Why 5 digit multimeters? - Page 1
Forum section: electronics / beginners

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: April 25, 2015, 09:56:42 am
content: Loads of people seem to lust over 5 (or more) digit multimeters. Forgetting they are not that accurate on any range except perhaps DC volts, why does anyone need that accuracy anyway? I can understand the need for accurate frequency meters for broadcast etc, but why voltmeters? OK, there are some applications like calibrating lower accuracy meters, but not many people do that. Is there anything more to this than a "mine's better than yours" desire?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: April 25, 2015, 10:24:04 am
content: QuoteThe resolution of these meters makes them so valuable. You are able to take a look at a 1mV change in a 10V system for instance. Therefore you can detect changes in voltage or current or whatever, when aregularDMM show's the same value.

author: mzacharias
author_rank: Frequent Contributor
timestamp: April 25, 2015, 11:05:40 am
content: Quote from: ralphrmartin on April 25, 2015, 09:56:42 amI'm a repair tech 30+ years (consumer electronics). In my business, I'd be hard pressed to remember a time when anything more than 2000 counts was really required - perhaps once or twice. Nowadays I would say 4000 counts is a practical minimum, like a Fluke 85 or original 87 (the 87V is 6000 count native resolution).I understand your point, though. It's definitely a horsepower war, and I'm as guilty as anyone.Nevertheless, there are some modern applications, not that uncommon, which require extended resolution. One example would be monitoring the charge / discharge status of ultra-capacitors being charged by solar cells. You might want to see those last few digits of a 500,000 count meter trending up or down.I did have a situation recently when the AC + DC function of a Fluke 289 came in very handy. The DC voltage drop across a large power supply resistor did not explain why it was getting so hot. Add in the AC ripple caused by the defect, and it became clear.

author: G0HZU
author_rank: Super Contributor
timestamp: April 25, 2015, 12:32:24 pm
content: Obviously, there is a genuine demand for DMMs with 7 or more digits in some niche areas of industry/research. However, for the vast majority of people a couple of basic DMMs will do pretty much everything they will ever need.However, some of the more exotic DMMs offer a 4 wire kelvin connection and this can be a very useful feature for measuring very low resistances with reasonable accuracy. I have two fairly decent bench DMMs here and the 4 wire feature on one of them (Keithley 2015 THD) has proven to be the most valuable feature. The dB and dB REL feature is useful too.But I don't 'need' lots of display digits on either of them and I don't plan to adjust/calibrate them. I rarely use the Keithley (horrible display and UI, too big, too heavy, too thirsty) so it sits in a storeroom most of the time but the Fluke 45 (4.5 digits?) is quite a nice meter and it gets used when I can't find my cheapy H/H metersI too can't understand why so many people on this forum have such a fixation with DMMs and frequency references and OTT calibration targets. I've seen quite a few 'home' work benches on here where there are several 19" rack sized DMMs (7+ digits?) stacked on top of each other and then they have a huge commercial DMM calibrator box next to them. Alongside that can be several huge frequency counters and (most likely) a bunch of GPSDO and RB frequency references.... and not much room for anything else

author: owiecc
author_rank: Frequent Contributor
timestamp: April 25, 2015, 12:48:37 pm
content: When measuring efficiency of power converters you need the accuracy. Otherwise it is easy to go over 100% with very efficient convertersWorking with very small voltages/small voltage changes (you can see LED heating up) or currents (leakage currents).

author: JackP
author_rank: Regular Contributor
timestamp: April 25, 2015, 01:00:40 pm
content: In repair, a higher resolution meter helps track down a short. Obviously 7 digits is overkill for this, but for some people it is a status thing (and others have genuine requirements I'm sure)

author: retrolefty
author_rank: Super Contributor
timestamp: April 25, 2015, 01:16:57 pm
content: QuotePretty much that is it for the electronic hobby world.In the world of professional electronics there will be justification for the features and accuracy specification they do or may have to support.

author: wiss
author_rank: Frequent Contributor
timestamp: April 25, 2015, 01:22:18 pm
content: Quote from: JackP on April 25, 2015, 01:00:40 pmTracking shorts is probably the only time I needed the 6 digits.It might not be about status but a genuine interest in high res meters!My multimeters by them selves is a hobby, sometimes I do use them to build/repair other things as well

author: wraper
author_rank: Unknown
timestamp: April 25, 2015, 01:23:16 pm
content: Quote from: ralphrmartin on April 25, 2015, 09:56:42 amAnd still beingmuchbetter on those ranges than cheap meters which also have worse spec on anything other than volts too.For example, keysight 34461a which have 0.0035% 1 year 10V DCV accuracy, have 0.01% accuracy on the most resistance ranges. Not too bad IMO compared with something like 0.5-1% of some cheap meter.

author: plazma
author_rank: Frequent Contributor
timestamp: April 25, 2015, 01:26:45 pm
content: Real word use cases:Finding short location in assembled PCBs.Measuring very small currents for optimising sleep modes.Etc.Many cases need very good precision and stable readings.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: April 25, 2015, 01:53:23 pm
content: Quote from: PSR B1257 on April 25, 2015, 10:24:04 amI understand that. But can you give me an example when that would be useful?

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: April 25, 2015, 01:56:36 pm
content: Thanks. So a few special cases like shorts and charging and change in operation as the device warms up. But it seems a lot extra to pay for a few obscure use cases...

author: German_EE
author_rank: Super Contributor
timestamp: April 25, 2015, 02:01:55 pm
content: The one time I ever saw a high resolution voltmeter in use it was a weird task. Somebody reckoned that plants felt pain so he was measuring the tiny voltages that occur between one part of a plant and another then pulling bits off and measuring the result.As for me, I can measure frequency down to 1 Hz on a 144 MHz signal but I'm happy with a four digit DVM (which has been calibrated).

author: G0HZU
author_rank: Super Contributor
timestamp: April 25, 2015, 02:27:33 pm
content: In recent years, the most demanding DMM based measurement I've had to make here at home (in terms of accuracy) was when recalibrating my Advantest TR4172 spectrum analyser YIG controller board.There were several tests/adjustments asking for 5.000V +/- 3mV and one test for 10.000V +/- 3mV.I suspect that there may have been a typo in the service manual because it was quite tricky to set the trimmer pot to get within this window and the manual called up a basic 4.5 digit Advantest TR6841 DMM to do this. So something didn't seem right. But I cross checked a few cheapo Analog Devices voltage references I have here against the Fluke 45 DMM and the Keithley 2015 and they all agreed to <1mV.However, all but one of the test points were still in spec anyway and I doubt that this aspect of the analyser has ever been calibrated before since the analyser was new in 1986? I've had it here at home for >10 years. The one that was out of spec was only out by 1mV according to my meters. So this part of the YIG calibration was probably a waste of time. I seriously doubt this kind of thing would be adjusted in a routine annual calibration because the labour charges would be huge and you need specialist extender cards to access the reference test points and the adjusters. I reckon it would take several days to do all the detailed service alignments inside this analyser

author: suicidaleggroll
author_rank: Super Contributor
timestamp: April 25, 2015, 04:06:25 pm
content: You should also remember that DMMs don't have a continuous range, it's broken up into discrete steps using relays. You only get the stated resolution when your measurement is just below one of those steps. Just above the step you lose an entire digit. If you only have 3 digits to start with, you're pretty much SOL (who wants a 2 digit meter?), but if you have 4-5 it's less of an issue.

author: Seekonk
author_rank: Super Contributor
timestamp: April 25, 2015, 04:22:33 pm
content: I have a 6.5 digit Guildline on the shelf. Daily meter is a FREE Harbor Freight that often lasts till the battery dies. Keithly 192 or 192 is near if there is a question. If you know what you are doing most problems can be solved with a green magic eye tube.

author: G0HZU
author_rank: Super Contributor
timestamp: April 25, 2015, 04:41:14 pm
content: In some cases the reason for purchase might be for the extra features.Eg the Keithley 2015 THD offers onboard DSP that allows THD or accurate SINAD measurements and also a decent onboard DSP based audio generator and this has appeal to me. (although I rarely measure SINAD these days)There's also the 4 wire kelvin feature and dB/dB REL and the GPIB and/or RS-232 interface.QuoteI usually reach for my old Maplin Gold DMM with 3.5 digits that I bought new in the 1980s. I very rarely buy new test gear and I'm amazed at how many people on here buy new gear even when starting out.My other favourite meter is a little 3.5 digit auto ranging thing I bought for about £1 in the 1990s and I also bought an ancient 'MODEL 30A' 4 digit DMM for a similar price. All have given sterling service for 15-20 years or more

author: sync
author_rank: Frequent Contributor
timestamp: April 25, 2015, 04:45:20 pm
content: Beside the higher resolution these have other advantages. Usually they are faster, have instantaneous autoranging, better displays, math functions, better computer control, ...Also used 5 digit DMMs can be cheap. A used Fluke 87 costs more.

author: KJDS
author_rank: Super Contributor
timestamp: April 25, 2015, 05:37:53 pm
content: I keep a Fluke 25, 3 digits, a Keithley 2015THD, 6.5 digits but I've only got that as it's one of a batch of 50 I bought. I also have an Agilent LCR meter which using the L range is far better at tracking down shorts than using resistance.

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2015, 05:42:14 pm
content: A common need for a high-resolution voltmeter is to measure drift of a voltage over time. This requiresresolution, but not necessarilyaccuracy, which are parameters often confused.Years ago, one could measure drift directly with adifferential voltmeter, which was a sensitive analog voltmeter connected between the output of a high-resolution switchable voltage source (a stable voltage through a Kelvin-Varley voltage divider) and the input terminals. Connecting the voltmeter's recorder output to a suitable chart recorder, etc. gave the operator a direct measure of the drift over a long period.

author: zapta
author_rank: Super Contributor
timestamp: April 25, 2015, 05:51:40 pm
content: Quote from: wiss on April 25, 2015, 01:22:18 pmI think you need lower range, not necessarily more digits.

author: switcher
author_rank: Regular Contributor
timestamp: April 25, 2015, 07:25:29 pm
content: Quote from: G0HZU on April 25, 2015, 04:41:14 pmMe too!Is that one of the yellow ones? Very good meters.

author: G0HZU
author_rank: Super Contributor
timestamp: April 25, 2015, 08:45:54 pm
content: It's a 'precision gold' model in a kind of dark gloomy grey colour. I bought it on a special promotion they had and it was one of the ones that also measures capacitance and temperature. I also chose it for the 200uA current range it offers and the 'instant' continuity buzzer ( as fast as any I've used). However, it's only a 2000 count meter so it isn't anything special. I don't think I've adjusted it since the 1990s and I just keep sticking PP3 batteries in it when it runs low. It still seems to be as accurate as when I last adjusted it although it can only display 12V as 12.00V for example.

author: Cliff Matthews
author_rank: Unknown
timestamp: April 25, 2015, 09:25:44 pm
content: Safety?Most 5 digit meters are built to real Class-3 specs it allows us to live another day (could be important).If a 220v arc-plasma starts inside a cheap 3 1/2 digit DVM, who can say where it goes?EEVblog #432 - Brymen MultimetersEEVblog #75 - Digital Multimeter Buying Guide for Beginners

author: wiss
author_rank: Frequent Contributor
timestamp: April 25, 2015, 09:27:56 pm
content: Quote from: zapta on April 25, 2015, 05:51:40 pmSure! Anything with uV resolution will do. Usually means a 6 1/2 digit meter.

author: jpb
author_rank: Super Contributor
timestamp: April 25, 2015, 09:57:02 pm
content: Precision (rather than absolute accuracy) is important in some circumstances.As part of a previous job I needed to calibrate voltages in a pulsed measurement instrument and a standard DVM was simply too coarse (I can't remember the details but I think it involved balancing two separate quantities). Though even in this case 4.5 digits was ok.Though I agree that some meters have many more digits than they can justify from their intrinsic accuracy and the last few dance around so much as to be useless.I do like my Keithley 2000 and 2015THD and it is nice to be able to monitor small adjustments in voltages on the OCXOs I play around with.

author: ElectroNub
author_rank: Contributor
timestamp: April 25, 2015, 10:16:28 pm
content: I got my 6.5 digit meter for playing with thermocouples and to measure tempco of various parts. And to also help keep all my cheapo hand held meters in spec. An older model is not that much money. I paid less than $200 for a HP 3456A. A high quality modern multimeter with less digits costs a lot more.My philosophy on all tools is... It's better to have it and not need it then need it and not have it! I just wish I could afford the expensive stuff

author: Phoenix
author_rank: Frequent Contributor
timestamp: April 26, 2015, 01:53:39 am
content: We recently had a power supply to service, fairly catastrophic failure. After tracking down and replacing all the failed components to get it up and running again it passed all acceptance tests except for efficiency. It was measuring 81.88%, with a pass of 82%. The problem was traced to a completely fried relay (15x nominal contact resistance).The efficiency test is done using volts x amps using a calibrated shunt (it's a DC output 12V 70A). I haven't done the math on how many digits/accuracy required to find this problem, but if the accuracy and calibration of the DMMs and shunts involved weren't up to spec the power supply may have been returned to the customer with a fried relay. It looks like our 34401A and a 34410A were used in this service.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: April 26, 2015, 03:05:41 am
content: HelloPardon my love to Hp/agilent old stuff my reason was calibrating abuillity/cost (400 dolars for two hp34401A's is awsome deal asspecialy when you can calibrate and abjust them to be within 1ppm of each other for free )I do have to say my words though , as part of my spare time lately , i do appreciate "brain power" rather then "hourspower" .as I like to read free-electron's long posts , i Also enjoy analyzing the circuit myself and asppecially as the blogger from "wattsup" power blog have written(http://powersupply.blogs.keysight.com/2015/02/when-measurements-and-mathematics-agree.html?m=1) I am super happy when math and practicality are going hand crossed , so my case I've learned Alot from been Able to read RMS values and understand the releashionship to the power circuit with transformers Etc ..The main point I'm trying to rais here is the huge luck of schematics in our enviorment , as i understand ther's majority of companies who'se hiding from us the real deal .. and I'm afraid some guys having hard time raising their comfidance and actually do electronics using brain power (i am pointing to that lovely feeling you either solved or created (new)circuit .. )So for the 5 digit race :Comfidance is what am i going to sum it up to , IMHOSo all of that rubbish about he's capabilities ?Yea .. he can defenetly read fast , read accurate , do math ,communicate to GPIB etc .. and measure kelvin type resistance , you've mentiond shorts ?Well when I've had to fix for my job like 23 out of 40 prodigit modules , i did noticed like 4-7 of them had shorts with two examples , one was shorting trace (i did apply surge from our high current supply in order to vanish he's appearnce . forgotten the exact output but we have had two swichers . one was like 5V 500A .. and the other was some voltage at 1000A ) so that solved that , and the other case was rainging from one fet shorted to 4 tops ( out of like 8-9 ) .And I admit i've had the access to pretty good gear for A begginer , hp6632B at current mode (i've once measured he's stabuillity for given time , it was superb of other supplies after warmup periode )and keithley 2000 (at 5A output and math function of the keithley "just becouse I could" i told him to tallk to me Ohmic language so that was fun )But otherwise ? , damm build your own 1A CC and kelvin measure with your own 10$ meter it is fucking good enough at mv range to see shorts .. so maybe at 200A switcher you'll have too lower values to measure , but how often one needs that ? )Good article punch=> "Practical Low Res Measurements Aero Electric Connections" in google , first resultExcuse me becouse I am going to post and later fix becouse my point is valid and i am almost late to my new daygood day everyone

author: PA4TIM
author_rank: Super Contributor
timestamp: April 26, 2015, 08:37:29 am
content: Why you want to know there are 5,5 digit multi-meters ?Why not then also ask why there are :- capacitance meters with aF resolution- L meters with pH resolution- resistance meters with uOhm resolution- meg ohm meters that can measure pohm- Volt meters that can measure 5kV- scopes that can show 40GHz signalsOr is it you secretly want one yourself ?The answer is different per user. A year ago I used my gear for hobby only. Now I'm glad I bought good stuff because now I need it for my work.I repair measurement and calibration gear, my most used meter is a Keithley 2000. I have two 5,5 digit, two 6,5 digits and one of my two 7,5 digit meters on my bench. I have some 3,5 and 4,5 meters and lots of analog meters but (except for 3 special analog meters) not on the bench.Non of my gear is cheap and chinese. I rather buy an older repairable top-product as a new cheap toy with more digits then accuracy

author: Howardlong
author_rank: Super Contributor
timestamp: April 26, 2015, 08:53:23 am
content: Quote from: JackP on April 25, 2015, 01:00:40 pmThis. I, too, have been a naysayer, but I did discover very recently that tracing shorts on a board is made an awful lot easier with a 50000 count meter. I used to have to gingerly remove parts off boards to isolate a short across power rails, a very common fault. With a high resolution meter, you can trace where on the board that short is without lifting any parts. You don't need absolute accuracy though, just as long as the device's ADC is monotonic that's all that's required.There are also cases particularly in the microcontroller world where you are trying to work out the current draw of turning on a particular piece of functionality, and having the resolution helps.You can teach an old dog new tricks, but forabsolutemeasurement (as opposed to measuring relative or delta data) I personally don't have any need for 5 digits.Regarding frequency references, I do have a rubidium source, and use it for frequency measurement in the GHz for narrow band devices, where you need a reasonable amount of accuracy. In the past I have used it to perform doppler ranging for orbit analysis as well as characterising thermal and even bus voltage characteristics of satellites in orbit by measuring frequency aberrations from a prediction model, but I guess those are a bit of an edge case.

author: Grapsus
author_rank: Regular Contributor
timestamp: April 26, 2015, 10:00:31 am
content: Here are my reasons for having five or more digit multimeters as a total hobbyist. I was contaminated fairly recently, mainly because of this forumThe most impressive thing with a 6.5 digit meter is the ability to see an underlying physical reality of components and circuits. A regular 4000 counts DMM sees a battery as a super stable voltage source but with more resolution you start seeing all sorts of interesting events. Likewise you can witness the value of resistors and the voltage drop of diodes change as you touch them or as the temperature in the room increases. You can measure the offset voltage of various op amps etc. It may not be immediately applicable to building better circuits, but it sure gives you a better understanding of components and physics as it all becomes less abstract and all this data and graphs in datasheets make more sense.There are also many practical applications as others have pointed out. You can directly measure various sensors like thermocouples or strain gauges and make sure that your circuit does a good job at reading those sensors.Finally it's just a hobby like many others. For example, with digital electronics, a cool project might be the design of a 8*8*8 LED cube. You learn a lot and it's super cool, but it won't have any use in your everyday life. Building a 10 ppm voltage source is exactly the same. It may not have a lot of use apart from checking DMMs, but you will learn a lot and it's super cool. Well the last part is subjective, but it will become obvious if you start reading the Test Equipment forum here.

author: Cliff Matthews
author_rank: Unknown
timestamp: April 26, 2015, 01:32:50 pm
content: Quote from: ralphrmartin on April 25, 2015, 09:56:42 am3 digits reflect the early DVM's and still found in pocket junk under $103 1/2 digits reflected the DAC's prevalent before ~20004 1/2 digits reflect the DAC's after ~20005 digits may just be evolution (hopefully accompanied by better fusing, shunts, cases, etc.. again, maybe safer)I thought I saw Dave expose a 4200 count DAC found in one 5-digit teardown...

author: wraper
author_rank: Unknown
timestamp: April 26, 2015, 01:43:30 pm
content: Quote from: Cliff Matthews on April 26, 2015, 01:32:50 pmIIRC that was Dave's mistake. Actualy ADC was 40k or 50k count if I'm thinking about the same thing.BTW ADC, not DAC.

author: robrenz
author_rank: Super Contributor
timestamp: April 26, 2015, 02:22:43 pm
content: My thoughts from theSo what exactly do you need a 6-1/2 digit multimeter for again?thread.Personally I find I gain a deeper understanding of a topic when I attempt to learn all the nuances involved in high levels of precision. Being a machinist my real appreciation for high precision started when I bought my first electronic indicator with 1 micro inch resolution (38 years ago and I still use it frequently). My eyes were opened when I could breath on a piece of metal and watch it grow or press on my lathe (which I always assumed to be infinitely rigid) with one finger and watch it deform. Did I actually need that indicator when I bought it? No, but the educational value and gut level understanding of how materials behave was invaluable. The same applies for me with electronics. I bought a 6.5 digit 24ppm accuracy bench meter. Do I actually need it? No, but I am learning a lot by being able to see things happening that are not apparent with a regular meter. As with all metrology, knowing what is involved in making accurate measurements at the bleeding edge of precision helps you improve your understanding and the accuracy of your every day measurements.

author: zapta
author_rank: Super Contributor
timestamp: April 26, 2015, 04:27:38 pm
content: Quote from: Cliff Matthews on April 25, 2015, 09:25:44 pmPeople brag about their digits. I am yet to see safety related bragging.;-)

author: switcher
author_rank: Regular Contributor
timestamp: May 05, 2015, 03:18:22 pm
content: Quote from: G0HZU on April 25, 2015, 08:45:54 pmCold war grey; very nice!Mine has long gone, unfortunately.The meter I always reach for is a Tek TX3; I love the large, dual display, and it has the fastest, loudest continuity buzzer....ever!