I am planning on working on a project for Arduino based digital pressure thermometer and have most of the planning phase worked out. Basic idea is a pressure sensor will be tightly sealed with a machined aluminum cylinder with an open top and closed bottom so no air escapes. Using ideal gas law, P=ρRT where R is specific gas constant for air, I should be able to calibrate for air density after measuring pressure by comparing with another temperature sensor and go from there since air density should not change much in a sealed environment. For this project, an A/D pressure sensor will be used which can be grabbed from places like Mouser for bit over $10 (Currently eyeing at MPX5100AP).
At this point, I'm wondering if I should go with an absolute or gauge pressure sensor for measurement. My understanding is that since the air inside the aluminum cylinder is closed, neither choices matter much so to save on headache an absolute pressure sensor appears to be the more reasonable route.
It is also possible that the way I am going through this is wrong but nevertheless would appreciate any guidance on the subject.
The aluminum cylinder is supposed to be a container for air inside. This will be fitted with a pressure sensor (Looks something like this: http://www.mouser.com/images/freescale/lrg/344b-01.jpg) of choice and later sealed. When the cylinder is cooled or heated I'm hoping for the air pressure inside the cylinder to change which makes the seal important since no air inside the cylinder should escape. Please let me know if there's anything else that should be clarified.
Absolute will give you the absolute pressure inside the cylinder.
Differential or dual-port will give you the difference between inside and outside. If you move the cylinder+sensor up and down in altitude then the measured pressure difference will change, even if the temperature and pressure inside the cylinder hasn't changed. For the pressures you are looking at, 1m altitude will be a significant, detectable, difference.
@MorganS: Thanks for the clarification! I'm not interested in outside pressure since there will be no measurements done outside the cylinder but the additional information is making me lean towards absolute pressure sensor since calibrating atmospheric pressure for gauge sensor at different altitudes seems rather unnecessary. I'll pull the gun on absolute sensor and see how good this compares with the simpler (and probably more accurate) temperature sensor for now
Did you get any traction on this? I'm looking at doing something similar. I need to measure PSI of a gas container, looking from 0-20PSI on the low end to 0-50 PSI if reasonable in price. Looking to keep the sensor as cheap as possible and still get .5 psi resolution.
looking at this one right now. I'm admittedly very new and have little idea what I'm doing here..
The MPXV series of sensors is pretty good although I don't think you'll get to 50psi with them. I had a recent requirement for 70psi and ended up with some Honeywell sensors at Mouser which were $50 each.
