| 摘要 |
A loop impedance meter is provided for testing an A.C. electrical mains supply. The meter comprises an electronic control circuit for connecting a load resistance intermittently between the A.C. mains supply terminal and the earth terminal to measure the potential difference between those terminals and to provide an indication of the loop impedance of the A.C. mains supply from that potential difference. The control circuit is arranged to allow a train of short pulses of current to flow through the load resistance and the loop, the pulse train beginning its sequence with a first train of pulses for preconditioning any residual current device-present in the loop to temporarily desensitize it. The first train of pulses is followed by one or more measurement pulses, the pulses of the first train being of generally increasing width.
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