Panel meter help - Page 1
Forum section: electronics / beginners

author: nnills
author_rank: Contributor
timestamp: March 05, 2019, 05:44:51 pm
content: Hi I just bought 26 panel meters from "Marktplaats"(dutch ebay). Some of them are evident(voltage or shunt resistor written on it) but others I don't understand(shunt resistor/operation). Does one of you know? Here are the images(almost 20):https://imgur.com/a/9ZNBnjT

author: Totalsolutions
author_rank: Contributor
timestamp: March 05, 2019, 06:50:26 pm
content: Cannot see photos, voltage is volts as you know and shunt resistor must be current meters. You send the current through and “tap” off a small voltage from the shunt resistor. So the current meter’s are voltage meter’s really. Moving coil meter’s are voltage driven. Hopefully I am correct.

author: rdl
author_rank: Super Contributor
timestamp: March 05, 2019, 07:43:38 pm
content: Those are moving coil meters. The meter movement will have a specific current rating which gives full scale deflection. To measure a value other than that, shunt (parallel) or series resistors are added. These will often be internal to (inside) the meter. The resistor may be nothing more than a piece of wire when current is being measured. Sometimes, if you're lucky, the full scale deflection current is printed somewhere in the meter, often you have to figure it out by making measurements.

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2019, 09:04:47 pm
content: Quote from: Totalsolutions on March 05, 2019, 06:50:26 pmNope, it's the exact opposite, moving-coil meters are current-driven.

author: nnills
author_rank: Contributor
timestamp: March 05, 2019, 09:26:20 pm
content: Thank you for your answer(I will eventually find out the right values). I'm new to the forum so what do I do now? Do I need to close the topic/question?

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2019, 09:38:04 pm
content: Nope, just let it be. (Members can't close topics anyway.) A nice courtesy is to return later and reply with your discoveries, since those often help others learn.

author: rdl
author_rank: Super Contributor
timestamp: March 06, 2019, 12:55:24 am
content: If you google "how to use moving coil analog meters" you should find plenty of info. Forum member w2aew has a video about analog panel meters (and lots of other great videos).Personally, I prefer them to digital meters in bench power supplies. They are often more readable and informative.

author: jeroen79
author_rank: Frequent Contributor
timestamp: March 06, 2019, 02:57:07 am
content: Quote from: nnills on March 05, 2019, 09:26:20 pmJust put a known currentmeter or multimeter and resistor in series with the meter you want to test.Start with a 1M resistor.Then hook this up to an adjustable powersupply set at 0V.Set the meter's needle to 0 with the little screw at it's base.Then increase the powersupply's voltage until the needle swings full scale.If you cannot get a full scale swing then reduce the resistor to 100k, 10k, etc until you get a full scale readout.Then note the current needed to get this.

author: nnills
author_rank: Contributor
timestamp: March 06, 2019, 10:21:04 am
content: Can I emulate the burden/shunt voltage by connecting a power supply directly to the terminals of a current meter?

author: nnills
author_rank: Contributor
timestamp: March 06, 2019, 04:41:14 pm
content: I tested a first one and think it might be 5K ohm, is that reasonable?I can't seem to add images in my post but here are 2 of them, first is 4K7 second 5K1https://imgur.com/a/VRJKHvXEdit: Vin=5VEdit2: No no no...more like 6K. 5K1 and 270 in series is still a bit overEdit3: When hooking up a PSU it seems more like a 100mV full scale

author: tecman
author_rank: Frequent Contributor
timestamp: March 06, 2019, 05:55:46 pm
content: Many panel meters will have, in small print at the bottom of the faceplate, something like "FS=1ma". This would indicate that the base meter movement is 1 ma full scale. beyond that, there could be series resistors internally for a voltmeter. For ammeters, some have internal shunts, generally for 1 amp or under. Others will require an external shunt.As stated, use a series resistor to get a reading. Once a resistor value in combination with a know voltage you can determine the movement's scaling. Typical meters, w/o internal resistors or shunts, are 1ma or 100 ua FS.My uncle worked for Weston as a first job until he retired. As a result I acquired quite a few analog meters of various sizes, scales and shapes. His work highlights were assembling and testing panel meters for the Gemini and Apollo capsules. He received a commemorative medal for his work made from aluminum that was taken from some part of the spacecraft that orbited the moon. The aluminum was melted with a quantity of virgin metal and used to produce the medals.Paul

author: Zenith
author_rank: Frequent Contributor
timestamp: March 06, 2019, 07:01:36 pm
content: Quote from: nnills on March 06, 2019, 04:41:14 pmIf the meters you are talking about are 5V full scale deflection as in the last two photos, 5K is reasonable. 5 volts divided by 5KOhms = 1mA. 1mA is a likely full scale deflection for the meter movement.Buying a lot of old panel meters like that often produces a mixed bag. Specialised scales, odd things like three phase voltmeters and hot wire meters. Some of those are moving magnet ammeters, they have a very non linear scale but were tougher and cheaper than moving coil meters. You're quite likely to find some of the meters don't work and occasionally you can fix them.Just proceed with caution as Jeroen79 described above. As for connecting an ammeter directly to the terminals of a power supply, it's possible that unless it was a current limited PSU, things could go bang. Look before you leap. In your photos there's a 20-0-20µA centre zero meter and you could easily damage that if you were careless.When I bought a lot of about 50 old panel meters years ago, with a bit of fiddling and fixing I found about half were good and likely to be useful, so it was worth the money.

author: jwrodgers
author_rank: Unknown
timestamp: March 15, 2019, 12:21:52 am
content: Have a look at:https://myclassbook.org/darsonval-meter-movement-principle/I have also attached some old class notes from my Uni days circa late 90's. The equations don't seem to render correctly now, but there is useful information in there to steer you in the right direction.Also, wikipedia has this:https://en.wikipedia.org/wiki/Galvanometer