| 摘要 |
PURPOSE:To make it possible to obtain effect equal to the detection of a current wave form, by automatically changing over the current wave form of a current supply line to the detection of a voltage wave form even if a detection difficult state is brought because of the extreme lowering in a load current. CONSTITUTION:A current is supplied to load 1 from a single phase AC power source through a current supply line 2 and a current transformer 3 applies a measured current proportional to the current flowing the current supply line 2 to obtain voltage proportional to the voltage of the current supply line 2 at both ends of the secondary winding of a transformer 5. The values of the current transformer 3 and the transformer 5 and the values of resistors R1, R2, R3 are set so as to sufficiently lower the current due to the transformer 5 among synthesized currents as compared with the detection current due to the current transformer 3. A current wave form is sent out from a load current is not lowered but, when it is detected that load current is lowered to the set value or less, a change-over order circuit 9 sends a change-over order signal to a change- over control circuit 10 which in turn changes over the wave form output thereof to voltage mode from a current mode.
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