JPS59202049A - Microwave moisture meter - Google Patents

Abstract

PURPOSE:To measure the level of moisture at a high accuracy by arranging a pair of receiving horn for receiving a microwave passing through an object to be measured after projected from a transmitting horn to be a specified value of the difference in the distance thereof from the object being measured respectively to reduce the influence on variations of the sheet-shaped object being measured. CONSTITUTION:A microwave transmitted from an oscillator 1 is projected to an object 9 to be measured through an isolator 2, a waveguide 4 and a transmitting horn 3. The microwave passing through the object 9 being measured is received with receiving horn 13 and 14. The output thereof reaches to a magic T 15 via waveguides 16 and 17 and evenly distributed in the directions (a) and (b). The microwave transmitted in the direction (b) is annihilated at a non-reflection final terminal 18 while that in the direction (a) is detected by a detector section 11 and computed by an arithmetic section 12 to obtain the level of moisture. On the other hand, the receiving phones 13 and 14 are arranged at the distances l1 and l2 from the object 9 being measured to satisfy l2-l1 nlambda+lambda/4 thereby reducing variations of the object 9 being measured.

Description

[Detailed description of the invention] The present invention relates to improvements in microwave moisture meters.

Generally, microwave absorption of water is extremely large in the microwave band. For this reason, using microwave absorption of water,
BACKGROUND ART Conventionally, it has been widely used to measure the amount of water in a measured object from the amount of attenuation of microwaves.

FIG. 1 is a diagram illustrating the configuration of a conventional microwave moisture meter. An isolator that allows waves to pass through but hardly allows microwaves to pass in the opposite direction; 3 is a transmission horn connected to the isolator 2 via a first waveguide (or coaxial cable, hereinafter simply referred to as "waveguide") 4; , 5 is a receiving horn arranged at a predetermined distance e from the transmitting horn 3, and 7 is a second horn 7.
A receiving horn 9 is arranged to be spaced apart from the transmitting horns 3 and 7 and the receiving horns 5 and 8. An object to be measured made of, for example, a sheet of paper, 11
is, for example, a crystal diode, etc., and the third waveguide 10
A detecting section 12 detects the output of the receiving horn 8 via the detecting section 12, and a calculating section 12 receives the output of the detecting section 11 and performs predetermined arithmetic 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 transmitted through the isolator 2 and the first waveguide 4.
It is projected onto the object to be measured 9 from the transmitting hole 475 through. Further, the microwaves transmitted through the object to be measured 9 and attenuated by water molecules are received by the receiving Bohr 5 and then sent to the second waveguide 6.
After that, it is projected from the transmitting horn 7 onto the object to be measured 9 again. 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 arithmetic processing performed in the arithmetic section 12 results in the following:
The amount of water in the object to be measured 9 can now be determined.

However, in the above-mentioned conventional example, since the object to be measured 9 is sheet-shaped, it is easy to cause the object to fluctuate, and the standing waves generated by such flapping K cause the path line characteristics to become a major measurement error factor. There was a drawback.

The present invention has been made in view of the above drawbacks, and the purpose of the present invention is to provide a microwave moisture meter that uses microwaves to measure the amount of moisture in an object to be measured. To provide a microwave moisture meter capable of measuring the amount of moisture in a measured object with high accuracy without being subjected to large amounts of water.

A feature of the present invention is that in a microwave moisture meter that uses microwaves to measure the amount of moisture in an object to be measured, the microwaves projected from one transmission horn and transmitted through the object to be measured are transmitted to first and second channels. The object is received by receiving horns, and the distance difference between the receiving horns and the object to be measured is Ωλ+λ/4.

Hereinafter, the present invention will be explained in detail using figures. Second
The figure 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 meanings, and repeated explanation here will be omitted. Further, 13 is a first receiving horn that is placed at a predetermined distance □ from the object to be measured 9 and receives the microwaves transmitted through the object to be measured 9; A second receiving horn 15 that receives the microwaves transmitted through the measurement object 9 is connected to the receiving horn 13.14 via second and third waveguides 16 and 17, respectively, and is input from the receiving horn 13.14. The magic T118, which equally divides and sends out the microwaves in the two directions (1) and (2), is a non-reflection terminating element that receives the microwaves sent out in the (2) direction of the magic T15 and terminates the transmission line. The microwaves emitted in the direction (2) of the magic T 15 are detected by a detection unit 11 made of, for example, a crystal diode. Also, first and second receiving horns 13, 14 are arranged to correspond to the first and second receiving horns. Furthermore, L1=see, -9,1ζ nλ force input/4
(1) (where n: natural number, λ: wavelength) The three-dimensional circuit that processes the microwaves received from the reception horns 13 and 14 and causes them to reach the detection unit 11 is limited to the embodiment shown in FIG. Various modifications are possible without modification.

The operation of the embodiment of the present invention having the above configuration will be described below. In FIG. 2, microwaves transmitted from an oscillator 1 are projected onto an object to be measured 9 from a transmission horn 3 via an isolator 2 and a second waveguide 4. Furthermore, the microwaves transmitted through the object to be measured 9 and subjected to attenuation and phase rotation by water molecules are received by the first and second reception horns 13 and 14.

The outputs of these receiving horns 13 and 14 reach the magic T 15 via second and third waveguides 16 and 17, respectively, and are equally distributed and sent out in both directions. The microwaves sent in the direction (2) reach the non-reflection termination element 18 and are extinguished. Further, the microwave transmitted in the direction (2) is detected by the detection unit 11, and the detection signal is sent to the calculation unit 12.
The water content in the object to be measured 9 is calculated by the calculation process.

By the way, in the conventional example shown in FIG. 1, the voltage waveform on the line is derived by the wave equation as shown in equation (2) below.

V = V"e-j" + rV"ejBx (2) where F: reflectance From the above equation (2), the voltage amplitude IVI is derived as shown in the below equation (3).

= Orchid 1 + re””” 1-1V + Mountain 1+I”) 2-2r (1-cos 2βx)
11/2 From the above equation (3), the maximum value of voltage amplitude IVI “m”
When ax' and pole/' 1 value IV l are determined and their ratio is taken, the following formula (a) friin is obtained.

On the other hand, in the embodiment of the present invention shown in FIG. 2, the transmitting/receiving horn 3. :L3. :L4 is arranged so as to satisfy the above formula (1). In this case, as the amplitude IVI of the voltage waveform on the line, in addition to the above formula (3), the above formula (3
) is also detected by the detection unit 11 in the following equation (5), which is a signal of a portion whose phase is separated by λ/4 (that is, 9o·). Therefore,
After finding the minimum value 1v, 1, and taking their ratio, we get 1
n The following formula (6) is obtained.

In the above equations (4) and (6), since 0<r<1, 1+r>stone τ7 holds true. Still, the above formula (4
) and (6) show the amplitudes of the respective output signals when the path line of the object to be measured 9 changes in the conventional example and the embodiment of the present invention. Therefore, from the comparison of the above equation (4) and the above equation (6), it is found that the second
It can be seen that the pass line characteristic of the object to be measured 9 is better in the embodiment of the present invention shown in the figure.

FIG. 5 is a graph showing the effects of the above-described embodiment of the present invention. In Figure 3, (a) indicates the value when the reflectance F is 0.1 in the above equations (3), (5), and (3) Bushi (5), and υ, (b) indicates the value when the reflectance r is 0.2. The characteristic curves of equation (3) and equation (3)+(5) in FIG. 3 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 the pass line characteristics of the object to be measured 9 are greatly improved according to the embodiment of the present invention.

According to the embodiment of the present invention as described in detail above, the transmitting/receiving horns 3°13, 1
4, it has the advantage that it is less susceptible to the effects of standing waves caused by the flapping of the object to be measured compared to the conventional example. Also, reception horn 13.1
4 could be mechanically moved up and down by λ/4, but even compared to such a method, according to the embodiment of the present invention, there is no need to worry about failure of moving parts, etc., and the product life is long. There are also advantages.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the configuration of a conventional microwave moisture meter; FIG. 2 is a diagram illustrating the configuration of an embodiment of the present invention; and FIG. 3 is a graph showing the effects of using the embodiment of the present invention. 1... Oscillator, 2... Isolator, 3, 7...
Transmission horn, 5.8.13.14...Reception horn, 4
．． 6.10.16゜17... Waveguide, 9... Measured object, 11... Detection section, 12... Calculation section, 15...
Magic T118... Non-reflective termination element. Figure 3

Claims (1)

[Claims] A microwave moisture meter that uses microwaves to measure the amount of moisture in an object to be measured includes a transmission horn that projects microwaves emitted from a microwave source onto the object to be measured, and a microwave that passes through the object. 1. A microwave moisture meter comprising first and second receiving horns for receiving wavelengths.