Aneng SZ20 25,000 count, 1uV, 10nA, 20A

[DC1MC]

What's the diode test voltage on this meter?

(and why do they never publish that number?  )

If the 0.05%spec is the correct one then this could be a meter worth owning. Maybe the ZT219 (AN870) has a successor...

I like that it has a separate dial position for each function.

To answer this question:

- Diode mode voltage: 3.3234V
- Resistance mode voltage 0.502V

Equipment used: Fluke 8060A

Test point P.7 not scoped, if there is data there then I have to fall into a rabbit hole and use the "flashlight" LED to send it out, then make an adapter to receive it and so on, too much scary work  and what if it works ?!?!

Cheers,
DC1MC

[floobydust]

You are no fun, scope "Pt. 1.7" so we can see if it's possible to get serial data out of this...

[Kleinstein]

Getting data logging could help judging on the noise. Manual reading is a bit slow and maybe subjective if the update rate is not very slow.

[DC1MC]

Getting data logging could help judging on the noise. Manual reading is a bit slow and maybe subjective if the update rate is not very slow.

If Dr. Kleinstein says it could be useful, I'll do it, zum Befehl  , is actually due to the (small)garden work of today that I'm early in the bed, I still try to fully recover from the C19, I'll scope it tomorrow and if it spits data, I will try to decode it. Actually I will scope all test points.
If anyone knows any "tricks" on similar but smarter instruments to enable somehow data logging, please say, I'll try (almost) anything tomorrow.

Cheers,
DC1MC

[DC1MC]

Every frigging time, ones try to do something a quick google search shows that someone else did it already seven years ago   

Please have a look on this google cache of a long gone page:

http://webcache.googleusercontent.com/search?q=cache:fg0T_DOmrEYJ:www.kerrywong.com/2016/03/19/hacking-dtm0660l-based-multimeters/&cd=1&hl=en&ct=clnk&gl=de

I'll save a pdf of it and eventually attach it here, it has all the info needed to enable logging.

Cheers,
DC1MC

EDIT: Not only this, but an EEVBLOG post as well:
https://www.eevblog.com/forum/testgear/hacking-dtm0660l-based-multimeters/

EDIT2: MCU translated datasheet added.

EDIT3: Kerry Wang's excellent tutorial added as PDF (his website is not working anymore )

[floobydust]

No- DTM0660L has many different faces. 4,000 or 6,000 or 9,999 or 25,000 count along with different functions - it's not guarateed to be the same IC. My belief is Dreamtech does the application firmware for the OTP multimeter MCU+ASIC which seems to be made by Hycon. We don't know all of the mystery here. Try the scope probe The serial TX pin is not bonded on the COB versions.

[tooki]

I’d actually love to see BS1362 fuses used in cheap multimeters, combined with an honest CAT I or II rating, instead of little glass fuses or none at all.

Don't expect it from China. The precedent has been set, the horse has bolted, the ship has sailed.

I said that I’d love to see it. I didn’t say I expect it to happen!

[floobydust]

ICK    BS1362 aren't used in North America. We have 5x20mm and then 1/4"x 1-1/4" (6.3*32mm). Going beyond 250V brings us to specialty fuses.
Specialty 1/4"x 1-1/4" Littelfuse 508 are good to 1A 1,000V 10kA interrupt. Seems high 3.572Ω resistance for 0.5A part. For say 15A, 506 series is good to 600V 10kA.

[DC1MC]

First preliminary tests with the data logging issue:

- Holding long the REL button does not bring anything on display.

- At startup there is a moment where all the LCD annunciators are on, there is nothing that I can see that suggest any kind of PC link or data logging.

- Looking closer on the PCB around EEPROM there was some rework stuff done, a resistor (WP ?!?)  seems to have been removed.

This post will be edited after scoping the test points and/or if I can read the EEPROM.

EDIT1: these are the test points scoping results:

Pt1.7 - Beautiful buzzer signal, 'cause this is so much need 

Pt1.0 - Some signal ONLY when pressing once REL, it looks like some very shot spikes with 30ms spacing, RIGOL's anemic RS-232 decoder is not avle to do anything with it.

Pt1.1 - Solid one.

The bloody buzzer produces a 200mV signal mirroring on the power supply, probavly the consumtion is enormous, but the electricians want loud buzzers.

Now, I can unsolder and read the EEPROM as well as trying to do the modifications in the previous PDF, please tell me seriously if it is worh doing.



Cheers,
DC1MC

[tooki]

ICK    BS1362 aren't used in North America. We have 5x20mm and then 1/4"x 1-1/4" (6.3*32mm). Going beyond 250V brings us to specialty fuses.
Specialty 1/4"x 1-1/4" Littelfuse 508 are good to 1A 1,000V 10kA interrupt. Seems high 3.572Ω resistance for 0.5A part. For say 15A, 506 series is good to 600V 10kA.

I think you missed the point: the reason that BS1362 fuses would be ideal isn’t because of their size, but because BS1362 fuses are manufactured in gargantuan volume (thanks to being used in every single British AC power plug), making them incredibly cheap, likely the cheapest ceramic fuses that in any way resemble a HRC fuse. Specialty fuses from Littelfuse won’t be cheap, so they wouldn’t get used by cheap DMM makers.

[DX1]

Instead of Cat II, cat III etc we should rate most cheap meters as protected for connection directly to consumer 230V. Which covers 99% of hobby users.

And a fail safe rating of, for example, 8kV 2 ohm surge and 2000V DC.
With fail safe suitable for dead short across consumer 230V, for example a BS1362 fuse.
The manufacture would be required to provide a survive rating.
Tests for fail safely are used, for example, on 230V wall sockets.
Fail safe basically means no expelled parts and no fire.


 

[tooki]

Isn’t that exactly the purpose of the CAT ratings? The only part that’s non-obvious about them is knowing which category means what. That could be easily solved with a little diagram in the manual.

[DC1MC]

Out of nothing better to do I've desoldered the 24C08 and read it, maybe the more enterprising people will be able to see if there are special settings for 25k count, now that the bloody Amtech flux spread allover I have to ultrasound clean the board and this being said I've also removed the LCD just because it seems that the UART TX is going somewhere in an unknown area, I hope they didn't repurpose it for some strange stuff or on the 25K chip is somewhere else as in the data sheet.
EEPROM dump attached, average res pictures of what's under LCD will follow.

 Cheers,
 DC1MC

NOTE: Remove the .zip extension from name, this is a pure bin file, needed for forum file types restriction.

[floobydust]

Availability - BS1362 1"x1/4" fuses are nowhere to be found in North America, and being rated to only 250VAC they have the same ability as 5x20mm    I don't quite get their allure.
To keep multimeters small yet have a high voltage say 1,000V rating, in the utility industry the fuse is located in the probe where there is lots of room.
Many multimeters have bad PC board designs and arc "somewhere" else. They are untested. This is the main problem.

There is serial data in order to do factory calibration, and without the beep beeeeep beep beep. So PT1.7 should have something on it? Calibration mode is a jumper to GND on PT1.3 or about that resistor you say is removed. Or maybe it's a special button press on power up.

[DC1MC]

Well, not so cool news, the EEPROM content doesn't make any sense to me, at least compared with the known 6K/9K datasheets, it seems that there's some difference in the organization, to make things worse, the alleged TxData pin (the one that goes under U2(EEPROM) is now part of the buttons matrix  so if you don't suggest any directions to proceed, I'm stuck.

 HALP  !!!

 DC1MC

[Gyro]

Availability - BS1362 1"x1/4" fuses are nowhere to be found in North America, and being rated to only 250VAC they have the same ability as 5x20mm    I don't quite get their allure.
...

The 6kA interrupt rating, something you can't get in 5x20mm.

[tooki]

Availability - BS1362 1"x1/4" fuses are nowhere to be found in North America

I know that. But they’d be inexpensive to procure. It’s not like you can get multimeter fuses at your local hardware store, either.

and being rated to only 250VAC they have the same ability as 5x20mm    I don't quite get their allure.

Because voltage isn’t the only criterion!! A standard 5x20mm fast-blow glass fuse has a current breaking capacity of just 35-100A (using Schurter as an example). That is nowhere near enough to be working on mains where thousands of amps are often available. 5x20mm ceramic fuses are already a lot better, 500-1500A. But a BS1362 fuse is rated to 6000A breaking capacity, closer to the 10kA of a real multimeter fuse than not.

Using them would be a really inexpensive way to increase safety a lot. Not to real CAT III or IV, but to a whole lot better than a tiny glass fuse.

Simply due to economies of scale, BS1362 fuses are among the cheapest sand-filled ceramic fuses in existence.

Another cheap option would be sand-filled ceramic 1/4” x 1-1/4” fuses, which have even better breaking current ratings than BS1362, and cost only slightly more.

[floobydust]

I respectfully say no, they are not inexpensive or commonplace in North America and many fuse manufacturers here don't even bother making them. Years ago I had to special order them for customers returning from the UK running devices off a 120-240 transformer here. Is BS1362 relevent in your homeland or Germany as well? IDK ordering them for multimeter use, the mini ANENG fuses [urkl=https://www.aliexpress.com/item/4000375930617.html]3.5*10mm[/url] "ceramic British plug fuse"    are a special order as well.

The required interrupt rating is up in the air. Spec is different between UL and IEC standards. This is another trap I guess with smaller sized fuses. I have not read the IEC test for interrupt compared with UL, that could even be different.
UL 248 seems to be 10kA/125VAC and IEC 60127 1.5kA/250VAC, likely Cat. II residential branch circuits but I'd have to dig for that.

It looks like size matters and at least 20-32mm length is needed, even when sand-filled.

[Someone]

Instead of Cat II, cat III etc we should rate most cheap meters as protected for connection directly to consumer 230V. Which covers 99% of hobby users.

Household wiring, already CAT III
https://www.worksafe.qld.gov.au/news-and-events/newsletters/esafe-newsletters/esafe-editions/esafe-electrical/2022-newsletters/june-2022/multimeter-incidents
lol, $100 for a guide to select a multimeter

Isn’t that exactly the purpose of the CAT ratings? The only part that’s non-obvious about them is knowing which category means what. That could be easily solved with a little diagram in the manual.

Attachment below, having escaped the paywall. But obvious and clear documentation is a standards requirement....

[Fungus]

I respectfully say no, they are not inexpensive or commonplace in North America and many fuse manufacturers here don't even bother making them.

Most multimeter fuses have to be ordered specially.

The problem with Fluke-type fuses is that they're so low volume and lucrative that the market is flooded with fakes. There's no way to trust ordinary sellers and buying from somewhere "reputable" will double the already-outrageous price.

BS1362 are almost as cheap as glass fuses and there's thousands of legitimate manufacturers for the fakers to compete with. Less profit=less fakery.

the mini ANENG fuses 3.5*10mm "ceramic British plug fuse"    are a special order as well.

I don't know why Aneng use those ridiculously small special fuses, or why they don't use BS1362. You'd think BS1362 would be a no-brainer for somebody trying to save pennies. 

PS: Those are NOT "British plug" fuses. British fuses are one inch long (what else would they be?)

[DC1MC]

Well, I guess that was it ? If the discussion devolved in savant debates about fuses, then I believe that there is nothing more to say about SZ20  ?

This being said, I will close it permanently later today and let it run as it is, with good or bad, you have some pictures, EEPROM dump so this should be enough for everybody.

 Cheers,
 DC1MC

[DC1MC]

Here's another average resolution picture, if you can say where the TX UART pin is ? If you say that there's the one with a via in between the pads of U2, there is not, this one is going to the keys.

[Gyro]

Sorry for another minor diversion, but as it relates to CAT rating rather than fuses specifically...

Instead of Cat II, cat III etc we should rate most cheap meters as protected for connection directly to consumer 230V. Which covers 99% of hobby users.

Household wiring, already CAT III
https://www.worksafe.qld.gov.au/news-and-events/newsletters/esafe-newsletters/esafe-editions/esafe-electrical/2022-newsletters/june-2022/multimeter-incidents
lol, $100 for a guide to select a multimeter

Isn’t that exactly the purpose of the CAT ratings? The only part that’s non-obvious about them is knowing which category means what. That could be easily solved with a little diagram in the manual.

Attachment below, having escaped the paywall. But obvious and clear documentation is a standards requirement....

They really seem to have messed up that diagram. The table is appropriate to the CAT rating requirements, but the way it translates to what is shown on the diagram isn't. There's no way that the house socket wiring can be CAT III and then magically transform to CAT II as it comes out of the socket outlet  (apart from maybe the UK with fused plugs - and even then the transition would occur in the plug, not the socket outlet).

The diagram doesn't give sufficient clarity and granularity: They should have distinguished it as follows...

- Distribution lines and feed into the house: Most definitely CAT IV teritory, no (relevant) overcurrent protection, those lines could be feeding an entire street and fed by a multi kA fuse.

- They haven't defined the 'Meter Board' correctly. The Meter board is property of the energy supplier. It terminated the incomming feed, immediately fusing it down (typically 80-100A in the UK, I don't know about AUS) and holds the supplier's Electicity meter. The supplier fuse provides protection that takes the environment down to CAT III.

- They have missed out theConsumer unit / Distribution board / fuse panel, depending on terminology.  This is the home owner's property. The tails from the Meter into the unit and internal bus bar(s) are still at CAT III. The Consumer unit contains fuses, or hopefully breakers, protecting individual circuits down to the lower current required for their use and wiring capacity. The circuits that leave the consumer unit are at CAT II... There is no magical transition at the socket outlets.

You might have hoped that a paywalled document would be a bit clearer.

[Someone]

They really seem to have messed up that diagram.

Not really, things that plugs into the mains are CAT II, while the power socket is CAT III. Your UK centric (only?) view is really unrepresentative of the rest of the world.

[Gyro]

They really seem to have messed up that diagram.

Not really, things that plugs into the mains are CAT II, while the power socket is CAT III. Your UK centric (only?) view is really unrepresentative of the rest of the world.

What's the electrical difference (in fault current terms) between the wiring going into the socket and the plug coming out of it then? There are only bits of copper / brass inside the plug and socket. You are implying that the circuit is CAT III right the way into the consumer equipment. Edit: (Which is not what the diagram shows)

P.S. I don't think there is anything UK centric about what I described (you can ignore the fused plug bit as it isn't particularly relevant in this context), it's pretty much international. I'd be interested in how your installation differs.