A pressure ratio measuring system is disclosed. The system includes two quartz capacitive pressure transducers (16, 22). Each capsule contains a pressure sensitive capacitor (Csa, Csf) which is fed by an alternating excitation signal. Capacitance (Csa) is fed by excitation signal (Vr) and Capacitance...http://www.google.es/patents/US4434664?utm_source=gb-gplus-sharePatente US4434664 - Pressure ratio measurement system
