Should I buy an Analog Ampere meter?

[kosPap]

well my world turned upside down when I compared 2 chaep DMM that read different....

So a friend (that knows my hobby) suggested an Analog meter that is "more accurate and cheaper" than a usual DMM.

If indeed it IS so, and considering the fact that Amp draw is the most demanding everyday measurement we do here in CPF (voltage & resistor metering and short detection are easier)

So, are there any reasons NOT to buy one?

(excluding the urge and itch to buy high grade)

 

[MarNav1]

As with most things, you get what you pay for. Accuracy and inexpensive don't usually go together. I don't see any advantage to an analog in your situation. How much accuracy do you need? 1%? .1%? .01%? This is something to consider before buying. DMM's have all but replaced analog in the large majority of situations, technology has improved alot. Depending on your budget and what's availible in Greece I can recommend Fluke for a digital, and a Simpson 260 for an analog. But they don't come cheap, even here in the states.

 

[DM51]

This doesn't belong in MMM - I'm moving it to Batteries/Electronics.

 

[lctorana]

If you want to measure current draw of flashlights with an analog meter, there is nothing better than an Avometer Model 7.

 

[precisionworks]

I can recommend Fluke for a digital

+1

The 179 is one of their less expensive meters, fairly small, tough, accurate, etc.

Simpson analog meters are often available on eBay for very little. A year ago, I sold two for about $10 USD each.

 

[rushnrockt]

What two meters were you comparing and how much did each cost? That would be a good place to start.

 

[qwertyydude]

I find my Inova multimeter from walmart to be fairly accurate for current measurement, once I replaced the leads with thicker wire. I think your current measurements might be suffering because the thin wire leads add resistance which make higher current measurements inaccurate.

 

[Justin Case]

I have an old Simpson 260, which is a reasonably good meter. DC amps accuracy spec is 2% of full scale, which means +/-0.2A for the 10A setting. However, if you are measuring something closer to 1A, then your percent accuracy is going to be a lot worse (0.8A-1.2A, or 20%), which is why you typically want to measure things as close to full scale as possible with an analog meter. In contrast, a typical, inexpensive DMM might have a DC current accuracy spec of around +/-(2% of reading + 10 digits). Since the DMM probably can read out to 3 decimal places for the same ~1A measurement, accuracy can range from 1A +/- 0.03A or 0.97A to 1.03A.

Unless your DMM is really cheap, it's hard for me to picture that an analog MM is going to give a more accurate DC current measurement than a DMM.

An analog meter is useful for things like visual indications of measurement change. You can see the meter needle deflect and also get a sense of the rate of change. This is useful for things like continuity testing. Of course, with a DMM, you can just switch the meter into continuity testing mode, where the DMM typically gives a go/no-go continuity beep.

 

[kosPap]

ahmmmm....so there IS a reason NOT to buy one...metering range....

thanks justin, you have been a savior...

Jumping to ebay now...bye for now...

 

[Turak]

Gentlemen.....

Keep in mind that when trying to measure current using a DMM there are a few problems that can come into play....especially with the cheaper (anything under $100) DMM's.

1. The problem I see most often is that someone is trying to measure a pulsed current with a DMM. The problem is that many of the cheaper DMM's are not 'fast' enough and the current measurement ends up being incorrect. Even some of the cheaper Flukes are not accurate sometimes, depending on the application. Generally speaking, meters labeled 'True RMS' tend to be a bit better for current measuring, especially if you happen to be measuring AC current.

2. When measuring a constant current, not too many problems.....but when measuring a constantly changing current.....again it goes back to the speed that the meter samples the measurement at. If it samples too slow, your reading may be off by quite a bit. You will almost never find this info in the specs on the cheaper meters.

3. DC current with excessive AC ripple current present. This can also have an effect on your measurements. Although there are debates that a 'little' AC ripple is a good thing for charging DC batteries.

4. The meter WILL affect the accuracy of the current measurement. Meaning that the measured current will actually be off by a small amount.


For current measurement....

In many cases an analog meter (good luck finding them nowadays) can actually be a better choice, especially when it comes to charging larger wet lead acid, gell cells, SLA batteris, or the AGM variety of batteries.

 

[lctorana]

In many cases an analog meter (good luck finding them nowadays) can actually be a better choice, especially when it comes to charging larger wet lead acid, gell cells, SLA batteris, or the AGM variety of batteries.

Absolutely.

And the reason is burden voltage.

The burden voltage of most DMMs is astonishingly high, and that affects the results hugely.

This is why I specifically recommend the Avo Model 7 - that and that only - for this kind of work.

 

[TakeTheActive]

Re: Progress?

:thinking:​

 

[Justin Case]

At the usual flashlight tail current magnitudes, the burden voltage for my Simpson 260 is much larger than that for a Fluke 87.

In any case, here are some links that discuss VOMs vs DMMs:

http://www.electro-tech-online.com/general-electronics-chat/17567-analog-meter.html

http://www.twysted-pair.com/forum/viewtopic.php?id=45

http://en.wikipedia.org/wiki/Multimeter

http://www.repairfaq.org/sam/semitest.htm

http://mccworkshop.com/setup/Meter1.htm

Survey of instrumentation and measurement, Volume 50

 

[lctorana]

At the usual flashlight tail current magnitudes, the burden voltage for my Simpson 260 is much larger than that for a Fluke 87.

Agreed. This is why I specifically recommend the Avo Model 7.

 

[Burgess]

Any Link for that instrument ?



Found Avometer Model 7

but only 1 mention of it.


No photograph or description,

but it was listed at $1,675 U.S. ! ! !

:eeksign:
_

 

[Mr Happy]

Avometers are retired, sadly. The Model 7 looked like this:

http://www.portabletubes.co.uk/testing/avo7.htm

The current production model was this one:

http://www.electronicsweekly.com/Articles/2008/09/24/44553/megger-bids-farewell-to-iconic-avo-8.htm

...but as you can see, it is no more. Used examples only from now on, unless you can find some new old stock somewhere.

We used them in my physics classes in high school, long before digital meters were to be found.

 

[lctorana]

Avometers are retired, sadly. The Model 7 looked like this:

http://www.portabletubes.co.uk/testing/avo7.htm

The current production model was this one:

http://www.electronicsweekly.com/Articles/2008/09/24/44553/megger-bids-farewell-to-iconic-avo-8.htm

...but as you can see, it is no more. Used examples only from now on, unless you can find some new old stock somewhere.

We used them in my physics classes in high school, long before digital meters were to be found.

It is the Model 7 I recommend, not the Model 8. And yes, late Model 8s are $1000+. But they're not what I'm talking about. Model 7's can be had for A$20-ish on eBay.

 

[uk_caver]

1. The problem I see most often is that someone is trying to measure a pulsed current with a DMM. The problem is that many of the cheaper DMM's are not 'fast' enough and the current measurement ends up being incorrect. Even some of the cheaper Flukes are not accurate sometimes, depending on the application. Generally speaking, meters labeled 'True RMS' tend to be a bit better for current measuring, especially if you happen to be measuring AC current.

I can see that for actual AC measurement, true RMS can be useful, but for essentially DC work, if it was a case of a meter taking brief samples from a fluctuating current such as a PWM signal without sufficient smoothing, wouldn't that tend to mean that even with a consistent PWM duty cycle, the meter should give a fluctuating reading?

If a meter reading is steady, wouldn't that indicate that there was some kind of integration/averaging going on?
Is even cheap smoothing with a simple RC circuit as a low-pass filter going to give a figure away from the real average?

Maybe I'm lucky - the cheap DMMs I use for some measurements seem to agree pretty closely with my more expensive one.

I'd certainly agree with the comments about meter resistance - the voltage drop across the meter can really skew some measurements.

If measuring output current from an LED driver with a current sense resistor, it is possible to connect a DMM reading voltage across the resistor and do the appropriate calculations, rather than use the meter on a current setting.
Alternatively, if that isn't possible, as a check on how much influence a meter might be having, it's possible to measure the voltage across an LED with and without another meter in circuit measuring current, and get some idea of the meter's effect from the voltage difference.

 

[SemiMan]

Lead resistance on multi-meters for low voltage circuits with relatively high currents like what we are doing on flashlights is always going to be a problem....and one that is very very easy to solve.

Go to Digikey and gets yourself some low value resistors, i.e. 0.1, 0.05 ohms. Put them in circuit and measure the voltage across them. What is nice is with one probe movement, you can get the current and the voltage.

Semiman