The humidity detector was designed in collaboration with biomass power plant operators. Since the heating value of pellets depends strongly on its moisture the humidity detector ensures high efficiency. The humidity detector performs a resistance moisture detection. This means that the humidity detector measures the resistance of the test sample in order to gain information about its moisture due to its characteristic curve. Therefore it is of great importance to select the appropriate characteristic curve and temperature of the humidity detector. The humidity detector is applicable for comparative measurements of pellets that are made of either sawdust, wood chips, straw, hay, scraps of pellets, shells of sunflowers, buckwheat, corn, soy, etc. Therefore, simply plunge the 1000 mm long sensor into the pile of pellets and the measuring data will be collected after its stabilization. The humidity detector only measures at the tip of its sensor-probe. It is advised to perform several measurements at different points in order to achieve an adequate overview of the water content of the pile. Thus the humidity detector helps providing quick, easy and low-cost information about pellets moisture.