[R-390] OT: Meter Internal Resistance

[Barry]

> I have a Triplett panel meter that was originally shunted to 1A DC full
> scale.  I want to use this as a voltmeter so am in the process of analyzing
> the meter movement.
<snip>> 
> Barry - N4BUQ 


Sometimes it's the little things that are so much fun.

Using 8 mA as Full Scale, I wanted to make the meter a 10 VDC Full Scale volt meter.  A quick calculation showed the resistance should be around 1242 ohms.  Scrounging through my stuff, I came up with a set of resistors that came to around 1260 ohms.  I hooked that in series with the meter and cranked the power supply up to 10 V.  Nearly perfect.  I put a larger resistor across one of the larger resistors in the chain (dropping the overall resistance by just a bit) and the meter started tracking just as it should.

I don't know why, but something's rewarding about doing something so simple like this.  I've had these meters sitting on the shelf and wanted to use them at some point.  They were both originally 1 ADC and I want to make a 9VDC power supply that can supply at least 1 A so using these meters will give me a nice matching set of meters - provided I can get a new faceplate for the volt meter.

If it comes to it, I can print a new meter face, but I have a line on a possible source for a junk meter that matches with the right lettering.  If so, I'm set.

Thanks for listening...

Barry - N4BUQ