  ** LMS Impedance Bridge ** 

* Set Mixer. You need to set the mixer  controls for your sound card.  Mixer software for the sound card is already
installed on your system by  Windows.  The mixer has a Play and Record section.  You need to adjust the Volume out
control and Spkr (or wave) to maximum in Play and the "line in" to max in the Record sections.  Mute all others. Also set
 the stereo Balance sliders to the center position.  If your mixer has a record gain option, set it to a gain of one.   If these
 setting are changed between uses of the program, they will need to be reset as described here to maintain accuracy.
 See calibration below for more info.  Also see the Readme file. 

* Start Buttons.  This causes the program to initialize the sound card for capturing data. Start1 does a single capture while
 Start2 captures continuously.

* Stop Button.  This stops the process that began with the Start2 button.  It is good practice too stop capturing before changing
 any parameters.

* Oscilloscope. L Ch and (R-L) Ch control the gain of the left and right channels for display only.  The actual captured data
 is not affected by these settings.

* Reset Clears the internal data array. Used for debugging only.

* Time Base.  This control selects the time scale used for display of data.

* Tare. To find Ctare use Rm=100K and Z open.  To find Ltare and Rtare let Rm =10 and Z=0.

* Cursor.   Clicking this box enables the cursors.  There are two cursors for the normal data vs time displays  The left button
of the mouse selects the measurment cursor. The right mouse button selects the other cursor. Time or frequency is
measured between the two cursors.

* Calibration Of System.

 First you need to set the mixer line input control for your sound card.  Mixer software for the sound card is already installed on
 your system by  Windows.  The mixer has a Play and Record section.  You need to adjust the Volume control and the
 Spkr (wave) to maximum in both the Play  section and the Line out to max in Record section.   Mute all others. Also set the
 stereo Balance sliders to the center position.  If your mixer has a record  gain option, set it to a gain of one.   If these setting
 are changed between uses of the program, they will need to be reset as described here to maintain accuracy.  See SB
 example below.

The calibration of the LMS program needs to be done only one time.  If it is done precisely, accuracy approaching 1% can be
 achieved.   Here is a general overview of how it is done.  Select a 1225 Hz frequency in the signal generator. Next, on the
 circuit, insert an Rm = 100K and remove the the unknown Z.  Capture some data.  Measure the AC voltage  Vx, at the output of
 op-amp, with a good voltmeter, preferrably a digital type.  Write down this number so you won't forget it.  Look at the data
 captured by the program.  You should see a large sine wave on L channel (Green) and very small sine wave on (R-L)
 channel (Blue).  The data should be clean without much noise.  

Now that the data is captured it can be used to calibrate the program.  There are two items that need to be calibrated.  Click
 on Calibrate to begin.  You will change the values shown in the Calibrate box as needed.   This  may be repeated until the
 best calibration is achieved.   All calibration is done on the originally captured data.  It does not need to be
 recaptured  each time.

   1.   Volts per bit.   This (optional) calibration is done on the L channel of the sound card.  Activate the cursors and measure
    the peak voltage of the L channel.   Adjust until the peak value  is close to 1.414 times value you measured with the AC
    voltmeter earlier.

   2. Channel Balance.  Adjust this value until the (R-L) channel is close to zero. Use small changes. You will not be able to
    go all the way to zero and there will be a very small sine wave remaining.  Also make a tiny adjustment to make Rs
    positive. 

Each time you click  "Apply", these values are applied to the captured data.   You will immediately see the results
 on the screen.  Use the cursor to measure the data on the L and (R-L) channels as needed.  Repeat the procedure until the
 best calibration is achieved.

Once you have balanced the stereo channels and (optionally) calibrated the scope, you are ready to start measuring.
 By the way, all calibrations are saved so that you only need to do it once. Next, the mixer that came with your software or
 the one that came with Windows  needs to be checked as you may have changed its settings. When you start the
 program, there is a little notice that comes on the screen to remind you to do this. Basically you want to set the output
 level, input gain and stereo balance to the center. The details on how to do this will obviously vary from system to system.
 Here is how its done with the SB. In the mixer Play section, enable  "Wave" and "Spkr", set the sliders to max and mute all
 others (including "Line" to avoid audio feedback). In the Record section, enable "Line", set it to max and mute all others.
 Set balance to center. 

* Calibration Defaults. These are assigned if you delete the LMSinit file (which stores your values) and start anew.	

* Files missing.  See Readme file for more information.

* Copyright 2004,     Dr. George R. Steber






