How does one calculate the current accuracy and the capacitance accuracy from the spec/data sheet for the PXI-4072?

[ndizon@vi]

I believe I calculated the current/voltage/resistance accuracy correctly.  For example, for a reading of 0.1 uA and range of 20 mA I get an accuracy of +/- 20 nA.  Could someone please verify this?

For the capacitance accuracy, what does "% of reading" and "% of range" refer to?  A percentage of what?  Just divide by 100?

Thanks to anyone that is able to help.

Neil

[Elijah_K]

Hey Neil,

The percentage of reading and range are specified in the chart for various ranges.  It can be hard to understand because it's listed under the "2 Year" category as X + Y, where X is the percent of reading and Y is the percent of range. 

For example, consider a reading of 200pF.  You calculate it's accuracy for the worst case scenario, ie: 2 years.  The percent of reading will be .15 and the percent of range will be .5. 

Accuracy = (+/-) [ 200 * ( 0.15 / 100 ) ] + [ 300 * ( 0.5 / 100 ) ] = .45

So your reading will be 200pF +/- .45

Hope this helps!

[Elijah_K]

To answer your first question:

0.1uA is in the 20mA range, so 300 is the ppm of reading and 75 is the ppm of range.

[.01uA * ( 400 / 1,000,000 ) ] + [ 100mV * ( 75 / 1,000,000 ) ] = ( +/- )75nA

so .1uA (+/-) 75nA

[ndizon@vi]

Thank you it makes perfect sense now!