Signal data received from the A/D device is for SIGVIEW only a sequence of samples with different numeric values. For example, each sample from the sound card usually has a value between -32767 and 32767 (16-bit resolution). Of course, these values have no physical meaning. To transfer these values into meaningful physical values such as Volt, meter, Celsius, etc., you have to tell SIGVIEW how to convert generic numeric values into real word units. This complete transformation is described in a ‘calibration file’. You can create as many calibration files you want, and use them for different data acquisitions.
Each calibration file can contain calibration data for multiple channels. You can choose the number of channels in the combo-box in the upper part of the dialog. To switch between channels during editing, use the '<‘and '>' buttons on the right side of the dialog.
By selecting the “Data acquisition/Sound card calibration” option from the main menu, you will open a calibration dialog where you can create a calibration file in 6 simple steps:
- Use the “Data acquisition” menu option to record constant signal with known amplitude (for example 5V) from your DAQ device. Use only the "default.cal" calibration file for this step.
- Measure the average value of the signal recorded by SIGVIEW during the first step and enter it in the “Recorded input level” field.
- Enter the actual amplitude level in physical units which corresponds to the signal recorded during the first step in the “Input level in physical units” field. You can also define if this value should be considered as peak or RMS value.
- Enter the description of your physical units (for example V or Volt) in the “Physical unit used” field.
- You can also define offset to be added to recorded values (in physical units).
- Save your calibration file and use it later for data acquisition in the “Data acquisition” dialog.
All calibration files should be saved in the “Calibration” folder located in the SIGVIEW's application data directory (usually C:\Documents and Settings\<UserName>\Application Data\Sigview\). Each of these calibration files can be used later for data acquisition.
There is one special data acquisition file, “default.cal”, which is distributed with SIGVIEW and used by default. It leaves recorded data from the DAQ device just as they are, without any conversion. You should not change the content of this file.
Using Calibration function for unit conversion
Calibration function can also be used for a conversion of values delivered from a sensor into a different unit. For example, if your sensor is delivering values in m/s2 , and you would like SIGVIEW to display values in "g" units (Acceleration of gravity), you would create a calibration with the following values:
Recorded input level: 1.0
Input level in physical units: 0.101972
Physical unit used: g