Can the level values from different ultrasonic testing devices be compared or converted directly?

Level values from different ultrasonic testing devices are generally not directly comparable. The unit dB alone does not define the measurement. It is also necessary to know the reference value and the measurement method on which the displayed value is based.

For airborne sound measurements, the SONAPHONE displays a sound pressure level in dB using the acoustic reference value of 20 µPa. Other devices, particularly narrowband or older ultrasonic testing instruments, may display an electrical voltage level in dBµV or use device-specific scale divisions.

The displayed value can also be influenced by:

• the sensor used and its frequency response,
• the evaluated frequency range,
• signal filtering,
• device calibration,
• time weighting or averaging,
• the measurement distance,
• the orientation of the sensor.

For this reason, there is no universally valid conversion between dB, dBµV, and device-specific scale divisions.

For comparative and trend measurements, the same testing device, sensor, settings, measurement position, and test conditions should be used whenever possible.