JP3105094B2 - Moisture measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring moisture using absorption of microwave energy by moisture.

[0002]

2. Description of the Related Art Microwave transmitters and receivers are arranged facing one another in a moisture measuring apparatus utilizing absorption of microwave energy by moisture, and an object to be measured is arranged in a microwave propagation path therebetween. There is a transmission type in which the moisture of the object to be measured is calculated from the attenuation rate of the microwave energy transmitted through the object to be measured (JP-A-2-19750, JP-A-2-19750).
-205758).

[0003] In this case, the object to be measured may be a tangible object or a tangible object, in addition to an object having a plate-like shape, an assemblage of powder, particles or small pieces flattened, a flattened viscous material, and the like. In some cases, the surface of the set is generally flat. These DUTs are placed in the propagation path, or move or flow across the propagation path, and their flat surface (referred to as plane B) usually has a plane perpendicular to the propagation path (plane A). ).

FIG. 1 schematically shows an experimental apparatus similar to this type of apparatus, in which a support plate 2 is horizontally supported between left and right supports 1, 1 and a transmitter 3 ( 9.4G
H _Z ) and the receiver 4 are vertically opposed to each other. That is, a vertical microwave propagation path is formed between the transmitter / receivers 3 and 4, and the device under test 5 is arranged so as to cross the path at right angles.

In FIG. 1, dimension a = 102, dimension b = 1
35, dimension c = 80 (projected aperture of transmitter / receiver) and dimension d = 100 (projected width of object to be measured) (each mm). The oscillator 6 of the transmitter 3 receives and outputs power from the control board 7 (transmission output), and the output of the detector 8 of the receiver 4 is input to the control board 7 (reception input). The control board 7 has a circuit configuration that compares the transmission output with the reception input and outputs a voltage proportional to the difference between the terminals CP and CPE. This output is read by the voltmeter 9. The higher the moisture value and the greater the difference between the transmission output and the reception input, the more the terminal CP-CPE
A large voltage appears between them.

Using this experimental apparatus, an external wall board (water content 0% to 25%, thickness 13
mm) were placed on the support plate 2 one by one, and the water content thereof was measured. This outer wall board is a glass fiber reinforced concrete plate containing glass fibers and organic fibers. FIG. 2 is a graph showing the result. The difference between the circled line and the squared line is a reservoir having a different type of microwave absorber mounted on the receiver 4. "ECCOSORB" shown in the figure is a brand name of a microwave absorbing material, and exhibits a higher absorbing performance than a conventional product. A close examination of this graph shows that the slope of the graph is loose in the region of 5 to 15% moisture and is inconsistent with other parts. This means that the reception input (detection value) does not change in the above-described region in the same manner as other parts in response to a change in moisture of the device under test, and the degree depends on the material and thickness of the device under test. Although different, this phenomenon also appears in a graph of a result obtained by experimenting with another measured object. If there is a portion in the moisture measuring device where the reception input does not change in the same manner as in the case of other moisture values in response to such a change in moisture, an accurate moisture value cannot be detected in a certain region, or it is special and difficult. It requires an appropriate correction means.

[0007] In the case of the above-mentioned outer wall board, the area of 5 to 15% of moisture prevents cracks on the outer wall board surface,
This is an important area for controlling the maintenance of a good coating state and preventing the generation of mold, and requires an accurate measurement value.

The greatest cause of this tendency is that the plane B of the object to be measured is parallel to the plane A which traverses the microwave propagation path at right angles. This is considered to be due to interference with the incident wave from the vessel 3. That is, the microwave has a property of being reflected on the surface where the propagation medium changes, and the incident wave from the transmitter 3 is transmitted to the surface of the object 5 and the object 5 on the back side of the object 5 and the air. And the reflected waves interfere with the incident wave. Then, the interfered microwave passes through the DUT 5 and reaches the receiver 4. Further, the microwave has the property that the wavelength changes depending on the dielectric constant of the medium, and the dielectric constant of the device under test 5 changes when the moisture is different. Further, the phase of the reflected wave transmitted through the DUT 5 and reflected on the boundary surface between the back surface of the DUT 5 and the air changes with respect to the incident wave for the time required to reciprocate through the thickness of the DUT.

For this reason, a reflected wave having a particularly strong interference effect with respect to the incident wave is generated in a certain specific region of the moisture content of the measured object 5 having a certain thickness, and the detected value in this portion is inconsistent with others. It is thought to cause a tendency without. 13m thick
m, this special area has a moisture of 5-15
% Area. Note that, even on the back side of the device under test, the microwave transmitted through the device under test collides with the device surface of the receiver when it reaches the receiver and is reflected, and the reflected wave is further reflected on the back surface of the device under test. The light is reflected and received by the receiver. Also in this case, the reflected wave generated by colliding with the device surface interferes with the transmitted wave transmitted through the device under test, and changes the output of the receiver different from that due to the moisture of the device under test.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a microwave transmitter / receiver is arranged to face each other, an object to be measured is arranged in the middle of a microwave propagation path therebetween, and a microwave transmitted through the object to be measured is arranged. It is an object of the present invention to provide a moisture measuring method that can obtain an accurate measurement value in the entire moisture region to be measured in a moisture measuring device that calculates the moisture of an object to be measured from an attenuation rate of wave energy.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a moisture measuring method in which an object to be measured is arranged in the middle of a microwave propagation path, and the moisture of the object to be measured is calculated from an attenuation rate of microwave energy passing through the object to be measured. A microwave propagation path is formed therebetween by a transmitter and a receiver arranged opposite to each other. Object to be measured is arranged in a plane B which is inclined to the plane A perpendicular to the traveling direction of the microwave in the least measurement zone. flat
The inclination angle of the surface B is only for the microwave transmitted through the DUT
At an angle C or more. This angle C is determined by the following condition.
Is determined by C = 1/2 · tan ⁻¹ e / f e... The dimensions of the emitting surface and the incident surface when viewed from the projection of the transmitter / receiver.
Method f: Transmission / reception in projection view of microwave propagation path
The vertical side and the cover when the launch surface and the incident surface of the
From the point of intersection with the center line for the thickness of the
The distance to the launch or launch surface.

A microwave absorber may be placed around the transmitter and the receiver at a position where the reflected wave collides.

[0013]

The object to be measured is at least at the above-mentioned angle
The configuration arranged at the degree C, that is, the configuration in which the plane B on which the object is arranged is inclined with respect to the plane A orthogonal to the direction of propagation of the microwave eliminates the interference of the reflected wave with the incident wave, and It is possible to obtain a reception input corresponding to absorption of microwave energy by an object.

[0014]

FIG. 3 shows an overall configuration of an apparatus for carrying out the method of the present invention, and FIG. 4 is an enlarged view of a main part for explaining functions. In FIG. 3, a transmitter 10 and a receiver 11 are arranged to face each other, and a vertical microwave propagation path 12 is formed therebetween. The transmitter 10 is 9.45GH _Z
The receiver 11 has a detector 14. The oscillator 13 is connected to an output terminal of the control board 15, and the detector 14 is connected to an input terminal of the control board 15. The control board 15 outputs a voltage between the terminal CP and the terminal CPE according to the difference between the transmission output to the oscillator 13 and the reception input from the detector 14. This output is read by the voltmeter 16. Outer wall board as the DUT 17 (same as above)
Is mounted on a styrofoam inclined support plate 18 disposed between the transmitter and receiver 10 and 11.

[0015] As shown in FIG.
Is the launch surface (dimension e = 80) of the transmitter 10 in the projection view.
mm) and the incident surface (same dimension e) of the receiver 11 as a lower side and an upper side, and a line connecting both ends thereof (dimension b = 135 mm)
Is a rectangle having left and right sides, and the DUT 17 (outer wall board) is inclined by 35 ° with respect to the plane A with respect to the plane B with respect to the middle point P in the vertical and horizontal directions of the propagation path 12. . That is, the inclination angle of the inclined support plate 18 is 35 ° with respect to the plane A.

A part of the microwave (incident wave A) emitted from the transmitter 10 is reflected on the surface of the DUT 17 (reflected wave B), and the rest passes through the DUT 17 to be measured. A part is further reflected on the boundary surface that emerges from the object 17 into the air (reflected wave C), and the remainder (transmitted wave D) reaches the receiver 11. The energy of the transmitted wave A is converted into a corresponding voltage by the detector 14, and after A / D conversion, is transmitted to the control board 15 as a reception input. The reception input is compared with the transmission output in the control board 15, output as a corresponding detection value, and read by the voltmeter 16. FIG. 5 is a plot of this value. Outer wall board 17 is 100 × 95 × 1
25 pieces each having a size of 3 (mm) and a known moisture value (0 to 25%) were used and placed one by one on the inclined support plate 18.

FIG. 5 is a graph showing the results. Square lines and crosses indicate the case where a microwave absorber (ECCOSORB) is arranged around the outer wall board 17, and the circles and triangles indicate that the transmitter 10
And the position of the receiver 11 are in the opposite relationship. As shown in FIG. 5, there is a difference in the slope of the graph between the case where the microwave absorber is used and the case where the microwave absorber is not used. However, reversing the positions of the transmitter and receiver 10 and 11 in any case Almost irrelevant to detection results. Further, in each case, the output of the terminal CP-CPE and the moisture value of the outer wall board 17 at that time substantially linearly correspond to each other.
In the region of １５15%, the inclination of the graph does not tend to be loose.

This is because the flat surface on which the outer wall board 17 is arranged is perpendicular to the plane A perpendicular to the direction in which the microwave travels.
A plane B inclined at an angle such that a reflected wave B from the front side of the device under test due to an incident wave A from the transmitter 10 does not reach the transmitter 10
It is considered that the interference with the incident wave A due to the reflected wave B from the surface of the outer wall board 17 is almost completely eliminated even in the specific region. Actually, the surface of the object to be measured has some irregularities and slight interference occurs when viewed strictly, but it is not necessary to consider it. The inclination of the plane B may be such that it does not affect the actually required measurement accuracy. However, as the angle, the reflected wave B from the plane B due to the incident wave A from the transmitter 10 does not reach the transmitter 10. The angle is considered to be optimal.

In this embodiment, since the outer wall board 17 as an object to be measured is arranged at the center of the micro propagation path 12 in the vertical direction and has a symmetrical inclination, the primary reflected wave E due to the transmitted wave D transmitted through the outer wall board 17 is used. The same is true for the secondary reflected wave F, and the interference due to the reflected wave F is eliminated.

Further, in this embodiment, around the receiver 11, a microwave absorber 19 changes its plane C into a plane B
Are arranged in parallel with each other so as to absorb the reflected wave from the DUT 17. This eliminates the situation in which the reflected wave that jumps out of the microwave propagation path 12 repeats reflection and is eventually received, so that the detection value becomes more accurate. The configuration in which the plane C is arranged in parallel with the plane B is also to avoid the influence of microwaves that may be reflected without being absorbed.

As described above, the plane B on which the object to be measured is placed
Is tilted with respect to the plane A in the middle of the microwave propagation path, the interference of the reflected wave due to the incident wave A and the transmitted wave D can be greatly reduced, and the accurate measurement value can be obtained in any region where the moisture measurement is required. Can be obtained. In this case, the optimum inclination angle C of the plane B with respect to the plane A is substantially the distance between the transmitter / receivers 10 and 11 and the device under test 17, and the emitting surface and the incident surface of the transmitters / receivers 10 and 11 as viewed from the projection. C = １ ／ · tan ⁻¹ e / f e... The dimensions of the emitting surface and the incident surface of the transmitter / receiver as viewed by projection.
Method f: Transmission / reception in projection view of microwave propagation path
From the intersection of the vertical side when the launch surface and the incident surface of the instrument are the upper side and the lower side, and the center line m (FIG. 4) relating to the thickness of the DUT,
The distance to the nearest entrance or launch surface. In a relationship. Therefore, the larger the distance f of the device under test 17 away from the transmitter 10 or the receiver 11 and the smaller the projected viewing dimension e of the emitting surface or the incident surface,
The inclination angle of the plane B may be small.

The above is an example of an apparatus for carrying out the present invention, and the present invention is not limited to the apparatus having the illustrated configuration. For example, it is substantially the same even when the device under test is arranged horizontally and the microwave propagation path is inclined. The device under test is not limited to the outer wall board.
Further, the arrangement of the device under test in the microwave propagation path is such that the angle C is achieved only on the transmitting side where the highly reflected wave B is generated, and the receiving side is not particularly considered. is there.

[0023]

According to the present invention, accurate measurement values can be obtained over the entire required moisture measurement area in transmission moisture measurement using microwaves.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a mechanism (conventional example).

FIG. 2 is a graph (corresponding to a conventional example) showing the correspondence between a detection voltage and moisture.

FIG. 3 is a schematic diagram of the mechanism (the present invention).

FIG. 4 is an enlarged view for explaining functions.

FIG. 5 is a graph (corresponding to the present invention) showing a correspondence between a detection voltage and moisture.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transmitter 11 Receiver 12 Microwave propagation path 13 Oscillator 14 Detector 15 Control board 16 Tester 17 Device under test 18 Inclined support plate 19 Absorber

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeshi Matsuura 830-2 Shigaraki, Kakegawa-shi, Shizuoka (72) Inventor Nobuto Tsukamoto 1-2-3 Nakajima, Kikugawa-cho, Shizuoka (72) Inventor Akihiro Sugiyama Shizuoka 3482-91 Kanaya, Kanaya-cho (72) Inventor Takio Suzuki 45, Toyota-cho, Toyota-machi, Iwata-gun, Shizuoka Prefecture

Claims (1)

(57) [Claims] 1. A moisture measuring method for arranging an object to be measured in the middle of a microwave propagation path and calculating the moisture of the object to be measured from an attenuation rate of microwave energy passing through the object to be measured. A microwave propagation path is formed between the transmitter and the receiver, and the device under test is disposed on a plane B inclined at least in a measurement area with respect to a plane A orthogonal to the traveling direction of the microwave. Above angle C , and around the transmitter and receiver.
The microwave absorber at the position where the reflected waves collide
Projection view of the then moisture measurement method, wherein the are, C = 1/2 · tan -1 e / f e ... firing surface by the projection view of the transmission and receiver, the size of the entrance surface f ... microwave propagation path In the above, the distance from the intersection of the vertical side of the rectangle with the upper and lower sides of the launch surface and the entrance surface of the transmitter / receiver and the center line relating to the thickness of the DUT to the nearest entrance surface or launch surface.