JPH0240543A - Moisture measuring method using microwave - Google Patents

Abstract

PURPOSE:To adjust the energy of a microwave electrically and efficiently by detecting the attenuating amount of the microwave energy owing to a specimen which is arranged on a propagation path. CONSTITUTION:Detected voltage corresponding to the energy of a received microwave and detected values from a load cell 12 at this time are transferred into a detected value processing part 11 for the case wherein a specimen 5 is arranged on a propagating path 3 and for the case wherein the specimen 5 is not arranged. An attenuated voltage and the weight of the specimen are computed in the processing part. The moisture value of the specimen is computed by said values and a specified expression of correlation. The result of computation is connected to a driving control part which automatically controls industrial equipment with regard to the moisture from the processing part 11. When the magnitude of the energy of the received microwave is located outside of a suitable range based on the relationship between the energy of the transmitted microwave and the attenuated amount due to the specimen, the duty ratio of a rectangular wave voltage that is applied on Gunn diode 6 is adjusted to the larger or smaller value with the volume control in a pulse-interval adjusting circuit. In this way, the processing part 11 is normally operated, and the accurate moisture value can be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a moisture measuring method that utilizes the property that microwaves are absorbed by moisture in a sample.

Conventional Moisture Measuring Devices Using Microwave Absorption by Moisture in a Propagation Path are disclosed in, for example, Japanese Unexamined Patent Publication No. 132938/1983;
Many of them are known, as described in Japanese Patent Nos. 56-92435 and 59-87346.

In both of these, a microwave propagation path is formed by a microwave emitting device (i5) equipped with a Gunn diode, etc. and a receiver equipped with a microphone (microwave detection diode), and when no sample is placed in the propagation path. The received microwave energy is detected as a voltage by a detection diode (hereinafter referred to as the reference voltage VO), and the voltage due to the received microwave energy affected by the sample in the propagation path detected in the same manner (hereinafter referred to as the voltage V1), and the difference therebetween (attenuation voltage vO) is understood to correspond to the amount of attenuation of the transmitted microwave energy. Then, the attenuation amount, sample weight, and
The moisture value is calculated by substituting this attenuation voltage (vO) into the moisture correlation equation.

In this case, the received microwave energy needs to be within an appropriate range depending on the characteristics of the receiver and circuit requirements.

However, in reality, the microwave absorption rate by the sample may be unexpectedly large or small, and the received microwave energy may fall outside the above-mentioned appropriate range. In such cases, the emitted microwave energy is increased or decreased in order to adjust the received microwave energy. Conventionally, the input voltage to the Gunn diode is adjusted, or the input voltage remains constant and the transmitter's output is increased or decreased. A method is adopted in which an attenuator is placed in the waveguide to increase or decrease the propagation microwave as appropriate.

However, when the input voltage to the Gunn diode is changed, the mixing ratio of higher-order frequencies to the main frequency of the oscillated microwave changes. For example, as shown in Figure 3, the mixing ratio of high-order frequency (18 GHz, 36 GH2, etc.) microwaves that are always present with respect to the main frequency (9 GHz) changes, but the amount of attenuation due to moisture differs depending on the wavelength. , since the attenuation amount differs as a whole even for the same sample, there is a drawback that consistency with the above-mentioned correlation equation is lost.

Furthermore, if an attenuator is interposed in the middle of the waveguide, the measurement device equipped with the attenuator and the members necessary for adjusting the attenuator will become large as a whole.

Problems to be Solved by the Invention The present invention provides a microwave system that can electrically and efficiently adjust the energy of microwaves without changing the frequency of the transmitted microwaves or without using an attenuator. Our goal is to provide a moisture measuring device by

Means for Solving the Invention A method is provided in which a sample is placed in a microwave propagation path, and the amount of attenuation of microwave b-wave energy by the sample is detected to measure the water content of the sample.

The input voltage to the microwave oscillator is a square wave.

The transmitted microwave energy level is adjusted by changing the duty ratio of the rectangular wave.

Operation The configuration in which the input voltage to the microwave oscillator is a rectangular wave and the duty ratio of the rectangular wave is changed makes it possible to increase or decrease the amount of transmitted microwave energy without changing the input voltage to the oscillator.

Embodiment FIG. 2 shows an outline of a measuring device, in which an electromagnetic horn-shaped transmitter 1 and a receiver 2 of the same type are placed facing each other, and a microwave propagation path 3 is formed between them. A sample mount 4 made of a material with high microwave transmittance, such as acrylic resin or foamed polystyrene, is arranged in the middle of the propagation path 3, on which a sample 5 is placed.

The oscillator 1 includes an oscillating section 7 mainly including a Gunn diode 6, to which power is supplied from a power supply section 8.

The receiver 2 includes a receiving section 10 mainly including a microwave detection diode 9, and a detected value processing section 11 is connected to this.

Further, a load cell 12 is attached to the sample mounting table 4, and its detected value is connected to the detected value processing section 11.

The oscillating section 7 and the receiving section 10 are ordinary microwave transmitting/receiving circuits, and the detected value processing section 11 uses a so-called personal computer equipped with a part of memory and an arithmetic section.

The power supply circuit 8, as shown in FIG.
Constant voltage power supply circuit 1 via a rectifier circuit to a 00V AC power supply
On the other hand, a pulse interval adjustment circuit 15 is connected to a pulse generation circuit 14 using an astable multivibrator, and the output of the constant voltage power supply circuit 13 and the output of the pulse interval adjustment circuit 15 are connected to a switching circuit using a power transistor. They are connected by 16. The pulse interval adjustment circuit 15 uses a resistor as a pulse interval adjustment volume 19 so that the time constant portion 18 of the monostable multivibrator 17 can be operated from the outside.

The output of the switching circuit 16 is connected to the oscillation section 7.

When a sample is placed on the sample mounting stage 4 in the middle of the propagation path 3 and this measuring device is activated, the constant voltage power output from the constant voltage power supply circuit 13 is triggered by the pulse from the pulse interval adjustment circuit 15 in the switching circuit 16. It is assumed to be a square wave voltage power.

This rectangular wave voltage is fixed by the constant voltage power supply circuit 13, and is 9V (sufficient to excite the Gunn diode to the microwave oscillation state) when it is at a high level, and Ov when it is at a low level. The frequency is determined by the pulse generation circuit 14.
It is determined to be constant (40H7). Further, the duty ratio of the rectangular wave is normally used at about 80%, but this can be changed by adjusting the volume 19 described above.

The power of the rectangular wave voltage thus formed is output from the switching circuit 16 to the oscillating circuit 7, and the Gunn diode 6 of the circuit 7 outputs 9.4 GH only when the rectangular wave voltage is at a high level.
2 microwaves are oscillated, and the oscillations are stopped when the level is low. Therefore, when the duty ratio of the rectangular wave voltage is adjusted, the amount of transmitted microwave energy per unit time (time that is sufficiently longer than the panel cycle of the rectangular wave voltage) changes. The microwave emitted from the electromagnetic horn of the transmitter 1 becomes a traveling wave and propagates along the propagation path 3 towards the electromagnetic horn of the receiver 2, and reaches the detection diode 9 from the electromagnetic horn of the receiver 2, where it It is detected as a voltage approximately proportional to the amount of retained energy.

Note that in reality, the energy of the traveling wave may be attenuated due to interference of reflected waves from equipment around the sample or from the sample itself, so it is necessary to take measures to eliminate reflections as much as possible.

Since the input power to the oscillator 1 has a rectangular wave voltage and the oscillation of the Gunn diode 6 is pulse-like, the detection voltage of the detection diode 9 is output in a pulse-like manner due to this influence, but it is smoothed by the receiver 10. detected value processing unit 11
A smooth eroding voltage is transmitted to the .

Note that the detected value from the load cell 12 is constantly transmitted to the detected value processing section 11.

Therefore, first, the operation is performed without placing the sample 5 in the propagation path 3, and a smooth erosion voltage, that is, a reference voltage (VO) is obtained from the receiving section 10 to the detected value processing section 11, and this and the detection of the load cell 12 Store the value in the memory section (initial value setting mode). Note that a preset correlation equation between attenuation ω, weight, and water content is also stored in a part of the memory.

Next, the measurement mode is set, the sample 5 is placed in the propagation path, and the detected voltage (Vl) corresponding to the received microwave energy and the detected value from the load cell 12 at this time are input to the detected value processing section 1.
1. The detected value processing unit 11 inputs these detected values transmitted to the calculation unit at appropriate timing, sieves out the attenuation voltage (vO) and sample weight, and further substitutes these into the above-mentioned correlation equation to calculate the value of the sample. Calculate the moisture value.

The calculation result is connected from the detected value processing section 11 to a drive control section (not shown) such as a driver device or a meter for automatically controlling industrial equipment regarding moisture.

Then, the detected voltage (■
The magnitude of 1) depends on the magnitude of the transmitted microwave energy and the amount of microwave absorption by the moisture in the sample, and the magnitude of the transmitted microwave energy is determined by the duty ratio of the rectangular wave voltage of the power applied to the Gunn diode 6. .

On the other hand, the received microwave energy needs to be within a certain range as described above.

Therefore, in the above embodiment, when the magnitude of the received microwave energy is outside the above-mentioned appropriate range due to the relationship between the transmitted microwave energy and the attenuation caused by the sample 5, the volume 19 of the pulse interval adjustment circuit 15 is adjusted. Then, the duty ratio of the rectangular wave voltage is adjusted to be large or small. Thereby, the detected value processing section 11 can operate normally and output an accurate moisture value.

Although a well-known example of the circuit configuration of the power supply section 8 has been shown, other circuit configurations may be used.

Effects of the Invention In a moisture measuring device that uses microwaves, it is possible to electrically easily and precisely adjust the amount of microwave energy emitted from the transmitter while maintaining the input power voltage constant. .

When adjusting the received microwave energy in the receiver, the proportion of high-order waves mixed in will not change and errors will not occur in the measurement results.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the power supply section, FIG. 2 is a schematic diagram of the moisture measuring device, and FIG. 3 is a graph for explanation. 1... Transmitter, 2... Receiver, 3... Propagation path, 4
... Test Fl mounting table, 5... Sample, 6... Gunn diode, 7... Oscillator section, 8... Power supply section, 9... Detection diode, 10... Receiving section, 11 ...Detection value processing unit, 12...Load cell, 13...Constant voltage power supply circuit, 14...Pulse generation circuit, 15...Pulse interval adjustment circuit, 16...Switching circuit, 17...・Monostable multivibrator 18...time constant part, 19・
...Volume for adjusting pulse interval. input voltage

Claims (1)

[Claims] This is a method of placing a sample in a microwave propagation path and detecting the amount of attenuation of microwave energy by the sample to measure the water content of the sample. A moisture measurement method characterized by adjusting the amount of transmitted microwave energy by changing the duty ratio.