Density-Independent Measurement of High Moisture Contents Using Appropriate Frequencies

Conventional moisture measurement methods often have problems with accuracy when the material density varies or high moisture ranges are to be determined. This paper addresses density-independent moisture measurement in moving bulk materials using microwave techniques. Four measurement methods are compared, one using a fixed frequency and the other using different frequency ranges. The characteristics, limitations, and material dependencies of these methods are examined, as well as their suitability for continuous moisture measurement in moving bulk materials. These fluctuating bulk materials occur frequently, especially in materials such as wood chips. Using the transmission method of microwave transmission with two antennas, material moisture can also be determined independently of density on the basis of permittivity. By cleverly choosing the frequency and processing attenuation and phase shifts, moisture contents of up to 20% can be measured independently of the material density. Moisture measurement methods often have problems distinguishing between high and low moisture contents at extreme moisture contents due to signal saturation. By measuring a wide frequency range, much higher moisture contents and ranges can be determined. In addition, a variant is presented that detects high moisture content with a small frequency range. Our approach allows high-resolution measurements to be performed on continuously changing materials at significantly accelerated rates. This accelerated process allows near instantaneous visualization of frequency sweep results. The measurements were performed on moving bulk materials.