Re: Input Power Measurement

To: tesla-at-poodle.pupman-dot-com
Subject: Re: Input Power Measurement
From: Tesla List <tesla-at-stic-dot-net>
Date: Fri, 30 May 1997 01:26:47 -0500
Approved: tesla-at-stic-dot-net
Subject: Re: Input Power Measurement
  Date: Wed, 28 May 1997 10:51:30 -0500
  From:  "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To:  Tesla List <tesla-at-pupman-dot-com>


> Date:          Tue, 27 May 1997 00:46:40 -0500
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       Input Power Measurement
> From:          Tesla List <tesla-at-pupman-dot-com>

> Subject:     Input Power Measurement
>        Date: Mon, 26 May 1997 23:42:39 -0700
>        From: Skip Greiner <sgreiner-at-wwnet-dot-com>
> Organization: Greiner, Ltd.
>          To:  tesla list <tesla-at-pupman-dot-com>
> 
> 
> Hi All
> 
> It is obvious to all that any given transformer can be run in excess of
> its rating. Thus, a 1kva transformer may be run with 2kva input and
> live. This does not mean that the TC is being run at 1kva since the
> transformer is rated at 1kva.
> 
> How can the actual input power to the TC be measured????????
> 
> We can know the input voltage, I think, since most of us run from the
> mains (except those that insert a variac and transform the mains voltage
> up to 130v or 140v). We can still measure the output voltage of the
> variac, I think, and therefore know the input voltage.
> 
> BUT....how can the input current be measured. I seriously doubt that it
> is sinusoidal. There are ac ammeters, several different types which give
> an indication. Is there one type of ammeter, the reading of which could
> be multiplied by the voltage as obtained above, which would give an
> input power which all of us could use for comparison purposes?  
> 
> I have a commercial instantaneous reading wattmeter. Does it provide any
> usable information? For instance....if I compare the input power to two
> different systems which use different types of input
> transformers....will I indeed be able to say that one system is more
> efficient than the other?
> 
> Any suggestions would be appreciated.
> 
> Skip
> 
 
Skip,

I think you could install a voltage probe and wideband current
transformer on 
the mains input to your variac, connect it to a CRAY with a powerful 
program that someone on this list would no doubt love to write, and 
get a three dimensional color printout of your true RMS and peak 
power.

I would think you could also go the route of the good old hotwire
ammeter 
(good way to measure RF power coming out of a transmitter) in series 
with your variac input and settle for knowing average RMS power with 
a fair degree of accuracy.  Any fellow deciples of the KISS Principle
try this yet? 

rwstephens