JP2003315285A - Microwave concentration meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave concentration meter that uses an insulating material for its measuring tube, has no recessed section nor projecting section on the internal surface of the measuring tube, and can measure the concentration of a liquid to be measured with high accuracy by eliminating the influence of a microwave propagated through the insulating material. <P>SOLUTION: In the microwave concentration meter for measuring the concentration of the liquid 1a to be measured by disposing microwave transmitting means 2, and a microwave receiving means 3 to face each other on both sides of the measuring tube 19, the transmitting frequency of the microwave is adjusted to 1.7-2.0 GHz, and the specific inductive capacity of the measuring tube 19 is adjusted to 2.0-8.0. In addition, the measuring tube 19 is formed of the insulating material having a thickness of 1.7-3.0 mm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave densitometer for measuring the concentration of solids or suspended substances in an object to be measured, and more particularly to Teflon (registered trademark) at the liquid contact portion of the measuring tube.
The present invention relates to a microwave densitometer using an insulator such as ceramics and ceramics, which is suitable for use in the food field, for example.

[0002]

2. Description of the Related Art In recent years, a microwave densitometer has been developed and put into practical use as a densitometer that is not easily affected by bubbles and dirt. FIG. 6 shows a configuration example of a microwave densitometer.

As shown in the figure, a microwave transmitting antenna 2 and a microwave receiving antenna 3 are arranged opposite to each other on the outer peripheral surface of a measuring tube 1 in which liquid flows, and a microwave is generated from a microwave oscillator 7. It is being supplied. A power splitter 4, a transmission antenna 2, a measuring tube 1 are provided as a passage path of microwaves from the microwave oscillator 7.
A first path that is introduced into the phase difference measuring circuit 5 through the liquid 1a inside and the microwave receiving antenna 3, and a second path where microwaves are similarly introduced into the phase difference measuring circuit 5 through the power splitter 4. And the path of.

Further, the output of the phase difference measuring circuit 5 is input to the concentration calculator 6. Then, the phase difference measuring circuit 5 is configured to obtain the phase difference from the phase delay of the microwave from the first path with respect to the microwave from the second path.

In this densitometer, the liquid 1a to be measured in the measuring tube 1 for the microwave (second path) which is directly received from the microwave oscillator 7 via the power splitter 4.
Measurement is performed under the same conditions as the liquid 1a to be measured by filling the measurement pipe 1 with a phase delay θ2 of the microwave (first path) propagating in the inside and a reference fluid (for example, tap water that can be regarded as zero concentration). Compared with the microwave phase delay θ1 when
From the phase difference Δθ = (θ2-θ1), for example, the concentration is obtained using a calibration curve as shown in FIG.

Specifically, the density is calculated by calculating the density X = aΔθ + b. Note that a is the slope of the calibration curve, b is the intercept of the calibration curve, and usually b = 0.

Next, FIG. 8 shows a mounting structure of the transmitting antenna 2 and the receiving antenna 3 to the measuring tube 1 in the conventional microwave densitometer.

A pipe made of metal such as stainless steel is used as the measuring pipe 1, and window holes 8 and 9 for transmitting and receiving microwaves are provided at positions facing each other with the pipe axis of the metal pipe interposed therebetween. Window plates 13 and 14 made of an insulating material such as plastic are provided in the window holes 8 and 9, respectively, and airtightly attached to the measuring tube 1 via sealing materials 11 and 12. Further, the microwave transmitting antenna 2 is provided on the window plates 13 and 14, respectively.
The receiving antenna 3 is attached.

In this way, window holes 8 and 9 are formed in the metal pipe in this way.
The reason for providing is that even if an attempt is made to inject microwaves from the outside to the inside of the metal pipe, the microwaves are absorbed by the wall of the metal pipe and cannot be incident. Therefore, window holes 8 and 9 are provided in the metal pipe, and microwaves are made incident and received through the window plates 13 and 14 made of an insulating material attached thereto.

The microwave type densitometer as described above is a method for measuring the phase difference of microwaves, and the window for entering or receiving microwaves does not need to be transparent, so that bubbles and dirt can be prevented. It is hardly affected and the concentration can be measured continuously.

However, for long-term use, if dirt or foreign matter accumulates in the irregularities of the receiving antenna mounting portion or in the gaps near the sealing material, the effect cannot be ignored.

In particular, when applied to the food field, etc., the solid content in the liquid to be measured remains in the irregularities and gaps in the pipe,
A sanitary structure that does not have any irregularities or gaps on the inner surface of the pipe is required so that it will not accumulate and rot.

However, when a metal pipe is used as the measuring tube, there is a problem that it is inevitable that the microwave transmitting / receiving antenna mounting portion has irregularities or gaps as described above.

Further, in the case of a strongly acidic or strongly alkaline measuring fluid, a measuring tube made of metal or plastic having high corrosion resistance is required.

Therefore, Japanese Unexamined Patent Publication No. 2001-74671 discloses a microwave densitometer having a structure in which irregularities and gaps are not formed on the inner surface of the microwave transmitting / receiving means mounting portion of a measuring tube, and a structure in which dirt is unlikely to adhere. It has been described.

In this structure, the measuring pipe is made of an insulating material such as a plastic pipe or a glass pipe, and a window is provided in the metallic measuring pipe as in the conventional case, and an insulating material is provided there. It eliminates the need to attach a window plate made of metal via a sealing material, and has a structure that does not have irregularities or gaps on the inner surface of the measuring tube, and has a structure with excellent corrosion resistance.

Further, the outside of the measuring tube is covered with a shielding member for shielding microwaves, such as a metal cover, so that unnecessary radio waves (microwaves) from the insulating measuring tube can be prevented. We are trying to reduce leakage.

On the other hand, as a conventional technique for improving the accuracy of the microwave densitometer, there is, for example, JP-A-11-83758. In this description, in order to improve the accuracy of the microwave densitometer, it is necessary to determine the frequency range of the microwave used by the tradeoff between the measurement resolution and the attenuation amount of the microwave. Above, the upper limit is 2.0 from the cost-accuracy trade-off.
It is described that the frequency is GHz.

[0019]

Since the conventional microwave densitometer described above has a structure in which no irregularities or gaps are formed on the inner surface of the measuring tube, the solid content in the liquid to be measured required in the food field etc. Although the problem of decay caused by the residue and accumulation of objects in the measuring tube and the problem of corrosion of the measuring tube in the case of strong acidity and strong alkali could be solved, this insulator is used because the inner surface of the measuring tube is made of an insulator. Microwaves propagating through and microwaves propagating through the fluid to be measured interfered with each other, which caused a problem that the phase detection accuracy deteriorates, and it became impossible to perform high-precision measurement.

The present invention has been made in view of the above points, and an object of the present invention is to provide a microwave densitometer capable of highly accurate measurement even when an inner surface of a measuring tube is made of an insulating material.

[0021]

In order to achieve the above object, a microwave densitometer according to claim 1 of the present invention comprises:
In the microwave densitometer, the microwave transmitting means and the microwave receiving means are arranged to face each other on the outer peripheral surface of the measuring tube so as to sandwich the tube axis of the measuring tube, and the concentration of the liquid to be measured in the measuring tube is measured by microwave. , The microwave is 1.7G
Hz to 2.0 GHz frequency range, the measuring tube,
The inner surface of the outer tube covered with the microwave shielding member is made of an insulator, and the relative permittivity of the insulator is 2 or more and the thickness thereof is 3.0 mm or less.

Therefore, according to the microwave densitometer of the first aspect of the present invention, by limiting the thickness of the insulator on the inner surface of the measuring tube, the microwave propagating through the insulator is attenuated. It can be measured with high accuracy.

In order to achieve the above-mentioned object, in the second aspect of the microwave densitometer according to the present invention, the microwave transmitting means and the microwave receiving means are arranged so as to face each other with the measuring tube interposed therebetween.
In a microwave densitometer for measuring the concentration of a liquid to be measured in the measuring tube by microwave, the measuring tube is an insulator, and the electromagnetic wave emitting surface of the microwave transmitting antenna and the electromagnetic wave receiving surface of the microwave receiving antenna. Is covered with a metal so as to block a micro propagation path propagated through the measurement tube, and the metal is grounded.

Therefore, according to the microwave densitometer of the second aspect, even when the measuring tube is made of only Teflon (registered trademark) or ceramics, the microwave propagated through the measuring tube by the metal ring is transmitted. Since it is cut off, it is possible to measure with high accuracy.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a block diagram of a first embodiment relating to a microwave densitometer of the present invention. The section showing the mounting structure of the measuring tube 19 and the transmitting antenna and the receiving antenna is shown in a sectional view. FIG. 2 is a sectional view taken along the line II-II of FIG.

In FIG. 1, reference numeral 19 denotes a measuring tube of a microwave type densitometer, which is composed of an insulating pipe such as Teflon (registered trademark), a plastic pipe, a glass pipe, or a ceramic. The liquid 1a to be measured flows through the inside of the measuring tube 19. 22 and 23 are measuring tubes 19 respectively
The antenna mounting portion made of an insulating material is provided at a position opposite to each other on the outer side surface with the tube axis interposed therebetween.
The microwave transmitting antenna 2 is mounted on the antenna mounting portion 23, and the microwave receiving antenna 3 is mounted on the antenna mounting portion 23.

The antenna mounting portions 22 and 23 are
A member made of the same material as the measuring tube 19 may be bonded to the measuring tube 1, or may be integrally molded with the measuring tube 19. Further, 24 is a metal pipe that covers the measuring pipe 19, and metal flanges 25 and 26 for pipe connection are provided at both ends thereof. In addition, the measuring tube 19 is also provided with flange portions at both ends thereof.

Further, the microwave is supplied from the microwave oscillator 7 to the microwave transmitting antenna 2 on the outer peripheral surface of the measuring tube 19 through which the liquid flows. The microwave from the microwave oscillator 7 passes through the power splitter 4, the transmitting antenna 2, the liquid 1a in the measuring tube 1 and the microwave receiving antenna 3, and is introduced into the phase difference measuring circuit 5 through a first path, Similarly, a second path through which the microwave is introduced into the phase difference measuring circuit 5 through the power splitter 4 is formed.

Furthermore, the output of the phase difference measuring circuit 5 is input to the concentration calculator 6.

Next, the operation of the embodiment configured as described above will be described. Microwaves are supplied from the microwave oscillator 7 to the transmitting antenna 2 attached to the antenna attaching portion 22 of the measuring tube 19 via the power splitter 4, and the receiving antenna 3 arranged opposite to the transmitting antenna 2 is provided inside the measuring tube 19. The microwave signal transmitted through the liquid to be measured 1a is received and the signal is sent to the phase difference measuring circuit 5 (first path).

Further, the microwave from the microwave oscillator 7 is directly sent to the phase difference measuring circuit 5 via the power splitter 4 (second path). Then, the phase difference measuring circuit 5 obtains the phase delay of the microwave from the first path with respect to the microwave from the second path.

In the concentration calculator 6, the phase delay θ2 of the microwave propagating in the liquid 1a to be measured in the measuring tube 19
And a phase delay θ1 of the microwave when the measurement tube 1 is filled with a reference fluid (for example, tap water that can be regarded as zero concentration) and measured under the same conditions as the liquid to be measured 1a,
From the phase difference Δθ = (θ2−θ1), the concentration is calculated using the calibration curve as shown in FIG.

Since the measuring pipe 19 is made of an insulating pipe as described above, a metallic measuring pipe 19 is provided with a window hole as in the conventional case, and an insulating material window is provided there. Microwaves can be passed through without the need for the plate to be attached via a seal.

Therefore, the structure is suitable for use in, for example, the food field, where dirt and foreign substances do not adhere to or accumulate on the unevenness or gap as in the conventional case.

The metal pipe 24 serves to reduce the amount of microwaves that enter the measuring pipe 19 leaking out as unnecessary radio waves from the portion other than the receiving antenna mounting portion 23 to the outside and to increase the pipe strength. There is. Further, the flanges 25 and 26 for connecting the pipes provided at both ends of the metal pipe 24 have the function of increasing the pipe strength.

Next, an experiment was conducted on the microwave type densitometer constructed as described above to examine the relationship between the thickness of the measuring tube 19 and the measurement accuracy of the densitometer. The experiment has the same configuration as the microwave densitometer shown in FIG. 1, and the measurement accuracy is obtained when the thickness of the measuring tube 19 is changed from 0.5 mm to 3.5 mm. At this time, the material of the measuring tube 19 was Teflon (registered trademark), the microwave transmission frequency was 2.0 GHz, and the liquid 1a to be measured was set at about room temperature (20 ° C.).

The reason for selecting the material of the measuring tube 19 and the microwave frequency will be described below. The microwave frequency is
From the relationship between accuracy and cost, it is set to 1.7 to 2.0 GHz. As for the transmission frequency, the condition where the measurement accuracy is the worst,
That is, the frequency is set to 2.0 GHz, which maximizes the attenuation factor of the microwave, which has the lowest S / N of the receiving circuit.

On the other hand, as the material of the measuring tube 19, the material having a larger relative permittivity value has a larger microwave attenuation factor, and the influence of the microwave propagating through the measuring tube 19 becomes smaller. Therefore, as long as the material has a relative permittivity higher than that used in the experiment, a measurement error higher than the experimental result does not occur. Therefore, Teflon (registered trademark) suitable for sanitary applications having a relatively low relative permittivity value, Dielectric constant of about 2.
0) was used for the experiment.

Further, the dielectric constant of the measured liquid 1a is
Since the temperature dependence is large, the temperature is set to about room temperature so as not to affect the measurement accuracy.

The results are shown in FIG. In this figure, when the thickness of the measuring tube 19 exceeds 2.5 mm, the measurement accuracy deteriorates sharply, but if the thickness of the measuring tube 19 is 3.0 mm or less, the accuracy of 1.0% that can be used as a concentration measuring device is obtained. It turns out that I can secure. In addition, Teflon (registered trademark)
It is unavoidable that pinholes are generated in the forming process, but as shown in Fig. 4, it was confirmed that the number of pinholes generated can be kept at the required quality level or higher if the thickness is 1.7 mm or more. did it.

As described above, according to the microwave densitometer of the present embodiment, the microwave propagating through the measuring tube 19 can be attenuated, so that the inner surface of the measuring tube 19 has no unevenness, which satisfies the sanitary requirement. Accurate measurement is possible.

When a material such as glass is used for the measuring tube, the relative permittivity is about 7 to 8 and the influence of microwaves is further reduced, but the strength of glass is taken into consideration. Must be used below.

(Second Embodiment) FIG. 5 (a) is a sectional view for explaining the structure of a transmitting / receiving antenna mounting portion of a microwave type densitometer according to a second embodiment of the present invention. . FIG. 5B is a sectional view taken along the line VI-VI of FIG. 5A and shows the structure of the metal ring 20.

The liquid 1a to be measured is constructed so that the pipe strength is satisfied only by the measuring pipe 21 made of an insulating material such as ceramics or resin having mechanical strength. Further, in order to block the microwaves propagated through the measurement pipe 21 and received, the microwaves propagated along the path from the transmission antenna 2 and the antenna mounting portion 22, the measurement pipe 21, the reception antenna mounting portion 23 to the reception antenna 3. A metal ring 20 for shutting off is embedded in the transmitting side and the receiving side of the measuring tube 21 and is set to be grounded respectively.

The antenna mounting portions 22 and 23 are
The measuring tube 21 may be integrally molded with the same material. Since other configurations are similar to those of the above-described first aspect of the invention,
The description is omitted.

Since the microwave densitometer constructed in this way holds the liquid 1a to be measured only by the measuring pipe 21, there is no heavy object such as a metal pipe and the weight can be reduced. On the other hand, this structure does not shield external electromagnetic waves or microwaves leaked by itself, but for example, if the entire device is used by being incorporated in a metal housing, it can be shielded sufficiently. There is no problem above.

As described above, according to the microwave densitometer of the present embodiment, the microwave propagating through the measuring tube 21 can be shielded, so that lightweight and highly accurate measurement can be performed.

[0049]

As described above, since the transmitting and receiving antennas are made of an insulating measuring tube which does not need to be attached to the measuring tube via a sealing material, a structure having no irregularities or gaps on the inner surface is provided. realizable. As a result, it is possible to provide a highly accurate microwave densitometer because dirt is unlikely to adhere, foreign substances do not accumulate, sanitary specifications are easily satisfied, and the microwave propagating from the measuring tube is attenuated or blocked.

[Brief description of drawings]

FIG. 1 is a configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the measuring tube according to the first embodiment of the present invention.

FIG. 3 is an operation explanatory view according to the first embodiment of the present invention.

FIG. 4 is an operation explanatory view according to the first embodiment of the present invention.

FIG. 5 is a sectional view of a measuring tube according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional microwave densitometer.

FIG. 7 is an explanatory diagram of a calibration curve of a microwave densitometer.

FIG. 8 is a cross-sectional view showing a mounting structure of a transmission / reception antenna of a conventional microwave densitometer.

[Explanation of symbols]

1 measuring tube 1a Liquid to be measured 2 transmitting antenna 3 receiving antenna 4 power splitter 5 Phase difference determination circuit 6 Concentration calculator 7 microwave transmitter 8 window holes 9 window holes 11 Seal material 12 Seal material 13 window 14 window 17 Transmission cable 18 Receive cable 19 Measuring tube (insulator) 20 metal rings 21 Measuring tube (insulator) 22 Antenna mounting part 23 Antenna mounting part 24 metal pipes 25, 26 flange

Claims (2)

[Claims] 1. A microwave measuring means for measuring the concentration of a liquid to be measured in the measuring pipe by arranging a microwave transmitting means and a microwave receiving means on an outer peripheral surface of the measuring pipe so as to sandwich the pipe axis of the measuring pipe. In the microwave densitometer, the microwave has a frequency range of 1.7 GHz to 2.0 GHz, and the measuring tube has an inner surface of an outer tube covered with a microwave shielding member made of an insulating material. The relative permittivity of the product is 2.0 to 8.0, and the wall thickness is 1.7 mm to 3.
A microwave type densitometer characterized by having a thickness of 0 mm. 2. A microwave measuring means for measuring a concentration of a liquid to be measured in the measuring tube by arranging a microwave transmitting means and a microwave receiving means on an outer peripheral surface of the measuring tube so as to sandwich the tube axis of the measuring tube. In the wave densitometer, the measurement tube is an insulator, and the propagation path of the micro wave propagated through the measurement tube between the electromagnetic wave radiation surface of the microwave transmission antenna and the electromagnetic wave reception surface of the microwave reception antenna. A microwave densitometer, characterized in that it is covered with a metal so as to shut off the metal, and the metal is grounded.