understanding absolute accuracy spec of USB-6216

[echemist]

Hi,

I am looking at the AI Absolute Accuracy Table for the NI USB-6216 device.  I found this on p. 5 of the NI USB-621x Specifications document.

Question: am I to understand the Absolute Accuracy at Full Scale spec of 2,710 microvolts on the +/-10V range as meaning that 10V applied to this channel will give a reading between 9.99729V and 10.00271V (i.e. 10V +/- the uncertainty calculated as the absolute accuracy) when the assumptions outlined under footnote (1) apply?

Thank you.

Jason

[Diego_Sanchez]

You should be able to use an absolute accurate calculator, which is posted in the community in order to get the real value.

calculator

In the pg 5 of the document that you have, there is an example using a voltage range   of +-10V in the ADC, and the result is 2,710 μV, that means that if you are acquiring 1volt, with this scale, the value is between [0.99999729-1.00000271], remember that, the lower voltage range you use, better absolute accuracy you will have.

How Do I Calculate Absolute Accuracy or System Accuracy?

[echemist]

Hi Diego,

Thank you for your reply and the links to more information.

Just one question - I was trying to follow the sample calculation that you gave for acquiring 1V.  It looks like you added and subtracted 2.710 microvolt from the 1V reading.  But the accuracy is 2,710 microvolts at full scale(10V in this case).  So it looks like using the absolute accuracy eqn on p. 5 of the referenced document, at a 1V reading, the accuracy I came up with was 1521 microvolts, so 1V applied would show between 0.9985 and 1.0015V.  (To get this, I only changed the value of 'Reading' from 10V to 1V in the sample equation).

I guess what I wanted to make sure of is that this 'absolute accuracy' gives the expected span in reading around the actual voltage applied to the input.

Thanks again for the help.

Jason

[Diego_Sanchez]

Hello again echemist, 

Yes you are right, I mistaken the reading value of 1V with 10V, with a reading value of 1 Volt, the absolute accuracy will be 1520.8μV, and that range that you posted is absolutly correct.

Regards

[echemist]

Hi Diego,

Thank you for confirming this for me.  I appreciate it.

Jason