摘要
流量测量无论是在工业生产还是日常生活当中都有着不可忽视的作用,超声波流量计以其非接触式的测量方式以及测量范围广等优点受到众多科研人员的重视,而时差法超声波流量计作为超声波流量计中很重要的一种,具有测量精度高,适用范围广等优点。
本论文详细给出了时差法测量流量的基本原理,并分析了影响测量精度的非理想因素的种类,产生原理和对测量结果的影响。在此基础之上,提出了各种设计方案,以消除非理想因素对测量结果的影响,提高测量的精度,主要包括信号强度检测电路的设计,解决了一般时差法流量计在安装过程中换能器无法完全对准造成的信号强度弱,导致测量精度下降甚至无法测量的问题;提出了电路对称以及电子通道互换的设计思路,消除了电路延迟以及温度变化所引起的时间测量误差;系统时差归零的设计方式可以抵消掉换能器性能不一致引入的时间差,使测量系统突破了以往换能器只能固定位置安装的限制,并使其可以适应不同环境不同温度下的测量,提高了系统的测量精度。
系统的设计中采用了ACAM公司的新一代高精度的时差测量芯片TDC-GP2和TI公司的低功耗单片机MSP430F1611,并配以FAT32文件形式进行数据存储的CF卡以及读卡器电路设计,形成了一个可以脱离计算机独立工作,数据采集同时将数据以文件形式存储的流量测量系统。总线切换的电路设计又使计算机可以直接访问CF卡,将测量的结果以文件的形式读取和处理。最后在水池走车试验中验证了系统的测量精度和测量稳定性,达到了预期的目标。
Flow measurement, whether in industrial production or daily life of all, has a significant role. Ultrasonic flowmeter is paid attention by many researchers for its non-contact measurement and wide measuring range. And time difference ultrasonic flowmeter as a very important one of ultrasonic flowmeters has the advantages of high accuracy, wide application and so on.
Details of the time difference flow measurement of the basic principles were introduced. And the type, the generate theory and the impact to the measurement results of non-ideal factors which effect the measurement accuracy, were analyzed in this thesis. On this basis, a variety of designs were designed to eliminate the effects on the results of measurement which caused by non-ideal factors to improve measurement accuracy. The signal strength detection circuit was proposed to solve the problem in general time difference flowmeter that the transducers can not be completely aligned during the assembly process lead to weak signal strength; the weak signal strength results in decreased of accuracy or even the flow can not be measured. The design ideas of circuit symmetry and electronic channels exchange were used to eliminate the circuit delay and time measurement errors caused by temperature. A way of resetting the system time difference was designed to offset the time difference lead by the differences of the transducer performance, by which the restrictions that transducers must be fixed in previous measurement system were broken out, and it was able to adapt to various measurements environmental to improve the system's measurement accuracy.
The ACAM Company’s next-generation high-precision measurement of chip TDC-GP2 and TI Company's low-power microcontroller MSP430F1611, matching with the CF cards, FAT32 file system of data storage and CF-Reader circuit were used in this system, all of which formed a flow measurement system that can work independent from the computer and store data collected in CF card. Bus-switch circuit was designed to enable a computer access the CF Card directly, so the results of the measurement can be read and processed in the form of a document. Finally, the accuracy and measurement stability of the system were achieved in the pool of walking-car validation tests.
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