Differential pressure cell with diaphragm tension and overpressure protection

A differential pressure sensing cell, comprising:

• a) a measuring chamber having electrically insulating walls,
• b) a measuring diaphragm mounted within the measuring chamber and dividing it into first and second closed chambers,
• c) measuring diaphragm displacement sensing elements mounted on the insulating walls,
• d) an auxilliary chamber,
• e) an auxilliary diaphragm mounted within the auxilliary chamber and dividing it into third and fourth closed chambers, the auxilliary diaphragm being more flexible than the measuring diaphragm,
• f) casing means surrounding and mounting the measuring chamber and the auxilliary chamber, and defining a first recess surrounding the auxilliary chamber and a second recess surrounding the measuring chamber,
• g) a first pressure-receiving diaphragm movably responsive to a first input pressure and mounted within the casing means to define a first pressure-receiving chamber,
• h) a second pressure-receiving diaphragm movably responsive to a second input pressure and mounted within the casing means to define a second pressure-receiving chamber,
• i) fluid sealed within and filling the measuring and auxilliary chambers, the first and second recesses, and the first and second pressure-receiving chambers,
• j) first fluid passage means interconnecting the first pressure-receiving chamber, the first recess, and the first and third closed chambers, and
• k) second fluid passage means interconnecting the second pressure-receiving chamber, the second recess, and the second and fourth closed chambers, whereby radial tension of the measuring diaphragm due to static differential pressure between the interior and exterior of the measuring chamber is minimized by substantially equalizing the interior and exterior pressures through said first and second fluid passage means, and over-pressure protection of the measuring diaphragm when the pressure differential between the first and second pressure-receiving chambers becomes too large as attained by causing the first or second pressure-receiving diaphragm to contact the casing before the measuring diaphragm contacts the casing before the measuring diaphragm contacts the casing while absorbing the change in volume of the first or second pressure-receiving chamber by the action of the auxilliary diaphragm through the first or second fluid passage means, respectively.