LOOP IMPEDANCE METER

摘要

A loop impedance meter for testing A.C. electrical mains supplies, 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, wherein the value of the load resistance measured in ohms is in the range of one sixth to twice times the value of the r.m.s. mains voltage rating of the meter measured in volts, so as to deliver about'/2 A to 6A intermittent current flow. Further, a loop impedance meter is disclosed in which the control circuit is arranged to allow a train of short pulses of current flow through the load resistance and the loop, the pulse train beginning its sequence with a first train of pulses for preconditioning any RCD present in the loop to temporarily desensitise it to one or more measurement pulses which then follow, the pulses of the first train being of generally increasing width. In addition, a loop impedance meter is disclosed in which the control circuit is arranged to: allow a train of short pulses of current flow through the load resistance and the loop, the pulse train beginning its sequence with a first train of pulses for preconditioning any RCD present in the loop to temporarily desensitise it to one or more measurement pulses which then follow; and take reference measurements before, during and after at least one measurement pulse to calculate a compensation for ring generated on each measurement pulse. Also disclosed is a loop impedance meter for testing A.C. electrical mains supplies, comprising 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, wherein the control circuit is arranged to allow a train of short pulses of current flow through the load resistance and the loop, the pulse train comprising measurement pulses of a range of different widths all less than one millisecond, the control means being arranged to extrapolate the impedance measurements to provide an indication of the effective impedance at the A.C. mains supply frequency.