Precautions of ultrasonic thickness gauge measurement (2)

Several methods in measurement

1—Single measurement method: measurement at one point
2—Double measurement method: Perform two measurements with a probe at one point. The probe crosstalk spacers should be perpendicular to each other in both measurements. Selecting the minimum value in the reading as the exact thickness of the material.
3—Multi-point measurement method: bluetooth d-meter-for ultrasonic thickness

performs multiple measurements within a certain measurement range, taking the minimum value as the material thickness value.

The probe cross-talk separator wear will affect the measurement, and the probe should be replaced when the following phenomena occur.

1—When is measuring different thicknesses, the measured value always shows a certain value.
2—The couple probe or measured value appears when the probe is inserted without measurement.

Casting measurement

Casting measurements have their own particularities. The grain of the casting material is relatively coarse, the structure is not tight enough, and the measurement is often carried out in a matte state, thus making the measurement encounter a great difficulty. First, the coarseness of the grains and the intimacy of the structure cause a great attenuation of the acoustic energy. The attenuation is caused by the scattering and absorption of the acoustic energy by the material. The degree of attenuation is closely related to the grain size and ultrasonic frequency. The attenuation at the same frequency increases with the increasing of the piezo crystal grain diameter, but there is a highest point. Above this point, the crystal grain diameter increases again, and the attenuation tends to be basically a fixed value. The attenuation for different frequencies increases with the increasing frequency. Secondly, due to coarse grain and coarse out-of-phase structure in the casting, abnormal reflection, ie grassy echo or tree echo, which will cause abnormal readings in the ultrasonic thickness measurement equipment, resulting in misjudgment. In addition, as the crystal grains are coarse, the elastic anisotropy in the direction of metal crystals is more pronounced, which causes the difference in sound velocity in different directions, and the maximum difference is even 5.5%. Moreover, the compactness of the tissue at different locations within the workpiece is also inconsistent, which will also cause a difference in sound speed. These ultrasonic meta thickness gauge will all produce inaccuracies in the measurement. Therefore, special care must be taken in the measurement of castings.

Pay attention to the measurement of castings:

1. When measuring castings that are not machined on the surface, it is necessary to use a large viscosity oil. Butter and water glass act as a coupling agent.
2. It is best to use the same material as the object to be tested, and measure the sound velocity of the standard test block calibration material with the same direction as the object to be tested.