| 摘要 |
PURPOSE:To attain miniaturization and ease of settling processing by adding a settling value to an AC analog input, applying A/D conversion to the added result, separating the added result into an input amount and the settling value and applying comparison based on the input amount and settling value. CONSTITUTION:A current detected by a current transformer CT is inputted to an adder circuit 9 as a voltage Vin through a load resistor (r), while a DC settling value set by a setting section 10 is inutted to the circuit 9. An output of the circuit 9 is subject to sample-and-hold 2 via an LPF 1, scanned sequentially by a multiplexer 3 and converted into a digital quantity by an A/D converter 4. The digital output is fed to a CPU, which uses a fundamental wave extraction filter 7 to extract an input signal fundamental wave from the digital quantity for effective value conversion. Further, the DC component is extracted by a DC component extraction digital filter 8. The effective value and the input quantity converted into the DC settling value are compared and when the result of operation of the effective value is larger than the settling value, the CPU generates an output as overcurrent taken place in the power system. |
