Output Voltage vs. Firing Rate (fwd)

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Output Voltage vs. Firing Rate (fwd)
From: Tesla List <tesla-at-stic-dot-net>
Date: Fri, 14 Aug 1998 23:45:40 -0500
Approved: tesla-at-stic-dot-net

----------
From:  FutureT-at-aol-dot-com [SMTP:FutureT-at-aol-dot-com]
Sent:  Friday, August 14, 1998 9:08 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: Output Voltage vs. Firing Rate (fwd)

Antonio, all,

I hadn't realized about the rms problem.  This wattmeter says it's 
accurate to 1/4 of 1 % up to 125 Hz.  I wonder how severe the errors
might be?  Has anyone compared such wattmeters with true (electronic)
reading wattmeters in TC circuits to get a ball park figure of possible
errors?

I posted a long post some time ago telling of my wattmeter vs.
thermocouple tests and didn't get any responses, so i had thought the 
tests were valid.

I wonder if we're talking 10%, 30%, or 200% error.  Someone once
suggested they thought the errors might be around 10% using a
wattmeter.  Does this seem reasonable?

Also any clue as to how inaccurate the rms technique might be
(ignoring power factor issues for now)?

Thanks,

John Freau
--------------------------------------------

In a message dated 98-08-14 01:31:18 EDT, you write:

<< ---------
 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
  >>