The ultrasonic thickness gauge does not belong to the Class A measuring instrument. According to the "Measures for the Classification and Management of Measuring Instruments", the ultrasonic thickness gauge belongs to the Class B measuring instrument.
Class A measuring instruments mainly include instruments of the highest measurement standards of construction enterprises and working measuring instruments used for value transfer, such as first-level flat crystals, zero-level knife-edge rulers, level gauges, square rulers, vernier gauges, dial gauges, micrometer gauges, autocollimators, vertical optical gauges, standard piston pressure gauges, megohmmeters, ground resistance measuring instruments, X-ray flaw detectors, etc.
The ultrasonic thickness gauge measures thickness based on the principle of ultrasonic pulse reflection. When the ultrasonic pulse emitted by the probe passes through the object to be measured and reaches the material interface, the pulse is reflected back to the probe, and the thickness of the material to be measured is determined by accurately measuring the time it takes for the ultrasonic wave to propagate in the material.