Modern power quality monitors are digital devices, which
can capture voltage and/or current waveforms; typically using
a sample frequency of 10 to 50 kHz. Figure 2 shows an
example of a power quality monitor; the Ranger PM7000 [4].
In theory, the sample rate needs to be at least twice the
maximum frequency being measured. Practically, the sample
rate should be nearer to ten times the maximum frequency
being measured to reproduce the original waveform [5]. This
means that a power quality monitor sampling at 50 kHz
would be able to capture transient waveforms up to 5 kHz in
detail.