PURPOSE: To prevent a locking phenomenon from generating by a method wherein the driving current of an electrically driven pump is continuously or periodically measured, and the generating and growing states of a locking cause of the pump are judged based on an absolute value of the driving current, and the pattern of an instantaneous variation of the driving current.
CONSTITUTION: A clamp meter 3 is installed on an electric supply line of an induction motor 2, and the current value is detected, and the detected signal is input in an automatic predicting device 4. The input signal is converted into a voltage signal by a current/voltage converter 4a, and is input in operation circuits 4b, 4c, and an operation is performed with an interval of a specified period of time by a timer circuit 4f of the operation circuits 4b, 4c. The operation result is input in a judgement circuit 4d, and a generation of an abnormal current which is an indication of a pump locking is judged when the operation circuits 4b and 4c are formed, and a warning lamp 5 or alarm buzzer 6 is operated, and at the same time, the judgement is stored in a memory device 4e. By this method, a locking phenomenon can be prevented from generating.
TAMURA SHUNSUKE
NAKAJIMA TOMIO
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