PLASTIC COATING FILM THICKNESS-METER

PROBLEM TO BE SOLVED: To measure thickness of a film provided an plastic material by providing a non-connecting part inside of an ultrasonic sensor, providing the material for pushed against a film thickness to-be-measured body, and, when the ultrasonic signal reflected on both the surfaces of the to-be-measured body is converted into film thickness, correcting the thickness with the use of the reflected ultrasonic signal from the non-connecting part. SOLUTION: When pulse voltage is applied to an ultrasonic vibrator 1, the vibrator 1 emits the ultrasonic wave of unique frequency, and propagates to a delay material 2, a to-be-measured coating film 3, and a plastic 4 of an element. A part of it is reflected on the boundary between the delay material and the coating (reflected wave U2), and another part is reflected on the boundary between the coating and the element (reflected wave U3). The time difference t1 between the electric signal s2 corresponding to the U2 and the electric signal s3 corresponding to the U3 is the time in which the ultrasonic wave goes and comes back between the boundary between the delay material and the coating and that between the coating and the element. So that, on condition that the acoustic velocity of the coating-film material is already known, the thickness is decided.