JPH02249958A - Method for measuring moisture contained in object and measuring instrument thereof - Google Patents

Abstract

PURPOSE:To continuously measure the content of the moisture contained in an object by using a microwave Doppler sensor and utilizing the change in the reflectivity thereof. CONSTITUTION:Microwaves are transmitted (arrow A) from a transmitter 1 to a specified direction from a signal transmission and reception surface 7 by a horn antenna 6 when a suitable voltage is impressed to an input terminal 14 of the transmitter 1. The microwaves (arrow C) reflected by the object 3 are converged by the antenna 6 from the transmission and reception surface 7 and the reception signal is obtd. the received signal from the sensor 4 is passed through an amplifier 8 and an A/D converter 9, is read as a digital value into a computing element 10 and is stored as data into a built-in memory 11. Further, a microcomputer is built into the computing element 10 which reads the data value and processes the same to compute the change thereof. The result thereof is displayed 12. The content of the moisture contained in the object is continuously measured in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION The present invention relates to a method for measuring moisture 1 contained in an object and a measuring device therefor. Objects include hygroscopic solids such as wood, granular materials such as grains, powdered materials for processed foods, and sheet-like materials such as textiles and paper. When microwaves are irradiated onto this object to be measured, the reflectance and transmittance change depending on the amount of water contained therein. Among these, an object of the present invention is to provide a measuring method and a measuring device thereof, which use a general-purpose microwave Doppler sensor to easily measure water content by utilizing the phenomenon of change in reflectance.

Conventional technology and problems to be solved Conventionally, methods have already been put into practical use to measure moisture content by utilizing the fact that when microwaves pass through an object, the attenuation rate, or transmittance, changes depending on the moisture content. ing.

FIG. 6 illustrates the principle.

(1) is a microwave transmitter, and (2) is a microwave receiver, which are arranged opposite to each other with a fixed interval (S), and between them is a measured object (3) (hereinafter simply referred to as the object). )
put Microwaves (arrow A) emitted from the transmitter (1) are absorbed by moisture when passing through the object (3), are attenuated, and reach the receiver (2) (arrow B). Since this attenuation rate changes within a certain range in proportion to the amount of water, the amount of water can be measured by measuring this.

However, it is not so easy to accurately measure this attenuation rate. When using a commonly used transmitter and receiver, the distance (S) between them must be kept constant and the object (3) must be placed at a specific position between them.

If the object (3) shifts even slightly or the distance (S) changes, the received signal (voltage) obtained from the receiver will fluctuate, making stable measurement impossible. This is because a part of the irradiated microwave is reflected by the object (3) and becomes a secondary irradiated wave (dotted arrow C), but the phase shift due to the position of the object (3) affects the irradiation. This is because the strength of the composite wave (combined wave of A and C) fluctuates, and therefore the received signal at the receiver (2) fluctuates.Also, secondary reflection of the transmitted microwave (arrow B) The phase shift of the wave (dotted arrow D) also occurs depending on the position of the object (3), which affects the received signal of the receiver in a complex manner.In order to eliminate such fluctuations, the above-mentioned secondary The transmitter and receiver must be specially designed to avoid being affected by reflected waves (dotted lines C and D), and as a result, the transmitter and receiver have to be specially designed, and their installation requires precision. This required an expensive stationary structure.

As described above, all of the conventional microwave-applied moisture measuring devices that have been put into practical use are limited in their usage because they utilize transmission attenuation factors. For example, in the case of solids, granules, powders, etc., there are restrictions such as being able to measure only a small amount of sampled material, not being able to measure continuously, and being expensive and being usable only at the location where it is installed. However, it did not meet the needs of customers when continuous measurement was required during the processing process.

I have not yet seen or heard of any method that utilizes changes in the reflectance of microwaves. This is because when using reflected waves, the influence of phase shift due to the position of the object (3) as described above is an inevitable phenomenon, and a method for eliminating this has not yet been solved.

In view of the above-mentioned conventional drawbacks and problems, the present invention uses a microwave Doppler sensor that integrates a commonly used microwave transmitter and receiver,
In order to easily measure the amount of water contained in an object, the relationship between the change in reflectance and the phase shift of the reflected waves, which was the cause of the instability described above, was cleverly utilized. In this way, we aim to provide a convenient measuring method and measuring device to meet the needs of consumers.

Structure and operation of the invention Below, embodiments of the invention will be described in detail with reference to the drawings.

First, a case where a microwave Doppler sensor incorporating a microwave transmitter and a microwave receiver is used will be described with reference to FIG.

In Figure 1, the Doppler sensor (4) is the transmitter (1)
A Gunn diode (1) as a transmitter and a mixer diode (2) as a receiver are integrally built into a waveguide (5).

A suitable voltage (e.g. D
When C8V) is applied, microwaves are transmitted from the Gunn diode (1) to the transmitting/receiving surface (7) by the horn antenna (6).
It does not necessarily have to be a real surface, and may be considered a virtual surface without substance. ) in a certain direction (arrow A
). Microwave reflected by object (3) (arrow C)
is converged by the horn antenna (6) from the transmitting/receiving surface (7) and received by the mixer diode (2) to obtain a received signal (voltage).

The received signal from the sensor (4) is read into the arithmetic unit (io) as a digital value via an amplifier (8) and an A/D converter (9), and is stored as data in a built-in memory (11). The amplifier (8), A/D converter (9), arithmetic unit (10), memory (11), and display (12) collectively constitute a processor (13). The arithmetic unit (10) incorporates a microcomputer, reads data values, performs arithmetic processing on changes in the data, and displays the results on the display (
12).

The surface of the object (3) is the horn antenna (6) of the sensor (4).
) transmission and reception 1 (7), k1) distance ii1 (X) (1)
They are spaced out.

If the object (3) is completely dry, the irradiated microwaves will be absorbed or transmitted without being reflected except for the reflection peculiar to the object (dotted arrow B).
), at this time, the mixer diode (2) is excited by the self-oscillated wave and receives a constant reference signal (voltage). (Illuminate the straight line (E) on the graph in Figure 2.) However,
Depending on the object, there may be slight variations due to unique reflections.

When the object (3) contains water, the dielectric constant of the object increases, so some of the irradiated microwaves are absorbed by the object (3).
) and the shallow layer of the surface (arrow C), and is absorbed in deeper parts. This reflected wave excites the mixer diode (2) with a composite wave of the self-oscillated wave and the reflected wave. This reflectance increases within a certain range in approximately proportion to the amount of water contained in the surface layer of the object.

Since the reflected wave is out of phase with the emitted wave depending on the distance (x), the combined wave may resonate or be canceled at the detection position of the mixer diode (2). FIG. 2 shows this relationship graphically. The vertical axis is the received signal (voltage) (V) from the mixer diode (2), and the horizontal axis is the distance! (X), the peaks (M +, M3...) of the waveform curve (F) of the graph are the resonance parts, and the valleys (M2, MA ・
・) is the cancellation part. As the distance II (X) increases, the reflected wave capture rate decreases and the curve (F) gradually attenuates.

Note that the length (L) of two periods of this curve coincides with the wavelength of the microwave in principle.

The amplitude of this waveform curve (F) increases almost in proportion to the product of the reference signal (vO) and reflectance, so it changes in proportion to the water content, but the phase of the curve with respect to distance (X) is completely It does not change.

The straight line (E) shows the reference signal (voltage) that the mixer diode (2) receives when it is excited by only the self-oscillated wave,
It has nothing to do with the distance (X), and its value is set as (V o).

Therefore, for example, if you calculate the difference (ΔV=V+-Vo) between the value (V+) obtained by measuring the received signal at a position (M1) at a certain distance and the reference signal (Vo), this value can be used as the water content. can be set as the parameter (Y). Reference signal (■
0) is affected by the transmission output, temperature, etc., so (Y=Δ
V/Vo) is a more stable parameter.

The most effective measurement position is a position (M+) at a certain distance, but positions (M2), (M3), etc. may also be used. (See FIG. 2) However, in the case of continuous measurement using a non-contact method, the distance <X> tends to fluctuate, and it is difficult to maintain it at a fixed position. For example, as shown in Figure 2, distance <
> oscillates by (ΔX) from the position (M1), the received signal fluctuates by (Δ■), making stable measurement impossible.

This embodiment solves this problem and enables continuous measurement even in a non-contact manner.

In FIG. 1, the Doppler sensor (4) is periodically oscillated perpendicularly to the surface of the object (3). The amplitude of the t1 shift is at least one part of the wavelength of the irradiated microwave, and the oscillation range is, for example, ffi(M+), (
Specifically, when microwaves with an oscillation frequency of 10.525 GHz are used, the amplitude only needs to be 20 m1m.

While the sensor (4) is oscillating, the received signal from the receiver mixer diode (2) is read momentarily to the arithmetic unit (10) via the amplifier (8) and A/D converter (9). , are stored in the memory (11) as a large number of data. - The waveform curve (G) in FIG. 3 is obtained by superimposing the data sampled during the period (T o) and the waveform obtained by the oscilloscope. Since this waveform curve (G) is obtained by tracing the received waveform in Fig. 2 within a certain range (R) while the sensor swings back and forth, the time (T+)
, (T4) coincides with 1i (V+) at the time of passing the position (M1) in FIG.
) is the same as the value (V2) at position (M2).

If the sampling interval is short enough, the maximum value can be regarded as the value (■I), and the minimum value can be regarded as the value di (V2).

Since this difference (ΔV=V+ -V2) has a value proportional to the amount of water, it can be used as a parameter (Y) for the amount of water contained in the object.

Since the sum of the maximum and minimum values (ΣV: Vl + V2) is proportional to the reference signal value (■0), a more stable parameter (Y) can be obtained by calculating Y=Δ■/Σ■. can.

In addition, the parameters can also be obtained by calculating differential values or integral values of measurement data.

In this way, the amount of moisture can be measured by forcefully oscillating the microwave sensor periodically within a certain range and using the change in the fluctuation value of a large number of data sampled during that period as a parameter. .

In this case, similar measurements can be made even if the sensor is fixed and the object is swung.

In this example, the positions (M1) and (M2) in FIG.
As long as the swing range of the sensor (4) is selected so as to include this, the moisture content can be continuously measured in a non-contact manner without being affected by slight swings or tilts of the object or sensor, which is a great advantage.

In the above, the maximum value and minimum value of the data are used as the change in the fluctuation value, but the present invention is not limited to this, and electrically detectable values such as differential values and integral values can also be used.

For example, it may be detected as an analog value using a detector that combines a capacitor and a rectifier.

FIG. 4 shows an example of a measuring device according to the present invention, in which a box (15) containing a sensor (4) is connected to a rod (1
6), and the base of the rod is the rocking device (17
) is connected to. The swinging device (17) is configured to swing the sensor box (15) in the axial direction of the rod within a certain range at a certain period using a built-in motor and a crank mechanism (not shown). There is an electric fi (2) inside the control box (19).
0) and processor (13) are installed, and the electric! (20) is connected to a motor and a processor (13), and the processor (13) is connected to the sensor (4) via a rocking device (17) and a rod (16).

The received signal obtained while the sensor (4) is oscillating is momentarily read into the arithmetic unit as a digital value via the amplifier and A/D converter in the processor (13), and is stored as data in the built-in memory. be remembered. The arithmetic unit performs arithmetic processing on the amount of change in the data fluctuation value, and displays the result on the display (12). For example, the value (α
・Δ■) as the measured moisture content value on the display (12)
to be displayed. Alternatively, display the value (β・ΔV/Σ■) obtained by multiplying the ratio (Δ■/Σ■) of the difference (Δ■) between the maximum and minimum values and the sum (Σ■) by a certain coefficient (β). .

Using a device configured in this way, the moisture content can be continuously measured in a non-contact manner by bringing the sensor box (15) close to the surface of the object (3) and installing the rocking device (17). be able to. At this time, as mentioned above, some shaking and tilting of the object is allowed.

The parameter (Y) shown in the above example represents the amount of water contained in the surface layer of the object (up to a depth of several mm), but if the water is uniformly distributed,
Amount of water contained in the entire object (weight of water per unit volume)
(W) can be considered to be representative. The relationship between this parameter (Y) and the water content (W) changes depending on the material of the object and the properties of the solvent contained in the water, and is not necessarily fixed. FIG. 5 generally shows the relationship between (Y) and (W) in a graph.

Therefore, in order to accurately measure the absolute value of water It (W), corrections are made for the material of the object, density, properties of the chemical in the solution, etc., and in order to linearize it, W = f (Y). Numerical number correction must be performed.

Effects of the Invention As described in detail above, according to the present invention, the microwave transmitter and receiver constituting the sensor use a commonly used microwave Doppler sensor as is, and measurement cannot be performed using conventional methods. By skillfully utilizing the unstable factors that were inhibiting this, it becomes possible to easily and continuously measure the amount of water contained in objects. Therefore, it is possible to obtain a moisture content measuring device that can continuously measure a moving object during a processing process without contacting it.

Furthermore, there is no need to use specially designed and expensive microwave transmitters and receivers, and there are no strict requirements for mounting accuracy, making it possible to provide an inexpensive and convenient measuring device.

Furthermore, since it can be measured using a non-contact method, it will not leave contact marks or damage even moving objects.

In this way, the present invention brings about extremely beneficial effects that have not been seen before.

[Brief explanation of drawings]

The drawings show an embodiment of the moisture content measuring method and its measuring device according to the present invention. Fig. 1 is a configuration diagram when a microwave Doppler sensor is used, and Fig. 2 is a diagram showing the received signal (
Figure 3 is a graph showing the relationship between the received signal and time/close, Figure 4 is a diagram showing an example of the measuring device, Figure 5 is the parameter and actual moisture content. FIG. 6 is a graph showing the relationship between water content and water content. (1)...Microwave oscillator (Gun diode) (2)
...Microwave receiver (mixer diode) (3)...
Object to be measured (4)...Microwave Doppler sensor (8)...Amplifier, (9)...8/I) Converter (
10)...Arithmetic unit, (11)...Memory (12)...
・Display device, (13)...processor (17)...oscillating device

Claims (1)

[Claims] 1) Microwave transmitter (1) and microwave receiver (2)
A microwave Doppler sensor (4) that is integrally equipped with a microwave sensor (4) that emits and receives microwaves from a single emitting/receiving surface is brought close to the surface of the object to be measured, and the emitting/receiving surface of the sensor (4) and the object are brought close together. By periodically varying the relative distance to the surface of the object, the change in the fluctuation value of the received signal obtained from the receiver (2) is measured as a parameter of the amount of water contained in the object. A method for measuring the amount of water contained in an object, characterized by: 2) Microwave transmitter (1) and microwave receiver (2)
a microwave Doppler sensor (4) that transmits and receives microwaves from one transmitting and receiving surface; a processor (13) that calculates and processes the change in the fluctuation value of the received signal obtained from the receiver (2) as a parameter of the amount of water contained in the object to be measured; ), and is configured to measure the amount of water contained in the object in a non-contact manner by moving the transmitting/receiving surface of the sensor (4) close to the surface of the object to be measured and swinging it. A device that measures the amount of water contained in a characteristic object.