Posted 03 Jan 2011 17:30
The basic principle of ultrasonic thickness gauge is based on the principle of ultrasonic pulse reflection to the thickness measurement, when the ultrasonic pulses emitted by the probe measured object to reach the interface material, the pulse is reflected back to the probe, through the accurate measurement of ultrasonic wave propagation in the material time to determine the thickness of the material being tested. Where can a constant speed of ultrasound to the spread in its internal materials can be measured using this principle. Click the design principles of various sheet metal thickness can be precisely machined parts and a variety of measurement equipment can also produce all kinds of pipes and pressure vessels, monitoring of their use after the process of thinning the extent of corrosion . Can be widely used in petroleum, chemical, metallurgy, shipbuilding, aviation, aerospace and other fields. Ultrasonic thickness gauge ultrasonic thickness measurement of four methods of measurement are common measurement method, accurate measurement, continuous measurement, the grid method of measurement. 1, the general measurement methods: (1) point on thickness measurement with the probe twice, in two separate measurements in the surface of the probe 90 to each other, whichever is less is the workpiece thickness. (2) 30mm multi-point measurement: When the measured value is unstable, with a measuring point as the center, about 30mm in diameter and multiple measurements within a circle, take the minimum value for the thickness of the workpiece. 2, precise measurement: the required number of measurement points around the increase in measured thickness changes are so thick lines. 3, the continuous measurement method: using single-point measurements along the designated route for continuous measurement, at intervals of not more than 5mm. 4, measurement grid: grid planning in the designated areas, according to point thickness measurement records. This method is high-voltage equipment, stainless steel lining is widely used in corrosion monitoring. Ultrasonic Thickness Measurement cause of the error indication is too large or too small because of the actual testing work, often encountered with the design value of indicated thickness (or expected value) are obviously too large or too small, Reasons are as follows: 1, layered materials, composite (non-homogeneous) materials. To measure the coupling of the stacked material is not impossible, because ultrasound can not penetrate the space without coupling, and can not be in the composite (non-homogeneous) materials in the uniform spread. For the dressing made of multiple materials, equipment (such as urea, high-pressure equipment), to pay special attention thickness, thickness of the indication in contact with the probe, said only that the layer thickness. 2, the speed of sound wrong choice. Measure the workpiece before, according to material type or according to preset the speed of sound measured against the standard silent speed of the block. When the instrument calibration with a material (often used for the steel test block) went to another measurement of materials, will produce erroneous results. 3, the temperature. The general speed of sound in solid materials with its temperature decreases, there is experimental data show that hot material for each additional 100C, the speed of sound decreased by 1%. For the high temperature encountered in service equipment is often the case. 4, the impact of coupling agent. Coupling agent is used to rule out the probe and the air between the measured object, so that the effective penetration of ultrasound to detect the purpose of the workpiece. If you choose to type or incorrect use, will result in errors or coupled sign flashing, can not be measured. Actual use of the coupling agent because of excessive use, causing the probe to leave the workpiece, the instrument showing the value of the coupling agent layer thickness value. 5, the measured object (a pipe) within the sediments, when the sediment acoustic impedance with the workpiece or less, the display is wall thickness plus the thickness of sediments. 6, the metal surface oxide or coating of paint. The compact metal oxide surface coating or paint, although tightly with the base material, the interface was unknown, but the speed of sound in the propagation velocity of the two substances are different, resulting in errors, and with the cover thickness, the size of the error also different. 7, when the defects inside the material (such as inclusion, mezzanine, etc.), the display is about 70% of the nominal thickness (in this case for further use ultrasonic flaw detector defect detection). 8, stress. In-service equipment, pipes most of the existence of a stress, the stress status of solid materials have a certain impact on the speed of sound, when the stress direction and communication in the same direction, if the stress is compressive stress, the stress to the workpiece to increase flexibility, speed of sound to speed up; contrary If the stress is tensile stress, the slow speed of sound. When the stress wave propagation direction and different to, the volatility process of the stress trajectories of particle vibration interference, wave propagation direction is off. According to the information that the general stress increased slowly increasing the speed of sound.