Block Size
- Updated2024-06-07
- 1 minute(s) read
Block Size
When you use NI-DAQmx to control the data acquisition (DAQ) hardware, you must take the block size—in either number of samples or block duration—into consideration.
You can measure the block size either in terms of samples or time as long as the sampling rate is constant.
The following equation calculates the acquisition duration:
T = N * dt
where
T is the acquisition duration
N is the block size
dt is the sample interval
The acquisition duration determines the maximum length of an event that you can measure in a finite acquisition or the time resolution that you can achieve in a continuous acquisition. In a continuous acquisition the duration of each measurement block impacts the rate at which the data acquisition loop must run, the time/frequency resolution of all block-based measurements, and the latency of your DAQ application. The sound and vibration analysis tools in the NI Sound and Vibration Measurement Suite generally check for either time continuity or block size. For example, time-domain weighting filters, resampling, level measurements, octave analysis, zoom FFT analysis, and order analysis require continuous blocks of data even though the blocks do not have to be of equal size. Limit testing, baseband FFT analysis, and subset FFT analysis requires a constant block size but place no restrictions on the timestamp of each block of data.
Related Information
- Methods for Acquiring and Simulating Dynamic Signals
Dynamic signals can be acquired using a DAQ device system or they can be simulated using generation VIs.
- Sampling Rate
The scan rate, or the sampling rate in NI-DAQmx, determines how often an analog-to-digital (A/D) conversion takes place.
- Time Continuity
When you acquire data in a continuous acquisition, you can use the timestamp parameter in the waveform data type to verify no gaps exist between successive blocks of waveforms returned by sequential calls to the DAQmx Read VI or AI Read VI.
- Weighting Filters
The NI Sound and Vibration Measurement Suite provides acoustic weighting filters and human vibration filters.
- Resampling
The NI Sound and Vibration Measurement Suite provides order analysis tools for software resampling that can circumvent the challenges of hardware implementation.
- Level Measurements
A level measurement provides a quantitative description of the overall vibration acquired from a transducer. You can perform sound level and vibration level measurements with time-domain or even-angle signals.
- Fractional-Octave Analysis
Fractional-octave analysis is a technique for analyzing audio and acoustic signals. Fractional-octave analyses, especially 1/3 and 1/12 octave, exhibit characteristics analogous to the response of the human ear. Many industry standards, such as ANSI and IEC, require fractional-octave analysis.
- Zoom FFT Analysis
Zoom FFT analysis achieves a finer frequency resolution than the baseband FFT.
- Supported Data Types for Limit Testing
The NI Sound and Vibration Measurement Suite supports a range of different data types including: waveform measurement, frequency spectrum measurement, XY data, peak measurement, and scalar measurement.
- Baseband Analysis
Baseband analysis involves applying the FFT to each component of a time-domain signal from the minimum resolvable frequency, 0, to the maximum resolvable frequency.
- Subset Analysis
Subset analysis enables you to compute a subset of the baseband FFT measurement.