The latest version of the ultrasonic flaw detector purchase instrument principle
The latest version of the ultrasonic flaw detector purchase instrument principle
Ultrasonic Flaw Detector is a portable industrial non-destructive testing instrument that can detect, locate, evaluate and diagnose various defects (cracks, looseness, pores, inclusions, etc.) inside the workpiece quickly, easily, without damage and accurately. It can be used in both laboratories and engineering sites. Widely used in boilers, pressure vessels, aerospace, aviation, electric power, petroleum, chemical, offshore oil, pipeline, military, shipbuilding, automotive, machinery manufacturing, metallurgy, metal processing industry, steel structure, railway transportation, nuclear power, universities, etc. industry.
Physical basis
Wave wave classification
All the mass points of the medium are related to each other by elastic force. A particle vibrates within the medium to excite vibrations from surrounding particles. The propagation of vibrations in an elastic medium is called a wave. Waves, there are electromagnetic waves (electric waves and light waves) and sound waves (or mechanical waves).
Sound wave
Sound waves are elastic waves that can propagate in gases, liquids, and solids. It can be divided into divided sound waves, audible sound waves, ultrasonic waves and special ultrasonic waves. The sound waves that can be heard by the human ear are between 20-20000 Hz. Ultrasonic waves, which are more than 20,000 Hz, are inaudible to the human ear. The higher the frequency of the sound wave, the more similar it is to certain properties of the optical (such as reflection. The law of refraction).
Instrument principle
When the ultrasonic wave propagates in the material to be tested, the acoustic properties of the material and the changes in the internal structure have a certain influence on the propagation of the ultrasonic wave. The technique of understanding the material properties and structural changes by detecting the degree and condition of the ultrasonic wave is called ultrasonic testing. Ultrasonic testing methods generally include a penetrating method, a pulse reflecting method, a tandem method, and the like.
Digital ultrasonic flaw detectors usually send ultrasound to the object to be measured (such as industrial materials, human body), and then use its reflection, Doppler effect, transmission, etc. to obtain information inside the object under test and process it to form an image.
Doppler effect method
Is to use the Doppler shift effect that occurs when the ultrasonic encounters a moving object to derive the characteristics of the moving direction and speed of the object;
Transmission method
The internal characteristics of the object are obtained by analyzing the changes after the ultrasonic wave penetrates the object to be measured, and its application is still in the development stage;
Reflection method
The ultrasonic flaw detector here mainly introduces the most widely used method for obtaining the internal characteristic information of the object by the reflection method.
The reflection method is based on the principle that ultrasonic waves will be strongly reflected when the interface is organized by different acoustic impedances. As we know, sound waves are transmitted from one medium to another at the interface between the two. Reflection will occur, and the greater the difference between the media, the greater the reflection, so we can emit an ultrasonic wave that is strong and capable of linear propagation to an object. The ultrasonic flaw detector then receives the reflected ultrasonic wave and according to The order and amplitude of the reflected ultrasonic waves can be used to determine the size and distribution of various media contained in the tissue and the degree of contrast between the various media (the echoes reflected back can reflect The distance from the reflection surface to the detection surface, the amplitude can reflect the characteristics of the size of the medium, the degree of contrast difference, etc., and the ultrasonic flaw detector determines whether the object to be measured is abnormal. In this process, there are many aspects involved, including the generation, reception, signal conversion and processing of ultrasonic waves.
The method for generating ultrasonic waves is to generate an excitation electric signal through a circuit and transmit it to a crystal having a piezoelectric effect (such as quartz, lithium sulfate, etc.) to vibrate to generate ultrasonic waves; and when receiving the reflected ultrasonic waves, the piezoelectric crystal is again The electrical signal is generated by the pressure of the reflected sound wave and transmitted to the signal processing circuit for a series of processing, and the ultrasonic flaw detector finally forms an image for observation and judgment.
Here, the type of the image processing method (that is, the image into which the obtained signal is converted) can be further classified into an A-type display, an M-type display, a B-type display, a C-type display, an F-type display, and the like.
The A-type display processes the received ultrasonic signal into a waveform image. According to the shape of the waveform, it can be seen whether there are any abnormalities and defects in the measured object, and how large, and the ultrasonic flaw detector is mainly used for industrial detection;
The M-type display is a chronological expansion of a luminance-processed detection information to form a one-dimensional "space multi-point motion timing diagram" suitable for observing internal motion objects, ultrasonic flaw detectors such as moving organs and arteries. Blood vessels, etc.
The B-type display is a two-dimensional "anatomical image" that combines a plurality of brightness-processed detection information side by side to reflect the internal tomographic section of the measured object (the B-mode used in hospitals is made by this principle). ), the ultrasonic flaw detector is suitable for observing objects that are static inside;
The C-type display is also an image display. The abscissa and ordinate of the flaw detector screen are mechanically scanned to represent the position of the probe on the surface of the workpiece. The amplitude of the received signal of the probe is expressed by the brightness of the spot. Therefore, when the probe moves on the surface of the workpiece, the flat image of the internal defect of the workpiece is displayed on the screen, but the depth of the defect cannot be displayed.
The C-type display and the F-type display are now used less.
Ultrasonic flaw detector detection can not only be very accurate, but also more convenient and faster than other detection methods, and it will not cause harm to the detection object and the operator. Therefore, it is more and more popular and popular. Development prospects.
Purchase
There are some digital ultrasonic flaw detectors on the market that do not meet the relevant national standards. In 2005, the state promulgated the latest standard "GB/T10061-1999: General technical conditions for A-type pulse reflection ultrasonic flaw detector". At the same time as the new standard was launched, the "JJG746-2004 Ultrasonic Flaw Detector Verification Regulations" was also promulgated. For the first time, the state has explained in detail the verification procedures for digital ultrasonic flaw detectors.
Because the ultrasonic flaw detector is a very professional instrument, not a professional, it is impossible to understand the instrument, so many counterfeiters have drilled the loophole. Some domestic manufacturers use digital ultrasonic flaw detection to make false features, and Daxie produces unqualified products.
If you don't have a professional testing tool, the following simple testing methods can help you identify the authenticity:
1. When the probe is not connected, the gain is adjusted to the maximum, and the waveform on the screen cannot exceed 10% of the screen. If it is exceeded, the instrument fails.
2, see if vertical linearity is qualified, method
3. There are also some indicators that require a dedicated test block. It is recommended that the new instrument be sent to the provincial metrology test station for identification to avoid being fooled.
4, the price is extremely low.
Pay attention to the production process and supporting documents. Generally, ultrasonic training requires professional training.
The consequences of using an unqualified ultrasonic flaw detector are more serious. Since ultrasonic non-destructive testing is used for quality inspection or safety inspection, such as quality accidents and even endangering personal safety, you can save a little money to buy back unqualified instruments that will cause you a very unfavorable situation. We condemn those who are counterfeiters, please raise your level of technological development, and do not harm others. If a major accident occurs, it will also make you ruin your family.
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