Methodological characteristics of small absolute gas pressure measurement at high flow rates

In wind tunnel measurements of small absolute gas pressures at high velocities of the oncoming flow, the measuring system is usually a pneumometric duct containing a pressure transmitter. The errors arising in inlet pressure measurements, due to the sorption, desorption, and diffusion properties of such duct materials as vacuum rubber, copper, etc. are evaluated. It is shown that measurement errors for a 3-m long, 3-mm diam copper duct operating at atmospheric pressure are appreciably greater than for operation in a vacuum. A small-scale thermocouple manometer, whose principle of operation is based on the dependence of the heat conductivity of the gas on intermediate-vacuum pressure is proposed for measuring pressures up to 5 mm Hg.