I am designing a system to record respiration rate and flow rate for people using a CPAP machine for Sleep Apnea. The air goes from the air pump through a 3 ft hose to the user's mask. I measuring the differential pressure across the hose, which is 1 in in diameter. To keep electronics off the face, I run 1/4in plastic tubing back to the measuring device. I want to calculate the flow from this pressure differential with my microprocessor and store on an SD device. The input pressure varies from 7 to 25 in/H2O. I have no idea what typical flow will be.
Jim