Method and apparatus for the determination of moisture content of fibrous and granular materials

An apparatus for the determination of moisture content of fibrous and granular materials, comprising:

• a first measuring bridge circuit having a first arm, a second arm, a third arm, a fourth arm, a first diagonal and a second diagonal;
• first resistors inserted in said first arm, second arm, and third arm, respectively, of the first measuring bridge circuit;
• a sensitive element comprising a pulse heat emitter inserted in the fourth arm of the first measuring bridge circuit;
• a selector switch inserted in the fourth arm of the first measuring bridge circuit;
• a second measuring bridge circuit having a first arm, a second arm, a third arm, a fourth arm which is a common arm with the fourth arm of the first measuring bridge circuit, a first diagonal, and a second diagonal;
• second resistors inserted in the first arm, second arm, and third arm, respectively, of the second measuring bridge circuit;
• a zero detector having a first input, a second input, a third input, and an output, said zero detector being inserted in the first diagonals of the first measuring bridge circuit and second measuring bridge circuit, respectively, so that in one position of said selector switch the first input and the second input of said zero detector are connected to the first diagonal of the first measuring bridge circuit, and said zero detector receives a signal from this bridge circuit, and in the other position of said selector switch the second input and the third input of said zero detector are connected to the first diagonal of the second measuring bridge circuit and said zero detector receives a signal from this measuring bridge circuit;
• a control unit having a first input, a second input, a first output, and a second output, the first input being coupled to said output of said zero detector and the second output being coupled to said selector switch;
• a recording instrument graduated in units of moisture content of a fibrous or granular material under study, having an input coupled to the second output of said control unit, the moisture content of the material under study being evaluated by means of the recording instrument;
• and
• a power supply unit coupled to the second diagonals of the first measuring bridge circuit and second measuring bridge circuit and to the second input of said control unit, respectively.