Study Pointer Instrument Automatic Interpretation

The pointer instrument can visually reflect the change trend of the measuring instrument’s magnitudes. And it has the advantages of simple structure, ease use and inexpensive in price, etc. Therefore, it is wildly used in scientific experiments and industrial production.There is a provision of the state that the accuracy of the pointer instrument should be verified in batch or regularly by instrument manufacturers and metrological verification departments. Most pointer instruments, especially those with high precision, are still verified by human to compare the difference between the instrument reading and the standard input. Due to work for a long time, the testing personnel will have visual fatigue inevitably, which will lead to low calibration accuracy.In order to solve the shortcomings of traditional methods, this thesis, combined with the actual needs of the Meter Verification of Measurement and Testing Technology of Yunnan Province, has a research on the automatic interpretation method of the pointer instrument by using the technologies of image processing and pattern recognition while combining theory with simulation experiment. The main contents are as follows:(1) To build the pointer instrument image acquisition hardware and software environment, and the pointer instrument image model library.(2) To study the image preprocessing algorithms about pointer instrument. Image preprocessing mainly includes the dial scale, gray level, the Hough transform to detect the arc scale instrument, polar coordinate conversion parameter, edge detection and so on.(3) To study the pointer positioning method. This paper presents a pointer positioning method that curves scale expands into horizontal rectangular dial based on Hough transform, and scans the region from bottom to top in line until finds a vertical rectangular area which contains pointer only, and then detects the pointer position with Hough transform in linear theory in this region. Experiments show that this approach can quickly and efficiently complete the positioning of the instrument pointer-pointer position with high accuracy.(4) To study the pointer instrument scale figures and the scale line positioning method. Through scanning the image line by line from the top to down until the gray value less than the setting threshold, and we can see that the position of the line is the bottom end of the scale figures. As a boundary of the figures, the instrument image can be divided into line scale contains scale digital and scale line. Graduated in the top image, the template matching method is adopted to identify scale digital while the Hough transform is used to position the scale line about the lower end of the image. Experiments show that this method can quickly and efficiently complete the positioning of pointer instrument dial number and calibration.Finally, on the study of the above algorithms, the author uses the method of Visual C++and Open CV to programming to design the software framework of pointer instrument automatic interpretation system and realize the building of pointer instrument automatic interpretation experimental platform. Through doing comprehensive experiments with the platform, we get an excellent result.