An Evaluation of Pneumatic Transmission Line Propagation Functions

Abstract

The results of pressure response tests are given for a wide range of dead-ended pneumatic transmission lines. The tests were conducted on lines of commercial quality PVC tubing of length 1 ft to 50 ft, inside diameter 1/8 to 3/8 in., and over a frequency range from 2Hz to 1000Hz. Air at approximately 60 deg F and a mean gauge pressure of 1.0 lb/in.2 was used as the working fluid, with input signal amplitudes of ±0.1 lb/in2 . The resulting data have been used to calculate the propagation function and hence to determine best-fit values of the constants which appear in the approximate theoretical expression of F. T. Brown. While the performance of many lines of interest may be predicted accurately by using Brown’s theoretical constants, the tests have shown significant changes in the experimentally determined values of the constants as line length decreases. These changes may be due, at least in part, to the increasing significance of wall elasticity at higher frequencies, an effect which is not included in Brown’s analysis. The data are given in a form which is directly applicable to calculating transmission line response.