USB multimeter please? - Page 1
Forum section: electronics / testgear

author: DavidMellor
author_rank: Newbie
timestamp: September 28, 2018, 03:37:12 pm
content: Hi group.Could I get some recommendations for a multimeter please?I'm looking for a USB model that either provides a programming API or has intuitive message formats that I could decipher.As a personal preference I would really like to use USB rather than bluetooth.The meter would be used primarily to learn electronics.Mainly I'd like to ask for some guidance on which models have good build quality and good accuracy at around £130 sterling ($170) perhaps so I can prioritise research toward decent models.All measurements taken by the meter should be able to be sent to the computer.Ideally the unit of measurement including indication of voltage vs current vs resistance etc. and whether AC or DC should be communicated as well.Ideally any change of mode using the dial or buttons would be communicated immediately.The goal here is eyes-free use.Where function/mode changes are not communicated I need to look carefully at how easy it would be to determine or assert/reset the state of a function without reference to the LCD display.I'd like probes that have a button that can be pressed to trigger the computer to speak the measurement on demand.Failing that I could use a USB foot pedal or try and attach some kind of button to the probes.I don't mind whether it's manual or auto ranging though I think most decent quality meters would be auto ranging.I'm in the UK.I have ruled out Fluke as their USB meters start from £500. They do have a bluetooth unit (not ?USB) for around £100 and I don't think that would couple with a PC or raspberry pi and allow me to program with it.Any guidance would be much appreciated.Very many thanks,David

author: HKJ
author_rank: Super Contributor
timestamp: September 28, 2018, 03:45:59 pm
content: You can find some on my list:https://lygte-info.dk/info/DMMReviews.htmlClick the header of the interface column twice to get the meters with a interface listed first.Interfaces cost money for most meters, except some of the cheap ones (Exception is Keysight that includes a usb cable with some of their meters).

author: jpb
author_rank: Super Contributor
timestamp: September 28, 2018, 05:42:37 pm
content: You can get some very cheap meters with USB - I have a Precision Gold meter N56FU I bought from Maplins years ago - it was around £50 I seem to remember but I'm not sure I'd recommend it though I've not had any problems with it.You don't say if you want a bench top or a hand-held. For £130 you might get a used 5.5 digit bench top which would talk to USB or at least to RS232 and then you can use an adapter. But to be realistic this would push things nearer to £200. For example Eurofox is selling one at the moment for 225 euro - I think it has RS232 as well as GPIB but I'm not sure:https://www.eevblog.com/forum/buysellwanted/fs-eu-fluke-8842a-bench-top-5-5-digit-multimeter/The problem with good quality meters like Fluke or Gossen or Keysight is that not only are they expensive but the comms adapters are extra and in fact Gossen charge way over your budget just for the cable and adapter!

author: myf
author_rank: Regular Contributor
timestamp: September 28, 2018, 05:48:28 pm
content: Hello,For my hobbies, I use a multimeter that sends on the USB port of all measures and has 22000 counts : the ut-61e. It has a very good value for money. 40eur the multimeter + 10eur the cable usb + 10eur for the pouch = 60eur on ebay. I'm thinking of buying a second one soon.It is supported by sigrok and other standard programs under linux and windows. According to the versions, the usb plug sometimes bugs but a reset command found on internet has never prevented me from doing the measurements. I don't know how accurate it is.Have a nice day !Francois.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 28, 2018, 06:03:26 pm
content: The reason why you don't see as many USB meters is that the shielding on USB is grounded, which if connected to the meter circuitry, means your meter is no longer floating and there's risk of grounding large floating voltages you're measuring through the ground path over the USB - a significant safety risk when the situation applies. Fully isolated USB interfaces exist, but the chips tend to be pricey, so they're unlikely to be implemented as side features in less expensive meters.That said, the most common way to get isolation is with optical communication or bluetooth. Many meters should have an infrared/optical communication option with a dongle, otherwise bluetooth is somewhat common and is very cheap to implement, plus you can get a USB bluetooth dongle easy enough. I think both are good options to look into.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 28, 2018, 06:14:22 pm
content: What DAJMasta saidEven though you might be only be measuring low voltages, the ground loops created by a non-isolated interface could give you bad readings at best, component damage at worst.I also think that bluetooth-enabled meters are the safest bet. Bluetooth is ubiquitous.EDIT: HKJ's comment below is correct!

author: myf
author_rank: Regular Contributor
timestamp: September 28, 2018, 06:20:18 pm
content: The USB dongle for ut61 has this complete isolation because the link between the multimeter ut-61 and the dongle is an optocoupler.

author: HKJ
author_rank: Super Contributor
timestamp: September 28, 2018, 06:27:14 pm
content: Nearly all meters use a isolated interface, I have only seen one exception (It got a very bad safety rating in my review).It is usual opto isolation and in most cases done internally-externally through a transparent part of the enclosure , but a few meters have it build in.

author: DavidMellor
author_rank: Newbie
timestamp: September 28, 2018, 10:20:29 pm
content: Could I ask some newbie questions here please...How much accuracy do I sensibly need for electronics, mainly in getting the voltages into micro-controllers and other ICs correct?When a display is described as 5.5 for example, does that mean 5 digits either side of a decimal point?If a meter has 22000 counts, what does this mean please?David

author: sleemanj
author_rank: Super Contributor
timestamp: September 28, 2018, 10:38:13 pm
content: 5.5 means 5 and a half digits, a half digit can generally display "1" but not other numbers.Eg a 20000 count meter needs 4.5 digits, the first digit only needs to be able to display the number "1" (for all readings 0 -> 19999, the position of the decimal is determined by the range selected/auto-ranged).QuoteFor your purposes a 3.5 digit 2000 count meter is fine, or better, two of them. More recently 6000 and higher count meters have been produced for not-much-money (search Aneng here for most of them), but all you realistically need is 3.5 digits in your present use-case.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 29, 2018, 12:05:47 am
content: Quote from: DaJMasta on September 28, 2018, 06:03:26 pmThey've solved that by using IR interfaces.How about a Keysight U1231A with a USB connector? I believe most Keysight models speak SCPI, but be sure to double check.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 29, 2018, 12:33:16 am
content: Yep, IR and BT are the standards on handheld meters, and they offer most of the same functionality as USB plus the isolation and inexpensive price.As for resolution, really 3.5 digits and 5000ish counts will get you a pretty good read on most things, but as with many analytical tools, finer detail can show you more about your problem and help diagnose some extra stuff. Because it's easy to get a fair bit of resolution nowadays, I'd start at 5000 counts minimum and anything above is nice. It's probably easy to find 10-20,000 counts or more within your budget. That said, look for other features too, a multimeter can be really versatile and pack in a lot of features. I'd look for a high and low current range (usually means 3+ input jacks), a capacitance and resistance range, an AC voltage range with a true RMS converter, a diode check mode, a continuity mode, a relative measurement mode, a basic frequency counter - there are plenty of other options that are common, but those seem to come up most often for me. I'd look at some of Dave's videos on the subject, some of the multimeter reviews he does give you a good idea about common and useful features, and some of the shootouts, while somewhat dated, offer really good info of things to look for in a meter. Then there's tons of information in threads and spreadsheets here to compare and contrast models.5.5 digit handhelds exist, I think, but are generally benchtop models (which, to be fair, are more likely to have an isolated USB interface).

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2018, 02:32:28 pm
content: There is on Ebay an Owon brand meters who seems nice, feature packed start at 4000 count display, and dont cost a fortuneBluetooth connectivity on some modelsI think there was an teardown thread here ?In the sames serie, number seems to change a little ??b33t bt33b35tb41t 4 1/2 dgit with data logging and better funcitons rangesOr if you get very lucky an Fluke 187 or 189, but you have to get the usb adapter another 100$ or an clone for 25-30$And finally an Bluetooth dongle cost almost nothing, a few $$$ and you will have full isolation, and the possibility to do probing without the wiring hassle to the computer.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2018, 02:36:49 pm
content: [quote}5.5 digit handhelds exist, I think, but are generally benchtop models (which, to be fair, are more likely to have an isolated USB interface).Metrix / Chauvin Arnoux and Gossen meters, 120000 counts and up, very high priced.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 29, 2018, 02:39:53 pm
content: Quote from: coromonadalix on September 29, 2018, 02:36:49 pmThe BM867S and BM869S should have 5 digit accuracy on the DC range and have USB connectivity. Both are fairly affordable and are only slightly over OP's budget. I don't think they do SCPI, though.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2018, 02:52:09 pm
content: yepBut they are not an full 500k count on all ranges, its an publicity gimmick ... 3 or 4 range thats all. They are true 50,000 count meters. I had an Brymen 857s before, sure it is well build, but loved the 189 better, because i dont have to dismantle the meter each time an fuse blow, unscrew the battery lid and voila. For brymen You still have to buy the usb inteface $$You have some mastech 22000 count hand held modelsMASTECH MS8340Bto who are very well build and have an direct mini usb port on it, not sure it is isolated tough, they have gone thru revisions, the first series had the 2 fuses under the battery lid, the next generation has 1 fuseon Ali express for 77$ usd not badYou can find some usb isolators on ebay starting at 25$The OP will have lot of choices and price ranges, just take your time to choose wisely and evaluate your needsfor OPYou have an very good list of meters by David Jones here on EEVblog who can help

author: bd139
author_rank: Super Contributor
timestamp: September 29, 2018, 02:57:17 pm
content: Worth looking at Telonic if you're in the UK as they are the cheapest Brymen outlet in the UK and a respectable company (I've put about £2k through them over the last 2 years):Brymen USB cable - fully opto-isolated:https://www.telonic.co.uk/Brymen-BRUA-20X-USB-Interface-Kit-p/bm-brua-20x.htm- £33Then pair it with a suitable Brymen DMM depending on your requirements. Have a look at Telonic's web site for your requirements. I've got a BM867S (500,000 count in hi res mode) but that's top end of your budget.Fluke meters that cost £500 don't come with the USB cable. That costs a lot more.Another mid-price one to look out for is the Keysight U1241C. Around £268 from RS but it comes with a USB interface and isn't made of poo. That's 10,000 count. Another DMM I own. Very nice bit of kit.A note on accuracy. The count is the number of digits it will show. But that isn't an accurate measure of accuracy. There's an additional +/- some percentage and a number of digits. That's absolute measurement from zero. If you're doing relative measurements that's less of a problem.Please don't buy a Uni-T or Mastech if you have a £130 budget. You can do so much better.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2018, 03:03:35 pm
content: Carefull for the Brymen usb adaptersYou have at least 2 or 3 models, they dont cover all the models, the previous link is for bm2xx seriesThere is one for the bm85x and another for the BM86x series. Thats what the Brymen support told me ??At the time they were listed almost at 75$ usd or 100$ CAD, outch the same as Fluke, another outch.

author: bd139
author_rank: Super Contributor
timestamp: September 29, 2018, 03:06:31 pm
content: Good point. Probably worth calling Telonic then

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 29, 2018, 03:36:38 pm
content: Quote from: coromonadalix on September 29, 2018, 02:52:09 pmI clearly mentioned the DC range, so I'm not sure what the fuss us about. Many if not most people are mainly interested in DC accuracy and it's a 5 1/2 digit meter in that regard. There's nothing gimmicky about that and it's not misrepresented by Brymen. The USB interface should be less than $100. They aren't as stupidly expensive as those of some of the other manufacturers.I agree that having to open up a meter to replace fuses can be annoying. The Fluke 87V isn't any different, though.As bd139 said, please don't buy a Uni-T or similar class meter with this budget. There's more quality to be had.