I want to design a data-logger with PIC MCUs. This data-logger is going to work in chamber in the oil wells in the depth o 500 meters. and it is going to record temperature and pressure for 20 hours.
The pressure in that depth is about 9000 PSI and the temperature is about 130 degreeC. I want to know what kind of elements is the best elements for this project. I mean if I need a 1uF capacitor, which kind of capacitors is my best choice? Electrolytes? Polyester? Ceramics? Multi-layer? Which one is less temperature sensitive? What about the resistors? and also all the other elements.
Please shed any light you can on this issue. Any point will really highly appreciate. Does any body have similar experience?
Best Answer
I don't have borehole experience, but I do have a lot of generalized experience, including space environments.
First, temperature. PICs won't do it. Go look up some data sheets. Their max is 85 C. You need MCUs rated for automotive or full mil-spec temperature (125 C). The same applies to all other components - full automotive (not industrial) or mil ratings.
Second, pressure. That's easy, no special pressure requirements on your circuits. The reason is simple: if you're going to operate the circuit at ambient pressure, you have to allow ambient materials into your electronics. And water and drilling mud are not what you want inside your data logger. This leads to the biggie:
Third, housing. You must learn to build hermetically sealed housings for your units, and they must withstand temperature and pressure. Think lots of stainless steel. And finally,
Test facilities. If you do not have the ability to apply a good replica of the operating conditions (temperature, pressure, material), and if you do not use this ability to run prolonged stress tests on your product, you are doomed.