This invention pertains generally to pressure transducers and more particularly to a transducer system which is particularly suitable for use in connection with the pitot system and the air data computer of an aircraft.
The pitot system of an aircraft provides pressures which can be utilized to determine Mach number and other aircraft data. These pressures generally include the static pressure P.sub.s, which is the absolute pressure of the ambient still air at the altitude of the aircraft, and the total pressure P.sub.t, which is the sum of the static pressure and the rise in pressure due to aircraft motion. Altitude is a nonlinear function of static pressure, and airspeed and Mach number are non-linear functions of the pressure Q.sub.c, which is the difference between total pressure and static pressure. The pressure Q.sub.c represents the pressure rise due to motion of the aircraft and it is commonly known by several names including ram pressure, impact pressure and dynamic pressure. Mach number is defined as the ratio of the true airspeed to the speed of sound in ambient air, and this ratio can be closely approximated by Q.sub.c /P.sub.s.
Heretofore, there have been several attempts to provide mechanical transducers having an output motion corresponding to Q.sub.c /P.sub.s. Such transducers generally include a first diaphragm which has P.sub.t and P.sub.s applied to opposite sides so that it moves in accordance with Q.sub.c, a second diaphragm which moves in response to P.sub.s, and a linkage which responds to the motion of the two diaphragms to provide an output motion corresponding to the ratio of the diaphragm motions. The motion of the linkage is monitored by an electromechanical transducer which provides an output signal corresponding to the desired ratio. This approach has certain disadvantages. For example, the linkage gives rise to friction and backlash which result in errors in the output signal. In addition, the linkage constitutes an inertia load on the diaphragms which causes additional error during vibration or acceleration.