Suitable Multimeter for Research Student Working With High Voltages (2.1kV) - Page 1
Forum section: electronics / testgear

author: gowdy
author_rank: Newbie
timestamp: January 25, 2019, 05:28:39 pm
content: I am a master's student working on high temperature plasma produced by controlled arc discharges. Power of systems will be around 21kW (2.1kV @ 10A DC).Budget is around US$200 to US$400.I will not be measuring 2.1kV directly but through a voltage divider (built by the university electrical department), whose reduction is 1:100 (Vout / Vin)My supervisor suggested me to get a Keysight DMM (he had good experience with Agilent DMMs in the past), U1242C caught my eye, I heard from several anecdotal evidence that the U1242C had some issues being slow to measure, spongy connectors, and not having a true hold like the higher end Fluke(s). But I thought the Vsense was a good thing to have since I'll be around energized systems and a IP67 rating doesn't hurt.I will be troubleshooting around these systems until a permanent voltage indicator is put up. I had been using a $80 cheapie for previous work with Neon Transformers (15kV @ 100mA), I know that's dangerous but I was not much involved with the actual measurements (someone else did the measurement), but now I'll be near live wires most of the time.Keysight and Fluke both have great support in my city and I'll be needing to calibrate the DMM every year. So, can I go ahead with Keysight or do you guys have any other suggestions? (CAT IV is a must)

author: maginnovision
author_rank: Super Contributor
timestamp: January 25, 2019, 05:43:53 pm
content: I bought a 1242C new recently for someone as a gift but until they pick it up I've been using it. The sponginess is likely from the ip67 rating. You can switch readings/s to 5 or 40, you can log at regular intervals, it comes with the usb ir connector for connecting it to a PC. I usually use a 1252b but I do like the 1242C. If you don't need the 1242C features I'd probably just go for the B though. I haven't used the hold feature(ever, on any meter) so can't say anything about that.

author: gowdy
author_rank: Newbie
timestamp: January 25, 2019, 06:14:11 pm
content: How about the reliability of U1242C?It'll be operated in pretty much high varying magnetic fields 90% of the time.I know it's too much to ask of a sub US$500 DMM to be accurate and precise in such environment, but will it sustain the fields or flicker like crazy (my old cheapie used to do it even far from the field source)

author: maginnovision
author_rank: Super Contributor
timestamp: January 25, 2019, 07:06:40 pm
content: What is the strength of the fields, how large are they? I'd need to know that to see what I can test. I haven't had an issue with that around motors, but only around small-med AC motors(couple hundred watts at most). Their meters are very good though and they do stand behind them.

author: gildasd
author_rank: Frequent Contributor
timestamp: January 25, 2019, 07:20:44 pm
content: Ships often use 6.6 MW drives...If they realllllly really need to be probed, the bog standard Fluke is used, with high voltage probes, attached to sticks, held with high voltage gloves by an electrical engineer with high surface conductivity (sweating).I don’t know your project, but why not use differential probes with an oscilloscope?You will get finer data, screenshots of stuff, and so forth that will make your final presentation way slicker!And using triggers, you can set off the experiment at a distance, the scope records at it’s trigger, your chances testing the limits of human capacitance are reduced!Dave sells probably the best bang for buck (that won’t kill you - probably).https://www.eevblog.com/product/hvp70/It’s a at the limit of your budget, but paired with even a basic digital scope that is lying unused under a bench in your uni, you are golden.That said, Dave is out of stock, so you will need to bribe him with handwritten single page explanation of your objective inside a large heart shaped box of chocolates.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: January 25, 2019, 07:44:13 pm
content: Quote from: gildasd on January 25, 2019, 07:20:44 pmThe Micsig DP20003 would be within his budget and goes up to 5.6kV if that is a valid route to take. If he needs precision though, a scope is 100% NOT the way to go.

author: gildasd
author_rank: Frequent Contributor
timestamp: January 25, 2019, 07:50:51 pm
content: Yup, you are right.Just a silly question, could you splice the output of the diffencial probes to get a scope and a meter reading at the same time?

author: Fungus
author_rank: Super Contributor
timestamp: January 25, 2019, 08:51:59 pm
content: Quote from: gowdy on January 25, 2019, 05:28:39 pmI could suggest far cheaper meters that will do this (eg. Fluke 101 is bomb-proof and under $50 delivered) but if you have a budget then go ahead and get something more expensive.A sensible choice would be a big Brymen. After that you could look at overpriced brands like Fluke and Agilent.I wouldn't get an OLED meter though. Battery life is rubbish and the screens tend to die after a couple of years.If this is going to be attached to a big machine though, surely a bench-style meter is a better choice. You can leave it on all day and it won't ever run out of batteries or do auto power-offs every 15 minutes.

author: maginnovision
author_rank: Super Contributor
timestamp: January 25, 2019, 09:12:57 pm
content: Quote from: Fungus on January 25, 2019, 08:51:59 pmThe 101 isn't catIV.

author: Fungus
author_rank: Super Contributor
timestamp: January 25, 2019, 10:55:08 pm
content: Quote from: maginnovision on January 25, 2019, 09:12:57 pmLuckily for the 101, he's not planning on connecting it to a mains AC supply.PS: The 101 is one of the very few meters that joe hasn't managed to zap yet. It survived all his tests, unlike the keysight.https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/OTOH: His superviser told him to get a Keysight meter, so... whatever.

author: maginnovision
author_rank: Super Contributor
timestamp: January 26, 2019, 12:19:56 am
content: Quote from: Fungus on January 25, 2019, 10:55:08 pmWell his requirement was Cat IV, so not being rated for that rules it out.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 26, 2019, 02:39:05 am
content: If you have a proper 100:1 voltage divider built by people who know what they are doing, you only need to read 21V, which any good DMM can do, " standing on its head".The university electrical dept are much more likely than not to make the voltage divider extremely rugged & safe to use.In fact, after adding in the materials used & the labour, it probably cost more than the DMM.Back in the day, HT meters on tube type radio transmitters were usually provided in this way, using voltage dividers down from the high voltage (often much more than 2.1 kV), although they used analog meters.

author: Calvin
author_rank: Regular Contributor
timestamp: January 26, 2019, 06:26:17 am
content: Hi,OTOH: His supervisor may not even know of Brymen, so... whatever.regardsCalvin

author: Fungus
author_rank: Super Contributor
timestamp: January 26, 2019, 10:48:17 am
content: Quote from: maginnovision on January 26, 2019, 12:19:56 amI have no idea where that requirement comes from, it's certainly not needed for the stated project.Quote from: vk6zgo on January 26, 2019, 02:39:05 amYep. Even a $10 meter can handle the voltage.To me the requirement me seemed to be more for a big name brand that can have a calibration certificate attached to it. If the supervisor said "Get Keysight" and you have a local office then there's not much to argue about. Just don't get OLED.If you don't need to move it around then I still think a bench meter is amuchbetter choice than a handheld though.

author: gowdy
author_rank: Newbie
timestamp: January 26, 2019, 02:35:46 pm
content: Quote from: Fungus on January 26, 2019, 10:48:17 amThe divider is solidly built, no doubt about that, but the CAT IV is just for the safety of the individual working with those systems should anything go wrong.And, the university will be providing the funds for the purchase of the DMM, I just need to produce the bill of sale to get compensated.I asked some of the guys in the electrical department who built the thing, they suggested me to go with Fluke 179.Asked my supervisor about Brymen, he doesn't know about them plus they don't have a presence in my country for support. But he's open to Fluke 179.How's the continuity of 1242C, I watched Dave in the multimeter buying guide for beginners video demonstrating a high end Agilent DMM (I don't remember the model) barely latching on in continuity mode?There's plenty of reviews and videos on the 179, not so much on U1242C (there's a french video on YouTube but, I can't understand that). Do you happen to know any reviews?

author: Fungus
author_rank: Super Contributor
timestamp: January 26, 2019, 03:08:58 pm
content: Quote from: gowdy on January 26, 2019, 02:35:46 pmIf the only exposed wires are on the voltage divider then you'd need something like a half million volt transient to put even a $20 Chinese multimeter in danger.The big problem with true CAT ratings is getting a rating on the current inputs. Those big HRC fuses you get in Flukes would make the $20 Chinese multimeter cost $40, plus getting all the certifications and stamps of approval isn't cheap.It would be interesting to know why the Fluke 101 only gets a CAT III rating when testing seems to show it's capable of much more than that (as mentioned earlier, our joesmith has yet to damage one with his zapping machines but he's killed a few Fluke 87Vs, Keysights, etc). Maybe it's simply a marketing decision by Fluke ("If we put CAT IV on the front of a $40 meter then we'll sell a lot less of the expensive ones"). Still, a rating is a rating, if it says "CAT III" then best to treat it as such.Quote from: gowdy on January 26, 2019, 02:35:46 pmCertainly capable of doing the job.If you have the budget then there's no need to fight the suggestions, they aren't bad meters or anything like that.I don't knowexactlywhat you're doing but from what you said in the first post I'd have thought that something with logging abilities would be good - keep a record of voltage over time. With that voltage divider you could easily attach an oscilloscope though.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: January 26, 2019, 08:20:57 pm
content: Quote from: Fungus on January 26, 2019, 10:48:17 amIt may be a company/institutional policy in that area that a CAT IV rating is required. There may also be an approved list. A public forum is no place to ask if your dealing with company policy.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 26, 2019, 09:28:27 pm
content: If you will only be using it for these measurements, you can't go wrong with the 179 - I had one and its build quality is impressive. If there is a need to go to the field or the environment is harsh (dust, humidity, gassing) then I would probably check the Fluke 27 II or 28 II (the optimal would be the 28 II EX, but it goes well above your price range). If you need more features for electronics, the 87V is a good option.From Keysight, meters such as the U1242C and the more featured U1282A (both CAT IV and IP67 Rated) are also good options. I have a U1282A and it feels very sturdy (but not as much as the Fluke 27 or the 179).

author: joeqsmith
author_rank: Super Contributor
timestamp: January 26, 2019, 11:09:15 pm
content: Being in the masters program, I am sure you are checking things like the RMS converter's BW and such. While you didn't mention which voltage rating is required for CAT IV, I assume you know what you are looking for.I don't think the calibration would be a big problem for any meter but alignment and service are another mater. If the cost of the meter was figured into your tuition and the university is really just keeping the leftover as profit, I would buy something right to the limit.

author: David Hess
author_rank: Super Contributor
timestamp: January 27, 2019, 04:47:07 am
content: If the high voltage divider is passive and accuracy matters, I would look for a meter which has a consistent 10 megohm input resistance which Keysight/Agilent and Fluke portable meters do not have.

author: maginnovision
author_rank: Super Contributor
timestamp: January 27, 2019, 05:00:11 am
content: Quote from: David Hess on January 27, 2019, 04:47:07 am1240B is 10Mohm nominal. 1242C is 10Mohm or 1Gohm for mV ranges(Nominal 10M ohm for all ranges).

author: David Hess
author_rank: Super Contributor
timestamp: January 27, 2019, 05:37:56 am
content: Quote from: maginnovision on January 27, 2019, 05:00:11 amI specifically looked into these meters last year for a similar high voltage application. 10 megohms "nominal" is marketing speak for "close to but not 10 megohms and it changes on different ranges which would seem bad if we gave details" and is common on portable autoranging multimeters because of their common referred range switching. These meters *cannot* be calibrated to meet their basic DC accuracy specifications with a passive high voltage probe on all ranges.Is it a problem? I can be if you are expecting consistent measurements on different ranges.

author: maginnovision
author_rank: Super Contributor
timestamp: January 27, 2019, 05:46:03 am
content: Quote from: David Hess on January 27, 2019, 05:37:56 amFair enough, so what meter did you get?

author: joeqsmith
author_rank: Super Contributor
timestamp: January 27, 2019, 06:01:50 am
content: Quote from: David Hess on January 27, 2019, 04:47:07 amIt depends how the passive divider is made. Many will attenuate the signal in the divider and present a fairly low impedance to the meter. The OP, being in the university masters program should be able to calculate the errors easy enough.

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2019, 06:28:21 am
content: Quote from: gowdy on January 25, 2019, 06:14:11 pmProbably the majority of meters on the market are not rated for a V/m field strength, but many of the better ones are. In which case the usually specify an additional accuracy spec for a given V/m field.e.g. the BM235:

author: joeqsmith
author_rank: Super Contributor
timestamp: January 27, 2019, 06:07:21 pm
content: Quote from: EEVblog on January 27, 2019, 06:28:21 amWhat I never understood about this is why they use 3V/m. If I were selling something as for Industrial use, it would be ran at 10V/m, which to me is still pretty low. At one point something was going on at work where I needed to rent some time. When I arrived and walked in, there was a cruse missile. I was running some 100V/m tests and they chuckled at me. They will run much wider frequencies and up to 1000V/m. This at the time is apparently what the guidance system would be exposed to flying into a radar.I took a few low end meters into the chamber to compare with the Gossen. The Gossen was by far the most sensitive. That meter has a lot of problems. Seeing it's latching relays change states with nothing more than a magnetic hanger was a real eye opener. I've placed my old magnetic tape eraser next to meters that have also been very sensitive to it.Maybe one day I will toss your new meter back into the chamber and we can see how it compares.https://youtu.be/wYuzFtoHMqg?t=829

author: rsjsouza
author_rank: Super Contributor
timestamp: January 27, 2019, 07:22:38 pm
content: Joeqsmith, I haven't seen that video! The Gossen really looks a POS from the susceptibility standpoint. Your test with the styrofoam charged with static electricity is quite interesting; I have a field voltmeter and will try to create a "dirty" environment and subject the Keysights I have here.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 27, 2019, 08:51:12 pm
content: There is a playlist for the Gossen. You can see me doing similar tests using some of my wife's fabric. Adding the Netic shield to that meter was a big improvement. It could be a very good meter but the Germans dropped the ball on it. I never did hear anything more from them.The tape eraser makes for a decent test. Most meters, even the cheap ones I have looked at, don't have a problem with it. I'm guessing most designers understand the need for the 50/60Hz notch.https://youtu.be/_u_34E5ZUOI?t=103

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: January 28, 2019, 02:51:01 am
content: Get a vintage Unigor 3p for backup. It has a integral 5000V range. not to be handheld above 1000V, although.

author: David Hess
author_rank: Super Contributor
timestamp: January 28, 2019, 04:17:14 am
content: Quote from: maginnovision on January 27, 2019, 05:46:03 amI did not get another meter but I did some research. After flailing around for 10 minutes trying to explain why different meters were returning results inconsistent with their accuracy, I understood the problem and used my 5-1/2 digit HP3478A bench meter on its 30 volt range to force a 10 megohm input resistance. Its extra resolution made it sufficient even on a higher voltage range.My research turned up a couple of things. I have no idea about manual and automatic ranging meters from Uni-Trend. Manual ranging meters from B&K and Amprobe may be good. Automatic ranging meters from Amprobe might be good but I doubt it. Automatic ranging meters from B&K are not good. Basically there are meters I can point to and know that they have a variable input resistance and some which I can point to that may not because the datasheets suck. Except for some exceptions like the automatic meters from B&K and two from Amprobe which are bad, the only way to know for sure is to test them yourself.Quote from: joeqsmith on January 27, 2019, 06:01:50 amAll modern high voltage probes include a shunt for safety reasons which does help. However Gowdy wrote that he will be using a probe made by the university electrical department. Maybe they should supply him with a meter also.