DMM Questions: Protection, Hz Measurement, Shunt? - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: September 10, 2020, 06:07:30 am
content: I have a few question, and I hope some of you can answer.Why do some MM use 9V but some use 2 AA batteries?I just got a new MM and it has NCV and what they call "NCV LIVE." From what I can make of the manual, the NCV LIVE function is the same as NCV, but you just use the V side (Red) lead w/o the COM lead to test for live voltage?This MM displayed Hz with Voltage measurements. However, it has a dedicated Hz option too. The manual states for the dedicated Hz measurement option, "Voltage above 10V can't be measured ; otherwise the instrument may be damaged." I don't understand how it can measure Hz when in Voltage mode over 10V, but not in the dedicated Hz mode?I didn't see a shunt in this unit (See image), and I was also wondering if anyone can look at the board picture and see how well it is protected? I think the image is good enough to see resisters, diodes, etc., if any.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2020, 07:07:30 am
content: Old meters used 9 V as the older meter chips needed something like 5-10 V. Some newer meter us AA batteries and a step up converter or 3/4xAA. 2 x AA is usually a little cheaper.The dedicated frequency mode may use a different input path, that is not that well protected. When in volts mode the maximum frequency may be limited.One of the shunts is R7 at the edge (right side on the picture) of the board. R8 and R9 may also be shunts.Anyway the R7 looks tiny, so it may heat up quite a bit with higher currents. It looks like the board cold alternatively have a more standard bare wire shunt.There are 5 diodes for protecting the shunts (except R7). However the connection through 2 tiny vias could be a weak point. The fuses look like 32 mm ceramic fused - so not great, but also not very bad and at least the clearance looks good. The PTCs look like a bit close to ground - so this could be an issue, when used with mains voltage.

author: MosherIV
author_rank: Super Contributor
timestamp: September 10, 2020, 07:29:25 am
content: HiThe Hertz thing is more to do with being able to measure the freq of mains voltage and warning you NOT to try and measure mains freq in the dedicated freq measurement mode.It is there to measure freq of low voltage circuits eg oscillator circuits.However, looking at the protection devices in the dmm, it is NOT a good idea to measure mains. There are no MOVs or GDT (over volt protection)

author: DW1961
author_rank: Frequent Contributor
timestamp: September 10, 2020, 05:21:21 pm
content: Quote from: MosherIV on September 10, 2020, 07:29:25 amInteresting. Can you elaborate on that a little? Are you saying that the CAT rating on this unit is bogus, because that those are suppose to take into consideration over voltage spikes. Or did you mean if it does get a spike above the CAT spike rating, you're in trouble?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2020, 06:28:27 pm
content: The cat rating is definitely bogus. It may still meet some thing like 300 V CAT2, though not for sure.The fuses may be good for 500 V or maybe 600 V with not that much breaking capacity - so no way to get a CAT4 rating.The over-voltage protection (especially for the Ohms part) with only the tiny PTC is likely also a weak point, possibly even for CAT2. There is no absolute need for MOVs or visible spark gaps - but it helps.The limitations on the frequency mode makes me even doubt about CAT 2 with a significant voltage.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 10, 2020, 11:11:32 pm
content: Quote from: Kleinstein on September 10, 2020, 07:07:30 amI have two brand new meters that use 9V. Does 9V have anything to do with testing a battery on load? Or could a MM also test a battery on load with two AAs?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 10, 2020, 11:27:02 pm
content: Quote from: Kleinstein on September 10, 2020, 06:28:27 pmWhy would you need over voltage protection on Ohms? You mean the over voltage could cross over to the Ohms circuit?Could you further explain why this meter cannot meet its CAT rating? I'll report it to Amazon. That's deadly. I mean someone could actual die. If you could give me you specific reasons why the CAT rating is a lie, I'll send that information to Amazon.

author: Nusa
author_rank: Super Contributor
timestamp: September 11, 2020, 01:20:27 am
content: Here, educate yourself on what CAT ratings are:https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdfThe rating is nice to have, but the average user should never work in the CAT4 environment -- leave that to the professionals who have better equipment, safety gear and training. Also because your homeowners authority and ownership of the wires generally stops at the electric meter.I note the current inputs are labeled 250V max at the jacks, which is actually a pretty common restriction on the cheap meters. Besides, if you want to use the current ranges on mains voltages, you're usually not thinking straight. Not a good idea, except in controlled bench situations.

author: bob91343
author_rank: Super Contributor
timestamp: September 11, 2020, 01:28:22 am
content: There is probably a bare wire shunt for 10A range under the circuit board.9V used to be the power supply of choice but these days it seems lithium cells are used more. 9V batteries are expensive, maybe a few dollars each, while CR2032 cells are a few pennies. The AG13 cells are popular too, still cheaper than 9V.I have converted some hand held units to a pair of CR2032 cells, giving about 7V and a 'low battery' warning but it works great.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 03:19:12 am
content: Quote from: Nusa on September 11, 2020, 01:20:27 amRead over what you said about current and volts and read it several times, and that is so true. "Not thinking straight" is right, or just ignorant.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 03:54:11 am
content: Quote from: bob91343 on September 11, 2020, 01:28:22 amOK, so curiosity got the best of me, and I took the circuit board out. No shut that I can see.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 03:59:17 am
content: Quote from: bob91343 on September 11, 2020, 01:28:22 amI get my 9V batteries at the dollar store. lol You know, because the only place I sue them is in a MM.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 04:17:42 am
content: Quote from: Kleinstein on September 10, 2020, 07:07:30 amIf R5 and 6 are shunts, then there seems to be 6 more top left: R1-R6However, aren't those resistors, not shunts? They say Rx on them, and they look like resistors, not shunts.So the2 PTCs are current limiting like a resistor, but uses increasing heat to lower current?

author: Nusa
author_rank: Super Contributor
timestamp: September 11, 2020, 05:07:08 am
content: Other way around. Shunts are resistors, but most resistors are not shunts. Shunts are usually very low value precise resistors that can handle the required current. Knowing the value of the resistor and measuring the voltage drop across it tells you what the current is. In this case, looks like R7 (marking R005 = 0.005 Ohms) is serving that purpose. But those unpopulated holes are likely there so that a calibrated wire shunt (all wire has resistance) could be used instead.R1-R6 look more like they're input protection on microcontroller inputs, but hard to say without a schematic.PTCs increase their resistance rapidly when they are passing more than their rated current to protect the rest of the meter. So basically an input-protection fuse, except that they will reset when a minor overload is removed. A major overload may turn the PTC into ash, in which case they don't reset...and if you're lucky they still protected the meter.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 05:35:50 am
content: Quote from: Nusa on September 11, 2020, 05:07:08 amYou mean if the PTC turns to ash, they won't reconstitute themselves? What a rip.So are R8 and R9 shunts or resistors? Also, the R7 shunt, what is it protecting? Is that the current shunt?So, in your opinion, is this meter well enough protected for up to 250V and 10A current?

author: Nusa
author_rank: Super Contributor
timestamp: September 11, 2020, 06:14:18 am
content: The fuses are the main protection for the current ranges. R7 isn't protecting anything...it's acting like a piece of wire that's being measured, and the fuse should fail before it does. R8 and R9 I don't know from a poor picture and no schematic.The PTC's are protection for the other ranges (when the red lead is in the V input). What I don't see are any MOV's or power resistors, which is likely why the others are saying the CAT ratings are likely somewhat fictional and self-certified.That said, for low-voltage electronics, it's safe enough. For mains voltages, not as much. But I'll let Dave lecture you on the subject:

author: Wytnucls
author_rank: Super Contributor
timestamp: September 11, 2020, 06:57:06 am
content: The meter is not legal in the US or Europe. There is no such thing as a 250V voltage limit on current input.The fuses must have the same voltage rating as the CAT rating of the multimeter.If the meter is rated CAT III 1000V, the HRC fuses must be rated for 1000V also.Don't buy cheap meters with no certification to work on household mains.The SMD current shunt looks like a 2 watt part and may suffer some damage before the fuse blows, in case of a short across a power supply.

author: floobydust
author_rank: Super Contributor
timestamp: September 11, 2020, 07:53:47 am
content: It's your typical chinese DMM with fake safety claims; it's the the norm.Habotestadvertises "Safety Rating EN61010-1,-2-030 EN61010-2-033, EN61326-1 CAT III 1000V, CAT IV 600V"The spacings and fuse (length) are a bit better than usual but still pcb layout errors and the three current shunts should be able to clear the fuse first. The 10A fuse- overloaded it may just first melt the pcb trace, they are a disaster coming off the jack.It's like there's one person in china doing pcb layout on multimeters and they still don't know what they are doingAmazon also puts in under Festnight,Kaiweets,Taiss brandnames. Mastech also has dibs."A new version of this multimeter will have Bluetooth function in the future. It is under development and will be available about 6 six months later, please pay attention to our KAIWEETS Facebook page."

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 08:38:24 am
content: @floobydust @WytnuclsWho do I contact to report the illegal sales of this meter in the USA?Does anyone have a Fluke (or other legal brand) they can show images of for a meter of this CAT category and how it should look inside?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2020, 09:17:42 am
content: It is the typical low cost Chinese meter with false claimed cat ratings. This is very common can found on something like 90% of the cheap meters in the US. The fuses are a dead giveaway - proper fuses for CAT 3 1000 V are twice the size and maybe more expensive than the meter. If you see a sub $50 meter with CAT4 rating one can be nearly sure it is fake. With a 1000 V CAT 3 rating it is highly suspicious. I don't know a proper place to report for the US, but it seems like there is no effective system to take those parts with false ratings off the market.The fuses here are even slightly better than found in many cheap meters - so it maybe OK for a CAT2 300 V rating and thus OK to use with 110 V mains with some care.It does not really matter if one only wants to do voltage measurements. The typical mistake / accident scenario where you need a proper fuse is to accidentally have the wires in the current terminals when you want to measure voltage.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 11, 2020, 10:04:43 am
content: You could try to alert this US department:https://www.cpsc.gov/About-CPSC/Contact-Information/Contact-Specific-Offices-and-Public-Information/Information-Center/If unsuccessful, ask Fluke to assist you with the reporting.

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: September 11, 2020, 10:34:40 am
content: but what brand of this multimeter would it be? It doesn't seem to me to have been mentioned..

author: MosherIV
author_rank: Super Contributor
timestamp: September 11, 2020, 10:40:23 am
content: QuoteWhile yes, you can do voltage measurements. Particularly on low voltage circuits, be very careful when measuring mains.Yes, most common mistake is user leaving probes in current jacks and blowing the fuse.The point of CAT safety rating is guarrentee the user will be safe from energy surges.Yes, the chances of getting a high energy surge through mains is very very low.If you do get one, the CAT rating means that the meter will protect you from explosive damage inside the dmm. You are protected - not the dmm.Just check out eevblog video on blowing up dmms.MJ Lorton also got a demonstration from Fluke labs on how bad dmm explode - yes this one is over exagerated but yes dmm do explode like that.My advice is to not worry too much, just like the others are saying. The meter is ok to use on low voltage circuits.Avoid using the dmm on live mains measurements. Be very careful if you do. Avoid holding the dmm if you do.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2020, 10:44:33 am
content: The silk-screen on the PCB says HT118A. There is a Hobotest 118A that looks similar (sightly different color). It seems to come with other "brands" too.

author: MosherIV
author_rank: Super Contributor
timestamp: September 11, 2020, 10:50:43 am
content: QuoteDid you not watch the eevblog video nusa posted?It clearly explains the typical input protection circuits. If I remember correctly, Dave points to the insides of an old Fluke 23 to illustrate.There are also dozens of dmm tear downs with images in the test equipment section.Many of them have comments on how safe the input protection is for that dmm.In general, all the name brand (Fluke, HP/Agilent/Keysignt, Hioki, Gossen, AVO, Brymen, to mention a few) will have proper safe input protection.Anything cheap (less than 75$) is not likely to have good safe input protection. You get what you pay for.

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: September 11, 2020, 10:55:14 am
content: I wanted to know the brand, because HT on the pbc could lead you to think HT, which is a renowned brand ... which I guess is certainly not the brand of this DMM

author: E-Design
author_rank: Regular Contributor
timestamp: September 11, 2020, 11:22:14 am
content: Quote from: MosherIV on September 11, 2020, 10:50:43 amAnd the name brands actually document and test the meters to the CAT levels that are claimed.Fluke in particular is especially competent in their designs for these higher measurement categories. They take a conservative approach to the protection design. They are the GOLD standard for lineman and other electrical workers who actually work in those environments.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 05:27:38 pm
content: Quote from: Kleinstein on September 11, 2020, 09:17:42 amI have an Amazon brand that is rated as Cat III 600V. It has Klein fuses and a copper shunt wire, but not the fuses you mention. So, Amazon is guilty of marketing these bogus CAT rating meters also.However, what if you are measuring Voltage correctly, and you get a 3000V spike? Isn't CAT IV III suppose to be something like capable of taking care of a 6-8, 000V transients?This is really disturbing to me, guys. It just rubs me all sort of wrong ways. It's not right.Just read through this and others too. The PTCs in this unit are suppose to work as voltage clamps?https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

author: E-Design
author_rank: Regular Contributor
timestamp: September 11, 2020, 05:36:16 pm
content: Quote from: DW1961 on September 11, 2020, 05:27:38 pmYes there are surge requirements for the CAT rating the meter must withstand and remain safe to the operator.Amazon cant be held responsible for ensuring the specifications are met for all the products it allows to transact.Its disturbing that companies are able to make claims they cant meet and sell things where we would not like to see them. Buyer be ware!The world is full of this kind of stuff.In the end, each person is responsible for their own safety --not the company in China with the bogus silkscreen print on a $10 meter.

author: MosherIV
author_rank: Super Contributor
timestamp: September 11, 2020, 05:50:01 pm
content: QuoteDepends on whether the Amazon employee knows what they are doing when specifying the product.The ultimate garenttee of compliance to CAT rating is verification by independant test laboratory like 'UL'My understanding of the CAT rating is that it is not just the voltage but the energy.MOVs will try to limit the voltage spike by conducting but there is a limit to the amount of energy they can surpress, in fact they are rated by power (suppression).What happens is that the voltage surge causes high enough currents to flow that it vapourises tracks and conponents. The sudden conversion to gas causes a pressure wave which if not designed correctly, blows open the case of the dmm. This can spread some of the molten metal from the vapoursied stuff.Like I said watch eevblog blow up dmms and MJ Lorton. Fun to watchWhile it is very very unlikely to happen in the home, the point is not to take the risk.

author: floobydust
author_rank: Super Contributor
timestamp: September 11, 2020, 08:30:23 pm
content: There are no electrical/electronic component/product safety import regulations enforced in the West. There is no safety watchdog. The chinese are forever opportunists and it's our fault for letting in this stuff. Don't let Peter Navarro know about it.So the low-end multimeter market gets ruined- legitimate players go out of business because real safety parts and approvals adds cost. The chinese industry is doomed because Mr. Honest now saying Cat. II when liars are saying Cat. IV, they can't go backwards for claims or be competitive. Funny thing is it's not that difficult to fix these issues (protection, certification) but they don't have to.In the USA it trickles down to employers following OSHA regulations where the safety specs are important, but for the casual user or hobbyist, sellers - it doesn't matter. Wallwarts/phone chargers, Christmas lights, soldering/hot air stations, inverters, DVD players etc. many are not safe. But Amazon has no qualms about selling it.It's ironic that a trademark infringement had US Customs stopping Sparkfun's multimeter import over Fluke's yellow cosmetics. But safety? let'em products roll in.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 09:21:05 pm
content: Quote from: MosherIV on September 11, 2020, 10:50:43 amI did and it's a Fluke 27 and he then opens a more modern Fluke model, which is an updated Fluke 27. It was very informational.The main thing is like someone else said, aside from whether or not the fuses can protect, where are the MOVs?What is that bank of what look like either diodes or resistors upper left?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 11, 2020, 09:29:35 pm
content: Quote from: E-Design on September 11, 2020, 05:36:16 pmIt's an Amazon brand. They could be held accountable for that.

author: MosherIV
author_rank: Super Contributor
timestamp: September 11, 2020, 10:49:52 pm
content: Here is alink for tear down of my favourit Fluke - 187https://www.eevblog.com/forum/testgear/fluke-187/msg536455/#msg536455Tear down of a Keysight/Agilent dmmhttps://www.eevblog.com/forum/testgear/keysight-agilent-u1241b-teardown-video-and-high-resolution-images/msg2119102/#msg2119102Another Keysight/Agilent dmmhttps://www.eevblog.com/forum/blog/eevblog-832-keysight-u1282a-multimeter-teardown/Finally, Brymen dmm teara downhttps://www.eevblog.com/forum/testgear/brymen-bm869-short-review/100/MOV - Mercury Oxide Varistor - they start to conduct at a threshold voltage, thereby limiting the max voltage seen by the dmmThey are the blue things looking like large ceramic capacitors.Keysight/Aglient (and some other manufacturers) prefer to use a gas discharge tubes to limit the voltage

author: E-Design
author_rank: Regular Contributor
timestamp: September 11, 2020, 11:15:15 pm
content: Quote from: DW1961 on September 11, 2020, 09:29:35 pmYou would think so but sadly, no it wont happen.

author: floobydust
author_rank: Super Contributor
timestamp: September 12, 2020, 12:19:35 am
content: Amazon is only concerned about selling counterfeit products. I bought a cheap phone charger and it was terrible wrt safety, the power cord was like a shoelace so I gave it a bad review noting it has no safety approvals and shortly afterwards the brand name vanished and just changed to a different name.Amazon commercial multimeters, their ones made by CEM (Shenzhen Everbest Machinery Industry Co. Ltd.) have 61010 certification. They use two or three MOV's and big PTC like90DM600 pics.I followed OP's multimeter through at least four chinese shell companies, it's kinda crazy how many names and hops are involved.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 12:56:11 am
content: Quote from: floobydust on September 11, 2020, 08:30:23 pmThe reason the US has those standards is because American business is also "opportunist." It's still mind numbing to think these things are not certified, but, rather, screen printed. It's even worse to think that China has electrical standards too, but neither those nor ours are getting implemented in these devices.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 01:23:35 am
content: Quote from: floobydust on September 12, 2020, 12:19:35 amI have two of the Amazon brand commercials. Mine have a CAT III rating of 600V. 90DM120https://www.amazon.com/AmazonCommercial-Manual-Ranging-Digital-Multimeter/dp/B07VY41YHM/ref=sxin_9_pb?cv_ct_cx=amazon+multimeter&dchild=1&keywords=amazon+multimeter&pd_rd_i=B07VY41YHM&pd_rd_r=4d164cc3-cc96-4c8e-8797-2c65c781245d&pd_rd_w=J40H5&pd_rd_wg=tLr5x&pf_rd_p=ffb450f7-bfad-4e7e-95e8-f2bd147e99a4&pf_rd_r=5HBR1D5W21DDW4YQA6DR&qid=1599873442&sr=1-1-8065ff8c-2587-4a7f-b8da-1df8b2563c11They sell them for 16 bucks. I'm still wondering how they can NOT use some sort of MOV in the MM here we are talking about.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 05:19:55 am
content: Quote from: floobydust on September 12, 2020, 12:19:35 amThe Chinese do that with many products I've seen on Amazon (ask my how I know in a PM). One factory makes xx widgets, screen prints whatever name on the widget, then vendors buy them in lots and sell them. They are all the same, just different names. Well, everyone does that.I remember back when CDs and DVD for computers were the main way to transfer information, and lots of companies would do the same thing. For instance, you could get a "Light-ON" DVD that was a rebranded Ben-Q. LOL--we were always talking to the poor vendors asking them to send us an XX made DVD instead of the xy, and so on. One time we found a $200 DVD rebranded to a Ben-Q I think, that sold for something like 33.00 bucks. It was a Sony OEM model, with the Ben-Q screen print. I guess Sony was offloading that model. But, what a buy.The MM we're looking at comes from a shitty manufacturer, or not shitty manufacturer, but making cheapo MMs. I'm sure their factory can turn out a Fluke level MM anytime they wanted to, but that's not where the money is. I mean, imagine a Chinese Amazon seller trying to sell a quality MM that is the same or nearly the same quality and price as a Fluke? What are you going to buy?Amazon is putting out some cheap but well made MM, but CEM rebranded. Their top line is another CEM unit going for 223 bucks.https://www.amazon.com/AmazonCommercial-Heavy-Digital-Multimeter-Display/dp/B07VX431NK/ref=sr_1_5?dchild=1&keywords=Amazon+multimeter&qid=1599887284&sr=8-5What am I going to do, spend $233 on a CEM Amazon rebrand, or $223 on a Fluke? I'm buying the Fluke. People are buying it, though. so there it is, I guess.--Just as an Aside, I did not pay for this MM. IF you want to know why, PM me.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 05:21:27 am
content: Quote from: Wytnucls on September 11, 2020, 06:57:06 amI want to add that to my review because I want to rake this MM on Amazon. Is there a link you have I can use for substantiation? Or, do others here concur this is not even legal in the USA?

author: Wytnucls
author_rank: Super Contributor
timestamp: September 12, 2020, 08:19:55 am
content: I dont have original regulations.Relevant extracts were published on this site. Search for it.UL 61010-1 standards can be purchased here:https://standardscatalog.ul.com/PurchaseProduct.aspx?UniqueKey=24268Like 60601-1 before it, CENELEC and IEC 61010-1: 2010 – along with CSA and UL 61010-1 Third Edition, 2012 – are moving to Third Edition. 61010-1 is the internationally harmonized safety standard for laboratory, process control, and test & measurement equipment. Products sold into the EU must comply with the 3rd edition of EN 61010-1 by October 2013.

author: E-Design
author_rank: Regular Contributor
timestamp: September 12, 2020, 11:51:49 am
content: Quote from: DW1961 on September 12, 2020, 05:21:27 amThose crap designs should get raked on Amazon.Why not consult an attorney about the actual legalities of it (there are even free legal advise websites) - Everybody else is just providing speculation. Who knows what actual laws are broken (an attorney does)If you want have a credible legal complaint, you had better have a sound legal basis for it.And the comment about no such thing about 250V rating on current input - that individual doesn't understand the reasoning or design. All meters have a voltage limit on this input despite the low impedance.

author: Nusa
author_rank: Super Contributor
timestamp: September 12, 2020, 12:00:55 pm
content: "legal" is one of those words that requires you to find the relevant laws for the country/region in question. "not in compliance" with an established standard is an easier statement to make. Whether it's "legal" to sell a meter that's "not in compliance" in the USA is an answer I don't know. Professionally, industry safety regulations can require that only tested meters with certificates of compliance from a recognized testing agency be used. But at the consumer level, I don't know what the "legal" situation is in the USA. I suspect it's caveat emptor and there is no enforcement of the standard.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 12, 2020, 12:04:58 pm
content: Some earlier discussions:https://www.eevblog.com/forum/projects/cat-ratings-and-interpretation/75/

author: tooki
author_rank: Super Contributor
timestamp: September 12, 2020, 12:07:01 pm
content: Quote from: DW1961 on September 10, 2020, 11:27:02 pmNo.A quality multimeter will not suffer any damage (other than a blown fuse in current mode) if connected to a circuit while in the wrong mode, provided you stay within the meter's stated limits. So if, on a meter that's specified to 1000V AC in volts mode, you accidentally connect to 400V AC in ohms, capacitance, mV, or whatever, no damage should occur. Cheap meters lack the protection circuitry needed to allow this kind of insult, and thus may be damaged.(In contrast, CAT ratings specify the (massive) fault voltages the meter will protect the operator from. For example, a typical industrial meter like a Fluke 87V is rated for CAT III 1000V and CAT IV 600V. Both of thosecategoriesspecify a transient overvoltage of 8000V, meaning that an 8000V surge will not cause the meter to explode in the user's face. The meter, however, doesnothave to survive the event in order to comply with its CAT rating.)

author: Gyro
author_rank: Super Contributor
timestamp: September 12, 2020, 02:56:15 pm
content: Quote from: MosherIV on September 11, 2020, 10:49:52 pmMOV -MetalOxide Varistor.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 04:55:21 pm
content: Quote from: E-Design on September 12, 2020, 11:51:49 amSpecifically, he said that the CAT voltage rating applies to the current circuit as well. Is that a true or false statement?I was really interested in that because if true, then it is not a CAT certified device. (We don't need to know the laws, then, because the argument is logically true--follows directly from premises to conclusion with no leaps.)

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 05:00:48 pm
content: Quote from: tooki on September 12, 2020, 12:07:01 pmVery clear, got that. I read that in the Fluke CAT explanations also. Thanks.Did you see any protections in this unit for accidentally measuring volts when in another non-volt mode? I'd be willing to try it unless you think definitely it will just fry it.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 05:02:23 pm
content: Quote from: E-Design on September 12, 2020, 11:51:49 amI have quite a few problems with this unit listed so far, such as no visible MOVs, no PCB gaps, no case blade protections, the 250V limit on current. Anything you would also add in?

author: Wytnucls
author_rank: Super Contributor
timestamp: September 12, 2020, 05:37:13 pm
content: Quote from: DW1961 on September 12, 2020, 04:55:21 pmOf course it's true. Logically, if you measure 1000V under CAT III conditions, with the probes in the wrong sockets, your A/mA fuses must be rated for that voltage or your backside might get a little crispy. That 250V fuse won't save you.On top of that it must be a very fast (FF) fuse of the right rupture capacity.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 05:44:11 pm
content: Quote from: Wytnucls on September 12, 2020, 05:37:13 pmWytunds,Just to be clear, I wasn't calling you out in anyway. Your comment bout the 250V current limit was important.I'm just looking for factual information to report in my review of that meter. Obviously, if they have that 250V limit, then the fuses are NOT rated for 1000 volts. That is logical. I should take out the fuses and see what they say on them, if anything.I just want to make sure that if I post this is NOT CAT compliant, that I'm accurate in my review. If the fuses are only rated to 250V then that's that. They can't reliably be expected to stop an arc over 250V. However, and correct me if I am wrong, an HRC fuse can stop arc many times it's rated voltage?

author: Wytnucls
author_rank: Super Contributor
timestamp: September 12, 2020, 06:54:42 pm
content: A. Voltage Rating (Littlefuse)The voltage rating, as marked on a fuse, indicates themaximum voltage of the circuit for which the fuse isdesigned to operate safely in the event of an overcurrent.Therefore, the fuse’s voltage rating must equal or exceedthe available circuit voltage where the fuse will be installed.System voltage exceeding the fuse’s rated voltage mayresult in fuse damage.The answer is no.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 12, 2020, 07:07:56 pm
content: Does anyone want to add anything before I post my full review?1. No metal-oxide varistor (MOV) protection could be found. It has PTC protection, but in a surge situation, PTCs can’t react fast enough, and need MOVs . PTCs are also small.2. PCB is not guard protected.3. The casing is not bladed to section off high voltage area from arc inside the case.4. The current protection fuses say they are MAX 250V, but the CAT rating is 1000V. That is NOT a CAT certified meter. The CAT voltages also apply to the fuses on the current side.The only thing CAT about this meter is the screen printing.

author: bc888
author_rank: Regular Contributor
timestamp: September 12, 2020, 07:36:38 pm
content: Quote from: DW1961 on September 12, 2020, 05:19:55 amYes, buy the Fluke, don't buy a $10 meter or free in your case) and expect it to be the same. As an aside, fella who runs this web site, Dave Jones, had a competent company (Bryman) mfg a little meter for him that sells for @ half that, the BM235. Meets the specs and kicks ass. Click the link at the top of the main page that says "Shop" the $ is in Aussie money so don't comeback calling me a liar too fast.https://www.eevblog.com/product/bm235/Furthermore, Eevblog user JoeSmith has some great testing and has a spreadsheet on which meters meet their specs (he doesn't have every $5 cheapassed meter listed), and the Fluke 101, a Fluke branded meter mfg in China does great. It may not do as much as the $5 meter, so look carefully to make sure that the features it has are what you want before you pull the trigger. Cheap meters that do not meet their specs are likely owned AND USED by most people reading this thread BTW. When you buy that meter from Dave, suggest getting extra fuses from him as well, you'll be shocked that the ebay and Amazon fuses are often fake. When you look at the price of an authentic replacement Bussman, don't be tempted to get one that is called and looks the same but for $1/10th of the money from an unofficial source. You'll be disappointed.Good luck!

author: joeqsmith
author_rank: Super Contributor
timestamp: September 12, 2020, 09:40:17 pm
content: Quote from: bc888 on September 12, 2020, 07:36:38 pmI just want to be clear once again that the tests I run have nothing to do with the specs or ratings of the meters. Providing bad information helps no one.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 13, 2020, 04:31:39 am
content: This seems like a really good meter. Let me know what you think about the brand name especially:https://www.amazon.com/DRUnKQUEEn-Multimeter-Digital-Current-Resistance/dp/B08D8NDZ45/ref=sr_1_5?dchild=1&keywords=DRUnKQUEEn+Clamp+Meter&qid=1599971457&sr=8-5

author: DW1961
author_rank: Frequent Contributor
timestamp: September 13, 2020, 05:34:37 pm
content: Just wanted to ask another question about protections here. No one can actually see any MOVs in this meter. Is there any other circuitry that could serve the same purpose as an MOV?

author: Gyro
author_rank: Super Contributor
timestamp: September 13, 2020, 08:34:02 pm
content: No.(Or, should I say, none that would be invisible.)

author: E-Design
author_rank: Regular Contributor
timestamp: September 13, 2020, 08:53:12 pm
content: Quote from: DW1961 on September 13, 2020, 05:34:37 pmYou seem quite focused on looking for MOV's - Yes there are other components/circuits.. GDT's, TVS, zeners and possibly some other types of semiconductors with breakdown characteristics.Dont worry so much about it. Even if you see they are present, it doesn't mean the design is good. Not seeing them doesn't prove the design is bad either.The PCB layout and sizing of them also needs to be done correctly. and most importantly - the overload / transient testing! - the results of which only the MFG knows.So there is only so much we can conjecture about. While I believe these cheap meters (likely) do not meet their CAT ratings, this belief doesn't constitute a proof of such.You are free to put them under all the relevant testing and report actual results.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 13, 2020, 10:20:26 pm
content: Quote from: Gyro on September 13, 2020, 08:34:02 pmGyro, that's what I was meaning to say. And, that no one sees any other type or resistor that would function like an MOV on the board?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 13, 2020, 10:26:09 pm
content: Quote from: E-Design on September 13, 2020, 08:53:12 pmIt's not really the MOVs I'm concerned about but I just called this company out hard for stating a CAT rating and not being complaint at the same time. I want to make sure my ducks are in a row as much as possible.If there are any other items that anyone can see that would serve the same function as MOVs, then I wanted to know that. I'm just trying to be a thorough as I can.For instance, Wytnucls pointed out a very valid pit that the fuses can't be 250V and the CAT rating 1000V at the same time. You don't need to do a test the unit to see that is not CAT approved.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 14, 2020, 01:43:16 am
content: Reply from teh seller:Hello Associates,Thank you for your email!We are very sorry, we use diode protection for this multimeter, so there is no metal-oxide varistor (MOV).

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 02:15:32 am
content: If the meters are not required to survive the 61010 (and I am not suggesting that but several on this forum have), and the only requirement is to keep the user safe, then there may be little need for MOVs. As long as the blast is contained and no one was injured, many people on this forum seem to feel that is good enough.I really don't care about such things and if I have to work in CAT III, I use name brand equipment. At home, on the bench, I just want the meter to survive some basic transients. This is really what I was attempting to show with the tests I ran.As a beginner, I doubt very much you are working in CAT III and up. So ask yourself, what really is your requirement. If you, like me are just playing around with low energy circuits and are wanting the MOVs and other parts to ensure the meter is robust enough to survive on the bench, as EDesign stated: "Even if you see they are present, it doesn't mean the design is good." Very true. I have a UNI-T sitting here that had some very nice protection but a poor layout. It looks impressive but that's about the extent of it. Many meters I have looked at fall into this category.If you want to hedge your bets on a meter that will survive at least some basics, I would recommend you stick with brands like Fluke, Brymen, Hioki and Gossen.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 14, 2020, 04:58:02 am
content: IEC 61010-1:2010 Edition 3The purpose of the standard is to ensure that hazards to the operator and surrounding area are reduced to a tolerable level.https://www.intertek.com/blog/2020-02-25-iec-61010/https://www.analog.com/media/en/technical-documentation/white-papers/IEC-61010-1-Edition-3.pdf

author: DW1961
author_rank: Frequent Contributor
timestamp: September 14, 2020, 05:00:12 am
content: Quote from: joeqsmith on September 14, 2020, 02:15:32 amYeah, I get all that. As long as I don't get hurt using it when F-ing up, I'm ok with that, and as long as the meter really is a CAT meter, I'm ok with that too becasue the meter was 17 bucks--hardly even worth replacing a blown fuse. If I need it, I'll just grab another one. I got another reply from the vendor because I asked about CAT ratings and Current Fuse rating. I also asked what type of diodes they were using instead of MOvs.------------Hello,We use 9013 or 8050 transistors.The CAT.III 1000V voltage value is the pulse withstand voltage value, which is an insulation voltage value inside the shell protection, which is different from the voltage value of the current fuse.The fuse of this multimeter can only reach 250V.-------------I then asked how it can have a CAT rating of 1000V with a Current Fuse of 250V? We'll see what they say.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 14, 2020, 09:02:32 am
content: From an Intertek test report dated 2013 (Fluke Amprobe meter) several requirements come to light:1. Multimeters are tested for single fault condition onvoltage terminals:Shorted varistors and resistors in turn with 1100V AC and DC applied for something like 3 hours if CAT III 1000VThe meter must be able to indicated an hazardous live voltage up to the max rated voltage after the test.2. The test voltage (impulses of 8000V) is only applied between each pair of terminals used tomeasure mains voltage. It is unclear if the meter has to remain functional after the test.3. The a.c. and d.c. RATED voltages of the over current protection device (fuse) shall be at least the highest a.c. and d.c. RATED voltages of the multimeter.http://content.amprobe.com/certifications/34XR-A_LVD.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 10:59:50 am
content: Quote from: Wytnucls on September 14, 2020, 04:58:02 amFrom the actual standards themselves rather than a summery for laymen:https://www.eevblog.com/forum/testgear/what-are-for-you-the-3-biggest-disadvantages-of-your-benchtop-dmm(s)/msg3215752/#msg3215752

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 11:05:20 am
content: Quote from: DW1961 on September 14, 2020, 05:00:12 amI would doubt very much that you would be too concerned with achflash. If you assume the meter has no CAT rating at all, you should be fine.I doubt very much that you will find a distributor is going to be an expert in safety or design. At best they may have read something from Wiki and became an instant expert in 30 seconds or less.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 14, 2020, 05:03:27 pm
content: Quote from: joeqsmith on September 14, 2020, 10:59:50 amJoe,You are the man. Watched your entire video testing those Flukes.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 14, 2020, 05:13:52 pm
content: Quote from: joeqsmith on September 14, 2020, 11:05:20 amAll true. I just like understanding as much as possible, and if this meter is not CAT compliant, I want to understand why. I wrote a review for it and based on what you all said here, and what Jon Gerow said over at his forumshttps://www.jonnyguru.com/forums/(He's the manager for Corsair power supplies) and also said that a CAT rating applied to the fuses too, then this meter is not CAT anything complaint. This is the last response I got from them:----Hello,CAT safety level certification only represents the shell safety voltage level of the multimeter and has nothing to do with the voltage value of the internal fuse.Ruoshui---Well, that is 100% wrong according to all of you and Jon at jonnyguru. So, I did the review, gave props for the meter measuring almost everything, having the Hz read out automatically when taking a voltage measurement, in the rather large LCD, props to capacitor option to test caps, etc., and explained since it says it is CAT complaint and is not, I gave it one star.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 14, 2020, 07:58:31 pm
content: Quote from: DW1961 on September 14, 2020, 05:13:52 pmThis understanding of CAT ratings would explain how some Chinese meters get there CAT rating.So a good reason not to trust a Chinese CAT rating.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2020, 10:53:38 pm
content: Quote from: DW1961 on September 14, 2020, 05:13:52 pmAs far as the fuses, I think I posted the fault currents for the various CAT ratings (from the actual standards). I'm not a safety expert and have never been involved with designing or testing DMMs for the safety standards. I have read the relevant standards more than once and have obviously gone down my own path with testing DMMs but that's really the extent of it.If you are planning to do reviews for Amazon you get your free products, you may want to make them all 5 stars like most channels. I remember watching a review once where the guy starts out calling Dave a meter snob. Then proceeds to 5 star some cheap meter. It seems typical.Good luck with your own reviews.

author: E-Design
author_rank: Regular Contributor
timestamp: September 14, 2020, 11:29:42 pm
content: This might be disappointing to some.. the CAT ratings and standards only dictate the test requirements. More specifically, they do not govern how the hardware design accomplishes passing the tests. Unlike UL, there is no investigation into the components used and their ratings (or lack thereof) As typical with standards like these, they don't dictate how to design the hardware, only the test. Professional designs make good choices for these components and then go on to have the design tested and passing (having NEVER had these component choices scrutinized by the compliance authority)Because of this, any hardware that passes the tests with what would be considered poor choices of components (or none at all) - Is not strictly in violation if it passes the testing. Now, it may be a lot less likely to pass. But I would just like to point out that *nobody* can look at a PCB and claim the design is in violation of CAT rating. Its a lousy thing I know, but the only *surefire* way to really rake these products is to get a hold of them and run the test yourself and post the result publicly like JoeQ did. When I look at some of these, I personally do not trust them because of what looks like shoddy design, but I also know that claiming CAT violation is actually inappropriate until further test results support the claim.You should massacre these cheap products in your reviews for sure! Go for it, but I would stop short of claiming violations / mislabeling until there is evidence. In fact, its probably quite easy to run a test and easily show a failure. But looking at the PCB isnt evidence of anything.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 12:05:03 am
content: The problem is in the way these 'ratings' are implemented. The way it should be is that anyone who sells a product should be required to provide proof that the testing has been done. It could be argued that to sell a product with the mark but not have proof of a satisfactory test is a deceptive trade practice, but until the stakes are sufficient--somebody gets hurt--nobody will bother. And even then, there will be nobody to actually serve and sue, unless a plaintiff manages to make a case against Amazon. The only ones currently with both an interest and the money to take legal action would be competitive companies, but they probably are better off letting someone get fried because that makes good advertising for them.The OP probably shouldn't use terms like 'violate CAT standards', but might rather say "Experts have looked at the design and concluded that it is very unlikely to meet the CAT III/IV standards. The manufacturer was unable to show any evidence that the appropriate tests were performed and could not even answer basic questions about what a CAT III/IV rating entails". I'm not sure buyers care, at least not the $10 meter crowd.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 01:26:27 am
content: Quote from: bdunham7 on September 15, 2020, 12:05:03 amYes, what you have explained is indeed part of the problem. Also, when requesting such information, when you reach out through Amazon, I am fairly certain you wont be talking to the person who is qualified to provide the answer you are seeking (even if the tests are documented / filed).Anyhow, as you said, most people don't care about such things.. that is until somebody gets hurt and then all of a sudden the lawyers care.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 04:41:18 am
content: Quote from: Kleinstein on September 14, 2020, 07:58:31 pmLOL. Well, they are going to get our rating posted on Amazon soon--just waiting for the editors to release it. And, it ain't pretty. I have the chance to get another one of these meters that look almost the same as this one, but with a CAT III 600V rating only. Think I should get it and we can tear it down too?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 04:46:37 am
content: Quote from: joeqsmith on September 14, 2020, 10:53:38 pmWell, I'll let you be the judge of how I review it.(Doing all 5 star reviews gets you kicked from the program pretty fast, so I have heard. Those algorithms are smarter than you think.)

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 04:57:51 am
content: Quote from: E-Design on September 14, 2020, 11:29:42 pmThe only thing I say that is not CAT is using fuses that are not the same voltage as the CAT designation. Everyone seems to be in agreement that the fuses must be the same voltage as the CAT rating. The second point I make is that I (with all the help here) could not see anything on the PCB that would do the job of a MOV, and the PCB had no MOVs on it.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 05:03:32 am
content: Quote from: bdunham7 on September 15, 2020, 12:05:03 amI completely agree with that, but if the CAT standard is that current fuses must be the same as the CAT voltage rating, then this meter clearly is in violation of CAT standards. I mean, the only way around that is if everyone here is wrong about the fuse voltage and CAT standards. I'm assuming not.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 05:10:16 am
content: Quote from: DW1961 on September 15, 2020, 04:57:51 amI have not actually seen that spelled out and I don't have actual access to the standard. Perhaps someone who does could clarify it that is an expressly stated rule, or if it is logically derived somehow. It makes sense, but that doesn't mean that anyone got around to actually writing it down.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 08:57:15 am
content: 101.3 Protection against mismatches of inputs and ranges101.3.1 GeneralIn NORMAL CONDITION and in cases of REASONABLY FORESEEABLE MISUSE , no HAZARD shall arisewhen the highest RATED voltage or current of a measuring circuit TERMINAL is applied to anyother compatible TERMINAL, with any combination of function and range settings.NOTE 1 Mismatches of inputs and ranges are examples of REASONABLY FORESEEABLE MISUSE, even if thedocumentation or markings prohibit such mismatch . A typical example is inadvertent connection of a high voltage toa measuring input intended for current or resistance. Possible HAZARDS include electric shock, burns, fire, arcingand explosion.NOTE 2 T ERMINALS that are clearly not of similar types and that will not retain the TERMINALS of the probe oraccessory need not be tested.The equipment shall provide protection against these HAZARDS. One of the followingtechniques shall be used.a) Use of a certified overcurrent protection device to interrupt short- circuit currents before aHAZARD arises. In this case, the requirements and test of 101.3.2 apply.b) Use an uncert ified current limitation device , an impedance, or a combination of both toprevent the HAZARD from arising. In this case, the tests of 101.3.3 apply.Conformity is checked by inspection, evaluation of the design of the equipment, and asspecified in 101.3. 2 to 101.3.3, as applicable.These tests shall be performed with any probe assemblies supplied by the manufacturer, andrepeated with the test leads of 101.3.4.101.3.2 Protection by a certified overcurrent protection deviceAn overcurrent protection devic e is considered suitable if it is certified by an independentlaboratory to meet all of the following requirements.a) The a.c. and d.c. RATED voltages of the overcurrent protection device shall be at least ashigh as, respectively, the highest a.c. and d.c. RATED voltages of any measuring circuitTERMINAL on the equipment.b) The RATED time- current characteristic (speed) of the overcurrent protection device shall besuch that no HAZARD will result from any possible combination of RATED input voltages,TERMINALS, and range selection.NOTE In practice, downstream circuit elements such as components and printed wiring board traces areselected to be able to withstand the energy that the overcurrent protection device will let through.c) The a.c. and d.c. RATED breaking capacities of the overcurrent protection device shallexceed, respectively, the possible a.c. and d.c. short- circuit currents.The possible a.c. and d.c. short- circuit currents are calculated as the highest RATEDvoltage for any TERMINAL divided by the impedance of the overcurrent- protectedmeasuring circuit, taking the impedance of the test leads specified in 101.3.4 into account.The possible a.c. short - circuit current need not exceed the applicable value of Table AA.1.Additionally, spacings surrounding the overcurrent protectio n device in the equipment andfollowing the protection device in the measuring circuit shall be sufficiently large to preventarcing after the protection device opens.Conformity is checked by inspection of the RATINGS of the overcurrent protection device andby the following test .If the protection device is a fuse, it is replaced with an open - circuited fuse. If the protectiondevice is a circuit breaker, it is set to its open position. A voltage of two times the highestRATED voltage for any TERMINAL is a pplied to the TERMINALS of the overcurrent- protectedmeasuring circuit for 1 min. The source of the test voltage shall be capable of delivering500 VA. During and after the test, no damage to the equipment shall occur.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 11:29:25 am
content: There you have it.. the devices should be at least as high as the RATED levels.. ("at least" means equal to is valid) which for most meters is like 250V for current and up to 1kV for voltage. In other words, the standard says you should design to the normal expected maximum RATED levels. Helpful.The CAT testing scenarios can go to 5kV and HIGHER (if I am recalling correctly)... whos got that 8kV rated fuse....DW1961- This means that explicitly, the fuses are NOT REQUIRED to have the same ratings as the CAT testing levels. Nobody doing meters has fuses that high and more importantly, the standard does not demand it. But it does specify needing ot support the max breaking level (below)If you want a logic path through possibly violating the standard, this paragraphThe possible a.c. and d.c. short- circuit currents are calculated as the highest RATEDvoltage for any TERMINAL divided by the impedance of the overcurrent- protectedmeasuring circuit, taking the impedance of the test leads specified in 101.3.4 into account.The possible a.c. short - circuit current need not exceed the applicable value of Table AA.1.would mean that the breaking capacity of the fuse would need to be able to break that higher current of 1kV divided by impedance of the AMPS pathway. Most of those smaller types are unlikely to be rated for that high of current, yet probably still pass the over voltage / over current CAT tests anyhow. It could be a stretch to argue it though.. but it would support your efforts..The reality is though, that the 1kV (larger) arc-extinguishing type fuses with high breaking capacity (10 kA etc..) can usually fail cleanly in these higher voltage CAT testing scenarios and thus are considered a better form of protection for sure (than say the smaller types)Then again, nearby lightning strike surges (and the Ldi/dt that ensues ) might cause them to explode anyhow.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 15, 2020, 12:01:01 pm
content: QuoteThat's the idea although, there are separate test for the fuses. I have ever read them.I don't see a time where I create a 1KA to 100KA fault current generator at home.I recently posted a link to an article on how this is done. Maybe we can collect a bunch of fuses and rent the lab for a day of video recording.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 01:39:49 pm
content: Quote from: E-Design on September 15, 2020, 11:29:25 amUnless I'm missing something, it seems clear that the fuses must have a voltage rating of 1000V for any 1000V CAT-rated (even CAT I) meter. And by 'rated voltage', they mean the CAT x/xxxx rating. It states that the voltage requirement is based on the highest voltage rating of any terminal, precluding the practice of having a lower voltage rating for current. Perhaps this is one reason for some bench DMMs being CAT II/300 with no CAT I/1000V rating, even though they work up to 1000VDC. If it says CAT x/1000, you need a 1000V rated fuse.RATED means the CAT voltage rating specified, not the corresponding overvoltage transient testing voltage. This is consistent with the requirement that there be no hazard when a non-voltage terminal is energized with the full rated voltage. There is no requirement that wrong terminals withstand the transient test, only that they withstand the maximum rated voltage. So there's no need for 8kV fuses.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 02:07:20 pm
content: You're not missing anything. It is all spelled out in proper English.There is a special test, where double the rated voltage (2000V if CAT III 1000V) is applied to the current terminals (A/mA/uA), with a ruptured fuse in place, for one minute to test clearance and creepage.China has yet to move to the new regulations for multimeter fuses, which would explain the statement made by the Chinese manager. As an exporter though, he should be aware of local requirements.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 02:29:44 pm
content: Quote from: Wytnucls on September 15, 2020, 02:07:20 pmI saw that and wondered about the definition of an 'open fuse', since there are many ways to blow a fuse and I would guess that the end state would vary. I wouldn't expect that test to be a big challenge though, at least to the fuse, although they appear to be demanding something of it that wouldn't seem to be part of the fuses own rating.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 02:40:29 pm
content: The fuse is a certified component already (UL/CSA/ANCE 248-14 “Fuses for Supplementary Overcurrent Protection”).There is no need to test it.The voltage is applied to make sure no short can happen between fuse, fuse holders and traces.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 04:06:48 pm
content: Quote from: bdunham7 on September 15, 2020, 01:39:49 pmI know there is no need for 8kV fuses, that was a joke.I didnt think these cheap meters claimed 1kV CAT rating on the *current* input. So the question originally was are they in violation on this terminal based on the fuse rating to be the smaller 250V fuse type.yes of course, obviously if it says 1000V CAT rating you need a fuse at least for that high.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 04:16:02 pm
content: Quote from: Wytnucls on September 15, 2020, 02:40:29 pmThose tests and certifications do not translate necessarily to meeting a particular CAT x installation and use.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 04:36:16 pm
content: The CAT rating is on voltage terminals only. They are the only ones subjected to high pulsed voltage to mimick overvoltage on the mains.You're not likely to encounter mains and high voltage spikes at the same time with the probes in the wrong sockets. The fuse will blow straightaway.The fuse requirement is in addition to the CAT rating.An inadequate fuse makes the meter unsafe and illegal.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 05:09:25 pm
content: Quote from: Wytnucls on September 15, 2020, 04:36:16 pmAgreed, those fault conditions not likely.Unsafe yes, illegal? Thats not so clear. The only reason the fuse discussion came up was because somebody made the claim that the fuse must meet the CAT rating as well. If I recall, I thought somebody mentioned that to the OP.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 05:09:49 pm
content: Quote from: E-Design on September 15, 2020, 04:06:48 pmThe info Wytnucls posted clears up a lot of what isn't made totally clear in the Fluke brochure. The overvoltage transient tests are only one part of the CAT rating and it is the whole meter that is or is not CAT rated, not certain terminals. You can't disclaim your way out of that. In order to have current terminals that cannot withstand voltage at the CAT rating, they would have to be incompatible with the voltage terminals. IOW, a CAT I/1000V meter with sheathed banana jacks on all terminals has to withstand the rated voltage--1000V--on any combination of terminals in any range.QuoteBut they do, because the CAT specification explicitly states that those ratings are one way to meet that particular CAT requirement. Of course there are other tests andnon-test requirements, such as physical clearance and creepage minima, to contend with--so one rating or one passed test cannot be enough to meet the requirements. And, in this case, the meter manufacturer could contend that they are compliant under 101.3.1(b) somehow, we don't have 101.3.3 to read and see how ridiculous that claim might be. Perhaps blowing the traces off the board is good enough for meters priced less than proper fuses.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 05:13:17 pm
content: Quote from: Wytnucls on September 15, 2020, 04:36:16 pmSome perfectly good meters have an 'inadequate' fuse in series with another protective device or design thatisadequate. The mere presence of an 'inadequate' fuse doesn't absolutely prove noncompliance.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 05:37:23 pm
content: Absolutely, but we were talking about a handheld multimeter and few of those have fuses in series, except for some old Fluke ones.There is a clause for uncertified current limiting devices.My Gossen 30M does not have a fuse on its mA range and is rated CAT II 600V with a PPTC resettable fuse.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 05:49:11 pm
content: Quote from: Wytnucls on September 15, 2020, 08:57:15 amThe way I read that, the Vendor response is factual.I read it to mean that the fuses don't matter. As long as the internal electronics can stop the rated voltages and over voltage requirement--it's CAT complaint.Obviously, there is more to it than we first lit on.I've requested Amazon NOT submit the review until I can edit it. That wouldn't be fair to the manufacturer or the vendor.Currently, I'm assuming this meter is CAT III and CAT IV compliant, as it states, until someone can show a CAT guideline that means it is not. Cheap or not, it "seems" that the vendor responses are qualified. They said over voltage is done with a series of diodes, I think, is what I posted. As long as they work to CAT standards, they're good to go. No, there aren't any PCB guards or case blades, but it is what it is and we can't fudge things because of our opinions--and I think everyone here agrees with that.I have no alternative, in the spirit of honesty and accuracy, to retract my bad review and edit it to reflect accuracy. It may not last as long as a Fluke, and most likely would not be any stretch (those things are bullet proof), but for 35 bucks, it's a decent meter that does most everything--given it is CAT complaint, and it now seems most likely it is.Just to be clear, I never wanted to rake this meter simply because it is cheap or from China. My intent was honesty of CAT compliance. I know damn well that a 35.00 meter isn't going to be as robust as a 200.00 meter. My problem was some hobbyist or DIYer working around his or her house, like myself, making a mistake and having a couple fingers blown off or becoming blind. Or, even someone working on mains using this for some reason, too. I specifically just wanted it to be what it says it is.Anything else anyone would like to add, please do. The CAT discussion is educational and productive, if nothing else.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 15, 2020, 06:04:40 pm
content: Quote from: E-Design on September 15, 2020, 05:09:25 pmThe CAT rating is invalid if the fuse voltage rating doesn't match or exceed the maximum CAT voltage. Very simple.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 06:59:41 pm
content: Quote from: Wytnucls on September 15, 2020, 06:04:40 pmThat's not how I'm reading it.--------101.3.2 Protection by a certified overcurrent protection deviceAnovercurrent protectiondevic e is considered suitable if it is certified by an independentlaboratory to meet all of the following requirements.a) The a.c. and d.c. RATED voltagesof the overcurrent protection deviceshall be at least ashigh as, respectively, the highest a.c. and d.c. RATED voltages of any measuring circuitTERMINAL on the equipment.--------------The way I'm reading it, it means theovercurrent protection devicehas to equal or be greater than the CAT voltages. It doesn't say the fuses need to do that.Working phrase:overcurrent protection deviceThe device could be in addition to the current fuses?

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 08:29:11 pm
content: Quote from: DW1961 on September 15, 2020, 06:59:41 pmI would expect them to make an argument like that if challenged in a way the required their response. I'd agree with Wytnucls as far as stating that if the fuse doesn't meet the voltage requirement it is very unlikely that anything else will, but not that the fuse rating is dispositive. If the burden of proof falls on the person challenging the mark, they would likely have to perform testing as specified in 10.3.3. Perhaps there is more in the standard elsewhere that clears this up, but the main issue here is that the CAT standards aren't regulations (at least here in the US) that mandate certification of testing by the seller.At this point, unless you can find a creepage or clearance mistake, you don't know for sure how the device would test. I'll bet on badly. Diodes my ass.I think maybe we make too big a deal out of this stuff. Sure, it appears fraudulent. However, the likelihood of an actual serious injury is pretty low. Very few people will use these meters at over 250VAC mains voltage. No respectable electrician would be caught dead with one of those meters. There are probably many things we can all do in our lives to increase our health and safety that will have much more impact than obsessing over whether we should use a CAT III or CAT IV meter. You could use the free Harbor Freight meters (DT830) on all of your work and it probably wouldn't even be in the top ten of your daily injury risks. I'm quite sure I'm more likely to stab myself to death while slicing an avocado.

author: E-Design
author_rank: Regular Contributor
timestamp: September 15, 2020, 09:14:29 pm
content: QuoteYeah, actually I think the spirit of these CAT and most safety standards were to ensure no hazardous condition exists for the user. As such, absolutely the meter can be utterly destroyed. As long as there is no shock, burn, chemical, radiation or inhalation hazard created, its perfectly fine. No matter the guts are blown to oblivion.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 15, 2020, 10:03:16 pm
content: Quote from: bdunham7 on September 15, 2020, 08:29:11 pmOkay, that's a start. Why can't a series of diodes, then, act as that 1000V protection? Diode protection was my mistake. I asked what diode protection they are using and this is what he said:"We use 9013 or 8050 transistors. The CAT.III 1000V voltage value is the pulse withstand voltage value, which is an insulation voltage value inside the shell protection, which is different from the voltage value of the current fuse. The fuse of this multimeter can only reach 250V."So, can those transistors offer 1000V protection?

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 10:43:51 pm
content: Quote from: E-Design on September 15, 2020, 09:14:29 pmFor overcurrent, perhaps. For the CAT overvoltage transient test, the meter needs to still be able to indicate the presence of hazardous voltages, although it need not be precise or accurate anymore.

author: bdunham7
author_rank: Super Contributor
timestamp: September 15, 2020, 11:01:18 pm
content: Quote from: DW1961 on September 15, 2020, 10:03:16 pmI don't really understand the question or the answer, but if you (or they) make an extraordinary claim, the burden of proof thereof falls on you (or them), at least in most rational discussions. We'll leave courts of law outside of that domain for now.How you could protect against several kiloampere overcurrents, 1000V accidental overvoltages or 8 kilovolt transients using mystery diodes or transistors with a 25 volt Vce rating all in 0805 or SOT-23 packages is beyond me. I think that their answer is preposterous and that either they don't understand the issue or they're hoping you don't. But I've been proven wrong before.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 16, 2020, 12:57:19 am
content: Quote from: bdunham7 on September 15, 2020, 11:01:18 pmOK so some clarification. He actually said in one reply that they use TRIODE protection, but when I looked up "triode" it said it was old tube technology and tube oriented, although I didn't get in depth researching it. so I assumed he meant DIODE.I just got a reply back and he said it is "Triode" protection.So a little more research and I found this: Mosfet N-CH 900V 4A to-220 Transistor Triode Fqpf4n90c here:https://www.made-in-china.com/products-search/hot-china-products/Triode.htmlI'm not sure what "triode" could do the voltage protection, but I'm sure someone here knows. After the image is open, right click (Windows) and choose, :View Image." Then you can get a good look at them.So, just got a reply back with the "triodes" they are using in a picture of the PCB he gave me."We use 9013 or 8050 Triode. I have marked the position of the triode on the PCB with a red box on the picture. Please check the attachment."

author: Wytnucls
author_rank: Super Contributor
timestamp: September 16, 2020, 07:34:39 am
content: They probably are crowbar components (NPN transistors). Very common on multimeters.Here is one on my Uni-T 71D multimeter.

author: E-Design
author_rank: Regular Contributor
timestamp: September 16, 2020, 02:29:13 pm
content: Quote from: bdunham7 on September 15, 2020, 10:43:51 pmalthough it need not be precise or accurate anymore.whos definition of *precise* and whos definition of *accurate* -- those are subjective terms. If the standard calls out specific ways the measurements can be in error after a likely failed test result, those would need to be quantified perfectly.

author: bdunham7
author_rank: Super Contributor
timestamp: September 16, 2020, 02:43:23 pm
content: Quote from: Wytnucls on September 16, 2020, 07:34:39 amWhere in the circuit are these placed? I would expect those (as shown on the OPs circuit board photo) to fail short at 40-50 volts or less and to blow off the board over a few amps or so.

author: bdunham7
author_rank: Super Contributor
timestamp: September 16, 2020, 02:46:46 pm
content: Quote from: E-Design on September 16, 2020, 02:29:13 pmThat was't a direct quote from any standard--I don't have a copy of it to refer to. I read it once somewhere, but I don't remember the exact details. I believe that the standard does quantify, or at least specify, the requirements quite clearly.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 16, 2020, 03:06:37 pm
content: Quote from: bdunham7 on September 16, 2020, 02:43:23 pmUsually as protection for inputs to micro-controllers.

author: TimFox
author_rank: Super Contributor
timestamp: September 16, 2020, 03:19:11 pm
content: Those NPN transistors are connected to use the Base-Emitter junctions as PN diodes. The transistors are cheap, are not in transparent housings, and typically have lower leakage current than "regular" diodes. (Good diodes in glass packages can easily have enough photocurrent to upset the rest of the circuit.) The BE diode has a low breakdown voltage, but since it is in parallel with another diode in the reverse direction, it should not see breakdown.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 16, 2020, 03:56:27 pm
content: The Chinese rep was probably thinking of the triode region of a MOSFET, named as such because the device is dependent on the drain source voltage like a tube triode, although these parts are more likely to be BJTs.With the base and collector connected, the transistor acts like a fast switching Zener diode.

author: bdunham7
author_rank: Super Contributor
timestamp: September 16, 2020, 04:30:40 pm
content: Quote from: TimFox on September 16, 2020, 03:19:11 pmI'm not seeing the parallel part in Wytnucls' schematic. It looks like one or the other BE junction has to break down before the pair conducts anything at all. The transistors in the OPs photos appear to be these:https://www.mouser.com/datasheet/2/258/MMSS8050(SOT-23)-1626440.pdfso that breakdown is going to happen a bit north of 5 volts.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 16, 2020, 05:13:42 pm
content: Quote from: DW1961 on September 16, 2020, 12:57:19 amSo what about what the rep said about the triode protects and the image he sent to me. Does that change anyone's mind about the CAT ratings of this meter? (see image)

author: bdunham7
author_rank: Super Contributor
timestamp: September 16, 2020, 05:52:55 pm
content: Quote from: DW1961 on September 16, 2020, 05:13:42 pmNO. But proving it would be another matter in the face of deliberate obfuscation.The only way your 'triodes' could help would be keeping the meter alive to meet the requirement that it still indicate hazardous voltages after the transient test.My exception to Wytnucls' statement about fuses was purely academic. Looking at the board there appears to be no conceivable secondary overcurrent protection unless the PCB traces happen to vaporize in just the right way. I would call it a clear fail on that account alone.Since there aren't any MOVs or devices physically large enough to absorb the required transients, I'd want hear their explanation as to how that is handled. Good luck!

author: TimFox
author_rank: Super Contributor
timestamp: September 16, 2020, 06:02:44 pm
content: My mistake. The connection is two Zeners back-to-back in series on each leg, where the Zener voltage would be 5 to 6 V.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 16, 2020, 06:49:48 pm
content: Quote from: bdunham7 on September 16, 2020, 05:52:55 pmI sent the question. So far the rep/vendor has been very upfront about my questions, even taking the time to post a photo for me and outline the triodes. That doesn't force teh CAT ratings to be met, but it at least shows some transparency.If I understand you correctly, your concern is how does something so small (the triodes) absorb a CATIII 1000V rating surge, up to 8000V? (I think it's 8000v, but you get my question.)

author: Gyro
author_rank: Super Contributor
timestamp: September 16, 2020, 06:54:14 pm
content: Ask him if he means transistors, this whole triode thing is confusing the issue.

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2020, 08:18:24 pm
content: chinese use the term "triode" for transistor. Lost in translation or too many syllables.

author: E-Design
author_rank: Regular Contributor
timestamp: September 16, 2020, 10:06:03 pm
content: The speculation and conjecture meter for this thread is off the scale.Just ask the Chinese vendor for the schematic and BOM already. He might just give it to you if you tell him you will buy 10 of them.

author: floobydust
author_rank: Super Contributor
timestamp: September 17, 2020, 12:37:00 am
content: As far as safety compliance goes, the manufacturer/seller must be able to produce a certificate of compliance, or at least a file number with the agency used (certificates are public information) meeting the claims such as "61010". Otherwise- the product is completely untested and considered unsafe. Who wants to use this at 600V?It's unfortunate the expression/term "CAT xxx" is not legally protected, and thoroughly abused by Asian DMM manufacturers.There are three ways you can overload a multimeter. You could write a book about it, there's Youtube videos too.We've looked at the current measurement function which is protected solely by the fuses, with (OP's DMM) five diodes D1-D5 to protect the mid/high R shunts R8, R9. The fuses are not suitable past their rated 250V, or for an HRC environment like Cat. III/IV.For overload during voltage measurement, there are no MOV's or gas tubes, only the usual diode-connected transistors Q1, Q2 SS8050 giving light protection to the DMM IC for overload.But if you are on the Ohms/Continuity/Diode-Test function and accidentally connect to say 240VAC, something has to drop the voltage down to prevent it from burning up and here it is the PTC thermistors. This DMM features two, not sure how they are wired up. You can't put them in series.The big question is if the cute little PTC's can take rated voltage and if they are UL or agency approved parts. UL requires the safety components to be suitable (rated voltage and current) and have agency approvals. It makes sense the parts are tested. Little PTC's are rarely good to 600V with approvals. They just do a little crack and shoot a bit of stuff.Beyond this, the pcb spacings are untested and usually the rotary switch has a bad design and any arcing occurs there.Just because a meter has some protective elements doesn't mean they are suitable or will even work as hoped. This is why stuff is sent out to a lab for testing and certification.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 01:02:18 am
content: Quote from: Gyro on September 16, 2020, 06:54:14 pmYes, transistors."We use 9013 or 8050 transistors."I think these may be the spec sheets:9013 spec sheet:https://pdf1.alldatasheet.com/datasheet-pdf/view/33678/WINGS/9013.html8050https://pdf1.alldatasheet.com/datasheet-pdf/view/956716/FOSHAN/8050T.html

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 03:12:04 am
content: Quote from: floobydust on September 17, 2020, 12:37:00 amCould the transistor be slowing down the surge before they burn out just enough to let the PTCs heat up and take over that job? Also, maybe the PTCs are small, but all they need to do is stop the surge long enough to prevent user from harm, right?

author: floobydust
author_rank: Super Contributor
timestamp: September 17, 2020, 03:28:28 am
content: The diode-connected transistors clamp the overload hard at first, then the PTC heats up and the fault current backs off.Usually a ~1.5k ohm PTC, so at 240VAC on ohms it sees around 222mA or 75W and then heats up fast in maybe 1sec. It's just a lot of heat generated in a small part, that would love to shatter, while the transistors are taking abuse too.In multimeters with stronger input protection like Fluke and Brymen they also include a 1k ohm surge resistor (in series with PTC) to lower the fault current so the PTC survives. Their PTC's are also pretty huge. Look at curves forYS4020to see time and current for a multimeter large PTC.

author: bdunham7
author_rank: Super Contributor
timestamp: September 17, 2020, 03:38:49 am
content: Quote from: DW1961 on September 17, 2020, 03:12:04 amNo, because those transistors are connected to and protect an internal circuit and aren't connected to anything anywhere near the inputs. They can't withstand even a tiny fraction of the normal maximum inputs. 50 volts would vaporize them. And even if there was a large resistance between them and the inputs, they make the meter useless for anything over few volts. You couldn't even measure a 9V battery if they were your input crowbar.Also, in order to shift the load to the PTC, whatever is used as a clamp has to have low impedance after being triggered otherwise the dissipated power will be excessive.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 04:38:06 am
content: Quote from: bdunham7 on September 17, 2020, 03:38:49 amSo, what Flooby said?

author: MosherIV
author_rank: Super Contributor
timestamp: September 17, 2020, 07:42:38 am
content: QuoteYes.I thought you had watched the eevblog video on dmm input protection?All this had been covered in that video.Multiple techniques are needed in order to fully protect a dmm:Over voltageSurge suppressionOver currentEnergy dissipationIf you skip some of them, then better make sure the dmm will fail in a safe way for the user.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2020, 02:03:11 pm
content: Quote from: MosherIV on September 17, 2020, 07:42:38 amIt's a beginner area and I wouldn't expect the OP to have a formal education in EE or to be able to watch a technical video and understand the information being presented.Actually, much of what is being asked, I would need to ask a few safety experts who specialize in handheld meters to answer with any level of confidence.When I run meters that use the 5mm PTC with no series resistance, typically the PTCs fail (see attached). Once they short (arc over), there is nothing but my generator's source impedance (2 ohms), traces, leads and the function switch to limit the current. We basically end up with a fair bit of current going to the clamp. 20 Joules isn't much but for these small devices, they typically come apart. The next in the chain is the IC which will commonly end up with a cracked case.The small clamps are normally located downstream from the function switch. Sometimes I get lucky and some unintended area with breakdown (arc) and absorb enough to save the meter from the recycle bin. The UNI-T UT90A has been a very good example of this. You can see the last repairs in the attached pictures. I would not suggest the UT90 survived my tests, nor would I suggest it is an electrically robust meter.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 05:07:53 pm
content: Quote from: MosherIV on September 17, 2020, 07:42:38 amI did watch it but I was specifically addressing how MOVs assist PTCs in that reply becasue I do not understanding how a transistor could or could not do that.I wish he would send me the schematic on it.I did asks how a tiny transistor could protect against voltage surge and over voltage, and he replied it was a technical discussion that was too involved to go into, or something like that. You have to really watch for language miscommunications. So, I asked for the schematic.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 05:12:27 pm
content: Quote from: joeqsmith on September 17, 2020, 02:03:11 pmHey Joe, thanks.I did understand much of it in a simple way, such as how MOVs assist in letting PTCs catch up to regulate voltage, since the PTC reacts to heat much more slowly than an MOV can. I can follow that. Dave was really clear about it too. How the diode bridge worked was really interesting also, but since I don't understand exactly what and how diodes do and work, I'm going to have difficulty putting it all together in one cohesive idea, such as how much energy can diodes redirect and when you need to use something else. I'm learning.

author: bdunham7
author_rank: Super Contributor
timestamp: September 17, 2020, 05:13:16 pm
content: Quote from: joeqsmith on September 17, 2020, 02:03:11 pmHow would that work out in a fully energized CAT test?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 17, 2020, 05:18:38 pm
content: Quote from: floobydust on September 17, 2020, 03:28:28 amThat is what I wish my motherboard had on its LED circuits. That way if an LED strip's resistors let go or there is a short in the strip, it doesn't melt the RGB Fets. (Like what happened to me, and I still haven't gotten my main rig back up yet)I've almost finished rebuilding my LED strips. I've tested each connection after soldering and have no shorts that I can detect using continuity. I'm going to do a current test tonight and let them run 24 hours on full blast to make sure they don't short or whatever they do when something isn't right. I figure if I can leave them on 24 hours WFO without any current problems, they're good to go back into my computer and I can wrap it up (Given the motherboard replacement they sent me is not defective itself.). Scared to let the magic smoke out again.

author: Gyro
author_rank: Super Contributor
timestamp: September 17, 2020, 06:07:55 pm
content: Quote from: DW1961 on September 17, 2020, 05:07:53 pmI think you have your indication from the above discussions, to a good level of confidence, that the manufacturer has used a little bit more silk-screen ink on the front panel than he was entitled to. He is, after all, trying to compete with other low cost manufacturers who are doing exactly the same thing. It's just an option for them, if the customer (distributor) wants a 'IV' on the front then they will happily print one at no extra charge. If an internal inspection doesn't show that it is not a Class IV 600V product, then the selling price should.I sometimes enjoy winding up telephone scammers for long periods (other times I can't be bothered). Feel free to keep torturing the seller (who isn't the manufacturer, probably not even the distributor) for as long as gives you satisfaction. You might get the schematic, which might be of minor interest, although it is pretty clear what is and isn't on the board (The PCB layout might be more interesting so that you can see both sides without dismantling the switch), but I don't think you can expect him to come up with some miracle vindication at this point.There's no particular harm in making life awkward for him though, just so long as you don't have expectations of a meaningful answer.

author: MosherIV
author_rank: Super Contributor
timestamp: September 17, 2020, 06:52:16 pm
content: QuoteThe diode/transistor clamp is usually used close to the meters ADC inputs to protect them from over voltage. This will be after resistor divider network to drop the voltage to a range the ADC can handle. The over voktage clamp are not able to cope with large currents. When they turn on, they will just short out the over voltage, in shorting they must be capable of passing the current. That is what some of the other were saying, that under some circumstances, they doubt the clamping devices can handle the current.Typically, MOVs are used before the resistor divider networks. They will short out the over voltage and allow the PTCs time to increase resistance, thereby reduce any current.As I said these are 2 different mechamsims to protect the dmm. They should not be confused with each other. Relying on just one of them to protect the dmm will not work under all circumstances.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2020, 07:00:52 pm
content: Quote from: bdunham7 on September 17, 2020, 05:13:16 pmHard to say but I doubt burst and surge would do near the damage as an arcflash test would.I built what I refer to as a half cycle line simulator. It can put out a low voltage fairly high current wave. It is used in conjunction with the high voltage generator. Basically the high voltage short duration transient rides on top of the low voltage high energy wave. If a meter, like the UT90A were to break down from the high voltage transient, rather than the 20 Joules, we can feed in roughly 600 J to sustain the arc. The half cycle line simulator still uses a 2 ohm source and the energy it produces is normally absorbed by the high voltage generators output network. 600J is no where near what even a combo generator would typically provide. It does command some respect as coming in contact with the output could prove lethal. Again, nothing new and has been explained many times in various videos.If you watch this video, starting at the link you can see where the UT90As damage came from.https://youtu.be/aRuI_q_K5RY?t=351A toy compared with an arcflash, or even a real surge test.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2020, 07:07:37 pm
content: Attempting to determine the root cause of failure for an old Fluke 87V. Video goes over the front end and there is a model of it that I transient test. Should give some visual idea of what is happening with the various stages of clamps.

author: E-Design
author_rank: Regular Contributor
timestamp: September 17, 2020, 11:57:46 pm
content: Quote from: Gyro on September 17, 2020, 06:07:55 pmWhile the discussion and topics in this thread are all very enlightening and interesting for all of us, I predict that pestering the seller wont lead to anything at all. At some point, they will tire of the inquiries and just go away.Also, if the end goal is to expose these cheap meters as being untrustworthy, thats already been established for a long time and more so even now to the few people in the know.If the goal is to affect change in the marketplace offerings against Chinese companies because they are "Illegal" - Its a waste of time.What is the OPs time worth to him to carry on with sellers. And all the talk of illegal products and rating... , Pshhh nobody on Amazon is going to react to that without theLawyersinvolved. And exactly how many lawyers are here in this thread rallying behind the OP ? Joe Blow can make claims to Amazon all day long. Could be that as soon as a Lawyer writes the the Shenzhen based company, they produce the documentation showing compliance. They dont have to give anybody anything. As I understand it, its also mission impossible trying to litigate against Chinese companies anyhow - that is if you can even find out who it is. Unfortunately, it will likely require somebody getting injured for a Lawyer to get involved with motivation.Not trying to stifle the efforts, but I think that if there is an expectation that this brings change, it is incorrect. Give them bad ratings, learn something about CAT ratings and cheapo meter design and move on?

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 03:45:15 am
content: Quote from: Gyro on September 17, 2020, 06:07:55 pmI'm not trying to tie him up. I'm just wanting to understand if the meter can withstand voltage surge and arc flash for the CAT rating without harming the user. The problem is that in order to get that information, without assuming it, is to find someone with a voltage spike machine and spike it with 8000V while the leads are in the current or other than voltage or hit it with whatever current it is suppose to be able to withstand and see what happens.I just submitted the review saying there weren't any MOVs on it and that the resistors and PTCs were small, no guard tracks on the PCB, no case blades, etc. But in honesty I can't say anything else because no one knows how it will fail. I'm not going to give it a bad review on speculation.I never heard back from him since I asked for schematics, so I'm done with it.

author: MosherIV
author_rank: Super Contributor
timestamp: September 18, 2020, 08:23:16 am
content: QuoteMany forum members have already expressed their view that it is unlikely.The most practicle way to know is to have the dmm tested by a test laboratory which certify these safety things, such as UL (underwriters laboratory) - others exist but I do not remember right now.Quality dmm manufacturers do this for you, you will find that the quality name have the logo of the certifying lab somewhere on the dmm.These tests are not cheap and that and the engineering effort is reflected in the price.You get what you pay for!There are a few exceptions:https://www.eevblog.com/forum/testgear/heads-up-cheap-multimeter-lidl-uk-(080218)/25/Around $20 and it has a certified safety logo, some have even checked the lab report.Safety rating is not great 250V CAT2The point is that it has been tested by independant lab and verified to protect the user (not the dmm).The dmm is basically a dt830 in a larger form factor.BTW even the quality name brand dmm may not surviveNear the end, Dave blows up a classic Fluke 70, it does not survive but the dmm contained the internal explosion (apart from the flying knob) FYI these 70 series 1 predate the CAT ratings.

author: Gyro
author_rank: Super Contributor
timestamp: September 18, 2020, 08:47:18 am
content: Quote from: DW1961 on September 18, 2020, 03:45:15 amSure, this thread has turned into a very useful educational one.I just wanted to be sure that you didn't have greater expectations of what the the seller, Amazon etc. would do. As I said, there is sometimes some satisfaction to be gained from winding up particularly persistent phone scammers and dodgy sellers, but it's unlikely that it will ever get past that individual, itcanbe fun though.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2020, 12:30:13 pm
content: Quote from: DW1961 on September 18, 2020, 03:45:15 amAt what level? The typical internet Wiki level? From the EE level? The designer? The safety inspector? The people writing the standards? The people running the tests? ... I would imagine to be an expert in safety for handheld meters, you would make a career out of it.The voltage spike machine is a combo generator. There are both current and voltage waveform requirements. I am not aware where the surge or burst are applied to the current inputs. It would seem rather dumb as you would be shorting out the generator, blowing the fuse before the test even starts.Quote from: MosherIV on September 18, 2020, 08:23:16 amAgree, that the only way for a laymen to know is to have them certified.I watched that video you linked when it first came out and like my own tests, I don't believe you will find it has anything to do with the safety standards. I will need to go back and watch it. So if a meter survived what they were exposing them to or not would have little to do with how they would handle the actual surge or burst tests. If you believe I am wrong about this, I will watch it again.

author: MosherIV
author_rank: Super Contributor
timestamp: September 18, 2020, 12:43:05 pm
content: QuoteThe video has nothing to do with testing safety standards. Sorry if you got that impression.I wanted to point out that even the best protected dmm may not survive (work again) if exposed to high energy surges. They will however protect the user.The video is in no way meant to demonstrate proper safety testing.It does show the difference in how cheap dmm explode and properly designed dmm contain the explosion.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2020, 02:04:35 pm
content: Quote from: MosherIV on September 18, 2020, 12:43:05 pmThis is a very specific transient. At best we can say is how these meters perform against it. We can't say how these same meters would perform if they were exposed to the surge waveforms called out by 61010. Trying to tie the two together in anyway will just add confusion. Worse, it can give a false sense to the beginner that a meter is somehow safe when it may not be.It would be fun to see all of them, with their stock fuses run through an arcflash test on the current inputs. But again, does it matter? It's the internet. In the real world, I would expect a trained electrician will use the proper tools and beginners don't get to play professionals.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 05:01:44 pm
content: Quote from: MosherIV on September 18, 2020, 08:23:16 amYep, watched that video last night. I'm much less interested, and really not interested at all, if the meter can survive after a surge or arc, but user safety.The main reason I posted is because of questioning wheter or not a 35.00 meter with a CAT III 1000V rating and CAT IV 600V rating can protect the user when hit with over voltage/current.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 05:37:03 pm
content: Quote from: joeqsmith on September 18, 2020, 12:30:13 pmIt's a good question.The understanding level I was looking for was from a consensus of authority, whether or not this MM would protect the user up to its CAT rating.I have the authority with all of you, but not the consensus.Also, I got the same impression as you did that this 'test' does not say much about how a meter will survive like it should.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 05:39:41 pm
content: Quote from: Gyro on September 18, 2020, 08:47:18 amI do and did not. I was hoping to have something concrete as evidence that I could report is DEFINITIVELY not CAT certified. However, that definitive evidence has proven elusive.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 05:44:06 pm
content: Quote from: MosherIV on September 18, 2020, 12:43:05 pmThat's what I would be interested in also, not if it can survive, but if it protects the user.

author: Gyro
author_rank: Super Contributor
timestamp: September 18, 2020, 06:06:10 pm
content: Quote from: DW1961 on September 18, 2020, 05:44:06 pmThere is also the tricky question of whether you actuallywantit to survive (operationally)...1. Can you be sure that its performance and calibration are unaffected (without sending it in for calibration)?2. Can you be sure that its protective components haven't been damaged to the point that it would not protect the (a future?) user in a future similar event?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 18, 2020, 06:23:59 pm
content: Quote from: DW1961 on September 18, 2020, 05:39:41 pmThat's easy enough to find out but you won't get it playing on the internet. Just contact what ever agency/s you are interested in and have them provide you with a quote. Going through that process would be a VERY good learning experience, especially if you wanted to work in the industry.QuoteEven if you were able to filter out enough opinion to form a consensus, you shouldn't expect that suggests you have good answers. It's an open internet forum. You may feel better about it but that's about the extent of it.

author: E-Design
author_rank: Regular Contributor
timestamp: September 18, 2020, 08:31:33 pm
content: Quote from: DW1961 on September 18, 2020, 05:39:41 pmDW1961Concrete evidence,Buy 2 of the meters. take one apart and discover its bill of materials. Look up the likely offending parts (fuse comes to mind and any silly sot-23 clamps etc..) Decide on some number of components are possibly in violation and have an effect on the CAT testing/compliance..Send the second meter with the components and your findings to a 3rd party test house. Pay them. Have them do full CAT and safety compliance testing and evaluation of it. Get that report and hand it to the MFG legal dept if there is one - along with Amazon and the governing body in the US for consumer product safety.Otherwise,really!all you have is a lot of mixed opinions ranging from sensible to wild speculation. A lot of great anonymous web forum people here-- oh and some photos along with more speculation of the circuit design. If you want to get real about it -then get real about it. You are not going to be able to DEFINITELY say much about anything without your own real evidence.. not sure why you would think otherwise.I think the folks on this forum are great and have high expertise in the matter. Sadly, not good enough for you seeking concrete evidence.Are you going to go and tell the MFG they 'likely' dont meet a CAT standard (here is a link to a web discussion)orwill you tell them they have demonstrably FAILED the CAT standards they claim - here is a test report filed with Amazon legal dept, and US consumer safety.eh?

author: floobydust
author_rank: Super Contributor
timestamp: September 18, 2020, 08:54:00 pm
content: It's as easy as the manufacturer providing the 61010 certificate of conformance, in backing their claim "Safety Rating EN61010-1,-2-030 EN61010-2-033, EN61326-1 CAT III 1000V, CATIV 600V". "Certification: CE,ROHS,EMC etc."Dongguan Habotest Instrument Technology Co.,Ltdshows one for their voltage detector. What about their multimeters?You can also find the 61010 CofC for UniT multimeters, some tests seem to uh have been glossed over. At least they make the effort. It's common-place and low cost to get products safety approved in china, it's just that here you don't have to, so they don't bother. The test process can also be corrupted, as one multimeter popular here on the forums has 61010 approval only as a 3V battery-powered appliance, never connected to anything with a voltage source.OP gives a picture and asks "will this bridge collapse?" manufacturer claims "supports 1,000 elephants" and well, it's missing most of the trusses so I know it can't do it and it was stuffed elephants on the bridge lol.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 18, 2020, 09:20:32 pm
content: Quote from: floobydust on September 18, 2020, 08:54:00 pmLOL, exactly.Well, I do have some concrete evidence that I didn't before, guys, thanks to all of you.1. It does not have any MOVs in it.2. Second, the current fuses are not 1000V.3. No PCB guard tracks.4. No Case Blade protection.5. Small PTCs.Conclusion: weak protection, but inconclusive as to harm to user.And, that's how I framed it in the review. I've done the most I can do for an Amazon review. If I were getting paid hourly to investigate, you can be assured I'd do what you all suggested and get the facts on it asap. However, I have to do other things too. I've done x10 more than any other reviewer has on Amazon. I'm pretty over it, as of now.As always, thanks for all of the insight and help.

author: bdunham7
author_rank: Super Contributor
timestamp: September 18, 2020, 09:30:26 pm
content: Quote from: DW1961 on September 18, 2020, 05:39:41 pmIf the fuse ratings aren't definitive enough for you, I don't see what will be. Disproving that it might 'survive' a hypothetical test that hasn't been done yet is a rather ambitious goal. If I claim to have vacationed on the moon last year, can you disprove that? Or how about if I claim that I'm building a spaceship in my basement and I will vacation on the moon next year?

author: bdunham7
author_rank: Super Contributor
timestamp: September 18, 2020, 10:02:16 pm
content: Quote from: joeqsmith on September 18, 2020, 02:04:35 pmI don't see anything wrong with doing different tests, just like there are different crash tests for cars--NCAP, NHTSA, IIHS and Youtube videos of demo derbies. In the real world your meter, just like your car on the highway, may be subject to an event that will most certainly not correspond perfectly with any of the tests. A well designed product--car or meter--should distinguish itself against inferior ones in any reasonable test. Whether a test is reasonable or not would likely be a topic of endless debate. Excessively easy or difficult tests are not helpful--nobody expects to survive a 200MPH head-on collision with a train nor do we expect our DMMs to withstand direct lightning strikes.Take this scenario. Suppose I'm working on a machine with a very large 480VAC three-phase motor on a 100A circuit breaker. For some reason, the motor is humming a bit and getting warm, so I start looking for voltage drops and for whatever reason I decide to check the voltage drop across the breaker. So I hang my 289 on the panel and connect it across the input and output of the breaker, then reduce the voltage range to the 5V scale and read a volt or two or whatever. I check the next one and it is dropping a bit more, so I reach over to bump the range switch up one and just as I do, the breaker trips. That seems like a good time to have a CAT iV/600 rating. If I need a new meter, so be it. I just don't want to have its molten parts embedded in my face.OTOH, I'm working on my bench with a calibrator and I'm using a meter only rated CAT I/1000V and perhaps CAT II something. Suppose I accidentally enter something wrong or the calibrator goes haywire or gets an GPIB signal crossed and decides to put out 1075VAC when the DMM is set to ohms. Or volts for that matter, since many bench DMMs only go to 750VAC. I'm not concerned about high energy or molten parts--there isn't enough current to worry about unless I come in contact with it directly. What I would like is for the meter to simply display OVER, or 1, or OL, or even better, 1075VAC if it is on the volts setting. I don't want the protection to kick in and save the day, I would like it to simply continue to operate. So for this, the CAT tests only tell me a little bit about what I want to know, which is what is the peak voltage that I can accidentally input to the meter without any malfunction or stress on it.You're right that only an actual CAT-spec test can tell us exactly how the meter will perform on a CAT-spec test, but two things are also true. First, unless the tests are ridiculous or poorly controlled, looking at how and when the failures occur can give us some ideas as to how robust they are--which is what you are doing--and that is quite valuable. CAT-specs may be well thought out, but they are not going to be perfectly predictive of how DMMs fail in real life anymore than crash tests perfectly predict crash survival rates. Second, CAT-specs don't tell every user what they want to know--I have two meters that will, in response to the accidental 1075VAC input, will simply display 1075VAC without complaint. One is CAT II only, the other is old and not CAT-rated at all.

author: floobydust
author_rank: Super Contributor
timestamp: September 18, 2020, 11:44:45 pm
content: Any hardware connected to the mains distribution network will experience overvoltage transients. In IEC 60664 they did extensive studies and then came up with the transient overvoltage CATegories based on real-world measurements and some statistics.One important safety issue is an insulation breakdown occurring (anywhere inside the multimeter) will start an arc that will crowbar whatever energy source is being measured. If there is a lot of follow-through current then the arc triggers a blast or arc flash as it is called.So there is a lot of extra insulation required just because of these mains transients. It adds to the size and cost of a product.Part of 61010 inspection and tests are to check for sufficient high voltage spacings and that the materials (pcb+plastics) are suitable insulators. Nobody wants a multimeter with mistakes in spacings, clearances on the pc board or the rotary switch, or plastics that burn, arcs to your hand, or is just a stupid design with the protection circuits, that can breakdown.On the bench, a calibrator set to 1,000VAC does not generate 8kV mains-transients and is low stress for any multimeter, and even if it arcs there is no blast. The only safety issue then is if the meter does not read properly i.e. fails to indicate the presence of hazardous voltage.I have done designs and put products through 61010 approvals. Not multimeters and their specific 61010-2-033 but industrial gear that measures voltages and currents on mains to Cat. IV 1,000V. You could write a book about it, because it's fairly difficult and very expensive getting approvals. A lot of misunderstandings are out there about the tests, their intent etc. even I make mistakes interpreting clauses.Nobody would use these unapproved low cost chinese DMM's in measurement category III or IV environments. The point is the product needs to be third-party tested to flush out any engineering mistakes and instead we have fake approval claims common in the marketplace.

author: E-Design
author_rank: Regular Contributor
timestamp: September 19, 2020, 12:50:10 am
content: Quote from: DW1961 on September 18, 2020, 09:20:32 pmThats a fair assessment.

author: bdunham7
author_rank: Super Contributor
timestamp: September 19, 2020, 01:04:23 am
content: Quote from: floobydust on September 18, 2020, 11:44:45 pmI'd be curious to know the typical source of those transients. I think there may be a common misconception that they are freak occurrences like lightning or high-voltage cables shorting to low voltage, things like that. AT least those are the things I see mentioned. You can generate some pretty good transients just by uncommon but plausible scenarios like the one I mentioned.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2020, 01:27:00 am
content: Quote from: bdunham7 on September 18, 2020, 10:02:16 pmAgree. 61010 is full of them.Quote from: bdunham7 on September 18, 2020, 10:02:16 pmAnd we are back to cars. It's always cars.... If there was a point there having to do with the quote you reference, I am sorry but I glossed over it as soon as I saw it was about cars.

author: MosherIV
author_rank: Super Contributor
timestamp: September 19, 2020, 09:43:43 am
content: If you really want to make the point, the dmm is branded Amazon?Just ask Amazon for proof of CAT rating compliance ie the conformance certificates.Amazon should have done their due diligance and made sure the supplier have fully compliance.That is what Lidl did for their cheap dmm.If it is not compliant, Amazon have 2 choices:1 Pull the product2 Have the CAT rating removed from the dmm

author: Wytnucls
author_rank: Super Contributor
timestamp: September 19, 2020, 01:21:35 pm
content: Cars again...disgusting.Only use motorbike analogy, like Fluke:Don’t overlook safety—yourlife may depend on itWhere safety is a concern, choosing a multimeter is like choosing a motorcycle helmet—ifyou have a “ten dollar” head, choose a “tendollar” helmet. If you value your head, get asafe helmet. The hazards of motorcycle ridingare obvious, but what’s the issue with multimeters? As long as you choose a multimeterwith a high enough voltage rating, aren’t yousafe? Voltage is voltage, isn’t it?https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2020, 03:22:23 pm
content: Quote from: Wytnucls on September 19, 2020, 01:21:35 pmIs Fluke's marketing group some biker gang? Does their research show that the majority of their customers drive motorcycles? No matter, at least it's not cars again.QuoteSo it's like choosing a motorcycle helmet. Do you ride around in the back yard with no obstacles and can only get up to a couple of MPH? Maybe your priceless head is fine with the $10 helmet.Does the $10 helmet have both DOT & Snell approvals?https://smf.org/aboutYou bought an old used $1000 helmet that has Snell and DOT approvals and want to know if that is good enough to save your priceless head.All you could afford was a $10 helmet.All your internet friends don't believe in the DOT and Snell ratings and they feel the $10 helmet is just as good as the name brands.You bought a new helmet that is certified for safety but then forgot about every other part of your body.If you drive on the road in the USA, many of our states no longer require helmets. As a result, I see a lot of people without them. Yet we have seat belt laws.From my experience the racetracks will inspect your equipment. They will check the date in your helmet. Older helmets are not allowed. Depending on how fast/quick you are will require different PPE. There's rule books that explain the requirements. Gloves are always required, but zip together leathers or a 1pcs suit is not.There are other safety requirements like a dead man switch.https://prfactorystore.com/product-tag/dead-man-switch-tether/Depending on the bike, a diaper may be required.https://www.bbracingllc.com/Engine-Diapers_c_760.htmlSteering dampeners and dead stops may also be required.There is a driver license as well. You don't want someone without proper training getting on a fast/quick bike. So some tests and paperwork.I'm sure that there is an analogy in there somewhere.....***Attached is a friend of mine testing their helmet.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 19, 2020, 05:19:06 pm
content: Quote from: bdunham7 on September 18, 2020, 09:30:26 pmYeah, I'm a rank novice at electronics, but I'm pretty up on the logic behind basic epistemology (Rather I used to be. Man, where has the time gone?). I didn't major in electronics, but I do have a BA in philosophy with a focus in logic and epistemology.Yes, I can disprove both of those easily.1. I can find where you were last year at the same time you claim to have been on the moon. (Since you cannot be at one place and be at the same place at the same time, that would be definitive evidence that you were NOT on the moon: P V ~P but never P and ~P, because the latter produces a logical contradiction, and all contradictions are false. Or, more in laymen terms, "X is either a rose, or it is not" is always a true statement, otherwise you produce a contradiction.)2. I can get access to your basement to check if there is actually a viable 'spaceship' in your basement, depending on your definition of a 'spaceship'. (There is X at Y location, easy enough to prove or disprove.)I'm not really sure what your original intent was about 'disproving.'The reason I kept searching after the Fuse Voltage deal was because someone cited the CAT ratings guidelines, and it was not clear the fuse had to be the same voltage as the CAT rating. What it did say is that the "device" that protects the current side must offer the same protection as the CAT rating. It did NOT say the FUSE must be the same voltage.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 19, 2020, 05:23:20 pm
content: Quote from: floobydust on September 18, 2020, 11:44:45 pmI'd be interested in your evidence for fake approvals.

author: Gyro
author_rank: Super Contributor
timestamp: September 19, 2020, 05:43:41 pm
content: Quote from: joeqsmith on September 19, 2020, 03:22:23 pmOf course helmets, seat belts and child car seats lose their approval rating after an impact and insurance companies require them to be replaced as overstressed.Does / should the same apply to a DMM? (Edit: A protection event).

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2020, 06:49:31 pm
content: Quote from: Gyro on September 19, 2020, 05:43:41 pmBecause we are talking about motorcycle helmets, they have a shelf life. This is why the race tracks typically inspect the dates.Not being an industrial electrician or working in that profession, I can't answer what is required.I doubt that most meters would provide any indication that they were exposed to a transient. They may be inspected before use but even with that, I am not sure you could detect anything. I don't want to use the term "over stressed" as it's very possible the product may have been designed to handle it.As I have said many times, the meter I use for CAT III has been exposed to many transients. Before procuring the first one, I exposed a demo unit to the actual IEC burst and surge tests. Of course, I had approval to run these tests as part of my evaluation.Quote from: floobydust on September 18, 2020, 11:44:45 pmI suspect from the above, I am not the only one in this forum that has performed similar tests. If you are going to design products that run on the mains, it may be a good idea to know something about them....

author: floobydust
author_rank: Super Contributor
timestamp: September 19, 2020, 07:16:44 pm
content: Quote from: E-Design on September 17, 2020, 11:57:46 pmDownvoting the products to push back against deception... well... Democracy does not work without pitchforks. We're all enabling this practice of fake safety certification claims to keep on going. Those who sell, allow advertising of these products are a part of it IMHO. Amazon multimeter reviews all appear as 4-1/2 stars for some reason and no less exist.Quote from: DW1961 on September 19, 2020, 05:23:20 pmA product's Certificate of Conformance is also in the agency's database, where you can search for the manufacturer or model number. It's public information where you can check your products to see if they are certified.ULis railroading you into needing an account or phoning them lol and they don't say to which standard the product was assessed towhereIntertekandCSAare straightforward.i.e. you can findCEMmultimeters there, who make Amazon Commercial. Also UniT, 121GW, Klein, Tektronix, Fluke, Agilent etc.Can we find this mystery Habotest/Taiss/Kaiweets/KMoon HT118A? Not a sign of the company or its products to be found. Agencies behind the great wall are hard to find and get certificate information from- although legit manufacturers are proud to provide them. Intertek Shenzen's certs appear Intertek's global database.The fake approvals I'd found the ANENG AN8008 61010 certificate and it was for only 3V. So tested as if nothing was connected to it. Since then, their website is gone and the certificates I can't find anywhere. I wonder if any ever existed.Certification agencies will only assess to the standard you specify. They do not tell you which ones because they are liable if one gets omitted. One way to fudge certification is test it to a lax use-case or just mislead about it.It is also common place the certifier is a noob (they don't fully understand electronics or the product) and either skips a test or tests it under ideal conditions - giving out a false pass.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 20, 2020, 05:04:16 pm
content: Quote from: MosherIV on September 19, 2020, 09:43:43 amIt's not an Amazon brand I posted. Otherwise, as you stated, it would be a LOT easier, for sure. I doubt Amazon is going to take a chance of a milti-million dollar wrongful death law suit over a 50 cent MOV. lol (Not to mention the damage it would do to Amazon business in general.)

author: DW1961
author_rank: Frequent Contributor
timestamp: September 20, 2020, 05:19:08 pm
content: Quote from: floobydust on September 19, 2020, 07:16:44 pmFlooby,I think you may be on to something here. Did you say that the Amazon brand is listed on the non UL sites? (Remember this is not an Amazon brand.) However, if the Amazon meter I have is listed at one of those non UL sites, it would be inductive that if the Amazon brand is certified, and uses no MOVs, then it is possible for other brands to certify without using them too. I'll open up my Amazon brand to see. The one I have it CAT III 600V. It's not 1000V CAT III rated like the MM here in question. That may be a difference that makes any inference invalid (I don't know).I'd have to ask the vendor who the manufacturer is, I suspect, or are all of the rebranded units listed also? (They screen print whatever you want.) I think that is a fair question, that is, to ask for certification information.I just requested the information necessary to track down any CAT certs from the vendor. Did you find the Amazon brand under the Amazon name, or did you have to search for CEM and match them up to the Amazon branded CEM models?So, UL, you can ask them, but they won't tell you which certification it has? If so, then that is useless.

author: floobydust
author_rank: Super Contributor
timestamp: September 20, 2020, 08:40:28 pm
content: Either I'm wrong about it (instant visual of pcb for 61010 approvals)or the safety certification was done by Clown Co.Amazon Commercial DMM's like 90DM120 (DT-912) or 90DM600 (DT-9560) have Intertek approvals for 61010-1 and 61010-2-033 (but no mention of Cat. rating).Code:Title: ELECTRICAL EQUIPMENT FOR MEASUREMENT, CONTROL & LABORATORY USECompany: SHENZHEN EVERBEST MACHINERY INDUSTRY CO., LTD - BaiWangXin Industrial Park, Baimang, Xili, Nanshan CHINAProduct Information: Trade Name(s): CEM, CRAFTSMAN, KOBALT, UTILITECH.AC/DC TRMS Clamp Meter, Model Nos. DT-3360, DT-3361, DT-3363, DT-3367, DT-3366, DT-3368, DT-3368T, DT-3369, DT-3369T-BT, 19745. Also tested to: CSA 61010-2-033. Model Nos. DT-9380, DT-9381, 80CM801, 80CM811, DT-9380A, DT-9381A, DT-9382B, DT-9382. Also tested to: CSA 61010-2-033. Model Nos. DT-9280, DT-9281, 80CM800, 80CM810. Also tested to: CSA 61010-2-033.AC CLAMP METER, Model Nos. DT-330, DT-330H, DT-331, 80CM300. Also tested to: CSA 61010-2-033.Autoranging Digital Multimeter, Model Nos. DT-9660, DT-9660B, DT-9660D, DT-9660T, DT-9660T-BT, DT-9661, DT-9662, DT-9663, DT-9664, 19746, 19737, DT-9560, DT-9561, DT-9562 ,DT-9663H, DT-9664H. Also tested to: CSA 61010-2-033.Battery Tester, Model Nos. DT-203B, 1634354.Cable Locator, Model Nos. LA1012, LA1012B, 70TR120.Digital Multimeters, Model Nos. DT-912, DT-912T, DT-912N, DT-914, DT-916, DT-916N, DT-918, DT919, DT-921,DT-930, DT-931, DT-931N, DT-932, DT-932N, DT-920N, DT-920, DT920L, DT-921N, DT922, DT-940, DT-940N, DT-940NV, DT-941, DT-941N. Digital Multimeter, Model Nos. DT-99FC, DT-991, DT-992, 82141.Non-Contact AC Voltage Detector, Model Nos. AC-6, AC-6F, AC-6B, AC-6S, AC-8, AC-8B, AC-8S, AC-9, AC-9B, AC-9C, AC-10, AC-10S, 19738. Non-Contact AC Voltage Detect, Model Nos. AC-11, AC-11B, AC-11S, AC-15, AC-15B, AC-15S, AC-16, AC-16B, AC-16S, 19733, 19739.Receptacle Tester, Model Nos. ET-19L, 1634355.Receptacle Tester and GFCI Tester, Model Nos. ET-15, ET-16, ET-17, ET-18.Testers, Model Nos. ET-21, ET-202, ET-204.True RMS Thermal Multimeter, Model Nos. DT-9889, DT-9889A,DT-9889B,DT-9889H. Also tested to: CSA C22.2#61010-2-033.True RMS Multimeter & Insulation Tester, Model Nos. DT-9985, DT-9985RF, DT-9986, 90DM860. Also tested to: CSA 61010-2-033.AC/DC TRMS CLAMP METER, Model Nos. DT-9280, DT-9281, 80CM800, 80CM810, DT-9180B, DT-9180C, DT-9282, DT-9180, DT-9181, DT-9182, DT-9180A, DT-9180AH, DT-9180H, DT-9180D, DT-9181H, DT-9281A.Digital Multimeter, Model Nos. DT-216, DT-218, DT-218T, DT-219.Digital Multimeter, Model Nos. DT-946, DT-946F.Evaluated to the following: A representative sample of the listed devices have been tested, investigated and found to comply with the requirements of the Standard(s) for Electrical Equipment for Measurement, Control & Laboratory Use; Part 1 General Requirements (UL-61010-1) and are identified with the ETL Listed Mark.========================================================================================================Title: Electrical Equipment for Measurement, Control, & Labaratory Use - Part 3-033: Particular Requirements for Hand-held Multimeters & Other Meters, For Domestic & Professional Use, Capable of Measuring Mains VoltageCompany: SHENZHEN EVERBEST MACHINERY INDUSTRY CO., LTD - BaiWangXin Industrial Park, Baimang, Xili, Nanshan CHINAProduct Information: Trade Name(s): CEM, CRAFTSMAN, KOBALT.AC/DC TRMS Clamp Meter, Model Nos. DT-3360, DT-3361, DT-3363, DT-3367, DT-3366, DT-3368, DT-3368T, DT-3369, DT-3369T-BT, 19745. Also tested to: CSA 61010-2-033. Model Nos.DT-9380, DT-9381, 80CM801, 80CM811, DT-9380A, DT-9381A, DT-9382B, DT-9382. Also tested to: CSA 61010-2-033. Model Nos. DT-9280, DT-9281, 80CM800, 80CM810. Also tested to: CSA 61010-2-033.AC CLAMP METER, Model Nos. DT-330, DT-330H, DT-331, 80CM300. Also tested to: CSA 61010-2-033.Autoranging Digital Multimeter, Model Nos. DT-9660, DT-9660B, DT-9660D, DT-9660T, DT-9660T-BT, DT-9661, DT-9662, DT-9663, DT-9664, 19746, 19737, DT-9560, DT-9561, DT-9562 ,DT-9663H, DT-9664H. Also tested to: CSA 61010-2-033.True RMS Thermal Multimeter, Model Nos. DT-9889, DT-9889A,DT-9889B,DT-9889H. Also tested to: CSA C22.2#61010-2-033.True RMS Multimeter & Insulation Tester, Model Nos. DT-9985, DT-9985RF, DT-9986, 90DM860. Also tested to: CSA 61010-2-033.AC/DC TRMS CLAMP METER, Model Nos. DT-9280, DT-9281, 80CM800, 80CM810, DT-9180B, DT-9180C, DT-9282, DT-9180, DT-9181, DT-9182,DT-9180A, DT-9180AH, DT-9180H, DT-9180D, DT-9181H, DT-9281A.Digital Multimeter, Model Nos. DT-216, DT-218, DT-218T, DT-219.Digital Multimeter, Model Nos. DT-946, DT-946F.Evaluated to the following: A representative sample of the listed devices have been tested, investigated and found to comply with the requirements of the Standard(s) for Electrical Equipment for Measurement, Control, & Labaratory Use - Part 3-033: Particular Requirements for Hand-held Multimeters & Other Meters, For Domestic & Professional Use, Capable of Measuring Mains Voltage (UL-61010-2-033) and are identified with the ETL Listed Mark.They are made by CEM and look quite decent... until...DT-9560Cat. III 600V. has two MOV's, PTC and surge resistor as expected.DT-912 Cat. III 600Vdoes not have MOV's,just a surge resistor, usual PTC and a pair of big clamp diodes, smaller 5x20mm250V fuses.Amazon (90DM120) Question: "How is this surge protected? does it have movs in it?"Answer: "Yes, It does have MOVs built-in and rated at CAT III 600V. By [A manufacturer] Manufacturer on September 14, 2020"More fake bullshit, the operatives are clearly reading this thread and acting fast lol.pic taken fromhttps://cxem.net/review/review37.phpSpot the MOV's for free chicken dinner. It could survive the 6kV impulse.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2020, 12:57:03 am
content: I've watched enough meter reviews to know where the MOV is.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 21, 2020, 03:15:19 am
content: Quote from: joeqsmith on September 21, 2020, 12:57:03 amIs that a MOV or PTC--I didn't get the joke, sorry

author: DW1961
author_rank: Frequent Contributor
timestamp: September 21, 2020, 03:19:25 am
content: Quote from: floobydust on September 20, 2020, 08:40:28 pmDid you actually contact Amazon and ask them? If they told you it has MOVs and it doesn't, that's illegal, not from a CAT perspective, but from a marketing perspective. You cannot do that.

author: floobydust
author_rank: Super Contributor
timestamp: September 21, 2020, 05:21:03 am
content: The rat's nest of close traces is there to protect the tiny green ptc from the transient lol.If Intertek actually did a proper spacings analysis - you provide the pcb Gerbers and they confirm the spacings meet 61010, like other agencies do- you would see this DT-912 pcb fails.Cat. III 600V (PD2, Table K.3) requires 5.5mm trace spacings which is pretty huge.Because MOV's clamp and lower the transient voltage from 6kV to say 1.5kV the pcb spacings get reduced to a more manageable ~2mm. This most importantly includes the rotary switch. Things can remain tight and small with MOV's. It's not that difficult to do a multimeter pcb with 5.5mm spacings at the input jack and then 2mm after the MOV's.Without the MOV's you still have a 5.5mm clearance requirement for the input jack pcb trace, which can be seen not the case here with the naked eye in this DMM pic. So I would suspect this DMM tomfoolery.Also, the tiny ptc's seem to have fake claims of 1,000V UL approvals but no evidence to support that outside of the chinese datasheet.I pulled the Amazon bullshit answer by "A manufacturer" saying the DMM has MOV's from the "Customer questions & answers" section of the product page.Anybody can post a answer to product questions. Safety-related ones should be answered by qualified people but Amazon doesn't vet who answered.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2020, 04:20:55 pm
content: Quote from: DW1961 on September 21, 2020, 03:15:19 amWatching non-EEs trying to review the circuitry of an electronic device and you get all sorts education. That is obviously a MOV.https://youtu.be/nXjVc4Rmg7Y?t=3085

author: DW1961
author_rank: Frequent Contributor
timestamp: September 21, 2020, 05:36:36 pm
content: Quote from: joeqsmith on September 21, 2020, 04:20:55 pm"Do you think that little rubber condom is going to protect that fuse when it comes part? Well, there's one way t find out." - lolThat's what I like to hear!Just to be clear, the meter Flooby posted that is charged with not having a MOV does actually have one? (Most importantly, because you win a free chicken dinner from Flooby.)

author: DW1961
author_rank: Frequent Contributor
timestamp: September 21, 2020, 06:01:52 pm
content: The vendor sent me the certificates. They're from a Chinese testing outfit, and I don't know how to read it, but I did notice at one point it says the test is for DC 3V. That can't be right. But, like I said, I can't understand the report.890C+-VII 890D-VII 890E 890F 890G 890H 890Z EMC TR.pdf(1307.93 kB - downloaded 175 times.)890C+-VII 890D-VII 890E 890F 890G 890H 890Z EMC.pdf(753.61 kB - downloaded 125 times.)890C+-VII 890D-VII 890E 890F 890G 890H 890Z LVD TR.pdf(1406.5 kB - downloaded 211 times.)890C+-VII 890D-VII 890E 890F 890G 890H 890Z LVD.pdf(752.49 kB - downloaded 91 times.)

author: bdunham7
author_rank: Super Contributor
timestamp: September 21, 2020, 07:36:18 pm
content: Quote from: DW1961 on September 21, 2020, 06:01:52 pmIn order to read it you would need a complete copy of the standard to see what clauses apply for the CAT ratings, which ones are included in the report and which of those got a '-' or an 'N', since there are no 'F' ratings.The 3V appears to apply to the batteries that power it. They list test equipment for the EMC test. They don't list ANY test equipment for the LVD test, so it sort of looks like they only did inspections and tests with the meter itself. They mention shorting the outputs. Woo-hoo!

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2020, 07:40:06 pm
content: I suspect that's 3V/meter. Hardly what I would expect for some industrial bit of equipment....https://youtu.be/wYuzFtoHMqg?list=PLZSS2ajxhiQBTCU8Mq_i9jidT024A0dV6&t=826

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2020, 07:42:48 pm
content: Quote from: DW1961 on September 21, 2020, 05:36:36 pmIf you don't believe it's a MOV, you are not watching enough reviews. Obviously all these experts can't be wrong.

author: floobydust
author_rank: Super Contributor
timestamp: September 21, 2020, 09:35:12 pm
content: It's a PTC thermistor- there is no MOV in the photo of the DT-912 board.DatasheethereSCD-102ARNF 1,000ohm 1,000VAC. They tend to blow up during Cat. xxx transient testing because there is no surge resistor and they take too long to heat up, so the impulse kills the DMM.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 21, 2020, 09:43:26 pm
content: That's 3 experts vs 1. Maybe we should vote on it.

author: Nusa
author_rank: Super Contributor
timestamp: September 22, 2020, 12:00:56 am
content: Quote from: joeqsmith on September 21, 2020, 09:43:26 pmThe board itself gets a vote, since it was presumably designed by an expert who helpfully identified it as a "PTC" in the silkscreen.Me, I'm merely a hobbyist, but I agree with the silkscreen.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 22, 2020, 12:27:47 am
content: Quote from: Nusa on September 22, 2020, 12:00:56 amI've seen a lot of meters with SGn marked in the silkscreen with no SparkGaps. The majority is always right. Never mind those data sheets. Who uses data...

author: DW1961
author_rank: Frequent Contributor
timestamp: September 22, 2020, 05:30:55 pm
content: Well, I got another DMM. This one is smaller. I asked the vendor for the cCAT certification,a nd he replied that there was "No CAT certification" although the screen printing on the meter says CAT III 600V.Unless there is something misinterpreted about the question and meaning, that's pretty blatant. A meter with a CAT rating on the front and the vendor says the meter isn't even CAT rated.We were discussing possible legalities forpossiblenon-Certification, but this vendor said right out--none.So, no laws about that?

author: rsjsouza
author_rank: Super Contributor
timestamp: September 22, 2020, 10:02:12 pm
content: Bookmark this one. Will comment later.

author: DW1961
author_rank: Frequent Contributor
timestamp: September 23, 2020, 03:59:06 am
content: Quote from: rsjsouza on September 22, 2020, 10:02:12 pmI asked why teh meter was marked CAT III 600V without certification, and she said, "This is a security level. Haven't heard of certification."Obviously we're having a language barrier here. I asked him, "Do you have the documents that show it was tested and passed CAT guidelines?"We'll see if that makes sense to his understanding of English. He speaks better English than I do Mandrin

author: E-Design
author_rank: Regular Contributor
timestamp: September 23, 2020, 07:56:49 pm
content: Quote from: DW1961 on September 22, 2020, 05:30:55 pmThe FTC has laws against false advertisement and there are consumer safety laws. Yes, I think blatent lies about the ratings could be considered illegal.lets say you establish without a shred of a doubt that these are illegal devices. Lets say everybody agrees these could be dangerous to a user.Just what do you think will happen? You're really focused on the legality of these devices.Will you tell us what your plan is to that end? Have you told the vendor he shouldnt be selling these to you?How much money do you have to spend?

author: bdunham7
author_rank: Super Contributor
timestamp: September 23, 2020, 08:00:46 pm
content: Quote from: DW1961 on September 22, 2020, 05:30:55 pmhttps://www.ftc.gov/news-events/media-resources/truth-advertising

author: Oleksii
author_rank: Contributor
timestamp: October 05, 2023, 12:39:50 am
content: I have a good question to you guys - why in different DMMs, manufactures always/often(?) use a proper shunt resistors (usually a thick "П" shape wire ~20 mm length) but in serial conjunction with a PCB trace, which is a cooper?Usually ratio is that ~95% of resistance (and voltage drop) is on the proper shunt, and ~5% is on PCB traces. As a result, even not cheap DMMs (imagine UT61E+) have a current measurement drift in time, on bigger current.For example the UT61E+ (20A rated) with 6A, after 10 minutes of current passing through, will increase reading by 15mA, while other current measurement devices in the same circuit keep current exactly the same and stable, up to 1mA precision.I tried to google and could not find a good answer for that.To compensate non-zero TCR of the proper shunt? Then why it's worse than other not-DMM type of devices, where only shunts are used current sensing?Help please to get this point.

author: Nusa
author_rank: Super Contributor
timestamp: October 05, 2023, 01:06:21 am
content: The 20A rating isn't a continuous rating. Notice that that actual fuse is only 10A. Pull 20A for more than a few seconds and it's gonna blow.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 05, 2023, 07:01:19 am
content: At least the better meters sense the voltge largely separate from the current path going to the shunt. E.g. the current comming from the top and coltage sensed from the bottom.Some meters may not be that good at it and thus include more copper.At high current the shunt still gets quite warm as there is not good way to get rid of the heat in the closed case and the TC of the relatively cheap shunts may not be that small. So even with perfect 4 wire contacts the self heating of the sunt gets a problem for the higher currents.External shunts are usually larger form factor and have better cooling.

author: E-Design
author_rank: Regular Contributor
timestamp: October 06, 2023, 03:15:49 pm
content: Quote from: Oleksii on October 05, 2023, 12:39:50 amWell you have to run copper and wire up to the shunt.. however, sensing the voltage on the shunt is done at the right location (local at the shunt leads or a kelvin sense) so that you avoid those copper drift errors you've mentioned.Also keep in mind, when you see drift, another large contributing factor is the temperature rise of the device when doing that high current. If you are really going to compare the performance, you will need to look at the datasheets of the two shunts being compared to see what the heat dissipation situation is and the TCR etc...

author: Oleksii
author_rank: Contributor
timestamp: October 06, 2023, 06:24:35 pm
content: Thank you guys for replies !I managed to cut and rearrange some traces on the UT61E+, related to current passing and voltage drop sensing.As a result: before the mod, with 6.000A stable current (I could guarantee its stable over time), I had 13-14 mA sensing increase after 20 minutes. First 7mA in first 2 minutes, following 7mA - later during 18 minutes. I did not see a sense to track it longer.After my mod: with the same 6.000A current source, I had maybe 1-2mA increase over the same 20 minutes.With a 10A current source (which was less confident before the mod), I get 2-3mA increase over 1 hour period! This also includes an addition hack to avoid the 10A fuse usage and supplying current to the PCB without original socket contacts.Yes, I know you may not like it, but my goal was to track high current stability in a circuit for longish time.And my UT61E+ now does not overheat and I do not get the "Cut!" alert and stopped current reading.Here is an offender on PCB - cooper track with solder, on left from COM label!:even just removing a bit of solder, current reading has increased by 50mA on the 6.0A flow:Note - this is a place where input jack plate soldered too. Imagine if you needed to resolder it for a reason. You cannot do it without breaking the join resistance, which actually is "a part" of shunt !!!Woahhh, ... I needed to try and test then with the shunt position and after a few attempts I was lucky to catch -2mA reading on the 6.000A flow.Note - before the mod it was -7mA reading from cold state. So accuracy became even better!I knew it was a risky attempt, but I did similar things in the past and I knew how it should be made.I'll try to record a video what I did.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 06, 2023, 06:51:50 pm
content: Back in 2017 I showed something similar with the UT61E where I was attempting to measure 20A with it (for fun).https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1168820/#msg1168820https://youtu.be/ns02v6ebCGU