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Calibration

Click the Options | Processing Settings menu and click on the Calibration tab or click the calibration toolbar button.  

By default, the analyzer shows the relative power levels where 0dB is the strongest possible 8, 16 or 24 bit signal.  You can calibrate the analzyer to a variety of engineering units; there are three calibration methods:

1) External Reference Signal

This method requires an external signal with a known level.

Procedure:
  • Connect a steady state reference tone to the input of the sound card (do not use a DC level or noise signal). 
  • Enter the reference signal level in the edit control (you can use an oscilloscope or voltmeter to measure the signal level at the input to the sound card).
  • Select the reference signal type: "Peak",  "RMS" or "Peak to Peak" as appropriate (e.g. voltmeters produce RMS values).
  • Select the applicable units for the input reference signal or enter custom labels.  
  • Select the desired Display mode: "Peak", "RMS" or "Peak to Peak".
  • Press the "Measure Input Signal" button.  The analyzer will acquire several seconds of input data and compute the corresponding scale factors for each channel.  

    Note: The "Measure from Wave File" button will compute the calibration scale factors from an existing wave file.  This is useful in cases where you only have a recording of the reference signal - please note that this recording must have been made with the same input gain for the results to be meaningful.

    2) Internal Hardware Calibration 

    This method requires the SpectraDAQ-200 hardware.

    Select the desired engineering units (Volts, Millivolts or dBu).  

    3) Directly to Transducer Sensitivity 

    This method requires the SpectraDAQ-200 hardware.

    Select the desired transducer type (microphone, accelerometer, hyrdophone).

    Enter the transducer sensitivity from the datasheet provided by the transducer manufacturer. The analyzer will convert the detected voltage to the corresponding engineering units based on this sensitivity. 

    Converting Acceleration to Velocity or Displacement

    If you are calibrating to acceleration the "Convert Spectrum To:" field will be enabled and allow you convert the spectrum to velocity or displacement.  These conversions do not apply to the time series display.

    Additional Notes:

    You may customize the labels by directly modifying them in the edit box.

    You may save the calibration settings in a file and reload them as needed.  The current calibration settings are always saved in configuration files and restored when loaded.

    Digiducer USB Accelerometer - if this device is installed and selected as the input device, a special button will be shown that will read the embedded calibration values directly from the device.  

    Quick Calibration - If you Right Click on the spectrum plot a menu will popup. The option "Set Calibration to 0 dBr at this Frequency" will quickly set the 0 dBr reference.

    Very Important - Most sound cards provide a mixer utility to allow you to set the input gain of the sound card.  If the input gain is changed, the calibration is no longer valid.  

    Note: If you change the SpectraDAQ-200 input voltage range the analzyer will automatically recalculate the internal calibration values for you.  This applies for all calibration methods when the SpectraDAQ-200 hardware is used

    Independent Channel Calibration
    When the "Independent Scaling and Calibration" option is selected in the Settings dialog box, the calibration dialog box will change to display separate parameters for each channel and each channel will be plotted in a separate window.  This allows you to use two completely different types of scaling at once.  For example you can configure the analyzer to show accelerometer data scaled in G's in one channel and 1/3 octave data scaled in SPL from a microphone in the other.

    See also:  SpectraDAQ-200, Scaling, Microphone Compensation  Settings,  Dual Channel Processing