An Ionization Device for Air Velocity and Mass Flow Measurements

A novel type of flowmeter is described that is based upon the deflection of air ions in an airstream by a transverse electric field. The ionization is produced by alpha radiation from a source mounted on one of the electrodes. The resulting ions follow a path determined by the air velocity, combined with a superimposed electric field having two components: a control or deflection field and a collection field. Variation of the shape and magnitude of the control field produces an ion current that varies as a function of the air flow. The use of the control field allows the device to be used over a broad range of flows with very little loss of sensitivity. Depending upon the design it can function as an anemometer, volume flowmeter, or a mass flowmeter. The device produces no obstruction to the flow and is ideally suited to in-line monitoring applications that require very low pressure losses.