Larson Davis HVM200, Справочное руководство

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HVM200 Reference Manual Downloading Data 3-11
3.3.1 Working with RAW Data Files
TAKE NOTE
The RAW data is not frequency weighted, not integrated if integration
is selected, and includes a DC bias. However, all of these factors can be added
after the code is parsed.
The analog converter outputs a raw data file. This is a binary file that
contains raw data samples in a float format for the x, y, and z axes after
sensitivity has been applied. The samples represent scaled ADC
samples in m/s
2
with a DC bias. Each sample contains 12 bytes in the
following format:
The byte order within each float is little endian.
You can create raw data files with each measurement if you checked
Store Raw Data
in the Setup File. For more information, see 3.1.2
Selecting a Setup File by Using Your Mobile Device . While the HVM200 is
connected to G4, you can download a raw file from the Data Manager
tab. This file will always be much larger than an HVM file.
FIGURE 3-12
Raw Data File
In order to work with a raw file, you will need MATLAB, GNU Octave, or
similar program. The following script can be used to parse the data.
Consider the following items when using the script:
• You must adjust the file name to match the file name of your raw
file.
• Remove the DC bias from data.
• After the file is parsed, you can adjust the weighting filters for
hand/arm or whole body vibration purposes. For more
information, see 3.3.2 Weighting Filters for Raw Data .
Raw Data Script
%% Example Matlab / GNU Octave code for parsing HVM200 raw data format
close all ; clear all ; clc ;
%% Number of Samples to read
Sample_Rate = 7161.45833 ; % Hz (Hard wired sample rate)
Sample_Time = 10 ; %second
num_samples_to_read = Sample_Rate * Sample_Time ;
%% Open file, Read, Close
Byte 0 1 2 3 4 5 6 7 8 9 10 11
Definition X Axis Sample Y Axis Sample Z Axis Sample
TAKE NOTE
If using GNU Octave,
the bi-linear function takes
period instead of frequency as
a parameter. Wherever used,
replace:
fs
with
1/fs