LabView: A Data-Acquisition Package
( Project Lab Writeups |Computer Programs |sample graph )
This page gives details of how to use LabView in the integrated lab. Some general instructions are given, and specific instructions for several experiments are also given. Starter programs for several exjperiments are given.
When the computer boots up, a window entitled "NI-488-2 Getting Started Wizard" may come up. If it does, click on "Verifying your hardware and your software installation." the "488" referes to the IEEE-488 (or GPIB) instrument bus. This aplet will check for a GPIB card on the computer and see if it is working. It also tells you the name given to this interface for programming purposes, probably GPIB0.
When you get back to the Getting Started Wizard, connect the meter or whatever GPIB instrument you plan to use to the interface card via a GPIB cable. Then click on "Communicate with your istrument." Follow the instructions. Under "Devices and Interfaces" you should see "GPIB0 (PCI-GPIB)." If your computer has the National I/O board installed too, you should see "PCI-MIO-16De=4 (Device 1)" too.
Now (following instructions) scan for instruments on the GPIB bus. This may be more or less successful. For instance, with the KiethelKiethley 197 DVM, the presence of thsan instrument and its address were recognied, but an identification string was not successfully received.
Next try to "Communicate with the Instrument." The bvarious tools available for setting up GPIB instruments are to be found with the Windows Explorer at c:\Program files\National Instruments\NI488-2\Bin.
  1. Belly up to a computer .
  2. Make yourself a directory in your name, where you can store data, programs, etc.: 
    	c:\usr\schmuck
    or 
    	d:\usr\hero

    

  3.   Make a sub-directory, named "gaussian."

  4.   Enter

    	MINSQ

    
or, from Windows, double-click on the MINSQ icon.


       The fitting program will load and execute.  The following instructions 
are for MINSQ version 
4.02.  There is a later version, much more menu driven and mouse 
oriented.  It is harder to use, 
though.


  5. Go through "Utilities" to "Misc," and set "default directory" to where
you want your 
files to be stored, e.g., c:\usr\noah\gaussian\  . 
Otherwise when you save data, parameters, etc., 
you will have a terrible time finding them afterwards.


  6.   "Get model," "define model."  This defines the formula that will 
be fit to your data.  
(When you have a model file saved, you can use "retrieve model"
instead.)  Names are given to 
the variables and parameters.  Here is what you should enter:

            independent variables:        FK
        dependent variables:          FN
	parameters:                   FNTOT, X, SIGMA	
	equations:
        	pi = 3.14159
		fnwide = 1.	Width of the bins of your histogram.
		fact1 = 1./(sqrt(2.*pi)*sigma)
		fact2 = exp(-(fk-x)^2/(2.*sigma^2))
		fn = fact1*fact2*fntot*fnwide

    
These equations represent the form for the general Gaussian, as given in
the writeup for lab B2,
but multiplied by a parameter, fntot, which changes the normalization.
FNTOT should come out to 
be equal to the total number of entries in the histogram, if the 
fit is good.



       Enter two returns to finish entering the model; it will be compiled.
Now do "model compile."  
If the compilation works, without errors, save the model as the file 
d:\usr\schmuck\gaussian\gauss.eqn .

  7.   "Get parameters," "enter parameters," then enter initial guesses for 
the three 
parameters.  When done, "save parameters" to the file 
d:\usr\schmuck\gaussian\gauss.par .

  8.   Now enter the data.  I give a sample set of data below; you may
want to enter it in, just to make sure the program is working.  Then you
would enter in your data.
  "get data," "enter:"

    	9. 	 3.
	10.	25.
	11.	132.
	12.	111.
	13.	19.
	14.	6.
	15.	1.  

    You could read in a data file from disk if you wanted to.  It should 
start with a line with the 
variable names:

    	FK  FN

    
and it should end with the line

    	ENDDATA

    

  9.   Do the fit:  "calculate," "least squares."  For the data given, you should find:

    		chi-squared = 46.381
		FNTOT = 288.21
		x = 11.411
		F = 0.75806

    
(The numbers for your data will be different, of course.)


       Now let the program determine the errors:  "statistics," "90%," etc.
For the data given, the 
errors on fntot, x, and F are 7, .02, and .02, respectively.

  10.   Get a graph of the fit:  "graphics," "draw plot," "printer output."  
Get two.

  11.   Graphics File Conversion.  There are (at least) two ways to
convert the graph of your data on the screen into a computer file.

      

    • To make a PostScript file to use in LaTeX, go to plotter setup and 
configure the 
"Apple Laserwriter" option to write to a disk file.  FTP this file 
to stars, and you can incorporate 
it into a paper.

    • To convert to a file which you can post on your web page, follow the
following steps:

        

      •  MINSQ should be running under Windows 3.11, in a separate window.
If it is running in full-screen mode, press Alt-Enter to go to window
mode.

      •  Now copy the window to the clipboard, by pressing Alt-PrintScrn .

      •  Open Paintbrush, and Paste in the contents of the
clipboard.  

      • Save as a file in .bmp format (256 colors is certainly
good enough).  Ideally, connect over the network to your stars
file system, and save the file directly to your web-page directory.

      •  If you saved the file locally, now either FTP the file to your
account on
stars, or connect over the network to your stars file
system, and just move the file over using the File Manager.

      • Using one of the computers in TH 117, convert this file 
to .jpg or .gif format, using 
Lview or some other program.  Here is an 
example of the result.