NI PXI-4070 DMM Resolution

[Oren_Y]

Hi,

I am trying to understand the number of bits of NI PXI-4070 DMM.

At the NI PXI 4070 its written that 6.5digits resolution is equal to 22 bits.

I did my calculation:

6.5digits DMM has 2M available counts(levels), so the number of bits equals to log2(2M)=20.9bits.

The specified bits is 22 bits which correspond to 2^22 levels=4.19M levels.

I would appreciate any help understanding this difference, between my calculation which yields 20.9bits(2M levels) and the 

specified value 22bits(4.19M levels).

Thanks,

Oren Y.

[patrick.o]

Oren,

Thank you for posting to our forums. The equation we use for calculating the number of digits of resolution for our multimeters is:

Digits of Resolution = log10 (Number of Least Significant Bits), where the Least Significant Bits (LSB) is the number of 'levels' available at a given resolution.

Doing the math, at 22 bits of resolution (2 ^22 LSB), you will get approximately 6.62 digits of resolution. We tend to be conservative in our accuracy specifications, and because digits of resolution traditionally represented actual digits on a desktop multimeter, we have rounded down and listed the digits here as '6.5' in the specification sheet rather than '6.62'. 

You can find more information as to our multimeter resolution specifications in the Help article below:

NI Digital Multimeters Help - Resolution

http://zone.ni.com/reference/en-XX/help/370384T-01/dmm/resolution_bits_digits/

I hope this was helpful!

[Oren_Y]

Thanks Patrick.

I understand that 6.5digts is approximately 22 bits of resolution which equals to 2^22 LSB.

Please help me understand the resolution for 6.5 digits which is in the below table and also at the NI DMM Soft Front Panel.

For 10V range (Total span=20V) it is specified that the resolution is 10uV.

I tried to calculate this resolution value using the following math:

Resolution=20V/(2^22)=4.7uV.

It is seen that the specified value used a different calculation , please help me understand the calculation which yields 10uV.

Thanks,

Oren Y.