Re: Coil Efficiency (and true wattmeter)
Sent: Thursday, June 26, 1997 4:01 AM
Subject: Re: Coil Efficiency (and true wattmeter)
> Agreed. I think that's where a lot of false figures are coming from.
>In many cases the waveforms are terrible. However, I have scoped
> transformer primary currents using a very low value resistor in series
> and probing across it with an isolated scope which not only shows
> waveform but peak current as well. For an RMS figure, a bit of
> calculus can be used. A valve scope is a must for a running coil.
> I like your idea better though. The thought of a blown up scope
> makes me blanch.
Thanks, I'll try the EHT probe with scope. By the way, I've been using a
solid state scope to measure my quench times, and it hasn't blown out
yet, so I guess I'll use it for the cap voltage measurement too (maybe
lady luck will continue to be kind to me) :^)
Can you give any idea of the results you've obtained using calculus to
figure the input power compared with an ordinary wattmeter, and how
different the results were with different break-rates? For instance,
(I'll just make this up) suppose wattmeter read 1000 watts at a low
break-rate, did calculus results show (let's say) 700 watts, in other
words a lower figure? And if wattmeter read 1000 watts at a high
break rate, did calculus method show (let's say) 500 watts, or an
even lower figure? Intuition tells me to expect these kinds of general
results...but since I don't trust my intuition very much, I'd be interested
in your general findings...ballpark of course.
I spoke to Dave Sharpe, and he suggested that by using a different
op amp in the opto-wattmeter, that the accuracy can be increased
to 1%. The plans for the opto-wattmeter were published in Electronic
Design magazine, October, 14 1994. This is a solid state unit, so
hopefully it can survive in a Tesla environment with suitable sheilding