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I need to find the time difference between two pulses that are generated by my circuit. For this, I need to know how reliable the time stamps are in data collected from the NI ELVIS DAQ Board (i.e. if I sample data at 1kHz, how sure can I be that the delta t between two data points is 1 ms) ?
Are you using ELVIS I or ELVIS II? If you are using ELVIS I, the specs will depend on which DAQ card you are plugging into. With ELVIS II, the DAQ is built-in, so the specifications are available in this manual: http://www.ni.com/pdf/manuals/372590b.pdf which specifies that the timing accuracy is 50 ppm. If you are not familiar with ppm used to describe clock accuracy, I recommend looking through this article: http://www.best-microcontroller-projects.com/ppm.html. One caveat to keep in mind is that the sampling rate that you specify will be generated by dividing down the internal base clocks. Therefore, the sampling rate you specify should be an integer multiple of the internal timebase (ELVIS II has a 0.1, 20 and 80 MHz timebase). Otherwise, the DAQ will just round to the nearest sampling rate that can be derived by dividing the internal timebase by an integer value. See this document for more information: http://digital.ni.com/public.nsf/allkb/4BBE1409700F6CE686256E9200652F6B.
