6 1/2 digits Volts and amperes meter, under $60, can this be true?

[LinuxHata]

Hello.

When scrolling thru taobao, found this EH-ME010 meter. http://www.ehengio.com/file/tool/EH-ME010_USER.pdf  (specs are at very bottom, all in chinese, btw.)

They claim very high precision and accuracy. They even have a video, where this meter is compared with keysight 34461A, and it displays comparable precision. PC connectivity and various filtering options are available as well.

The asking price on taobao is 468 CNY, which is around $60.

I'm going to buy this just out of curiosity, but maybe someone already have bought this, so if this is a junk, I can save a bit of money and time?

[ch_scr]

It's easy to see how they got the price down - drastically reduced complexity (at the cost of drastically reduced features).
Only 4V, 30V and 30ma, 300mA ranges and no input protection to speak of (it says "50V max" right on the front panel). No ACV (or ACI), no Ohms.
Also the input impedance is uncommonly low with 3.22Meg, at 6 1/2 digits this can create an significant error even if the source has an impedance in the single digit kiloohms.
It makes sense for industrial automation, but an optional high impedance input would be cool for a lab bench device.
So they don't need: input protection, 1000V capable input divider with all it's ranges, divider compensation for AC, TRMS converter, switcheable current source for ohms, high impedance buffer for the divider; and all the mux-ing, amplifying, controlling and initial engineering (and verification) that would come with all that.
I would also assume they don't pre age them, so expect to calibrate after a year or two to get it back to accurate after all the stuff has gone through it's initial aging (and hope it settles there...).
If this capability is all you need for the job (they seem to have industrial automation in mind) or your mixed signal home workbench, why not? I could see a place in the latter case, if you have a scope and a more rugged (but less precise) full-featured handheld already, this would allow to enter the DC precision realm very cheaply. They question is, does it hold true to the specifications.
With all that said, I'd love a look under the hood

[Aldo22]

Looks like this started as a hobby project.
I think the text here refers to this device: http://www.dt830.com/thread-4771-1-1.html
Paste it into https://translate.google.com

1. Preface
It seems incredible to do six-and-a-half figures at a cost of 200 yuan. But as the price of 24-bit ADCs continues to drop, achieving six-and-a-half-bit resolution has become very commonplace. As long as the long-term stability requirements are abandoned, a complete six-and-a-half-digit voltage and ammeter can be made for 200 yuan.
Before starting the implementation, let's explain the concept of six and a half digits. Six-and-a-half digits means that the resolution reaches more than 1 million, and it generally appears as a high-end watch. It is matched with high absolute precision, mainly because of its long-term stability. However, to achieve long-term stability, expensive and difficult-to-buy devices such as voltage references above LM399 and metal foil resistors must be used, so low-cost must give up long-term stability.
After giving up absolute precision, is there any point in high resolution? I think there is. For example, sometimes it is necessary to test a small signal of uV level or uA level, compare the size of two signals, or observe the short-term change of a signal, etc. These only need high resolution, and do not need too high absolute precision. . So I decided to make such a product.
Due to my limited level and energy, the article will definitely contain omissions, incompleteness or even errors. I will not be responsible for direct or indirect damages caused by the content of this article, and will not provide any technical guidance.

2. Design goals
1. Design a desktop voltage and current meter with six-and-a-half-digit resolution
2. All adopt brand-new devices that are easy to purchase, and the BOM cost is controlled within 200 yuan
3. Excellent short-term stability performance, noise less than one millionth , the overall temperature drift is 5ppm/℃ (typical value)
4. It is hoped that the annual drift will be controlled below 300ppm (the annual drift of the basic file of Keysight 34461A is 30ppm)
5. The voltage file can test 24V to 10uV, and measure 3.3V to 1uV
6. The current range can be tested from 300mA to 100nA, and from 30mA to 10nA.
7. Equipped with a communication interface, it can be connected to a host computer to display waveforms, collect and export data
8. There are casings, face stickers, etc. that can be used as a complete product

etc.

[iMo]

$60 - it is possible, imho, with larger quantities produced and under the assumption claiming 5ppm/C and 300ppm long term (with none INL, PLC and noise data claimed). Almost any 20-24bit delta sigma ADC chip and a cheapo bandgap reference chip would do it. Also when using ie. standard 50ppm resistors as the dividers (like the "statistical arrays").
To see 1-10uV resolution is not extremely difficult to achieve, but the other parameters make the "big meters" at least 20x more expensive.

[coromonadalix]

it could be based on any mcu board ??

They claim modbus compatibility,  for sure some mcu can do that ??

if a somewhat good front end W  low parts count is designed  ??


attached some of their software piece      some sniffing in them may reveal something ?

[LinuxHata]

A lot of people PM -ed me, asking whenever I can buy this for them too.
Unfortunately, I can't. A friend of mine will be shipping a container next month and I can ask him to send me one piece, but I can't really ask him to send me say 3 or 5 of these. So please, help yourself.

Registration on taobao is quite hard and they don't directly send to US, so you'd better use some kind of forwarder, which will handle delivery and purchase for you, for some extra fee of course.

So here's the link to it: https://item.taobao.com/item.htm?id=618361377982

Regarding that "830" project, it have grown to different meter I think - also a good resolution and even lower price, here's the link to it too: https://item.taobao.com/item.htm?id=727925625665

It also got PC connectivity and it is 3x cheaper - around $20. Some PCB and components can be seen there, so some guesses can be made I guess

Regarding for what purpose I want this?
I actually don't need it at all, I'm just building my own multimeter, so for calibration purposes, I bought AD584 and bunch of various value, 0.01% tolerance resistors from digikey. So my idea is, whenever this can be a reference meter for my DIY build?

[iMo]

..I'm just building my own multimeter, so for calibration purposes, I bought AD584 and bunch of various value, 0.01% tolerance resistors from digikey. So my idea is, whenever this can be a reference meter for my DIY build?

A "reference meter" should have 5-10x better parameters compared to your DIY meter.

AD584 is a low cost reference (intended for 12-14bit ADCs max) and, imho, cannot be considered as a reference for a 6.5 digits meters (perhaps for early stages in your DIY experiments only). It has been popular with makers when in metal package and because it outputs 2.5/5/10V directly.

The internal reference for a DIY 6.5digits meter starts at LM399, ADR1399, ADR1001* type references, and in order to somehow characterize such a DIY 6.5digits meter you would need the external references like LTZ1000, ADR1000, LTFLU, etc..

* should be released in FEB2024 afaik

[LinuxHata]

No I'm not making 6.5 digit multimeter mine will have 4.5 digits, but 30 fps refresh time

[thm_w]

The manual states 220V input.

If you want a reference you can buy those AD584 reference modules that has been calibrated and voltages recorded. Of course you'd have to trust the seller it was done correctly.
https://www.aliexpress.us/item/3256802893225259.html

[dobsonr741]

No AFE or input protection other than the ADC’s internal protection diodes. It’s not an instrument, it’s a basic demonstration kit for a sigma delta ADC in bipolar measurement mode. It has a place, it’s not even mentionable on the metrology scene.

[LinuxHata]

How do you know about the circuitry?
Already taken this apart?

[Kim Christensen]

There was a partial schematic on the forum:

[dmmguy]

No I'm not making 6.5 digit multimeter mine will have 4.5 digits, but 30 fps refresh time

Just in case you want to buy a reference with correct values:

https://www.ebay.ca/itm/155751553394

https://www.ebay.ca/itm/155763974742

Thanks