Study And Realization Of Wetness Measurement System For Wet Steam

Wetness which is defined as the content of vapor in gas is an important environment parameter. The accurate measurement of wet steam wetness has great significance for guiding the economy and security of the condensing turbine in conventional power station.According to the characteristic that the resonant frequency of the resonant cavity shifted with the change of the air permittivity, this paper developed the wet steam wetness measurement system based on the perturbation cavity, and carried out system error analysis. The dielectric constant can be got by measuring the offset of resonant frequency of the cavity. And, then the humidity can be got according to the relation between dielectric constant and steam wetness. The system mainly consists of frequency tracking and measurement modules. Frequency tracking module uses MCU and realizes that the output of VCO is equal to resonant frequency of the resonator. A new method of frequency measurement is used in frequency measurement module, which is the combination of multi-cycle synchronization and quantization delay. The measurement resolution gets to 0.1Hz. It uses CPLD chip and VHDL language programming in this design, having improved the efficiency of the design.