High 3rd harmonic on the neutral

To a physicist, the definition of frequency is subtly different, and relates to the concept of cyclostationarity - not a made up word I promise. - namely that a full 'cycle'  has only passed when you get back to the same (or at least an indistinguishable ) place on the waveform again (so it looks stationary, if you move back and forth one cycle you cannot tell you have moved) - so the waveform may have all sorts of fast ringing, and maybe multiple zero-crossings, but the repetition period, and therefore the fundamental frequency only relates to the repetition of the full pattern.

Anyone who has tried to line up flowered wall paper while decorating, where the pattern cuts more than one flower that looks similar, will be familiar with this problem, and the related one of variable phase modulation as the paper stretches a bit once pasted and you hang it under its own weight before brushing it - though not all of us will use the same language to describe it. ( even me ! )


 For a more electrical example,  if we had a circuit design that suppressed every 10th cycle from the mains, substituting a flat line for 20ms between bursts of 9 oscillations, then by the physics definition you would have a 5Hz fundamental, though the 50Hz component would be stronger (being present for 90% of the time after all). A spectrum analysis would show this correctly (thanks Mr Fourier), but any frequency counter based on zero crossings would read 45Hz, although that is one frequency clearly not really present in the generation of the waveform  (!)

regards Mike.

To a physicist, the definition of frequency is subtly different, and relates to the concept of cyclostationarity - not a made up word I promise. - namely that a full 'cycle'  has only passed when you get back to the same (or at least an indistinguishable ) place on the waveform again (so it looks stationary, if you move back and forth one cycle you cannot tell you have moved) - so the waveform may have all sorts of fast ringing, and maybe multiple zero-crossings, but the repetition period, and therefore the fundamental frequency only relates to the repetition of the full pattern.

Anyone who has tried to line up flowered wall paper while decorating, where the pattern cuts more than one flower that looks similar, will be familiar with this problem, and the related one of variable phase modulation as the paper stretches a bit once pasted and you hang it under its own weight before brushing it - though not all of us will use the same language to describe it. ( even me ! )


 For a more electrical example,  if we had a circuit design that suppressed every 10th cycle from the mains, substituting a flat line for 20ms between bursts of 9 oscillations, then by the physics definition you would have a 5Hz fundamental, though the 50Hz component would be stronger (being present for 90% of the time after all). A spectrum analysis would show this correctly (thanks Mr Fourier), but any frequency counter based on zero crossings would read 45Hz, although that is one frequency clearly not really present in the generation of the waveform  (!)

regards Mike.