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# Multifunction DAQ

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## which card to go?

Hello everyone,

I am a newcomer to DAQ and have some concerns about choise of DAQ card. Here is two options:

Model 1: NI 6132 S series, 2.5MS/s; 14bit; minimal voltage range is 1.25V.
Model 2: NI 6289 M series, 250kS/s; 18bit; minimal voltage range is 0.1V.

Above sampling rate has taken multichannel into account.

Here is my thinking.
LSB of NI6289 is 0.38uV, while NI6132 is 76uV, but with 10 times more data to average to reduce noise.
If I have one signal at 100uV, within 1ms I get 2500pts from NI6132, or 250pts from NI6289, which one will be more accurate? which one is less noise?

Thanks.

sipher

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## Re: which card to go?

I am not sure if I calculated it correctly. What I understand is LSB = (Voltage range)/2^(bit).

I also tried to do some calculation following the decription of absolute accuracy in your data sheet. What I got is:

NI6132: AbsoluteAccuracy at 1.25V is ~ 700uV

NI6289: at 0.1V is 30uV.

I know that it is not fair to compare since they are at different voltage range. So my basic question becomes: is NI6132 good to measure signal ~ 100uV (or lower) accurately compared with NI6289?

Thanks.

sipher

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## Re: which card to go?

Hello SiPHER,

The formulas for calculating absolute accuracy and the necessary constants are listed in the Specifications sheet for each board.  For example, page 4 of the 6132/6133 Specifications document and pages 4 and 5 of the 628x Specifications contain tables with this information.  The tables list a value for "Absolute Accuracy at Full Scale" which corresponds to the accuracy achieved when taking a measurement of the maximum voltage for a given range.

If you want to calculate the accuracy for a particular reading other than the full-scale voltage, you can use the formulas listed in the table for this purpose.  I did a quick calculation for a voltage reading of 100 uV on each board, and I got the following results:

6132 - Absolute accuracy at 100 uV (1.25 V range):  358 uV
6289 - Absolute accuracy at 100 uV (0.1 V range:  13.6 uV

You can also use the Accuracy Calculator on our website to find the same results for certain boards.  Based on these results, I would recommend the 6289 for your application.  I hipe this information helps.

Best regards,
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