The Design Of Vortex Flowmeter Secondary Instrument Based On Digital Filter

The vortex flowmeter is suitable for the gas, liquid and other fluid flow measurement, it has a lot of advantages such as without moving parts inside, simple structure, high precision, strong adaptability, making it widely used in many industrial productions. But, it still has some problems, especially in the case of low velocity, small flow rate, the frequency will be greatly affected, the Signal-to-Noise ratio is low, original signal is easily submerged by the noise, so it can not finish the measurement work. And the traditional vortex flowmeter mostly use the analog signal processing method, it has high precision in the regular folw range; while at low flow rate, the vortex original signal is very weak, it is difficult to extract the useful information, which leads to unsatisfying lower limit and a smaller Signal-to-Noise ratio of flow measurement.To solve above problems, this thesis designs a vortex flowmeter based on digital filter with the microcomputer of MSP430. This digital vortex flowmeter with double MSP430 microcomputer structure, in the case of low flow velocity, the initial vortex signal is controlled by MSP430AFE253 microcomputer with digital methods and filtering the vortex signal, converted it into a standard signal; with a new type of frequency measuring method the MSP430F413 microcomputer can measure the frequency of the standard signal, this design solve the problem of the accuracy of measurement, at the same time overcome the problem of a smaller Signal-to-Noise ratio in the low flow velocity, compared with the common simulated vortex flowmeter, on the basis of ensuring the accuracy and real-time performance of the system, the power consumption is reduced, and the output of 4~20mA frequency signal is realized.This thesis according to the sequence of the vortex flowmeter measuring principle, working principle, hardware system, and software system, and introduces a new multicycle frequency measuring method. This vortex flowmeter secondary instrument consists of 3 piece of circuit board, power board, signal processing board, data processing board; according to these boards this topic design a complete circuit structure and the software system, realizing the vortex flowmeter can switch the filtering procedures coefficient in different range flow, it can measure the vortex signal frequency and flow value accurately. Finally, through the experiments it has low range limit and enlarged the range ratio, on the spot noise it has very strong inhibition ability, a good real-time performance, high application value.