EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: FenderBender on May 28, 2012, 05:45:17 pm
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Hey guys,
I'd like to use something like this in my power supply build:
http://www.amazon.com/Amico-Class-Accuracy-Current-Panel/dp/B006Z955SW/ref=sr_1_1?ie=UTF8&qid=1338226425&sr=8-1 (http://www.amazon.com/Amico-Class-Accuracy-Current-Panel/dp/B006Z955SW/ref=sr_1_1?ie=UTF8&qid=1338226425&sr=8-1)
I'm thinking about just using analog meters since if I REALLY cared about the voltage/current, I'd just measure it with meters that I actually trust, not some cheapass Chinese panel meter. $7 a pop isn't bad plus don't have to worry about separate power for digital meters.
Anyway. It says 0-1A and no mention of a shunt. Is this normal? Or does this one just normally do 1A full scale no shunt? Perhaps just the way they wind the coil inside etc. I don't know too much about electro-mechanical stuff, but I thought a galvonometer works on like the uA scale? A bit confused!
Any information would be great!
Thanks.
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Product Description
Quickly and accurately for testing.Screws for simple installation are included.Can be directly connected to the equipment tested.Note: please choose the right meter to testing different range voltage, which should be not over the meter scale range.
and by just looking at the terminals size i guess it has the shunt integrated
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Okay, thank you. Sometimes I don't trust descriptions. But yeah now that makes sense. Thank you again!
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Terminal size is not an indicator of current rating.
Compare the same meter in ammeter and voltmeter forms.
http://www.ebay.co.uk/itm/YS-50-Analog-DC-Current-Panel-Meter-Ammeter-Gauge-0-1A-/400299473931?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5d33b53c0b (http://www.ebay.co.uk/itm/YS-50-Analog-DC-Current-Panel-Meter-Ammeter-Gauge-0-1A-/400299473931?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5d33b53c0b)
http://www.ebay.co.uk/itm/YS-50-DC-0-2V-Analogue-Needle-Panel-Meter-Voltmeter-/400297987492?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5d339e8da4 (http://www.ebay.co.uk/itm/YS-50-DC-0-2V-Analogue-Needle-Panel-Meter-Voltmeter-/400297987492?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5d339e8da4)
Meters are usually (but not always) marked if they need an external shunt e.g.
http://www.ebay.co.uk/itm/YS-50-0-500A-DC-Current-Square-Panel-Meter-Ammeter-New-/180883154502?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1d79e646 (http://www.ebay.co.uk/itm/YS-50-0-500A-DC-Current-Square-Panel-Meter-Ammeter-New-/180883154502?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1d79e646)
With an unknown meter always test starting with a very low current in case it needs an external shunt. waste time no the meter. :)
(No connection with this seller, it was the first I found with all three variants.)
Jim
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Thanks. Good point.
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I believe that this meter (and the similar Shurite brand) are not D'Arsonval (moving coil) meters; the moving part is a magnet instead of a coil. The meter pivots are dimpled metal (vs. jewelled bearings) and they are generally only 5% accurate and inexpensive, have no zero adjust, but are rugged as compared to D'Arsonval movement meters. The main point is that the various models of it can handle huge currents by virture of the simple construction; thus they don't need separate shunts for the higher ranges. This is not to say that the most sensitive of them couldn't be used with a shunt (mixing sow's ears and silk purses).
Just to give you an idea, there is a version of this kind of meter that is used by mechanics to check auto starter draw of hundreds of amps http://www.stuttgartperformanceengineering.com/inductiveammater.html (http://www.stuttgartperformanceengineering.com/inductiveammater.html). There is no coil in it at all and there are no meter terminals; the meter is placed next to the starter lead and the moving magnet to which the pointer is attached deflects due to the interaction with the magnetic field of the lead.
One amp? Piffle!
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Wow. Well again, I don't need amazing precision on these things. And if I REALLY did, then I'd use a multimeter to do that. Just generally speaking, I want to know whether I'm in the ballpark. Is my microcontroller drawing 50mA or is it drawing 1500mA and HOLY **** I should turn this thing off?
They say these are Class 2.5 which I think means 2.5% accuracy. Of course, whether they actually meet that spec, I don't know, but 2.5% isn't terrrible. So if I have it lined up for 5V, it could be anywhere between 4.875-5.125. Not too much error, really. Not doing mission critical equipment where I need 5.0000000V on the dot.
"Real" analog panel meters like from Simpson etc...well those aren't worth it IMO. At that point, a digital meter will serve you much better for the price. $80-120 for a panel meter? No thanks.
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I believe that this meter (and the similar Shurite brand) are not D'Arsonval (moving coil) meters; the moving part is a magnet instead of a coil. The meter pivots are dimpled metal (vs. jewelled bearings) and they are generally only 5% accurate and inexpensive, have no zero adjust, but are rugged as compared to D'Arsonval movement meters. The main point is that the various models of it can handle huge currents by virture of the simple construction; thus they don't need separate shunts for the higher ranges.
The limiting factor with moving coil meters is the hairsprings (or torsion wires) which have to carry the full current to the coil as well as controlling its deflection.
If you make them thick enough to carry a high current (without significant heating), the torque required to move the coil will be too high to be practicable.
A relatively low current meter with a shunt, which may be inside the meter case, is the usual solution to this problem.
Moving iron (or moving magnet) meters do not have this problem as the current carrying coil is fixed, but have an inherently non-linear scale.
Jim