JPH0734001B2 - Microwave water content measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a measuring device for measuring the water content of a sample by utilizing the absorption of microwaves by water.

2. Description of the Related Art There are many water content measuring devices that utilize the absorption of microwaves by water. In many cases, the energy of the transmitted microwave is detected as the amount of attenuation that is absorbed by the moisture of the sample located in the propagation path to the receiver, and is usually used to make the measured value accurate. Temperature, sample weight,
It has various correction means relating to the transmission intensity. For example, regarding temperature correction, JP-A-56-43540 and 5
7-100339, and Japanese Patent Laid-Open No. 60-13575 for weight correction.
No. 2 and No. 60-18745, and Japanese Patent Application Laid-Open No. 56-92435 and No. 57-118147 are disclosed with respect to correction of transmission intensity.

However, in all of these, the principle is that the sample is always and uniformly present in the range (measurement range) where the microwave is radiated.

By the way, there is a distribution in the electric field strength of the microwave passing through the measurement area (usually the center of the measurement area is the highest), and the microwave energy depends on which part of the measurement area the high electric field strength is located. There is a change in the amount of attenuation and the detected value fluctuates.

FIG. 5 (a) is an experimental result of detecting the voltage on the microwave receiving side by arranging the microwave absorber d at various positions in the measurement area S in the middle of the microwave propagation path (in air).
It shows the variation of the detected value due to uneven distribution of the sample.

In this experiment, as shown in (b) of the same figure, an acrylic resin flat plate c was placed across a microwave propagation path between a transmitting horn a and a receiving horn b arranged facing each other with a space therebetween. The upper surface thereof is divided into c1 to c9 as shown in FIG. 3C, the same absorber d is placed in each of the above divisions, and the received energy of the microwave is detected as a voltage.

The absorber d is a commercially available absorber sheet based on urethane foam (ECCOSORB ... trade name, Grace Japan Co., Ltd.) cut into a rectangle, and the microwave frequency is 9.45 GHz. Acrylic resin plate is 9.9 mm thick The wavelength of microwave in vacuum, ε: dielectric constant of acrylic resin plate, μ: half-wave plate of the same permeability), and the detection voltage (reference voltage) when the absorber is not mounted is 4.80V. Furthermore, the detected value is the average value of the detection results of three times, and the value in parentheses is the difference from the reference voltage.

As described above, even within the same measurement range, the detected value differs depending on the position of the absorber d (uneven distribution of the sample).

And, in fact, in the microwave measuring apparatus applied to the industrial equipment, the sample is not always arranged evenly in the measurement area depending on the characteristics of the sample itself and the aspect of the sample supply. When the carrier path is divided into narrow bands along the carrying direction, the sample exists only intermittently in some bands.

As a result, when the position where the electric field strength of the microwave is strong becomes the position of the slit where the sample exists only intermittently as described above, the amount of the sample passing through becomes intermittent intermittently, and the basis for calculating the water content is The detected value of the received microwave energy largely fluctuates even under other conditions, which is one of the causes of the error in the measurement result.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention ensures that a sample is always present in a position where the electric field strength is high in a measurement area, and does not cause a large fluctuation in the detected value of received microwave energy, thereby measuring the water content by microwaves. The object is to provide a device.

Means for Solving the Problems In a sample transporting device in a water content measuring device, at least a portion of a sample transporting surface which is a measurement area is formed of a material having a high microwave transmittance.

The microwave transmission section and the reception section are arranged with a measurement area on the conveyance surface sandwiched therebetween, with a microwave propagation path formed between the two sections.

It is assumed that the measurement region has a groove shape that is long in the sample transport direction and that the groove cross section has a deep portion formed by an inclined surface, and the position of this deep portion and the position where the electric field strength of the microwave in the measurement region is high are matched.

The sample is secured at a position where the microwave electric field strength is high in the deep part formed by the inclined surface on the transfer surface of the sample transfer device, and there is a large fluctuation in the received microwave energy detection value due to the presence or absence of the sample and an extreme increase or decrease. Prevent.

Example FIG. 1 shows a water content measuring apparatus 1 using microwaves, which receives a measurement sample, which is a part of a product being processed, from a supply port 2 of an industrial apparatus (not shown) to produce the inside of the industrial apparatus. It is intended to measure the water content of a product and use it to control the processing of the product.

A sample transfer device 3 is provided so as to be connected to the supply port 2, and a transmission side electromagnetic horn 4 as a microwave transmission part and a reception side electrode horn 5 as the same reception part are arranged above and below the sample transfer device 3 to sandwich both electromagnetic waves. Microwave propagation path 6 between horns 4 and 5
Is formed in.

An oscillation device 7 mainly composed of a Gunn diode is attached to the electromagnetic horn 4 on the transmission side, and the electric power from the power supply circuit 8 causes 9.45GH.
emits microwave of z. The receiving electromagnetic horn 5 is attached with a receiving device 9 mainly composed of a receiving diode, and the detected value m1 of the received microwave energy is transmitted to the detected value processing device 10 as a voltage. Commercially available power supply circuits and transmitters and receivers are used.

The detection value processing device 10 uses a so-called personal computer and receives the detection value w1 (voltage value related to weight) from the load cell 11 provided in the sample transfer device 3 in addition to the detection value m1.
The water content of the sample is calculated from both detected values m1 and w1 and the known correlation equation of “microwave energy attenuation amount m, weight w and water content G” and used as the measurement result. The output of the detection value processing device 10 is transmitted to a water content display device or a driver of industrial equipment.

The sample transfer device 3 is configured as a vibrating trough in this embodiment, and in FIG. 1, the trough 12 has leaf springs 14 on the front, rear, left, and right sides on a pedestal 13 supported on the machine frame side via the load cell 11. It is mounted so that it can be vibrated back and forth through. The rear portion of the trough 12 is located below the supply port 2 and is also connected to a vibrator 15.

The trough 12 is entirely made of a polypropylene material having a plate thickness of 1 mm, and as shown in FIG. 3, a measurement area S is set on a bottom surface L serving as a sample transport surface. A portion of the measurement area S is cut out and a Styrofoam plate (foaming ratio 10 times) 16 is attached with its upper surface flush. Styrofoam is a material having a very high microwave transmittance.

The entire bottom surface L of the trough 12 has a groove shape that is long in the sample transport direction, and the groove-shaped cross-section including the measurement area S is inclined from both sides and has a deep portion 17 at the center.

As shown in FIG. 2, this deep portion 17 is made to coincide with the position p where the electric field strength of the microwave radiated from the transmission side electromagnetic horn 4 is the highest.

As shown in FIG. 2, the pedestal 13 is cut out at least in a region slightly larger than the measurement region S so as not to interfere with microwave propagation.

When the water content measuring device 1 is operated, a microwave propagation path 6 is formed between the oscillator 7 and the receiver 9. On the other hand, the vibrator 15 causes the trough 12 of the sample transfer device 3 to move the leaf spring 14
The sample from the supply port 2 is vibrated in the direction of the arrow u via the trough 12, passes through the measurement area S, and advances toward the front end while being finely rocked.

The sample supplied from the supply port 2 to the trough 12 first falls into the deep portion 17 due to the inclined surface of the sample transfer surface (bottom surface) set in the trough 12, so that the sample always exists in the narrow zone including the deep portion 17. Will be done. Of course, depending on the mode of supply, the sample may initially be agglomerated or may be biased to one side of the bottom surface of the trough 12 (sample transport surface).
Even in such a case, the sample moves to the deep portion 17 due to the vibration of the trough 2 and the inclined surface of the transport surface, and when the sample passes through the measurement area S, it exists on both sides with the deep portion 17 as the center. This deep portion 17 is a position where the electric field strength of the microwave is strong as described above.

In the measurement area S, the microwave from the electromagnetic horn 4 on the transmitting side is radiated to the sample in the measurement area, and the microwave transmitted through the sample is detected by the receiving device 9, and is received by the detection value processing device 10 as the received microwave energy value m1. Transmitted.

The detection microwave processing value m0 and the load cell detection value w0 when the sample does not exist in advance are stored in the detection value processing device 10 M = Σ (m0−m1) …… W = Σ (w1−w0) …… G = The processing of a × M / W + b is performed at a predetermined time interval of 60 seconds and the measured value G is output.

The detection value processing device 10 captures the detection values m1 and w1 10 times / second. Therefore, the formula means that the attenuation of the microwave energy detected every 1/10 second and the sample weight are integrated 600 times. The formula is a correlation formula obtained experimentally by the total dry method, and the relationship between the attenuation of microwave energy due to water content of the sample and the weight and water content of the sample. The constants a and b are the type of sample and the structure of the measuring instrument. It is highly reliable though it depends on the conditions such as. As a result of an experiment using the apparatus of this embodiment using tea leaves in the tea making process as a sample, numerical values of a≈100 and b≈0 were obtained.

The water content G measured in this manner is output to the display device or the industrial equipment driver as described above.

In the trough 12 of the embodiment, there is no particular problem even if the styrofoam part in the measurement area S is made of the same polypropylene material as the other parts. Further, the polypropylene material may be replaced with the acrylic resin plate having the half-wave thickness of the microwave used.

As shown in FIG. 4, the conveyor belt 18 may form the sample transfer surface.

In this case, the outward path surface of the circulating conveyor belt on which the sample is placed serves as the transport surface, and the receiving section for the transmitting section is disposed with the conveyor belt 18 in between or between the outward path and the return path of the belt. The conveyor belt 18 also has a deep portion 17 ', which is also entirely groove-shaped and whose groove-shaped cross section is formed by an inclined surface. Then, at least the portion that becomes the measurement region S, that is, the portion that corresponds to the width of the measurement region S in the width direction of the belt has a high microwave transmittance, such as a Teflon belt (Teflon ... It is made of a highly flexible synthetic resin material (dotted area in the figure). The deep portion 17 'coincides with the position p where the electric field strength of the microwave is high in the measurement area S.

Regarding the operation, there is no particular difference from the case of the above-mentioned embodiment, but in the case of using the conveyor belt 18, the action of gathering the sample in the deep portion 17 'is weaker than that of the vibrating trough 12, so that it is relatively fluid such as powder or granules. Suitable for good samples. However, even without a vibrating device, most of the samples are deep enough due to the natural vibration during conveyor belt operation.
Move to 17 '. It should be noted that, if necessary, the forward path of the conveyor belt may be vibrated.

Further, in the case of a belt, since the conveyor belt 18 is flexible in the width direction as well, the conveyor belt 18 may not be formed in a groove shape, but may be formed in a groove shape by raising the belt from both sides only at a portion in the measurement area S by rollers or the like.

In general, the electric field strength of the propagating microwave in air has a Gaussian distribution with a high center and a low peripheral, so the deep portion 17 on the sample transport surface may be aligned with the center of the microwave propagation path as described above. However, depending on the microwave mode, there may be two areas where the electric field strength is high. In this case, two rows of the deep areas 17 may be provided, or the deep areas 17 may be formed at two areas where the electric field strength is high. It will be aligned with the connecting straight line.

Note that the inclined surface includes a curved surface and a surface that is inclined toward the deep portion 17 as a whole even if there is unevenness.

Further, since the propagation path inside the waveguide may be used as the microwave propagation path for detecting the water content of the sample, the transmitting unit and the receiving unit are not limited to the electromagnetic horn.

Effect of the Invention A sample is always present at a place where the electric field strength of the microwave is high in the measurement region, and the presence or absence of the sample at this place or the extreme amount of the sample causes a large fluctuation in the received microwave energy. Since there is no disturbance due to these fluctuations, a stable water content measurement value can be obtained.

[Brief description of drawings]

1 is a block-like front view, FIG. 2 is a side view showing a part in section, FIG. 3 is a plan view, FIG. 4 is a perspective view of another embodiment, and FIG. 5 (a). (C) is a figure used for description. 1 ... Water content measuring device, 2 ... Sample supply port, 3 ... Sample transport device, 4 ... Transmitting side electromagnetic horn, 5 ... Receiving side electromagnetic horn, 6 ... Propagation path, 7 ... Oscillating device, 8 ... Power supply circuit, 9 ... Receiving device, 10 ... Detected value processing device, 11 ... Load cell, 12 ... Trough, 13 ... Stand, 14 ... Leaf spring,
15 …… Vibrator, 16 …… Styrofoam plate, 17 ……
Deep, 18 …… Conveyor belt.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiharu Matsushita 87-9 Yokooka Shinden, Kanaya-cho, Haibara-gun, Shizuoka Prefecture (56) Reference JP-A-1-287450 (JP, A) JP, U) Actually open Sho 60-170767 (JP, U)

Claims (1)

[Claims] 1. A sample carrying device in a sample carrying device, wherein at least a portion serving as a measurement region is formed of a material having a high microwave transmittance, and the microwave oscillating unit and the receiving unit are sandwiched across the measuring region of the carrying face, A microwave propagation path is formed between both parts, and the measurement area has a groove shape that is long in the sample transport direction, and the groove shape has a deep part formed by an inclined surface. A microwave moisture content measuring device characterized in that the position where the electric field strength of the microwave is high is matched.