Larson Davis System 824, Technical Reference Manual, Page: 57 / 673

9/29/09 Overview 2-17
Correction of Calibrator Output Level
The CAL200 provides a nominal pressure level of 94 dB or
114 dB. The exact levels are printed on the Larson Davis
calibration sheet that is delivered with the calibrator. The
free field level is -0.12 dB from either of these levels. If the
calibrator and instrument are near room temperature and
near sea level then no other corrections need to be made. If
the calibration sheet for the CAL200 indicates 113.98 dB for
it's level when set to 114 dB then set the Cal Level in the 824
to 113.86 dB.
When the microphone and instrument are at a temperature
other than near room temperature or static pressures not near
sea level, then corrections need to be added for the ambient
temperature and the prevailing static pressure. Check the
calibration data shipped from Larson Davis with the
CAL200 to get these corrections. The corrections can be
added to the level obtained in the previous paragraph to get
the actual level of the CAL200.
The 377B41 microphone's sensitivity varies with static
pressure. The coefficient of static pressure is -0.01 dB/kPa.
If the system is calibrated at 85 kPa for instance then it will
be 0.16 dB less sensitive at sea level. The 377B41 and 824
vary with temperature. The coefficient of temperature is
+0.012 dB/°C. If the system is calibrated at 25°C then it will
be 0.024 dB less sensitive at 23°C.