Fellow travelers,
I'm pleased to see the explanations put forward on this discussion
thread.
It all fits with my own issue of measuring Touch Current leaking to
ground which has grown with the advent of SMPS.
If you want to see a collexion of TC waveforms that I've collected
>from an assortment of equipment go to Art Michael's www.safetylink.com and
search on my name (Perkins) and you will find the waveform paper.
My ongoing interest has been in the LF portion of this current (up
to 1 MHz) rather than the HF EMC effects.
But the data shows that the current to earth has grown away from
sinusoidal waveforms since SMPS were introduced in equipment. As some have
noticed, the crappiness factor has increased with time, especially with the
addition of PFC.
We electric shock folks understand that the body reacts to peak
currents rather than the RMS currents normally considered in safety
standards. Getting rid of those old RMS meters and moving to a peak reading
meter or scope gets to the correct TC value to be considered for protection
>from electric shock. A large portion of the world still lives in the Dark
Ages in this regard.
I remember dealing with the triplen harmonics in the 80's when they
were not well understood or attributed to SMPS in 3 phase systems. The
resulting transformer fires from these harmonics which circulated in delta
primaries clouded the analysis (not my problem seemed to be a first analysis
result). Accepting responsibility allowed the problem to be addressed in a
rational way.
As with all of life, unintended consequences cloud perfectly clear
decisions that were made in good faith.
So all our lives keep getting more difficult as the technology is
improved.
Well, us technical folks see trouble as opportunity.
Keep the faith.
Enjoy the waveforms. :>)
Br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
[email protected]
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