OWON XDM1041 the unknown multimeter...

[Kleinstein]

As far As I see it, there is still a ready made DCDC converter to power the analog part. So the SMPS noise may not be the relevant noise source.
The DMM chip set uses a SD-ADC that could have simultaneous 50/60 Hz supression. It still needs the correct clock frequency.  I remember seeing a change in the clock for the XDM2041 that is internally similar.  Has someone checked if the clock is correct for mains hum suppression ?

Edit:
From the pictures it looks like they have the same 4 MHz clock and may thus have a similar poor mains hum suppression problem as here:
https://hackaday.com/2021/07/14/fixing-noisy-measurements-on-an-owon-xdm2041-bench-multimeter/

Changing the clock could still be tricky as this may also effect seriel speed.

[raphaelCoelho]

I already read about it...
What it seems is that the problem happens when the main power frequency is 50Hz, on the 60Hz it doesn't.
Anyway, a linear power supply, with transformer, isolated from the network, could not improve the performance of the DMM?

[Kleinstein]

An old style 50/60 Hz transformer would have some advantage, as it does not have as much higher frequency common mode bakcground and could get away without a Y cap. It is still not sure if the improvement would be very visible. It could be worth a try - at least for a quick test with an external power supply.  User kwass may be able to tell how much improvement he sees.

The 4 MHz clock is slightly better for 60 Hz than for 50 Hz, but still not really good. So I don't understand why they don't use the correct crystal - that frequency is available (some 50 cents at Mouser) and the 4 MHz one should be only marginal cheaper, if at all.
It looks like the interface to the DMM chip is SPI and thus not sensitive to the clock. So changing the clock should be OK, though it will invalidate the calibration, not just for the frequency measurement. Chances are the BW for AC RMS would also go up a little.

[Johnny B Good]

 From all the teardown videos I've seen and what's been said here, I reckon replacement of the 5v 2.1A smpsu board with a conventional analogue, mains transformer based psu will be a total and utter waste of time and energy (both yours and that of its annual electricity costs).

 As it stands, it only draws a maximum of 1.5W (NOT the claimed 15W which seems to be a typo that lost the decimal point). At a 25% backlight setting, it only draws a tad less than 1W and just a tad over at the 50% setting. Since, unlike a signal generator, all of that input energy lands up heating the bench meter's innards. Indeed, when measuring current, the thermal load sees an increase over and above that basic energy input (another watt when testing a 10A current with (afair) a 0.01 ohm shunt).

 In view of all those downsides, such a psu mod seems doomed to failure in its primary goal of improving the bench meter's noise immunity and performance stability. IOW, I'm strongly suggesting that you don't waste your time (let alone the costs) of replacing the existing smpsu board.

[BugCatcher]

I did a few simple experiments:

- recorded the voltage of two alkaline cells (5V fixed, slow mode)
  The Owon DMMEasycontrol App is recording the gain-corrected 24bit ADC-data. This
  is equal to a 6.5 digit resolution. That's resolution, not precision! -> see diagram

  -> No visible noise problem!
        (the spacing of the horizontal lines is 0.1mV ... equals the resolution of the displayed measurement results)

- resistance mode
  two 1m long banana-cables are hanging down "flapping in the breeze", not twisted. Cables are a few cm away from a 230V/50Hz cable
  -> reading: 50MOhm-range "overload"
  connected a 20MOhm resistor at the end of the banana-cables
  -> when I'm sitting still   -> stable reading with the normal 1 unit quantization noise
  -> when I'm moving          -> up to 20..30kOhm variation
                                          -> a few kOhm even if I'm a few meters away

  -> Pure electrostatic effect!   No 50/60Hz interference!


 I don't see any problem!

[Kleinstein]

The performance looks really good for a 50000 count meter. There is quite a bit extra resolution for the PC, though not clear about the stability and accuracy. The battery may actually show some drift.

The 1 sample per second mode may have good hum suppression even if the integration time is no matching full multiples of 20 ms. To get a good response on the screen, more than 1 SPS (midium speed mode) may be the more relevant case. This would be more sensitive to hum and thus the better mode for a test to hum sensitivity.

The example with the batteries is likely low hum anyway.
The high resistance case would be an example that can be sensitive to hum, but here things can even get nonlinear, especially relatively close to the end of the range.

To judge how good or bad the 50/60 suppresion is would better use a defined identional 50 Hz part. So maybe look at 1 V RMS 50 Hz int the 5 V DC range and record the data to see if there is some beat frequency / residual AC visible.
A SD ADC can have a different filter from the SINC response one gets for simple integration over a fixed time (e.g. dual slope ADC). It still helps to have the frequency about right. Looking at the hum suppression at different frequencies could give an idea about the fitler used and how much a different clock could change.  Loosing the calibration is still a good reason not to change the HW.

[BugCatcher]

Voltage drift is most likely dominated by temperature of battery.
Beside TC and PTxx a third method for temperature measurement ;-)

Additional information regarding high impedance measurement:
before adding the 20MOhm resistor
- switched mode to ACV
- could measure 450mV AC-voltage
-> that's an indication for 50Hz attenuation ... at least sufficient for normal use cases!

The Owon app has pros and cons
pro
- extended resolution
- unlimited recording length
con
- sampling rate heavily impacted by jitter (see the two diagrams)

the XDM internal recording
pro
- more precise sampling rate
- faster sampling
con
- limited number of samples
- only "original resolution"

[Johnny B Good]

Yeah, same here. After I saw Misk's post, I send an email to OWON asking about it....  but no response (so far). I'll post if I hear anything

I did an interesting test yesterday using a Peltier element cooling an old heat sink = chunk of aluminium. I had a PT100, the unknown K-type I normally use for the XDM1041 and a known (RS-components) K-type which I use for my BM869S all attached to the same area on that heat sink.  Long story short, it seems as if the XDM1041 was much closer tracking the PT100 when it used the RS-components K-type. That one, RS stock# 409-4920  costs nearly £8 (incl. VAT) and is still only rated as +- 1.5 degC, so I'd imagine the unknown one to be much worse. Side note. To use the RS K-type (or other more professional sensors) you need a K-type adapter. I use the Brymen BKB32 for around £5 from Telonic

 I've been trying, without any success, to obtain K-type to 4mm 19mm spaced banana plug adaptors that do actually use chromel and alumel pins as per a set of four cheap mini K-Type plugs I'd bought to upgrade my collection of K type TCs and was wondering if that BKB32 adaptor would be worth buying.

 I tried to track down information regarding the proper use of chromel/alumel pins in the BKB32 without any success. The only ones I've seen that boast the use of chromel/alumel pins are the rather ubiquitous cheap Chinese ones of which I'd purchased two on the strength of this claim (shown in the attached image below). Unfortunately, they both failed the magnet test rendering this boast a work of fiction.

 I suspect that, since there is no significant temperature differential with battery powered hand held meters, the BKB32 adaptor will very likely not be using chromel/alumel pins so I was wondering if you'd care to verify whether this is the case or not with a magnet test?

 Incidentally, I've just discovered that the HI socket runs 0.5K cooler than the LO socket which seems to be about 1.5K above ambient (the SDM3065X sockets both run within 0.1K of each other, about another 1.5K higher again).

 Neither of these meters can really do any justice to K type thermocouples, the Owon because of its reliance on the meter behaving like a mW powered hand held with hopefully, some sort of calibration offset applied to approximate the difference between its internal temperature and ambient, and the expensive 6 1/2 digit Siglent for its reliance on seemingly very rare chromel/alumen K to banana plug adaptors to ensure that the isothermal reference extends all the way into the socket where it measures the reference temperature at the back of the LO banana jack inside of the meter's significantly warmer interior.

 The Owon, once warmed up, performs almost as well as the Siglent in regard of K type thermocouple sensors. The Siglent has the potential for better accuracy if only a chromel/alumel adapter could be found to maximise the benefit of chromel/alumel mini K-type plug ended thermocouples.

 If you need a very fast response thermometer with better accuracy, those cheap Chinese TM-902C K type thermometers seem a cost effective way to go regardless of whether you use chrome/alumel mini-K plug ended thermocouples or not.

 The later versions which use a pair of AAA cells, only draw 0,35mA from the battery, a mere 1.5mW, barely enough to raise the temperature by more than a few tens of mK which significantly simplifies the issue of reference end compensation and any need to use chromel/alumel in the mini K type socket or the thermocouple plug. The biggest source of uncertainty will most likely come from the warmth of your hands but you can always get round that issue by wearing winter weather gloves or an oven mitt,

[Kleinstein]

The material in the adapter plugs does not have to be actually Alumel / Chromel like a type K thermoelement. The temperature difference over that adapter part is quite small (e.g. < 1 K) and the temperature range is small. So a different alloy with similar thermal EMF is OK. This also applied to thermo couple extension cables. With type K this may still be lower grade Alumel / Chromel, but for something like the plugs other materials that are easier to machine can be a justified alternative.

If the adapter / plug part is small and thermally isolated the temperature difference over the plug is very small (e.g. < 0.1 K) and the material does not really matter. Littel heat flow also helps with the meter internal temperature gradients.  So a good thermal design can be more important than the "correct" material.

If higher accuracy is needed, the option would be to use an external electronic cold junction compensation. That is a small external circuit to correct for the cold juntion and give the TC voltage as if the cold junction temperature would be 0 C. The meter would than measure voltage and the conversion would be done on the PC side or as a math function.  I have used such small yellow units from Omega, that were powered by a single Li cell and worked quite well together with HP3478 / 3457. For some reason they seem to be no longer available and alternative one are quite expensive.

If multiple channels are needed, an external DIY cold junction box with a sensor could be an alternative. The temperature may be stable enough to only need a single reading.  The scanner cards for DMMs often include a reasonable cold junction sensor, much better than via the normal inputs.

For the SDM1041 the slight problem is that there is no really good low voltage range and the resolution may be limited.  There may still be enough resolution via the PC interface.

[piit79]

I am working on reversing firmware...

I'm very glad to hear that! Out of curiosity, any progress? The ONE thing I'd like to see fixed/patched somehow is the LONG delay on startup - it's very annoying. I wish I could just short-press the power button to put the meter on :/

[kwass]

The ONE thing I'd like to see fixed/patched somehow is the LONG delay on startup - it's very annoying. I wish I could just short-press the power button to put the meter on :/

I agree.  My solution is to just leave it on all the time.  Mine's been on for almost a year with no ill effects and power consumption is negligible.

[UniSoft]

Out of curiosity, any progress?

Nope... I put the project on pause...
I can't find latest firmware (or at least same version as mine), to start testing etc..
Need to extract bootloader first, and to do this I need to write custom code, what will erase current firmware, so I will not be able to restore the same version.
There is only old version posted by @theHWcave.
It actually stops me from further experiments.
Shit OWON no even reply for request of update.

The ONE thing I'd like to see fixed/patched somehow is the LONG delay on startup - it's very annoying. I wish I could just short-press the power button to put the meter on

This can't be changed by firmware...
Power switch is implemented by standalone MCU ATTINY202-SSF...
It is really not hard to write firmware for this MCU. But it cannot be updated via USB/COM.

[BugCatcher]

Owon released a new version of the XDM1041!

The new XDM1241 offers internal lithium battery instead of AC power. All other features look identical ...
Banggood is already offering the new device!

http://files.owon.com.cn/probook/OWON_XDM1000_Digital%20Multimeter_USER_MANUAL.pdf

BugCatcher

[mapleLC]

Trying to understand why anyone would want this.

[Johnny B Good]

 Consumer demand? 

[Kleinstein]

Battery operation has its advantage: no power cable needed and better isolation / less common mode signal injection to worry about. Even if the possible injection of a common mode signal is not often a problem it helps if you don't have to consider this as a possible source of an unexpected signal.
With the moderate power consumption operation on a rechargible battery and still have a well visible screen is nice.  Keithley / Fluke had early 4.5 digit bench top meters with battery option, so it is not a new invention.

[mapleLC]

Battery operation has its advantage: no power cable needed and better isolation / less common mode signal injection to worry about. Even if the possible injection of a common mode signal is not often a problem it helps if you don't have to consider this as a possible source of an unexpected signal.
With the moderate power consumption operation on a rechargible battery and still have a well visible screen is nice.  Keithley / Fluke had early 4.5 digit bench top meters with battery option, so it is not a new invention.

Consumer demand? 

I'm one of those consumers that demands a bit more reputation, so this is my old workhorse.  While reputation is on the decline, period specific, reputation still matters.

I wouldn't trade mine for yours.

[akisnas]

Hello everyone, i bought 2 of them a few months before, tested and then storage in original boxes for 2 -3 months before my project started.
Today unpackage and i test them, both of them were dead no powered at all.
I notice the psu is working and 5V is present, have you any idea what is going on?
Is there any member with the same issue?
The rechargeable battery MS621FE measured at 2.6V.
Do you think there is an issue with this battery?
Its really weird...
Thanks for your time.
Best Regards

[akisnas]

Problem solved, after 10mins the battery charged and its working again.

[sigxcpu]

I will leave this information here, for all others that may be hit by my problem.

I've tried to use the utility & firmware provided here https://github.com/TheHWcave/OWON-XDM1041/tree/main/OWON%20firmware , but the meter didn't exit bootloader/restart - finished with error at "checking new version".
I tried to re-flash lots of times with the same result.

Diode/continuity was broken (showing 0 and beeping continuously), "Utility" menu was also broken. Most likely the "calibration" data was corrupted.
I wrote to Owon but I didn't get any response yet, then I've found this repository https://github.com/PetteriAimonen/owon-xdm2041-info/tree/main/bootloader and a crazy idea was born. What if I write the calibration data from 2041 (thank you PetteriAimonen) to my 1041?
To my surprise, it worked, the meter is fully functional again and, based on few tests I did, accurate enough.

Of course, now it thinks it is a 2041 on version 1.7.2 (the actual version is 2.1.2), but I can live with that.

Attached a picture with the broken "utility" menu.

LE: If somebody would be kind enough to dump the calibration data from their 1041, I would be forever thankful
The script to do that is here https://github.com/PetteriAimonen/owon-xdm2041-info/blob/main/bootloader/backup_calibration.py

[mapleLC]

I will leave this information here, for all others that may be hit by my problem.

I've tried to use the utility & firmware provided here https://github.com/TheHWcave/OWON-XDM1041/tree/main/OWON%20firmware , but the meter didn't exit bootloader/restart - finished with error at "checking new version".
I tried to re-flash lots of times with the same result.

Diode/continuity was broken (showing 0 and beeping continuously), "Utility" menu was also broken. Most likely the "calibration" data was corrupted.
I wrote to Owon but I didn't get any response yet, then I've found this repository https://github.com/PetteriAimonen/owon-xdm2041-info/tree/main/bootloader and a crazy idea was born. What if I write the calibration data from 2041 (thank you PetteriAimonen) to my 1041?
To my surprise, it worked, the meter is fully functional again and, based on few tests I did, accurate enough.

Of course, now it thinks it is a 2041 on version 1.7.2 (the actual version is 2.1.2), but I can live with that.

Attached a picture with the broken "utility" menu.

LE: If somebody would be kind enough to dump the calibration data from their 1041, I would be forever thankful
The script to do that is here https://github.com/PetteriAimonen/owon-xdm2041-info/blob/main/bootloader/backup_calibration.py

Why don't you call Chinese customer service bro?

[UniSoft]

If someone interested, there is a hidden calibration menu (I saw it in code)
UTILITY-MATH-UP-RANGE-DOWN : Enter manual calibration mode (MATH for exit)

DO NOT RUN IT!!! You will lose all calibration values!!!
It requires some additional equipment.
UTILITY-DUAL-UP-RANGE-DOWN : Enter automatic calibration mode (I never run it)

[msquared]

Here' the cal data from my XDM1041. Hope this helps.

[Markus2801A]

Owon released a new version of the XDM1041!

The new XDM1241 offers internal lithium battery instead of AC power. All other features look identical ...
Banggood is already offering the new device!

http://files.owon.com.cn/probook/OWON_XDM1000_Digital%20Multimeter_USER_MANUAL.pdf

BugCatcher

Has anyone ordered the battery powered XDM 1241 version?
I ordered it a few weeks ago but then got the email that something went wrong with delivery and the package was returned.
Banggood immediately offered a refund, so I don't know should I try it again? is it worth?

[theHWcave]

If someone interested, there is a hidden calibration menu (I saw it in code)
UTILITY-MATH-UP-RANGE-DOWN : Enter manual calibration mode (DUAL - exit)
UTILITY-DUAL-UP-RANGE-DOWN : Enter automatic calibration mode (I never run it)

That is cool! But in mine I get a DEBUG, KEY, and LCD menu for the first sequence. The KEY and LCD menu are tests for checking key response and LCD, the DEBUG shows two additional values in the normal measurement menus which are called ZERO and COEF. Are these the calibration constants? They appear to be editable. For example in the 5V DC range ZERO is 0000000 and COEF is 0800000 in mine.

The 2nd sequence seems to run a program automatically (no choice, it starts right away) that shows all cal values line by line for all ranges. it is possible that this expects inputs for calibration but it runs quite fast not waiting for inputs. I might possible use the serial port to communicate with a calibrator connected...  Yes, it appears that's what they do in the factory with an automated calibrator attached
DONT RUN IT!  I completely lost calibration on all ranges! !!   
I do have a dump of my CAL values, now to see if I can load it back ... will report on it