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. Only the AH2010 and AH2020 are sold with an EOC calibration as standard. Other hydrophone/preamplifier combinations will require a custom calibration.