TEARDOWN - RuoShui 86E - 22000 count DMM - 50 EUR

[hve]

 ES51932_log.zip (1.6 kB - downloaded 38 times.) ES51932_log.zipJust decided to replace my 40 year old expensive non-auto ranging DMM with 2000 counts for an inexpensive 22000 count meter:
https://www.aliexpress.com/item/4000178957414.html

So in conclusion:
- 22000 counts
- Nice big screen
- Rugged pretty sturdy case
- Temperature, in device and with external thermocouple (included in package).
- Manual HOLD
- Chipset documentation online
- Trimmers on the mainboard, so you might be able to calibrate the device yourself.
(please share if you know how TODO this) 
- Cheap-ass fuses as Dave would say and minimal clearances so keep well below the suggested maximum voltages.
- Only low voltage stuff with RS232 connected. Even though it seems optically isolated.
- DMM Chip-set: ES51932
- UART: CP2102
- Serial Communication protocol: 19200 baud, 7 data-bits, 1 stop-bit, odd parity
  Data packet out: 14 Bytes = [ range, digit[4,3,2,1,0], function, status, option[1,2,3,4], CR , LF ]
  In the attachment is a little Perl serial decoder script as a proof of concept, it expects device at /dev/ttyUSB0 but you can easily change that.

Example session:

Code: [Select]

./ES51932_log.pl
...
00060e-4 V DC auto
-22112e-5 V DC
OL V DC
OL Ω auto
00061e-12 F auto
00000e-2 Hz auto
00207e-1 °C
00000e-8 A DC auto

All in all not a bad investment for 50 euro.

[hve]

[LeonR]

Is the PCB discolouration around RT1 just flux residue or is it a heating issue?

[coromonadalix]

i would say flux residue

[DaneLaw]

IN lack of software included , it looks like RuoShui is an official name of Victor and highlighted on their site-banner alongside Victor & Yitensen so same-same Victor86E and likely identical software.
http://www.china-victor.com/index.php?m=content&c=index&a=show&catid=42&id=31

Got the 70C myself.
https://imgur.com/a/JwvLzlx

// http://www.china-victor.com/index.php?m=content&c=index&a=show&catid=42&id=18

[Pinpi]

What would you say is a good thing for novice people to pay attention to as a red flag when tearing down things and observing the board?

[Algoma]

That USB port doesn't appear to have any real isolation at all. Avoid testing anything remotely high voltage with that USB connected.

[Kleinstein]

With mechanical trim pots this looks like a really old design. The main chip seem to have a 2014 date-code. One other code looks like 2018 - which is odd for a meter usually made in at least some quantety.

The solder quality (or lack there of) is not that great - the flux residue with white discolurations may be future corrosion problem.

Safety wise there is not much to expect from 600 V CAT rating with 250 V fuses (kind of Chinese standard). Besides the fuses the optocoupler for the PC interface is also a bit odd: they take the effort of the cut out under the OK, but the LCD interface is closer, with no cut  .

The 2 metal encases blocks look odd - are these relays ?

[DaneLaw]

On the older model 70C from Victor / RuoShui that is like a 35Euro meter, though numerous years back (2012 dated)..
They do seem to use an optical chain before the USB Mini socket..

IMO not a bad relae-meter and the used feels plastichousing feels way more sturdy than I usually remember seeing in multimeters in this price bracket, and comes with with a PC interface and software incl from scratch..(haven't tested the PC SW., so not sure how useable it is)
- as long you have the price in mind, it's a decent meter, so far been a pleasant companion for the last 6 years in my case, and after pod-adj., quite accurate. https://imgur.com/a/JwvLzlx

[hve]

Totally agree with Algoma & Kleinstein

I would say definitely a red flag that the serial interface seams not optically isolated,
Might be interesting to hook up a scope to see the impact on noise levels, might do that later on.

Do not recommend doing any serious high voltage stuff keep, it well below the advertised 1000 DC and 750 AC.
I would probably not harm to probe the 240V AC mains voltages and the 400V DC, with serial disconnected!
But further than that I would not go...

[hve]

The 2 metal encases blocks look odd - are these relays ?

I have wondered about that, no markings in the cans. Only thing I can think of, since there are two,  is some sort of precision resistor / resistor array..
Bottom of PCB:

[hve]

Looking at the weird diode configuration now I would assume the serial interface is optically isolated. The USB2serial chip is powered from the host and then the data is transmitted over the (foto)diode....

Revisiting the 86e:


This is indeed an optocoupler, so same arrangement as in the 70C...

Did you have any luck  in decoding the serial output?

[Kleinstein]

There is optical isolation, but the creep distance on the baord does not look great.

The old VC70 design looks even worse in some aspect.  Powering a USB-UART bridge chip via USB and than have an optical isolated UART is kind of the logical way, but there is no clear separation visible between the chip and rest of the circuit.
With just RS232 one can kind of hack togeter a direct optical link with no extra power. It would not fully meet the RS232 levels, but most of  the old style serial mice were working with similar levels (e.g. usually no negative voltage).

[Algoma]

The Opto-Isolation is between U1 and U4 .. its U4's (Serial-USB interface) Isolation that is in most question. and doesn't benefit at all from the cut below the opto-Isolation.

[hve]

Have found a datasheet on the 70C chip  https://datasheetspdf.com/datasheet/FS9922-DMM4.html

On page 30 there is a complete info on the serial protocol, might be a good start for the 86E

Code: [Select]

...
RS232 transmission format is 14 byte. Its transmission rate is 2400 bps. The format is as follow

14 byte output code location:

a) Sing byte 1: 0f0H； h) SB1 byte: 0f7H；
b) Data byte 2: 0f1H； i) SB2 byte: 0f8H；
c) Data byte 3: 0f2H； j) SB3 byte: 0f9H；
d) Data byte 4: 0f3H； k) SB4 byte: 0faH；
e) Data byte 5: 0f4H； l) BAR byte: 0fbH；
f) Space byte: 0f5H； m) EOF byte: 0fcH；
g) Point byte: 0f6H； n) ENTER byte: 0fdH.
...

[Kleinstein]

U4 is a standard  USB to UART bridge chip (CP2102)  the pins may only look odd as not connected pins may not show up. So the isolation distance is even worse than I originally thought. There is only margunal spacing from U4 to the rest of the circuit. The UART signal than goes via the opto-coupler near the USB connector to U1.  It looks like only 1 way data from the DMM to the ouside.

[hve]

Yep now it makes sense:  19200 baud, 7 data-bits, 1 stop-bit, odd parity

[Pinpi]

How can you tell if it has optical isolation?

[Kleinstein]

The 4 pin part DB1 is an optocoupler - at least it very much looks like one and it in the right spot.

[DaneLaw]

Yep..

 (Opto) NEC2501

2501 Pin-out

Product code: 07042020T
Brand: Other
Photo (opto) NEC2501 PS2501 2501 SOP-4.
https://linhkienst.com/products/photo-quang-dan-opto-nec2501-ps2501-2501-sop-4-moi-chinh-hang-100

[hve]

I think in theory this multimeter might be supported by sigrok:
https://sigrok.org/wiki/UNI-T_UT61E

Unfortunately I could not get it to work, despite using the latest git version:

Code: [Select]

/usr/local/bin/sigrok-cli --driver=uni-t-ut61e-ser:conn=/dev/ttyUSB0 -O analog --samples 5
No devices found.
So i wrote a little Perl serial decoder as a proof of concept:

Code: [Select]

./ES51932_log.pl
...
00060e-4 V DC auto
-22112e-5 V DC
OL V DC
OL Ω auto
00061e-12 F auto
00000e-2 Hz auto
00207e-1 °C
00000e-8 A DC auto

Feel free to experiment if you like, I have attached the script to the first post in this topic.

[Trader]

RuoShui 86E # AC Frequency Response (Bandwidth) (40~400Hz)

UNI-T UT161E is up 20kHz AC