeration system has a variety of condition sensors including means to sense a low refrigerant pressure and timing means to override the sensing of low refrigerant pressure for a time period during motor start-up. A lockout circuit prevents re-start of the motor following a fault condition.

A control circuit, such as a motor control circuit, includes a capacitance connected at one side with a timing resistance to the gate of a field effect transistor (FET) which inhibits energization of a load, such as a motor. The FED controls a semiconductor switch which is connected by a diode to the other side of the capacitance to prevent reactuation of the circuit during a time delay determined by the rate of current flow through a timing resistance to the one side of the capacitance.

Control circuit with time delay

In a protection circuit for a device such as a motor, the unused half or a dedicated half of an AC signal on the secondary of an isolation transformer is sensed to disconnect the AC line from the device if the line voltage is abnormal, such as being too low. Conveniently the protection circuit is employed in a complete motor protection system which may include a thermal protection circuit, a low oil pressure protection circuit, and/or a time delay circuit to prevent start-up too soon after shut-down.

Voltage protection circuit

A motor protection circuit employs a resistance bridge circuit with one side having multiple branches containing temperature responsive resistances for sensing an overheat condition in the motor. Semiconductor voltage sensing devices, such as high gain amplifiers, are responsive to voltages between a standard sensing node and each of the sensing nodes in the multiple branched side of the bridge circuit. Logic facilities respond to any of the sensing devices to operate switching facilities controlling energization of the motor. Additionally, the protection circuit may include a lubricating oil pressure responsive control which is not affected by power loss or spurious signals, and which may be controlled by the operation of a motor control switch.

Motor protection circuit

A contactor or switch to an electrically powered unit, such as a motor, is controlled by a condition responsive circuit which may include facilities for changing the response condition of the circuit and/or facilities responsive to several conditions, such as temperature and excessive current.

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El Segundo, CA, United States of America

Dennis E Newell