Author Topic: Hacking the Siglent SDM3055 Bench DMM  (Read 3968 times)

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Offline alexvg

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Hacking the Siglent SDM3055 Bench DMM
« on: August 10, 2019, 12:37:52 am »


During my SDM3055 reverse engineering... I've got 2 questions to you ?

Would you agree to pay a small amount for a new SDM3055 software (and maybe for the SDM3045) ?
http://www.pixule.com/39863606081_would-you-agree-to-pay-small-amount-for-new-sdm3055-software-and-maybe-for-the-sdm3045.html

Would you like to improve your SDM3055 by adding a some options ? (The SDM3045 may be compatible with these options.)
http://www.pixule.com/398636486944_would-you-like-to-improve-your-sdm3055-by-adding-some-options.html

Thanks for your help !



Hi,

I'm working on a hack to show more digit to the Siglent SDM3055
I've got a source voltage of 2.5V (not a reference voltage)

Original : 240 000 points / 5 1/2 digits


First hack result : 2 400 000 points / 6 1/2 digits


The hack does not work correctly but give interresting result.
To be continued.
« Last Edit: August 19, 2019, 07:28:28 pm by alexvg »
 
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Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #1 on: August 10, 2019, 08:55:24 am »
 :clap:

Alexia, as requested. 2 of the latest app versions attached. Good luck!
« Last Edit: August 10, 2019, 04:16:04 pm by tv84 »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #2 on: August 11, 2019, 11:59:47 pm »
New results with 7.5 digits
The calibration data are not currently loaded :



 

Offline Mr. Scram

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #3 on: August 12, 2019, 12:12:33 am »
Nice experiment! Not to rain on your parade, but are these numbers relevant? Do we know whether the 6.5 digit versions maybe have cherry picked or simply better references? I'm asking because many meters can show more digits but it's generally noise. Don't let it discourage you though and be sure to hack on!
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #4 on: August 12, 2019, 12:23:57 am »
I've noticed some mistake into the code :
A real value of 1.499995 is displayed 1.4999 instead of 1.5000.

But a value of 1.4999995 is displayed 1.5000. It's because the rounding is done with a value of 5.0x10-7


« Last Edit: August 12, 2019, 12:25:58 am by alexvg »
 

Offline coromonadalix

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #5 on: August 12, 2019, 12:46:22 am »
I would love to see this hack against a AC / DC / Ohms  calibrator ??
 

Online tautech

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #6 on: August 12, 2019, 01:40:40 am »
Not to rain on your parade, but are these numbers relevant? Do we know whether the 6.5 digit versions maybe have cherry picked or simply better references?
Yes of course measurement stability can be questioned as SDM3065X uses the better LM399 reference.

Avid Rabid Hobbyist
 

Offline coromonadalix

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #7 on: August 12, 2019, 07:26:30 am »
Could the 3065 and 3055  share the same design, minus the reference quality ?? 

Q: The hacked firmware, does it come from the 3065 ??
 

Online tautech

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #8 on: August 12, 2019, 08:20:52 am »
Images from SDM3000 series thread
https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/

SDM3045X


SDM3055


SDM3065X
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #9 on: August 12, 2019, 08:56:31 am »
Could the 3065 and 3055  share the same design, minus the reference quality ?? 
The SDM3065X uses a LM399H (0.3ppm/C with 20ppm/1000h and 7uV noise) voltage reference and AD7175-2 "B" A/D (up to 24 peak-to-peak bits and 24 effective bits at 5 to 16 SPS).
The SDM3055 uses a MAX6325 "C" (0.5ppm/C with 30ppm/1000h and 1.3uV noise) voltage reference and AD7190 "B" A/D (up to 22.5 peak-to-peak bits and 24 effective bits at 4.7 SPS).
The SDM3045X uses TI REF5025K "High grade" (2.5ppm/C with 100ppm/1000h and 3uV noise ) and AD7190 "B" A/D (up to 22.5 peak-to-peak bits and 24 effective bits at 4.7 SPS).

Edit 2019-08-18
Difference vs SDM3055 :
- SDM3065X uses a separate power supply
- SDM3065X uses a LM399H voltage reference and a higher resolution ADC
- SDM3045X uses lower grade components but with a SDM3055 design (or SDM3055X-E PCB)

I suspect the SDM3055 could have a better ADC (see un populated U503 SSOP28) like ADS1256 (seems to be compatible)



Q: The hacked firmware, does it come from the 3065 ??
I'm only using the original SDM3055 firmware.
« Last Edit: August 18, 2019, 10:08:44 pm by alexvg »
 

Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #10 on: August 12, 2019, 09:10:28 am »
If anyone with a 3045X wants to test the 3055 in his DMM, I can easily prepare an .ADS.

BUT, no responsibility for my side.
 

Online tautech

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #11 on: August 12, 2019, 11:34:16 am »
I'm working on a hack to show more digit to the Siglent SDM3055

To be continued.....................
And he busted it !  :palm:

PM pleading for help ...............
And returned.
Avid Rabid Hobbyist
 

Offline BillB

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #12 on: August 12, 2019, 12:12:52 pm »
Well, that escalated quickly!   ???
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #13 on: August 12, 2019, 01:36:40 pm »
I've done some bash correction to correctly use XML calibration file.
Now the value displayed is correct and the result is very interresting.

I'm investigate to display digits with a little lower font size.

With the input shorted to the ground :
« Last Edit: August 12, 2019, 01:46:22 pm by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #14 on: August 13, 2019, 08:59:19 am »
Quote
How to test the sdm-mod ? (only with the latest 1.01.01.19 firmware)

Step 1
Plug a formatted FAT32 USB Key (I use 4GB) into the SDM3055

Step 2
Connect to telnet (username:root, password:ding123)

Step 3
Backup all Siglent data into the USB key :
"cp -R /usr/bin/siglent /usr/bin/siglent/usr/mass_storage/U-disk0/"
After copying, unplug the USB key

Step 4
Plug the USB key into your computer
Copy "sdm-mod.app" into the "/siglent" of the USB key
Unplug the USB key

Step 5
Plug the USB key into the SDM3055 and go to telnet
Stop the current sdm.app application : use "ps" to list all application PID and kill the "./sdm.app" PID.
Generally it's the PID 550, you could kill it with command "kill 550"

Step 6
Prepare and run the mod
"mkdir /usr/bin/siglent/usr/mod"
"cd /usr/bin/siglent/usr/mod"
"cp -R /usr/bin/siglent/usr/mass_storage/U-disk0/siglent/ /usr/bin/siglent/usr/mod/"
"cd siglent"
"./sdm-mod.app"

Step 7
To stop sdm-mod.app, just press "Control C".
Restart the device to return to normal operation.

Step 8
To remove the mod folder
"rm -r /usr/bin/siglent/usr/mod"


Code: [Select]
sdm-mod.app 20190812 v01
SHA1 : 85ceab5b27570de364ab127d0c67a7deb17903ab
SHA256 : d26b360d6db9a89b058b4d44a2116c546b492e402df37fa1d491276a415fd5d0

Features
- Add 2 digits (7 1/2 digits)

Drawback
- On some menu the sign and/or the last digit is not display correctly
« Last Edit: August 13, 2019, 09:11:53 am by alexvg »
 
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #15 on: August 13, 2019, 09:11:23 am »
I'll post later 2 other versions :
- sdm-mod.app with only one additionnal digit
- sdm-mod.app with two additionnal digits and some special text display (if it's work !!!)

I've not currently found the solution to change the font size.
It takes very long because my ARM debugger does not work...

If anyone know a solution to do a remote debugging of an ARMv7 GDBServer using Windows (or Debian)...

If you have a voltage reference, could you post your result ? (I use the BARmeter menu to display all digits)
« Last Edit: August 13, 2019, 09:14:13 am by alexvg »
 

Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #16 on: August 13, 2019, 09:54:58 am »
If anyone know a solution to do a remote debugging of an ARMv7 GDBServer using Windows (or Debian)...

IDA?
 

Offline Zorc

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #17 on: August 13, 2019, 01:35:42 pm »
 :-+ Very cool you've got this far!
Interesting to find out how usefull this actually is!
I don't have a benchtop DMM but maybe in the future this might be a model I would consider buying (whenever I decide I really 'need' (read: want to have) one to supplement my handheld multimeters)
 

Offline coromonadalix

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #18 on: August 13, 2019, 05:17:27 pm »
Has it been compared against a precision source  ??,  nice to have more digits,  are they worth displaying ??
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #19 on: August 13, 2019, 05:45:06 pm »
Has it been compared against a precision source  ??,  nice to have more digits,  are they worth displaying ??
I would like to know if additionnal digits are usefull or not.
The only thing I could say, there are an internal rounding error.

IDA?
I've tested IDA but it does not support this application and/or GDBServer integrated into the SDM3055.
 

Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #20 on: August 13, 2019, 05:46:35 pm »
I've tested IDA but it does not support this application and/or GDBServer integrated into the SDM3055.

What about via JTAG?
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #21 on: August 14, 2019, 06:31:30 am »
Here's the 6 1/2 digits version :

Code: [Select]
SDM 3055 m1-1908-01

Feature
- Add 1 digit (total of 6 1/2 digits or 2 400 000 points)

SHA1
cb89541b22959c8cdae8a7a917b29ca7042d4bcf

SHA256
73bef60988a4b4ec684132795c0f6b99bb4fcf4d4e1824f0acad414d9f9f64cb

Quote
How to test the sdm-mod ? (only with the latest 1.01.01.19 firmware)

Step 1
Plug a formatted FAT32 USB Key (I use 4GB) into the SDM3055

Step 2
Connect to telnet (username:root, password:ding123)

Step 3
Backup all Siglent data into the USB key :
"cp -R /usr/bin/siglent /usr/bin/siglent/usr/mass_storage/U-disk0/"
After copying, unplug the USB key

Step 4
Plug the USB key into your computer
Copy "sdm-mod.app" into the "/siglent" of the USB key
Unplug the USB key

Step 5
Plug the USB key into the SDM3055 and go to telnet
Stop the current sdm.app application : use "ps" to list all application PID and kill the "./sdm.app" PID.
Generally it's the PID 550, you could kill it with command "kill 550"

Step 6
Prepare and run the mod
"mkdir /usr/bin/siglent/usr/mod"
"cd /usr/bin/siglent/usr/mod"
"cp -R /usr/bin/siglent/usr/mass_storage/U-disk0/siglent/ /usr/bin/siglent/usr/mod/"
"cd siglent"
"./sdm.app"

Step 7
To stop sdm.app, just press "Control C".
Restart the device to return to normal operation.

Step 8
To remove the mod folder
"rm -r /usr/bin/siglent/usr/mod"
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #22 on: August 14, 2019, 10:13:37 am »
If anyone with a 3045X wants to test the 3055 in his DMM, I can easily prepare an .ADS.

BUT, no responsibility for my side.

Never try to use SDM3045X or SDM3065X into the SDM3055
- The SDM3065X app program have an error loop
- The SDM3045X app program seems to work, but there no value on the display.

I'm currently testing a modification : I've removed the 0.5uV add/sub.

Edit: If you want to use the initial mod version I've posted (7 1/2 digits), You need to use the stat menu to display all digits and sign without any artefact.
I've noticed after a measurement of a battery (around 8V), using 20V range, there's a +/-20uV variation. This corresponding to a +/-2uV at the input of the ADC (with its 2.5V reference).
This seems to be very good.
« Last Edit: August 14, 2019, 10:17:06 pm by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #23 on: August 16, 2019, 07:31:44 am »
I've add 2 little heat sink on voltage reference and ADC and I removed the fan.
The result is interresting (using 200mV range, short-circuit on the input and more than 4000 samples) :
- Previous noise result was 1.75uV
- Now the noise is reduced to 1.34uV (difference between min/max) and standard deviation is 0.207uV

I've mesured a -90dB noise into the 5V line... Why Siglent integrated the analog/logic power supply on the same board ? (except for lowering cost).
I'm thinking about adding a pre-rectifier/filter/regulator, changing the 5V regulator and probably changing the voltage reference to the LTC6655B-2.5 (if I could access to an excellent reference voltage).

I've received a AD584LH voltage reference, I've measured 20K samples at 2.5V with 20V range :
- 78uV span (+/-39uV)
- 11,1uV standard deviation

I think the SDM3055 seems to be more interresting than I though first (It only need some modifications to be more better).



« Last Edit: August 16, 2019, 05:15:41 pm by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #24 on: August 16, 2019, 11:23:49 pm »
I've tested IDA but it does not support this application and/or GDBServer integrated into the SDM3055.

What about via JTAG?
I've successfully running the remote debug using Texas Instrument Code Composer Studio...
 

Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #25 on: August 17, 2019, 12:32:49 pm »
I've successfully running the remote debug using Texas Instrument Code Composer Studio...

Must study that.   :clap:
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #26 on: August 18, 2019, 05:39:42 pm »
I've done a very long measurement to check the quantification level.
All measured values are using 22.5bits (slow mode or 4.7SPS). There's no loss during calculation.
22.5 bits corresponding to 6.77 digits. A full 24bits ADC (as seen in the SDM3065X) could provide 7.2 digits.
A long integration time with a sinc filter could provide more bits.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #27 on: August 19, 2019, 07:48:41 pm »
I need your help, and I've added 2 questions on the first post :
https://eevblog.com/forum/testgear/hacking-the-siglent-sdm3055/msg2605347/#msg2605347



I've done multiple meaures with an AD584 at 2.5V with 7.5 digits.
- Statistic averaging of 500 samples give 2.496551V
- Averaging of 23 values in 5 seconds give 2.49655078V
- Sinc filter of these 23 values give 2.4955098V

measurements of a 10K 0.1% 30ppm resistor with 7.5 digits
- Statistic averaging of 500 samples give 10.005007k
- Averaging of 23 values in 5 secondes give 10.0050084k
- Sinc filter of these 23 values give 10.0050086k
- Statistic averaging of 4k samples give 10.005006k


The noise level during A/D conversion is very low in Resistance mode (much more lower than DCV).
« Last Edit: August 19, 2019, 07:52:03 pm by alexvg »
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #28 on: August 19, 2019, 08:09:23 pm »
Are you comparing what you get to something that is actually more accurate, or are you just assuming this is giving you relevant data(not noise)?
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #29 on: August 19, 2019, 10:27:56 pm »
Are you comparing what you get to something that is actually more accurate, or are you just assuming this is giving you relevant data(not noise)?
Actually I trying to identify all most important noise sources (ADC, Voltage ref, op-amp, relay...).
I measure the distribution of data to see if internal processing maintain all available bits (from ADC).

The SDM3055 PCB analog-part is the base of the 4.5 and 6.5 digits DMM and I think it could be go to 7.5 digits (but with another ADC and some addtitionnal important modifications).
I don't know if 7.5 digits could be really possible with less minor modification, but I'm currently working on these little hardware modifications to check that (with software modifications and/or new software).
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #30 on: August 20, 2019, 08:47:08 pm »


Would you agree to pay a small amount for a new SDM3055 software (and maybe for the SDM3045) ?
http://www.pixule.com/39863606081_would-you-agree-to-pay-small-amount-for-new-sdm3055-software-and-maybe-for-the-sdm3045.html

Would you like to improve your SDM3055 by adding a some options ? (The SDM3045 may be compatible with these options.)
http://www.pixule.com/398636486944_would-you-like-to-improve-your-sdm3055-by-adding-some-options.html

Thanks for your help !
Sorry for double-post.
 

Online tv84

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #31 on: August 20, 2019, 08:51:51 pm »
That's a wrong move!
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #32 on: August 20, 2019, 09:05:15 pm »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.
 

Offline joeyjoejoe

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #33 on: August 20, 2019, 11:10:07 pm »
Asking for something to go wrong. Anyone needing more resolution would probably spend on the 3065 for supported 6.5 digits. Only hacker community would entertain this, and these are the folks who wouldn't pay for something like that.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #34 on: August 20, 2019, 11:20:01 pm »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.
That's not what I want.
My first tests was only done for evaluation only, I don't want to bother Siglent (I appreciate theirs products !).
I prefer providing my own firmware (not related to Siglent) but compatible with their product while offering additionnal, new or different features.
The SDM3055 is very good, I think it could be even better. My goal is to maximize this device.

Asking for something to go wrong. Anyone needing more resolution would probably spend on the 3065 for supported 6.5 digits. Only hacker community would entertain this, and these are the folks who wouldn't pay for something like that.
You could be right... In the Android community some people are ready to pay some OS updates and advanced features for their old device. The SDM3055 is an old device.


I really appreciate your help, yours advices and opinions. Thank you.
« Last Edit: August 20, 2019, 11:26:29 pm by alexvg »
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #35 on: August 20, 2019, 11:35:55 pm »
As far as I can see the 3055 is not old, it's a current product.
 

Offline blacksheeplogic

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #36 on: August 21, 2019, 12:26:42 am »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.

OK, just so I have this straight. It's OK to steal but no OK to charge for stolen items? I was obviously under the misunderstanding that both were wrong.

If your providing a patch to 'extend' functionality (your own work, not enabling someone else work) to a device not sure where the legal issue comes from (sold or given). If your providing FW that's been patched which includes the original FW that's quite different as you are giving/selling someone else work.
 

Offline maginnovision

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #37 on: August 21, 2019, 12:43:01 am »
You start charging and you might be asking Siglent to challenge you. Since you're modifying their firmware it could be a legal issue.

OK, just so I have this straight. It's OK to steal but no OK to charge for stolen items? I was obviously under the misunderstanding that both were wrong.

If your providing a patch to 'extend' functionality (your own work, not enabling someone else work) to a device not sure where the legal issue comes from (sold or given). If your providing FW that's been patched which includes the original FW that's quite different as you are giving/selling someone else work.

Both are wrong, but if you're charging people are more likely to take notice. It's not open source software, modifying it could be illegal.

To add some context Keysight Daniel bogdanoff once said they don't care if you hack your scope but they do care if you try and sell hacked scopes.
« Last Edit: August 21, 2019, 01:14:23 am by maginnovision »
 

Offline Mr. Scram

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #38 on: August 21, 2019, 10:13:08 am »
Both are wrong, but if you're charging people are more likely to take notice. It's not open source software, modifying it could be illegal.

To add some context Keysight Daniel bogdanoff once said they don't care if you hack your scope but they do care if you try and sell hacked scopes.
He's saying he'd provide his own firmware not related to Siglent. Writing your own firmware and selling it is fully legal but not trivial to pull off.
 

Offline coromonadalix

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #39 on: August 21, 2019, 10:39:04 am »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
 

Offline Mr. Scram

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #40 on: August 21, 2019, 10:42:53 am »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
Apparently not. Writing your own code completely from scratch is legal. Patching existing firmware with your own code also tends to be legal as you don't copy or provide someone else's code.
 
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Offline JohnG

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #41 on: August 21, 2019, 01:52:37 pm »
This is really nice work, and the related discussion interesting as well.

But, there is a practical matter. A modified meter will have no warranty and reduced odds of support. Have you checked the prices of used 34401 meters lately? Not as many modern features as the 3055A, but they use a LM399 reference and do 6.5 digits without mods. The reference has a good chance of being aged and stable.

I have both meters. The 3055A is easier to use, for sure, but not much of a track record regarding accuracy. A modified version, even less so.

Just my $0.02.

John
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #42 on: August 22, 2019, 09:23:16 pm »
Is it me   or its going in the wrong direction ?   even if he provide his code,  where the code base came from ? Siglent   no/yes ?
The SDM3055 is based on Linux operating system with only a binary file written (partially) by Siglent launched during startup. Used internal libraries and all external libraries come from Texas Instrument, Linux system...

As far as I can see the 3055 is not old, it's a current product.
It's an old device from 2014... Lots of units have been sold : maybe some people would be interested in updating or improving their device without buying a new more powerful and perhaps more expensive DMM.
« Last Edit: August 22, 2019, 09:36:58 pm by alexvg »
 

Offline NoisyBoy

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #43 on: August 23, 2019, 01:19:20 am »
Since you are trying to build something to sell, I doubt this is an appropriate discussion for this forum especially when you try to do a product interest survey. 

The 3055 is not designed as an open hardware platform for open source firmware development.  I will never pay for “enhanced” firmware that does not come from the manufacturer, it is a sure way to void the warranty plus I will never trust the reading. 

I am not saying it is a bad idea, just that it is more appropriate to be discussed in another venue.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #44 on: August 26, 2019, 07:10:36 am »
Thank you for this very interesting and informative discussion.

About software, I'm continuing working on the new firmware :
- I've successfully access to the display and keyboard.
- I'm waiting for the Lattice USB programmer.
- I'm currently investigate the protocol between digital and analog boards.

About hardware, I've received the components to build a pre-regulated power supply.
I'm waiting for the LTC6655BHLS8-2.5 voltage reference. I'll try one chip to measure ADC noise.
I'd like to build a 6-chip voltage reference : 6x LTC6655 in parallel to limit noise and deviation.
I'm waiting for a brand new calibrated voltage reference (based on the LM399AH).
I'm always searching for a calibrated LTZ1000ACH voltage reference module, I could not find it. Any ideas ?
« Last Edit: August 26, 2019, 11:09:22 am by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #45 on: August 30, 2019, 04:22:37 pm »
I've found some interresting things :
- Only low-23 of 24 bits are used in the software (the 24th bit is used as a polarity bit - shame)
- I've done some precision simulations using datasheet ADC and I presume the ADC used have an internal precision of 24bits (instead of probably 32bits ADC used in the SDM3065X). Using software filtering and fast ADC sampling rate, it's seems to be possible to have a some better results.
- I've found some better Op Amp at the same price (ADA4528-2 instead of AD8629 and LTC1151 instead of AD706)
- I've received a LM399AH-based voltage reference calibrated at 10.00000V (my SDM3055X displays up to 10.001V)
- Resistance measurement (2 or 4 wires) is more stable than current or voltage measurement.
- The internal +5V, +15V and -15V have some 100Hz (from 50Hz AC).

« Last Edit: August 30, 2019, 06:54:56 pm by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #46 on: August 30, 2019, 08:04:01 pm »
It is kind of normal that 1 bit is used for the sign. So 23 bits + sign is kind of normal. Chances are the noise of the ADC is high enough, that there is very limited value to more resolution. With long time averaging a slightly high resolution can be possible, but this does not need the numbers from ADC chip itself.

The ADA4528-2 OP is not per se better than the AD8629 - they are different:  the ADA4528 is very low voltage noise, but higher bias and much higher current noise. The ADA4528 is good for signal sources with less than some 10 K impedance. However the AD8628 is much better for high impedance sources, like the input divider for the higher voltages.

In case one really want's to get sub 100 nV resolution, it would be more like an extra external preamplifier based on an OP like ADA4528. This could also add more gain and have a higher precision protection part (though possibly lower maximum voltage, more bias). Chances are in the lower cost meters the protection is just a resistor, maybe PTC. This could add enough resistance and noise so that it does not make sense to use the ADA4528.

Similar the LTC1151 and AD706 are good for different applications. So it depends on the use. AZ OPs can add quite some spikes, that might upset other circuit parts.

If resistance measurement is more stable than voltage and current measurements, this indicates that the reference noise is a mayor contribution. This might also be the external reference. A lower noise reference may be one of the few actually possible hardware mods, especially if the reference noise is really that bad. Usually the voltage readings near 0 V should be not effected by reference noise, but a reading near to the full scale (e.g. 2 V range, maybe 20 V range) should.

The chip SD ADCs are usually more like good for the lower end 6 digit meters, as the INL can be relatively high. The other problem is the limited range, so that there can be additional gain errors from resistors. So one may get more resolution (low enough noise), but the accuracy is still limited. These SD ADC chips are good for 5.5 digits, and they can even have a good point: the bandwidth for the input noise can be low, as they may not loose time to AZ phases.
 
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #47 on: August 30, 2019, 08:25:57 pm »
Kleinstein> Thanks for your very interresting post !!!

I've intercepted data from the FPGA to get the used protocol.
Now I could convert the raw value into voltage value using the DMM calibration XML.

I've detected the real range of the analog input (VDC mode) :
- 200mV range : -312.33mV to +312.55mV (without ADC overflow)
- 2V range : -2.4984V to +2.5110V (without ADC overflow)

In VAC mode (100Hz sine)
- 2V range : 0 to +5.0356V (without ADC overflow)

Measurements done using Rigol DG4102 (as a DC voltage generator) and UNI-T181A (as a voltage measurement)

The VDC mode uses 23bits and 1bit for the polarity (sign)
The VAC mode uses 24bits but within a range from 2^23 to 2^24-1 (like 23bits)
The resistance mode (2W and 4W) uses the same limitation as VAC mode (23bits)

I'm also working on 2 mods in parallel : power-supply low-noise preregulation (plug and play) and multiple LTC6655BHLS8-2.5 chip for the voltage reference (need soldering).
« Last Edit: August 30, 2019, 09:10:30 pm by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #48 on: August 31, 2019, 02:58:58 am »
It was hard to do but now I could access to ADC raw data.

Done :
- Read keyboard state
- Access to display
- Read ADC raw data

To do :
- Control capture mode
- Speaker
- External trigger
- VMC Output



 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #49 on: August 31, 2019, 08:20:08 pm »
I've done the investigation of the 20V VDC range... It's very funny :
-31.25V to +31.25V (without calibration)

 

Offline Nornand

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #50 on: August 31, 2019, 08:52:04 pm »
Gainsetting seems to be 8 for the PGA.
Vref/8=0.3125V
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #51 on: September 01, 2019, 02:04:09 am »
Yes the PGA is used... Shame.
The DMM is not an internal 240.000 points because it's possible to have up to 312500 points.

I've done a continuous decimation with a sinc function over 4096 samples captured with speed=FALSE. The result is similar to the speed=SLOW with 30sec statistics.
I confirm the fact that it's possible to have a super fast (with a low resolution) bar meter and a high precision (slow) display number simultaneously.

I'll try to enable a more faster tranfert between ADC, FPGA and ARM (4800SPS). I'll need to check if the current onboard Linux is compatible with critical realtime processing (or change to another Linux).

I've found the LT6657 voltage reference... Better than the LT6655...
Probably a stupid idea (or not) : If I'll build a LTZ1000AH voltage reference to supply multiple LT6657A-2.5. Does the final output voltage have a lower drift than a standard low-noise 5V voltage regulator powering multiple LT6657A-2.5 ?
« Last Edit: September 01, 2019, 02:12:39 am by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #52 on: September 02, 2019, 03:44:38 pm »
A standard 5 V regulator (if not getting too much heat and variable current) is good enough to supply a LT6655 or similar reference. The next step up would be a bootstrapped supply - though it should not be needed here.

In many aspects the LT6657 is not better than LT6655 (especially the LS8 version). Both are lower noise than the max6325, but the TC may be higher.
The big weakness of all these reference is not so much the noise, but the drift, hysteresis and sensitivity to humidity. So the difference between the MSOP and LS8 case may be significant.  Anyway for a 5.5 digit meter they should be good enough.
As the ADC needs the 2.5 V reference level, there are not that many better references to choose from. Several in parallel help with noise, but only little with long term drift rate.

The other limitation of the DMM design is that it is only +- 2.5 V (may be a little more, but not much) with high impedance.
So there are limitations to the design, that can not be circumvented.
 
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #53 on: September 02, 2019, 08:07:59 pm »
The LTC6655 (LTC6655BHLS8-2.5) and LTC6657 (LT6657AHMS8-2.5) have a better long term drift than MAX6425 after more than 1000Hr and the noise is lower : the ADC used does not like the noise into its reference.
It's possible to use a LTZ1000A into the SDM3055 with a programmable voltage divisor (based on Vishay high precision low drift resistances). It's simple to do.
I study all possibility : After some little modifications on the device, I would like to know what level of precision it is possible to reach.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #54 on: September 04, 2019, 07:26:46 pm »
A standard 5 V regulator (if not getting too much heat and variable current) is good enough to supply a LT6655 or similar reference. The next step up would be a bootstrapped supply - though it should not be needed here.

In many aspects the LT6657 is not better than LT6655 (especially the LS8 version). Both are lower noise than the max6325, but the TC may be higher.
The big weakness of all these reference is not so much the noise, but the drift, hysteresis and sensitivity to humidity. So the difference between the MSOP and LS8 case may be significant.  Anyway for a 5.5 digit meter they should be good enough.
As the ADC needs the 2.5 V reference level, there are not that many better references to choose from. Several in parallel help with noise, but only little with long term drift rate.

The other limitation of the DMM design is that it is only +- 2.5 V (may be a little more, but not much) with high impedance.
So there are limitations to the design, that can not be circumvented.

You're right ! Using the LT6657 will provide lower performance than the LT6655 (LT6655BHLS) with the AD7190.
So what to do ?
1. I could try to use up to 6x LT6655 ? (with a thermal isolation)
2. I could try to use up to 4x LM399A ? (but with a voltage conversion adding drift and low pass filter)
3. I could try to use one LTZ1000A ? (like LM399 with a similar voltage conversion adding drift and low pass filter)

Don't know what to do...
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #55 on: September 04, 2019, 08:40:41 pm »
The rest of the DMM (like gain stage and input divider - already used for the 20 V range) are still more suitable for 5.5 digits. So there is limited use in replacing just a a few points and hope to get much better performance.
It starts with having high impedance up to some 2.5 V only.
At some point is would be more like building your own DMM from scratch.

So I would consider anything more like a single LT6655 (with maybe some simple thermal regulation) overkill. 
The main advantage of an LM399 would be better long term stability - still needs a very stable divider stage. It would also mainly help the 2 V range. The divider (+ buffer)  from a 7 V level down to a 2.5 V (maybe 3.5 V ?) level is probably more tricky than the LTC6655.
One also has to keep in mind that the power supply and thermal design may not allow much more power.

A change in the HW would mainly make sense if there is a simple, easy upgrade possible because of something like a design fault (could be a cost driven decision)  causing an isolated weak spot. Not sure if there is one such weak point -  chances are multiple source of similar size add up.

So a first point would be an in depth analysis of the performance of the original hardware. So how much of the noise is due to the input amplifier, possibly the input buffer, the ADC and the reference ?
For the drift this is more tricky as the result is valid for the one unit only.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #56 on: September 05, 2019, 06:19:27 am »
The rest of the DMM (like gain stage and input divider - already used for the 20 V range) are still more suitable for 5.5 digits. So there is limited use in replacing just a a few points and hope to get much better performance.
It starts with having high impedance up to some 2.5 V only.
At some point is would be more like building your own DMM from scratch.

So I would consider anything more like a single LT6655 (with maybe some simple thermal regulation) overkill. 
The main advantage of an LM399 would be better long term stability - still needs a very stable divider stage. It would also mainly help the 2 V range. The divider (+ buffer)  from a 7 V level down to a 2.5 V (maybe 3.5 V ?) level is probably more tricky than the LTC6655.
One also has to keep in mind that the power supply and thermal design may not allow much more power.

A change in the HW would mainly make sense if there is a simple, easy upgrade possible because of something like a design fault (could be a cost driven decision)  causing an isolated weak spot. Not sure if there is one such weak point -  chances are multiple source of similar size add up.

So a first point would be an in depth analysis of the performance of the original hardware. So how much of the noise is due to the input amplifier, possibly the input buffer, the ADC and the reference ?
For the drift this is more tricky as the result is valid for the one unit only.
You're right, it's possible to use a 5V voltage reference but I need to check if this voltage is compatible with the analog input (AD7190 is compatible).
It's also possible to change the ADC... But I don't want to do this.
I'll need to check the noise from the input to the ADC (I'll need to build a LF amplifier probe).

I've also successfully set to 4800Hz the ADC and done a sinc filter to enhance the final resolution, the result is better than the original "Speed - Slow" (or 5 SPS)

« Last Edit: September 05, 2019, 07:18:25 am by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #57 on: September 05, 2019, 09:14:32 am »
I don't think a 5 V reference would be practica, as it's too far of the original 2.5 Vl. However a 3 V or 3.5 V (7 V / 2) ref. level could be working.

For checking the noise source, much can be done with the meter itself, reading data and look at the noise under different conditions. With s short, there should be no reference noise (at least not the normal one). With high gain in front chances are the amplifier noise would be dominant.
With the SD ADC there is however the ADC internal "gain"  (Usually actually only more frequent input sampling), that can make the analysis more complicated.

Is there an analog gain stage, or are they only using the ADC internal PGA stage for the 0.2 V range ?
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #58 on: September 05, 2019, 07:13:03 pm »
It's possible to use a +5V voltage reference with the AD7190, but with the design of the SDM3055, I don't know...

Using VDC mode :
- 200mV - PGA = x8
- 2V - PGA = x1
- 20V - PGA = x8
- 200V - PGA = x1
- 1000V - PGA = x1

When I finish the logic analysis, I think I'll do an in-deep inspection of the analog part, and do lots of measurements.

At the moment I'm having trouble understanding the measurement of resistance of very large values (10M to 120M).
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #59 on: September 05, 2019, 09:32:10 pm »
For very large resistors a common method is to add some resistance like 10 M in parallel. This allow to measure very large resistors, though with reduced accuracy and a nonlinear function to convert from the raw reading to resistance.
As the SDM3055 is more like a budget instrument, I would expect this method.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #60 on: September 06, 2019, 09:17:31 am »
For very large resistors a common method is to add some resistance like 10 M in parallel. This allow to measure very large resistors, though with reduced accuracy and a nonlinear function to convert from the raw reading to resistance.
As the SDM3055 is more like a budget instrument, I would expect this method.
Yes, I've tested multiple methods without the correct results (I need to find the exact value displayed by the original DMM software). I continue my investigations.
 

Offline Nornand

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #61 on: September 06, 2019, 10:46:39 am »
Datasheet says
Range:  100 MΩ              200 nA || 10 MΩ

 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #62 on: September 07, 2019, 03:01:28 am »
Datasheet says
Range:  100 MΩ              200 nA || 10 MΩ
Yes it's a current generator.
But I could not find the exact result.

Edit: I think I've found it... I need to do multiple checks.
« Last Edit: September 09, 2019, 08:35:16 am by alexvg »
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #63 on: September 13, 2019, 02:30:46 pm »
I've finally found 2-wire and 4-wire measurement method.
I'm working to found how calibration work...
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #64 on: September 14, 2019, 07:47:45 pm »
I'ts ok !!!
I've successfully found the method used for 2-wire and 4-wire resistance measurement.

I've discovered 2 problems with 2-wire and 4-wire 100M measurements :
- I've measured 144mV p-p 50Hz at the input of the ADC (with open input but with LO/Losense shorted)
- The XML calibration is not fully used : 0-50M segment is used for 0-120M and 50-120M is not used at all !!!

A interresting information :
- I've success fully generate a 0V ADC input with 0x800000 output data (with +/-1LSB precision during more than a minute- 7FFFFF to 800001)

I've done my measurements with :
- 10K to 130M with 0,01% 0,1% or 1% resistance value (for 2-wire and 4-wire)
- I use a Rigol DG4102 with filtered output and 20dB or 40dB attenuation for simulate resistance (only 4-wire)
« Last Edit: September 14, 2019, 07:59:04 pm by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #65 on: September 14, 2019, 08:15:00 pm »
It is not a surprise to find some hum for the high resistance values. Normally the high Ohms ranges should use relatively high voltage ranges. Here this seem to be the 2 V range. It may take some shielding to get good readings. Ideally the DMM would detect if there is too much AC background (e.g. to cause clipping in peaks).

144 mV_pp is not too bad, less than some 5% for the full range.  For a good measurement one may need to use a shield to keep hum away and maybe avoid using long unshielded cables.

For the 10 M range 4 wire Ohms measurement does not make much sense.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #66 on: September 14, 2019, 10:57:45 pm »
It is not a surprise to find some hum for the high resistance values. Normally the high Ohms ranges should use relatively high voltage ranges. Here this seem to be the 2 V range. It may take some shielding to get good readings.
The voltage range could go up to 2V, it's current generator of (around) 200nA

For the 10 M range 4 wire Ohms measurement does not make much sense.
I think you're right :
- Right because it's a nonsense to mesure high resistance value.

But I need to add something I'm thinking :
- Using a 4-wire cables it's possible to use shielded cables and differential input (for sense wires) for a more precise measurement.
But I could be wrong with this, I'm not sure (never tested, never simulated...)


I've also notice a strange math simplification inside the original software :

You could write :
f1(x) = 1/(1/x)
f2(x) = x
It's okay to say f1(x) = f2(x)
But it's false for a CPU !

Original Siglent Software uses a function like f1(x) that could cause a "divide by zero". But without simplifying the function, it's possible to avoid the "divide by zero" like f2(x). I don't understand why Siglent have done this...

 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #67 on: September 15, 2019, 07:49:53 am »
The capacitive coupled mains hum during the high ohms measurement is present at the DUT and the hum is thus directly added to the voltage to measure.  So a differential measurement does not help here. The main things that helps is the usually good suppression of mains hum by the ADC, because it is integrating over a multiple of mains periods.
Shielding for the high ohms measurement can be tricky, as there may be more leakage. Some high end DMMs offer a special driven shield for ohms shielding, that reduced the voltage over the isolation and also help a little with settling.

I sometimes makes sense to measure high resistors, but in the MOhms range one does not really care about cable resistance and could thus use a 2 wire measurement.  Some meters only offer 4 wire Ohms for the lower ranges.

Using only 2 wire ohms reduces the cables to 2 and thus less leakage and less surface to pick up . So there is a point at high resistors when 2 wire ohms is more accurate than 4 wire ohms. It is not just the external leakage, but also leakage at the input protection.

 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #68 on: September 16, 2019, 09:28:37 am »
Measuring using 100M range with this device is a joke (using 4-w and 2-w).
The precision is awful (even with 50 and 60Hz filter)
« Last Edit: September 16, 2019, 10:51:28 am by alexvg »
 

Offline Kleinstein

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #69 on: September 16, 2019, 03:19:09 pm »
The accuracy gets worse with high resistors already due to leakage and bias currents (e.g. at the protection). With only a 2 V range (compared to often 5-10 V for other 6 digit DMMs) this also makes things more tricky. 4 Wire resistance is likely worse than 2 wire. The 100 M range is about 10 times less accurate than the 10 M range as there is the 10 M in parallel and thus only a relatively small change used.  Anyway getting 1% or so accuracy is not that bad with such high resistors.

A really accurate measurement would need a special instrument, more like an electrometer. This usually is with applying a fixed (e.g. 20 V or 100 V) voltage and than measure the current. This also need shielding and special, short cables. Also touching the resistors with the hand can change things from contamination.
 

Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #70 on: September 16, 2019, 07:02:15 pm »
My Applent AT2816 is more precise for high value... But it's a specific device.

I ve done 2 simple tests (with 2-wire and 4-wire)
- a 110M resistance measurement with 4-wire display 111,7M to 112,5M over a minute
- a 110M resistance measurement with 2-wire display 111,84M to 111,87M over a minute



A funny thing I see each time...
Code: [Select]
===============================================
|SIGLENT SDG800 project        /dev/pts/0
===============================================
SIGLENT Project http://         (none)
(none) login: root
Password:

Processing /etc/profile... Done
(SDG800 app and data are present inside the SDM3055 firmware)
« Last Edit: September 16, 2019, 07:04:19 pm by alexvg »
 
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Offline alexvg

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Re: Hacking the Siglent SDM3055 Bench DMM
« Reply #71 on: September 18, 2019, 05:53:06 am »
I'm currently working on the frequency counter... It works up to 2,2MHz... Very limited ! My UNI-T181A (half the price) works up to 60MHz.
 


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