JPH0718819B2 - Microwave moisture analyzer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for measuring the moisture content of a sample by detecting the amount of attenuation of microwave energy by the sample.

[Conventional technology]

Conventionally, many methods and devices for measuring the water content and water content of a sample using the absorption of microwaves by water have been proposed.

The applicant of the present invention has a measurement area in the middle of a microwave propagation path, as seen in the technologies recently filed as JP-A-1-287450, JP-A-1-301152, and JP-A-1-312448. A trough made of a material with a high microwave transmittance is placed, and the amount of microwave attenuation by the sample is measured while vibrating this trough and transporting the sample. We have developed a device for seeking.
After that, as a result of further research, the following improvements were discovered.

[Problems to be Solved by the Invention] It is known that when a dielectric material such as a trough or a sample is inserted in the microwave propagation path, a standing wave is generated more or less. Since the state of this standing wave varies depending on the position of the dielectric in the propagation path, if the position of the trough itself or the sample changes due to the vibration of the trough, it causes the detected value of microwave energy to vary widely. Cause. Of course, the detected value can be processed smoothly by averaging a certain period of time or multiplying it by a time constant, but the variation of the underlying data should be as small as possible.

FIG. 7 shows the distance L between the transmitting antenna a and the receiving antenna b.
This is an experimental device in which a microwave propagation path is formed so as to face each other with a distance of (161 mm), and an acrylic plate c having a plate thickness of 5 mm is arranged so as to substantially cross the propagation path. With this device 9.
When the distance 1 between the receiving horn b and the acrylic plate c is moved by 2 mm while oscillating a microwave of 4 GHz, the detection voltage of the microwave received by the receiving horn b changes with the movement of the acrylic plate. The graph will be displayed. In addition,
The detection voltage is 1.35V without crossing the acrylic plate c.
In the circuit for detecting the voltage of the received microwave energy, the larger the attenuation amount of the microwave energy, the higher the detected voltage. Referring to FIG. 8, the detected voltage has a sine curve with a cycle of about 16 mm (≈half-wavelength of microwave of 9.4 GHz) as the distance 1 increases and decreases. In this experiment, the voltage value was used as the detected value of the microwave energy, but even if it is the current value or the power value, the same cycle cycle results. Then, a difference of about 0.47 V is recognized in the voltage value between the peak and the valley of this curve.

This result indicates that when the acrylic plate c is used as the bottom surface of the trough of the vibration conveyor and this portion is used as the measurement area, the amplitude range of the trough in the propagation path direction extends from the peak to the valley of the curve. When the trough is arranged as shown in the figure (exemplified as the range A of the amplitude in FIG. 8), even if the condition of the sample on the trough is exactly the same, the position of the trough bottom surface due to the vibration at the moment when the received voltage is taken Depending on the existence, it shows that the detected value varies in the range of about 0.47V.

Therefore, in the present invention, the transmission antenna and the reception antenna are opposed to each other to form a microwave propagation path, and a trough formed of a material having a high microwave transmittance is disposed in the propagation path in a portion corresponding to the measurement area. , A device for measuring the amount of microwave attenuation by a sample while oscillating this trough while transporting the sample, wherein the microwave energy received is not affected by the vibration of the trough as much as possible. The purpose is to provide.

[Means for Solving the Problems]

In order to achieve the above object, the microwave moisture measuring apparatus of the present invention forms a microwave propagation path by facing a transmitting antenna and a receiving antenna, and transmits a microwave through a portion corresponding to the measurement area in the propagation path. In a device that arranges a trough formed of a material having a high rate, oscillates the trough back and forth in the direction of microwave propagation, and measures the amount of microwave attenuation by the sample while transporting the sample, the trough The center point of the longitudinal vibration is arranged so as to almost coincide with the peak position of the peak or trough of the energy intensity waveform indicated by the standing wave of the microwave generated between the transmitting antenna and the receiving antenna, and its amplitude is 1/1 of the microwave used. It is characterized by being set to 4 wavelengths or less.

[Action]

In the present invention, in order to measure the amount of microwave attenuation, the microwave is propagated from the transmitting antenna to the receiving antenna, while the trough is vibrated to convey the sample into the microwave propagation path. Then, the microwave is attenuated almost in proportion to the amount of water contained in the sample. At this time, since the trough and the sample vibrate in the propagation direction of the microwave in the propagation direction, the energy value of the received microwave fluctuates under the influence of the vibration, but the fluctuation width is slight. .

〔Example〕

Hereinafter, the device of the present invention will be described based on the first embodiment shown in FIGS.

Reference numeral 1 is a trough, and as an example, the whole is formed of an acrylic plate having a plate thickness of 5 mm. The trough 1 is supported on a hollow frame 3 by a leaf spring 2, and a transport surface 1'of the trough 1 is parallel to a horizontal plane. The angle α formed by the leaf spring 2 and the vertical direction is 30 degrees. The hollow frame 3 is formed by cutting out a portion corresponding to a main portion of a microwave propagation path so as not to obstruct the propagation of microwaves. As an example, a vibrator 4 is connected to one end of the trough 1 to apply vibration to the trough 1. The vibrator 4 includes a drive spring 5, an eccentric shaft 6 for periodically reciprocating the drive spring, bevel gears 7 and 7'for rotating the eccentric shaft 6, and a motor 8 having an output end having the bevel gear 7'attached at its tip. Consists of. The rotation speed of the eccentric shaft 6 is, for example, 500r
pm. The angle α ′ formed by the drive spring 5 and the horizontal direction is also 30 degrees. Since the eccentric shaft 6 is eccentric by 5 mm from the center of rotation, the trough 1 vibrates in the range of 10 mm in the length direction of the drive spring. Therefore, the vertical amplitude B of the vibration of the trough 1 is 10 mm × sin 30 ° = 5 mm. Reference numeral 15 is a sample supply unit.

A microwave transmitting antenna 9 and a microwave receiving antenna 10 are arranged above and below the trough 1. At this time, the transmitting antenna 9
The positional relationship between the receiving antenna 10 and the trough 1 is important. In this embodiment, the same distance between the antennas 9 and 10 as in FIG.
161 mm, and the trough 1 is arranged so that the vertical amplitude thereof is in the position shown by the amplitude range B in FIG. That is, the amplitude of the trough in the microwave propagation path direction is defined as the cycle of the curve (constant of the constant formed by the microwave energy received by the receiving antenna when the trough is moved back and forth in the microwave propagation path direction with no material placed on the trough. Period of standing waves ...
16 mm), and the range of the amplitude of the trough in the propagation path direction includes only the peak of the curve, and this peak is located approximately in the center of the range of amplitude, that is, the trough is , The center point of the front-back vibration is made to almost coincide with the peak position of the peak or trough of the energy intensity waveform indicated by the standing wave of the microwave generated between the transmitting antenna and the receiving antenna, and its amplitude is 1 / of the used microwave. It is arranged with 4 wavelengths or less. Therefore, the range of variation in measured values due to the change in the position of the trough 1 due to vibration is about
As low as 0.1V. It should be noted that the range of the amplitude is substantially halved in view of the influence of the microwave on the detected value.

A microwave oscillator 11 is connected to the transmitting antenna 9, and electric power from the power supply circuit 12 causes microwaves of 9.4 GHz (wavelength).
32mm) oscillates. A receiver 13 is connected to the receiving antenna 10, and the detected value of the received microwave energy is
The received voltage is transmitted to the detected value processing device 14.

The measurement of the water content of the sample by the apparatus of this embodiment is performed as follows.

The vibrator 4 is activated to vibrate the trough 1, and a 9.4 GHz microwave is oscillated from the transmitting antenna.
The microwave is slightly attenuated and reflected by the trough 1, and then received by the receiver 13 via the receiving antenna 10, and the received microwave energy is sent to the detected value processing device 14 one after another as the detected value m. Normally, if the frequency of the trough 1 is 50 times / second (corresponding to 500 rpm of the eccentric shaft 6), six detection values m can be obtained during one vibration period. The detection value processing device 14 accumulates this value for a certain period of time, calculates the average, and sets the average value as the reference value M0. At this point the sample has not yet been loaded onto the trough 1.

Next, the sample is supplied onto the trough 1 from the sample supply port 15.
The sample may be any material suitable for trough transportation, such as powder or granules and flakes, and examples thereof include gravel, tea leaves, tobacco and rice.

The sample receives the vibration of the trough 1 and is transported while spreading on the trough. In this case, if the sample contains a large amount of water, the samples adhere to each other, and as a result,
Although it may be possible to affect the detected value, such a problem is small due to the vibration of the trough 1, and the sample traverses the microwave propagation path on average.

The microwaves attenuated by the water content of the sample are received by the receiver 13, and the energy thereof is sent to the detection value processing device one after another as the detection value m. Detection value processing device
At 14, the received voltage is accumulated for a certain period of time, the average is calculated, and the value is set as the measured value M1. Then, the difference between the reference value M0 and the detected value M1, that is, the attenuation amount of the microwave energy due to the sample is calculated, and the water content of the sample is obtained from the relational expression of the known attenuation amount and water content. The water content of the sample obtained by the detection value processing device is used for displaying the water content and controlling the industrial equipment.

Next, a second embodiment shown in FIGS. 4 to 6 will be described.

The transmitting antenna 16 and the receiving antenna 17 are opposed to each other with an appropriate gap. A microwave oscillator 18 and a power supply circuit 19 are connected to the transmitting antenna 16 and oscillate a microwave of 24 GHz (wavelength 12.5 mm). The receiving antenna 17 has a receiver 20,
The detection value processing device 21 is connected.

A trough 22 is formed of polypropylene having a plate thickness of 1 mm, and is supported by a hollow frame 23 by a plate spring 24. The bottom surface of the trough 22 is inclined in the sample transfer direction, and both sides are inclined toward the center so that the center of the sample transfer direction is the deepest part, and a cutout hole 25 is provided in the portion corresponding to the measurement area. A plate 26 of expanded polystyrene is fitted in the notch hole 25 so as not to hinder the transport of the sample. Foamed polystyrene is a material with a very high microwave transmission. Note that the acrylic plate also has a high microwave transmittance, and in the first embodiment, the measurement area was not specially made of different materials.

The angle θ formed by the leaf spring 24 with the vertical direction is 25 degrees.
The angle θ ′ formed by 27 with the horizontal direction is also 25 degrees. Drive spring 27
Reciprocates in the direction of the arrow in the figure, and its amplitude is 6 mm. Therefore, the amplitude of the trough 22 in the microwave propagation path direction is 6 mm × sin 25 ° ≈2.5 mm.

The hollow frame 23 is supported by a load cell 28, and the load cell 28 measures the total weight of the trough 1 and other members together with the hollow frame 23, and sends the result to the detection value processing device 21. 29
Is a sample supply unit.

In the second embodiment, the position of the trough 22 between the antennas 16 and 17 is determined as follows. First, in the actual measurement, the average amount of the sample flowing on the trough 22 is obtained in advance, and with the amount of the sample placed on the trough 1, the trough 22 is slowly moved up and down in the microwave propagation path direction. At that time, the sine curve indicated by the received microwave energy is obtained. Then, the trough position is set so that the range of the amplitude of the trough in the propagation path direction includes only one of the peak and the valley of the curve. In the case of the second embodiment, the microwave wavelength is about
Since it is 12.5 mm, the curve increases and decreases in a cycle of about 6.3 mm. Then, the position of the peak or the valley of this curve is obtained, and the trough 22 is arranged so that the range of the amplitude (2.5 mm) of the trough 22 in the microwave propagation path direction is arranged in the front and rear with one of the peak and the valley as the center. Are placed.

In the second example, since the weight of the sample is measured together with the amount of microwave attenuation by the sample, it is possible to measure not only the amount of water contained in the sample but also the water content of the sample. When measuring the amount, the sample weight can be used as a correction factor for improving the measurement accuracy. Here, a method of measuring the water content of the sample by the apparatus of the second embodiment will be described.

Vibration of trough 22 and 24GH from transmitting antenna
The microwave of z is oscillated and the sample is supplied from the supply unit 29. The microwave is attenuated by the sample flowing on the trough 22, and is received by the receiver 20 via the receiving antenna 17,
The received microwave energy is sent to the detection value processing device 21 one after another as the detection value m. The load cell 28 sends the detected weight as the detected value w to the detected value processing device 21 one after another. In the detection value processing device 21, these detection values m and w are accumulated for a certain period of time, and their averages are calculated to obtain measured values M1 and W1. On the other hand, the average value of the detected values of the received microwave energy when the sample is not placed on the trough 22 and the average value of the detected values of the load cell 28 are respectively the reference value M0 by the same procedure as in the first embodiment. , W0, the detected value processing device 2
Remembered in 1. Then, in the detection value processing device 21, from these values (M0, M1, W0, W1) and the relational expression of the water content,
Calculate the water content of the sample. An example of this relational expression is the following expression.

Moisture content = a * (M0-M1) / (W1-W0) + b where a and b are constants obtained by experiments.

In addition, the curve that becomes the basis when determining the position of the trough,
In the first embodiment, the trough is obtained by moving the trough back and forth in the propagation path direction while the material is not placed on the trough, whereas in the second embodiment, an average amount of the sample at the time of measurement is placed on the trough. The trough is moved back and forth in the direction of the propagation path in the state of being mounted on. Which method should be adopted may be appropriately selected.For example, the one in which the reflection in the measurement area of the trough is relatively large, the one in which the sample reflection is relatively small, and the amount of the sample flowing at the time of measurement is uncertain The former may be selected for which a value is difficult to obtain, the latter may be selected because the reflection in the measurement area of the trough is relatively small, the sample may be relatively reflected in the measurement area, or the latter may be selected if the sample flows uniformly during measurement.

In the first and second embodiments, an electromagnetic horn is used as a transmitting / receiving antenna, but in addition, a slot,
Various antennas such as a parabolic antenna can be used. Further, not only the antenna but also various members such as trough, vibrator, oscillator, receiver and the like can be selected as required.

〔The invention's effect〕

According to the microwave moisture measuring apparatus of the present invention, it is possible to obtain a detection value with little fluctuation in the received microwave energy due to the vibration of the trough and the sample, and the variation in accuracy. As a result, it is possible to measure the water content of the sample with high accuracy.

[Brief description of drawings]

FIGS. 1 to 3 show a first embodiment of the present invention.
The figure is a partially broken side view, FIG. 2 is a front view, and FIG. 3 is a simplified front view for explaining the amplitude of the trough. 4 to 6 show a second embodiment of the present invention, and FIG. 4 is a front view,
FIG. 5 is a partial sectional view, and FIG. 6 is a plan view of the trough.
FIG. 7 shows the experimental apparatus, and FIG. 8 shows the experimental results. 1, 22 ... Trough, 9,16 ... Transmission antenna, 10,17 ... Reception antenna, 11,18 ... Oscillator, 12,19 ... Power supply circuit, 13,20
... Receiver, 14, 21 ... Detection value processing device

Claims (1)

[Claims] 1. A microwave propagation path is formed by making a transmission antenna and a reception antenna face each other, and a trough formed of a material having a high microwave transmittance is disposed in the propagation path along a portion corresponding to the measurement area. In a device that measures the amount of microwave attenuation by the sample while transporting the sample by vibrating the trough back and forth in the direction of microwave propagation, the trough sets the center point of the front-back vibration between the transmitting antenna and the receiving antenna. Microwaves that are arranged so as to almost coincide with the peaks or troughs of the energy intensity waveform indicated by the standing wave of the generated microwaves, and that their amplitude is 1/4 wavelength or less of the microwave used. Wave moisture analyzer.