JPH0136897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in microwave moisture meters.
Generally, in the microwave band, microwave absorption of water is extremely large. For this reason, it has been widely practiced in the past to utilize the microwave absorption of moisture and to measure the moisture content of the object to be measured from the amount of attenuation of the microwaves.

FIG. 1 is a diagram illustrating the configuration of a conventional microwave moisture meter. An isolator that allows almost no microwave to pass through the microwave in the opposite direction, 3
5 is a transmitter horn connected to the isolator 2 via a first waveguide (or coaxial cable, hereinafter simply referred to as "waveguide") 4, and 5 is a receiver disposed at a predetermined distance l from the transmitter horn 3. Horn, 7 is second
A transmitting horn 8 is connected to the receiving horn 5 via a waveguide 6, and a receiving horn 8 is disposed at a predetermined distance l, which is the same as the distance between the transmitting and receiving horns 3 and 5, from the transmitting horn 7. Reference numeral 9 denotes an object to be measured made of, for example, a sheet of paper, placed between the transmitting horns 3, 7 and the receiving horns 5, 8; 11, made of, for example, a crystal diode; 8 is a detection unit that detects the output, 12 is a detection unit 1
This is a calculation unit that receives the output of No. 1 and performs predetermined calculation processing to calculate the amount of water in the object to be measured.

In the conventional example having the above configuration, the microwave transmitted from the oscillator 1 is projected onto the object to be measured 9 from the transmission horn 3 via the isolator 2 and the first waveguide 4. Further, the microwave that has passed through the object to be measured 9 and has been attenuated by water molecules is received by the receiving horn 5, passes through the second waveguide 6, and is projected onto the object to be measured 9 again from the transmitting horn 7. Ru. The microwaves that have passed through the object to be measured and are attenuated by water molecules again are received by the reception horn 8 and then passed through the third waveguide 10 and detected by the detection unit 11. Based on the output of the detection section, the amount of water in the object to be measured 9 can be determined by arithmetic processing performed in the calculation section 12.

However, in the above conventional example, the object to be measured 9
Since it is in the form of a sheet, the object to be measured tends to fluctuate, and the standing waves generated by such fluttering have the disadvantage that the pass line characteristics become a major source of measurement error.

The present invention has been made in view of these drawbacks, and its purpose is to reduce the effects of flapping of a sheet-like object to be measured in a microwave moisture meter that uses microwaves to measure the amount of moisture in an object to be measured. It is an object of the present invention to provide a microwave moisture meter capable of measuring the amount of moisture in a measured object with high precision without being subjected to large effects.

The feature of the present invention is that in a microwave moisture meter that measures the amount of moisture in a measured object using microwaves, the interval between the first transmitting and receiving horns is _l1 , and the distance between the first transmitting and receiving horns is l1.
When the distance between the receiving horns is l ₂ , l ₂ −l ₁ ≒nλ+
The first and second transmitting/receiving horns are arranged so that λ/4 (where n: natural number, λ: wavelength) holds.

Hereinafter, the present invention will be explained in detail using figures. FIG. 2 is an explanatory diagram of the configuration of an embodiment of the present invention,
In the figure, the same symbols as in FIG. 1 are used with the same meaning, and repeated explanation will be omitted here. Further, each transmitting/ _receiving horn ₃ ,
5, 7, and 8 are arranged. l ₃ =l ₂ −l ₁ ≒nλ±
λ/4 (where n: natural number, λ: wavelength)……(1)
Although not shown in FIG. 2, a fine vertical adjustment mechanism is often provided for moving each transmitting/receiving horn 3, 5, 7, 8 up and down, respectively.

The operation of the embodiment of the present invention having the above configuration will be described below. In FIG. 2, microwaves sent out from an oscillator 1 pass through an isolator 2 and a first waveguide 4, and then from a transmission horn 3 to an object under test 9.
is projected on. Furthermore, the microwaves transmitted through the object to be measured 9 and attenuated by water molecules are received by the receiving horn 5 and then reach the transmitting horn 7 via the second waveguide 6 . The microwave is projected again from the transmission horn 7 to the object to be measured 9 and transmitted therethrough, and is attenuated again by water molecules in the object to be measured. Thereafter, the signal is received by the reception horn 8, passes through the third waveguide 10, and is detected by the detection section 11.

By the way, in the conventional example shown in Fig. 1, the voltage waveform along the line is expressed by the following equation (2) using the wave equation.
be guided as follows.

V=V ⁺ e ^-j 〓 ^x + ΓV ⁺ e ^j 〓 ^x ………(2) However, Γ: Reflectance, V ⁺ : Peak value of sine wave representing voltage, β: Phase,
x: Distance from the reference position From the above equation (2), the voltage amplitude |V| is derived as shown in the below equation (3).

｜V｜=｜V ⁺ ｜｜(1+Γe ^j2 〓 ^x /e ^j 〓 ^x ｜ =｜V ⁺ ｜｜1+Γe ^j2 〓 ^x ｜ =｜V ⁺ ｜｛(1+Γcos2βx) ² +Γ ² sin ² 2βx}
^1/2 = |V ⁺ |{(1+Γ) ² −2Γ(1−
cos2βx)} ^1/2 = |V ⁺ |{(1+Γ) ² −4Γsin ² βx} ^1/2
………(3) From the above formula (3), the maximum value of voltage amplitude |V| |V _nax |
By finding the minimum value |V _nio | and taking their ratio, the following equation (4) is obtained.

|V _nax |/|V _nio |=1+Γ/1−Γ ......(4) On the other hand, in the embodiment of the present invention shown in FIG. It is arranged to satisfy 1). Therefore, as the amplitude |V| of the voltage waveform along the line, in addition to the above equation (3), the following equation is used, which is the signal of the part whose phase is separated from the above equation (3) by λ/4 (that is, 90 degrees). (5) is also detected. The object to be measured 9 is cardboard or the like, and each transmitting/receiving horn 3,
5, 7, and 8 (that is, the object to be measured 9 moves parallel to each transmitting/receiving horn 3, 5, 7, and 8 on the paper surface of FIG. 2 without wavering). (move up and down). Therefore, by simply taking the arithmetic average of the above equation (3) and the below equation (5), it is possible to consider the phase fluctuation based on the distance difference of the waveguide 6, etc., and the average value (i.e., {( After finding the maximum value |V _nax | and the minimum value |V _nio | of equation 3) + equation (5)}/2),
By taking their ratio, the following formula (6) is obtained. Note that the distance from trough to trough of the envelope (not shown) indicating the standing wave distribution is not one wavelength λ but half a wavelength (λ/2). Therefore, the phase of the standing wave between the transmitting and receiving horns 3 and 5 and the standing wave between the transmitting and receiving horns 7 and 8 is set to π
(ie, by λ/2), the voltage waveform along the line is only amplified. Therefore, in the present invention, in order to eliminate the influence of the standing waves generated by the fluttering of the object to be measured 9, the standing waves between the transmitting and receiving horns 3 and 5 and the standing waves between the transmitting and receiving horns 7 and 8 are removed. The phase is shifted by π/2 (that is, λ/4).

Furthermore, in the present invention, it is necessary to measure the amount of water in the object to be measured without contacting the object to be measured 9, and moreover, the object to be measured 9 flutters (moves up and down) during the measurement. Therefore, the transmitting/receiving horn 3,
In practice, it is difficult to make the distances between 8 and the object to be measured 9 the same, or to make the distances between the transmitting/receiving horns 7 and 5 and the object to be measured 9 the same, and this is an essential feature of the present invention. It is not a configuration requirement either.

Furthermore, the waveguides 4, 6, and 10 are fixed during manufacturing of the microwave moisture meter, and the waveguides 4, 6, and 1 are fixed except in exceptional cases such as repair or on-site modification.
The position of 0 usually does not change. Even if the positions of the waveguides 4, 6, and 10 were to change during the measurement of the moisture content of the object to be measured 9, the amount of variation would be extremely small and would not pose a problem in measuring the moisture content of the object to be measured 9. It's not like that. Moreover, such minute positional fluctuations only occur as offsets, and are fundamentally different from the fluttering (vertical movement) of the object to be measured 9, which tends to become noise when measuring the moisture content of the object to be measured 9. It is. Therefore, the waveguide 4,
In principle, positional fluctuations (and thus phase fluctuations) of 6 and 10 do not occur. Further, as mentioned above, there is no need to take into consideration exceptional or minute positional fluctuations (and even phase fluctuations) of the waveguides 4, 6, and 10 to compensate for deviations in the standing waves.

|V|=|V ⁺ |{(1+Γ) ² −4Γsin ² (βx+
90゜)｝ ^1/2 =｜V ⁺ ｜｛(1+Γ) ² −4Γcos ² βx} ^1/2
………(Five) In the above equations (4) and (6), since 0<Γ<1, 1+Γ/1-Γ>√1+ ² holds true. In addition, the above equation (4) shows the amplitude of the output signal when the path line of the device under test 9 changes in the conventional example, and the above equation (6) shows the amplitude of the output signal when the path line of the device under test 9 changes in the embodiment of the present invention.
It shows the amplitude of the output signal when the path line changes. In other words, since the amplitude of the voltage waveform (standing wave) along the line corresponds one-to-one to the output signal when the path line of the device under test 9 fluctuates, the ratio between the maximum value and the minimum value of the voltage amplitude is corresponds to the amplitude of the detection signal when the path line of the object to be measured 9 changes. Therefore, from the comparison of the above equation (4) and the above equation (6),
It can be seen that the pass line characteristic of the object 9 to be measured is better in the embodiment of the present invention shown in FIG. 2 than in the conventional example shown in FIG.

FIG. 3 is a graph showing the effect of the above-described embodiment of the present invention. In the graph, the vertical axis shows the received voltage fluctuation after passing through the object to be measured, and the horizontal axis shows the variation in the received voltage after passing through the object to be measured and the receiving horn. (i.e., the path line of the object to be measured). In Figure 3, (a) shows the values when the above equations (3), (5), and (3) + equation (5)/2 reflectance Γ is 0.1, and (b) shows the values when the reflectance Γ is 0.1. Reflectance Γ is 0.2
It shows the value when . Above (3) in Figure 3
The characteristic curves of equation (3) + equation (5)/2 correspond to the pass line characteristics of the conventional example and the embodiment of the present invention, respectively. Therefore, by comparing these, it can be seen that according to the embodiment of the present invention, the pass line characteristics of the object to be measured 9 are greatly improved.

FIG. 4 is a configuration explanatory diagram showing another embodiment of the present invention. In the figure, the same symbols as in FIG. 2 are used with the same meanings, and redundant explanation will be omitted here. Further, 13 is a receiving horn arranged at a predetermined distance _l2 from the transmitting horn 3, 14 is a transmitting horn connected to the receiving horn 13 via the second waveguide 6, and 15
16 is a receiving horn arranged at a predetermined distance _l1 from the transmitting horn 14, and 16 is a fourth waveguide similar to the second waveguide 6.
A transmitting horn 17 is connected to the receiving horn 15 via a waveguide 19, and is connected to the transmitting horn 16 at a predetermined distance l ₂
A receiving horn 18 is a transmitting horn connected to the receiving horn 17 via a fifth waveguide 20 similar to the second waveguide 6. In FIG. 3, the microwave transmitted from the transmitter 1 is transmitted through the isolator 2 → the first waveguide 4 → the transmitting horn 3 → the object to be measured 9 → the receiving horn 13 → the second waveguide 6.
→Transmission horn 14→Transmission through the object to be measured 9→Reception horn 15→Fourth waveguide 19→Transmission horn 16→Transmission through the object to be measured 9→Reception horn 17→Fifth waveguide 20
-> Transmission horn 18 -> Passes through the object to be measured 19 -> Receiving horn 8 -> Third waveguide 10 and is detected by the detection unit 11. Further, the amount of water in the object to be measured 9 is determined by arithmetic processing performed in the calculating section 12 based on the output of the detecting section 11 in the same manner as in the embodiment shown in FIG. Note that the present invention is not limited to the embodiments shown in FIGS. 2 and 4, and can be modified in various ways. For example, the number of transmitting/receiving horns in FIG. 4 may be increased from 8 to 12. good. Furthermore, although the formula serving as the principle of the invention described in JP-A-59-197842, which was filed on the same date as the present invention, and the formula serving as the principle of the present invention are the same, l ₁ , Since the meanings of l ₂ are different in each case, the two are not the same invention.

According to the embodiment of the present invention as described in detail above, each transmitter/receiver horn is arranged so that the above formula (1) is satisfied, so that the fluctuation of the object to be measured is less than in the above embodiment. It has the advantage of being less susceptible to the effects of standing waves caused by In addition, a predetermined movable part is provided to mechanically move each transmitting and receiving horn to λ/4
Although it is conceivable to move the product up and down, the embodiment of the present invention has the great advantage that there is no need to worry about failure of movable parts, etc., and the product life is long, even compared to such a method.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the configuration of a conventional microwave moisture meter, Fig. 2 is an explanatory diagram of the configuration of an embodiment of the present invention, Fig. 3 is a graph showing the effect of using the embodiment of the present invention, and Fig. 4 is an explanatory diagram of the configuration of the embodiment of the present invention. FIG. 7 is a configuration explanatory diagram of another embodiment. 1... Oscillator, 2... Isolator, 3, 7, 1
4, 16, 18... Transmission horn, 5, 9, 13, 1
5, 17...Reception horn, 4, 6, 10, 19, 2
0... Waveguide, 9... Measured object, 11... Detection section, 12
...Arithmetic section.

Claims (1)

[Claims] 1. In a microwave moisture meter that uses microwaves to measure the amount of moisture in an object to be measured, a first device that projects microwaves sent from a transmitter onto the object to be measured
a transmitting horn, a first receiving horn that receives the microwaves transmitted through the object to be measured, a second transmitting horn that is connected to the first receiving horn and projects the microwaves again to the object to be measured; Several pairs of transmitting/receiving horns are provided, each consisting of a second receiving horn that receives the microwave transmitted through the object to be measured, the distance between the first transmitting/receiving horn being l ₁ , and the second receiving horn receiving the microwave transmitted through the object to be measured.
When the distance between the transmitting and receiving horns is l ₂ , l ₂ − _{l 1} ≒
A microwave moisture meter characterized in that the first and second transmitting/receiving horns are arranged so that nλ+λ/4 (where n: natural number, λ: wavelength) holds. 2. The microwave moisture meter according to claim 1, wherein the several sets of transmitting/receiving horns are one set. 3. The microwave moisture meter according to claim 1, wherein the several sets of transmitting/receiving horns are two sets.