Ultrasonic Sensor 372-0971 AP655F AP355F Asphalt Paver Grade Control Grade control on a paver only works as well as the sensor feeding it. This ultrasonic grade sensor measures the reference surface without touching it, sending a continuous height signal to the screed control so the tow point is corrected before the error reaches the mat. Supplied as a direct replacement unit under reference number 372-0971, covering AP655F and AP355F tracked pavers. Non-Contact Measurement,