PEM introduces low frequency measurement probe

An LFR AC probe with low frequency performance has been introduced by Power Electronic Measurements (PEM).

This compact, clip-around probe is dual range, optimised to give minimal phase measurement error at frequencies from 45Hz to 20kHz.

It is a Rogowski current probe, similar to PEM's CWT range, which covers 1Hz to 20MHz.

The LFR unit can be used as a general purpose power frequency AC probe with oscilloscopes, acquisition cards, data loggers, power analysers and meters.

Other applications include power measurement, leakage current and power quality where minimal phase error, low noise and accuracy are key measurement criteria.

All Rogowski current probes generate noise, but the noise floor of the LFR is very small, and the LFR1/15 model is only 2.0mVrms on the 300A range.

The rated output voltage is 6Vpeak for a 300A peak current, thus at 20-per-cent-rated current the noise contributes less than 0.1deg additional uncertainty to the phase error.

The same unit with peak current rating 300A/3000A and coil length of 300mm has minimal phase measurement error at 50Hz of <0.35deg and at 20kHz of <1.8deg.

Each probe is supplied with a traceable calibration certificate, with the probe calibrated to an accuracy of +/-0.3 per cent of reading with a conductor central in the LFR coil loop.

If the conductor is large and fills the coil area, or the conductor is kept central, the overall accuracy will approach the calibrated value.

Even if the conductor is not central the LFR's accurately-wound coil keeps the variation in accuracy with position to typically +/-1 per cent.

The LFR has a flexible, clip-around coil of 8.5mm thickness, which enables measurement in confined spaces or with otherwise difficult to reach cables and busbars.

The probe is non-intrusive, very linear with current magnitude and frequency, undamaged by overloads and the coil size can be specified independently of current magnitude.

The instrument can be specified with coil lengths 300 to 1000mm as standard, with longer coils also available.

It is EN61010 safety compliant and can be powered by either a single 9V battery or an external 12/24V DC supply, with alternative power supplies also possible.

It features a dual-range switch allowing measurement ranges from 60A/600A to 6kA/60kA.

It is also suitable for operation within a temperature range of -20C to +70C.

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