Design Of An Automatic Calibrator For Pluviometer

Precipitation is an important meteorological element. It is significant to measure precipitation not only for the observation of meteorological phenomena, hydrology, marine climate and environment but also for the traffic safety of aviation and railway. Pluviometer is an important instrument to measure precipitation. Its accuracy directly affects the reliability of the measurement data, especially for testing the effect of artificial precipitation and meteorological research, so its measurement accuracy is very important. In order to make sure the precision and reliability of pluviometer, it is very necessary to check the pluviometer. Currently the calibration method for pluviometer is mainly using standard containers or a high accuracy tilting bucket rain-gauge, or through manual method using measuring cup to check out. The entire process is inefficient, and could easily introduce human errors, so we need a calibrator for pluviometer which can generate the desired rainfall automatically.In the paper, a portable automatic calibrator for pluviometer which can be set simulative rainfall intensity and precipitation was designed. It can automatically adjust the current velocity and the flow of water. The calibrator for pluviometer consists of a water container, a unit of ultrasonic liquid level measurement, a valve, a stepper motor and the man-machine interface. The water container connect with outside through the valve and a drainage pipe. The valve opening is controlled by stepper motor to regulate the current velocity. The ultrasonic transducer above the water container is used to measure the current liquid level and then to estimate the current velocity and the flow of water. The instrument can be set simulative rainfall intensity and precipitation through the man-machine interface. According to the simulative rainfall intensity, the system calculates the number of steps which the stepper motor should move to adjust the valve opening. At the same time, the system uses ultrasonic to detect the current liquid level and then controls the stepper motor regulating the current velocity and the flow of water automatically by way of feedback to keep the water flow evenly and accurately. When the flow of water dose not reach the desired precipitation, the valve maintains the drainage state. When the flow of water reaches the set precipitation, the processor controls stepper motor rotate reversely to close the valve. Different rainfall intensity and precipitation can be set to simulate the real rainfall via the man-machine interface. Finally, by comparing with the pluviometer readings, we judge whether it meets the precision demand. To ensure the precision, we use a high-frequency ultrasonic transducer whose frequency is 200KHz and the processor is selected with ARM7 chip which has a 32-bit timer and the clock frequency of CPU reaches 50MHZ. The unique function of external capture and fast timer interruption can enhance detection accuracy of the ultrasonic pulse edge and improve system response time, thus helping to improve accuracy of the calibrator for pluviometer.Compared with traditional calibration methods, automatic calibrator for pluviometer can avoid the uncertain factors by manual operation. It can maintain the water flow evenly, in addition, the equipment is small, easy to operate and can use rechargeable batteries. So it is convenient for checking the pluviometer in the open air and has a good prospect.