Development of a multi-frequency dielectric sensing system for real-time hay and forage moisture measurement

A previous study at Iowa State University has shown promise for the determination of hay and forage moisture content prior to compaction using multi-frequency dielectric measurements. This previous study used a sensing system to take sequential frequency measurements which takes considerable time. Due to the fast material flow through equipment, the measurements need to be taken in a very short time period. Taking multi-frequency dielectric measurements simultaneously will ensure all frequencies measurements are from the same sample mass. This study has shown 1 MHz, 3 MHz, 7 MHz, and 13 MHz frequencies extracted from a multi-frequency signal are capable of providing the same signal information as sequentially scanned frequencies in milliseconds rather than multiple seconds. Hay bale moisture sensing was performed at Stardell Farms in Fredericksburg, Iowa, and the University of Wisconsin Arlington Research Station in Arlington, Wisconsin. Sensor plates were insulated and contained a guard plate around and behind them. Stardell Farms had the sensor plates 49.6 cm apart on a table top and Arlington had the sensor plates 36.8 cm apart in a fabricated bale chamber. Density independent moisture predictions were considerably better at Arlington with an adjusted R² = 0.80 and RMSE = 1.0 %MC wet basis for best sequential frequency combination 3 and 13 MHz. Arlington\u27s density independent moisture prediction has an adjusted R² = 0.79 and RMSE = 1.0 %MC wet basis for best extracted frequency combination of 3, 7, and 13 MHz. Stardell Farms yielded a density independent adjusted R² = 0.68 with 7.4 %MC wet basis for best frequency combination of 7 MHz. The best extracted frequency combination of 3, 7, and 13 MHz yielded an adjusted R² = 0.67 with 7.5 %MC wet basis. At both locations the adjusted R² and RMSE was slightly higher for the sequential frequency combinations. At Stardell Farms the adjusted R² increased as the density increased while the adjusted R² remained approximately the same at Arlington regardless of density