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Measurement of temperature and pressure under water using sonar

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Vamsi Ch

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Hello,

I am student of masters and I am trying to implement a project in which temperature and pressure should be measured under water. For this I want to design a device which is equipped with temperature and pressure sensors interfaced with sonar transmitter. Required working principle should be sonar transmitter should send the required information of temperature and pressure underwater according to the condition mentioned by the user at the sonar receiver.

Thanks for consideration.
 

rca

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what is your problem?
 

Vamsi Ch

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Actually I want to design a remote sensing device interfacing temperature sensor with sonar transmitter which senses the temperature underwater and sends the information to sonar receiver (user). I think sonar receiver must be in water to receive signal or I don't know whether we can find advanced systems such that it can receive signal even it is out of water. I am not getting how to implement actually. Do I find sonar transmitter and receiver with such application. If so please help me with the required information.

Thanks.
 

Vamsi Ch

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I know that communication is with sonar under water but do I find sonar system devices to interface sensors directly or I should interface via micro controller.
 

Dan Mills

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I do sonar for a living, and given the very simple requirement you have I would skin this cat as follows:

Use a simple frequency modulation scheme, possibly involving a little micro, but you could do it in discreet parts...
The underwater gear has a suitable piezo ceramic transducer (Morgan make some off the shelf stuff that would probably do the job), which you feed with a few hundred volts at a frequency depending on the temperature or pressure, as read by your sensor.

At the top you have a transducer in the water, a low noise preamp and a pll which locks to the tone in the water and gives a voltage depending on the frequency receved.

You can increase range and reduce power consumption by making the thing transmit short bursts of tone periodically rather then running it CW, and you can do things like extend the bandwidth by placing a matching network between the power amplifier and the ceramic and an acoustic matching layer between the transducer and the water.

I would note that these units are a commercial off the shelf component from any number of people who make such things for survey and science applications, and would also note that sonar comms once the thing sinks to below a thermocline becomes increasingly problematic unless you lower the rx hydrophone to also be below the thermocline.

I am not sure I see a masters poject here.

Regards, Dan.
 
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