I have decided to go for a better voltmeter than my cheapies (3 digit) and would like one that gives an extra digit.
I want to measure my 18650’s (hopefully) more accurately.
I have been considering the Extech EX330 and the Amprobe AM240 … Both are 4000 count … I have a 5.0000V reference and at present my meters read 5.00V … I would like the new meter to read 5.000V … Most meter ranges seem to be 2.000V , 20.00V , 200.0V or 4.000V , 40.00V , 400.0V … If I measure my reference , it would be displayed on the 20.00V or 40.00V ranges as it is higher than the lower ranges … I would like to display on a 5.000V or 6.000V range to get that extra digit.
If I measure my 5.0000V reference on these two meters , will there only be two decimal places displayed because they would be measuring on a 20.00V or 40.00V range ? … If so they would not give the extra digit that I want.
Unfortunately there is nowhere in the area that I can try out these models against my reference.
I can’t really justify spending over £50 on a new meter , so that excludes the 6000 counts and above.
I probably have got it all wrong in my understanding of these meters … Will these two show 5.000V when measuring my reference (or not) ?
That last digit isn’t really useful for our purposes anyway. There’s far more variation (>0.1V) from the various other error factors in the measurement. A meter which happens to have the right range might offer a tiny bit more precision, but who knows if it’s accurate to what you’re trying to achieve.
I have a very accurate five volt reference to check the meter against.
It is 5.0002V at 72F … My other meters read 5.00V , but I would like a meter that would read 5.000V so would be within 0.5mV of the reference.
If it is going to be too expensive to buy a higher resolution meter then I will stick with the old ones which are pretty accurate anyway … When I read 4.20V at the moment , it could be anywhere between 4.195V and 4.205V … Perhaps being within five millivolts is OK with my 18650’s.
I might be just wasting my money on a more expensive meter when it isn’t really needed.
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If you have an accurate reference to check against, you can just calibrate to two reference points and do linear interpolation in between them. Meters tend to be much more precise than accurate.
My meters are reading correct at zero (leads shorted) and at 5.00 volts (as checked against my 5.0002V reference) … As such , I have assumed (rightly or wrongly) that they read correctly at 4.20V … One of my previous meters was slightly out (+10mV) against the reference , so I corrected the Li-Ion reading by a factor of 4.2 divided by 5.0 X 10mv … I subtracted 8.4mV from the reading … Since the meter only read to two places of decimals , I subtracted 0.01V … It was easy to do , but I gave the meter away as the others were reading exactly 5.00V on my reference.
I was hoping to get a cheap meter (under £50) that would read 5.000V rather than the 5.00V , but I might be spending money unnecessarily for use on Li-Ions.
I think that to get what I want at 4.200V , I would need a 5000 or 6000 count minimum … They are not available in my price bracket.
Looks as though I will be sticking with my 2000 count meters.
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Check out the stuff at http://www.voltagestandard.com/ He sells some very nice voltage references and meter standards for cheap. If you have a 4000 count meter, he has a 3.0000V reference for 25 bucks.
I have the equivalent of a national standards quality calibration lab (8.5 digit meters, sub-microvolt accurate references and dividers, 1E-13 accurate frequency, etc). For 25 bucks, it’s hard to beat those little references.
This was originally on my short list till I looked at reviews on meters under $50 (on the internet) and it came in the bottom two … I would like to find somewhere in South Wales that sells them so I can try one against my 5.0002V reference … If this meter gave a reading of 5.000V from my standard , I would buy one … I’m not worried about the physical size as it wouldn’t be carried about … It would be in my desk drawer.
I did also consider the Amprobe PM55A as it is a 5000 count meter … It is very small but only uses a CR2032 battery and has a drain of 6mA on auto range … So I didn’t know how long the battery would last.
I’m beginning to think that way … For mains use , I use my Avo 8 … I’ve had it since 1975 and it is still working OK … Good quality leads on it for any mains voltage work too.
I’m wondering if I really do need to go to the third decimal place when reading voltages on my Li-Ions … I’ve managed for a few years now with my 2000 count meters (on the 20V range) … There would be no advantage in going for a 4000 count meter (once the voltage goes over 4.00V).
I would not call it a bad DMM, compared to my 6½ digit Fluke it is only 3 mV wrong at 5 volt, i.e. it show 5.003 when the other meter shows 5.00010. The 5 volt is from a DMMCheck.
Today i used my colleges 287 rather than my 187 for some very basic mains checks, it damn well annoyed me having to wait for the silly little start up, heck id of been happy with my almost retired 70 series.
Is it user-adjustable ? … Can I use my 5.0002V as a reference and adjust the VC99 to read exactly 5.000V ?
This would be the ideal situation if there was just one “pot” to adjust to give the perfect reading … It would be a matter of which pot should I tweak ? … Unfortunately it would invalidate the warranty.
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If you have a 4000 count meter and want to check the accuracy on the lower voltage scales you DO need another reference. 5V will cause the meter to switch to the next higher range.
I have been thinking of another way to get more accurate readings … My reference is known to be 5.0002V … If I connect my reference positive to my battery positive and measure between the reference negative and the battery negative with a high impedance meter , the reading with a fully charged 18650 would be about 0.800V … If I subtracted the 0.800V (or whatever) from the 5.000V then that should give me a more accurate reading than I get at the moment … I realise that this is a bit long-winded , but it would cost nothing extra to do.
I might not bother … I think that two places of decimals will be OK for checking my Li-Ion voltages.
I recommend the HP3458A. And for a better reference a Fluke 732 or 734. Add a Fluke 720A Kelvin-Varley divider to it to get any voltage you want (< 10V).
But then, that brings up the question of how do you know it is all working properly? A man with one meter never knows what volt it is. A man with two meters can know something is wrong. Better get three of each… I did.
