altimeter reading at 30k feet

Found this with google in about 30 seconds (including typing search terms "air pressure above sea level"). So that's one bit answered.

PSI @ 30K is 4.3641

PSI @ Sea level is, 14.6959

so the difference is,,,

Now I have no idea as to what you are describing with the valve tho.

Here's your solution, put the altimeter in the chamber and use a simple contact on the needle to control your pump

http://www.amazon.com/s/?ie=UTF8&keywords=altimeters&tag=googhydr-20&index=aps&hvadid=3503740185&ref=pd_sl_46xo471gur_b

Altimeters for aircraft (especially pressurized cabins) take the outside air pressure from a static line.

Lots of commercial pressure transducers are available. A set "canned" setpoint controler would take care of the pump.

Why cycle it on and off? Why not use a mechanical pump and an air bleed to create a constant pressure?

It's for a product development to insure the alti sensor doesn't give the same reading to the micro 3 times in a row. Burn in.

Thx for the reply

I believe you are looking for a "blind altitude encoder". Those are widely available for less then 300US$ and while they were traditionnaly providing the output in binary Gray code, they are now widely available with RS232 serial output. Typically, those are hooked up to aircraft transponders so that Air Traffic Controllers can be provided with the actual altitude of the flying aircraft (after compensation for current local athmospheric pressure reading). A supplier for those would be Aircraft Spruce. Alternatively, just drop by the avionics shop at your local airport.

There is a thing called the "International Standard Atmosphere". It can be found in the back pages of Mayhew & Rogers, "Thermodynamic Properties of Fluids", in Perry, "The Chemical Engineer's Handbook", in "Kempe's Engineers' Yearbook", and many other places.