6 1/2 digits Volts and amperes meter, under $60, can this be true? - Page 1
Forum section: electronics / testgear

author: LinuxHata
author_rank: Frequent Contributor
timestamp: August 16, 2023, 04:53:54 am
content: 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?

author: ch_scr
author_rank: Frequent Contributor
timestamp: August 16, 2023, 07:38:51 am
content: 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

author: Aldo22
author_rank: Super Contributor
timestamp: August 16, 2023, 07:52:48 am
content: 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.htmlPaste it intohttps://translate.google.comQuoteetc.

author: iMo
author_rank: Super Contributor
timestamp: August 16, 2023, 08:54:36 am
content: $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.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 16, 2023, 09:35:05 am
content: 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 ?

author: LinuxHata
author_rank: Frequent Contributor
timestamp: August 16, 2023, 10:13:13 am
content: 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=618361377982Regarding 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=727925625665It 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 guessRegarding 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?

author: iMo
author_rank: Super Contributor
timestamp: August 16, 2023, 11:10:15 am
content: Quote from: LinuxHata on August 16, 2023, 10:13:13 amA "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

author: LinuxHata
author_rank: Frequent Contributor
timestamp: August 16, 2023, 12:20:24 pm
content: No I'm not making 6.5 digit multimetermine will have 4.5 digits, but 30 fps refresh time

author: thm_w
author_rank: Super Contributor
timestamp: August 16, 2023, 09:04:08 pm
content: 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

author: dobsonr741
author_rank: Frequent Contributor
timestamp: August 16, 2023, 11:23:48 pm
content: 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.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: August 17, 2023, 05:12:58 am
content: How do you know about the circuitry?Already taken this apart?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 17, 2023, 05:16:03 am
content: There was a partial schematic on the forum:

author: dmmguy
author_rank: Contributor
timestamp: September 11, 2023, 03:29:30 pm
content: Quote from: LinuxHata on August 16, 2023, 12:20:24 pmJust in case you want to buy a reference with correct values:https://www.ebay.ca/itm/155751553394https://www.ebay.ca/itm/155763974742Thanks