Abstract
A pneumatic RC circuit is a fundamental and important element in pneumatic control systems. This paper deals with the frequency response of a RC circuit taking the non-linear flow rate characteristics and the heat transfer in the chamber into account. Though this circuit is widely used in pneumatic systems it is not easy to calculate the dynamics of the circuit. This is caused by the non-linear flow rate characteristics of the restriction and uncertainty of state change of the air in the chamber. In this research, dimensionless non-linearity parameter composed of the amplitude of an input pressure signal and non-linearity coefficient of the flow rate characteristics has deen obtained theoretically.
Time has been m ade dimensionless by introducing pressure time constant. It is shown that the ratio of pressure time constant and thermal time constant is very important parameter in the circuit.
By the method of describing function, the dynamics of pneumatic RC circuit have been made clear. For the circuit designing convenience, normalized Bode diagrams with two parameter are shown in the figures.
In the experiments, frequency response tests of RC circuit have been conducted (0.5-7Hz)in different amplitude condition of input signals. Satisfactory agreements are obtained between theory and experiments.
