ULTRASONIC SYSTEM FOR MEASURING GAS VELOCITY

A system and method for measuring the velocity of gas flow between multiple plasma deposition chambers is provided. A passage atmospherically linking two plasma processing chambers conducts a gas flow therebetween due to differential pressures within the respective chambers. The gas flow velocity is measured by a linear or non-linear ultrasonic energy acoustic path between two transducers located exteriorly to the chambers using the difference in transit time in a forward and reverse direction due to the velocity of gas in the passage. The pressure of process gas in one or more chambers is adjustable based on the measured velocity of gas flow in the passage.