FAQ

Measured values vary greatly depending on the measurement range of the leakage current meter.

General MeasurementLogging (Recording)Photograph/DrawingEvent Recording

Issue

When the range of the leakage current meter is changed, the measured value may vary greatly between ranges. Normally, there is no significant difference in the measured value when the range is changed.

Instrument setting conditions

Cause

If the current being measured contains a large harmonic component over the range, the harmonic component cannot be removed correctly.

Countermeasure

When this symptom occurs, please measure with the upper range. For example, if the measured values differ significantly between the 60.00 mA range and 600.0 mA range, 600.0 mA in the upper range is the correct measured value.

Detailed Description

As an example, the following waveforms are measured in the 60.00 mA and 600.0 mA ranges.

For the 60.00 mA range

The specification sheet of the AC leak clamp meter indicates a crest factor of 3. (For the crest factor see below) This means that a waveform with a peak value of 180 mA, which is three times the range, can be measured. It is not possible to correctly measure waveform with a higher peak value. In this example, the peak value of the harmonic component is 300 mA, so it cannot be measured correctly. The leakage current component is lost in the internal circuit of the measuring instrument as shown below. If this waveform is filtered, harmonic components can be removed, but leakage current components cannot be extracted. Therefore, a meaningless number close to 0 mA is displayed as the measured value.

For the 600.0 mA range

Since the crest factor is 3, it can measure up to a waveform with a peak value of 1800 mA, which is three times the range. Since the peak value of the harmonic component is 300 mA, it can be measured correctly. By filtering this waveform, harmonic components can be removed and leakage current components can be extracted.

What is the crest factor?

The crest factor is the ratio of the rms value of the waveform to the peak value.

For a sine wave, the crest factor is 1.4 when the rms value is 100 V because the peak value is 141 V.

The crest factor is specified in the specification sheet as the range that can be correctly measured at the input terminal of the measuring instrument.
As an example, let us assume that the voltmeter specifications has a 600 V range and a crest factor 3.
The 600 V range means that the rms value can be measured up to 600 V. Since the crest factor is 3, it is possible to measure a waveform with an effective value of 600 V with a wave height of 1800 V or less, which is three times that of 600 V. Because the crest factor of sine wave is 1.4, 600 V sine wave can be measured.