A Transducer for the Measurement of Pulsatile Air Flow in High Vibration Environments 840139
The transducer operates as a drag-force flow meter. A thin flexible membrane, oriented perpendicular to the direction of flow, and a fixed plate form a capacitor. The dynamic pressure generated by the fluid flow (density times velocity squared) deflects the membrane, thus varying the capacitance and the resonant frequency of an electronic circuit. The frequency variations are sampled by a microprocessor. In order to obtain the mass flow rate, the microprocessor corrects the signal for nonlinearities such as the laminar-turbulent transition and fluid density variations. Because the membrane stiffens with increasing deflection and because of the high sensor resolution the sensor operates over a wide range (turndown ratio 100:1) with a flow rate uncertainty of less than 1%. The membrane natural frequency being above 20 kHz, fast flow transients and pulsations do not distort the measurement. With its small oscillating mass the transducer is insensitive to external forces such as engine vibrations.