Abstract: An ultrasonic impeller flowmeter for measuring fluid flow through a conduit includes a paddle wheel impeller rotatably mounted in a cylindrical protective housing which extends radially into the conduit through an aperture therein. A diametrical slot through the distal end of the housing admits fluid to rotate the paddle wheel. Ultrasonic transducers are embedded in the housing on opposite sides of the paddle wheel for establishing an ultrasonic carrier signal. Circumferentially spaced-apart openings in the paddle wheel modulate the ultrasonic signal to produce an output signal which is applied to detection and indicating circuitry. The depth of insertion of the housing and paddle wheel into the conduit is adjustable.