Determination of the Describing Function of Nozzle-flapper Type Pneumatic Valve With Two Ports

Abstract

In many pneumatic systems with a wider bandwidth, nozzle-flapper type valves are usually used for flow rate control. Because of their inherently nonlinear behavior and parameters variation, modelling of the servo valve is important for analysis and design purpose. The describing function was used for modelling of the mass flow rate characteristic of the servo valve. The paper presents two describing functions. One is for the fixed orifice with the subsonic flow regime, and the other is for the nozzle with the sonic flow regime. In the first case, the mass flow rate function is approximated by a polynomial.