基于谐振腔湿度测量系统的等精度频率测量系统设计

The Design of Equal Frequency Measurement Based on Resonant Wetness Measurem ent System

微波谐振腔的谐振频率随腔内介质的介电常数变化而发生偏移。当湿蒸汽流过微波谐振腔时,通过检测谐振腔谐振频率的偏移可以得到湿蒸汽的介电常数,由介电常数和蒸汽湿度的关系,进而确定蒸汽的湿度,频率测量的精度直接影响蒸汽湿度测量的精度。介绍了一种多周期同步与量化延时短时间间隔相结合的频率测量方法,在MSP430单片机的控制下完成宽频率范围内的等精度测量,消除了被测信号±1计数误差,使测量精度达到10e-7,满足蒸汽湿度测量精度的要求。给出了频率测量的硬件原理图,并利用可编程序逻辑器件CPLD来实现,使设计简单,集成度高,可靠性强。

The resonant frequency of microwave resonator is deflected with the different permittivity. When wet steam pass the microwave resonator, the permittivity of wet steam can be got through the deflection of resonant frequency, according to the relation between permittivity and wetness,then the wetness of steam is known. So the precision of wetness measurement directly depends on the precision frequency of measurement. A new method of frequency measurement is introduced which is multi-cycle synchronization combined with the short time interval measurement. Under the control of the MSP430 single chip, the function of equal precision in wide frequency range is carried out, which can remove ±1 counting error of the measured signal and get to the precision 10e - 7 ,satisfy the requirement of wetness measurement. At last, the hardware schematic diagram of frequency measurement is given. The design is simple and has high integrated degree,strong reliability.