9/29/09 Overview 2-17Correction of Calibrator Output LevelThe CAL200 provides a nominal pressure level of 94 dB or114 dB. The exact levels are printed on the Larson Daviscalibration sheet that is delivered with the calibrator. Thefree field level is -0.12 dB from either of these levels. If thecalibrator and instrument are near room temperature andnear sea level then no other corrections need to be made. Ifthe calibration sheet for the CAL200 indicates 113.98 dB forit's level when set to 114 dB then set the Cal Level in the 824to 113.86 dB.When the microphone and instrument are at a temperatureother than near room temperature or static pressures not nearsea level, then corrections need to be added for the ambienttemperature and the prevailing static pressure. Check thecalibration data shipped from Larson Davis with theCAL200 to get these corrections. The corrections can beadded to the level obtained in the previous paragraph to getthe actual level of the CAL200.The 377B41 microphone's sensitivity varies with staticpressure. The coefficient of static pressure is -0.01 dB/kPa.If the system is calibrated at 85 kPa for instance then it willbe 0.16 dB less sensitive at sea level. The 377B41 and 824vary with temperature. The coefficient of temperature is+0.012 dB/°C. If the system is calibrated at 25°C then it willbe 0.024 dB less sensitive at 23°C.
