PXIe-4081 accuracy calculation

[ZiadAlkhoury]

Good Morning,

   I have been trying to calculate the accuracy of the DMM PXIe-4081 with the resistance 4-wire measurement , 7 1/2 digits resolution , 100 OHM range and the resistor the I am reading is 0.5 mOHM. The number that I am getting is blowing my mind and it does not make sense at all specially this should be the most accurate DMM in the industry. I am getting 1.2 mOHM. I am pretty sure that I am missing something with my calculations. Any help please  

[aeastet]

Did you look at this document? It should give you everything you need to know about this device:

https://www.ni.com/pdf/manuals/375254d.pdf

[ZiadAlkhoury]

Yes sir,

  That is why I feel that I am doing something wrong with my calculations somehow and I wanted a second look at the thing.

Please and thank you 

[aeastet]

Why are you not using the numbers provided in the specification from NI? Do you think they misjudged or miscalculated something?

[ZiadAlkhoury]

Do you mean these numbers ?

These numbers are to calculate your accuracy right?

I am using them to calculate my accuracy while I am reading a 0.5 mohm with 100 ohm range  

[GerdW]

Hi Ziad,

what do you expect when trying to measure a 0.5 mOhm (or 0.0005 Ohm) value with a 100 Ohm range? That's just 0.0005% (or 50ppm!) of the measurement range!

So what do you expect when the DUT signal is in the same range as the accuracy specs?

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@ZiadAlkhoury wrote:

this should be the most accurate DMM in the industry.

Yes, that might be the case. But it's "just" a generic DMM - and apparently no device specifically made for measurement of very small resistance values.

There are other devices for this kind of measurement! Have you ever looked for "microohmmeters"?