Multimeters at 500.000 counts ... Do we need more than that ?  - Page 1
Forum section: electronics / projects

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 30, 2011, 04:01:33 pm
content: Multimeters at 500.000 counts ... Do we need more than that in a handhold DMM ?The question sounds simple, but, is it out there any easy answers ?Should we say to the manufactures .... stop we do not need more counts, use your R&D for making better other aspects than that.

author: BravoV
author_rank: Super Contributor
timestamp: October 30, 2011, 05:12:23 pm
content: Its easy answer, depends who "we" are talking about, andwhich market segmentis those manufacturers are targeting or planning for new product.If "we" are electricians that work mostly on high voltage power mains or power installations like yourself, then 500.000 counts is way overkill, c'mon, you have to admit that too.Have few friends that are experienced electricians, mostly they claimed that that those high counts meters especially hand held usually is not for the real job, but merely for bragging factor.But say if "we" are bunch of calibration operators that are working of ppm degrees everyday when doing high precision calibration job, I would say 500.000 counts still not enough, hell, even with 1.000.000 count / 1 ppm resolution will not make these guys completely happy.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 30, 2011, 06:02:33 pm
content: Well my own wish list about the 500,000 counts portable solutions, will be an sample rate of 6 times per second.Until now and probably the start of 2012, the max that we have see is up to 1.25/S nominal .. not bad, but still away from my liking.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 30, 2011, 06:59:56 pm
content: I like my 6 1/2 digit bench meters, but in a handheld it would seem like a distraction. My old Fluke 77 does everything I need in a handheld, but I'm old school. Now, if a meter also has a frequency counter function, I can see where having more digits would be nice. Even the counters built into digital scopes leave a lot to be desired in terms of resolution and update. IMO, fast update is a hugely desirable feature.

author: Unknown
author_rank: Unknown
timestamp: October 30, 2011, 07:10:31 pm
content: Fast sampling rates have always been the domain of the system/bench meters. Even a 1981 HP 3456A will do 120 readings per second with auto zero or 210 without at 5.5 digits of resolution. A modern Agilent 34410A will do 10k readings per second at 5.5 digits. I guess the main reason is that these specs are especially important in system applications, where reading rate is directly proportional to throughput. For example if you want to characterize a part at all possible combinations of parameters. Not much point in hundreds or thousands readings per second if the purpose is just to display them for the user, since the human brain is unable to process information that fast.Not sure why the handhelds are unable to sample at something like 10 readings per second, I find a meter with a faster update rate much nicer to use. So I use $100 bench meters instead of paying an order of magnitude more for a handheld with similar specs. Maybe the power budget and parts count of handheld meters makes it hard to increase the reading rate? Or maybe they just don't care.Resolution is not the important spec, I care more about accuracy. What's the point of a 5.75 digit meter if the accuracy is the same as a 4.5 digit one? But for most applications, usability issues like display quality (LED or VFD is much nicer than LCD) and reading rate are much more important in my opinion.

author: McMonster
author_rank: Frequent Contributor
timestamp: October 30, 2011, 07:24:27 pm
content: Quote from: Kiriakos-GR on October 30, 2011, 06:02:33 pmFor the little I could check where I am now for my SANWA PC5000a the refresh rate is actually much higher than 1.25 times per second. On V DC and mV DC it's almost identical on both settings while simply holding the probes in hands, about 5 times per second. I'll do more test when I'll be back at my lab tomorrow.

author: Balaur
author_rank: Unknown
timestamp: October 30, 2011, 07:36:58 pm
content: Personally, I'm perfectly happy with 4000 or 6000 counts with a good 0.1%+1d.I consider other features far more important, but it's difficult to find a multimeter with all these:- fast autoranging- a rotary switch with all the possible measurement choices, or at least with some reasonable defaults- decent AC bandwidth (at least audio, come on, it's not this hard)Also, I would really appreciate an extended diode range (up to at least 4.5-5V) with a selectable current up to 10mA (let's say) that could test all those white and UV LEDs. Most of the multimeters are pathetic in this field.

author: Tony R
author_rank: Regular Contributor
timestamp: October 30, 2011, 07:45:10 pm
content: I guess it depends on what you want to do with it. If I was an electrician I may not be concerned in anything past a decimal in my everyday work. My major is computer engineering, and many times I'm only concerned with if it is a high or low. But sometimes when I'm doing analog work knowing it as accurately as I can down. It also comes in handy when you are doing high precision stuff, like working with 0.01% tolerance resistors.You wonder at which point does the resistance/inductance/etc. in the probes and internals of the DMM make the least significance decimal meaningless...The point is perhaps the high counts is not for everyone, but they are useful if you need it.Sometimes the most significant data is in the most insignificant details.

author: Unknown
author_rank: Unknown
timestamp: October 30, 2011, 08:13:50 pm
content: Quote from: Tony R on October 30, 2011, 07:45:10 pmFour wire measurements help with this. But if you check the accuracy specs, the last digit is rarely accurate (how many 4.5 digit meters have a basic accuracy of 100ppm?), although it may help with relative measurements (resolution versus accuracy).Quote from: Tony R on October 30, 2011, 07:45:10 pmThere are definitely cases where everything but the last digits is boring and predictable. For example when measuring the temperature coefficient of resistors. Even a crappy resistor won't change from 1 kohm to 2 kohm due to small temperature changes.

author: EEVblog
author_rank: Unknown
timestamp: October 30, 2011, 10:11:14 pm
content: Quote from: alm on October 30, 2011, 07:10:31 pmPower consumption may have a fair bit to do with that?QuoteResolution can be very useful, even in a 1% accuracy grade instrument, to allow you to match components and do relative difference measurements etc.Generally, even a basic 1% class instrument will be just as short term stable and linear as a high class instrument, so it's possible to use it for such work.QuoteLED and FVD also rule out practical everyday use handheld instruments of course.LCD is the only solution for handheld meters.Dave.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 30, 2011, 11:34:55 pm
content: Quote from: McMonster on October 30, 2011, 07:24:27 pmI will use some terminology of car mechanics ...At 50.000 counts it works with a faster gear box 5 samples nominal, that is good enough.And at 500.000 uses a slower gear box, check yous Users manual. ( I have read it all ready )

author: Unknown
author_rank: Unknown
timestamp: October 30, 2011, 11:57:29 pm
content: Quote from: EEVblog on October 30, 2011, 10:11:14 pmThis assumes good linearity and low noise, which are rarely specified for affordable meters. Is the difference between 100.01 mV and 100.06 mV significant or is it just noise? Hard to tell without manufacturer specs or gathering statistics.Quote from: EEVblog on October 30, 2011, 10:11:14 pmWhat about OLED?Even in LCD there are varying degrees of suckiness, some have better viewing angle and contrast than others. The speed and better display does lead me to prefer bench meters for some tasks, though.

author: amspire
author_rank: Super Contributor
timestamp: October 31, 2011, 12:13:12 am
content: Quote from: alm on October 30, 2011, 11:57:29 pmWell not really. If the last digit or two is unstable, then yes that is not much use. But if it is fairly stable, then the extra digits are very useful. You can use the resolution for matching resistors, comparing voltage references.Also if the meter auto zero works well, then the extra resolution is great for measuring the null point on a bridge circuit like a wheatsone bridge.Richard

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 31, 2011, 01:30:46 am
content: Balaur- +1 on all your points. I hadn't even thought of them, but I'd sure buy a meter with those features.Concerning absolute accuracy, somebody tell me an application where 100.0 VDC vs 100.5 VDC actually makes any difference at all. Confirming some spec, sure, but I mean where circuit function is affected. I don't think anybody is making analog computers anymore. Come on, I'm waiting!

author: IanB
author_rank: Super Contributor
timestamp: October 31, 2011, 01:32:44 am
content: Quote from: amspire on October 31, 2011, 12:13:12 amTell me about auto zero. Every previous meter I have owned reads 0.000 on a voltage range if I short the probes together. By my new Protek 6500 is not following my expectation in this regard. On the mV range it has an offset of -0.009 mV with shorted probes, and on the V range it has an offset of -0.0005 V. This offends my sense of tidiness. What do other 50,000 count meters do with the same test? Do I have an oddball, or is this par for the course with a high resolution meter?

author: EEVblog
author_rank: Unknown
timestamp: October 31, 2011, 02:03:35 am
content: Quote from: Conrad Hoffman on October 31, 2011, 01:30:46 amI could start listing some reasons, but better to ask yourself:- Why do meters have an accuracy spec at all?- Why do various accuracy/price ranges exist if absolute accuracy doesn't matter in practice? (all the way from 1%+ to 0.0001%)- Why do people get their meters calibrated? (which is mostly checking it's absolute accuracy)Dave.

author: amspire
author_rank: Super Contributor
timestamp: October 31, 2011, 02:16:49 am
content: Quote from: Conrad Hoffman on October 31, 2011, 01:30:46 amThe most obvious case is when you are relying on two different meters to read a voltage drop. Say you are in one building and your mate is at the other end of the wires in another building.Say it is 100V at your end, and 99V at the other end.Ideally you would like to be able to trust the readings without having to construct a meter calibration chart to match up the two meters.The other much more important case is when you have just realized that your new $400 multimeter is out by 0.5% and that 100.5V reading is sending you into an extreme state of depression.

author: ToBeFrank
author_rank: Regular Contributor
timestamp: October 31, 2011, 02:46:51 am
content: Quote from: EEVblog on October 31, 2011, 02:03:35 amBecause if you don't give an engineer a spiffy spec to meet, he won't know what to do?

author: BravoV
author_rank: Super Contributor
timestamp: October 31, 2011, 03:28:45 am
content: Assuming we're talking "handheld" multimeter, I think we must agree to certain extend that no single multimeter will make all parties happy.Field electrician work meter is definitely different vs multimeter for EE or designer working in a nicely & comfy bench table in the lab environment.Although I'm not an electrician, I would imagine if I was a high voltage or heavy industry electrician that spend most of my times in harsh or even danger environment like in antenna tower or room with noisy filled with heavy machinery, rather than it can displays gazillion digits accuracy, I rather preferred if my multimeter's probe somehow can be used as a safety harness, or even better the meter itself can be used safely as a hammer blocklol .. like to bang out out a rusty metal enclosure door of the power distribution box that is hanging hundreds meters above the ground, thats stubbornly refused to open while I was still hanging up there (yeah, I'm exaggerating).Just a reminder, the thread starter is an industrial electrician, imo it is not realistic to expect an industrial electrician at the field task frequently to do resistors sorting to get a 0.0001% pair for the accurate voltage divider.Regarding display refresh speed, even it is capable to display at human eyes rates, c'mon, again realistically, do you trust your own eyes for a single event of a quick miliseconds reading spike rather than looking at the min or max value captured by the meter ?

author: Unknown
author_rank: Unknown
timestamp: October 31, 2011, 04:27:33 am
content: About the importance of refresh speed, I've had a fluctuating signal that appeared constant with a meter only updating a few times per second, but was clearly unstable on a faster meter. A fake-analog bar graph would also have worked in this case. Min/max might be used to quantify the fluctuations, but you have to be aware of them first.Another issue is adjusting trimmers so the voltage is 10.00 V. Humans need fast feedback since we don't have PID controllers. It's very annoying to start turning and have to wait a while before you even know if you're going in the right direction. A bar graph is not very useful if you're down to the least significant digits.

author: Lightages
author_rank: Unknown
timestamp: October 31, 2011, 05:06:42 am
content: Quote from: Conrad Hoffman on October 31, 2011, 01:30:46 amThat is easy. Solar power system batteries. Their life depends entirely on proper voltages while being charged, and the balance of the voltages and current involved within a bank of batteries.While not usually in the range of 100 VDC , voltages around 50 and 60 are quite common and a difference of 0.2 VDC between different batteries in a bank can mean many amperes imbalance between batteries causing some to not charge properly or discharge faster than the overall average.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 31, 2011, 10:32:50 pm
content: Quote from: BravoV on October 31, 2011, 03:28:45 amWhat is this ? another one " warning warning an electrician plays with our tools !! "Well I am from the modern ones.Equipped with the education of 90s so to handle the future.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 01, 2011, 01:59:11 am
content: Lightages, as long as only one meter is involved, absolute accuracy doesn't matter (within reason). It's only if you want to measure a bank, and somebody else wants to measure a bank with their meter, that you'd have a problem. Or, if you're recording data for future use. Even then the percentage accuracy you're talking at lower voltages is pretty undemanding. We all like resolution and many applications need as much as you can get, but in 35 years of doing this I've come across very few (none) situations where absolute accuracy (as in agrees with NIST or other international standards) amounts to a hill of beans. Most of the applications I can think of have been obsolete for years. Don't get me wrong, I'm a metrology nut and maintain multiple voltage standards plus a bunch of other stuff, and don't even get excited until an instrument has at least 7 knobs, but it's basically a high and low world today.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 01, 2011, 01:39:01 pm
content: Accuracy in measurements its a must have for example in the industry (makers) or repairs (technicians) of the electronic scales.Electronic scales of any size and capable for light weight items , or really huge.Every single gram or kilo stands for a pile of money, yes this tasks need accuracy and resolution.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 01, 2011, 02:22:55 pm
content: But don't you calibrate scales with weights?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 01, 2011, 02:56:04 pm
content: Its more complicate than that, there is pressure sensors, that must trigger correctly the electronics.And there is no just a single type of them, in the food industry the mix of flavors or ingredients,is a process based again in mini scales, or many pressure sensors.Here is where the process calibrators jump in, but this is another story just by it self.

author: Unknown
author_rank: Unknown
timestamp: November 01, 2011, 03:25:16 pm
content: Quote from: Conrad Hoffman on November 01, 2011, 01:59:11 amIsn't this discussion of absolute accuracy basically about standardized units? The reason why standardized units are important is communication, things get tricky if a UK volt is 1.016 times a French volt, which is why we standardized them. You could have your own company or personal volt, eg. a Conrad Hoffman volt (chV), and everything would be perfectly fine until you ask a supplier for a 6 chV diode, and they don't have a clue what to send you. So absolute accuracy is indeed important when multiple instruments are involved, like multiple engineers, suppliers/customers, or the same instrument at multiple points in time (is 1 chV today the same as tomorrow?). I agree that it's rare that it's critical to the 0.01% or better. Mainly when dealing with precision parts, like voltage references.Since linearity and short time / transfer accuracy are rarely specified, the absolute accuracy is the only figure we have to estimate uncertainty. I don't agree with the optimistic assumption that all digits are significant for relative measurements, so I will assume 1yr accuracy specifications if that's the only spec available.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 01, 2011, 03:40:10 pm
content: I think that is time to move up this conversation in to the next level ..Why 500.000 counts only at the DC ranges ?Currently most hand held can do the trick only at DC range V and mV.

author: amspire
author_rank: Super Contributor
timestamp: November 01, 2011, 03:45:38 pm
content: The A to D conversion method used in multimeters is inherently linear and monotonic. As long as you haven't hit the noise floor, relative measurements are useful, even if the linearity performance is not in the specs.So if you have a 5 1/2 digit meter and it says two voltages differ by 0.01%, that will be pretty close to being correct.Richard.

author: Unknown
author_rank: Unknown
timestamp: November 01, 2011, 06:14:24 pm
content: Quote from: Kiriakos-GR on November 01, 2011, 03:40:10 pmMultimeters are basically DC voltmeters with some add-ons for resistance, AC and current. So the DCV accuracy will always be more better. Doing the same for resistance, ACV and current would probably require improving the current source, RMS converter and current shunts. Manufacturers often limit the resolution if extra digits are not meaningful. I remember a Fluke wideband voltmeter (8920?) that had an extra digit which was covered during normal use. During calibration it was uncovered and set to exactly 1.0005, and covered again.Quote from: amspire on November 01, 2011, 03:45:38 pmDual-slope integrating ADCs are fairly linear, but dielectric adsorption in the integrating capacitor will cause errors for large values if not corrected for. Is this more than 0.01%? Depends on the quality of the cap and the charging scheme (eg. HP Multi-Slope II). This is not going to cause issues if the difference is only a single count (but that's likely to be down in the noise floor), but may for larger values. Do all multimeters still use integrating ADCs?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 01, 2011, 09:09:59 pm
content: My experience with meters have been very good in terms of linearity and monotonicity. I've yet to find a meter that won't better its specs by a good margin if carefully calibrated and treated decently. Still, trust but verify. I'd want to check out any new meter for calibration, linearity and such just because it's a good idea. Know your tools and all that.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 04, 2011, 10:52:46 am
content: Quote from: amspire on October 31, 2011, 02:16:49 amThe obvious thing is to swap meters & repeat the measurement!To get a little more organised,both of you go to one end & check the difference in readings---You then have a calibration for the very limited range you are interested in.This has been done in practical situations in the past.Or,you could use the same meter at both ends,hoping that nothing changes while you are travelling between ends.VK6ZGO

author: amspire
author_rank: Super Contributor
timestamp: November 04, 2011, 11:46:39 am
content: Quote from: vk6zgo on November 04, 2011, 10:52:46 amor a better solution would be to have higher accuracy multimeters so you don't have to waste time with extra traveling, calibrations and hoping that the reading doesn't change while you are sprinting between buildings. Sounds a lot of work to me just to allow you to use bad multimeter.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 04, 2011, 02:30:52 pm
content: Quote from: vk6zgo on November 04, 2011, 10:52:46 amOh my that's bad news... I have to find and a second 500,000 counts for review .. LOLI must to have an second comparison point.Ok I need suggestions, witch company makes the most accurate and stable 500,000 bench top , on our planet ?I would never need more counts than that.

author: Unknown
author_rank: Unknown
timestamp: November 04, 2011, 04:40:10 pm
content: The most accurate 500,000 counts meter is a 8.5 digit meter in 6.5 digit (2,000,000 count) mode.AgilentorFlukewill be happy to help if you have a spare $10k or so.

author: robrenz
author_rank: Super Contributor
timestamp: November 05, 2011, 01:22:27 am
content: Quote from: Kiriakos-GR on November 04, 2011, 02:30:52 pmI am not sure if it is the most accurate or most stable but I think the Fluke 8846A has the most bang for the buck for a bench meter.I got mine from tequipment.net for US$1282.50 It was built on order by Fluke in their Everett Washington plant. The do their own circuit boards and sheet metal right there and they do their own volt reference aging there also. I called the plant for technical support twice before the sale and twice so far after the sale. Each time in less than two minutes I talked with a very qualified technician that was able to answer my all my questions thoroughly. I considered Fluke, Agilent, and Kiethley and read the manuals and specs of each in this price range. For me the Fluke is the winner.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 05, 2011, 04:05:17 pm
content: Thanks for the first tips, keep them coming.I would try also to see if my new friends from Asia have spoke their last word about this category of products too.