Design And Implemention Of A New Liquid Level Sensor System

The liquid level sensor system is a device measuring the depth of liquid, it is widely used in industrial field level measurement, urban sewage treatment, irrigation monitoring, etc. Traditional liquid level sensor system is phased out because of it’s shortcoming:expensive、inaccurate and not easy to carry. With the continuous development of science and technology, computers、microelectronics、sensors and other high-tech widely used in our society, portable、high-precision intelligent liquid level sensor system become more and more popular.This paper is determined to realize a portable、high-precision(1%accuracy) liquid level sensor system(for open container), after analyzing a variety of liquid level sensors and absorbing their advantages on the market.Firstly, the paper expounds the principles of all kinds of liquid level sensors, analyzes their advantages and disadvantages. On this basis, discusses the feasibility of the reed switch as a liquid lever sensor net in detail, lists several points that should be taken attention, and designs a high-precision liquid lever sensor.Secondly, considering the long-distance signal transmission and the principle of interference, the paper adopts 4-20mA current loop to transmit the signal. The paper decide to use the integrated chip LM358 to design a cost-effective 4-20mA circuit after analysis of two kinds of 4-20mA current loop solutions, and designs a power providing 5V and 12V in accordance with the system requirements.And then, select PIC16F877A as system controller after analyzing the different types of microprocessor application of occasions. Use this chip to design a system control circuit, which is used to control、process and display the signal. Based on the upstairs, analysis the panel of each peripheral hardware interface circuit and function of practical circuit connection mode, lists the part program interface circuit and the explanation.Finally, in order to facilitate data communication and convenient second development, this paper designed the software of PC serial communication program based on VC++development environment. It can receive the level data from the MCU, and use the data to plot a line graph. User can know the real-time level value when viewing the line graph on PC, it is very convenient. At the same time, the interface can preserve the value of the level in computer to facilitate the secondary development.Through practical debugging, this liquid level sensor system can achieve the requirement of 1%accuracy, range with 1 meter. It can normal and stable work, and can realize data uploading function in the absence of harsh environment. Quite a distance with the equipment on-site in the outdoor, the user can monitor the lever changes in the room in real-time. It does have practical application value.