Reseach On Pulse Output Model Digital Vortex Flowmeters

The vortex flowmeter is widely used in different fields due to its flexibility to various media, non-mobile parts, simple structure and long life etc. However, it has poor performance when operating at low flow rate where the Signal-to-Noise ratio is very small or even the signal is submerged by the noise. The traditional analog vortex flowmeter has benefits of steady signal, high accuracy and good real time in the regular flow range, while it also has a disadvantage of weak signal difficult to detect at low flow rate, which leads to unsatisfying lower limit and a smaller range ratio of 10:1.Based on the previous efforts a pulse output model digital vortex flowmeter is developed successfully, which inherits the advantages of the analog one and make up its shortage mentioned above. The digital vortex flowmeter with its double-core structure that means a couple of CPUs made up of DSP and MSP430 identifies the vortex signals from noises by the frequency spectrum analyzing algorithm in DSP at low flow rate where the analog one is not accurate, or even can't work. Meanwhile it works out by its microcontroller MSP430 the frequency of the vortex signal that is square waves output from pre-amplifier for the vortex signals in the regular flow range where the Signal-to-Noise ratio isn't too much small and the analog one is accurate and real time.This dissertation consists of theory, hardware/software design and experiment. The main point includes:1. The scheme called double-channel work model of the pulse output model digital vortex flowmeter is designed. The principle is a switch of two different methods to detect the vortex signal. That is using spectrum analysis of digital signal at low flow rate and frequency counting like analog vortex flowmeters in the regular flow range. The critical criterion of the switch point is the uncertainty of the frequency.2. A pulse output model digital vortex flowmeter is developed successfully. The flowmeter is studied respectively at DN25 and DN50 pipelines of the water flow experiment facility and DN50 and DN100 pipelines of the gas flow experiment facility that locate at Process Detect & Control Laboratory in Tianjin University. And the data shows that the digital flowmeter has the property of a better lower limit than the analog one and a bigger range ratio of 1: 28.5～41.3.