초록 ▼

An electrical circuit for providing electrical energy to an electric motor which operates a liquid pump. The motor and the pump are adapted to be submerged in the liquid which is pumped by the pump. The circuit disclosed herein senses the phase angle between the current and the voltage applied to th

An electrical circuit for providing electrical energy to an electric motor which operates a liquid pump. The motor and the pump are adapted to be submerged in the liquid which is pumped by the pump. The circuit disclosed herein senses the phase angle between the current and the voltage applied to the electric motor. When the phase angle indicates that the motor is operating without a load, the circuit deenergizes the electric motor. Thus, the motor and the liquid pump are protected against damage. Recognizing that harmonics may exist in the current flow through the motor, the circuit provides for obtaining a filtered signal proportional to the fundamental frequency of the current flowing through the motor. Thus, an accurate measurement of the loading of a motor is obtained. The circuitry of this invention also provides an accurate method of compensation for applied line voltage variations, so that a change in the applied line voltage does not produce a false indication that the motor loading has changed.

대표청구항 ▼

The method of protecting a liquid pump which is operated by an electric motor to which alternating current electrical energy having a fundamental frequency is applied through a plurality of electric conductor members, and a switch operable to connect and to disconnect the electric motor with respect

The method of protecting a liquid pump which is operated by an electric motor to which alternating current electrical energy having a fundamental frequency is applied through a plurality of electric conductor members, and a switch operable to connect and to disconnect the electric motor with respect to the electric conductor members comprising: providing a first voltage signal, the first voltage signal being related to the current flow through the electric conductor members and through the electric motor, attentuating harmonic frequencies which exist in the first voltage signal, providing a second voltage signal, the second voltage signal being related to the voltage of the alternating current electrical energy which is applied to the electric conductor members, sensing the phase angle between the first voltage signal and the second voltage signal and obtaining a phase angle voltage signal proportional to the phase angle, generating a third voltage signal in accordance with the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, modifying the third voltage signal to obtain a fourth voltage signal which compensates for changes in phase angle which occur as a result of variations in the amplitude of the voltage of the alternating current electrical energy which is applied to the electric conductor members, comparing the phase angle voltage signal to the fourth voltage signal, and operating the switch when the difference between the phase angle voltage signal and the fourth voltage signal exceeds a predetermined magnitude.