Based On Ultrasonic Sensors, Automatic Rainfall Stations

Siphon type and tipping bucket type pluviometer are used for a long time for meteorological department. The siphon type can not realized automatic measurement and data handling and the tipping bucket type dynamic accuracy is not high. At the same time, the bigger inaccuracy exists in these two kinds of measurement methods. Along with the science and technology and the requirement of society development, the automation to the meteorological factor gathers and meteorological data saves and data handling have been put forward to the higher requirement. Use the property of the ultrasonic and high-powered MCU, rainfall can be measured with high precision at the real-time through the time interval by way of the ultrasonic sends and receives the echo. Based on this principle, automatic rainfall station can be developed. At the same time, data communications between automatic rainfall station and meteorological center through the telephone network, and form the rainfall measurement network system.Host computer system installed in meteorological center and automatic rainfall stations installed in each gathered spot are the two parts of the rainfall measured network system. These two parts can communicate with each other by the telephone or mobile telephone network.The host computer system software, with the character of efficiency and high speed, is programmed by the VC++ language MFC. The host computer system's functions are as follows: Duplex communicate with automatic station Data poll gather to each automatic station Save and handle the data Format and print diagram based on the gathered data Download the parameter to automatic station and adjust the clock Dial-up to network and long-distance controlAutomatic rainfall station consists of outer garment, meet rain bucket, water input and output electromagnetic valve, measure bucket, storage battery and circuit control. It can realize the automatic measurement rainfall and sequence record history datum on time withthe RTC; The system can be taken notes history datum more than 1 month at least; Communication interface supported by the serial communication interface can link with the PC's RS232, telephone network and mobile telephone network; It can persist in working with backup power more than 1 day when the local junction circuit stops providing electricity. These functions are realized by the circuits of power, clock, memory, ultrasonic pulse signal occurs and handle, temperature gathered and serial communication in system.The measurement of the time interval of ultrasonic send wave and echo used the catch method of 52 series MCU, and avoided the error that the ISR save the current value of counter.At the same time the clock chip PCF8563 and serial EEPROM chip CSI24C01 with Reset and WDT circuit of I2C bus are used hi the system. They have not only provided the non- volatility data storage area, the supervision ability of power supply and MCU and the RTC, and its I2C bus structure has been simplified the circuit design.The velocity of ultrasonic in water can be changed along with the change of the temperature. It will bring bigger inaccuracy and can not reach the requirement of system if the temperature factors are not considered in. Through the temperature of the rainwater the velocity of ultrasonic in this temperature can be calculated. The high measurement precision can be obtained using temperature compensation in software through the calculated velocity.The systematic reliability is one of the important factors that influence its spread prospect. The method that absorb return circuit design used in power design and electromagnetic valve drive circuit, system power and operating supervision to MCU and redundancy and digital filter technology to the time interval to send wave and echo are used in system design to ensure the reliability and accuracy of measure and control system.