ELECTROMAGNETIC FIELD FAST PULSES MEASUREMENT

The measurement of fast electromagnetic transients such as NEMP, IEMI or lightning requires realtime sensors with a broadband linear response. B-dot and D-dot derivative field sensors are small broadband antennas designed to measure fast electromagnetic transients down to less than a nanosecond.

The size of the precisely shaped field sensing element defines the sensor transfer function : a larger sensor has a better sensitivity, but a lower frequency limit as its dimensions are not suited for the measurement of short wavelenghts. On the opposite a small sensor has less sensitivity but can measure faster transients.

A typical measurement chain comprises a B-dot or D-dot sensor, a balun, an optical transmission system and an oscilloscope.

The electromagnetic coupling on cables and on electronic circuits may induce quite large measurement errors. The sensor, balun and optical transmitter module are exposed to the electromagnetic transient and shall be well designed and shielded to ensure a precise measurement.

The optical fibre cable enables measurements to be taken over distances of up to 1 km, what authorises the installation of the measurement receiver (i.e. the oscilloscope) at a long safe distance from the electromagnetic source. If this is not possible, the measurement receiver shall be installed in a shielded enclosure or in a shielded room.

It is not obvious for non-experts to determine the transfer function of a measurement chain made of a derivative sensor, a balun, some attenuators, an optical transmission link and a numerical integration. Montena has developped PULSELab, a software application dedicated to measurement of electric and electromagnetic transients. PULSELab tremendously eases the measurement by taking in account the transfer functions of each componant of the measurement chain and delivering the measured electromagnetic field transient in its native unit (V, A, V/m or A/m).

Montena proposes a full range of measurement equipment and software applications especially designed for the measurement of electromagnetic pulses, as for instance the NEMP.