Hydrophone and NI DAQ

[an3284]

Hello,

I need information if NI DAQ'S 9205 and 9263 can be used with Bruel & Kjaer 8103 hydrophones to record data in Labview. I am also using CCLD converter with the hydrophone but I dont have a data acquistion system so I would like to know If i can use these DAQS.

[LV_Pro]

Without knowing what the output level of the CCLD is makes determining whether the 9205 will work difficult. Your hydrophone has a freq response up to 180kHz, the 9205 to 250kHz, but Nyquist laws indicate that the highest frequency you can sample without aliasing would be 125kHz. If your band of interest is below that the frequency response is ok. Not know the signal level of your CCLD is the issue then, the 9205 having a +/- 200mV range, meaning with proper shielding/wiring it is pretty sensitive. Not sure your plans for the 9263, it is an analog output device.

[rolfk]

Your hydrophone has a sensitivity of -211dB at 1V/uPa. Most B&K CCLD devices have a maximum amplification of 40dB. You will also need to check the frequency bandwith of the CCLD device to be good enough for the signal you want to measure.

The questions would be therefore:

- what CCLD device are you planning to use? It will be almost certainly necessary to premplify the hydrophone signal to get it to the 200mV range for the 9205.

- what pressure signal are you expecting to measure, both the range of your signal of interest as well as the maximum pressure you expect to occur. Your maximum signal after preamplification should not exceed the 200 mV range for the 9205 inputs or you get saturation of the input amplifiers with according signal distortions?

- what's the frequency range of your signal you want to measure and does that fit with the frequency bandwith for your CCLD device?

- it would be helpfull if your CCLD device has selectable low pass filters to limit the frequency spectrum of the signal to be less than half of the intended sampling frequency.

Basically your hydrophone with a 40dB amplification will result in a signal of -161 dB at 200mV/uPa, which means you would need about 100 Pa to reach the full range of 200mV at the 9205 input. That's quite some pressure for underwater sound measurements but depending on the signal you want to measure quite possible. (Fin whale call sound is for instance 10 Pa at 100m distance. 100 Pa can be a large ship at 100 m distance.)

The more interesting challenge will come afterwards, once you have the hardware setup

Writing the software and dealing with dBm, dBp, Sound Level (SL), Sound Pressure Level (SPL), calibration issues, band power, etc, etc.

[Henrik_Volkers]

CCLD = constant current line drive .. also known as IEPE 🙂 

What do you need the AO module for? It wouldn't work as a current source for your CCLD.

Take a look at the NI 9232 or 9234 (noise, samplerate and supply current?), but as rolfk pointed out a detailed evaluation is important. There are dedicated signalconditioners for your task B&K , Kistler and many others build then in various tastes..

BUT since there is no offical IEPE standard a close look at the spec details is important.

Depending on the cable length and the frequency range (and amplitude) the driving current needs a verification. Since Sensor and CCLD is B&K  I would ask B&K what feeding current is needed when you know your cable lengths, frequency and amplitude (dynamic)  range.

[an3284]

Thank you very much for your response, I have attached data sheet for CCLD, let me know if that helps in determining anything.  

Thank you again

[rolfk]

That’s not the CCLD but a converter between a capacitive charge sensor and the CCLD device. I don’t think this converter is even useful for the hydrophone you mentioned earlier. Your hydrophone produces a voltage that is directly proportional to the sound pressure on the microphone so can be connected directly to a CCLD device or any appropriate amplifier.

The data sheet you show is for a capacitive microphone which produces an electric charge rather than a voltage in response to applied pressure.