Method and arrangement for measuring the moisture content in fibrous material

Claim 2

In a system for processing fibrous material and having high frequency oscillator means furnishing a high frequency output signal, tuned circuit means coupled to said high frequency oscillator means and measuring capacitor means connected to said tuned circuit means for varying the phase angle between the current and voltage in said tuned circuit means as a function of the moisture content of said fibrous material, a method for furnishing a measuring signal indicative of said moisture content of said fibrous material, comprising, in combination, the steps of generating a phase angle signal indicative of said phase angle between said current and said voltage in said tuned circuit means; changing an electrical parameter associated with said tuned circuit means in dependence on said phase angle signal until said phase angle signal is equal to a predetermined phase angle signal indicative of resonance in said tuned circuit means; and furnishing first output signal varying as a function of said change in said electrical parameter said so-varying first output signal constituting said measuring signal.

Claim 3

A method as set forth in claim 1, further comprising the step of furnishing a second output signal varying as a function of the amplitude of voltage in said tuned circuit means; and selecting one of said first and second output signals to constitute said measuring signal.

Claim 4

A method as set forth in claim 2, wherein said step of generating a phase angle signal comprises comparing the phase of a first electrical signal generated in said tuned circuit means to the phase of said high frequency output signal.

Claim 5

A method as set forth in claim 3, wherein said step of changing an electrical parameter associated with said tuned circuit comprises changing the frequency of said high frequency output signal, thereby changing the frequency of the signal applied to said tuned circuit means.

Claim 6

A method as set forth in claim 2, wherein said selecting step comprises furnishing said first output signal when said moisture content of said fibrous material is in a predetermined first moisture content range, and selecting said second output signal when the moisture content of said fibrous material is in a second moisture content range having moisture contents exceeding the moisture contents in said first moisture content range.

Claim 7

A method as set forth in claim 2, further comprising the step of drying said fibrous material at a drying rate varying as a function of said measuring signal.

Claim 8

An arrangement for furnishing a measuring signal indicative of moisture content of fibrous material, comprising, in combination, high frequency oscillator means furnishing a high frequency output signal; tuned circuit means coupled to said high frequency oscillator means in such a manner that electrical signals including a voltage and a current are generated therein in response to said high frequency output signal; measuring capacitor means connected to said tuned circuit means, said measuring capacitor means having lines of force passing through said fibrous material, whereby the phase angle between said current and Said voltage in said tuned circuit means varies as a function of moisture content in said fibrous material; phase comparator means connected to said tuned circuit means for furnishing a phase angle signal corresponding to said phase angle between said current and said voltage in said tuned circuit means; adjustment means connected to said phase comparator means, for changing an electrical parameter associated with said tuned circuit means in dependence on said phase angle signal until said phase angle signal is equal to a predetermined phase angle signal indicative of resonance in said tuned circuit means; and measuring signal furnishing means for selectively furnishing a first output signal varying as a function of said change in said electrical characteristic, said so-varying first output signal constituting said measuring signal.

Claim 9

An arrangement for furnishing a measuring signal indicative of moisture content of fibrous material, comprising, in combination, high frequency oscillator means furnishing a high frequency output signal; tuned circuit means coupled to said high frequency oscillator means in such a manner that electrical signals including a voltage and a current are generated therein in response to said high frequency output signal; measuring capacitor means connected to said tuned circuit means, said measuring capacitor means having lines of force passing through said fibrous material, whereby the phase angle between said current and Said voltage in said tuned circuit means varies as a function of moisture content in said fibrous material; phase comparator means connected to said tuned circuit means for furnishing a phase angle signal corresponding to said phase angle between said current and said voltage in said tuned circuit means; adjustment means connected to said phase comparator means, for changing an electrical parameter associated with said tuned circuit means in dependence on said phase angle signal until said phase angle signal is equal to a predetermined phase angle signal indicative of resonance in said tuned circuit means; and measuring signal furnishing means for selectively furnishing a first output signal varying as a function of said change in said electrical characteristic, said so-varying first output signal constituting said measuring signal.

Claim 10

An arrangement as set forth in claim 6, wherein said measuring signal furnishing means further comprise means for furnishing a second output signal varying as a function of a predetermined one of said electrical signals in said tuned circuit means; and selector means for selecting one of said first and second output signals to constitute said measuring signal.

Claim 11

An arrangement as set forth in claim 8, wherein said high frequency oscillator means comprise voltage-controlled oscillator means having a frequency varying as a function of a control voltage applied thereto; and wherein said adjustment means comprise means furnishing said control voltage to said voltage-controlled oscillator means.

Claim 12

An arrangement as set forth in claim 9, wherein said control voltage is a voltage proportional to the phase angle between said current and said voltage in said tuned circuit means.

Claim 13

An arrangement as set forth in claim 10, further comprising reference oscillator means furnishing a reference oscillator output signal having a constant frequency; and wherein said measuring signal furnishing means comprise frequency comparing means comparing said constant frequency to the frequency of said high frequency output signal and furnishing said first output signal as a function of the difference therebetween.

Claim 14

An arrangement as set forth in claim 8, wherein said high frequency output signal is a high frequency output voltage; and wherein said phase comparator means has a first input connected to said tuned circuit means and a second input connected to said high frequency oscillator means; and wherein said phase angle signal is a signal proportional to the difference in phase angle between said high frequency output voltage and said voltage generated in said tuned circuit means.

Claim 15

An arrangement as set forth in claim 11, wherein said means for furnishing a second output signal comprise high frequency rectifier means connected to said tuned circuit means; and wherein said selector means comprise means for furnishing said first output signal to constitute said measuring signal at a selector output when the moisture content of said fibrous material is in a low moisture range and for furnishing said second output signal to said selector output when the moisture content of said fibrous material is in a high moisture content range.