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Re: Watt Meter



I also just obtained a mint-condition, mirrored-scale moving-coil wattmeter
at a hamfest for $15; however, it is somewhat different from other
wattmeters I have seen and any assistance from anyone familiar with its
usage would be appreciated. I would like to use it to make measurements on
a low-power coil as I add power factor correction capacitors to the neon
sign transformer power supply.

It is made by Sensitive Research Instrument Corporation and is identified
as a "University Model" "single phase low power factor wattmeter", rated
for "DC & AC up to 400 cycles".

One side of the instrument has a pair of binding posts labeled "Potential",
and a plate with the following:
     Series fields 100 volts = 250 watts
                               200 volts = 500 watts

     Parallel fields 100 volts = 500 watts
                                 200 volts = 1,000 watts

The opposite side of the instrument has six bindings posts:
     Two are labeled "Current"
     The other four are arranged in a square pattern, and a shorting bar
can be positioned between three different pairs of the terminals, which are
labeled:
          "Field circuit, link for parallel"
          "Series only"
          "Parallel"

How are the source and load connected to this instrument, and how is the
shorting bar configured?

 Scott Hanson
Costa Mesa, CA





Tesla List <tesla-at-pupman-dot-com> on 06/29/99 04:29:18 AM

To:   tesla-at-pupman-dot-com
cc:    (bcc: Scott L Hanson)

Subject:  Re: Watt Meter




Original Poster: Neon John <johngd-at-bellsouth-dot-net>



Tesla List wrote:
>
> Original Poster: "Vivian Watts" <V.C.Watts-at-btinternet-dot-com>
>
> Hi All,
>     Being interested in the difference between the VA rating and the rms.
> power taken by my coil I managed to purchase a Watt meter at a local
Amateur
> Radio Rally.  It is rated for A.C and D.C. but I'm not sure it is
suitable
> for giving the true power on reactive loads and was wondering if anyone
> knew.  It is a Weston Model 310 made in Newark NJ USA dated 1941.  It is
> referred to as a electrodynamometer wattmeter.  Frequency range to 133Hz.
> Cost 10 ($15).
>

As that guy at the soccer game says, SCORRRRRRRRE!  You got a beaut
and at a tremendous price.  Until fancy electronics came along, the
electrodynamic wattmeter was the lab standard.  It will still handle
high crest factor power better than most electronic wattmeters.  It
will work equally well with AC and DC.  The only extra step with DC
is to take a reading, reverse the potential leads, take another
reading and then average the two.  This cancels out the residual
magnetism that may remain in the meter parts after a DC measurement.

John
--
John De Armond
johngdSPAMNOT-at-bellsouth-dot-net
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"