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Products => Test Equipment => Topic started by: npelov on June 08, 2013, 12:15:37 pm

Title: Choosing a high accuracy/resolution multimeter
Post by: npelov on June 08, 2013, 12:15:37 pm
Hi,

I want to choose high accuracy high resolution multimeter.

First I want to say that I make the difference between resolution and accuracy. I know that most high resolution multimeters' accuracy do not cover last digits (at least cheaper ones). But resolution is good even if accuracy is lower.

So what I need? First about accuracy - mission impossible. Everyone wants cheap and good stuff. Yes, I know that there is no full happines, but I can't spend $1000+ for high accuracy multimeter. Second - accuracy on what - mainly DC voltage, but also resistanse. DC current accuracy would also help, but it could be a little bit lower.

What I'll use the multimeter for. Calibration of voltage references and opamp circuits for ADC/DAC, sensors and others. I can't calibrate a voltage reference that's by specification 0.4% any further if the best accuracy multimeter I have is 0.5% (MASTECH MS8220R).
Resolution? Well it's useful thing to have. To measure small changes ... etc. If I have to choose I would sacrifise resolution for accuracy of course, but most cases for a price ragnge accuracy is the same.

My idea is to use combination of multimeter and fairly accurate voltage standard from http://www.voltagestandard.com/. (http://www.voltagestandard.com/.) Depending on the situation I will use either the multimeter or the voltage standard + multimeter to measure the difference.

Additionally it would be great to have double display - measuring 2 things at the same time is quite useful - min/max when averaging, frequency when measuring AC voltage. It must have relative measure. The display should be 7 segment, clear, easy to read, not dot matrix. I don't like fancy digits and graphs in multimeter. Most of them have PC connection for that.

I'm not yet mentioning the price because I don't know yet what are the options, but it should be not much more than 200USD.

I looked at these models:
BRYMEN BM867 (http://www.tme.eu/en/details/bm867/portable-digital-multimeters/brymen/) DC accuracy - 0.03%+2 digit, 50,000 counts + 500,000 counts mode ( :wtf:)
BRYMEN BM869 (http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/) DC accuracy - 0.02%+2 digit, 50,000 counts + 500,000 counts mode
UNI-T UT71D (http://www.tme.eu/en/details/ut71d/portable-digital-multimeters/uni-t/) DC accuracy 0,05% + 5 digits 40,000 counts

I haven't looked at  stationary multimeters ... mainly because they are expensive, they are bigger and have the same accuracy for higher price. I guess lower priced stationary multimeters aren't that great.

There is something else. Most of these multimeters have working temperature range quite wide. There might be slight difference between the cheaper ones and brands like Fluke, Agilent of how they specify accuracy. They should all specifyaccuracy in full temp. range, but do they? We saw before that specs not always match for lower priced brands. Yes, they are compensated, but I'm sure that accuracy change a bit with temperature. So my guess is that accuracy should be slightly better at room temperature.

So go on. Tell me how bad desision I'm making when I think of buying lower quality brand ... and thanks in advance.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: Wytnucls on June 08, 2013, 01:12:16 pm
If you want high resolution, one of the two 500,000 count Brymens is the obvious choice.
If you don't care about input protection, the cheaper 71D has everything you will need for bench electronic work, including PC connectivity, as standard.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: npelov on June 08, 2013, 02:54:47 pm
Yes, I read about the safety standards of some of those. I will not use it on more than 230V AC. I don't care if fuses are rated 600V or 1000V. Actually I will very rarely connect it to power line. I was hoping if someone had experience with some of those and also suggest me alternatives. I'm currently not searching for cheaper than those. I'm a little bit worried about other problems that may come with cheaper multimeter. For example my MS8220 is really slow. From proble to readings it takes 1 second and sometimes a bit more. I guess auto-range and protection has something to do with it, but when when you use it (especially conectivity beeper) doesn't make your work easier.

Actually 71D has less accuracy than the cheaper BM867 (at least at http://tme.eu (http://tme.eu)). So 71D is not the most inexpensive.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: nctnico on June 08, 2013, 03:08:50 pm
If you want to measure AC be sure to check the specs carefully. Making an accurate DC volt & current meter is easy. AC is not so easy.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 08, 2013, 03:21:47 pm
Hey

You might consider hp3478A .   great accuracy and 303,000 digit res .

I can sell you one

if you'd like 1.2milion count . I can sell you 34401A meter . assuming your budget will do

calibration and adjustment for both you'll get for free
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: Wytnucls on June 08, 2013, 03:26:11 pm
I don't know where you live, but the TME 71D has a 20% discount for the UK, making it cheaper, especially when you consider that the PC interface is included, unlike the expensive Brymen connections.

I have 2 UT71s and am thoroughly happy with them.
Title: Choosing a high accuracy/resolution multimeter
Post by: ddavidebor on June 08, 2013, 03:32:26 pm
Get an hp 34401a, super precise and reliable
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 08, 2013, 03:34:03 pm
Ddavidebor : I am glad you premote my selkings  :-DD
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: don.r on June 08, 2013, 03:54:17 pm
Bench meters (stationary as you call them) are expensive but only when purchased new. Many of the older ones are under $200 shipped and have up to 6.5 digit (over 3,000,000 counts) resolution and come with GPIB and are far more accurate than any handheld in that price range. You will probably lose dual display, min/max, freq and portability. You will have to purchase one that is still in calibration which is the tricky part.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: branadic on June 08, 2013, 04:07:32 pm
Quote
if you'd like 1.2milion count . I can sell you 34401A meter . assuming your budget will do

calibration and adjustment for both you'll get for free

How can you sell a 34401a for only 200USD? For a new device we have to pay 861,-€ plus (Merkel-) taxes. Damn, I had to pay 300,-€ for an old Prema 5000.
Do you ship also to germany? I'd be interested in such a good bench multimeter.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: alm on June 08, 2013, 04:19:40 pm
I would definitely consider used bench meters if resolution and accuracy are important. Calibration is going to be expensive regardless. For the ranges it can measure, you will get a reasonable amount of confidence with the voltagestandard.com products.

The older meters from the eighties are often light on features, however. For example, the HP 3468A/3478A curiously lacks a rel mode.  The HP 3456A lacks current ranges, but does have fairly extensive math features. I recently bought a 6.5 digit Keithley meter with minor defects for $40 shipped. Only DCV and 2-wire and 4-wire ohms are standard, even ACV is optional. Don't expect diode test, continuity or cap testing. It does have 6.5 digits of resolution and is specced for 0.007% 1 year basic DC accuracy. No calibration, but a quick comparison with other meters suggested that it was at least within 0.01%. This is quite typical for used high-end meters in my experience, it's quite rare to find one that has drifted significantly.

Newer generation (eg. HP 34401a, Keithley 2000) meters have more features, but these are going to be well over $200, even used.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: Lightages on June 08, 2013, 04:29:21 pm
Between the BM867 and the UT71D it depends on what you want.

The BM867 pros:
Better built, safe, fast update and continuity test, higher count, higher resolution, 500000 count option on some ranges
cons:
No PC connection included, no internal automatic logging, no temperature

UT71D pros:
PC connection and software included, 10000 memory logging, temperature
cons:
Basically no input protection, low safety fuses on current ranges, slow, slow continuity, built to a much lower standard, very high burden voltage on current measurement

I have both a UT71E and a BM869. If I were make my choice based on what I know after owning both of these I would have the BM867. I am happy to pay extra for the much better quality and reliability. If your need is to have the PC connection and internal logging for the same money, or close, then the UT71D is OK but only for low energy circuits. In reality one meter is not enough and you might want to consider getting both.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: G0HZU on June 08, 2013, 05:25:11 pm
If you don't mind buying an older bench meter then maybe you can consider the Fluke 45.

It has a dual display, can do relative measurements and also can zero the dB scale for relative measurements. Best of all it is easy to use even if you want to do something like measure voltage on one display and frequency on the other.

It can't match the top line bench meters for accuracy and 'only' has 5 digits but you can buy them quite cheaply now.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 08, 2013, 06:19:50 pm
Who said 200USD ?

the 34401 price is not yet in mt mind ,

the 3478A is 250USD including calibration and adjustment for free
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: don.r on June 08, 2013, 07:04:04 pm
Who said 200USD ?

In the OP, "not much more than 200USD".
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 08, 2013, 07:08:07 pm
I didn't noticed that  :palm:

I thought he's budget is up to 1K  :-//
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: G0HZU on June 08, 2013, 07:16:26 pm
I'd avoid any bench DVM with an old school LCD display like the 3478A because you can't read it easily from a distance or at an angle, especially in poor light or in a bright light.
Plus it doesn't appear to have a dual display, doesn't measure frequency, probably doesn't have a relative mode so is basically an unlikely candidate for the OP as the OP listed these features as desirable :)
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: npelov on June 09, 2013, 08:12:46 am
I checked specs. This thing is a beast.  1 year accuracy is 0.007% which is more than best of those multimeters. Plus there is a 30mv +- (0.0275+40d) range. With proper voltage standard it could be used for quite precise calibration. And that's for +/-5 degres C. Probably the display doesn't have that wide viewing angle. Well this is not everyday multimeter. It would be used for precise measurements.

The problem however is that they didn't know about eeprom back then. Then stored calibration data on battery backed ram. And there is no secondary battery slot to put another battery to keep data while replacing the primary(even though they know about diodes back then). And it's hard to say what life is left in the battery. Considering that calibration of this thing is quite expensive, that's a big problem.

Well 250 is not much over my budjet. However this thing should be quite heavy so shipping would would cost a lot too.

Ok. few questions about HP3478A:
1. What's the status of the battery? When was it replaced.
2. shipping costs to Bulgaria
3. Power - Is it/can it be set to 220V/50Hz
4. what's the average cost of calibration of such unit and how often should it normally be done.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 09, 2013, 05:25:45 pm
hey

I'll check for shipping cost

the power is already set to 50Hz 220V

the calibration for you will be for free and I belive it will last you for more then 5 years minimum

the battery state is unknown , I'll see if I can replace her for no charge and then I'll calibrate the thing

the calibration is 1 year I think

but the preformance is more like 10PPM per year ( the LSD )   so I suspect you don't have any problem  for the futural 10 years ( I belive It will drift no more then 15~19 PPM for that margine )

PM me if you are interest
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: npelov on June 10, 2013, 09:45:46 pm
well. I'm having second thoughts about HP3478A. It's an old thing ... Yes, it was good back then, but ... don't know. Relative feature was mostly needed for resistance measurement, but with 4 wire measurement you don't need it. Still it's a good feature to have. Also dual display. Frequency is not a big deal, but I have the feeling I might need it later. And it's lots of small things that combine into a big thing. I think I'll buy a portable voltmeter and use a voltage standarad for calibration with difference measurement.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: PA4TIM on June 10, 2013, 10:09:39 pm
the meters you want are not very accurate but more important cheap brands often do not meet their specs, often the specs are typical or not tracable. But more important is what they do over time.

I have a bunch of calibration equipment and besides a Prema and solartron 7,5 digit, and 3 Keithleys , two 6,5 digit and one 5.5 digit (a 2000, 196 and 199)
I also have a Agilent 50.000 count hand multimeter that was over 350 euro. I have the  keithleys now 2 to 3 years and all are still within the specs. (bought the 2000 new). The agilent hand multimeter is now after 3 years not within specs anymore but still more then good enough for my purpose as allround repair multimeter. It changed the first year but after that it stays rather stable.

And that is the problem with those cheap meters. The Vrefs they use will not be selected and aged. I made a Vref with a LM399, Adjusted it to 10.000,000 V but it changed about 150 uV the first months. Now after about a year it stays very constant. It still floats about 80 uV between extremes (temp 18-35 degrees and rH% between 15 and 40%) but that is 4.7 uV/C so less as 0.5 ppm/C
Even my Fluke 332 varies a bit ( about 0.1ppm/C)

So do not underestimate that. The voltage standard you want to buy will probably be less stable then that. (best is to build it in a battery powered metal compartiment because dirt and dust degrade it. Also EMC plays a role. To be real accurate you  will spent an amount of money on cables and connectors too. For resistance good kelvin clips (real good once cost more as 200) and for the measurement of standards triax or at least shielded cables with low seebeck effect connectors.

Be aware for the uV virus, it is an expensive desease  ;)
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 11, 2013, 04:27:10 am
I thought he's budget is up to 1K  :-//

For those on that sort of budget, hold out about a week...
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: JuanPC on June 11, 2013, 05:05:02 am
Hi,

I want to choose high accuracy high resolution multimeter.
.... :blah:
I looked at these models:
BRYMEN BM867 (http://www.tme.eu/en/details/bm867/portable-digital-multimeters/brymen/) DC accuracy - 0.03%+2 digit, 50,000 counts + 500,000 counts mode ( :wtf:)
BRYMEN BM869 (http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/) DC accuracy - 0.02%+2 digit, 50,000 counts + 500,000 counts mode
UNI-T UT71D (http://www.tme.eu/en/details/ut71d/portable-digital-multimeters/uni-t/) DC accuracy 0,05% + 5 digits 40,000 counts
I trust this brand...
http://www.testequipmentdepot.com/instek/dmm/bench-dmms.htm (http://www.testequipmentdepot.com/instek/dmm/bench-dmms.htm)
http://www.gwinstek.com/en/product/productmcategory.aspx?pid=39&&mid=80 (http://www.gwinstek.com/en/product/productmcategory.aspx?pid=39&&mid=80)

also UNI-T.. the others don´t know.
http://www.uni-trend.com/BM_M.html (http://www.uni-trend.com/BM_M.html)
download the .pdf manuals, web site specs are strange...
for example:
http://www.uni-trend.com/UT70A.html (http://www.uni-trend.com/UT70A.html)
web site says:
    20nF/200nF/ 2mF/100mF
    20mA/2mA/200mA/10A
but the actual hardware is:
    20nF/200nF/ 2µF/100µF
    20µA/2mA/200mA/10A

Rigol also look interesting...
http://www.rigolna.com/products/digital-multimeters/ (http://www.rigolna.com/products/digital-multimeters/)
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: eevblogfan on June 11, 2013, 07:51:01 am
hey

Quote
For those on that sort of budget, hold out about a week.

can you please explain my louzy brain what exactly did you meant ?  ( sorry  :scared: )
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: carpelux on June 11, 2013, 08:58:12 am
I suspect it means that there will be a new multimeter shootout available on Youtube in the near future.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: iloveelectronics on June 11, 2013, 09:04:41 am
I thought he's budget is up to 1K  :-//

For those on that sort of budget, hold out about a week...

The "that sort of budget" is the confusing part. Is it the >$200 range, or close to $1k range?
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 11, 2013, 09:11:00 am
The "that sort of budget" is the confusing part. Is it the >$200 range, or close to $1k range?

No confusion there. If anyone has $1K to spend, hold off for about a week and an option may present itself...
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: branadic on June 11, 2013, 08:18:08 pm
I suggest go for a simple handheld multimeter something like a UT-71D.
With the rest of the money you build yourself a few 4 1/2 digit voltmeters with the good old ICL7135 / TLC7135. You just need someone that can help you calibrate the 1.000 Vref. With something like LTC6655B-2.5LS8 you are on a good way for stability in this case but there are a few other voltage references that fit the requirements too.
In most cases you don't need more than 4 1/2 digits, but it was settled into the head of some beginners to need >5 1/2 digit multimeter, for what ever, same story as with oscilloscopes.
Remember, 4 1/2 digit equals 15bit, 5 1/2 digit equals 18bit, 6 1/2 digit equals 21bit. Refer to AN82 (Linear Technology).
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: KJDS on June 11, 2013, 08:22:25 pm
The "that sort of budget" is the confusing part. Is it the >$200 range, or close to $1k range?

No confusion there. If anyone has $1K to spend, hold off for about a week and an option may present itself...

Go on, tell us now. ...
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: Nermash on June 11, 2013, 08:29:56 pm
Rigol 6.5 digit?
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 11, 2013, 10:40:42 pm
Rigol 6.5 digit?

I've heard it's a nice unit, but I don't have one.
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: AlfBaz on June 12, 2013, 01:22:16 am
The signalpath youtube channel has a review of one here Rigol DM3068 6.5 Digit Digital Multimeter Review (https://www.youtube.com/watch?v=eR0TM3eitNk#ws)
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 12, 2013, 01:33:13 am
The signalpath youtube channel has a review of one here

I have a nicer one  ;D
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 12, 2013, 02:06:31 am
Go on, tell us now. ...

Tell you what?  :-DMM
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: AlfBaz on June 12, 2013, 02:27:01 am
The signalpath youtube channel has a review of one here

I have a nicer one  ;D
Love high end meter reviews, looking forward to it  :-+
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: EEVblog on June 12, 2013, 02:59:46 am
Love high end meter reviews, looking forward to it  :-+

https://www.eevblog.com/forum/testgear/new-agilent-34461a-6-5-digit-bench-multimeter (https://www.eevblog.com/forum/testgear/new-agilent-34461a-6-5-digit-bench-multimeter)
Title: Re: Choosing a high accuracy/resolution multimeter
Post by: npelov on June 14, 2013, 10:55:41 am
Be aware for the uV virus, it is an expensive desease  ;)

Yes I realize that it's not easy to have accuracy over time. I also understand that you can't have something good for $200. It'll age, but it should still be better than my 0.5% mastech. I'm reading reviews and information about high accuracy multimeters/standards and I'll eventually gonna buy one. I don't (yet) need uV accuracy. My idea is to have 10 times more accuracy than I need soat the end I could have 0.1-0.2%.

Aging of voltage references is something I would love to play with. I guess it has to work all the time?

Btw, I'm waiting for those up to $1000 multimeters reviews.