Precision pneumatic pressure measurement with diaphragm-based mechatronic devices

A clamped circular metallic diaphragm, with shallow spherical shell deformation, elongates spherically proportional to the pressure acting on it. By making use of the inflation characteristics and mechanical properties of the diaphragm, three types of pneumatic pressure sensor are proposed in this article. In the first type, an optical mirror is engraved on its outer surface in an optimal position falling midway between its vertex and circumference. A laser beam is made to incident on the mirror and it gets deflected to fall over a matrix of photocells; the excitation of a particular cell in the coordinates of the matrix determines the pressure acting on the diaphragm. In the second proposal, a weightless secondary coil of a transformer is fixed around the vertex of the diaphragm which would move around a stationary magnetic core. The excitation of the primary coil wound over the magnetic core causes a voltage to be picked up in the secondary coil which would depend upon the displacement of the vertex because of pressure. The third type of the transducer is a capacitance pickup arrangement wherein the pressure is converted into capacitance and it is sensed and displayed as pressure. Furthermore, as an extension of the work, the motion of the diaphragm is mechanically coupled to a stylus for producing hard copy of the pressure over a strip chart.