Author Topic: Suggestions for a millivolt DMM  (Read 4979 times)

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Offline Sultanpepper123

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Suggestions for a millivolt DMM
« on: October 20, 2019, 11:04:24 pm »
Hello everyone, I'm having a hard time in selecting a suitable multi meter that should measure AC voltages as low as 100 micro volts @ 50 Hz with steps of 50 microvolts. I've searched for quite some time and here they seem to have a problem in that range i suppose. My research shows that i can use Fluke's 8808A, 8845A, 287 or 289 , I may be betting on too high specs or vice versa. I would appreciate if someone sheds some light on some suggestions.

EDIT: This might be useful to some who tried to reach the reference but found out the link is dead, a screenshot from the deadlink of Gellar Labs link which illustrates the dead zone of the agilent 34401A DMM can be found here

Regards
« Last Edit: October 21, 2019, 11:52:05 am by Sultanpepper123 »
 

Online EEVblog

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Re: Suggestions for a DMM
« Reply #1 on: October 21, 2019, 04:54:57 am »
What you might need is a "millivoltmeter"
Analog ones are still handy:
https://www.alibaba.com/product-detail/MVT-171-Analog-Millivoltmeter-Electrical-Meter_60732310848.html

Most digital meter will only have a 200-500mV AC range full scale, so you need a 50,000 count meter to get 10mV resolution. 500,000 count to get 1mV resolution.
Some like the 121GW have a 50mV range.



Here is a digital one:

https://www.alibaba.com/product-detail/UNI-T-UT632-digital-AC-millivoltmeter_62341154520.html

« Last Edit: October 21, 2019, 10:53:36 am by EEVblog »
 
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Offline Gandalf_Sr

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Re: Suggestions for a DMM
« Reply #2 on: October 21, 2019, 09:44:53 am »
Well I learned something today; I was going to suggest the Keysight 34461A which is my flagship, best in house, expensive, reference, calibrated multimeter but, on checking the specs, I find that the lowest AC Volts range is 100 mV and it can 'only' measure down to 0.3% of range (on AC) which is 300 uV which misses the OP's requested resolution by a lot. 

That begs a question - What's the point of having a 6.5 digit multimeter if you can only get down to the 4th digit for any kind of measurement? Or am I missing something?
I'd like to make the world a better place but they won't give me the source code
 

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Re: Suggestions for a DMM
« Reply #3 on: October 21, 2019, 10:39:26 am »
Well I learned something today; I was going to suggest the Keysight 34461A which is my flagship, best in house, expensive, reference, calibrated multimeter but, on checking the specs, I find that the lowest AC Volts range is 100 mV and it can 'only' measure down to 0.3% of range (on AC) which is 300 uV which misses the OP's requested resolution by a lot. 
That begs a question - What's the point of having a 6.5 digit multimeter if you can only get down to the 4th digit for any kind of measurement? Or am I missing something?

It's only an issue with AC, that's a special snowflake.
 

Online EEVblog

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Re: Suggestions for a DMM
« Reply #4 on: October 21, 2019, 10:46:00 am »
 

Offline Gandalf_Sr

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Re: Suggestions for a DMM
« Reply #5 on: October 21, 2019, 10:48:25 am »
It's only an issue with AC, that's a special snowflake.
Yes, my wording wasn't the best but thanks anyway for the clarification.
I'd like to make the world a better place but they won't give me the source code
 

Offline Sultanpepper123

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Re: Suggestions for a DMM
« Reply #6 on: October 21, 2019, 11:19:05 am »
What you might need is a "millivoltmeter"
Analog ones are still handy:
https://www.alibaba.com/product-detail/MVT-171-Analog-Millivoltmeter-Electrical-Meter_60732310848.html

Most digital meter will only have a 200-500mV AC range full scale, so you need a 50,000 count meter to get 10mV resolution. 500,000 count to get 1mV resolution.
Some like the 121GW have a 50mV range.



Here is a digital one:

https://www.alibaba.com/product-detail/UNI-T-UT632-digital-AC-millivoltmeter_62341154520.html



Thank you Dave for the help and guidance. Just to let you know how ecstatic i am right now since i'm a fanboy of your channel and since a considerable part of reason where i am right now is due to watching your videos.

Just one question, which brand would you recommend as a reliable brand ( i prefer it to be digital one tbh ) ?.

Regards
Omar
« Last Edit: October 21, 2019, 11:24:00 am by Sultanpepper123 »
 

Offline Fungus

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Re: Suggestions for a millivolt DMM
« Reply #7 on: October 21, 2019, 12:01:45 pm »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.



$20 on Aliexpress:  :popcorn:

https://www.aliexpress.com/item/33001360039.html

(image from Dave's video review  :) )
« Last Edit: October 21, 2019, 12:19:03 pm by Fungus »
 
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Offline Performa01

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Re: Suggestions for a millivolt DMM
« Reply #8 on: October 21, 2019, 12:17:32 pm »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.
Can you demonstrate the measurement of a 100µV signal with reasonable accuracy as requested by the TO?
 

Offline Fungus

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Re: Suggestions for a millivolt DMM
« Reply #9 on: October 21, 2019, 12:19:55 pm »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.
Can you demonstrate the measurement of a 100µV signal with reasonable accuracy as requested by the TO?

Dave did:

https://youtu.be/xdGQEVdxmQQ?t=689

(at 11:28)
« Last Edit: October 21, 2019, 12:24:52 pm by Fungus »
 

Offline Performa01

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Re: Suggestions for a millivolt DMM
« Reply #10 on: October 21, 2019, 12:30:12 pm »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.
Can you demonstrate the measurement of a 100µV signal with reasonable accuracy as requested by the TO?

Dave did:

https://youtu.be/xdGQEVdxmQQ?t=689

(at 11:28)

Sorry, I can only see 9.66mV (and higher) there.
 
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Offline evava

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Re: Suggestions for a millivolt DMM
« Reply #11 on: October 21, 2019, 12:40:33 pm »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.
Can you demonstrate the measurement of a 100µV signal with reasonable accuracy as requested by the TO?

Dave did:

https://youtu.be/xdGQEVdxmQQ?t=689

(at 11:28)

It is known problem with RMS converter, he only gives reasonable values from few % of range upwards.
If only we could switch off RMS conversion, then we could use full resolution of DMMs.
 

Offline 2N3055

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Re: Suggestions for a millivolt DMM
« Reply #12 on: October 21, 2019, 12:50:33 pm »
At 50 Hz you could also use amplifier to amplify signal and then measure after amplifier...
 

Offline Fungus

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Re: Suggestions for a millivolt DMM
« Reply #13 on: October 21, 2019, 01:00:03 pm »
It is known problem with RMS converter, he only gives reasonable values from few % of range upwards.
If only we could switch off RMS conversion, then we could use full resolution of DMMs.

Maybe somebody could try it. I don't have anything calibrated that goes that low.

At 50 Hz you could also use amplifier to amplify signal and then measure after amplifier...

That, too.

« Last Edit: October 21, 2019, 01:02:34 pm by Fungus »
 

Offline evava

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Re: Suggestions for a millivolt DMM
« Reply #14 on: October 21, 2019, 01:24:23 pm »
It is known problem with RMS converter, he only gives reasonable values from few % of range upwards.
If only we could switch off RMS conversion, then we could use full resolution of DMMs.

Maybe somebody could try it. I don't have anything calibrated that goes that low.

Take Fluke 287/289 for example:
when 100uV at 50Hz, manual stated accuracy 0.3% +- 45counts, see picture.

Maybe it is actually better, who knows.
 

Offline Kleinstein

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Re: Suggestions for a millivolt DMM
« Reply #15 on: October 21, 2019, 01:50:10 pm »
Analog RMS converter have a problem if the signal gets too small (e.g. below some 1% of full scale). The problem starts with the rectification part detecting the sign - first it gets slower (reducing the BW at lower amplitude) and finally fails. Some version also get a rather sluggish response at low levels.
Things are better (or at least can be), with usually expensive (though it does not have to)  DMMs that use digital methods for RMS. So the Keysight 34461 could actually work well even below 1 mV, though the specs do no include this. The advantage here is that there is no need for a separate sign detection. So the BW can be constant and no magic limit where things break down.  Residual noise compensation is also easier in software than in analog HW.

100 µV are still 1 % of the 10 mV range of the cheap meter. So chances are it could still work - at least for low frequency. However such a test can vary from unit to unit - some may work better than others.

Turning off RMS is easy, just use the DC range  :-DD .  Of cause this does not solve the problem unless the meter is really fast and can do the math (like man DSOs can).
 

Offline egonotto

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Re: Suggestions for a millivolt DMM
« Reply #16 on: October 22, 2019, 04:24:26 am »
Hello,

I try my AN8009.
I feed a 50Hz sine wave so that the AN8009 shows about 50 µV.
Than i double the input and the AN8009 shows about 75 µV

My AN8008 shows with the above settings about 70 µV and 90 µV.

Best regards
egonotto
 
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Offline evava

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Re: Suggestions for a millivolt DMM
« Reply #17 on: October 22, 2019, 06:49:21 am »
Analog RMS converter have a problem if the signal gets too small (e.g. below some 1% of full scale).
...
Turning off RMS is easy, just use the DC range  :-DD .  Of cause this does not solve the problem unless the meter is really fast and can do the math (like man DSOs can).
This multimeter https://lygte-info.dk/review/DMMKyoritsu%20KEW1062%20UK.html Kyoritsu KEW1062 can switch RMS on and off:
Quote
It is possible to switch between RMS and mean in AC readings, default is RMS, but can be changed in configuration.
I think in this case it could be useful.
EDIT:  maybe I am not right, see picture: accuracy stated in manual is also in MEAN value detection from 10% of range!

P.S. Thank you very much for your reviews, lygte-info!
« Last Edit: October 22, 2019, 07:17:36 am by evava »
 

Online EEVblog

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Re: Suggestions for a millivolt DMM
« Reply #18 on: October 22, 2019, 08:29:29 am »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.

(Attachment Link)

$20 on Aliexpress:  :popcorn:

https://www.aliexpress.com/item/33001360039.html

(image from Dave's video review  :) )

Forgot about that, great!
Limited bandwidth though of course.
 

Offline Fungus

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Re: Suggestions for a millivolt DMM
« Reply #19 on: October 22, 2019, 08:54:23 am »
Those Aneng 8008 multimeters have a 10mV AC range with 1uV resolution.

Forgot about that, great!
Limited bandwidth though of course.

How low do they go? Some people are doubting they still work with a an input signal of 100uV (or lower).

Maybe you could do a quick test to prove them wrong...  :popcorn:

(I'd do it but I don't have the equipment)

 

Online BravoV

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Re: Suggestions for a millivolt DMM
« Reply #20 on: October 22, 2019, 09:07:00 am »
You should try to find your local market for those old analog millivolt meter, scored one last year locally as the crowd are flocking into digital meter, their lost.

A GWInstek analog, at 300uV range has accuracy about +/- 3% from 20 Hz to 200 kHz, not bad.

 
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Offline TurboTom

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Re: Suggestions for a millivolt DMM
« Reply #21 on: October 22, 2019, 12:32:36 pm »
I just tested the low AC ranges of three "cheapo" Angeng meters and an RM303 4.5 digit instrument with probably the same chipset:

All the instruments perform identically with only sub-percent deviation between them. 1mV 50Hz sine is accurate on all of them within maybe two or three least digits tolerance. At 100µV 50Hz they all indicate a little low, maybe by 3%. At 50µV, indication is 30µV with strong fluctuations. Below 30µV results in a displayed value of plain zero. The frequency ranges up to approx. 2kHz (sine) where the displayed value virtually doesn't differ at all from the readings at 50Hz, above that it quickly drops to zero (within one octave).

Seems like 100µV is the lowest AC value that can be measured decently accurate with the Aneng (and siblings) family of cheapo-multimeters.

Just for interest, my venerable Fluke 89 IV isn't usable at that low levels at all. Even though it has a mV AC range with 1µV resolution, it just dithers around heavily at signal levels below 5mV.
 
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Offline Gandalf_Sr

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Re: Suggestions for a millivolt DMM
« Reply #22 on: October 22, 2019, 12:55:24 pm »
I just a very quick and basic test with my Aneng 8008 fed by a DG1062Z, the lowest output I can get is 800 uV rms and, at 500 Hz the Aneng reads within 2%.
I'd like to make the world a better place but they won't give me the source code
 

Offline dom0

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Re: Suggestions for a millivolt DMM
« Reply #23 on: October 22, 2019, 04:23:15 pm »
HP 3400A has a noise floor of something like 60 µVrms. It's also a true RMS indicating meter. Supports very high crest factors.

For pure sine signals there are many more options, since it's easier to measure these simply by using a good amplitude detector. Look for "HF Millivoltmeter". For example, Philips PM 2554 covers a similar range as the 3400A (~50 µV - 300 V). Practically every instrument manufacturer built these, with varying sensitivity, accuracy and bandwidth.

Preamplifier for a scope is another option.
,
 
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Online SilverSolder

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Re: Suggestions for a millivolt DMM
« Reply #24 on: October 22, 2019, 04:34:48 pm »

If the source impedance is low...   the world famous uCurrent actually works as a decent amplifier at these kinds of frequencies.

 


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