How are SONAPHONE testing devices and their airborne sound sensors calibrated and adjusted?

When using airborne ultrasound sensors, the measured sound pressure is generally expressed as a level value in dB or dBµV. The use of a logarithmic level makes it possible to display measurement values over a wide dynamic range. The type of level displayed depends on the testing device, the sensor technology, and the reference value used.

Calibration of the SONAPHONE airborne sound sensors

The SONAPHONE airborne sound sensors BS10 and BS30 contain a broadband microphone capsule that converts sound pressure into an electrical AC voltage.

The SONAPHONE displays the resulting sound pressure level in dB using the standard acoustic reference sound pressure of 20 µPa:

• 20 µPa corresponds to 0 dB
• 1 Pa corresponds to approximately 94 dB
• 2 Pa corresponds to approximately 100 dB

The microphone capsule is calibrated and adjusted by comparing its electrical output signal with that of a reference microphone using a defined 40 kHz reference signal.

During adjustment, the frequency response of the broadband microphone capsule is corrected across the complete SONAPHONE measurement range from 20 to 100 kHz. The SONAPHONE then calculates the displayed level values from the broadband sound pressure measured within this frequency range.

The calibration therefore takes into account:

• the sensitivity of the microphone capsule,
• the individual frequency response of the sensor,
• the broadband measurement range from 20 to 100 kHz, and
• the acoustic reference value of 20 µPa.

The sensor is inspected and calibrated by the manufacturer. Calibration or adjustment by the user is not intended. If recalibration is required, the sensor should be sent to SONOTEC or an authorized service partner.

The appropriate recalibration interval depends on the applicable quality requirements, internal company specifications, measurement conditions, and the mechanical and environmental stress placed on the sensor.

Further information on the meaning of the displayed level values is provided in FAQ-U4. Information on the comparability of SONAPHONE values with dBµV values or scale divisions from other ultrasonic testing devices is provided in FAQ-U5.