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Ebay cheap Analog Ammeters for uA mA

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lk:
Greetings,
I must have taken some mental damage from the old Scifi movies i have been watching as i feel my self drawn towards analog Ammeters, i have several projects in that draw current in uA ranges, and i found many cheap ones on eBay. But as there are really no datasheets for them, i don't really know how they work, and I'm afraid that i could easily break them if fed too much current, but i don't for a fact know if this would happen. eg feeding 10mA through a 500 uA ammeter.

Then i have been pondering about how to make some sort of auto ranging for use with maybe couple a mA and uA. I have seen from Daves uSupply that the parts exist for doing this digitally, and i presume that this can be done analog as well, but the how is bit unclear.

And i don't know if my babbelings make any sense :)

-lk

TerminalJack505:
Yes, you can damage an analog meter by 'pegging' it.  I remember one of my classmates doing this to one of the instructor's meters in high school.

amyk:
Analog uA meters are very delicate and putting 10mA through a 500uA one is going to bend the parts out of calibration and probably destroy the coil by overheating.

You can see some typical analog meter specs here:
http://www.simpsonelectric.com/uploads/File/PanelMeterCatalog_Jan09.pdf
They can withstand 10x FS current for 1 second, or 1.5x FS continuously.

sonicj:

--- Quote from: lk on April 03, 2012, 08:55:24 am ---Then i have been pondering about how to make some sort of auto ranging for use with maybe couple a mA and uA. I have seen from Daves uSupply that the parts exist for doing this digitally, and i presume that this can be done analog as well, but the how is bit unclear.

--- End quote ---
you could use a ammeter that requires an external shunt. each range would require its own shunt to match the scale.
-sj

i have a HP 6200B with a single meter that displays 0-5V, 0-50V, 0-0.18A or 0-1.8A. *see attached schematic.

vk6zgo:
It's not exactly brain surgery!
If the meters are sold as microammeters,you can see what their Full Scale Deflection (FSD) is by connecting them in series with a 33k
resistor & a1.5volt AA cell.(if you are really namby pamby,you can use a 50k pot,& slowly reduce the series resistance.)

With 30k in series:

If they are 50uA FSD,they will show close to FSD
100uA FSD will be about half of FSD.
25uA FSD,you will "twang" the needle,but it shouldn't do any real harm.
500uA & 1mA FSD meters will show very low readings.
High current meters with built in shunts will show a zero reading.

Obviously,the meter coil has some resistance,but you can ignore it compared to the series resistor.
Once you know their FSD,you can then find out how to make & use shunts to increase their ranges.

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