Resolutions of digital recorder and evaluated impulse voltage waveform parameters

Whereas high resolution digital recorders are used in recording the impulse voltage tests in prominent accreditation laboratories worldwide, a usage of an 8 bit recorder is also allowed by IEC publication. An 8 bit recorder is, due to its nature, known to record a waveform with 0,4% vertical resolution and it has not been appreciated for determining a peak value of lightning impulse in the reference measuring system where the scale factor is often evaluated with 0,1% or better uncertainty. This paper demonstrates simulation in which an 8 bit record with an internal noise is fed into the lightning impulse parameter determination software and the computed parameters were compared with theoretical values. The results show that, if suitable software is used, errors in parameters deduced from an 8 bit record is as small as those derived from a 12 bit record, suggesting an inexpensive 8 bit recorder can replace a 12 bit recorder in the reference measuring system for the impulse voltage measurements.