APPARATUS FOR MEASURING THE VELOCITY OF A FLUID AND MAINTAINING IT CONSTANT

摘要

Apparatus for measuring fluid pressure and velocity, and in particular for maintaining an aspirator air velocity constant under varying atmospheric conditions. A precisely controlled air velocity is provided by a reference air source whose frequency is derived from a crystal oscillator. The total air pressure from the aspirator wind tunnel is compared with the total air pressure from the reference air source using a matched thermistor pair technique to convert the pressure difference into an electrical error signal which is used to control the main air source for the aspirator wind tunnel such that the error signal is maintained at zero, thereby maintaining the air velocity in the aspirator constant.