Research On Digital Vortex Flowmeter With Low Power Consumption Based On CPLD

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 a disadvantage what is obvious nonlinearity of the meter factor, when operating at low flow rate. The traditional analog vortex flowmeter has benefits of steady signal, high accuracy and good real time in the regular flow range, while it has poor performance on linearity at low flow rate, which leads to unsatisfying lower limit and a smaller range ratio of 1:10. The digital vortex flowmeter with double-core CPUs made up of MCU and DSP has a satisfying lower limit, while it has poor performance on reliability, real time and power consumption.A new design of meter factor modification based on CPLD is developed successfully, which inherits the advantages of the analog one and the digital one and makes up its shortage mentioned above. The digital vortex flowmeter system has its structure that made up of CPLD and analog vortex, which improves the linearity of meter factor over a wide flow range using"Look Up Table"technique. Cubic spline is applied to curve fitting through the analysis and comparation between three methods of curve fitting. A matlab program is designed to build the LUT and optimize its quantity based on the methods of cubic spline and meter factor modification.The power consumption of the digital vortex flowmeter was reduced to 3.48 mA, and thus the 4~20 mA current output by two-wire system was realized.Masses of experiments on the digital vortex flowmeter have been carried out at the water flow experiment facility in Tianjin University. The data shows that the flowmeter has the property of better lower limit in the water flow measurement than the analog one. The bigger range ratio reaches to 1: 26.4.The digital vortex flowmeter based on CPLD has a satisfying lower limit that increases the range ratio effectively, good stability, good real time and especially low power consumption, thus it is of great practicability.