Use of a SAW device for measuring flow rate of liquids

A delay-line stabilized SAW oscillator heated to a suitable temperature above ambient is placed in the path of the flowing fluid. To prevent attenuation of the surface wave, the flow cell through which liquid flows is designed such that there is no direct contact between the liquid and the propagating surface wave. Convective cooling caused by fluid flow results in a change in the oscillator frequency. The frequency of a 68-MHz oscillator operated at 9 degrees C above ambient is found to vary by more than 40 kHz for variation in water flow rate from 0 to 0.8 ml/min. Attractive features of this device include the ability to measure very low flow rates (less than 0.1 mu l/min) and direct digital output.<>