JPH076926B2 - Method and apparatus for measuring the amount of water contained in an object - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the amount of water contained in an object and a measuring apparatus therefor. For objects, hygroscopic solids such as wood,
Granules such as grains, powders for processed foods, or textiles,
Sheet-like materials such as paper are included. When the object to be measured is irradiated with microwaves, the reflectance and the transmittance change according to the amount of water contained. An object of the present invention is to provide a measuring method and a measuring device for easily measuring the water content by using a general-purpose microwave Doppler sensor by utilizing the phenomenon that the reflectance changes.

2. Description of the Related Art Conventional Techniques and Problems to Be Solved Conventionally, when microwaves pass through an object, a method of measuring the amount of water by utilizing the fact that the attenuation rate, that is, the transmittance changes according to the amount of water has already been put into practical use. ing.

FIG. 6 illustrates the principle.

(1) is a microwave transmitter, and (2) is a microwave receiver, which are arranged to face each other with a constant space (S) between them, and an object to be measured (3) (hereinafter, simply referred to as an object). ) Is put. The microwave (arrow A) emitted from the transmitter (1) is absorbed by water when passing through the object (3), is attenuated, and reaches the receiver (2) (arrow B). Since this attenuation rate changes in proportion to the water content within a certain range, the water content can be measured by measuring it.

However, it is not so easy to measure this attenuation rate accurately. When a generally used transmitter and receiver are used, the space (S) must be kept constant and the object (3) must be placed at a specific position between them.
If the object (3) is slightly displaced or the interval (S) changes, the received signal (DC voltage) obtained from the receiver fluctuates, and stable measurement cannot be performed. This is because a part of the irradiated microwave is reflected by the object (3) and becomes a secondary irradiation wave (dotted arrow C). This secondary irradiation wave (C) is generated by the object (3). ), A phase shift occurs with respect to the original irradiation wave (A), and the strength of these irradiation combined waves (combined wave of A and C) fluctuates. Therefore, the reception signal of the receiver (2) is changed. Is fluctuating. Further, the secondary reflected wave (dotted arrow D) of the transmitted microwave (arrow B) also causes a phase shift depending on the position of the object (3), and affects the received signal of the receiver in a complex manner. In order to eliminate such fluctuation, it is necessary to devise a special device for the transmitter and the receiver so as not to be affected by the secondary reflected waves (dotted lines C and D), and as a result, The transmitters and receivers have a special design, and mounting precision is also required, and it is unavoidable that the installation structure is expensive.

As described above, the water content measuring devices that have been practically used in the past and that utilize the transmission attenuation factor of microwaves are limited in usage. For example, in the case of solids, granules, powders, etc., it is possible to measure only a small amount of extracted substances, continuous measurement is not possible, or it is expensive but it can only be used at the place where it is installed. However, in the case of continuously measuring in the processing process, it did not meet the demand of the consumer.

On the other hand, we have not yet seen that moisture meters that use reflected waves of microwaves are on the market, but we are not aware of moisture measurement technology that uses the change in reflected waves depending on the amount of moisture to detect the amount of moisture. There are references disclosed. (For example, JP-A-59-8
7346, etc.) Microwave Doppler sensor [As shown in FIG. 1, the microwave transmitter (1) and the receiver (2) are integrated into one body, and the microwave from the transmitter (1) is directly introduced in the waveguide. The composite wave of the self-generated wave received and the reflected wave (C) from the object is received by the receiver (2) and detected (rectified and smoothed).
In the case of a system using a sensor to obtain a received signal (DC detection voltage) (V)], the receiver (2) may vary depending on the shape and size of the sensor, the distance between the sensor and the object to be detected, and the amount of water content. Since the phase shift between the self-generated wave and the reflected wave (C) changes at the position of, the intensity (amplitude) of these combined waves changes. Therefore, the reception signal (detection voltage) of the receiver (2)
(V) does not necessarily correspond to the strength of the reflected wave, but rather, the degree of being affected by the positional relationship such as the shape size and the distance becomes stronger. Thus, even if the reflected wave corresponds to the water content of the object, the received signal (V) does not always have a fixed value, and the detection of the water content is not as easy as expected.

The previously disclosed moisture measurement technology using reflected waves lacks the consideration of the receiving principle of the Doppler sensor as described above, and the misunderstanding that reflected waves decrease according to the amount of moisture (actually, reflected waves Is increased based on the amount of water, which is generally proportional to the amount of water.) However, in general, accurate detection of the amount of water could not be expected.

This is because, when the reflected wave is used, the influence of the phase shift of the reflected wave due to the position of the object (3) is an inevitable phenomenon as described above, and a method for eliminating this is still unsolved.

In view of the above-mentioned conventional drawbacks and problems, the present invention uses a microwave Doppler sensor integrally incorporating a generally-used microwave transmitter and receiver, and is easily included in an object. In order to be able to measure the amount of water, the relationship between the change in reflectance and the phase shift of the reflected wave, which has been the cause of the above instability, has been skillfully utilized in reverse, which makes it convenient. It is intended to provide a measuring method and a measuring device to meet the demand of consumers.

Configuration and Action of the Invention Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Prior to that, Sakae 5, the relationship between the reflected wave of the microwave from the object and the received signal (V) when the microwave Doppler sensor in which the microwave transmitter and the microwave receiver are integrated is used. It will be described with reference to FIGS.

In FIG. 1, the Doppler sensor (4) is a transmitter (1).
And a receiver (2) are integrated, and a Gunn diode as a transmitter (1) and a mixer diode as a receiver (2) are integrated in a waveguide (5).
When an appropriate voltage (eg, DC 8V) is applied to the input terminal (14) of the oscillator (1), microwaves are transmitted and received from the oscillator (1) through the waveguide (5) and the horn antenna (6). It is transmitted in a certain direction from the surface (7) (it does not necessarily have to be a physical surface and may be considered as a virtual surface without a physical body) (arrow A). The microwave (arrow C) reflected by the object (3) is converged from the emitting / receiving surface (7) by the horn antenna (6) and received by the receiver (2). The receiver (2) is a self-transmitted wave "a microwave emitted from the transmitter (1) directly reaches the receiver (2) in the waveguide (5). The same applies below." The combined wave with the wave is received, this is detected, and the received signal (DC detection voltage) (V) proportional to its amplitude is output.The received signal from the sensor (4) is the amplifier (8), A / D It is read as a digital value into the arithmetic unit (10) through the converter (9) and stored as data in the built-in memory (11).
The D converter (9), the arithmetic unit (10), the memory (11) and the display unit (12) constitute a processor (13) as a whole. A microcomputer is incorporated in the arithmetic unit (10) to read the data value and perform arithmetic processing for the change in the variation value, and display the result on the display unit (12).

The surface of the object (3) is spaced from the emitting / receiving surface (7) of the horn antenna (6) of the sensor (4) by a distance (X).

When the object (3) is completely dry, the irradiated microwaves are hardly reflected except the reflection peculiar to the object and are absorbed or transmitted (dotted line arrow B). At this time, the receiver (2) is excited by the self-oscillation wave, and this is detected to detect a constant reference signal (DC voltage).
(V ₀ ) is being output. (Straight line (E) in the graph of Figure 2
See. ) This value is determined by the intensity (output) of the irradiation microwave of the transmitter (1), the size of the waveguide (5), the performance of the receiver (2) and the like. However, depending on the object, there may be a slight reflection, which may cause a slight variation.

When the object (3) contains water, the dielectric constant of the object increases in proportion to the amount of water. Therefore, a part of the irradiated microwave is reflected by the surface of the object (3) and the shallow layer of the surface (arrow C), and is absorbed in the deep part. Due to this reflected wave, the receiver (2) is excited by a composite wave of the self-generated wave and the reflected wave. This reflected wave becomes strong in proportion to the amount of water contained in the surface layer of the object within a certain range. This is because the microwave reflectance in the boundary layer between substances having different permittivities increases as the difference in permittivity increases.

The self-transmitted wave reaches the receiver (2) with a constant intensity regardless of the distance (X), but the reflected wave changes in phase with respect to the self-transmitted wave depending on the distance (X). In the detection unit of 2), there are a position where the self-transmitted wave and the reflected wave resonate (become in the same phase) to strengthen the composite wave, and a position where they are canceled (become the opposite phase) to weaken the composite wave. . Therefore, the received signal (V) from the receiver (2) becomes higher or lower depending on the distance (X).

An example of this relationship is shown in the graph as the waveform curve (F) in FIG. The vertical axis represents the received signal (DC voltage) (V) from the receiver (2), and the horizontal axis represents the distance (X). The peaks (M ₁ , M ₃ ··) of the waveform curve (F) in the graph are the resonance part (the position where the self-generated wave and the reflected wave have the same phase) and the valleys (M ₂ , M ₄ ·).
・) Is the canceling portion (position with opposite phase). As the distance (X) increases, the capture rate of the reflected wave decreases and the amplitude of the curve (F) gradually decreases. In addition, the length (L) of two cycles of this curve agrees with the wavelength of the microwave in principle.

The amplitudes of the adjacent peaks and valleys of this waveform curve (F) are proportional to the intensity of the reflected wave and also to the reference signal (V ₀ ). In other words, it increases almost in proportion to the product of the reference signal (V ₀ ) and the reflectance, but when the amount of water increases, the reflected wave also increases almost in proportion, so this amplitude also increases almost in proportion to the amount of water. Become.

The straight line (E) shows the reference signal (voltage) (V ₀ ) output by the receiver (2) being excited only by the self-generated wave, and is independent of the distance (X).

Therefore, for example, the difference (ΔV) between the value (V ₁ ) obtained by measuring the received signal at the position (M ₁ ) at a constant distance and the reference signal (V ₀ ).
If = V ₁ -V ₀₎ calculate, it is possible to this value and water content of the parameter (Y). Since the reference signal (V ₀ ) is affected by the transmission output, temperature, receiver performance, etc., (Y =
The value of ΔV / V ₀ ) is a more stable parameter.

The measurement position is most effective at a position at a fixed distance (M ₁ ), but it may be at positions (M ₂ ), (M ₃ ) ...

(See FIG. 2) However, in the case of continuous measurement by the non-contact method, the distance (X) is apt to fluctuate and it is difficult to keep it at a constant position. For example, as shown in FIG. 2, when the distance (X) fluctuates from the position (M ₁ ) by (ΔX), the received signal (V) fluctuates by (ΔV) and stable measurement cannot be performed.

Thus, even if the water content of the object to be measured is constant and the intensity of the reflected wave is constant, the received signal (V) is equal to the distance (X).
It can be seen that the value does not correspond to the water content due to the large change.

This embodiment solves this problem and enables continuous measurement even in the non-contact method.

In FIG. 1, the Doppler sensor (4) is forcibly reciprocally oscillated periodically perpendicularly to the surface of the object (3). The amplitude of the oscillation is set to ½ or more of the wavelength of the irradiation microwave, and the oscillation range is set to the range (R) including the positions (M ₁ ) and (M ₂ ) in FIG. 2, for example. To do. Specifically, when a microwave having an oscillation frequency of 10.525 GHz is used, the amplitude may be 20 mm.

While the sensor (4) is swinging, the received signal (V) from the receiver (2) is sampled at very short time intervals via the amplifier (8) and the A / D converter (9). It is read every second by the arithmetic unit (10) and stored in the memory (11) as a large amount of data. The waveform curve (G) in FIG. 3 is obtained by superimposing a large number of data sampled during one period (T ₀ ) and the waveform obtained by the oscilloscope. The black dots are the loci of many sampled data, and the solid line is the waveform curve (G) obtained with an oscilloscope. Since this waveform curve (G) is obtained by tracing the waveform of the reception signal (V) in FIG. 2 within a certain range (R) while the sensor makes one reciprocating oscillation, the time (T ₁ ), (T ₄ ) received signal value (V ₁ ) is
It matches the value (V ₁ ) at the time of passing the position (M ₁ ) in Fig. ₂ , and the value (V ₂ ) of the received signal at time (T ₂ ) and (T ₃ ) passes through the position (M ₂ ). It agrees with the value (V ₂ ) at the time of doing. If the sampling time interval is sufficiently short, the maximum value of this sampled data may be regarded as the value (V ₁ ) and the minimum value thereof may be regarded as the value (V ₂ ). Then, this difference (ΔV = V ₁ −V ₂ ) is proportional to the intensity of the reflected wave, and therefore has a value almost proportional to the amount of water, so that this is a parameter of the amount of water contained in the object (Y ) Can be.

The sum of the maximum and minimum values (ΣV = V ₁ + V ₂ ) is the reference signal (V ₀ ).
Since it is almost proportional to Y = ΔV / ΣV (30), a more stable parameter (Y) can be obtained.

In addition to this, the parameter may be obtained by calculating a differential value or an integrated value of the measurement data.

In this way, the microwave sensor is forcibly reciprocally oscillated within a certain range periodically, and the variation of the variation value of the data of many received signals sampled during that period is used as a parameter. With this, the water content can be measured once per cycle.

In this case, the same measurement can be performed by fixing the sensor and swinging the object.

It should be noted that, although one cycle of reciprocating oscillation and the time required to process a large number of data sampled during that period depend on the operation speed of the computer, normally it is sufficiently within one second.
From the observer's point of view, the cycle for displaying the results of moisture measurement is sufficiently short, and it can be considered that the measurement is substantially continuous.

In this embodiment, if the swing range of the sensor (4) is selected so as to include the positions (M ₁ ) and (M ₂ ) shown in FIG. not,
There is a great advantage in that the water content can be continuously measured by the non-contact method.

In the above, the maximum value and the minimum value of the data are used as the variation of the variation value, but the invention is not limited to this, and a value that can be detected electrically such as a differential value or an integrated value may be used.
For example, a detector combining a capacitor and a rectifier may detect the analog value.

FIG. 4 shows an example of a measuring device embodying the present invention. The box (15) accommodating the sensor (4) is a rod (16).
Is fixed to the tip of the rod, and the root of the rod is connected to the rocking device (17). The oscillating device (17) is configured to forcibly oscillate the sensor box (15) in the axial direction of the rod within a fixed range in a fixed range by a built-in motor and a crank mechanism (not shown). . Power supply (20) in the control box (19)
And the processor (13) are housed, the power source (20) is connected to the motor and the processor (13), and the processor (13) is connected to the sensor (4) via the rocking device (17) and the rod (16). Connected.

The received signal obtained while the sensor (4) is oscillating is sampled at a very short time interval as a digital value through the amplifier and A / D converter in the processor (13) and is sampled every second. It is read and stored as data in the built-in memory. The arithmetic unit performs the arithmetic processing of the variation of the variation values of a large number of sampled data during one cycle, and displays the result on the display (12). For example, the difference (Y = ΔV = V ₁ ) between the maximum value (V ₁ ) and the minimum value (V ₂ ) of data in one cycle (T ₀ ).
-V ₂ ) multiplied by a constant coefficient (α) (α · ΔV),
The value of the measured water content is displayed on the display (12). Alternatively, the difference (ΔV) between the maximum value and the minimum value and the sum (ΣV = V ₁ +
The ratio of V ₂ ) (Y = ΔV / ΣV) is displayed.

By using the device configured as described above, the water content can be continuously measured in a non-contact manner by installing the rocking device (17) on the surface of the object (3) so that the sensor box (15) is close to the sensor box (15). be able to. At this time, it is the same as described above that some shaking and tilting of the object is allowed.

The value obtained by multiplying the parameter (Y) shown in the above embodiment by a constant coefficient (α) or (β) is the surface layer part of the object (several mm
It represents the amount of water contained in the whole body, but when the water is uniformly dispersed, it represents the amount of water contained in the whole object (weight of water per unit volume) (W). Can be regarded as The relationship between the parameter (Y) and the water content (W) varies depending on the material of the object and the property of the solvent contained in the water, and is not always fixed. As an example, FIG. 5 is a graph showing the relationship between (Y) and (W) in the equation (30). The three calibration curves show different slopes for different material materials. It should be noted that the received signal (V) is saturated in a range where the amount of water is high, so that it is not proportional.

Therefore, in order to accurately measure the absolute value of the water content (W), W = f (Y) is set in order to correct the material and density of the object and the property of the chemicals of the solution and to make it linear. Function correction must be done.

It should be noted that the coefficients (α), (β), and the function f (Y) that determine the amount of water are determined by the performance of the microwave Doppler sensor, and when the target material such as the material of the object and the property of the aqueous solution is determined.
It is determined from a calibration curve obtained experimentally by determining the unit of water content to be displayed.

Effects of the Invention As described above in detail, according to the present invention, the microwave transmitter and the receiver that constitute the sensor use the microwave Doppler sensor that is generally used as it is, and the measurement is performed by the conventional method. By reversely skillfully utilizing the unstable factor (phase shift between the self-transmitted wave and the reflected wave) that has hindered the above, it becomes possible to easily and continuously measure the amount of water contained in the object. Therefore, it is possible to obtain a water content measuring device capable of continuously measuring an object that is moving during a processing step in a non-contact state.

Further, since it is not necessary to use an expensive microwave transmitter and receiver which are specially devised, and the mounting accuracy is not strictly required, it is possible to provide an inexpensive and convenient measuring device.

Further, since the measurement can be performed by the non-contact method, even a moving object does not make a contact mark or hurt.

As described above, the present invention brings about an extremely beneficial effect which has never been obtained.

[Brief description of drawings]

The drawings show an embodiment of a method for measuring the amount of water and a measuring apparatus therefor according to the present invention. FIG. 1 is a configuration diagram when a microwave Doppler sensor is used, and FIG. A graph showing the relationship between the distance (X) and its reception signal (DC voltage), FIG. 3 is a graph showing the relationship between the reception signal and time, FIG. 4 is a drawing showing an example of a measuring device, FIG. Is a graph showing the relationship between the parameter and the actual water content, and FIG. 6 is a drawing showing a conventional method for measuring the water content. (1) …… Microwave transmitter (Gun diode) (2) …… Microwave receiver (mixer diode) (3) …… Measured object (4) …… Microwave Doppler sensor (8) …… Amplifier, (9) …… A / D converter (10) …… Computer, (11) …… Memory (12) …… Display, (13) …… Processor (17) …… Rotating device

Claims (2)

[Claims] 1. A microwave Doppler sensor (4) which integrally includes a microwave transmitter (1) and a microwave receiver (2) and transmits and receives microwaves from one emission / reception surface.
Close to the surface of the object to be measured, and the sensor (4)
The reception in which the relative distance (X) between the emitting / receiving surface of the object and the surface of the object is forcibly cyclically fluctuated, and a composite wave of the reflected wave from the object to be measured and the self-oscillating wave is received during that period. The value of the received signal (V) detected and output by the device (2) is read into the processor (13) at very short time intervals, and the round trip of the fluctuation value obtained from the large number of the read data. A method for measuring the amount of water contained in an object, wherein the amount of water contained in the object to be measured is measured using the amount of change during one cycle as a parameter. 2. A microwave Doppler sensor (4) which integrally includes a microwave transmitter (1) and a microwave receiver (2) and transmits and receives microwaves from one emission / reception surface.
A oscillating means (17) for forcibly and reciprocally oscillating the sensor (4) periodically in a direction perpendicular to the transmitting and receiving surface with a constant amplitude, and a measured object between the oscillating means (17). The receiver (2), which has received the composite wave of the reflected wave from the object and the self-generated wave, detects this and outputs the value of the received signal (V) which is output at very short time intervals, and reads the value. It is composed of a processor (13) that performs arithmetic processing to obtain the amount of water contained in the object, using the amount of change in the fluctuation value obtained from a large number of data during one round trip as a parameter. It is configured to measure the amount of water contained in the object to be measured in a non-contact state by bringing the emitting / receiving surface of the sensor (4) closer to the surface and periodically swinging back and forth. A device for measuring the amount of water contained in an object.