MEASURING METHOD FOR COATING THICKNESS BY ULTRASONIC WAVE

PURPOSE:To prevent an error in coating thickness measurement for measuring the coating thickness of a cable running in a cooling tank by an ultrasonic wave, by correcting the propagation speed of the ultrasonic wave by the temperature of cooling water. CONSTITUTION:A conductor is extruded by an extruder 2 and provided with a coating to obtain a cable 3, which is run through a cooling water tank 4. In the cooling water 5 in the cooling water tank, an ultrasonic-wave transmitter and receiver 6 and a water temperature detector 7 are dipped and installed. A microprocessor controller 8 controls the transmitter and receiver to transmit an ultrasonic wave beam as pulses, and finds thickness T=V.DELTAt/2, where DELTAt is a difference in arrival time between reflected waves from the coating surface of the cable and the interface between the coating and conductor. The ultrasonic- wave propagation speed V varies with the cooling water temperature, so the speed V is corrected in accordance with the water temperature on the basis of a signal from the water temperature detector.