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SigLab Virtual Instrument Application-Specific Questions
Is the SigLab virtual instrument software an additional expense on top of the hardware?
The following virtual instrument software ships with the SigLab hardware:
- Function Generator
- Oscilloscope
- Spectrum Analyzer
- Network (Transfer Function/Frequency Response Function) Analyzer
- Swept Sine Analyzer
- System Identification (Curve Fit)
- Transient Capture (Data Logger)
- Spectral mapping (real-time waterfall and intensity maps)
- Distortion Analyzer
- Automated Measurements
- Hardware Functional Check
The following software modules are sold separately:
- Octave Analyzer
- Order Tracking
- Machine Balancing
- Discrete-Time State Space Controller
- LabVIEW driver library
How do I access the notes I made with SigLab?
Your SigLab notes are saved in your SigLab setup file in a MATLAB variable called Cmprssd_Notes. For example, if your file is called default.vos, you would do the following:
>> load default.vos -mat
>> mynotes = notefig('un_compress',Cmprssd_Notes)
The M-file responsible for the "notes" figure window is called notefig.m.
Simply type >>help notefig to get more information on the use of notefig.m
How can I generate my own arbitrary waveforms using SigLab?
We have provided several utilities to do this.
I. We provide a small M-file called arbout.m with . It is very short, easy to follow, and even easy to modify should you wish. This command works from the MATLAB command window. We also provide in the vex directory the function playback.m and a demonstration of how to use this function called playdemo.m These functions do not require the vfg.
II. A utility called arbgen.m in the vex directory generates several arb files that can be read and output by the vfg. See Appendix C of the SigLab manual for more information.
III. MATLAB variables can be converted into VCAP (.vca) files using the utility mat2vca.m and then played back through either vcap or vfg. For more information type help mat2vca at the MATLAB prompt.
Recent versions of the SigLab software ship with all of these utilities.
How can I load transient capture data into MATLAB?
There are two methods to get data from the SigLab Transient Capture Buffer into MATLAB:
- From VCAP, save the data as a *.vca file and then use the utility vca2mat.m to read the contents of the file (or a portion thereof) into a MATLAB variable. Type help vca2mat at the MATLAB prompt for more information.
- The utility tbuf2mat.m can be used to go directly from the Transient Capture Buffer to a MATLAB variable. Type help tbuf2mat at the MATLAB prompt for more information.
Is there an easy way to write a MATLAB expression and then generate it using
SigLab?
A small M-file called arbout.m ships with the software. It is very short, easy to follow, and even easy to modify should you wish. This command works from the MATLAB command window.
Does the SigLab system identification application use the MATLAB system identification toolbox?
Not at all. The vid application uses a recursive lattice algorithm. This is explained in considerable detail in the following Application Note: "System Identification: A Practical Tool from a Fiddler's Paradise".
The vid page of this web site also provides some sample screen captures and explanation of the operation of vid.
How is SigLab spectrum information saved?
The auto- and cross-spectrum data is always saved in units of (Vrms)^2 no matter what engineering units were used. The engineering units can be retrieved from the setup
file (e.g. default.vsa) as the MATLAB variables ChanStat and EULabel.
How can I get grid lines to appear in the SigLab virtual instrument windows?Grid line control is a Menu Item Selection in
most Virtual Instruments. In VOS, VSA, VNA and VID, look for it under the Display Menu. In VSS,
SMAP, and VTO look for it under the File Menu.
What do all of the y-axis spectral unit selections mean?
For a full definition of all selections, click here to open yaxisunits1.txt now.
How do I modify the user interface to display sample rates instead of sample period and
bandwidth?
There is a short M-file called fp_list.m in the \vcom directory. You'll need to modify the 'Actions' labeled bw_list (bandwidth list) and per_list (period list) to look like the action Fs_list (sample frequency list).
Here is one clipping out of fp_list with the modification.
- elseif strcmp(Mode,'per_list')
- % string of sampling periods for popup
- for i=1:length(dec_tab),
- %Out1 = put_str(i,Out1,[sec2str(dec_tab(i)/SIGLAB_FS),'/sample']); % original line
- bw = SIGLAB_FS/(2.56*dec_tab(i));
- Out1 = put_str(i,Out1,['Fs = ',hz2str(bw*2.56)]); % modified line
- end;
How does SigLab compute transfer functions?
The transfer function is computed by taking the ratio of the cross-spectrum between the excitation and response channels and dividing this by the auto-spectrum of the excitation channel. This is a standard method in use for over the last 25+ years.. Please review the application note: "Estimating Transfer Functions with SigLab" for full details.
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© Copyright 2002 Spectral Dynamics Inc.
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