New UNI-T UT892 2000V AC/DC High Voltage Multimeter - Page 1
Forum section: electronics / testgear

author: jhoffman
author_rank: Contributor
timestamp: August 25, 2022, 06:17:47 pm
content: New UNI-T UT892 2000V AC/DC High Voltage Multimeter- 6000 Count- CAT II 1000V/CAT III 600V- DC 2000V ±(0.5%+3)- AC 2000V ±(1.0%+3)- WTF No current measurement- $32 USD Only !!!Is this the "Super Cheap Prodigal Son Fluke Killer" we have all been waiting for?Please note that the YouTube promotional video shows someone wearing electrical safety gloves, so you know what market this "Fluke Killer" is aimed at.[url=http://meters.uni-trend.com/product/ut892/]]http://meters.uni-trend.com/product/ut892/]http://meters.uni-trend.com/product/ut892/https://www.aliexpress.com/item/1005004225535194.html]https://www.aliexpress.com/item/1005004225535194.html[url=http://youtu.be/yFToksKX2pU]]http://youtu.be/yFToksKX2pU]http://youtu.be/yFToksKX2pU

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: August 27, 2022, 02:57:35 am
content: Main inputs are only CATII 1000 or CATIII 600V, but also has 2KV inputI really want to see this on Joe's HV tests.

author: TCbystander
author_rank: Newbie
timestamp: August 27, 2022, 04:46:24 am
content: All input terminals are then subject to 2kV, the highest rated voltage, protection tests per IEC. The planner might be flying by the seat of his pants.

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 27, 2022, 05:28:18 am
content: Quote from: NoMoreMagicSmoke on August 27, 2022, 02:57:35 amYou don't need CAT rating to measure 500V, 1000V or 2000V. Just that if you don't have CAT rating then no overvoltages are assumed, which is the standard case when working for example with HV psus.

author: TCbystander
author_rank: Newbie
timestamp: August 27, 2022, 08:12:41 am
content: Without a CAT rating, the 2kV function can't even be used on any locations of the mains including a socket outlet. Not to mention on the standard PV systems which are now CAT III.The meter is claimed to be CAT III 600V rated and 61010-2-033 applies. All compatible terminals are to be tested with the highest rated voltage 2kV for mismatches of inputs and ranges. I doubt they can survive.

author: bc888
author_rank: Regular Contributor
timestamp: August 27, 2022, 11:14:34 am
content: Thanks for the heads up. But Fluke killer? Isn't the Fluke 101 going for @ $50US and was shockingly way up near the top on Joe's tests?While browsing their site, this Multimeter, the UT196 "Solar Pro" looked interesting although I have zero knowledge of it. Will measure to 1500 V AC, and AC Current to 3000 Volts they say with a clamp add on. It suggests that they have discovered fuses I would suppose although given Uni-t's lack of sucess in Joes destructive tests.....https://meters.uni-trend.com/product/ut196/Quote

author: joeqsmith
author_rank: Super Contributor
timestamp: August 27, 2022, 03:48:12 pm
content: Bot trying to sell UNI-T products?I've looked at more UNI-T products than any other brand. The only UNI-T products that have performed VERY well against my tests were modified to improve their performance. This included the UT61E and UT181A. Both of these if purchased new wouldn't make it past the grill starter.***If you are interested in watching me walk through the mods for the 61E, watch the following:

author: jhoffman
author_rank: Contributor
timestamp: August 27, 2022, 07:03:15 pm
content: QuoteHow does one come to this conclusion?If you look at the official UNI-T marketing material you will quickly discover that UNI-T is promoting the UT892 multimeter for the "High Voltage Industrial Market".A $32 USD multimeter for "high voltage" applications should raise the interest, if not suspicion in this forum.Given that the UT892 multimeter forgoes current measurement capability suggests that any money that was saved from omitting current measurement capability might have worked in advantage to the meter's HV capabilities.When was the last time you came across a "multimeter" promoted for the "High Voltage Industrial Market" for only $32 USD?

author: joeqsmith
author_rank: Super Contributor
timestamp: August 27, 2022, 07:57:59 pm
content: And a smart bot at that! Google AI is impressive.

author: Martin72
author_rank: Super Contributor
timestamp: August 27, 2022, 08:12:16 pm
content: QuoteAll links are blocked ?

author: floobydust
author_rank: Super Contributor
timestamp: August 27, 2022, 08:30:47 pm
content: The UT892 looks like it's tailored for working with VFD's, hence the HV and LPF function. It just seems to be an extra 10MEG resistor array switched in on the extra banana jack input to get the 2kV range.I'd dislike having to switch to a special HV range, and move the input jack for the HV range, gee I wonder what could go wrong thereIf your finger is near the normal input jack but you're on the HV function... surely no shock hazard right?Overall I find Uni-T intentionally cheaps out on input protection, it's too bad the brand chooses to be fragile. They do know perfectly well how to do it decently as seen in their OEM offerings.

author: Martin72
author_rank: Super Contributor
timestamp: August 27, 2022, 09:02:10 pm
content: I´ve got serious doubts about the 2000V range on a meter which costs "nothing".I´ve started a thread not long ago because I´m (still) looking for a meter which can measure 1500Vdc at least.Because we got a new supply at work which can deliver 0-1500Vdc and I don´t want to play around with HV adaptors.There are very few meters avaible, like this here for example:Beha-Amprobe HD110CCosts more than 6 times, it´s very "bare" and got 1000V CAT IV...Then the UT-892 come along, for 42 bucks...I got doubts.

author: mqsaharan
author_rank: Regular Contributor
timestamp: August 28, 2022, 05:46:12 am
content: Quote from: Martin72 on August 27, 2022, 09:02:10 pmYou can try one of their "Professional" IP65 rated meters.https://meters.uni-trend.com/product/ut196/It has CATII 1700VDC and 1500VAC rated input as per specifications.I have my doubts about their safety ratings but in the lab I'm sure it will be adequate.Promotional video from the company:

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 28, 2022, 06:49:55 am
content: Quote from: joeqsmith on August 27, 2022, 07:57:59 pmyeah smart bot.. one example is...the-sv4401a-low-cost-vna-($350-usd)the impressiveness is that the bot can make hundreds of pages of VNA softwares + doing some rigs and testings...i'm one smart bot that can make jokes and argumentations. whats wrong with bot promoting some new products? there are many bots here doing just that since the beginning, why the hate and bitterness to uni-t products?

author: jhoffman
author_rank: Contributor
timestamp: August 28, 2022, 10:01:28 am
content: The question is...Is the UNI-T UT892 a good buy at $32 USD?What are the advantages of owning one?What are disadvantages of owning one?What kind of person should buy one?What kind of real world applications exist for such an instrument?At only $32 USD it makes the impression that it might be the "safest cheap option" to measuring HV.I cannot imagine that HV safety has been completely compromised in a meter that measures 2kV.Being a 6000 count meter suggests (see attached image) that can potentially make measurements up to 6kV if no over-voltage breakdown was to occur in the internal 10:1 attenuator (2kV input).I suppose you could construct your own 10:1 external attenuator to achieve similar results.I love the "RED LCD BACKGROUND" to warn the user that they are measuring over 1500V.P.S. The attached image illustrates this meter being connected to a 3-phase electrical circuit. It must be safe." alt="" class="bbc_img" />" alt="" class="bbc_img" />

author: jhoffman
author_rank: Contributor
timestamp: August 28, 2022, 10:56:17 am
content: The New UNI-T UT892 2000V AC/DC High Voltage Multimeter is the real deal !!!Here is a real life application how this brilliant piece of engineering should be used.Source: UNI-T UT892 marketing video.Look !!!High Voltage wiring !!!Impressive Red Electrical Safety Gloves !!!I'm all wet between the legs thinking about this beauty.

author: tomud
author_rank: Regular Contributor
timestamp: August 28, 2022, 11:15:52 am
content: Quote from: jhoffman on August 28, 2022, 10:01:28 ama person wanting to commit suicide ?

author: joeqsmith
author_rank: Super Contributor
timestamp: August 28, 2022, 03:39:08 pm
content: Quote from: Mechatrommer on August 28, 2022, 06:49:55 amI do not I hate or harbor bitterness towards UNI-T. I have certainly provided them with more opportunity to show case their products than any other brand. That also suggests I have invested more of my own personal time with UNI-T than any other brand. I've collected a lot of data. We all know that data can be a harsh and cold mistress, void of feeling.I'm not sure what my first posts were about here but I doubt I was attempting to promote any products. Seems I was more pointing out the idiots who where jumping their hand held meter's fuses with wire.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 28, 2022, 04:52:08 pm
content: the idiots still around whether you like it or not... havent heard bots with emotions though, maybe AI got too advanced nowadayssince i already posted...Quote from: jhoffman on August 28, 2022, 10:01:28 amfor normal household use, yes.Quote from: jhoffman on August 28, 2022, 10:01:28 amyou have one extra DMM at affordable price.Quote from: jhoffman on August 28, 2022, 10:01:28 amgetting fooled that really think it can measure 2KV safelyQuote from: jhoffman on August 28, 2022, 10:01:28 amanyone who dont own yet a DMM, or just want to add the collection, or who think has a thick skin to risk the life on 2KV with cheap DMM.Quote from: jhoffman on August 28, 2022, 10:01:28 ambrowse "normal multimeter purpose"Quote from: jhoffman on August 28, 2022, 10:01:28 amcertainly no. it actually a red flag. but then with chinese ingenuity, anything should be possible.Quote from: jhoffman on August 28, 2022, 10:01:28 amit possibly is for $32 DMM. but there is work around other than the not recommended short wire replacement for fuse, you should wear safety glove and boot too. 2KV high energy is not something forgiving, sometime even any brand of DMM is not required in death equation.Quote from: jhoffman on August 28, 2022, 10:01:28 amthats the theory..Quote from: jhoffman on August 28, 2022, 10:01:28 amyes if you are well versed in creepage and clearance... and components rating.Quote from: jhoffman on August 28, 2022, 10:01:28 am3 phase has nothing to do with 2KV.

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 28, 2022, 06:20:18 pm
content: Well, since I do a lot of work with HVU psus working in the 1000 to 2000V range I decided to buy one, I will test it before using for accuracy and internal clearances, and I'll use it if I like it.

author: floobydust
author_rank: Super Contributor
timestamp: August 28, 2022, 06:50:54 pm
content: Who would trust Uni-T for safety or minimal honesty?After that fiasco with the U-61E: obtain 61010 VDE approvals in Germany, then depopulate the three MOV's in production for the rest of the world. Really? Crappy ethics over $0.25 worth of MOV's causing most of the meters to fail and end up in landfill. That is a bullshit move.Even the UT892 is hilarious, I like the switch and input jack "LIVE" should it be re-labelled "DIE"?The only time you (i.e. electrician) need 2,000V is measuring a VFD DC bus and VFD's display that value anyhow. That also puts you in the over 1,000VAC league and WTF this meter has no place around CAT. IV gear. It seems to be a confused product "Designed according to CAT II 1,000V/CAT III 600V" but has no safety certifications or approvals. Are we still pulling that wool over the Westerner's eyes?I think at best it's a 2,000V range multimeter (with no CAT ratings for that channel). Have to see a teardown and BBQ lighter test lol.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 28, 2022, 06:59:03 pm
content: Quote from: floobydust on August 28, 2022, 06:50:54 pmWe could get one and treat it as a special case, cause it's a special meter. Maybe just test the 2kV input only. I ran one of their high voltage sticks. It died fairly early on as well.There have been several comments about the AVO meters. Maybe we could find one in decent shape run it against the UNI-T.

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 28, 2022, 07:04:56 pm
content: Quote from: joeqsmith on August 28, 2022, 06:59:03 pmI’ll do that when it arrives with my Hipotronics HD140

author: floobydust
author_rank: Super Contributor
timestamp: August 28, 2022, 07:05:03 pm
content: The UT892 manual says"... withstand surge voltage up to 1000V...""Do not measure ACV/DCV voltage over 1000Vrms. It is possible to measure higher voltage but it may cause damage to the meter or user!"so I'm assuming the usual functions have no decent input protection. That costs many pennies and the boss still wants a new Lambo

author: jhoffman
author_rank: Contributor
timestamp: August 28, 2022, 07:09:31 pm
content: Quote from: jhoffman on August 28, 2022, 10:01:28 amMy concern is that UNI-T is encouraging the use of the UNI-T UT892 multimeter (inc. the supplied crappy multimeter probes) in "high energy" application (coal mines !!!) electrical circuits.You falsely state "3 phase has nothing to do with 2KV" when you consider transient voltages in real world practical situations. Last time I checked we still use electric motors with coil windings which have a habit of generating back EMF when you switch them on and off.I originally created this post in the interest of public safety and awareness to "bait" people to see who would bite.The fact is that this meter might be useful to people who know what they are doing.For example if you are restoring (thermionic) valve equipment such as "valve radios" your not really going to encounter "high energy" from transient voltages.So the UNI-T UT892 is probably a cheap and viable option for someone working on vintage valve radios or SMPS for example (perhaps?).Just "horses for courses" and knowing your horses.I was simply concerned (horrified and disturbed !!!) that UNI-T created a "Trojan Horse Darwin Award Recipient Locator".Honestly... look at the UNI-T UT892 marketing material and you will conclude it is criminally irresponsible for such a organization to publish such sh!t.I can understand a potential Darwin Award Recipient attaching this UNI-T UT892 to the primary winding of an electrical sub transformer at the start of his street, but it's another when an OEM COTS test and measurement equipment manufacturer encourages this kind of stupid behavior.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 28, 2022, 07:27:19 pm
content: Quote from: PartialDischarge on August 28, 2022, 07:04:56 pmI remember a few people using low current leakage testers to look at meters. Even Dave did something similar. Of course, they can provide enough current to prevent them from folding back. Consider making a video of it when you run it. I would like to watch. Attached is a video I made to show a few cheap meters on my larger 1kVDC supply. It appears the HD140 has a Max Trip Current AC Test 5 mA. By comparison I've taken out the small half amp HRC fuses with this this supply by accident. This is the same supply I used to demonstrate to Dave that it is indeed possible to damage a DMM at 1kV after he had suggested otherwise (also attached).Quote from: floobydust on August 28, 2022, 07:05:03 pm?? So it's rated for 2kV but only use it to half the rated or you can damage it?

author: floobydust
author_rank: Super Contributor
timestamp: August 29, 2022, 12:41:33 am
content: Quote from: joeqsmith on August 28, 2022, 07:27:19 pmIt appears to be a normal (Uni-T) multimeter with the 'strong as bamboo' input protection, and the manual seems to refer to this - good for 1,000V typically... despite the Cat. III 600V rating which is a 6kV impulse...The extra 2,000V input there are no specs for it. I assume it's just another 10MEG resistor array in series with the main divider string.With no approvals and the owner's manual jibberish, who knows what voltage this thing can safely do before arcing internally.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 29, 2022, 01:36:06 am
content: I couldn't tell you anything about safety but could determine at what level it is damaged.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 29, 2022, 11:16:53 am
content: Without a current range the safety may be a little better than with many other cheap meters. No need to worry about a HRC fuses.The separate 2000 V input has a good chance to also give better protection for the ohms circuitry. So at least that input can be relatively robust, not going to the switch for the ohms part.I would not use it for higher mains voltage or CAT3 use, but it could still be a good meter for the few cases where you have 1000-2000 V with a limited current, like for PMT tubes or similar. Still 2000 V is only a rathersmall step up. The usual probe wires are typically only made with 1000V in mind. So to be on the safe side one would also need special test probes (at least 1).

author: jhoffman
author_rank: Contributor
timestamp: August 29, 2022, 03:25:23 pm
content: QuoteLess chance of a "high energy electrical explosion" (4th July Fireworks!!!) by accidentally connecting a multimeter in "current mode" to a HV power rail.Removing "current mode" is a valid "safety feature".Great point !!!Replace the test leads with8000 Series Probe Master Test leadsand it might become a half decentHV VOLTMETER(I deliberately avoid the word multimeter).Another point is that this UNI-T UT892 meter comes with asubstantial rubber holster(for a $32 USD meter) so there's quite a bit of electrical insulation.Given that there's no current mode and lots of insulation (just replace the test leads) this meter is beginning to appear as a viableHV VOLTMETER.

author: Fungus
author_rank: Super Contributor
timestamp: August 29, 2022, 03:36:05 pm
content: Quote from: Martin72 on August 27, 2022, 09:02:10 pmWhy? Voltage dividers are dirt cheap and there's no current ranges so they saved money there.Quote from: Martin72 on August 27, 2022, 09:02:10 pmEven Fluke sells a $50 meter.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 29, 2022, 03:56:05 pm
content: Quote from: jhoffman on August 28, 2022, 07:09:31 pmif talk about transient, we can have 12V automobile producing 25KV (i got the shock once its not fun) and normal household appliances that can produce the same level intentionally. once i fixed a mains strobe when spark occur across a through hole resistor, about 1cm legs apart go figure what KV can do that, i covered the path with double sided tape acting as dielectric modifier, problem solved. transient is everywhere even in static.Quote from: jhoffman on August 28, 2022, 07:09:31 pmso you are special kind of (troll) bot

author: jhoffman
author_rank: Contributor
timestamp: August 29, 2022, 04:43:43 pm
content: QuoteI sensed (without at the time understanding why) that there was something "unusual" about this meter.I will now buy this meter (replacing the original test leads for better ones) as in my humble opinion (after considering the evidence) that this is an excellent value HV voltmeter for $32 USD.When you consider the PCB real-estate gained by removing current measurement circuitry (inc. the shunt and fuses) it becomes obvious that there is more PCB real-estate available for physical insulation separation to avoid internal HV voltage breakdowns.I haven't seen a tear-down yet, but intuitively I've formed the opinion so far that this is a good HV voltmeter for $32 USD.It'ssold as a 2kV multimeterwhich in practice will "probably"work up to 6.0kVwith some minor mods possibly required.Mind you, I wont be holding onto this meter with my bare hands if I'm trying to measure the HV supply of a microwave oven's magnatron.I simply used this forum as a "Litmus Test" just to gauge what others might be thinking.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 29, 2022, 07:14:57 pm
content: Before using this meter for higher voltage is may be a good idea to look inside first. There is a chance it can be reasonable made, but we don't know.Besides the extra space from not having the amps ranges, the extra terminal also means there is no need to route the input to the switch / ohms ranges. The protection of the ohms ranges is often one of the weak points, more than just the voltage ranges.With the often not so good fuses in cheap meters it may be a good idea to have a look inside first too, so one knows if the CAT rating is somewhat legit or a bad joke.

author: Martin72
author_rank: Super Contributor
timestamp: August 29, 2022, 07:24:15 pm
content: Quote from: Fungus on August 29, 2022, 03:36:05 pmWell, it says what...I think I´ll try to get a UT892 and tear it down.The other Uni-T, UT196 I try to let it order by our purchase man.Amazon is not a problem to buy for us, but this one will be sold directly from china - Not so good for us..

author: Martin72
author_rank: Super Contributor
timestamp: September 06, 2022, 08:35:56 pm
content: UT-196 was ordered, when arrived I´ll tear it down..

author: Gyro
author_rank: Super Contributor
timestamp: September 06, 2022, 09:18:55 pm
content: Quote from: jhoffman on August 29, 2022, 04:43:43 pmAt 6kV, a standard 10MInput divider will be dissipating 3.6W -thatrequires PCB real-estate and more than minor mods!It's pointless going past 1kV (personally I would say 100V) with a 10Meg input resistance, the circuit loading gets too high.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2022, 09:33:36 pm
content: For the 2 KV range the meter is supposed to have 20 M ohms input impedance. So the higher range is more like with an additional resistor (10 M) in series to the normal divider.So the divider would see less heat than the standard 10 M divider.

author: Gyro
author_rank: Super Contributor
timestamp: September 06, 2022, 09:39:38 pm
content: I won't get on to my pet gripe about the 10Meg input resistance cop-out on DMMs then.

author: floobydust
author_rank: Super Contributor
timestamp: September 07, 2022, 12:18:53 am
content: This multimeter is supposedly for work on VFD's and of course a bit silly in that a 2,000VDC bus yet OVC Cat. II 600V rating makes no sense.I don't think you'll get that high a DC bus voltage in that AC environment. It's not a MV multimeter.If you turn on the VFD LPF and look at a phase output, the 20MEG surely needs compensation to really get an accurate RMS voltage.I'll bet it has none, they cost pennies and the boss will not get his new Lambo.

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: September 07, 2022, 01:02:26 am
content: Quote from: Gyro on September 06, 2022, 09:39:38 pmI mean this sounds like a good read regardless!!!

author: floobydust
author_rank: Super Contributor
timestamp: September 07, 2022, 01:35:59 am
content: Obviously never been a member of the 20,000 ohms/volt clubA multimeter for electricians should be in the other direction... LowZ. But not on the 2kV range.Once I got burned with a multimeter 22MEG input resistance, measuring good mains voltage- yet the fuse was blown. It was dirt/CNC coolant on the fuseholder giving enough leakage current for the bogus reading. Costly mistake.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 08, 2022, 09:52:04 am
content: Just received the UT892, had only 15 minutes to play with it, here are some observations:- It only displays up to 2200V then it shows OL- From 1900V display turns red and beeps.- 20Meg string is made up of 8 2.5Meg resistors, not shared with 10Meg input. At 2000V thats 0.025W per resistor.- Although string is mounted at the board side edge, there is good creepage to the outside thru the enclosure lip. The first resistor in the string (R29) should have been placed earlier. Still the whole string can be covered by silicone-.- Mine is reading 0.2% below at 1000/2000V scale, so very good- Continuity mode works nice, is fast- Display contrast is ok, does not have the low contrast problem.

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2022, 04:55:22 pm
content: Thanks for being the first to bite the bullet.An interesting meter (or manufacturere function combination choice). Thoughts that come to mind...- As you say, they would have been better to put the 2kV chain further inboard.- I was assuming that they would have added some more resistance in series with the main chain rather than having a separate one. Maybe they didn't want 1kV appearing on the main input jack?- Funny that they have only 8 resistors in the 2kV chain versus 10 in the main one - that's 275V per (1206?) resistor at full 2200 count!- I wonder what the voltage rating of that PTC is- although they have excluded the 2kV jack from the cat rating.- It's amusing that the display goes red at 1900V... Because that's where things get interesting, right?Thanks for the first look!P.S. I wonder if they have done anything different with the switch contact spacing?

author: Fungus
author_rank: Super Contributor
timestamp: September 08, 2022, 05:09:21 pm
content: Quote from: Gyro on September 08, 2022, 04:55:22 pmVery obvious and would have cost them absolutely nothing to do it. I wonder what else they overlooked?Quote from: Gyro on September 08, 2022, 04:55:22 pmHow many volts would you need to apply to heat up a PTC in series with a 20MOhm resistor?

author: Fungus
author_rank: Super Contributor
timestamp: September 08, 2022, 05:14:33 pm
content: What's the "live" socket for?It appears to go through the range switch after the PTC. Seems dodgy to me...what's the clearances on the other side of the PCB?

author: Fungus
author_rank: Super Contributor
timestamp: September 08, 2022, 05:20:43 pm
content: Quote from: Kleinstein on August 29, 2022, 11:16:53 amI'd want a much higher input impedance for that.The small, high voltage supplies I've used tend to have very limited current. Even 20MOhm could be enough load to give an incorrect reading.

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2022, 05:24:46 pm
content: Quote from: Fungus on September 08, 2022, 05:09:21 pmHa, good point, the PTC isn't thereforto protect the voltage function on normal meters is it!

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 08, 2022, 05:35:25 pm
content: Quote from: Fungus on September 08, 2022, 05:20:43 pmCAT rating does not mean higher input impedance, it means higher clearance/creepage and higher power rating of passives.I think the meter is fine, without current measurements which I seldom use it simplifies the board, protections and price of the meter. Also it has a 9V battery which will probably last longer than 2xAA.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 08, 2022, 05:59:57 pm
content: So I decided to modify the meter, since I don't know how good those 2.5M resistors are, I replaced them with 2.4M ones that I have. Also I removed the PTC and put there the rest of the resistance minus a bit to compensate for the low 0.2% reading. Now it is measuring +-1V.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 08, 2022, 06:20:29 pm
content: The live terminal is supposed to be for some non contact testing. Normally that function is more inside the case and not with a terminal.The PTC for the high voltage input is odd: it would hardly help. I very much doubt it could withstand a higher voltage that chain if 2.5 M resistors. The main means of the protection are the resistors and they could have used more of those instead of the PTC. The PTCs are already a bit boarderline at 1000 V.For the more normal meters there usually is a PTC (or multiple in series) for the protection of the ohms current source. There may also be one to protect the voltage sense path for the ohms function that can be shated with a mV function. The point here is that the function would go through the switch and there is a chance for arc over at the switch (or extra spac gaps) that may need extra protection. A decent CAT rating may want some protection for the case of arc over at the switch case, at least as a backup for transisents.The big simplifcation from the extra terminal for just high voltage but no ohms is that the signal does not have to go through the switches.There is some sense in not reusing the 10 M from the normal range: the normal range does have some connection to the switch for the ohms mode and this adds a little bit of leakage and capacitance. So A totally seprate chain of resistors makes sense for better accuracy and the resistors look relatively cheap, even if they would use 20x1 Meg instead.

author: Fungus
author_rank: Super Contributor
timestamp: September 08, 2022, 06:42:48 pm
content: Quote from: PartialDischarge on September 08, 2022, 05:35:25 pmI don't want it from a safety point of view, I want it from a measurement point of view. eg. Measuring the voltage at the output of a Cockroft-Walton generator can be delicate work.

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2022, 06:46:50 pm
content: It looks as if there would be sufficient space to insert a strip of insulating material down the side of the PCB, retained by the front and rear, to bolster the minimal isolation of the case flange. I think the 2.5M resistors are probably still above their element limiting voltage though.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 08, 2022, 06:52:38 pm
content: Quote from: Gyro on September 08, 2022, 06:46:50 pmThe case has a big lip + the outer silicone cover. If you are worried about that I’d simply put silicone over the string. Also the mod that I did makes it safer since now there is 800kohm right after the jack.

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2022, 06:54:46 pm
content: Quote from: Fungus on September 08, 2022, 06:42:48 pmThat's when it's a good time to build an external 100M+ divider (that's what we in the 20K Ohms-per-Volt club would do!)[Edit: Yes, I know 20k OPV at 2kV is only 40M]

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2022, 07:14:54 pm
content: Quote from: PartialDischarge on September 08, 2022, 06:52:38 pmNo critisism, just interested in how / why they've implemented things.

author: Fungus
author_rank: Super Contributor
timestamp: September 08, 2022, 08:57:35 pm
content: Quote from: PartialDischarge on September 08, 2022, 06:52:38 pmYep, you're in much more danger from holding the probes than from anything that might jump out of the case.As noted though, it's an obvious fix and would have cost them nothing.Quote from: Gyro on September 08, 2022, 06:54:46 pmYou still need a very high impedance meter to measure the voltage.(eg. A Fluke 8060A - is there anything that meter doesn't do well?)

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2022, 11:11:07 pm
content: Quote from: PartialDischarge on September 08, 2022, 05:59:57 pmthere you go a high voltage nuttery genius came to play clever than the designer... you just replaced 4 digit (more precise) resistors with cheaper 3 digit batch, how well you know your 2.4M batch? do they cost like $1 each? with rubbery stuffs surrounding their pins? and rated 2KV each? 8x of normal 0805 or 1206 is good for 1.2-1.6KV isolation theoritically (physically)https://www.vishay.com/docs/28705/mcx0x0xpro.pdf, there are more components downstream to provide extra isolations. and you just replaced a probably $1-5 PTC part that probably can save the DMM's or yours ass in case of downstream breakdown with $0.01 parts that provide no protection at all and much higher dielectric breakdown risk. you've probably screwed the factory's hygienic grade too.btw for those who asked why those dividers are so to the side, with concern that they are near to the user's side (with lips and extra rubber holster as isolation, wouldnt that be enough?). well i can think of that... creepage on pcb is real, and moving them closer to other components will increase risk of that, since they want to cheap out by not making extra costly slots between them. so they can achieve $40 price point that beginner users love. ymmv.https://www.tempoautomation.com/blog/understanding-pcb-creepage-and-clearance-standards/

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 09, 2022, 03:04:02 am
content: Quote from: Mechatrommer on September 08, 2022, 11:11:07 pmLol, I was expecting this kind of comment. I’m not going to explain you anything cause you like to assume and it seems that already know everything, let me just tell you that I design electronic HV stuff for power distribution, and I mean up to 36kV not the 200V people usually refer to HV. You haven’t even noticed what my username means, cause well you don’t know much about HV. Well you also haven’t even noticed that I took 40k off of the resistive string and are telling me about the precision of the resistors

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 09, 2022, 06:11:00 am
content: Quote from: PartialDischarge on September 09, 2022, 03:04:02 amLol I was expecting that kind of comment. btw, what matters my guru? if its 2000V? or 2004V? will it make any difference in your VHV circuit?If i'm the one who do your mod... wait for Joe the Que Smith to do the bashingor at least lets wait for his comment on that cheapy uni-t circuit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 09, 2022, 06:27:35 am
content: and i dont have to show you whats mine to prove anything... you've concluded...Quote from: PartialDischarge on September 09, 2022, 03:04:02 amthats enough to make you feel happy. for now, i'm looking forward to hear whats mr joe have to say about this... cheers.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 09, 2022, 11:32:02 am
content: Quote from: Mechatrommer on September 09, 2022, 06:27:35 amI would have no way of knowing anyone's level of intelligence except from their posts. That could be misleading.Quote from: PartialDischarge on August 28, 2022, 07:04:56 pmAssume this was done before mods to meter. I'm still waiting on results.Quote from: PartialDischarge on September 08, 2022, 05:59:57 pm+/-1V of reading or full scale? What are you using to make these measurements?Are you planning to do any other testing with it?Quote from: PartialDischarge on September 08, 2022, 06:52:38 pmIf I understand your first post about your modifications, you were concerned about the original 2.5M resistors being unsafe and the reason you made these changes was to improve safety? Your feelings that the accuracy was improved was a side effect?If this is correct, how did you determine that these mods are safer?I would like to see the backside of the PCB if you took any pictures when you made these modifications.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 09, 2022, 02:33:21 pm
content: The accuracy I did test full scale, although I quickly changed voltages and linearity did seem good, as mentioned I have not had much time. These is done with a Fluke 410B calibrated with a 3458A and Fluke 80E divider.No, the HD140 still have not used on the multimeter since I have it at another place.I don't think the meter is unsafe and the resistors were not changed for that reason. They were changed because not all 1206 resistors are HV and I don't know what the ppm of those resistors are. Plus that PTC is useless and the sooner there is high resistive impedance in a long PCB trace the better, less corona, less prob of "problems". So I'm happier with a 760k resistor up front rather than with a 1.5k PTC.I'll do more tests as time permits, but duty is first!

author: joeqsmith
author_rank: Super Contributor
timestamp: September 09, 2022, 11:31:37 pm
content: Sounds good. Look forward to seeing some additional data from it.

author: floobydust
author_rank: Super Contributor
timestamp: September 09, 2022, 11:47:33 pm
content: You can't tell if the multimeter is safe without doing a spacings analysis. Commonly there is an unexpected arc path- at the rotary switch, to a mounting screw or nearby part etc. We haven't seen the other side of the PC board.Uni-T is doing their usual cheap ass front end - no MOV, no GDT's, no surge resistor. PTC's are way too slow 10's msec to heat up- leaving the tiny SOT-23 clamp diodes. Hello BBQ lighter lol.Look at the PCB and see the option for a larger SOT-89 clamp transistor Q1A instead of Q1+Q2. Thanks for leaving that one out.They are fully capable of making a decent multimeter, they do this for OEM's but not for their brand name. Just stupid.I think MELF resistors are best for their voltage rating (operating and impulse). With 0805/1206 you run into the limitations with the pad spacing, and worse with a zig-zag because the spacing every four resistors is low.The VCR (voltage coefficient of resistance) is surely terrible with cheap parts. I think that would be an issue but there's not a lot of information about that.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 10, 2022, 12:10:12 pm
content: So here are some more testsFor the 1000V input, AC test up to 2kVrms, there is a limiting device that trips at around 1.9kVrms:For the 2000V input, AC test up to 4kVrms, no problems, although this is with the 760k resistor up front instead of the original PTC:For the 2000V input, AC test up to 5kVrms, no problem, current meter reads 250uA as expected, I don't really see the point in going further, 5kVrms is 7kV peak.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2022, 02:43:22 pm
content: Thanks for taking the time to make these clips. Would you consider getting a second meter to repeat the tests without the mods? May be interesting to see you sweep the voltage as well.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 10, 2022, 03:53:58 pm
content: Quote from: joeqsmith on September 10, 2022, 02:43:22 pmI don't just need another one cause this one is fine and I'm going to use it, but I can short the PTC and test again, that'll be easier.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2022, 05:25:12 pm
content: No concerns about the unknown resistors?

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 10, 2022, 06:03:25 pm
content: Quote from: joeqsmith on September 10, 2022, 05:25:12 pmI'm more concerned about a 2 inch trace running in the PCB from the input. Resistors if they are bad they will change their properties a lot but they are not going to suddenly short to 0.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 10, 2022, 07:38:43 pm
content: So I repeated the test with the resistors at the PTC shorted and it did arc at about 4.8kV. I did repeat the test 3 times after that, and each time the arcing voltage became lower, which is expected as what usually happens is that a carbon conductive layer forms and the HV already knows where to go to the next time.Also the humidity plays a role here, it is very dry here but in the winter or near the sea the result would have been probably 20%..30% lower.So as I expected having an initial resistance near the input port increases the overall arcing/corona resilience.

author: Fungus
author_rank: Super Contributor
timestamp: September 10, 2022, 08:39:00 pm
content: Quote from: PartialDischarge on September 10, 2022, 07:38:43 pmCool!Can you do it with the lid off and see where it arcs?

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 10, 2022, 10:27:00 pm
content: Quote from: Fungus on September 10, 2022, 08:39:00 pmyeah and then send back report to uni-t on where they should change the layout, but i think the carbon should already visible by now ymmv. its fun and tempting to some people to stress test an instrument beyond its rated operation just to find out which brand has more "air" inside

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 11, 2022, 07:03:08 am
content: Quote from: Fungus on September 10, 2022, 08:39:00 pmNot really, I'd have to solder the 9V battery terminals that are on the back cover, and do the test in the dark. This Hipotronics is designed to test, not to burn or destroy so the arcing is probably going to be very dim. Also it could also happen on the back side of the board since that PTC is through hole.Also this test was for AC but for DC which is what mostly everyone will use this meter for, the threshold is going to be much higher.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2022, 03:00:06 pm
content: Why does the battery need to be inserted?Quote from: Mechatrommer on September 10, 2022, 10:27:00 pmCertainly worth having a look.

author: PartialDischarge
author_rank: Super Contributor
timestamp: September 11, 2022, 05:44:44 pm
content: I don't really see the point, 1) it is not like anyone is going to modify the board and 2) these voltages are 3x..5x times higher than anyone would use this multimeter for.Also there is a chance that the board is getting punctured since the ground trace runs directly below the input trace and the board is only 1mm thick or so. If this is the case adding silicone or varnish would not help.I still think that removing the PTC and adding some 100kOhms in there is a nice improvement.

author: Fungus
author_rank: Super Contributor
timestamp: September 11, 2022, 06:01:10 pm
content: Quote from: PartialDischarge on September 11, 2022, 05:44:44 pmI still want to know why the PTC is there in the first place. Is it supposed to protect against any arcing that happensbeforethe resistors?

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: September 11, 2022, 06:26:49 pm
content: Quote from: Fungus on September 11, 2022, 06:01:10 pmTo give reviewers something to point at and say "look at this great input protection. 🤷PTC will only come into play with enough current to heat them up. If it's arcing before the resistors someone definitely messed up the design. Then again it's Uni-T... It's possible they did mess up the design.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2022, 06:41:47 pm
content: Quote from: NoMoreMagicSmoke on September 11, 2022, 06:26:49 pmThey may have a spark gap after the PTC on the backside (intentional or otherwise). Would be interesting to see it all apart. Maybe they swapped the parts without removing the board.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 11, 2022, 06:43:10 pm
content: Quote from: NoMoreMagicSmoke on September 11, 2022, 06:26:49 pmand you will only see that when the dmm breaks down, such as i've mentioned when high energy arcing occured AFTER the PTC. the reason you think its useless being there is because you havent seen its failing in such a manner yet. i dont think UNI-T is fool enough to put $1-5 part just as pure show off. you may argue that it is slow acting in ms range, but few ms second cutoff is better than few seconds of mass slaughter.

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: September 11, 2022, 06:59:07 pm
content: Quote from: Mechatrommer on September 11, 2022, 06:43:10 pmThe reason I think it is useless is based on previous Uni-T meters. A quick peruse of Joe's video's will show multiple Uni-T meters with PTC's in them that breakdown at surprisingly low voltages.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2022, 07:10:05 pm
content: Typically the low end meters I have looked at use a 5mm body. The small PTCs still have a lot of thermal mass (compared with how fast things would change with an arc). I would imagine if they did have a spark gap after the PTC, if it did come into play you may fine the PTC is missing it's coating after.

author: Fungus
author_rank: Super Contributor
timestamp: September 11, 2022, 10:03:18 pm
content: Quote from: NoMoreMagicSmoke on September 11, 2022, 06:26:49 pmWhich will be "never" when it's in series with 20MOhm, hence my curiosity.But without a surge-rated resistor it's going to undergo a rapid uncontrolled disassembly in the case of an arc. Let's hope they go open-circuit when they fail.Quote from: Mechatrommer on September 11, 2022, 06:43:10 pmThe only thing I can think of is they're using them as fuses.

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: September 11, 2022, 10:55:56 pm
content: Quote from: Fungus on September 11, 2022, 10:03:18 pmHonestly a lot of Uni-T designs scream what a junior engineer would do if shown a bunch of meters that are "good" and told to make a new meter. You will get a meter that mostly looks good, but will be full of not quites due to the engineer not understanding the why behind the design choices.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 12, 2022, 06:52:17 am
content: Quote from: Fungus on September 11, 2022, 10:03:18 pmwhat do you think it is? Its designed to go open, surge Resistor will go short. It will need something else to go open anyway. which one you want to put in your design?, i can understand the suggestion of more robust input such as surge+fuse etc on a budget device, even though they missed the point of the economy. What i dont understand is removing a better perfectly working protection component in exchange with component that provides no protection at all.

author: Fungus
author_rank: Super Contributor
timestamp: September 12, 2022, 10:08:56 am
content: Maybe there's an excess of cheap PTCs in Shenzhen right now, so ... use what you've got!

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 12, 2022, 10:35:22 am
content: better cheap than nothing. no? where to get $40 2KV meter verified to 4KV (modded with 2x 0806 resistors) safe?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 12, 2022, 12:39:42 pm
content: Quote from: Mechatrommer on September 12, 2022, 06:52:17 amOnce the PTCs arc, they become a very low impedance. Without anything to limit the current, the down stream protection will normally get damaged to where it goes open then it's everything after that. While testing the meters, we have seen the resistors go open.The PTCs come into play (will start to heat) when the low voltage clamps are active and you have applied a high enough voltage to the inputs for a long duration. For example, you have the meter set to ohms and then proceed to plug the meter into your wall socket.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 12, 2022, 01:49:32 pm
content: Quote from: joeqsmith on September 12, 2022, 12:39:42 pmand this happens when we violate its physical law (distance between naked pins) and we cant blame the manufacturer really, if we test it beyond its recommended limit.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 12, 2022, 02:42:44 pm
content: Quote from: Mechatrommer on September 12, 2022, 01:49:32 pmIf designers use a 100V part in a 10kV application, I most certainly will. There is a reason that the higher class meters use the larger parts and further limit the current. There also a reason I have never seen a PTC fail in the higher class of meters. Nothing to do with this particular meters 2kV input.

author: Martin72
author_rank: Super Contributor
timestamp: September 12, 2022, 05:29:48 pm
content: UT196 arrived at work...For appx 160€ it looks solid, but not the quality a brymen in this range do got.There are "air gaps" around the input, but this is not the input where you can measure up to 1700V.First test before giving it away for calibrating on the magna power 0-1500V supply.Martin

author: Kleinstein
author_rank: Super Contributor
timestamp: September 12, 2022, 07:30:09 pm
content: The combined Ohms and high voltage input could be tricky: the ohms part kind of needs a connection to the switch and there tend to be marginal creep paths. So the seprate higher voltage input with no ohms fuction is what make it relatively easy to provide a safe 2000 V range. It is still not safe from user error - but with 1000 V or more some case is advised anyway.

author: floobydust
author_rank: Super Contributor
timestamp: September 12, 2022, 08:54:29 pm
content: The UT196 they at least splurged on MOV's and four pair of bigger SOT-89 clamp transistors. But the spacings for R1 2MEG are hilarious if you follow the pcb trace.We don't know if it's actually 61010 certified, Uni-T removed their certificates from their website after it revealed their dodgy practices. It's common practice to deceive and say "designed to" or "follows" 61010 but nobody ever tested it. Provide the certificate and file number if the multimeter has passed regulatory.It's very difficult to find a PTC rated for 1,000V and UL approved. Putting two in series does not work because they have unequal resistance and heating times.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 13, 2022, 01:21:59 am
content: Larger PTCs as well. Are they using three MOVs in series for the V input side and two in series on the low voltage circuit?I have ran my BM869s up to 1.5kV but for a quick demo, the clamps start to conduct around 1.8kV and they don't blank the display. The prototype BM789 I have will run up a bit higher before it starts to clamp. I am uniquely qualified in the art of stupidity and am not suggesting anyone attempt to do this with your meters. It would be far better to buy a proper probe.