Why Does the niScope Fetch Measurement.vi Take So Long to Process? Primary Software: Driver Software>>NI-SCOPEPrimary Software Version: 3.2 Primary Software Fixed Version: N/A Secondary Software: N/A Hardware: Modular Instruments>>High-Speed Digitizers (Scopes)
Problem: I am acquiring a large record to my digitizer's onboard memory and then fetching chunks of data out using niScope Fetch Measurement.vi. However, even when I place a very small number into the Meas Waveform Size input the VI takes a very long time to process. This time seems to be directly related to the size of the record and not the value I place in Meas Waveform Size. What is happening? Solution: Whatever measurement has been selected is being applied to the entire record and not to the Meas Waveform Size input. There are two solutions to this problem: 1) Reduce the record size. However, this may not be practical for a long, sustained acquisition. 2) Use the Fetch Measurement Number of Samples property located in the niScope Property node under Fetch>>Fetch Meas Number of Samples. Choose to write to this property and feed the same value to this property and to the Meas Waveform Size input of the niScope Fetch Measurement.vi. This property node is circled in red in the screenshot attached below. Without this property node, an FFT would be performed on the entire 134 MB record rather than the 1 kB chunk that is being fetched. Note that if niScope Fetch.vi is used (instead of niScope Fetch Measurement.vi) there is no corresponding property node that needs to be used. Related Links: High Speed Digitizers Main Page KnowledgeBase [42JEC1OY]: What NI-SCOPE Signal Processing/Conditioning Occurs in Hardware Versus Software? Where Does Filtering Occur? Attachments: 
Report Date: 10/26/2006 Last Updated: 10/27/2006 Document ID: 42PAJAOY |
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