Calibration Parameters

All of the information about the experimental apparatus that SLControl needs to perform experiments is contained in a single calibration file. The file is called "apparatus_calibration_parameters.txt" (it cannot be changed) and it must reside in the same directory as the executable.

The default directory is c:\Program Files\UW_Madison\SLControl\Executable.

When SLControl starts, it scans the file looking for specific tags. (markers which start and end with an underline character i.e. _tag_). The values following the tags have special meaning for SLControl and are used by the program to adapt the data collection and analysis routines to the specific apparatus used. Definitions for each parameter are shown below. Further down the page is an example of a parameter file. If SLControl cannot find the calibration file, or if one of the parameters seems to be missing, SLControl will revert to default values. In most cases, this is likely to be an error. The values will certainly not correspond to your apparatus. SLControl issues a warning if this occurs, but it will continue to run with default values.

Parameters are defined as follows:

FL_POLARITY A floating point value defining the direction the motor moves when the driving voltage changes.
+1.0 means muscle length increases when the motor command increases.
-1.0 means muscle length decreases when the motor command increases.
No other values should be used.

FL_RESPONSE_CALIBRATION A floating point value defining the change in fiber length (in microns)for a one volt change in FL_RESPONSE voltage.

FL_COMMAND_CALIBRATION A floating point value defining the change in fiber length (in microns) for a one volt change in FL_COMMAND voltage.

FORCE_CALIBRATION A floating point value defining the increase in measured force (in N) when the FORCE input signal increases by 1 Volt.

CALIBRATION_DATE A single string which the user can update to show when the calibration parameters were last changed.

FL_OR_SL_CHANNEL_MODE An integer which may be used to control the display of certain dialog windows. If this is set to 0 only FL and FOR channels are displayed in the Experiment_display and Analysis_display dialogs. Otherwise FL, SL and FOR channels and associated XY-plots are displayed. Please note that this feature is not fully supported in all dialog boxes (as of Ver 3.1).

An example of a parameters file is shown below.

// Calibration Parameter Values
// Last updated 31st October, 2001

// Definitions below this point

_FL_POLARITY_ -1.0			// Fibre Length Polarity
					// +1.0 means fiber length increases with increasing
					// voltages
					// -1.0 means fiber length decreases with increasing
					// voltages

_FL_RESPONSE_CALIBRATION_ 70.204	// change in fiber length (microns)
					// (motor position) for a +1V
					// change in FL_Response voltage

_FL_COMMAND_CALIBRATION_ 70.204		// change in fiber length (microns)
					// (motor position) for a +1V
					// change in FL_Command voltage

_FORCE_CALIBRATION_ 5.326e-4		// increase in force (N) for a +1V
					// increase in Force voltage

_CALIBRATION_DATE_ Oct_31st_2001	// 31st October, 2001
					// Must be a single string

_FL_OR_SL_CHANNEL_MODE_ 0		// 0 for FL_channel_mode (FL and For channels)
					// 1 for SL_channel_mode (FL, SL and For channels)

The user sets the calibration values appropriate to their apparatus by modifying the parameter values in the ASCII text calibration file. It can be edited in a word processor (such as Word) but in this case, the file must be saved as a text file. Alternatively you could use a simple text editor such as Notepad or the much more powerful EditpadLite (available as shareware from EditpadPro.)

Note that SLControl only scans the calibration file when the program first starts. If any of the values in the calibration file are changed during run-time, the modified values will not be used until SLControl is restarted. The user can check the current calibration values at any time by selecting Help->Calibration Parameters from the main dialog menu.

Technical notes

These parameter values are used by SLControl as global variables and are defined in global_functions.cpp. If a function defined in another file requires one of these parameters, it is included as an external variable at the top of the source code file.

Last updated on 21th March, 2003 by Ken.