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SIGNAL/RTS APPLICATION NOTES

2 Application Note 11

Transferring Data between SIGNAL and MATLAB

Following is a discussion of the SIGNAL and MATLAB commands used to exchange data

files between the two programs. Note that SIGNAL files can be stored in two data formats -

integer or floating point - and two header formats - SIGNAL file header or headerless. See

the chapter "File Storage and Exchange" in the SIGNAL User Guide for background. The

basic strategies for file exchange are: 1) export data from SIGNAL in SIGNAL-header files

and let MATLAB skip over the SIGNAL header and 2) export data from MATLAB in

headerless files, supplying the essential file parameters when importing into SIGNAL.

Exporting integer SIGNAL time files to MATLAB

SIGNAL time buffers which have not been manipulated after acquisition can be transferred

without loss of precision by using integer format, which stores the exact values delivered by

the A/D converter.

SIGNAL-header integer files

SIGNAL-header integer files are read in MATLAB by skipping the header and applying a

data conversion factor.

1. Write the SIGNAL time buffer to a SIGNAL-header integer time file using the /I flag:

>W T 1 /I

Filename: IFILE

2. Read the file into a MATLAB array. The following MATLAB commands will read the

entire integer file IFILE into the array A. FSEEK skips the 1024-byte SIGNAL file header.

fid = fopen ('ifile','rb');

fseek(fid,1024,'bof');

A = fread (fid,inf,'int16');

3. SIGNAL-header integer files are stored in the native coding of the A/D converter (unlike

headerless integer files - see below). 12-bit SIGNAL A/D boards produce data with an offset

of 2048 and a gain of 2048 bits/10 Volts, while 16-bit SIGNAL A/D boards deliver an offset

of 0 and a gain of 32768 bits/10 Volts. See "Import / Export of Binary Files" in the SIGNAL

User Guide. These conversion factors are used to convert the file data to Volts after

importing into MATLAB:

A = (A - 2048.) / 204.8; 12-bit A/D

A = A / 3276.8; 16-bit A/D

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Engineering Design NIDisk Guía de usuario Pagina 26