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

[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.

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.

All the detail you rely on is pretty much UK specific. EN/BS/AS/ANSI/UL/etc 61010 (the standard measurement categories come from) sets it plainly and in an internationally uniform manner.

Appliances that plug into the distribution do not have the same heavy conductors, and are required to have sensibly low fusing currents so their fault currents are lower. Completely obvious to anyone who deals with the standards or went through training on these topics. Why try and make "clever" arguments about where the boundary should be defined, leading to yet another thread full of confusing and misleading content that beginners cant pick apart from the truth. You want to be a pedantic internet point winner? great have at, but don't try and pretend that is something more authoritative or useful than the international standards.

[Gyro]

No clever arguments. The wall wiring and appliance cable are the same in terms of fault current that you would expect. The breakers within the distribution board (or whatever you might call it internationally) will limit the fault current to way below the 25kA they are talking about on CAT III final circuits. In countries that have no plug fuse (and that's the only UK reference I'm going to make) [Edit: the appliance lead] must be rated to handle the full final circuit breaker current in fault situations. I don't know about the low fusing currents you are referring to - if they are the ones in the consumer unit / distribution unit or whatever, then they apply to both the socket circuit wiring and the appliance cord. Any internal appliance fusing is there to protect against appliance fire, not the mains cabling.

Please don't do the 'training on these topics', 'pretend to be authoritative' thing. I have designed industrial stuff for a living, have you?

Again please clarify how different parts of the same circuit on the same final circuit fuse / breaker can have different fault current - you really can't sensibly be putting it down to the thickness of the wire.

[DC1MC]

For the dear love of  Jesus, this was a thread about ANGENG SZ20, that is now covered in sterile, off-topic discussions of bloody fuses  , obscuring anything about the poor multimeter.
Now that you've buried in two pages of unrelated posts, could you gentle beings move this circus somewhere else, eventually on a special thread that I'm sure it will have 100+ pages in no time, please, please with cherry on top.

 Seriously disgruntled,
 DC1MC

[Gyro]

My apologies DC1MC, That was intended to be a quick comment.

[floobydust]

Sorry for drifting. I was wrong about the UART pin, compared to other COB which have different pinout.
I think the DreamTech DTM0660L is just a firmware load for Hycon HY12P65 family. No idea why the same part gets more A/D counts.
Pin 17 PT1.7/BZ/PSDO is for GPIO, buzzer output, PSD0 port for OTP R/W interface.
Pin 18 PT1.6 EEPROM SCL
Pin 19 PT1.5 EEPROM SDA
Pin 20 PT1.4/TX is for GPIO, UART TXD. *This is the one to scope. Goes to via under EEPROM then to ?
Pin 21 PT1.3/RX is for DI, UART RXD. This has a jumper to GND for Calibration Mode on older DTM0660.

OTP appears to be synchronous serial with PSCK, PSDI, PSDO.

The SZ-20 has pads for PT1.0, PT1.1 which are likely the function switch and pushbuttons. There has to be a way for automated calibration on a bed-of-nails and thus serial data, unless this is done using some kind of magic. Dreamtech/ANENG would sell a lot more if they opened up the data on these.

[DC1MC]

Sorry for drifting. I was wrong about the UART pin, compared to other COB which have different pinout.
I think the DreamTech DTM0660L is just a firmware load for Hycon HY12P65 family. No idea why the same part gets more A/D counts.
Pin 17 PT1.7/BZ/PSDO is for GPIO, buzzer output, PSD0 port for OTP R/W interface.
Pin 18 PT1.6 EEPROM SCL
Pin 19 PT1.5 EEPROM SDA
Pin 20 PT1.4/TX is for GPIO, UART TXD. *This is the one to scope. Goes to via under EEPROM then to ?
Pin 21 PT1.3/RX is for DI, UART RXD. This has a jumper to GND for Calibration Mode on older DTM0660.

OTP appears to be synchronous serial with PSCK, PSDI, PSDO.

The SZ-20 has pads for PT1.0, PT1.1 which are likely the function switch and pushbuttons. There has to be a way for automated calibration on a bed-of-nails and thus serial data, unless this is done using some kind of magic. Dreamtech/ANENG would sell a lot more if they opened up the data on these.

Well, the pins are exactly as I traced them, except TX is actually going to the keys, maybe I'm getting blind, if you can point on the last picture I published here, that is a close-up of of the MCU area, it will be nice, my guess was the pin that goes to the via between U2 pads, but this one goes to keyboard. For bed of nails calibration it may have been enough, but for logging is not usable, and most likely it was reassigned in the ROM as GPIO.

To make things worse the EEPROM content (also posted) make no sense compared with the datasheet and other EEPROM dumps, so  have no idea how to enable the logging.

 I guess that there is not too much that could be done, I hoping for someone to jump with some ideas and me being the hands to implement them, but nobody jumped in .

 DC1MC

RxD is connected to the EEPROM WP and the corresponding resistor is missing, see the pictures, probably they've found a way to calibrate it like that and use the missing R pads as jumper because it was a bit of sloppy rework flux there.

[Someone]

Please don't do the 'training on these topics', 'pretend to be authoritative' thing. I have designed industrial stuff for a living, have you?

I follow the standards, they're a collection of knowledge spanning far more than my experience..... which includes electrical apprenticeship and designing (A brand) test and measurement equipment (to 61010).

In countries that have no plug fuse (and that's the only UK reference I'm going to make) [Edit: the appliance lead] must be rated to handle the full final circuit breaker current in fault situations.

No, they don't. Please do provide a reference for that, because the references I have here (61010, 60335 , 62368, etc) certainly do not require appliance leads to support either the prospective fault current or even the maximum permissible hold current of an arbitrary power point/socket outlet. 0.75mm2 cables terminated with C13 plugs are pretty typical, around the office here they are the majority, and have test approvals and in service test tags that are current.

No clever arguments.

None? Why try and redefine the boundaries of CAT II, CAT III, and CAT IV ? Then dig in and make all sort of noise about things you clearly know very little about? Safety isn't the place to try and find loopholes, or muddy the water with your plainly incorrect misleading and heading into dangerous claims.

CAT III includes the wall mounted socket outlet, that's what 61010 defines. It's like trying to argue about the arbitrary steps in EMC regulations, 229MHz emissions affects things almost the same as 231MHz.... except 55011/55022/etc standards have 230MHz as a boundary between different requirements so they are treated differently. There may only be a slight distinction in reality between either side of a socket outlet in worst case conditions, yet there is a significant difference in most conditions. The line between different categories has to be drawn somewhere and the boundary of fixed wiring is easily recognisable, I think that is a pretty good place for the distinction.

For the dear love of  Jesus, this was a thread about ANGENG SZ20, that is now covered in sterile, off-topic discussions of bloody fuses  , obscuring anything about the poor multimeter.

.. and the OP asking why CAT ratings are required, apparently without realising where those ratings are applicable.

[DC1MC]

Before reassembling it I'm posting two top pictures with the detail of the LCD area that is usually covered when LCD is installed. Afterwards if it still work, I will try to do some precision measurements and that is the last time when you'll hear about this device from me, afterwards let the fuses, CAT ratings and building cabling penile measuring contests begin in full  .

 Cheers,
 DC1MC

[DC1MC]

Well, it survived resoldering the EEPROM and repacking  , I've measured against the few precision resistor and voltage source and it's spot-on  , if someone in DE (dr. Kleinstein, u.a) wants to spend some time characterizing it against some real stuff, please PM me.

   THE END

[mzzj]

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.

Rating pic is bit misleading or overkill for household short circuit currents. Yeah, maybe for 30 story condo the short circuit currents next to distribution panel can be at that level.
There is quite bit of difference between 1-family house and 1MW transformer switchboard.
In here typical feeder to single-family house has 300 to 1000A short circuit current. Typical circuit breakers are rated at 6kA max breaking capacity.
5kA short-circuit current would be reasonable expectation in installations with  3x200A or larger fusing nearby.

[floobydust]

I would be interested in the display quality - contrast and update rate. Both looked not so great.
The fake Cat. III, Cat. IV claims we are all used to as an ongoing dishonesty with chinese multimeters. I'm not sure why they just don't quit that and mark it "1,000V max." or something like they did in the 1980's lol.

Remember on ACV it is DC-coupled so the op-amps will saturate if DC is present while on ACV. After the op-amp, there is a coupling capacitor to the ADC so the multimeter never knows it's clipping. I had some strange firmware behaviour, the autoranging also malfunctions last time I played with this, on other products using the DreamTech DMM IC.
The test was measuring 0.1VAC 1kHz on something like 5VDC to flush it out.

[DC1MC]

Well, the display is not the most perfect, is mediocre but legible. On the other hand I find the refresh rate perfectly acceptable and compatible with the Fluke 8060A. If you have any idea on how to make evaluation pictures I'm all for, unfortunately I don't have any high-end LCD devices, I  can try to check at different angles to see if it fades away.

I think I can inject 0.1V 1KHz AC over 5V, what should be the result ?

[Fungus]

I would be interested in the display quality - contrast and update rate. Both looked not so great.
The fake Cat. III, Cat. IV claims we are all used to as an ongoing dishonesty with chinese multimeters. I'm not sure why they just don't quit that and mark it "1,000V max." or something like they did in the 1980's lol.

It's an arms race. Don't expect anybody to unilaterally stop putting it on their meters.

[floobydust]

It's all fine until someone loses an eye, or maybe it goes nuclear... many such lumens. Sure honorable Mr. Zhejiang would agree.

It is advertised to measure ACV and DCV at the same time so it doesn't have that old AC+DC limitation? 0.2% basic DCV accuracy, silicone boot (some offerings), A jack LED warning and more. It is a jump up in features, counts.
In review videos the Ohms function is a little sluggish to autorange and displays a 1/2 value or two before settling. It can measure 250MEG as 00250.0

LCD contrast is still unknown...

[Someone]

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.

Rating pic is bit misleading or overkill for household short circuit currents. Yeah, maybe for 30 story condo the short circuit currents next to distribution panel can be at that level.
There is quite bit of difference between 1-family house and 1MW transformer switchboard.
In here typical feeder to single-family house has 300 to 1000A short circuit current. Typical circuit breakers are rated at 6kA max breaking capacity.
5kA short-circuit current would be reasonable expectation in installations with  3x200A or larger fusing nearby.

Sure, that is your installation or typical. So now go around the world and tag out/de-energize anything that doesnt meet your magical new standard. 61010 is an international standard that covers almost worst case situations for the safety of the operator (who probably hasn't measured the fault current capacity before starting work, and if they had its the chicken and egg question of which rating should the fault current meter have?). CAT ratings have multiple dimensions that need to be satisfied, there might be absolutely zero real world installations at the corners of those dimensions but the limits are set to contain almost every conceivable situation.

[Kleinstein]

Having a mixed AC + DC signal and also AC frequencies higher than the digital RMS part can handle can lead to odd results. Quite some meters have problems with this - not just the cheap ones and may not detect clipping at some point in the signal chain. Sometimes a manual range selection helps.

I just had an oscillating voltage regulator and my UT139 meter (uses digital RMS up to only some 1 kHz - so similar to this meter) did not show any AC reading - just no result, which is still better than some wrong value. In other examples one can also get wrong readings or an somewhat unexpected overload from the DC background  (AC mV range).

[DC1MC]

Having a mixed AC + DC signal and also AC frequencies higher than the digital RMS part can handle can lead to odd results. Quite some meters have problems with this - not just the cheap ones and may not detect clipping at some point in the signal chain. Sometimes a manual range selection helps.

I just had an oscillating voltage regulator and my UT139 meter (uses digital RMS up to only some 1 kHz - so similar to this meter) did not show any AC reading - just no result, which is still better than some wrong value. In other examples one can also get wrong readings or an somewhat unexpected overload from the DC background  (AC mV range).

So, do you have interest in interrogate  my SZ20 for science, I can DHL it to you immediately, I'm actually curious on how good or bad it is ? You can subject it to any abuse you see fit, if it doesn't survive, than it wasn't worth.

 Cheers,
 DC1MC