Putting Confidence in Ultrasound

Related Pages

Converting EOC Sensitivity to Amplifier-loaded Sensitivity [PDF]

Hydrophone Calibration Method [PDF]

Ultrasonic and Acoustic Readings

Choosing a hydrophone

Hydrophone theory

Tips on using hydrophones

Hydrophone sensitivity

Hydrophone Sensitivity

All hydrophones manufactured at Onda Corporation are sold with an end-of-connector (EOC) calibration as standard. Custom calibrations can be provided on request. In practice, a hydrophone will be connected to an oscilloscope to make measurements. The hydrophone will therefore be connected in series to a combination of cables, adapters and possibly a preamplifier and this affects the sensitivity of the hydrophone. The optimal way to make a hydrophone measurement is to connect the output of the hydrophone directly into a preamplifier. This avoids spurious frequencies in the measured waveform arising from transmission line effects. To calculate the ‘loaded’ sensitivity of a hydrophone, ML(f) use the following formula:

ML(f) = G(f)*MEOC(f)*( CH/(CH + CC + CA))

Where G(f) is the gain of the preamplifier, MEOC(f) is the EOC sensitivity of the hydrophone, CH is the capacitance of the hydrophone, Cc is the capacitance of the cable/adapter and CA is the capacitance of the preamplifier. A derivation of this formula can be found in ‘Formulas for Converting Sensitivity’. Note, in order to calculate the loaded sensitivity of a hydrophone/preamplifier combination, a EOC calibration of the preamplifier must be available. Note the AH-20x0 and AG-20x0 models are offered with an EOC calibration as standard, but the AH-1100 is not. Other hydrophone/preamplifier combinations will require a custom calibration.

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