DMM Questions: Protection, Hz Measurement, Shunt?

[CharlotteSwiss]

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

[E-Design]

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? 

Did 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.

And 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.

[DW1961]

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.

I 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

[E-Design]

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.

I 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

Yes 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.

[MosherIV]

I 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?

Depends 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 watch

While it is very very unlikely to happen in the home, the point is not to take the risk.

[floobydust]

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.

[DW1961]

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? 

Did 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.

I 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?

[DW1961]

Amazon cant be held responsible for ensuring the specifications are met for all the products it allows to transact.

It's an Amazon brand. They could be held accountable for that.

[MosherIV]

Here is alink for tear down of my favourit Fluke - 187
https://www.eevblog.com/forum/testgear/fluke-187/msg536455/#msg536455

Tear down of a Keysight/Agilent dmm
https://www.eevblog.com/forum/testgear/keysight-agilent-u1241b-teardown-video-and-high-resolution-images/msg2119102/#msg2119102

Another Keysight/Agilent dmm
https://www.eevblog.com/forum/blog/eevblog-832-keysight-u1282a-multimeter-teardown/

Finally, Brymen dmm teara down
https://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 dmm
They 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

[E-Design]

Amazon cant be held responsible for ensuring the specifications are met for all the products it allows to transact.

It's an Amazon brand. They could be held accountable for that.

You would think so but sadly, no it wont happen.

[floobydust]

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 like  90DM600 pics.

I followed OP's multimeter through at least four chinese shell companies, it's kinda crazy how many names and hops are involved.

[DW1961]

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.

The 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.

[DW1961]

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 like  90DM600 pics.

I followed OP's multimeter through at least four chinese shell companies, it's kinda crazy how many names and hops are involved.

I have two of the Amazon brand commercials. Mine have a CAT III rating of 600V. 90DM120
https://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-1df8b2563c11

They 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.

[DW1961]

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 like  90DM600 pics.

I followed OP's multimeter through at least four chinese shell companies, it's kinda crazy how many names and hops are involved.

The 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=8-5

What 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.

[DW1961]

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.

I 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?

[Wytnucls]

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=24268

Like 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.

[E-Design]

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.

I 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?

Those 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.

[Nusa]

"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.

[Wytnucls]

Some earlier discussions:

https://www.eevblog.com/forum/projects/cat-ratings-and-interpretation/75/

[tooki]

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.

Why would you need over voltage protection on Ohms? You mean the over voltage could cross over to the Ohms circuit?

No.

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 those categories specify 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, does not have to survive the event in order to comply with its CAT rating.)

[Gyro]

MOV - Mercury Oxide Varistor - they start to conduct at a threshold voltage, thereby limiting the max voltage seen by the dmm
They 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

MOV - Metal Oxide Varistor. 

[DW1961]

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.

Specifically, 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.)

[DW1961]

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.

Why would you need over voltage protection on Ohms? You mean the over voltage could cross over to the Ohms circuit?

No.

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 those categories specify 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, does not have to survive the event in order to comply with its CAT rating.)

Very 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.

[DW1961]

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.

I 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?

Those 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.

I 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?

[Wytnucls]

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.

Specifically, 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.)

Of 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.