Author Topic: EEVblog #1007 - Is a $25 Multimeter Any Good  (Read 94385 times)

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Online joeqsmith

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #375 on: July 26, 2017, 03:52:37 am »
Looks like we are moving out of the 61010 standards now.   I've thought about trying to get my hands on a HV probe for the fun of it but price was more than I was willing to give up.   It would be interesting to see how they are made.     
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Offline BU508A

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #376 on: July 26, 2017, 06:35:23 am »
Looks like we are moving out of the 61010 standards now.   I've thought about trying to get my hands on a HV probe for the fun of it but price was more than I was willing to give up.   It would be interesting to see how they are made.   

Do you mean these Benning Duspol things?
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Online joeqsmith

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #377 on: July 26, 2017, 11:26:21 am »
Looks like we are moving out of the 61010 standards now.   I've thought about trying to get my hands on a HV probe for the fun of it but price was more than I was willing to give up.   It would be interesting to see how they are made.   

Do you mean these Benning Duspol things?
Since the 61243 standard is on the table, I was thinking about those voltage detectors on the poles that they use at the substations.  I don't know anything really about them or the 61243 standards.  It's a whole new world. 
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Offline tronde

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #378 on: July 26, 2017, 03:49:36 pm »
A place to begin.
Russian version of  61243-3-2014. Use google translate.

http://docs.cntd.ru/document/1200115411
 

Online joeqsmith

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #379 on: July 27, 2017, 04:10:34 am »
Did some searching.  Some of those non-contact overhead line detectors were good into the 400KV+ in wet weather conditions and safe.   

IEC 61243-1: Live working - Voltage detectors - Part 1: Capacitive type to be used for voltages exceeding 1kV a.c.
IEC 61243-2: Live working - Voltage detectors - Part 2: Resistive type to be used for voltages of 1kV to 36kV a.c.
IEC 61243-3: Live working - Voltage detectors - Part 3: Two-pole low-voltage type
IEC 61243-6:2017(E)  portable non-contact voltage detectors

I may look into getting 1-6.  It's pretty interesting stuff. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline kalel

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #380 on: July 27, 2017, 02:59:08 pm »
Did some searching.  Some of those non-contact overhead line detectors were good into the 400KV+ in wet weather conditions and safe.   

IEC 61243-1: Live working - Voltage detectors - Part 1: Capacitive type to be used for voltages exceeding 1kV a.c.
IEC 61243-2: Live working - Voltage detectors - Part 2: Resistive type to be used for voltages of 1kV to 36kV a.c.
IEC 61243-3: Live working - Voltage detectors - Part 3: Two-pole low-voltage type
IEC 61243-6:2017(E)  portable non-contact voltage detectors

I may look into getting 1-6.  It's pretty interesting stuff.

Speaking of non-contact voltage detectors (even cheap ones), what are the possible dangers of using those, e.g. is there a chance of some arcs crossing over to it during high voltage spikes?
 

Online xavier60

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #381 on: August 08, 2017, 12:25:46 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.
 The meter used in Dave's review appears to read normally.
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Offline FrankBuss

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #382 on: August 08, 2017, 01:17:59 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.

I got my AN8008 last week and can confirm this, it shows only 0 when below +/-5uV. Have to do a better setup, maybe Dave can test this, too, it is jumping a bit. Additionally it feels like it has a little bit of hysteresis, so when dialing it down from 10uV to -10uV, it stays longer at 0uV until it jumps to some value less than -5uV.
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Offline retrolefty

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #383 on: August 08, 2017, 01:46:37 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.

I got my AN8008 last week and can confirm this, it shows only 0 when below +/-5uV. Have to do a better setup, maybe Dave can test this, too, it is jumping a bit. Additionally it feels like it has a little bit of hysteresis, so when dialing it down from 10uV to -10uV, it stays longer at 0uV until it jumps to some value less than -5uV.

 Very interesting. We did similar in digital process control to quite down zero flow/pressure/level/etc. It was an optional parameter but the console operators seemed to prefer nice straight lines.   :-//
if i recall properly I think the parameter was named CLAMPING
 

Offline Mark Hennessy

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #384 on: August 08, 2017, 03:47:42 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.

I got my AN8008 last week and can confirm this, it shows only 0 when below +/-5uV. Have to do a better setup, maybe Dave can test this, too, it is jumping a bit. Additionally it feels like it has a little bit of hysteresis, so when dialing it down from 10uV to -10uV, it stays longer at 0uV until it jumps to some value less than -5uV.

Several people have picked up on this, but I don't think anyone has mentioned that the AN8002 and AN860B+ do it as well. These meters have less resolution, so it's +/-50uV in their case. This +/-5 LSB behaviour is clearly a function of the IC, but I wonder if it can be altered via the EEPROM?
 

Offline deflicted

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #385 on: August 08, 2017, 05:41:11 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.

I got my AN8008 last week and can confirm this, it shows only 0 when below +/-5uV. Have to do a better setup, maybe Dave can test this, too, it is jumping a bit. Additionally it feels like it has a little bit of hysteresis, so when dialing it down from 10uV to -10uV, it stays longer at 0uV until it jumps to some value less than -5uV.

Several people have picked up on this, but I don't think anyone has mentioned that the AN8002 and AN860B+ do it as well. These meters have less resolution, so it's +/-50uV in their case. This +/-5 LSB behaviour is clearly a function of the IC, but I wonder if it can be altered via the EEPROM?

I'm an electronics newb, so forgive me if this is a dumb question, but is this possibly an intentional deadband that they put in there due to excessive ADC jitter in that region? I deal with stuff like that on the software side of things at work, but I'm not an EE so I only have a fuzzy understanding of what the issues are on the electrical side of things. We apply a deadband in software to some of the ADC readings we get, for that reason (too much jitter near zero). But the stuff I work on is avionics related, with the ADCs embedded in various position sensors, etc. So I'm not sure if the same thing would apply to whatever's going on inside the DMM.
« Last Edit: August 08, 2017, 05:46:25 pm by deflicted »
 

Offline Specmaster

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #386 on: August 08, 2017, 05:58:49 pm »
I recently got an AN8008 mainly for the one microvolt resolution.  I notice that the display reads zero between the range of -5uv and +5uv.  I wonder if the manufacturer has recently done this purposely to try to hide drift.

I got my AN8008 last week and can confirm this, it shows only 0 when below +/-5uV. Have to do a better setup, maybe Dave can test this, too, it is jumping a bit. Additionally it feels like it has a little bit of hysteresis, so when dialing it down from 10uV to -10uV, it stays longer at 0uV until it jumps to some value less than -5uV.

Several people have picked up on this, but I don't think anyone has mentioned that the AN8002 and AN860B+ do it as well. These meters have less resolution, so it's +/-50uV in their case. This +/-5 LSB behaviour is clearly a function of the IC, but I wonder if it can be altered via the EEPROM?

I'm an electronics newb, so forgive me if this is a dumb question, but is this possibly an intentional "deadband" that they put in there due to excessive ADC jitter in that region? I deal with stuff like that on the software side of things at work, but I'm not an EE so I only have a fuzzy understanding of what the issues are on the electrical side of things. We apply a deadband in software to some of the ADC readings we get, for that reason (too much jitter near zero). But the stuff I work on is avionics related, with the ADCs embedded in various position sensors, etc. So I'm not sure if the same thing would apply to whatever's going on inside the DMM.
It could well be, if avionics don't require that level accuracy then I seriously doubt if most people involved in electronics do either, I expect that I'm about to get shot at here now  :scared: but sometimes I cant help but wonder if the precision of meters that go to 3 4 or 5 significant digits after the decimal point aren't like a case of more bragging rights, similar to the 0 to 62mph time of a car?
Who let Murphy in?
 

Offline Kalvin

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #387 on: August 08, 2017, 06:02:01 pm »
It could well be, if avionics don't require that level accuracy then I seriously doubt if most people involved in electronics do either, I expect that I'm about to get shot at here now  :scared: but sometimes I cant help but wonder if the precision of meters that go to 3 4 or 5 significant digits after the decimal point aren't like a case of more bragging rights, similar to the 0 to 62mph time of a car?

Sometimes you need high dynamic range which requires more digits.
 

Offline Fungus

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #388 on: August 08, 2017, 06:16:06 pm »
It could well be, if avionics don't require that level accuracy then I seriously doubt if most people involved in electronics do either, I expect that I'm about to get shot at here now  :scared: but sometimes I cant help but wonder if the precision of meters that go to 3 4 or 5 significant digits after the decimal point aren't like a case of more bragging rights, similar to the 0 to 62mph time of a car?

Sometimes you need high dynamic range which requires more digits.

Or you might want to watch a battery discharge - very small changes in voltage.
 

Offline Specmaster

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #389 on: August 08, 2017, 09:38:39 pm »
It could well be, if avionics don't require that level accuracy then I seriously doubt if most people involved in electronics do either, I expect that I'm about to get shot at here now  :scared: but sometimes I cant help but wonder if the precision of meters that go to 3 4 or 5 significant digits after the decimal point aren't like a case of more bragging rights, similar to the 0 to 62mph time of a car?

Sometimes you need high dynamic range which requires more digits.

Or you might want to watch a battery discharge - very small changes in voltage.
Is it really a requirement to watch every single mv? surely not, 5mv steps or even 10 mv steps should be enough. Don't get me wrong, I myself like to as many digits as possible, it looks very impressive but can also be a pain watching digits keep jumping back and forth when your trying measure something, so much so that at times I have to resort to my analogue meters, so much easier at times.
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Online xavier60

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #390 on: August 08, 2017, 09:53:46 pm »
Ill be using my AN8008 to find shorts on laptop main boards by measuring voltage drops on the ground plain while applying a safe bias current to the problem rail. Although the +-5uv dead band won't be a problem in practice, I would rather it not be present.
It would be too frustrating trying to get the ebay sellers to understand and pass it back to the manufacturer.
Just hope that the manufacturer finds this thread.
« Last Edit: August 08, 2017, 09:56:49 pm by xavier60 »
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Offline floobydust

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #391 on: August 09, 2017, 12:21:20 am »
I think that is a really good use of the uV range as you can see which traces have the largest voltage drop leading to the short.
I use a thermal imaging camera for this now.
 

Offline Brumby

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #392 on: August 09, 2017, 03:59:53 am »
Is it really a requirement to watch every single mv? surely not, 5mv steps or even 10 mv steps should be enough.
First, the range we are looking at is microvolt (uV) not millivolt (mV) - but your point is still valid.

The requirement for accuracy is dependent on the circumstance.  For most day-to-day situations I encounter at under 12V, 50mV accuracy is quite good enough - but there are some occasions where I found this would be totally inadequate and I needed those smaller units of resolution.

It is to those situations where this discussion is speaking - and I, for one, am not really happy about the idea that someone has made a decision to include an arbitrary "dead spot" - especially one that is not advertised.

Call me weird, but I would much rather have the "best guess" of the meter's ADC with a large error bar than not have any idea what's going on.  For example, if it gave me a reading of 2uV with an error range of +/- 2uV, then a change from zero would tell me something is happening.  With a 5uV dead spot - you just wouldn't know.

This is the thing about test and measuring equipment - they get used in all sorts of different situations where you cannot always make design decisions in that equipment that affect fundamental expectations without at least making those very clear from the outset.

It is always useful for someone to know the limitations of their equipment - and it is essential when they start pushing into those regions.  If I had the choice in a situation like this, I would strongly lean towards having a noisy measurement than a 'cleaned up' one.  At least with the noisy one, I would see the fluctuations - which would remind me of this limitation or prompt me to check if this was normal.  With a "cleaned up" reading - I just wouldn't have any indication ... and I might spend many hours chasing a "problem" in my circuit that simply wasn't there.

I have little doubt that any "dead spot" techniques used in avionics would be specific to the task - and that the implications of doing so would have been well examined before implementing them in respect to anything that leaves the ground.
« Last Edit: August 09, 2017, 04:07:14 am by Brumby »
 

Offline deflicted

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #393 on: August 09, 2017, 06:30:50 am »
I have little doubt that any "dead spot" techniques used in avionics would be specific to the task - and that the implications of doing so would have been well examined before implementing them in respect to anything that leaves the ground.

Please keep in mind this was just me being a newb and speculating in all of my newbishness as to what might be the reason for the blind spot in the DMM, and this was based entirely on me just trying to relate what we're seeing with this DMM to a situation I'm familiar with. It was just a question, not a statement of fact, or even an attempt at an educated guess. I was just wondering aloud whether the two situations might be related somehow. I have absolutely no idea what the designers of this DMM were thinking with regard to the +/- 5uV region.

Having said that, yes, the cases where one would use a deadband in avionics are limited and problem-specific, and tend to be carefully scrutinized.
 

Offline IanB

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #394 on: August 09, 2017, 08:07:24 am »
More than one person has posted that their (non-AN8008) meter was "faulty" as it displayed fluctuating and non-zero voltages when not measuring anything. So one can imagine the manufacturers might clamp the display to zero to placate naive users and stop them complaining.
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Offline Specmaster

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #395 on: August 09, 2017, 08:35:56 am »
I'm just being the devils advocate here.

With these DMM's high sensitivity to extraneous noise (induced voltages in the lower V ranges) how can you sure that what you're reading is factual or not? I'm sitting here now looking at my Philips bench meter not connected to anything apart from a set of probes and I'm getting anything from 0.51mv to 11.77mv dc depending on close I get to the meter and on VAC, I get from 0.5613V to 0.9638V. Things are much about the same with my handheld DMM's as well?

Given this, how is it possible to be certain that what you are reading is a true reflection of what is happening in the circuit your testing / working on, and not just natural background activity?
Who let Murphy in?
 

Offline Brumby

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #396 on: August 09, 2017, 08:54:50 am »
This is where you need the skill an understanding of your environment - and the antennae you connect to the input terminals of your meter.

All too often, people blindly ignore the effect of the measuring equipment on the circuit at hand - but even more ignore the effect of the environment on the measuring equipment.

When you get into low level and high precision measurements - you have to pay attention.  Just ask any volt nut.
 

Offline Specmaster

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #397 on: August 09, 2017, 09:10:48 am »
I agree, but just do you null out the environmental effects? And how can you be really sure that the measurements that you see are down to the circuit only and not having environmental effects on them?
Who let Murphy in?
 

Offline Brumby

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #398 on: August 09, 2017, 09:26:29 am »
Indeed.

The answer to that is far beyond the capability of a post on a forum - and there a far more people out there that can give better answers than I.

Understanding the basics is essential of course, but experience cannot be beaten.


You ask a good question.
 

Offline maukka

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Re: EEVblog #1007 - Is a $25 Multimeter Any Good
« Reply #399 on: August 09, 2017, 09:42:33 am »
Got mine the other day. It's very cute and small. Seems to be accurate in the voltage ranges as well.



 


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