Application of ultrasonic sensor in sand level detection
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In the engineering construction industry, if the quality of concrete is not up to standard, there will be a major safety hazard. Therefore, in the production of concrete, the precise measurement of the concrete components of the material is the basic guarantee of the quality of concrete, therefore, "GB10172-1988 concrete mixing station (building) technical conditions" for the production of concrete mixing equipment has specified the specific measurement precision requirements. Sand is one of the components of concrete, it is self-evident that the accurate measurement of sand is an important factor to ensure the quality of concrete.
At present, most of the measurement methods of sand and stone are weighing. Due to the water content of sand and other problems, this method has a large error in the measurement, and the structure is complex and heavy. The ultrasonic system has the characteristics of high precision, strong adaptability to harsh environment, light equipment, simple installation and debugging, easy to read and measure without direct contact with the measured medium. Only in level measurement, has been successfully used in a variety of materials, such as: coal bunker coal level monitoring and liquid level detection.
1. Theoretical basis of ultrasonic measurement of sand level
Ultrasonic ranging has time difference method, phase method and so on, because of the time difference method of low cost, simple implementation, wide range of ranging application, so this article chooses this method. See Figure l, that is, the ultrasonic transmitting end and receiving end are installed on the top of the sand hopper at the same time, the transmitting end sends out ultrasonic pulse, and when it meets the sand interface, the ultrasonic pulse is reflected back. The electronic unit calculates the time difference t between the transmitting end sending signal and the receiving end receiving signal, and the distance between the sand interface and the top of the hopper is h=vt / 2, and then the material level is L=H-h, where, Is the propagation speed of ultrasonic wave in the air, J is the height of material level, is the height of hopper.
2. Improve the overall accuracy key
2.1 Design of temperature compensation
Temperature is one of the main reasons affecting the ultrasonic measurement error, ultrasonic propagation speed in the air is different because of the temperature, therefore, in the design need temperature sensor to measure the ambient temperature above the hopper, sound speed compensation.
In addition, considering that sometimes the hopper is large and the measuring distance is large in practical application, it is difficult to measure the temperature distribution. At this time, an automatic calibration device can be installed. Attention should be paid to the proper installation of the calibration device to avoid the mixing of the calibration echo and the main echo.
2.2 Automatically increase the amplitude of the back wave
Although the system is used to measure the amount of sand used in the hopper discharge, it can avoid the ultrasonic sensor being affected by obstacles in the measurement direction, the shape of the measured medium, etc. However, the sand interface is very rough and uneven, and the reflected wave signal is weak. In addition, the echo will weaken when measured at a distance. Therefore, the automatic gain control circuit is used here to keep the amplitude basis of the received echo unchanged, and then output through the shaping circuit to improve the measurement accuracy _8].
3 System hardware design
The high-speed microcontroller W77E58 produced by Taiwan Huabang Company is used to measure the propagation time of ultrasonic wave, and the measurement resolution is 0.1s. When the ambient temperature is 20℃, the ultrasonic velocity is 343.6 m/s, and the propagation time is 2.91 s at a distance of 1mm. Therefore, the use of W77E58 timing, can fully ensure the measurement accuracy. See Figure 2 for the system design of the lower setting machine for measuring sand level
3.1 Ultrasonic transmitting and receiving module
3.2 Temperature Measurement module
3.3 Automatic gain control module
4 System software design
The main program is the core of the whole control system, through the call module subroutine to drive the hardware circuit of each module to work normally, in order to achieve the real-time measurement and display of sand level function. In practice, calculations can show how much sand is used, and control it. The flowchart of the main program is shown in Figure 4, where the software implementation of the automatic gain circuit adopts the method of stepwise approximation
5 Experimental Results
In the laboratory, a regular shaped cylinder was used as a simulation hopper for many measurements. As the hopper continued to discharge, the display showed different material levels.
In order to reduce the measurement error as much as possible, the sensor should be parallel to the ground as far as possible during installation, and the installation height should not be too low; In order to reduce the influence of ultrasonic bourbon, the distance between the two probes of the ultrasonic sensor should be greater than 3cm, and the distance during the experiment. At the room temperature of 25℃, the distance between the ultrasonic probe and the material surface is measured in
Table 1 Ultrasonic probe to the surface distance h data and error
The experiment shows that the accuracy of distance h measured by this system reaches 1mm with good repeatability. The measurement blind area within 20mm is relatively small.
Obviously, the material level height is multiplied by the effective area of the hopper to obtain the volume of sand, and the volume of sand is multiplied by the density of sand to obtain the mass of sand in the hopper G. Therefore, it can not only monitor the amount of sand remaining in the hopper through the computer, but also monitor the amount of sand material through the calculation, so as to achieve the accurate ratio of sand in various occasions.
6 Closing remarks
1) In this paper, a ranging system based on ultrasonic sensor is designed for continuous measurement of sand level; High - speed MCU automatic gain circuit is adopted. After testing, the system has high precision and the measurement error has reached the minimum level. The system can also communicate with the host computer and expand into storage, print output, offside alarm and other functions.
2) The material level measurement system is suitable for most solid material levels, such as cement and cereal and other extremely dry and dusty materials, even under dynamic conditions.
3) In order to further improve the accuracy, environmental humidity should be considered. Because ultrasonic waves travel faster in liquids and solids; The reference error should also be considered. The actual measured distance should be the distance between the piezoelectric wafer and the obstacle. Since the piezoelectric wafer is inside the probe, the reference error is induced.
References:
[1] Wu Kangxiong, Li Baihui, Chen Ying. Low cost sand metering Technology Based on Capacitive Sensing Principle [J]. Chinese Journal of Construction Machinery, 2006,4 (1) : 102-105.
[2] Liu Wei. Measurement Control of Continuous Asphalt Mixing Equipment [J]. Construction Mechanization, 2004(8) : 68-70.
[3] Jia Bonian, Yu Pu, Song Aiguo. Sensor technology [M]. Nanjing: Southeast University Press, 2000.
[4] Zhang Panfeng, Wang Yuping, Zhang Jian, et al. Design of Ultrasonic Wave Rangefinder with Temperature Compensation [J]. Computer Measurement and Control, 2012, 20(6) : 1717-1732.
[5] Shi Wei, Meng Jun, Liu Bo. Ultrasonic range control device for temperature correction [J]. Mechanical Engineering & Automation, 2005(6) : 85-87.
[6] He Guifang. Design of Ultra-sonic Distance Measurement System with High Precision [J]. Sensors and Microsystems, 2010,29 (4) : 111-113.
[7] WangJinjin, YuanDong, CaiPing. Rangeresolutionofultrasonic distancemeasurementusing singlebitcrosscorrelation Forrobot s [c] / / InternationalConferenceonInformation, 2010:917-923.
[8] YamashitaK, KatataH, OkuyamaM, eta1. Arrayedultrasonicmi -- cmsensorswith high dreetivity forin -- airuse using PZT thin film onsilicon diaphrams[J]. Sensorsand Aetuatom A: Physical, 2002, 97/98:302-307.
[9] Take it easy. Application of Ultrasonic Distance Measurement in Parking auxiliary System [D]. Dalian: Dalian University of Technology, 2010.
[10] Zhang Shuqing, Jin Shijiu, Li Jun. Research on the Method of Improving the Accuracy of ultrasonic level Detection [J]. Chinese Journal of Sensors and Actuators, 2007(7) : 1652-1654.
[11] Zhu Xiangqing, Chen Zhixiong. 360 with temperature compensation. Ultrasonic wave Distance Measurement System design [J]. Piezoelectricity & Acoustooptics, 2011, 33(2) : 315-319.
[12]HuangKenung, HuangYupei. Multiple -- frequencyultrasonicdis -- t using direct digital frequency frequency synthesizer -- s[J]. SensorsandActuatorsA, 2009,149:42-45.
[13] Zou Yi. Design of Short Range and High Precision Ultrasonic Distance Measurement System [D]. Dalian: Dalian University of Technology. 2009.
[14] Yang Huiyuan, Tu Chengjun, Tan Weijie. Design of Ultrasonic Wave Ranging System [J]. Journal of Chongqing University of Science and Technology: Natural Science Edition, 2009,11 (3) : 163-166.
