[Amps] Bird wattmeter

[Ed]

If Bird is so darn Bad an inaccurate, why has it been the gold standard all 
my adult life and still is the one EVERYONE else compares themselves to? My 
BS meter is pegging.
Ed-KV5I
----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: <amps at contesting.com>
Sent: Sunday, May 06, 2007 10:58 AM
Subject: [Amps] Bird wattmeter


> Has anyone measured the current thru the meter movement on the bird 43
> wattmeter? It is a 30 microamp full scale, so it says on the meter face.
>
> I have two very old ones that read low on power. I checked the full scale
> reading by putting 30 microamps of current into the meter. They do not 
> read
> quite full scale with that amount of current. Both are different too.
>
>
>
> I am wondering if they should read exactly full scale with 30 microamps or
> if bird has the scale slightly off of the normal full scale point of the
> meter?
>
>
>
> I was going to try and collaborate meter current with watts readings but 
> it
> does not work out with the square of the current as you might think. It is
> probably because of the non linearity of the diodes in the slugs. It looks
> like all slugs are set up to provide the same current thru the diode not
> matter what power slug is used. That would make the meter scale the same 
> for
> all power levels although not linear to current.
>
>
>
> If anyone wants to check their meter movement it can be done without even
> opening up the meter. Just take the element out and attach a small clip to
> the element contact in the slug hole side. That gets you directly to the
> meter. A 470k resistor and an adjustable 12 volt  power supply and a good
> microameter.  I have 3 different bench meters and all read within .01
> micromaps of each other. A fluke, HP and keithly. I also tried my fluke 70
> series handheld meter and it was off by about 1 microamp at 30 microamps.
> Yes 1 microamp makes quite a difference in reading on the bird meter
> reading!
>
>
>
> I also have another old bird meter movement that was replaced many years 
> ago
> and it will not go anywhere near full scale with 30 microamps and the
> movement is free and does not seem to stick.
>
>
>
> I am wondering what happens to these meters? Do the magnets go bad in them
> or something else?
>
> There is a 200 ohm resistor inside the meter movement case that is in 
> series
> with the meter. I wonder if that is used in final calibration of the meter
> movement?
>
>
>
> There are several articles floating around about adjusting the slugs for 
> the
> bird wattmeter to bring them back into spec but I am wondering how many of
> those problems are problems with the meter movement rather than the slugs?
>
>
>
> Thanks for any help
>
> Gary  K4FMX
>
>
>
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