Magnetic means for determining partial pressure of oxygen particularly in underwater breathing apparatus

Claim 1

Apparatus for determining the partial pressure of oxygen in a gas mixture containing oxygen and a background gas comprising: (A) a magnetic circuit including a magnetic flux source and opposing pole pieces defining a gap; (B) a piezoelectric bender unit; (C) a reference chamber having a magnetic susceptibility similar to said background gas; (D) said reference chamber being arranged for oscillatory movement into and out of said gap by means of said bender unit; (E) drive means for oscillating said bender unit; (F) circuit means for measuring the change in magnetic flux in said magnetic circuit due to said reference chamber oscillating into and out of said gap to provide an output signal indicative of said oxygen; (G) said reference chamber being hollow and containing a gas therein; and (H) means for equalizing the pressure of said gas within said reference chamber with the pressure of said gas mixture.