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mhrackin
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I forgot to mention earlier....
mhrackin   8/25/2014 12:12:59 PM
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The meter in the photographs was made by Weston Instruments, likely in the late 1950's, in New Jersey.  I grew up there, and got my BSEE from Newark College of Engineering (now part of NJIT).  Edward Weston was a major benefactor of the college; the main building was Weston Hall (which may actually have been the original home of Weston's company). That is almost certainly a moving-coil movement; I don't think Weston made moving-iron, as their meters were high-end and high quality.  I probably have a couple in my basement (bought surplus in the '50s or '60s).

mhrackin
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CEO
Re: New faceplates for analog meters
mhrackin   8/25/2014 12:02:14 PM
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As a former South Floridian who routinely went wading in the Everglades on fishing trips, this advice:  Alligators are fine, unless it's a momma guarding the underground nest.   Otherwise they don't bother you if you don't bother them.  Watch out for the crocodiles, though; THEY are NASTY (as are the water snakes).

Max The Magnificent
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Re: New faceplates for analog meters
Max The Magnificent   8/25/2014 10:06:57 AM
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@JGrubbs: Max: If you are going to print the faceplates for the meters take a look at "Meter" and "BasicMeter" software from Tonne Software. BasicMeter is free and Meter is $35. You can download the manual from their website.

Hi there -- I just checked into the hotel in Sao Paulo for ESC Brazil -- I'm up to my armpits in alligators at the moment -- but I will look at these apps as soon as I get a free moment.

David Ashton
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Re: AC meters
David Ashton   8/25/2014 1:22:52 AM
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@traneus ... " it dissipates 4 watts at fullscale deflection"

Sounds about right.  We use cheap moving iron meters for battery monitors in our radio sites.  The voltmeters are 15V fsd and run around 12-14V all the time.  The bare meter sensitivity is around 2-3V I think, so they have a high wattage multiplier resistor built in.   After a few years of service the plastic faceplates go brown because of being in proximity to the hot resistor for so long.  BUT I've never yet seen one go wrong!

PS - keep your meter under lock and key, Max'll be after it for his projects!!

traneus
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Rookie
Re: AC meters
traneus   8/24/2014 9:03:00 PM
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David Ashton, you are correct.

I have a moving-magnet center-zero DC meter made probably before 1920, likely before 1900. The meter has three terminals connected to two windings (one terminal is common to both windings): a low-resistance, few-turns winding for current measurement, and a high-resistance, many-turns winding for voltage measurement. The meter is so insensitive that it dissipates 4 watts at fullscale deflection! The voltage winding measures 30 ohms, and gives fullscale deflection at 11 volts DC. Perusing an electrical-equipment textbook copyright 1891, showed this was reasonable at that time.

JGrubbs
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Rookie
Re: New faceplates for analog meters
JGrubbs   8/24/2014 8:38:35 PM
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Max: If you are going to print the faceplates for the meters take a look at "Meter" and "BasicMeter" software from Tonne Software. BasicMeter is free and Meter is $35. You can download the manual from their website. 

 

 

Max The Magnificent
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Re: AC meters
Max The Magnificent   8/24/2014 10:53:22 AM
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@traneus: While you have the scale plate off, check the internal wiring of the meter. Many AC meters are actually rectifier-driver DC meters.

I'm currently sitting in Atlanta airport waighting for my flight to ESC Brasil ... but when I get back I will be taking a much closer look at what's inside thise little AC rascals :-)

Max The Magnificent
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Re: AC meters
Max The Magnificent   8/24/2014 10:51:36 AM
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@David: ...but only if the basic meter movement is of the moving-coil type.  If it is moving iron...

There's always something new to learn...

David Ashton
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Re: AC meters
David Ashton   8/24/2014 4:42:50 AM
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@traneus this is true, but only if the basic meter movement is of the moving-coil type.  If it is moving iron, forget it.  it will either have a coil of thick wire if it is an ammeter, or of thin wire and probably a multiplier resistor too if it is a voltmeter, but even if you take the multiplier resistor out you will have a fairly insensitive meter, needing a fainr bit of current for FSD.  Most AC ammeters are of the moving iron type, they are cheap to produce and rugged.

traneus
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Rookie
Re: AC meters
traneus   8/23/2014 11:06:32 PM
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Max, don't give up on those AC meters. Most AC meters will read DC, though may be nonlinear. near zero. For your custom-scale purposes, that might be OK.

While you have the scale plate off, check the internal wiring of the meter. Many AC meters are actually rectifier-driver DC meters.

High-voltage meters usually have external or internal "multiplier" resistors in series with a low-voltage low-current movement. Many high-current meters have low-resistance current shunts in parallel with low-voltage, low-current movements.

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