Minature Rogowski probes upgraded for power electronics market

17th September 2007
Posted By : ES Admin
Minature Rogowski probes upgraded for power electronics market
The highly successful CWT Ultra Mini range of ac current transducers from Power Electronic Measurements Ltd have been upgraded with improved mechanical features and uprated high frequency performance. The units feature a clip-around Rogowski coil thin enough (maximum cross section only 1.7mm) to ensure that it fits between the legs of a T0220 semiconductor device and also making it easier for use in confined spaces. Six models are available in the range covering sensitivity from 200 to 5.0mV/A with corresponding peak currents of 30 to 1200A. Higher current ranges can be made available on request.
These devices are ideal for measuring switching transients, sinusoids and pulsed currents of between 1 and 1200A in power electronic installations. Other applications include:
- Semiconductor switching waveforms in otherwise inaccessible areas of circuitry.
- High frequency sinusoidal, pulsed and transient currents.
- Ac currents superimposed on large dc currents.
- Harmonic current components.

The mechanical improvements to the product include the use of a new, tough and abrasion resistant coil insulation, together with a robust new coil clip-together mechanism and a rated peak voltage insulation of 1.2kV.

These are accompanied by improvements to the high frequency performance now covering -3dB bandwidth of 20MHz regardless of current rating. In addition, there is improved peak di/dt capability across the range, and capability of loading into 50 ohm to drive long output cables.

The established features of this equipment include typical accuracy of ±2%. The Rogowski coil loads circuits under test by only a few pH’s, while the circuit does not need to be altered to accommodate a bulky current probe which would effectively alter the circuit performance. The probe is also wide-bandwidth from a few tens of Hz to 20MHz enabling measurements of rapidly changing currents or relatively long duration pulses of several tens of microseconds (even hundreds for the higher current ratings). The instrument also provides an isolated measurement at ground potential (unlike co-axial shunts in high sided applications).

The Rogowski coil cable has a circumference length of 80mm, and cable length between integrator box and coil is one metre as standard. Operating temperatures are 0° to +40°C for the integrator and
-10°C to +70°C for the Rogowski coil assembly (with further information for operation at higher temperatures soon to be available).

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