Reasearch And Design Of The Household Ultrasonic Water Meter

As the progressive pricing scheme for water use carries out, an era, named “Internet + intelligent water meter 2.0”, has come. It is an era when the measurement performance of water meters improves and when water meters are access to Internet and wireless network. There are no moving mechanical parts which will lead to more pressure loss in the ultrasonic water meter. It also has low start-up flow rate. The error characteristic curve can be easily corrected and data far distance transmission is easy to realize based on the ultrasonic water meter. So it is a more appropriate choice for the next generation of the intelligent water meter. The research on the ultrasonic water meter will not only promote the establishment of progressive pricing scheme for water, but also achieve transformation and upgrading of the intelligent water meter. It has important implications for the development of our country’s water meter industry.It is hard to accurately capture the moment when ultrasound arrives using time difference method. In addition, under the condition of low flow rate, the precision of flow measurement is poor. Therefore an ultrasonic water meter is designed in this paper. The flow measurement is realized by phase difference method. The temperature is measured according to the relationship between the ultrasonic velocity in the water and temperature. However, there exist nonlinear errors affected by temperature in the results of flow measurement. Then a temperature compensation algorithm based on least squares surface fitting is proposed. The main contents are as following:Firstly, phase difference method is adopted through comparative analysis of different ultrasonic flow measurement methods. The measurement of micro-flow is realized by accumulating the phase difference. At the same time, it can weaken the effect of random disturbance. There are large fluctuations in the results of flow measurement. In order to improve precision and strengthen the anti-jamming ability of the system, arithmetic average filter, limit breadth filter and sliding mean filtering are adopted in the software.Secondly, the flow measurement results influenced by temperature have serious non-linear errors in ultrasonic water meter using phase difference method. To solve this problem and reduce cost, temperature is obtained by the measurement of the ultrasonic velocity in the water, not conventional methods such as temperature sensor. The error of temperature using this method is limited within +-2℃.Finally, a temperature compensation algorithm based on least squares surface fitting is proposed in this paper. Temperature compensation is realized through establishing a non-linear reflection model between flow and temperature. After that multi-temperature-spot error correction algorithm is introduced because of different metrological properties of each ultrasonic water meter. The error of flow rate at current temperature is calculated according to the flow measurement errors at two adjacent temperature spots and variable weight and flow measurement global optimization is realized through the second-order correction. Experimental data show that flow measurement error is limited within +-2.0%.Experimental verification shows that the ultrasonic water meter designed in this paper can achieve accurately flow measurement. It has low power consumption, low cost and high precision.