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Output Voltage vs. Firing Rate (fwd)
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From: Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
Sent: Friday, August 14, 1998 12:52 AM
To: Tesla List
Subject: Re: Output Voltage vs. Firing Rate (fwd)
John Freau wrote:
> At the 640 watts using 120BPS, I've carefully checked out the wattage
> using a thermocouple type ammeter, checked the power factor, then
> compared, etc. I found the wattmeter to be accurate within a few
> percent.
Some comments:
A termocouple ammeter measures the RMS current, including harmonics. A
fuse also "measures" the total RMS current. The problem is that, if the
input voltage can be considered as a 60 Hz sinusoid, only the 60 Hz
component of the input current contributes to the average input power.
Power measurements using the RMS current will always appear too high
(assuming that it is possible to measure the phase angle between voltage
and the 60 Hz component of the current).
A perfect moving-coil wattmeter -should- measure correctly the input
power, even with distorted waveforms. The problem is that they may filter
out high-frequency components. But if the voltage is a 60 Hz sinusoid,
the filtering of the current harmonics is not important, as they do not
contribute to the input average power.
Antonio Carlos M. de Queiroz