Author Topic: Are there any handheld DMMs that read ACV & DCV simultaneously?  (Read 10539 times)

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Offline alm

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #50 on: February 27, 2018, 11:20:45 pm »
Can you please elaborate on this?
On my Fluke 189, the AC offset in dual display mode on the 5 V range is about 5mV, so when measuring 10 mV, the error would be about 11% (which is about is pretty good for a ripple measurement), and for 20 mV the error is down to 3%. Note that the offset adds to the measurement value as the sum of squares. Obviously these are not guaranteed specs, but I find this a long way away from "unusable".
I would like to know more about this.
The offset and the input signal are two non-coherent signals, so the RMS (root-mean-square) value of their sum is \$\sqrt{V_{offset}^2+V_{in}^2}\$. See here for more information.

For example, if you RELed that offset before measurement, what would be the error then (and the measured/shown value)?
And why Fluke does not recommend or rather forbids to REL the offset for the sake of accuracy?
Keithley used to have a nice FAQ that discussed this, but I can no longer find it. Guess it got removed when their content migrated to the Tektronix website. The reason is that offset is a linear correction, while the contribution of the error is non-linear. Say you measure 5 mV with the leads shorted, and press the relative button. Now you measure 10 mV. The offset causes this 10 mV to be read as \$\sqrt{(10 mV)^2+(5 mV)^2} = 11.2 mV\$. Then the meter subtracts the 5 mV offset that you programmed, so the reading comes out as 6.2 mV, much worse than without the offset correction. For larger values like 1 V, the reading would be \$\sqrt{(1 V)^2+(5 mV)^2} = 1000.01 mV\$, but after offset correction, this would become 995.01 mV. In both cases, the offset correction makes the error much worse than without the offset correction.

And I noticed now, that in your example on Fluke 189 you are on range 5V, what about error on range 50V, would that be still
Quote
a long way from "unusable"
?
In the 50 V range, the reading with leads shorted is about 12 mV (resolution 1 mV), so it would be usable down to about 20 mV. (with 15% error). Should still be good enough to determine if a power rail is reasonably clean, or clearly lacks decoupling. For example, ATX allows up to 120 mV ripple on the 12 V rail. Measuring that should be possible with less than 1% error.
 
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Online 2N3055

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #51 on: February 28, 2018, 12:03:05 am »
It is all well explained in Analog Devices RMS-to-DC Application Guide:
http://www.analog.com/en/education/education-library/rms-to-dc-application-guide.html

Most meters use one of the AD logarithmic converters.

This is the pertinent chapter:
http://www.analog.com/media/en/training-seminars/design-handbooks/RMS-to-DC-AppGuide/SectionII.pdf

Basically, these converters have large errors, nonlinearities and  offset around zero.. It is all very well explained here...
Good read.

Also, log-antilog RMS detectors have different frequency response at low amplitudes than at higher amplitudes...

Linear Tech delta-sigma RMS converters also have problems around the zero... Different behaviour, a bit more linear conversion accuracy and frequency response trough the range, but also problems around zero...

Regards,

Sinisa
 
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Offline Electro Detective

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #52 on: February 28, 2018, 02:03:27 am »

...I too tried to measure ripple of some wall warts with Fluke 289 (and UT181a) parallel with scope,

and I came to the conclusion that this (measurement of ripple with MM on dual display) is not the way to do it .


Thanks evava, good show   :-+ 

Saved me some labour setting up the same scenario to verify that the limitations of one meter attempting to do both jobs well, may be a coin toss on accuracy depending on levels and ripple frequency/s,

when two meters (one with wide AC bandwidth) are a better no brainer method for a quick troubleshoot
without having to resort to a scope

So guys, is there any possibility of iffy readings having two meters piggybacked on a circuit/test point at certain levels?


and are AC and DC dual display meters switched to display AC+DC (one combined reading) of any real use ?  :-//

 

Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #53 on: February 28, 2018, 04:18:36 am »

[/quote]
ATX allows up to 120 mV ripple on the 12 V rail.
[/quote]
Is 120mV RMS? Then its Vp-p will exceed 600mV! Ordinary 12V power supply ripple will not be so high!
 

Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #54 on: February 28, 2018, 04:52:16 am »
Fluke189 USES dual display mode to measur ripple ,  is slow and inaccurate, and even have not  measured twice faster and accurately.
« Last Edit: February 28, 2018, 04:59:05 am by hgjdwx »
 

Offline bitseeker

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #55 on: February 28, 2018, 05:05:02 am »
Saved me some labour setting up the same scenario to verify that the limitations of one meter attempting to do both jobs well, may be a coin toss on accuracy depending on levels and ripple frequency/s,

Yes, there are accuracy sacrifices. However, if you need to know "exactly" how much AC is riding on the DC, just turn the mode switch to ACV (or mV as needed).

Quote
when two meters (one with wide AC bandwidth) are a better no brainer method for a quick troubleshoot
without having to resort to a scope

Well, to me, using one meter and turning a knob is faster and easier than setting up two meters, especially when troubleshooting involves having to move twice as many leads to multiple points in a circuit.

Quote
So guys, is there any possibility of iffy readings having two meters piggybacked on a circuit/test point at certain levels?

That depends on your meters and the circuit. With two meters measuring voltage, you have two parallel impedances introduced to the circuit. Does that lower the impediance enough to alter the measurement and/or circuit behavior enough to cause a problem?

Quote
and are AC and DC dual display meters switched to display AC+DC (one combined reading) of any real use ?  :-//

Well, that depends if knowing the overall AC+DC is of use in your situation or is it more important to know what is the DC voltage versus the AC that's riding atop it. Different measurements for different purposes.
« Last Edit: February 28, 2018, 05:06:54 am by bitseeker »
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Online 2N3055

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #56 on: February 28, 2018, 08:03:39 am »
There are many times that it is not AC riding on top of DC, but AC with DC component.....
I use DC+AC all the time to get general feeling what is going on...
Then switch to AC or DC only if that will get me some benefits (more resolution, faster response...)

So it all depends what and how you do it...

It is very useful, but not solution for all measurements...
 

Offline Terry01

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #57 on: February 28, 2018, 08:45:57 am »
I now know what will be keeping me busy for the next we while!

For a beginner like me this is a very interesting subject  :wtf:

Looking forward to getting stuck into this  :)
Sparks and Smoke means i'm nearly there!
 

Offline Electro Detective

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #58 on: February 28, 2018, 11:45:23 pm »
I now know what will be keeping me busy for the next we while!

For a beginner like me this is a very interesting subject  :wtf:

Looking forward to getting stuck into this  :)

...and the local talent here have done well to stay on topic with some relevant drifts   


Let's pray no one posts PDF file security concerns, or sneaks in some Fluke fanboy-ery..  :-DMM  Nah, can't happen, LOL   ;D


Actually gents, I have never been a fan of switching meter modes whilst hooked up to a circuit (unless very low voltages), due to a bad experience many years ago,
DUT blew up all over the shop, yet meter and me without protective eyewear (textbook dumbass) luckily intact  :phew:

I must have been in AC or DC mode and gone to the Ohms buzzer or something like that

Anyway, once bitten twice shy...  :scared:


So are meters 'designed' to handle   ?some?   switching between modes whilst hooked up to a device under test (DUT) or it's always been a no go ?

AFAIK I am not aware of any meter manufacturers giving the ok for this in their documentation  :-//

 

Offline Shock

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #59 on: March 01, 2018, 08:36:56 am »
So are meters 'designed' to handle   ?some?   switching between modes whilst hooked up to a device under test (DUT) or it's always been a no go ?

That is a good question this video here sort of answers it.

If it's both designed and tested well a good multimeter can withstand misuse.
From the Flukes 113 manual (which is the model I think they were testing):
Always use proper terminals, switch position, and range for measurements.

Careless operation is going to lead to more dangerous user mistakes down the track.
Anyway this is why Fluke is the best ever and if you don't have a Fluke you're a nobody (just kidding).
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Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
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Online 2N3055

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #60 on: March 01, 2018, 08:46:45 am »
@Electro Detective

I'm also in that group... I pretty much never rotate switch meter while connected..  I was taught how to use meter many years ago, before digital meters..
It was a moving coil world then... All manual and not much protection. Pretty much, if you made a mistake, BOOM and gone....
And dropping them to the concrete floor was a big NO...

And I still have my two meters to this day.. Still alive and in cal..
That teaches you not to abuse equipment..

I know they make them now that you can switch to ohms and apply 100V to it and nothing should happen...

BUT..... I just don't do it........ It is developing a bad habit...
You should know what are you trying to measure, make sure you can do it safely before you start probing around circuit...

Regards,

Sinisa
 
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Offline Electro Detective

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #61 on: March 01, 2018, 10:13:51 am »
Someone better word up the Fluke humble showman in that youtube video   >   youtube.com/watch?v=OEoazQ1zuUM&feature=youtu.be&t=325
that there is NO FUSE inside a Fluke 114, and no current inputs,
like hey, I own one for that reason (besides being a decent no frills meter) and have taken it apart to see what I paid for, and customary check for possible assembly-line dumbassery 

therefore NO  -quote- 'expensive fuse' exists in that 114 meter that he harps about, to protect the meter or operator in the event of a bad hair day turning the selector knob the way he did whilst applying 660 volts AC

He could have at least opened the 114 like he did the cremated red cheapie meter to show us the ummm... 'invisible expensive fuse'    :clap:


Double Dumbass and Darwin Award candidate points for not wearing gloves or eye-wear for his own anti-Murphy precaution handling the unholstered Fluke, 
nor supplying eye-wear for the audience/bystanders, thus setting a proper SAFETY example.

and aren't fuses usually in the current path on most meters anyway, not volts and ohms  :-//

and what happens if there's moisture ingress, or debris from a drop, inside the meter and the operator plays 'spin the dial' with power applied ?  :scared:


Surely Fluke can do better than this halfassed product promo     :palm:



FWIW our host Dave Jones has a dissected Fluke 114 video EEVblog #597 here >  youtube.com/watch?v=iFyEqcVpKLI

Skip to about 8.45 minutes where he gets to the main board...notice no 'expensive fuse' or gold plated fuse holder to be seen   ;D


Thanks to MJ Lorton for posting the video and useful summary at the end  :-+


EDIT:   It's a Fluke 113 the Fluke rep is using in the Youtube video   youtube.com/watch?v=OEoazQ1zuUM&feature=youtu.be&t=325
which is a basic 114 style idiot proof meter that auto selects between modes

It too has NO FUSE, either 'expensive' nor cheap glass

The 113 is too 'auto' for my liking, the fixed 'auto' Low Z can be a pita when prodding into RCD/GFCI circuits to confirm 240v or 120v etc, because it trips them!  :--


You would think Fluke would try and trash an 87V with 'spin the dial' games at 660VAC  >:D   versus a red manual range cheapie  :-[  guaranteed to issue magic smoke and fireworks,

instead they selected a Fluke with 3 position dial with auto select modes... basically a 'meter and leads' version of a a typical electricians dual wand voltage/continuity tester    :popcorn:


If their meters survive russian roulette 'spin the dial' games at high voltages, then it's some form of protection in the front end circuit/s, saving the meter,
not 'expensive' fuses in the current path AFAIK

and it's anyones guess how many times and for how long, and under what conditions any meter can survive such abuse,
or how much of it's accuracy and reliability compromised 


FWIW the only meter documentation I've ever seen suggesting  -dial changes-  is starting at the highest relevant manual range,
and selecting a lower range in the same mode if required for better accuracy and / or needle scale depending on the type of meter

« Last Edit: March 01, 2018, 11:57:37 pm by Electro Detective »
 

Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #62 on: March 01, 2018, 02:35:06 pm »
The CH2 looks at The average, CH1 to see The effective value, peak value, frequency and waveform.
Quickly evaluate power quality, have auto range and low pass filtering function, As convenient As auto range multimeter,display waveform and data within 2 seconds.


I'm sorry! Correct, the oscilloscope is set incorrectly in the picture, the probe should be set in the x1 range instead of the x10 range.
« Last Edit: March 05, 2018, 01:48:42 am by hgjdwx »
 
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Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #63 on: March 01, 2018, 03:43:10 pm »
DT4282 and U1272A
 
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Offline evava

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #64 on: March 02, 2018, 10:21:29 am »
Thank you.
Yes, scope is way to go.
Exactly my experience.
 

Offline joeqsmith

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #65 on: March 02, 2018, 01:17:45 pm »
It is the obvious answer if you wanted to characterize the AC part but not what the OP was asking.   I recently looked at an automotive meter that can detect problems with car's charging system.   Not all high ripple problems are so low a meter could not be used to detect them.

Offline ciccio

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #66 on: March 02, 2018, 01:24:41 pm »
My new UNi-t 171b measures AC+DC , and has dual display , worked out around 200 euros with tax and DHL fee's ,got it in from China via ebay.
What? I do not see dual display.
Are you referring to this model (from UNI-T website):
http://www.uni-trend.com/productsdetail.aspx?ProductsID=498&ProductsCateId=718&CateId=718

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Offline Electro Detective

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #67 on: March 02, 2018, 10:59:41 pm »
The Hioki meter above on the left is not doing as well as the Agilent for detecting low levels of AC in dual display mode

Would both meters perform better if not in Auto Range?

How well does the Agilent preform to indicate AC frequency at these low levels? Does the dual display work that way?


Would any cheap handheld scope be a better bet (and sensitive enough?) for DC and AC ripple measurements,
rather than blowing money on a cheap or big dollars dual display meter, if DC and AC ripple measurements was a main priority 

OP may be better off going that way, and have a scope to play with  :clap:   rather than adding another meter to the tool kit   :-DMM :-DMM
 
 

Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #68 on: March 03, 2018, 12:55:10 am »
DT4282's all AC range will be forced to zero when the measurement value is no more than 1000 words.
And there is no dual display  and PEAK mode in DCmV and ACmV range.
This is very bad.
« Last Edit: March 03, 2018, 01:04:12 am by hgjdwx »
 

Offline alm

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #69 on: March 03, 2018, 07:45:21 am »
Scopes generally need AC coupling to measure ripple superimposed on a DC signal. Unless it has a DC offset feature with a very wide dynamic range (unlikely, this is an obscure feature), or you connect two probes and two channels in parallel (clumsy). Their eight(ish) bit resolution is much worse than even a 3.5 digit DMM.

Offline joeqsmith

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #70 on: March 03, 2018, 07:27:55 pm »
Scopes generally need AC coupling to measure ripple superimposed on a DC signal. Unless it has a DC offset feature with a very wide dynamic range (unlikely, this is an obscure feature), or you connect two probes and two channels in parallel (clumsy). Their eight(ish) bit resolution is much worse than even a 3.5 digit DMM.

Get that old analog scope out that is not limited to the eight(ish) bits.  May also need an external LNA to get the uV signals above the scope's noise floor.   

For fun I tried to measure AC line power with my scope.  Because it's only 60Hz, I attempted to improve on the scope's resolution.

https://youtu.be/04I7nHA_HxM

Offline alm

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #71 on: March 03, 2018, 07:50:41 pm »
How would a LNA help if you want to look at the DC voltage and ripple at the same time, which was the point of this thread? Even on a low-bandwidth analog scope without expansion mesh (sharp trace), quantifying a few mV ripple on top of say a 12 V signal will be tough, if not impossible (you'd need to measure a thousandth of a division).

Offline joeqsmith

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #72 on: March 03, 2018, 08:06:48 pm »
If you are looking for uV signals and the scope has a noise floor of mVs, you can gain up the signal.  Of course you would want to set the gain to maximize the scope's dynamic range.  Of course, you are AC coupled into the LNA.  Of course, the LNA would need to have the BW and what not to look at what ever signal you were interested in.   If looking at your 1KVDC supply, best to get some HV caps.   Seems doable but more to your point, OP had asked about a meter, not a scope.  You and others seemed interested in discussing the merits so I tossed out some of my own thoughts.

Offline hgjdwx

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Re: Are there any handheld DMMs that read ACV & DCV simultaneously?
« Reply #73 on: March 05, 2018, 02:16:55 am »
I'm sorry! Correct, the oscilloscope is set incorrectly in my above picture, the probe should be set in the x1 range instead of the x10 range.
 


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