1 / 10

Data Acquisition

Data Acquisition. Seth Price Department of Chemical Engineering New Mexico Tech Rev. 10/9/14. Resolution. Resolution: the smallest “y” step measurable by measurement system Resolution is related to the number of states (and thus number of bits). Sampling Rate.

teegan-ayala
Download Presentation

Data Acquisition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Data Acquisition Seth Price Department of Chemical Engineering New Mexico Tech Rev. 10/9/14

  2. Resolution • Resolution: the smallest “y” step measurable by measurement system • Resolution is related to the number of states (and thus number of bits)

  3. Sampling Rate • How fast a system collects data • Generally expressed in Hertz, Hz • Means how many times a second • Trade off when choosing sampling rate • Sampling too fast -> generating larger files, some “useless” data, expensive hardware • Sampling too slow -> miss short-lived events, aliasing

  4. Aliasing • Consider a 10 Hz waveform sampled at a few different sampling rates:

  5. Nyquist (or Sampling) Theorem • MUST sample at a rate that is greater than twice the highest frequency you will see in the system to avoid aliasing S > 2*fm

  6. DAQ In LabVIEW • Using DAQ Assistant Express VI: • Handles much of the low-level configuration for you • Much easier than traditional DAQ • Does not work on all equipment • Can be the source of problems

  7. DAQ in LabVIEW • Place a DAQAssistant Express VI on the block diagram • Select whether you will be generating a signal or acquiring a signal • Select the type of signal (voltage, current, etc.) • Select the physical channel

  8. DAQ in LabVIEW • Choose a Sampling Method • For this class, choose “On Demand” • Choose a Grounding Method • For this class, choose “Let NI Choose” • Test in DAQAssistant Window • Press “OK”

  9. Data Conversion • LabVIEW uses a data type called “Dynamic Data” when interfacing hardware • We want a number (in this case), so we must convert it

  10. Data Conversion • For “Acquiring Signals”, use “From DDT” • On the popup menu, select “Single Scalar” • For “Generating Signals”, use “To DDT” • On the popup menu, select “Single Scalar”

More Related