JPH02238348A - Method and apparatus for measuring water content of material - Google Patents

Abstract

PURPOSE: To at a high speed and continuously measure water content of a material by a method in which a microwave signal is fed into the material and the speed change of the signal passed is measured, based on the known interdependent relationship between the speed change of the signal and the water content of the material. CONSTITUTION: A directionality coupler 6 divides a microwaver signal into a first component I and a second component II, and the component I is fed to a transmitter 7 and the signal is fed into a material to be measured. A receiver 8 receives a microwave signal I passed through the material to be measured. The transmitter 7 and receiver 8 are disposed counter to each other across the material. On the way of passing the material, the signal I is decelerated more than the signal component II used as the reference amount in a mixer 9, and delayed in a time manner. The mixer 9 mixes the signals I, II to generate an intermediate frequency signal Δf, which is fetched out from an output gate IF to measure frequency of the signal Δf in a counter 3. Water content of the material to be measured can be acquired from this frequency based on the known interdependent relationship between the signal Δf and the water content.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and a device for determining the moisture content of materials.

(Prior Art) The measurement methods and equipment currently used to determine the moisture content of materials online are capacitance, electrical conductance, neutron scattering, infrared radiation or microwave radiation. It is generally based on the use of .

(Problems to be Solved by the Invention) Microwaves are radio waves that belong to a frequency range of 300 Mllz to 300 Gllz. The microwave hygrometer is
It generally works by measuring transient attenuation or phase shifts. Measurements of transient attenuation are susceptible to interference due to reflections, and measurements of phase shifts are technically difficult to perform, especially when the material is thick and the phase shift can exceed 360°. be.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and a device for online determination of the moisture content of materials, primarily for application in the wood and paper industry; The goal is to use measurement results to adjust the process in real time.

Claims 1, 6, 10 and l described in the claims
The above problem was solved by the characteristic part 1. That is, the method for measuring the water content of a material according to the present invention involves sending a microwave signal into the material to be measured, measuring the change in the velocity of the signal passing through the material, and comparing the measured change and the velocity of the microwave signal. It is characterized by measuring the moisture content of a material based on the known interdependence between the change and the moisture content of the material.

In addition, the method for measuring the moisture content of other materials of this invention is as follows:
Generate a microwave signal by measuring the velocity change that occurs as the microwave signal passes through the material to be measured by frequency modulation, and adjust the frequency of the microwave signal to the lower limit of its frequency range within a fixed time period T. from the frequency f, to the upper frequency f2 or vice versa (or both) according to a mathematical function, splitting the microwave signal into a first and a second component, and dividing the first component into a material at the measurement location. After the first component has passed through the material, it is mixed with the second component, and from the thus obtained mixed signal an intermediate frequency signal Δ corresponding to the delay is formed, which determines the moisture content of the material to be measured. Content and intermediate frequency signal Δf
It is characterized in that the determination is made from the signal Δ[ based on the known interdependence relationship between the signals.

Furthermore, the apparatus for measuring the moisture content of a material according to the present invention includes a transmitter 1 that sends a microwave signal into the material to be measured, and a transmitter 1 that measures the change in velocity of the signal passing through the material. It is characterized in that it comprises a detection device 2 and a counting device 3, which determine the moisture content of the material based on the known interdependence between the change in the moisture content of the material and the moisture content of the material.

In addition, the device for measuring the moisture content of other materials according to the present invention includes:
It consists of a transmitting device 1, a detecting device 2 and a counting device 3, the transmitting device 1 generates a signal with a frequency within the microwave frequency range, and divides the signal frequency into a fixed time period T according to a mathematical function. an oscillator 4 whose purpose is to change the lower limit frequency f1 to the upper limit frequency r2, or vice versa (or both); and an oscillator 4 whose purpose is to pass the signal in only one direction within the oscillation circuit. a directional coupler 6 whose purpose is to divide the signal into a first component I and a second component 1; The detection device 2 consists of a receiver 8 intended to receive the first signal component I after passing through the material to be measured, and a first manual gate RF. A receiver 8 comprising a second manual gate LO and an output gate IF.
receives a first signal component I from the directional coupler 6 through its first manual gate RF, and directly receives a second signal component I from the directional coupler 6.
I through its second human-powered gate LO, mixes the signals input to the input gate LO and RF, generates from the signal thus formed an intermediate frequency signal Δf corresponding to the delay, and transfers the signal to the output gate IF. The counting device 3 controls the oscillator 4, measures the frequency of the intermediate frequency signal Δf taken out from the output gate IF of the mixer 9, and measures the frequency of the intermediate frequency signal Δf taken out from the output gate IF of the mixer 9. It is characterized in that it is aimed at determining the moisture content value of the material to be measured from the intermediate frequency signal on the basis of the known interdependence between the contents.

(Function) The present invention is based on the fact that the microwave propagation velocity in a certain material depends on the dielectric properties of that material, as shown in the following equation.

v = c/f (E,'+l E,l)/2
．． ．． ．． ．． ．． ．． ．． ．． ．． ．． ．． ．． (+1 However, ε, = Jε, 12 + ε lI1 ε, ′ = Real part of the relative dielectric constant of the material 81″ = Imaginary part of the relative dielectric constant of the material C = Speed of light The dielectric constant of water is the same as that of most other materials. This is why the speed of microwaves passing through a wet material is slower than the speed of microwaves passing through a dry material. From this, it is possible to measure the water content of the material. .

The time delay δ caused by the decrease in microwave speed can be calculated from equation (2) below.

δ= d/v= d/(c/7 (E,'+I ε
,+1/2)'. ．． ．． (2) Where, δ = Time delay d = Distance traveled by the microwave in the material V = Speed of the microwave in the material εr1 = Real part of the relative dielectric constant of the material ε, = Imaginary part of the relative dielectric constant of the material The method of the invention for measuring the moisture content of a material involves passing a microwave signal through the material to be measured, measuring the change in the velocity of the signal traveling through the material, and combining the measured change with the microwave signal speed. and the known interdependence between the moisture content of the material.

According to an embodiment of the method according to the invention, the velocity change of the microwave signal is measured by frequency modulation, by the transit time of the microwave pulse, burst or pulse train, or by correlation of the noise.

In an embodiment of the method according to the invention, the transit time of the microwave pulse, burst or pulse train traveled through the material is
Measured at a constant measurement gap.

In an embodiment of the method according to the invention, the transit time in the measurement gap is directly measured using a clock as the time interval between sending and receiving the microwave pulse, burst or pulse train.

In an embodiment of the method according to the invention, the transit time of a continuous or intermittent pulse-shaped or pulse-train-shaped microwave signal traveled through the material to be measured is determined using a correlation technique, that is to say transmitting a broadband noise. or by modulating the microwave signal with random noise or a random digital signal and measuring the transit time by the cross-correlation function of the transmitted and received signals.

In another embodiment of the method according to the invention, the velocity change that occurs when the microwave signal travels through the material to be measured is
Measured by frequency modulation.

That is, a microwave signal is generated and the frequency of the microwave signal is changed within a certain time period T according to a mathematical function from the lower limit frequency f, to the upper limit frequency f2, or vice versa (or both) of the frequency range. splitting the microwave signal into a first component and a second component, feeding the first component into the material at the point of measurement, mixing the first component passing through the material with the second component, and thus An intermediate frequency signal Δf corresponding to the delay is formed from the obtained mixed signal, and the moisture content of the material to be measured is determined based on the known interdependence between the moisture content and the intermediate frequency signal Δf.
It can be found from f.

The intermediate frequency Δ' can also be determined by calculation as shown in the formula below.

Δf =B-di i,'+Iεrl)/2""/
('I'c). ．． -, f3) However, B = r. -r. = Sweep width (width of the band within which the frequency changes) fl = Lower limit of the sweep band = Lower limit frequency fz = Upper limit of the sweep band = Upper limit frequency d = Travel distance of the microwave in the material ε,' = The distance of the material Real part of the relative dielectric constant ε, = Relative dielectric constant of the material ■ = Sweep time C = Speed of light Table 1 shows the values of typical intermediate frequencies Δf for certain materials, and these are given by Equation (3) This is what I got from. The parameter value adopted here is B = 2 Gl
! Z. T = 10 ms. d=30cm
and c=3·In8m/s.

Table 1. As is clear from the table of seven calculated values of Δf for different suppression materials, the dielectric constant of water is higher than that of other materials. Therefore, the intermediate frequency is higher for moist wood than for dry wood.

For any material, its moisture content can be determined by calculation or by graphical methods, provided that the correlation between the moisture content of the abrasive material and the frequency of the intermediate frequency signal is known. Determined from frequency. This correlation can be determined by performing multiple measurements using the method and apparatus of the present invention on materials whose moisture content and appearance are known or need to be measured. Based on the measurement results, a function is formed that describes the interdependence of these two quantities.

This function is then utilized in measurements performed using the method and apparatus of the invention to determine or calculate the moisture content of the material. Functions representing this interdependence can be incorporated into a computer program to calculate the final moisture content.

In an embodiment of the method according to the invention, the frequency of the microwave signal is changed continuously or cyclically from a lower limit frequency ``1'' to an upper limit frequency ``2'' and then from an upper limit frequency f2 to a lower limit frequency f.

In an embodiment of the method according to the invention, the material to be measured consists of a material flow passing through the measuring gap, such as wood chips, paper fibers (web), suspended water, e.g. chemical or mechanical wood pulp. ing.

In an embodiment of the method according to the invention, the determination of moisture-containing forgeries comprises:
It is carried out as a continuous measurement process.

The device according to the invention comprises a transmitting device for injecting a microwave signal into the material to be measured, and for measuring the change in velocity of the signal injected into the material, between the change in speed of the microwave signal in question and the change in the moisture content of the material. Based on known interdependencies,
It consists of a detection device and a counting device that determine the moisture content of the material.

In another embodiment of the device according to the invention, the transmitting device generates a signal with a frequency belonging to the microwave frequency range and modulates the signal frequency for a fixed time period T according to a mathematical function.
There are oscillators whose purpose is to change the lower limit frequency from the lower limit frequency to the upper limit frequency [2 or vice versa (or both), and oscillators whose purpose is to pass the signal in the oscillator circuit only in one direction. an isolator and a directional coupler for the purpose of splitting the signal into a first component and a second component;
and a transmitter (for example, a transmitting antenna) whose purpose is to introduce the first signal component obtained from the directional coupler into the material to be measured. The detection device also includes a receiver (e.g. a receiving antenna) intended to receive the first signal component after passing through the material to be measured;
a first input gate comprising an input gate, a second input gate and an output gate;
receiving a component from a receiver through its first input gate;
receiving a second component directly from the directional coupler through the second human powered gate, mixing the signals input to the first and second input gates, and from the thus obtained signal an intermediate frequency corresponding to the delay; It consists of a mixer whose purpose is to generate a signal and output that signal from an output gate. Furthermore, the purpose of the counting device is to control the oscillator, to measure the frequency of the intermediate frequency signal obtained from the mixer output gate, and to calculate the moisture content value of the material to be measured based on the intermediate frequency signal. It consists in determining from intermediate frequency signals based on known interdependencies between water contents.

In an embodiment of the device according to the invention, the transmitter and the receiver are arranged on mutually different sides with respect to the material being measured.

In another embodiment of the device according to the invention, the transmitter and the receiver are arranged on the same side with respect to the material to be measured, and on the opposite side a reflector is provided so that the microspheres emitted from the transmitter The wave signal is reflected and passed through the material before being sent to a receiver.

In an embodiment of the device according to the invention, the counting device continuously and cyclically changes the frequency of the microwave signal from the lower limit frequency "1 to the 4-limit frequency f2 and then from the upper limit frequency [2 to the lower limit frequency", It is designed to control the oscillator so that it changes.

In another embodiment of the device according to the invention, the device comprises a first electrical cable, a second electrical cable and a third electrical cable, through which the microwave signal is transmitted from the directional coupler to the second input of the mixer. the signal is sent from the directional coupler to the transmitter through the second electrical cable, and the signal is sent from the receiver to the first input gate of the mixer through the third electrical cable;
, the second and third electrical cables are selected to have lengths such that the frequency of the intermediate frequency signal is within a frequency range that technically facilitates measurements. The frequency of the intermediate frequency signal can also be adjusted to a desired level by changing the sweep width (B), the sweep time (Tl), or the distance (d) that the microwave travels within the material being measured.

Conventionally known technology uses so-called microwave frequency modulation (FM
- The CWl method is employed in single range radar applications, for example to measure surface level and ice thickness. Such applications are discussed in ``FM Radar for Precise Measurement of Levels'' (9th European Microwave Conference, Brighton 1979, pp. 712-715) and Jacula P. , Irinen P. , Chiuri M. Co-authored “Measurement of ice and frost thickness using rFM-CW radar” (
10th European Microwave Conference, Warsaw 1980).

In these conventional radar applications, the distance between the object to be measured and the radar transmitter/receiver varies, while the medium (usually air) between the transmitter/receiver and the reflecting object changes. ) remains unchanged as far as microwaves are concerned.

According to the present invention, the microwave frequency modulation method (FM-C
W method) can be employed in completely new fields of application, such as the measurement of moisture content of materials that have not been previously applied.

(Effects of the Invention) According to the present invention, there is an advantage that, for example, when the material moves as a flow, moisture measurement can be carried out very rapidly and continuously. Therefore, using the measurement results, it is possible to adjust the continuous processing ball rate in real time.

Another advantage of the present invention is that the output signal to be measured is an easy-to-process signal, i.e. a burst signal, and the measurement of its frequency is simplified and easy, making it demanding on the electronic circuitry used in the device. The conditions to be used are that the measurement can be carried out without necessarily being at a high altitude.

According to the invention, it is possible to measure the moisture content of a material using all the advantages of the FM-CW method.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

According to the measuring device shown in FIG. 1, when a microwave signal is sent from this device into the material to be measured, the change in the speed of the signal passing through the material is measured, and the change in speed of the microwave signal and the change in the speed of the material are measured. The moisture content of the material is determined based on the known interdependence between changes in moisture content.

This device includes a transmitting device 1, a detecting device 2, and a counting device 3.
It is composed of. The measurement of velocity changes can be based on frequency modulation, or on the transit time or noise correlation of microwave pulses, bursts or pulse trains.

According to an apparatus according to another embodiment of the invention shown in FIG.
When a microwave signal is similarly pumped into the material, using frequency modulation, the device measures the change in velocity of the signal as it passes through the material, and calculates the difference between the change in velocity of the microwave signal and the change in water content of the material. Determine the moisture content of the material based on known interdependencies.

This device includes a transmitting device 1, a detecting device 2, and a counting device 3.
It is composed of.

The transmitting device 1 includes an oscillator 4, an isolator 5, a directional coupler 6, and a transmitter 7. Detection device 2
consists of a receiver 8 and a mixer 9.

Oscillator 4 outputs a microwave frequency signal.

Under the control of the counter 3, this oscillator changes the frequency of the signal linearly within a certain frequency range and within a certain time period. Thereafter, the signal frequency is again changed linearly from the upper frequency limit to the lower frequency limit of the frequency range. These cyclical changes continue without interruption.

The isolator 5 functions to allow the microwave signal to pass through the oscillation circuit in only one direction.

The directional coupler 6 splits the microwave signal into a first component I and a second component II. The first component 1 of the microwave signal is
It is sent to the transmitter 7 through the electrical cable 12.

A signal is sent from the transmitter 7 into the material to be measured.

A receiver 8 receives the microwave signal I that has passed through the material to be measured. The transmitter and receiver are placed facing each other with the material in between. On the way through the material, the signal I becomes slower and delayed in time than the second microwave signal component I+, which is used as a reference signal in the mixer 9.

Mixer 9 has *1 input gate RF, second input gate at a glance,
0 and an output gate IF.

The second signal component II sent directly from the directional coupler through the cable 11 is input to the second human power gate LO of the mixer. The first input gate RF of the mixer 9 receives the first signal sent from the receiver through the cable 13.
A signal component I is input.

In the mixer 9, the signals 1 and TI input to the input gates RF, 1, and 0 are mixed. From the signal thus obtained, the mixer generates an intermediate frequency signal Δf,
Taken from the output game HF.

By suitably selecting the lengths of the electrical cables 11, 12 and I3, the intermediate frequency signal 8f, which corresponds to the delay, is adjusted to a level that facilitates the measurement technically.

The counting device 3 measures the frequency of the intermediate frequency signal Δf taken out from the output gate 1-IF of the mixer. The average moisture content of the material to be measured can be determined from this frequency on the basis of the known interdependence between the intermediate frequency signal Δf and the moisture content. For any material, if this interdependence is known, the moisture content value can be determined both by calculation and by graphical methods.

This interdependence can be determined by making several measurements using the method and apparatus of the present invention on materials with known moisture content 7. Based on these measurements, a function representing the interdependence of these rivers is formed. This function is then utilized in calculating the nominal moisture content of the material in measurements performed by the method and apparatus of the invention.

FIG. 3a shows a graphical representation of the frequencies of the microwave signals appearing at the first input gate RF and the second input gate LO of the mixer 9. The signal frequency changes from the lower limit frequency 11 to the upper limit frequency [2 during a certain time period T, but the slope of the change is constant. The signal (2) input to the first input gate RF of the mixer is delayed by 2 hours δ from the signal TI input to the second human input gate LO.

The solid line represents the signal I1 appearing at the second input gate 1, 0, and the dashed line represents the signal I1 appearing at the first input gate RF.
It represents. This time difference δ occurs because the microwave is delayed on the way from the transmitter 7 to the receiver 8. From the signals I and I+, the mixer outputs an intermediate frequency signal Δf which is proportional to the water content h1 of the material to be measured.

The curve in FIG. 3b represents the amplitude of the intermediate frequency signal Δ[ varying with time.

FIG. 4 shows an embodiment in which the transmitter 7 and the receiver 8 are placed on the same side of the material to be measured, and a reflector 10 is provided on the opposite side.

FIG. 5 shows the measurement results for wood chips.

These measurements were performed according to the method of the invention in order to establish the phase relationship between the water content and the frequency of the intermediate frequency signal.

The measurement parameters are B=B. 9 Gllz, T =
11.1 ms and d=5 cm. The measurements were carried out on wood chips with six known moisture content measurements, and as a result, six corresponding frequencies of the intermediate frequency signal Δ[ were obtained. Since the moisture content M of the wood chips is preferably expressed as a weight 1i ratio at each measurement location, the frequency value was divided by the density of the sample being measured to remove the influence of different densities on the results.

In the figure, the measurement results and the mutual relationship function obtained from the measurement results are represented in a graph.

The vertical axis represents the frequency of the intermediate frequency signal Δ' divided by the density of the material being measured. The horizontal axis represents the water content of the wood chips in terms of gravity M ratio. The wood data in Table 1 shows the magnitude of the value for solid wood by type, and therefore, wood 4. It should be noted that the results in FIG. 5 are not consistent with those measured on the chip.

It goes without saying that the present invention is not limited to the various embodiments described above, and that various modifications and improvements can be made within the scope of the concept of the present invention as described in the claims.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the circuit of the device of the present invention, Fig. 2 is a principle diagram of the circuit of the device according to another embodiment of the present invention, and Fig. 3 is the oscillation frequency and mixer of the device shown in Fig. 2 that change over time. 3(a) shows the frequency appearing at the input gate of the mixer, FIG. 3(b) shows the amplitude of the mixer output signal, and FIG. 4 shows the third embodiment of the present invention. Detailed view of the apparatus according to the example. FIG. 5 is a diagram showing the measurement results obtained with the method and apparatus according to the fourth example of the present invention. ... Transmitting device 2... Detecting device 3... Counting device 4... Oscillator 5... Isolator 6... Directional coupler 7... Oscillator 8... Receiver 9... ...Mixer 10...Reflector plate 11,
12, 13...Electric cable

Claims (1)

[Claims] 1. A microwave signal is sent into a material to be measured, a change in the velocity of the signal passing through the material is measured, and a relationship between the measured change and the change in velocity of the microwave signal and the water content of the material is determined. Method 2 for measuring the moisture content of a material, characterized in that the moisture content of the material is determined based on the known interdependence of the 3. Method for measuring moisture content of a material according to claim 1, characterized in that the measurement is performed by the passage time of a microwave pulse, burst or pulse train through the material, or by the correlation of noise. 4. Method for measuring moisture content of a material according to claim 2, characterized in that the measurement is carried out in a fixed measurement gap. The passage time in the measurement gap is determined by a microwave pulse,
Method 5 for measuring moisture content of a material according to claim 3, characterized in that the time interval between transmitting and receiving the burst or pulse train is directly measured using a clock. The transit time of a continuous or intermittent pulse-shaped or pulse-train-shaped microwave signal through a The method for measuring the moisture content of a material according to claim 2, characterized in that the measurement is carried out by modulating the water content with A microwave signal is generated by measuring the velocity change that occurs as it passes through the material by frequency modulation, and the frequency of the microwave signal is changed from the lower limit frequency f_1 to the upper limit frequency f_2 of the frequency range within a fixed time period T. or vice versa (or both) according to a mathematical function, splitting the microwave signal into a first component and a second component;
introducing a component into the material at the measurement point, mixing the first component with the second component after passing through the material and forming from the thus obtained mixed signal an intermediate frequency signal Δf corresponding to the delay;
Moisture content of a material according to claim 2, characterized in that the moisture content of the material to be measured is determined from the signal Δf based on a known interdependence between the moisture content and the intermediate frequency signal Δf. Method 7 for measuring the material according to claim 6, characterized in that the frequency of the microwave signal is continuously and cyclically changed from the lower limit frequency f_1 to the upper limit frequency f_2 and then from the upper limit frequency f_2 to the lower limit frequency f_1. Method 8 for determining the moisture content of: The material to be measured is passed through the measuring gap, e.g.
Method 9 for measuring the moisture content of a material according to any one of claims 1 to 7, characterized in that the method consists of a flow of materials such as paper fibers and suspended water.The method is characterized in that the measurement of the moisture content is carried out as a continuous measurement step. 10. A method for measuring the moisture content of a material according to any one of claims 1 to 8, comprising: a transmitting device (1) for sending a microwave signal into the material to be measured; and measuring a change in the velocity of the signal passing through the material. a detection device (2) and a counting device (2) for determining the moisture content of the material based on the known interdependence between the change in the velocity of said microwave signal and the change in the moisture content of the material;
3) A device 11 for measuring the moisture content of a material, characterized in that it is comprised of: The transmitting device (1) generates a signal with a frequency within the microwave frequency range, and converts the signal frequency according to a mathematical function. , an oscillator (4) whose purpose is to change from a lower limit frequency f_1 to an upper limit frequency f_2 or vice versa (or both) within a certain time period T, and an oscillator (4) for passing the signal into the oscillator circuit in only one direction. An isolator (5) whose purpose is to pass the signal, a directional coupler (6) whose purpose is to split the signal into a first component (I) and a second component (II), and from the directional coupler and a transmitter (7) whose purpose is to send the obtained first signal component into the material to be measured, and the detection device (2) transmits the first signal component (I) after passing through the material to be measured. a receiver (8) intended to receive a first signal component ( I) through its first input gate (RF) and a second signal component (II) directly from said directional coupler (6) through its second input gate (LO
), mixes the signals input to the input gates (LO) and (RF), generates an intermediate frequency signal Δf corresponding to the delay from the signal thus formed, and transfers that signal from the output gate (IF). The counting device (3) controls the oscillator (4) and the output gate (IF) of the mixer (9).
The purpose is to measure the frequency of an intermediate frequency signal Δf extracted from the intermediate frequency signal Δf and to determine from the intermediate frequency signal the moisture content value of the material to be measured based on the known interdependence between said signal Δf and the moisture content. Device 12 for measuring the moisture content of a material according to claim 10, characterized in that the transmitter (7) and the receiver (8) are arranged on different sides of the material to be measured. Claim 1
Apparatus 13 for measuring the moisture content of a material according to item 0 or 11. The transmitter (7) and the receiver (8) are arranged on the same side with respect to the material to be measured and reflect the transmitted microwave signal to the receiver. A measuring device 14 for the moisture content of a material according to claim 10 or 11, characterized in that a reflecting plate (10) is provided on the opposite side. Claim 10, characterized in that the object is to control the oscillator (4) so as to change continuously and cyclically from the lower limit frequency f_1 to the upper limit frequency f_2 and then from the upper limit frequency f_2 to the lower limit frequency f_1. Apparatus 15 for measuring the moisture content of the material according to any one of items 1 to 13. The first electric cable (11) and the second electric cable (
12) and a third electric cable (13), through which the microwave signal is transmitted from the directional coupler (6) to the second input gate (12) of the mixer (9).
LO), through a second electrical cable (12) the signal is sent from the directional coupler to the transmitter (7), and through a third electrical cable (13) the signal is sent from the receiver (8) to the first of the mixer. the length of the first, second and third electric cables being fed to the input gate (RF) such that the frequency of the intermediate frequency signal Δf is within a range that makes the measurement technically easy; The apparatus for measuring the moisture content of a material according to any one of claims 10 to 14, characterized by: