Application of Digital Ultrasonic Flaw Detector in UT Flaw Detection

1 Introduction

As one of the five conventional nondestructive testing technologies in industry, UT testing technology has been widely used. In UT, the A-type pulse reflection ultrasonic flaw detector has been used for a long time, and its circuit block diagram is shown in Figure 1.

The display of this instrument shows electric pulse signals. It is very difficult for flaw detectors to distinguish defect waves from other types of waves from these signals. Misjudgment and missed judgment often occur, which seriously hinders the application of UT technology at a deeper level. However, with the development of electronic technology, its achievements have been widely used in the UT industry. A digital ultrasonic flaw detector came into being. It has brought about a revolutionary change in UT technology. It can not only record ultrasonic signals in real time, but also give the properties of defect waves.

2 Working principle of digital ultrasonic flaw detector

Different from the A-type pulse flaw detector, the digital flaw detector has significant changes in the circuit. Its circuit block diagram is shown in Figure 2.

Digital signal processing is implemented in a computer program. Usually, the first thing to do is to remove the noise in the signal, and then the signal that has been de-noised is processed for UT detection, including gain control, attenuation compensation, and finding the signal packet route. After the ultrasonic signal is amplified by the receiving part, it is converted into a digital signal by the analog-to-digital converter and transmitted to the computer. The position of the transducer can be controlled by the computer or manually operated, and the converter converts the position into a digital signal and transmits it to the computer. The computer then appropriately processes the ultrasonic waveform that changes with time and position, and draws a conclusion to further control the flaw detection system, and then sets relevant parameters or displays the processing result waveform, graph, etc. on the screen, prints it out, or gives light, sound recognition and alarm signals.

3 Advantages of digital ultrasonic flaw detector

Compared with traditional flaw detectors, it has the following advantages:

(1) Fast detection speed: Digital ultrasonic flaw detectors can generally automatically detect, calculate, and record. Some can also automatically perform depth compensation and automatically set sensitivity, so the detection speed is fast and the efficiency is high.

(2) High detection accuracy: Digital ultrasonic flaw detectors perform high-speed data acquisition, quantification, calculation and discrimination on analog signals, and their detection accuracy can be higher than that of traditional instruments.

(3) Record and archive detection Digital ultrasonic flaw detectors can provide detection records and even defect images.

(4) High reliability and good stability. Digital ultrasonic flaw detectors can collect and store data comprehensively and objectively, and process or post-process the collected data in real time, perform time domain, frequency domain or image analysis on the signal, and grade the workpiece quality through pattern recognition, thus reducing the influence of human factors and improving the reliability and stability of retrieval.

4 Main technical issues of digital ultrasonic flaw detector

(1) Analog-to-digital converter (ADC) ADC is the only way for the ultrasonic signal of the flaw detector to be input into the computer, converting the continuously changing analog signal into a digital signal.

(2) Structure Currently, there are two types: full digital mode and analog-digital hybrid.

(3) Software: There are many different types of software for digital ultrasonic flaw detectors, and the success or failure of the flaw detector depends largely on the level of software support.

5 Development prospects of digital ultrasonic flaw detectors

With the further development of electronic technology and software, digital ultrasonic flaw detectors have broad development prospects. It is believed that in the near future, flaw detectors based on image display will be widely used in industrial inspection.

At present, some digital ultrasonic flaw detectors have simple manual and scanning functions, which can schematically display the cross-sectional images of the inspected workpiece. With the advancement of technology, we can realize phased array B-scan and C-scan imaging on portable instruments, making the flaw detection results as intuitive as medical B-ultrasound.

Defect characterization has always been a difficult problem in UT detection. The development of modern artificial intelligence has made it possible to realize automatic defect characterization by instruments. By using pattern recognition technology and expert systems, various characteristic quantities of a large number of known defects are input into the sample library, so that the instrument can accept human experience and have the ability of automatic defect characterization after learning.