【作者】 刘家祥；

【导师】 徐科军；

【作者基本信息】 合肥工业大学 ， 检测技术与自动化装置， 2009， 硕士

【摘要】 将数字信号处理技术应用于涡街流量计的信号处理,可以有效地提高测量精度和扩展量程比。但是,数字信号处理算法一般要通过DSP来实现。由于DSP功耗大,无法满足有些工业现场对低功耗、两线制仪表的要求。而现有的低功耗、两线制仪表一般采用常规的信号处理方式,性能指标不好,例如,测量精度比较差,量程比小。为此,我们课题组基于超低功耗单片机,采用数字频谱分析与模拟带通滤波器组相结合的方式,研制新型两线制数字涡街流量计。本文在软件方面对已有系统进行了很大的改进。通过用硬件定时器定时设标志、软件查询方式来实现各个功能模块的调度。用汇编语言编制FFT程序,并采用定点运算来减少运算量和存储量;采用对数据先判断再移位的方式,既防止计算结果的溢出,又保证足够的计算精度。采用多周期等精度方法测量涡街信号的频率,用标准时钟脉冲信号填充被测信号,保证测量精度。当相邻滤波器的频带有重叠时,根据其频带的交叉点来选择带通滤波器。在流量计算中,采用平均方法和加速方法,既保证了测量结果的重复性,又提高了响应速度。经过改进后的低功耗、两线制数字涡街流量计通过了实际流量的测试,并在工业现场稳定运行。更多还原

【Abstract】 Digital signal processing technique is applied to the signal processing of vortex flowmeter for improving the measurement accuracy and extending the turn-down radio of vortex flowmeter effectively. The digital signal processing algorithms, however, are implemented by DSPs generally. It cannot meet the requirement of the low-power and two-wire meter due to the high power consumption of DSPs. The performance indexes of the existed vortex flowmeter with low-power and two-wire are not good, e.g. the measurement accuracy is low and turn-down ratio is small, because these meters adopted the conventional signal processing method.In order to solve the aforementioned problems, our group developed a novel two-wire digital vortex flowmeter with a super low-power micro-controller, combining the digital spectrum analysis with the analog band-pass filters. This paper makes great improvement in the system software of the two-wire digital vortex flowmeter. The flags are set by the timer and checked by program to perform the call of the functional modules. The FFT program is developed with the assemble language, and the fixed-point calculation is employed to reduce the computational load and memory space of the algorithm. Before the data are shifted their values are checked first, which can avoid bit growth occurring and ensure the computation accuracy. The multi-period equal- precision measurement method is used to calculate the frequency of the vortex signal, and the measured signal is filled by the standard clock pulse signal to ensure the measurement accuracy. When the frequency bands of adjacent filters overlay, the band-pass filter is selected according to the junction of the frequency band. Averaging and accelerating methods are adopted in flow calculation to ensure the repeatability and reduce the response time. This system has passed the flow tests, and runs normally in the industrial field.更多还原