FI83268C - FOERFARANDE JAEMTE ANORDNING FOER BESTAEMNING AV MIKROVAOGORS DAEMPNING OCH / ELLER FASVRIDNING VID TRANSMISSION GENOM ETT MATERIAL. - Google Patents

Description

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The present invention relates to a method and apparatus for determining the attenuation and / or phase change of microwaves as they pass through a substance.

Such a method is mainly intended for use when it is desired to determine the so-called moisture quotient, utilizing microwave attenuation and phase change during the passage of the substance to calculate the moisture quotient of the material.

Patent application No. 852548 describes a method and apparatus for determining the moisture content of a substance. Po. the device is particularly well suited for use with the method and device of said patent application.

Po. An essential area of application of the invention is in the measurement of the moisture content of wood pieces in a saw. A particular problem in this case is that the measurement result is affected by the positions of the pieces of wood in relation to the antenna transmitting the microwave and the receiving antenna, between the antennas of which the piece of wood passes during the measurement.

Po. the invention completely solves the reported problem and provides a device in which the measurement result is independent of the location of the substance between the two antennas.

25 Po. thus, the invention is well suited for use when measuring changes in a microwave signal as it passes through a substance whose location between antennas is vague and variable. Thus, the invention is not limited to use in determining the moisture content, but can be used in all kinds of measurements.

Po. The invention therefore relates to a method for determining the attenuation and / or phase change of microwaves as they pass through a substance, the characteristics of which are set out in the appended claim 1.

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The invention further comprises a device, the type and main features of which are set out in claim 5.

The invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 shows a highly schematic view of a device of a known type for measuring the moisture content of wooden pieces; Figure 2 shows a block diagram of a device according to the invention; Figure 3 shows a vector diagram; Figures 4 and 5 show alternative locations of the antennas; Fig. 6 shows a block diagram of a device according to the invention in which a plurality of measurement channels are obtained; and Figures 7 and 8 show alternative locations for the antennas and use a plurality of measurement channels.

Figure 1 shows very schematically a meter for measuring the moisture of wood pieces 1, comprising two antennas 2,3 for transmitting and receiving microwave 20 and a unit indicated by 4, comprising a microwave generator, a microwave receiver and the necessary signal processing circuits for generating two output signals, of which one corresponds to the phase change F1 and the other to the attenuation A.

25 It is true that the change in phase F1 and the attenuation A which occurs to microwaves as they pass through a piece of wood can be determined by reference to the so-called kos-teusosamäärä. One way to determine the moisture content is described in the above-mentioned patent application. Such a 30 way is not part of po. invention, so it will not be described in more detail here.

When using the known device according to Figure 1, the transmission coefficient is affected by the location of the piece of wood between the antennas 2,3. This is because interference, such as standing waveforms, occurs between the surfaces of the corresponding antenna and the piece of wood 35. Namely, part of the signal is reflected at the surface of the board 3 83268. The variation of the transmission coefficient is obtained periodically as a function of the displacement of the board or the position between its antennas 2,3. The period length is half the wavelength for the transmitted microwaves. When the microwave frequency 5 is about 15 GHz, the wavelength is \ = 2 cm, i.e. said section length is 1 cm.

Po. the invention eliminates variations in the transmission coefficient.

Figure 2 shows an embodiment 10 of a device according to the invention, which operates on po. according to the method.

The device comprises a microwave generator 5 which generates a high frequency microwave signal (fQ), e.g.

16 GHz, an oscillator 6 designed to provide a low frequency signal f1, e.g. 10 KHz, to the modulator 7.

The device further comprises a signal processing unit 8 comprising a microwave receiver in the form of a mixer 9, preferably a dual balanced mixer with a simple sideband, and a reference circuit 10. The device further comprises antennas between which substance 11 is intended for import.

According to the invention, two pairs of antennas 12,13, 14,15 are used, of which the antennas 12,13 of the first pair of antennas are moved along a line extending through the antennas with respect to the antennas 14,15 of the second pair of antennas at a distance equal to λ / 4 or odd a multiple of the wavelength f of the microwave signal generated by the microwave generator 5. The antenna pairs are placed side by side. In addition, the distance between the two antennas in each pair is the same or substantially the same.

A measuring channel is formed comprising in series a microwave generator 5, a first antenna pair 12,13, said modulator 7 and a second antenna pair 14,15, the receiving antenna 14 of which is connected to a signal processing unit 8. The modulator 7 is intended to modulate 35 high frequency microwave signals f compared to the low frequency modulation signal f ^ generated by the oscillator 6. The frequency is e.g. 10 KHz.

A check channel is formed by connecting the microwave generator directly to the signal processing unit 8 5 ns. 3 through a 3 dB hybrid. The second output connector of the 3dB hybrid 16 is connected to the first antenna 12 of the first pair of antennas.

As mentioned, the oscillator 6 generates a signal for the modulator 7, which is then intended to modulate the microwave signal fQ transmitted by the first antenna pair 12,13 of the earth. The modulator is preferably a simple side-by-side modulator. The modulated signal fQ + is transmitted via the second antenna pair 14,15 to the signal processing unit.

Said mixer is intended to mix the signal f + f „obtained from the measurement channel with the signal fQ obtained from the inspection channel o 1, so that the signal f ^ is formed. This signal contains phase and amplitude variations depending on the throughput. through substance 11. The comparison circuit 10 is intended to compare this signal with the modulation signal f 1, which is supplied from the oscillator 6 directly to the reference circuit 10 via a conductor 17. The comparison circuit 10 includes circuits for providing two output signals, one corresponding to the phase change F1 and the other corresponding to the attenuation A.

Arranging the antenna pairs at a distance of 25 λ / 4 or an odd multiple thereof eliminates the effect of the position of the substance, as can be seen from the explanation below.

Figure 3 shows a vector diagram of phase change (F1) and attenuation (A). In the known method, which is presented in connection with Fig. 1, e.g. a measurement value a is obtained, which is indicated by the vector F1 ^ drawn with a broken line. As the substance is moved within the area between the antennas 2,3, the measured value moves along the circle 18 of the diagram. The measured value moves along a round circle, when the substance is transferred to the side of the Mik-35 roaallonpituuden somewhat towards or from the antennas. When the measuring channel is divided into two measuring points po. according to the invention, in which the pairs of antennas are shifted in proportion to each other, the average of the two diametrical points of the circle, namely the center of the circle c, is obtained.

Assuming that, according to a preferred embodiment of the invention, the antenna pairs are arranged 5 in relation to each other such that the substance is made to pass first through the second antenna pair 12,13 and then through the second antenna pair 14,15, since the antenna pairs are also displaced relative to each other in the plane in which said. the substance is intended to be transferred. In this case, the antenna pairs can be in succession 10 in the direction 19 of movement of the substance 11, as shown in Fig. 4.

As the substance passes through the first antenna pair 12,13, a microwave signal f is transmitted through the substance 11, and the second antenna pair 14,15 modulates the signal and transmits it to the signal processing unit 8 without transmitting it through the substance.

In this case, a measured value is formed, e.g. point b in Fig. 3, which is also shown by the vector F1 ^. As the substance passes through the second antenna pair 14,15, the first antenna pair 12,13 transmits the signal f, after which the signal is modulated and transmitted by the second antenna pair 14,15 through the substance, whereby the transmitted signal is passed to the signal processing unit 8.

In this case, a second measured value is formed, which is diametrically circular 18. The measured value is shown by point d and the vector F1 ^. When two measurements have been made, in this case the average of the measured values b and d is formed in the signal processing unit yk-25, which gives the measured value c.

If the antenna pairs are positioned so that in some cases it is considered best that the substance has to pass through both pairs of antennas simultaneously, only one measured value is obtained, namely the one corresponding to point c. In this case, the pairs of antennas are placed along a line at right angles to the the intended direction of transport of the substance.

Thus, the measurement result is always independent of the location of the substance between the antenna pairs.

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The position shown in Figure 4 means that both antenna pairs measure the same part of the material 20.

The placement according to Figure 5 is also considered to be the best. Here, the antenna pairs are arranged in succession in the conveying direction 19 of the substance 11, but also next to each other, so that the different parts 21,22 of the substance become examined. This shape is considered to be particularly good when it comes to measuring the moisture content of pieces of wood in a saw. The advantage of this form is that erroneous measurement results due to 10 mm can be detected. branches in pieces of wood.

The presence of branches in the measurable part of the piece of wood results in the measured moisture content being higher than the actual one. The large difference between the measurement results of the two measurements indicates that the higher value applies to the part with the branches, and 15 this value can be sorted out. This advantage is a direct consequence of the use of a measuring channel with two measuring points.

By dividing the measuring channel into several measuring points, other advantages can be achieved, which will become apparent from the following. The Ku-20 vio 6 shows such a device. According to this preferred embodiment of the invention, more than one measurement channel is formed by using, in addition to said second antenna pair 14,15, several antenna pairs, e.g. two antenna pairs 23,24; 25.26, which are also, as well as the second antenna pair 14,15, 25 shifted \ / 4 by the corresponding distance or this multiple to the first antenna pair 12,13. The microwave signal transmitted through the first antenna pair 12,13 is then modulated by a modulation signal having 14,15 for each subsequent antenna pair; 23.24; The 25.26 specific frequency modulation signals are utilized for comparison in the signal processing unit 27. The signal f received by the antenna 13 of the first antenna pair is passed through an isolator 28 to a three-way power splitter 29, which outputs the signal f to each of the three modulators 30,31,32. Each modulator 30,31,32 is supplied with a low frequency 7 83268 modulation signal specific to each measurement channel, developed by the corresponding oscillator 33,34,35. The frequencies are denoted as mentioned above f1; f2 '^ 3 - ^ a they can be e.g. 15kHz, 12kHz and 10kHz. The corresponding modulator 30,31,32 is preferably a simple si-5 tuning modulator and thus supplies the corresponding frequency fQ + f ^; fQ + f2; fQ + f2 to the corresponding antenna 15; 24; 26. After transmission, the signals are received in a so-called in a three-way combiner 36 which further feeds the signals to a mixer 37, preferably a dual balanced mixer with a single-10 fold sideband.

The microwave generator 5 is connected to the second antenna 12 of the first pair of antennas via the output terminal of the power divider 38. The second output terminal of the power divider 38 connects the generator 5 to the mixer 37. The output terminal 15 of the mixer 37 has signals compared in the reference circuit 39 to the corresponding modulation frequencies. from oscillator 33; 34; 35.

Figures 7 and 8 show two alternative locations of the antenna pairs, corresponding to the positions in Figures 4 20 and 5. In the arrangement shown in Figure 8, the first antenna pair 12,13 knows the part 40, after which the other antenna pairs each know their other part 41,42,43. In this case, a measurement point is formed in the diagram of Fig. 3 from the measurement of the first part 40, after which the signal processing unit 27 is designed to generate a corresponding measurement value for each other measurement performed in parts 41,42,43 and each of these values to average with the value.

It is clear that if the substance is consistent with the measured properties, three similar averages are obtained.

If, on the other hand, one or two averages exceed the averages of the other or others, this is due, for example, to the presence of a branch in the measured part when measuring pieces of wood, in which case this can be omitted. However, there remains an average 35 formed by the two measuring points diametrically located on the ring 18 of Fig. 3. This means that even in this case a measurement value is obtained which is independent of the position of the substance between the antennas.

Another antenna format, such as Figure 5 in Figure 7, may also be used. In this case, the first measurement of the part 44 is performed as described above in connection with Fig. 4, after which two other measurements are made of the same part 45, which must give the same result. Other antenna shapes are, of course, conceivable.

In Fig. 6, partly the same reference numerals are used as in Fig. 2 for similar parts.

The use of more than one measuring channel is particularly advantageous when the substance to be measured has properties that vary in the same amount of substance. 15 In this case, an average can be formed from all the measurements, which therefore corresponds to the average of the property of the substance.

The device and method according to Fig. 6 are a very advantageous embodiment of several measuring channels, since only one microwave generator 5 and only one mixer 37 are required, even if several measuring channels are used. This means significant cost savings compared to using separate microwave generators and mixers for each measurement channel.

In accordance with the description of Fig. 25 above, a signal corresponding to the phase change F1 / F2 / F1, and a signal corresponding to attenuation These signals are preferably processed in a microprocessor 46 or the like, where e.g. perform the deletion of one or more measured values when the obtained-30 and the measured values are compared with predetermined conditions.

The microprocessor 46 also stores the obtained values and can also control the operation of the reference circuit.

Po. the invention is not limited to the embodiments described above or to the values, measurable properties or fields of application given by way of example, but may be modified within the scope of the appended claims.

Claims (9)

9 A method for determining the attenuation and / or phase change of microwaves as they pass through a substance 5, comprising transmitting a microwave signal per substance and receiving the microwave signal after it has passed. through the substance and then by means of a signal processing unit comprising a microwave receiver, measuring the attenuation (A) and / or the phase change (F1) of the microwave signal as it passes through the substance, using at least two pairs of antennas (12,13; 14,15), and the antennas (12, 13) of the first pair of antennas are positioned so as to be moved along a line extending through the two antennas (12, 13) relative to the antennas (14, 15) of the second pair of antennas by a distance equal to 15 ^ / 4 or an odd multiple thereof; wherein the wavelength of the microwave signal is characterized in that the microwave signal is passed through a measuring channel comprising a first pair of antennas (12, 13) in series, a modulator (7) in which the microwave signal is modulated with a modulation signal having a frequency (f ·]) Is lower than the frequency of the microwave signal (fQ) / and through the second antenna pair (14,15), on the other hand, through a check channel comprising and that the microwave signal obtained from the measuring channel is compared with the microwave signal originally transmitted from the control channel on the one hand, and the modulation signal set in the signal processing unit {8 on the other hand; 2 7) · Method according to Claim 1, characterized in that the antenna pairs (12, 13; 14, 15) are arranged relative to one another in such a way that said the substance (11) passes through two pairs of antennas simultaneously. Method according to Claim 1, characterized in that the antenna pairs (12, 13; 14, 15) are arranged relative to one another in such a way that the substance first passes through the second antenna pair (12,13) and then through the second antenna pair (14,15). ίο 83268 Method according to claim 1, 2 or 3, characterized in that more than one measuring channel is formed by using, in addition to said second antenna pair (14, 15), one or more antenna pairs (23, 24; 25.26). ), which are also shifted by a distance corresponding to X / 4 or an odd multiple thereof, relative to the first antenna pair (12,13), and that the microwave signal transmitted through the first antenna pair (12,13) is modulated with a modulation signal having 10 the frequency (f1, f2, f3) specific to the measurement channel, which modulation signals (f1, f2, f2) are used for comparison in the signal processing unit. 5. An apparatus for determining the attenuation and / or phase change of microwaves as they pass through a substance, comprising a microwave generator, a modulator, antennas, between which said. the substance is intended for export, and a signal processing unit comprising a microwave receiver having at least two antenna pairs (12,13; 14,15), of which the antennas (12,13) of the first antenna pair are moved by two antennas (12, 13) along a line extending through the antennas (14, 15) of the second pair of antennas, a distance equal to, / 4 or an odd multiple thereof, where ^ is the wavelength of the microwave signal (fQ) generated by the microwave generator (5), characterized in that it has: a measurement channel formed on the one hand, and a check channel on the other hand, the measurement channel comprising in series a microwave generator (5), a first pair of antennas (12, 13), said modulator (7) for modulating a high frequency microwave signal (fQ) with a low frequency modulation ^), and a second pair of antennas (14,15) having a receiving antenna (14) connected to said signal processing unit (8,27), and that mai The control channel is formed by connecting the microwave generator (5) directly to a signal processing unit (8,27) for comparing the signal received from the measurement channel with the signal received from the control channel on the one hand and the modulation signal on the other hand. il 83268 Device according to Claim 5, characterized in that the antenna pairs (12, 13; 14, 15) are arranged along a line which is perpendicular to said antenna. in the intended direction of transport of the substance so that the substance passes through both pairs of antennas (12,13; 14,15) at the same time. Device according to Claim 5, characterized in that the antenna pairs (12, 13; 14, 15) are also offset relative to one another in a plane in which said. the substance is intended to be transported so that the substance passes first through the second antenna pair (12, 13) and then through the second antenna pair (14, 15). Device according to claim 5, 6 or 7, characterized in that more than one measuring channel is formed using one or more antenna pairs (23, 24; 25, 26) in addition to said second antenna pair (14, 15), also shifted by a distance corresponding to> / 4 or an odd multiple thereof, relative to the first antenna pair (12,13), and that the modulator is in each of the measuring poles comprising the second pair of antennas (14, 15) on the other hand and in other measuring channels containing other antenna pairs (23,24; 25,26), wherein the modulators (30, 31, 32) are for modulating the microwave signal (fQ) transmitted by the first antenna pair (12, 13) with a modulation signal having a frequency 25 (fQ) specific to each measurement channel; .j; f 2; f 2) ^ and that the signal processing unit (27) is intended to perform said comparisons for each measurement channel. Device according to Claim 8, characterized in that it has only one microwave generator 30 (5) and that between the first antenna pair (12, 13) and the other antenna pairs (14, 15; 23, 24; 25, 26). is a three-way power divider (29) for providing each modulator (30, 31, 32) with the same signals, and that a so-called three-way antenna pair and a signal processing unit (27) are arranged between them. a three-combiner device (36) for supplying a signal to only one mixer (37) in the signal processing unit (27). 12