Why are there deviations in the measurement results of ultrasonic thickness gauges?
1: The error of the ultrasonic thickness gauge itself. The following is the error of the national standard. This error is quite large for high-precision measurement:
National standard error requirements for ultrasonic thickness gauges
Ultrasonic thickness gauges with a resolution of 0.001mm have now appeared, such as Zhongke Pudao's high-precision ultrasonic thickness gauge PD-T7, and the error has stabilized at 0.01mm, that is, within 10 microns.
2: Measurement exceeds the limit. Ordinary thickness gauges use dual-element probes. The lower limit of measurement is generally 0.8mm for flat carbon steel and 1.2mm for curved carbon steel. The lower limit of curved surfaces will be greater than that of flat surfaces. Exceeding the limit will cause the indication value to be much larger. At this time, it has been Not an error, but an inability to measure. The PD-T7 ultrasonic thickness gauge with a single crystal probe can measure flat carbon steel to a lower limit of 0.15mm.
3: The surface roughness and flatness of the material are affected. This is easy to understand. The ultrasonic thickness gauge measurement is the average value below the probe.
4: The influence of surface coating is also very large and cannot be ignored.
No penetration coating effect measured with coating present
5: Internal defects of materials:
Castings, fiberglass reinforced plastics and other materials with many internal defects may not be able to measure low and only the location of the defects can be measured. In this case, a high-penetration probe and an instrument with gain adjustment should be selected, such as the PD-T8 ultrasonic thickness gauge. Better measurement results can be achieved by adjusting the gain.
6: Effect of temperature (material temperature and ambient temperature)
1. Influence of material temperature. The higher the temperature of the measured object, the lower the sound speed. The sound speed measurement result obtained at normal temperature will be higher than the actual value.
2. The influence of the hand on the temperature of the probe will cause temperature drift. After a while, calibration will be required. You can choose the PD-T7 ultrasonic thickness gauge, which can maintain high-precision measurement without calibration.
7: The most important point, the speed of sound
The ultrasonic thickness gauge must accurately back-calculate the sound velocity. It is not recommended to use the built-in reference sound velocity. The sound velocity of the same material and different brands will vary greatly. For example, the sound velocity of stainless steel ranges from 5200-5900. Incorrect sound velocity will also produce large errors.
