Void-particulate director

Apparatus for detecting voids and particulates in a flowing stream of fluid contained in a pipe may comprise: a transducer for transmitting an ultrasonic signal into the stream, coupled to the pipe at a first location; a second transducer for detecting the through transmission of said signal, coupled to the pipe at a second location; a third transducer for detecting the back scattering of said signal, coupled to the pipe at a third location, said third location being upstream from said first location; and circuit means for normalizing the back scattered signal from said third transducer to the through transmitted signal from said second transducer. The normalized signal provides a measure of the voids and particulates flowing past said first location.