An Example of Time Lag in Pressure Control Systems : Time Lag in Measuring Means
Sumiji FUJII, Yukio HORI · Transactions of the Japan Society of Mechanical Engineers · 1955
In pressure control systems, for example as shown in Fig. 1, we sometimes experience that when the initial disturbance in pressure is smaller than a certain limit the system is stable and the pressure fluctuation diminishes, but when the initial disturbance is larger than the critical limit the system is unstable and the pressure fluctuation grows. The author treated this phenomenon as caused by the non-linear resistance of flow in the pipe connecting the measuring element (diaphragm) and controlled medium (air in tank). And he found that the critcal value of pressure disturbance mentioned above was given as [numerical formual] supposing the resistance being proportional to the square of velocity of flow in the pipe, where α, b are constants in expression (2) showing the characteristics of controlled medium, K is the coefficent of resistance of flow as in expression (1) and κ is also a constant in expression (3) showing the characteristics of servomotor.