Abstract: Four ultrasonic probes in space quadrature are located near the input end of a water tank to define an opening for receiving extruded plastic tubing provided from an adjacent extrusion die. The probes are formed with passages that expel bubble-free water between the probes and tubing. Ultrasonic thickness measuring circuitry provides a wall thickness signal to a control signal source that also receives a diameter signal provided by a diameter sensor near the output end of the tank representative of the tube thickness.

Abstract: A pin is formed with an axial bore at the bottom end for receiving compressed air and containing a diffuser. This bored end has a portion of progressively increasing cross section toward the end. A pair of axially spaced diametrical openings in space quadrature intersect the axial bore. A bumper with a resilient face may be urged toward the pin when an air switch is open. A source of compressed air is coupled to the pneumatic cylinder through an air switch and to sample and reference conduits through a pressure regulator. There are needle valves between the pressure regulator and the sample and reference conduits, respectively. A meter measures the differential air pressure between the sample and reference conduits.