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Re: Meter Shunts ??

Original poster: "Jim Lux" <jimlux@xxxxxxxxxxxxx>


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, February 14, 2005 6:52 PM
Subject: Re: Meter Shunts ??


> Original poster: Thomas DeGregorio <tommacs@xxxxxxxxxxxxx>
>
> It's seems like a pretty normal meter to me. Here's a link to where
> it's sold at from allelectronics
> http://www.allelectronics.com/cgi-bin/category.cgi?
> category=385&item=PMD-200A&type=store
> But do you think the resistor ideal will work too?
>
> -Tom
>

This meter needs a 50 mV shunt (look at the enlarged picture and you'll see
that on the meter face).  That means that when there's 50mV across the
meter, it reads full scale.  So... R= E/I  50E-3/200 = 0.25 milliohms is the
shunt value.  That's about 3 inches of AWG10 wire.  Calibrating is always a
challenge with this sort of thing.  You can put a variable resistor in
series with the meter to reduce its sensitivity.  you'd have to know the
meter coil resistance (probably a few hundred ohms)..