Method and apparatus for determining the moisture content of a material

Apparatus for determining the moisture content of a material, comprising a transmitting device which is arranged to transmit a microwave signal through the material to be measured, and a detecting device and a counting device which are arranged to measure the change of velocity of the signal transmitted through the material and to determine the moisture content of the material on the basis of said measured change and a predetermined known interdependence between the changes in the microwave signal velocity and the moisture content of the material, wherein the transmitting device comprises an oscillator designed to produce a signal of a frequency in the microwave range and to vary the signal frequency from a lower frequency f.sub.1 to an upper frequency f.sub.2 within a given period of time T in accordance with a mathematical function, an isolator designed to pass the signal in the oscillator circuit in only one direction, a directional coupler designed to divide the signal into a first component (I) and a second component (II), and a transmitter designed to transmit the first signal component obtained from the directional coupler through the material to be measured;

• that the detecting device comprises a receiver designed to receive the first signal component (I) after it has travelled through the material to be measured, a mixer provided with a first input gate (RF), a second input gate (LO) and an output gate (IF) and designed to receive the first component (I) from the receiver via its first input gate (RF) and the second component (II) directly from the directional coupler via its second input gate (LO) and to mix the signals applied to the input gates (LO) and (RF), to produce from the signal thus formed an intermediate frequency signal .DELTA.f corresponding to the delay and to output it through the output gate (IF);
• and the counting device is designed to control the oscillator and to measure the frequency of the intermediate frequency signal .DELTA.f obtained from the mixer output gate (IF) and to determine the moisture content value of the material under measurement from the intermediate frequency signal on the basis of a known interdependence of said signal .DELTA.f and the moisture content.