The present invention is directed to an apparatus for sensing the total pressure and static pressure of a gas flowing in a passage. The flow or velocity pressure may be readily obtained from these sensed conditions of pressure and a control function can be accomplished by using either the total pressure and static pressure values or the velocity pressure value.
Various devices have been proposed in the past for sensing the flow of gas, particularly in a confined passage, such as the ducts in heating, ventilating and air conditioning systems. Many of the devices have been based on Pitot tubes or modified Pitot tubes. These devices have not been entirely satisfactory because of their low sensitivity, particularly at low flow velocities. Many of the devices have also been based on venturi type arrangements; however, the venturi arrangements have not been entirely satisfactory, particularly at low velocities.
It is therefore the object of the present invention to provide a flow sensing apparatus that has increased sensitivity even at low flow velocities.