Microwave moisture measuring instrument with switchable measuring regions

摘要

The generator for the microwave measuring arrangement consists of a frequency-modulated oscillator which feeds a cavity measuring resonator in a transmission arrangement. The sample to be examined is located in the center of the resonator. The microwave signal allowed through the resonator is detected as the peak amplitude of a detector circuit, the change in the signal corresponding to the change in the quality factor due to the presence of the sample introduced. The average frequency of the microwave oscillator can be switched over several stages in order to expand the range of measurement. Each time the frequency is switched over, a different field mode is excited in the measuring resonator so that the sample is located in a mode region of the electrical measuring field for measuring high water contents and in a maximum of the electrical measuring field for measuring low water contents.