Analog meters

[tsutt]

I have a few nos analog meter heads i would like to put into use but not sure how to go about it. one is a 0-1000 ac milliamp meter i know it needs a shunt but i havent a clue on where to find the proper one. I have ac volt meter 0-150 i would like to hook to my variac, i dont know if that needs anything. and a couple of dc amp meters. any body got any info. they are honeywell and weston.

thanks
Todd

[Stevem]

Forget the 1000 ma meter, the ac meter can fly just as is, and if the two dc meters are in ma than they can be used wired across a 1 ohm 1 % 2 watt resistor wired to ground in the cathode of a output tube to set the idle current.
if they do read in ma what is there ma range they are scaled at?

[tsutt]

I will check what they are. Thanks

[Leo_Gnardo]

I have a few nos analog meter heads i would like to put into use but not sure how to go about it. - - -

Come right down to it, ALL those type of meters are ammeters, some more sensitive than others. You apply shunts to scale the meter appropriate to what you're measuring. I woulnd't give up on the 1000 AC milliammeter just yet: it could make a very handy monitor for current draw on gear you're repairing/testing. Depending on what value shunt is applied you can scale it up or down. Now it's going to take some experiments, you wire your meter in series with a known good calibrated one (digital multimeter you probably already have) and try different resistance shunts until the reading on your mystery meter matches the one you can trust. If you want to get fancy put it in a box with a switch to select shunts so you can read higher currents.

Honeywell, Weston, two excellent brands. If you can put 'em all to work you're going to get that cool retro vibe going in your workshop. I have a couple busted ones I leave around for customers to gawk at.

[tsutt]

They are cool thats on reason i want to use them and i would like the ac ma working i was load testing a pt i repaired and would like to have used it. But I dont have any shunts and dont now how to get in the ballpark. it a honeywell 45t says fs - 10 at the bottom of the meter.

I got some other old stuff too. I got a knight signal tracer that is like new my dad built it a long time ago. got a knight cap box and a knight resister box and an old precision rf signal generator. looks good havent looked inside and dont know if it really has any use.

[tsutt]

I got this stuff from my dad and i think hes got a few more. anyway 1 is a 0-5amp dc and a dc volt up to 20 i think. so where can a guy get shunts cheap.

[John_P_WI]

Been way too many years since I figured shunts out, check this video out:

https://www.youtube.com/watch?v=jCSgc3xzy5g

[Leo_Gnardo]

I got this stuff from my dad and i think hes got a few more. anyway 1 is a 0-5amp dc and a dc volt up to 20 i think. so where can a guy get shunts cheap.

I'd get some low R resistors say 10 ohms down to 0.1 ohm and experiment with them. You may already have some lurking in your parts collection.

Mouser has lots of sub-ohm current-sense resistors (fancy name for shunt) once you figure out what values you need.

[tsutt]

Excellent video. thanks did you read the comments. some suggested putting in diodes for meter protections. how would you do that? may seem like a stupid question but its not working in my head yet.

[tele_player]

if the two dc meters are in ma than they can be used wired across a 1 ohm 1 % 2 watt resistor wired to ground in the cathode of a output tube to set the idle current.

Correction: The 1 ohm resistor from cathode to ground method is used with a voltmeter, not a DC ammeter.

Robert

[Merlinb]

Most DC analog meters are moving-coil meters, and work in exactly the same way. You put some current through it, and the needle moves. It is a simple matter of figuring out how much current is needed to push the needle all the way to the end, which is called the full-scale-deflection (FSD) current.

A lot of DC moving-coil meters have an FSD of 1mA, so as a start you can simply hook them up to a 9V battery with a pot in series, to find the FSD current. But whatever you do, don't feed them a whole lot of current too soon! (Try a 9V battery and 8.2k resistor, plus a 100k pot). Adjust the pot until the needle moves full scale, and measure the current however you want (e.g. measure the voltage across the resistor and use Ohm's law). Also measure the voltage across the meter itself. You can then treat the meter like a resistor equal to V/I. Many small meters are about 1k ohm.

Once you know the FSD current and meter 'resistance' it is a simple matter to calculate a suitable shunt, since you have two resistors in parallel. You can even remove the legend from behind the needle and print your own, turning a 10V meter into a 500amp meter, or whatever you like!

AC meters are more variable in design. SOme are just DC meters with a rectifier built in. Some aren't. More investigation needed there.

[tsutt]

Ok this is inside the 0-1000 ac ma meter. and i can post the photos of the other also.

[Merlinb]

Well, I can't see any rectifier in there, and it looks just like any moving-coil meter, so I would guess it is actually a DC meter and needs an external bridge rectifier to be used with AC:

[img:478:385]http://sub.allaboutcircuits.com/images/02225.png[/img]

So you can test it the same way as any DC meter.

[tsutt]

Thanks Merlin that is what i was thinking but want to be as i have no experience with these. Its great to have a resource of knowledge like this.

Thanks
Todd

[tele_player]

Well, I can't see any rectifier in there, and it looks just like any moving-coil meter, so I would guess it is actually a DC meter and needs an external bridge rectifier to be used with AC:

[img:478:385]http://sub.allaboutcircuits.com/images/02225.png[/img]

So you can test it the same way as any DC meter.

It might actually be an electrodynamic ac ammeter, which doesn't use rectification. If it's marked as an AC device, I suspect that is the case.

Robert