underwater temperature sensor

[Ken B]

Hello All,

I would like to build an temperature probe that I could tie to a line and drop over a boat so that I could tell the temperature on the bottom of the ocean. Where I sail would be around 200 feet. What do you guys think would be the easiest/best way to do this?

 

[stevez]

Not trying to be funny - buy one. How you define "easiest" and "best" is kind of important here. I am not a high tech fisherman but seems to recall seeing consumer electronics that will do what you want to do - reliably and accurately. While not rocket science, the time and material investment to develop, debug and package something like this is considerable - compared to the purchase cost. If your goal is learning then that's a different story.

A few things to worry about if you design your own -
1. Accuracy required - will determine sensor and cost of that sensor.
2. How you'll get the info back to where you need it. Lots of ways to do this - current loop (lots of wire/cable), digital, etc.
3. Corrosion problems with salt water.
4. Pressure at 200 ft - about 100 psi.
5. What do you want - digital output, computer interface, tone, etc?

If I had to shoot from the hip on this one - start with low cost thermistor and accept the limits of accuracy, pressure effects, etc. Connect with metallic fish line using the line as an antenna - transmit data representing temperature via RF along the line. Using line rated for salt water helps address corrosion issue. Pot the electronics in epoxy resin. Make simple test chamber from length of pipe and pressurize with tire pump (small amount of air over lots of water) to 120 psia (105 psig).

Hope this helps.