Fanhang Zhang, Winter Semester 2020-2021

Ultrasonic Measurement of Distance and Thickness is the use of ultrasonic transmission in the medium of time and speed to determine the thickness of the object and distance. Modern measurement technology is more and more combined with computer. This paper will introduce the structure of ultrasonic measurement system based on ARM (Advanced reduced instruction set computing Machine).

INTRODUCTION

Ultrasonic detection technology is a typical non-destructive measurement method, which is based on electronics, material science, physics, and is widely used. ultrasound has all the properties of a mechanical wave, which is an oscillation of matter, and therefore transfers energy through a medium[1]. Ultrasonic testing is a physical process that produces, propagates and receives ultrasonic signals. Ultrasonic waves are produced by mechanical vibrations and travel at different speeds in different media.

In scientific research projects, product development, electronic design and other activities, we often encounter 8-bit microcontroller speed, I/O ports, internal RAM and internal Flash memory is not and other issues. As the cost of 32-bit processors decreases, 32-bit processors are used as the upgrade and replace 8-bit microcontroller systems. Especially with the use of low-cost ARM processors with internal Flash memory, the cost is comparable to that of an 8-bit microcontroller. The ARM microprocessor has a Thumb/ARM dual instruction set, high instruction throughput, many registers, rich interfaces, and small size, low power consumption, low cost, high performance, fast running speed and other excellent characteristics. Using ARM processor to control ultrasonic ranging will greatly improve terminal data collection efficiency and processing speed.

This paper puts forward the research of ARM based ultrasonic ranging system, is based on embedded ARM processor as the control core of a set of integrated application system used in distance measurement, in line with the development trend of measuring instruments.[2] Products developed based on embedded systems have great potential and broader application prospects in various application fields.

INTRODUCTION TO ULTRASOUND

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. Ultrasound devices operate with frequencies from 20 kHz up to several GHz.[3]. Since ultrasound has many advantages, these people widely use ultrasonic technology in the fields of industrial and agricultural production, robotics, military detection, and medical pathological diagnosis. Carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) composite materials are widely used in a variety of applications such as aerospace structures, wind turbine blades, the automotive industry, and mass transit[4]-[7].

Ultrasonic technology is widely used in distance measurement. Due to its   non-destructive measurement method, low cost, easy operation, rapid measurement and other advantages, it is widely used in fields such as industrial surveying, safety prewarning, and robot scientific obstacle avoidance. Researchers explore and advance ultrasonic ranging technology, makes the measurement accuracy and stability of ultrasonic distance measurement more suitable for industrial control and high-level measurement instrumentation requirements. As seen Hand-held distance meter, simple structure, convenient operation, accurate measurement, , currently there is an ultrasonic [8]. The emergence of, although the accuracy is not high, it still reflects the potential of ultrasonic ranging technology.

INTRODUCTION OF ARM EMBEDDED SYSTEM

What is an embedded system? The embedded system originated from a microcomputer. Because it is embedded in the object system, it is a special computer system that realizes the intelligence of embedded objects.

First of all, the microcomputer cannot meet the requirements of most object systems for embedded space, price and reliability, embedded systems have become independent establish the development of the single-chip microcomputer. The single-chip microcomputer is the embryonic form of the early embedded system. It refers to the microcomputer chip, integrated monolithic microcomputer. In order to meet the control requirements of the, the single-chip microcomputer is constantly developing in the direction of the microprocessor/controller. The microprocessor/controller is constantly updated and is the development frontier of embedded systems. The emergence of embedded systems was a milestone in the history of modern computer development. After decades of development, embedded systems changed the way people live and work to a great extent.

The main characteristics of embedded systems are "embeddedness", "contained computer", and "specificity":

(1) Embeddedness refers to being embedded in the control system of the object to realize its intelligent operation control.

(2) The built-in computer is the core, and the system with the built-in microprocessor chip can realize the intelligent ability of the target systemization system.

(3) Dedicated means that according to the requirements of the controlled object, it can be designed into an application system suitable for the object's requirements by cutting the system (including software and hardware cutting) under the development tool platform.

APPLICATION STASTUS AND DEVELOPMENT TREND OF ULTRASONIC MEASUREMENT SYSTEM

At present, commonly used ultrasonic ranging systems are based on microcontrollers as the control core, combined with hardware circuit improvements and software algorithm programming, through the use of microcontrollers to achieve automatic compensation correction,  time corrected gain, delay interference and other methods to continuously improve the measurement accuracy and measurement range of ultrasonic ranging.

So far, the ultrasonic ranging system has been and can accurately analyze and process the received signal. For example, it can filter various interference signals, identify multiple echoes, detect and analyze signal strength, and monitor ambient temperature signals. In this way, external interference can be minimised and accurate measurement can be performed. While the ultrasonic ranging system can provide fixed-point and continuous measurement functions, it can also conveniently provide signals required for remote measurement, such as telemetry, and remote control for other measuring instruments or systems.

PRINCIPLE OF ULTRASONIC MEASURING

Ultrasonic ranging methods usually include transit time detection, acoustic amplitude detection and phase difference detection. Because the phase detection method is limited by the application conditions, the scope of application is limited[9]; the acoustic wave amplitude detection method is greatly affected by the reflective medium; Time of flight and amplitude are detection methods that are the most commonly used, with simple principle and wide application range. The so-called transit time detection method ultrasonic ranging is based on the two variables of the ultrasonic propagation speed in the propagation medium and the propagation time of the ultrasonic wave in this distance to find the distance of the ultrasonic propagation in the medium. The transit time is introduced below[10].. The basic principle of ultrasonic distance measurement is shown in the figure: the drive end of the ultrasonic transmitting transducer converts the voltage signal applied to it at a certain operating frequency into a mechanical vibration producing an ultrasonic wave which propagates in the medium and encounters the reflecting surface. Reflected back, the receiving transducer detects the ultrasonic echo signal returned by the reflecting surface, and then converts this acoustic signal into an electrical signal, which is processed as a signal that can be received by the processor system.

As shown in the figure 1, let t₁ and t₂ be the time taken by the ultrasonic wave from the transmitting end to the reflecting interface and the time taken by the reflecting surface back to the receiving end, respectively. Since the ultrasonic wave has the same propagation velocity under the same propagation medium. The time elapsed by the ultrasonic wave from the transmitting end to the reflecting surface is equal to the time elapsed from the reflecting surface to the receiving end, that is, t₁ = t₂. If d is the horizontal distance from the probe to the reflecting surface, S is the ultrasonic wave from the transmitting end to the reflecting surface. The actual propagation distance, h is the distance between the two probes of the ultrasonic transducer, and C is the propagation speed of the ultrasonic in the air medium, then the formula can be obtained:

$//<![CDATA[ \begin{array}{l}S=c(t_1+t_2 )/2\end{array} //]]>$

$//<![CDATA[ \begin{array}{l}d=√(s^2-(h/2)^2 )\end{array} //]]>$

Since h is relatively small compared to S, the influence of h is generally ignored, and d ≈ S is taken. When calculating the distance d measured in the figure, it is enough to directly calculate the distance S the ultrasonic wave propagates in the air. The propagation speed of ultrasonic waves in the air is only related to the temperature of the air environment. Therefore, in a certain temperature environment, the propagation speed C of ultrasonic waves in the air is fixed, and the sound speed measurement only needs to use a temperature sensor to detect the current ambient temperature. Then according to the relationship between sound speed and temperature, the current sound speed can be calculated and determined. Therefore, accurate measurement of propagation time is the most important measurement work when measuring.

OVERALL MEASUREMENT PROGRAM

The ultrasonic distance measurement system studied in this paper is composed of a lower computer ultrasonic distance measurement unit and an upper computer monitoring unit, and the two communicate through a serial port. The lower computer test unit is composed of a microcontroller and corresponding measurement modules. The upper computer monitoring unit is composed of a PC and a corresponding graphical user interface. The lower computer sends the distance measurement results to the upper computer through the serial port, and the upper computer can monitor the results. The overall design block diagram is shown in the figure 2.

The lower computer is composed of STM32 microcontroller and related modules, with functions such as distance measurement, real-time time, LCD display, and serial communication. The STM32 microcontroller is the core of the system and is responsible for controlling the normal and orderly operation of each module. The distance measurement function is completed by the ultrasonic distance measurement module, which uses the basic principle of the ultrasonic transit time detection method to obtain the corresponding value, which is displayed by the LCD display module. The display module can also display the real-time time controlled by STM32. The result of the distance measurement of the lower computer is transmitted to the PC through the serial port, so that the upper computer can realize the monitoring function.

The host computer of this system is a PC, and LabVIEW is used to develop a graphical user interface. Functions include sending and receiving data commands through the serial port, real-time monitoring of curves, test alarms and historical data records. It sends a "measurement" command to the lower computer through the serial port, displays the measurement result, and draws the real-time graph of the measurement. When the measurement result exceeds a certain range, an alarm is issued. The measuring system workflow is shown in the figure 3

CONCLUSION

This article has done preliminary research work on the ultrasonic ranging system. Although I checked a lot of related materials and learned a lot of related technologies during the period, due to the limited professional knowledge and research capabilities, the system completed in this article was not comprehensive enough in many aspects. Continuous improvement in future research. For the deficiencies in the design of this article, follow-up work can be done:

(1) The construction of the hardware circuit.

(2) The accuracy of ultrasonic ranging. The frequency and speed of ultrasonic propagation in the air generally vary with the temperature of the surrounding environment. Therefore, when accurately measuring the distance to a specific target or other object, we must pay attention to ensuring that the surrounding temperature is in the appropriate range.

(3) Monitoring interface problems.

REFERENCE

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