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Hacking the Siglent SDM3055 Bench DMM

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alexvg:

--- Quote from: Kleinstein 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.

--- End quote ---
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.

Nornand:
Datasheet says
Range:  100 MΩ              200 nA || 10 MΩ

alexvg:

--- Quote from: Nornand on September 06, 2019, 10:46:39 am ---Datasheet says
Range:  100 MΩ              200 nA || 10 MΩ

--- End quote ---
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.

alexvg:
I've finally found 2-wire and 4-wire measurement method.
I'm working to found how calibration work...

alexvg:
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)

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