On 8/14/2012 1:51 PM, David Roberson wrote:
He suggested that there was .5 volts across the coil when grounded. I
assume that he broke the ground and then connected some form of meter
across the turns. I suspect that this reading was not accurate and
most likely external noise or possibly RF interference to his meter.
Without making the measurements myself, I can only be skeptical as to
the actual effects.
Dave
To me it looks simpler: only that he grounded one coil terminal so that
he could conveniently measure the voltage at the other. This /does
/imply that the coil circuit is normally "floating", which is possible
if not likely.
For an example of "convenient", he may not have trusted the accuracy or
bandwidth of the usual handheld meter, or if a scope he may not have the
money for a scope that uses a balanced differential dual probe, and so
needed a single-ended measurement, - and thus the grounding.
Before differential scope inputs were affordable, and a certain waveform
just had to be seen, we on occasion had to "float" our scope at whatever
ungodly voltage and waveform was there, to accurately see what was
across a component. Tore the safety ground out of the scope power cord,
and then, /we were very careful! / lol.
Yours,
Ol' Bab, who was an engineer.
