Research On Key Techniques Of Ultrasonic Open Channel Flowmeter Based On AT89S52

Water for agricultural irrigation is large in China, but the efficiency is lower, only about half of that in the developed countries. At present, there are no measuring water facilities in many irrigated area, or a large deviation in measurement accuracy. Considerable irrigated area is mainly area-based fees collection, resulting in the peasants'water saving consciousness is indifferent, giving rise to substantial waste of water resources. With the increasing scarcity of water resources and the establishment of water markets, measuring water in irrigated area is the necessary measure to dispatch reasonably irrigation water resources, implement properly water plans and strengthen economic management, and is also one of the effective means to improve water use efficiency and promote water-saving agriculture.Ultrasonic flowmeter is a non-contact measurement equipment, it does not need to install the measuring element in the fluid flow, does not change the state of the fluid motion, does not produce additional head loss. Especially in open channel flow measurement, it has obvious advantages, and it is the ideal energy-efficient flowmeter for flow measurement in irrigated area.Key techniques of ultrasonic open channel flowmeter are discussed in this paper, and an ultrasonic open channel flowmeter is preliminarily designed, which is made up of measuring flume or weir, ultrasonic sensors and secondary instrument. The main research content as follows:(1) Through analyzing the ultrasonic sensor characteristics, a liquid level measurement plan of using air-coupled two-sensors is determined, which reduces the impact of the sensor blind zone to the measuring accuracy.(2) In order to be good for the time detection of the pulse echo, the pulse echo is preprocessed by three-level operational amplifiers, which consist of preamplification circuit, bandpass filtering circuit and programmable amplification circuit.(3) Through analyzing the pulse echo signal, a detection method based on peak time point has been put forward, realized by the hardware circuit, including the envelope detector circuit, differential circuit and the zero-crossing detection circuit, which has nothing to do with the signal amplitude, and has good detection characteristics of the transmission time.(4) Through analyzing the impact of temperature to the measuring accuracy, a plan of using single-bus digital temperature sensor DS18B20 to measure temperature is proposed, which can real-time correct the speed of sound with the changing temperature.(5) By using 24MHz crystal, the timing accuracy of AT89S52 timer is improved, and then the accuracy of flow measurement is improved.(6) With the core of AT89S52 microcontroller, the flowmeter provide a wealth of operational functions: 4×4 keyboard, 128×64 LCD display, real time clock, serial communications, and so on.(7) The system software is designed by modular programming. In order to improve the applicability of the flowmeter, the parameters and formulas of a variety of measuring flume or weir are stored in AT24C1024B, which can realize to choose different flow calculation in different applications.