NI-6363 USB and DAQmxCreateAIVoltageChan

[choa974]

Hello,

I have a question regarding the "DAQmxCreateAIVoltageChan" function (NI-DAQmx). For input parameters, the documentation indicate "minVal" and "maxVal" which are respectively the expected minimum and maximum value that we expect to measure. In my Labwindows application, I configured minVal and maxVal respectively to -0.5 and 0.5 (Volts), and during the acquisition some measures have exceeded 500mV (until 522mV), these measures do not "seem" to be in a saturation range and appear valid. So, my question is when the user indicates 0.5(V) for maxVal, what is the real maximum value that we can measure without reach the saturation? Can we trust the values superior but close to 0.5V?

One possibility could be to increase the input range to +/-1V, but for our applications, the objective is to keep the absolute accuracy of the nominal range +/-0.5V. The device we use is a NI-6363 USB.

Thanks in advance.  

[Kevin_Price]

My gut-level advice is that you better approach your trust in specs consistently.  If your driving motivation for wanting the +/- 0.5 V range is due to the trusted absolute accuracy specs, then you'd better also trust that those specs won't apply to any measurements you make slightly beyond the borders of that range.

I'd also compare the +/- 1.0 V range accuracy specs to your real-world noise floor before getting overly reluctant to use that range.  I realize that noise level doesn't *equate* to inaccuracy, but when you consider how data is collected, processed, and used in decisions, noise will often limit the practical usefulness of pure accuracy.

-Kevin P

[choa974]

Ok. Thanks for your advice and your reply.