The Design And Realization Of Wet Steam Humidity Measurement Sensor And Control System

It is great significant to have accurate measurement of the humidity of wet stream of large condensing steam turbine in conwntional pawer plant. In this paper, at first, the measurement principle and corresponding system of the humidity of wet stream are researched. The operating principle of the moisture measurement system with single-channel and dual-channel are elaborated theoretically, respectively, and the difficulty level of this two moisture measurement system are compared, the core microwave cavity of this system is optimized, to avoid frequency offset cased by its thermal expansion, in order to meet the experiment requirements. Then, the microwave cavity is designed. A cylindrical cavity is designed, whose operating mode is the TE011 mode, and two holes coupled the cylindrical cavity with the narrow wall of rectangular waveguide, there are several narrow slit in the side of the cavity so that the wet stream can through it freely; the cavity of the sensor is designed by ANSOFT HFSS9.0; the systematic errors caused by measurement methods and instruments are analysed; the equivalent circuit of the cavity is designed on equivalence principle of the cavity, the structure and the equivalent circuit of the cavity are simulated, when the resonant frequency is 9.575 GHz, the quality factor of TE011 mode is 30537, so it is appropriate to be the sensor to measurement the humidity of the flow wet stream. At last, the moisture measurement system is designed. The principle of frequency tracking module and frequency measurement module are introduce, and these modules are also designed by the SCM of MSP430F157, it is realized that the output frequency of VCO equals to the resonant frequency in the frequency tracking module, multi-cycle synchronous measurement and quantified delay measurement methods are both used in the frequency measurement module, with the measurement resolution ratio is up to 0.1 Hz; the communication between computer and SCM are realized by the serial communication interface, debugging results show that frequency measurements and frequency tracking module can work normally, and its performance indexes meet the measurement system requirements.