JP5443292B2 - Microwave densitometer - Google Patents

Description

  The present invention relates to a microwave densitometer, and more particularly to a microwave densitometer that reduces concentration measurement errors when the liquid temperature of a liquid to be measured changes suddenly.

  Conventionally, it has been equipped with a microwave transmitter / receiver arranged oppositely via a measuring tube through which a liquid to be measured containing a substance to be measured flows or a container containing the liquid to be measured, and is received from the transmitter by being emitted from this transmitter. The concentration of the liquid to be measured is measured by obtaining a phase difference Δθ between the phase delay θ2 of the microwave received by the instrument and the phase delay θ1 measured in advance using a liquid not containing the substance to be measured. Microwave densitometers are known.

  In such a microwave concentration meter, since the dielectric constant of the liquid to be measured changes with temperature and affects the phase difference Δθ, the liquid temperature is corrected by measuring the liquid temperature and correcting the phase difference Δθ. It is.

In this liquid temperature correction, the temperature difference Δt (= ts) between the temperature tw of the zero-concentration reference liquid that does not contain the substance to be measured, which has been measured and stored in advance, and the temperature ts at the time of measurement of the liquid to be measured. -Tw) and the phase difference correction value Δθε in advance, and the difference Δθt between the phase difference Δθ and the phase difference correction value Δθε.
Δθt = Δθ−Δθε
The relationship between the corrected phase difference Δθt and the concentration is obtained in advance as a calibration curve, and the concentration of the liquid to be measured is obtained.

  Further, recently, when the liquid temperature of the liquid to be measured has suddenly changed, the ambient temperature of the reference system path for obtaining the reference phase Δθ1 and the liquid temperature of the liquid to be measured for the measurement system path for obtaining the phase Δθ2 of the liquid to be measured When a temperature difference occurs, the propagation speed of the microwave fluctuates due to the difference in the temperature response characteristics of the microwave transmitting antenna and the microwave receiving antenna, and the temperature drift of the microwave transmitting and receiving antenna itself, resulting in a measurement error. Is also known.

  Furthermore, the temperature time constant of the microwave receiving antenna and the microwave transmitting antenna is different from the time constant of a small heat capacity metal such as a resistance temperature detector, and is composed of a dielectric having a low thermal conductivity such as ceramics. Since it has a time constant of several minutes to 60 minutes, there is a problem that a measurement error occurs for a long time when the liquid temperature changes suddenly.

  Therefore, the propagation phase difference between the microwave transmitting antenna and the microwave receiving antenna is obtained by obtaining the propagation phase difference between two microwave receiving antennas having different microwave propagation distances from the microwave transmitting antenna. There is a microwave densitometer in which the concentration is measured by canceling the speed fluctuation (see, for example, Patent Document 1).

  In addition, a microwave temperature meter that has a liquid temperature sensor and an antenna temperature sensor that measures the temperature of the antenna itself, and corrects measurement errors from the temperature difference between the liquid temperature and the microwave transmission / reception antenna when the liquid temperature changes suddenly. (For example, Patent Document 2).

Japanese Patent Laying-Open No. 2005-83821 JP 2010-2268 A

  However, in the configuration of the microwave densitometer disclosed in Patent Document 1, it is necessary to newly provide another microwave receiving antenna, and the antenna itself is inserted into the liquid to be measured. When the measurement liquid contains suspended substances such as sludge and pulp, there is a problem in that the deposit is volumetric or adhering to the antenna itself, resulting in measurement errors and problems.

  In addition, in the method disclosed in Patent Document 2, it is necessary to newly provide an antenna temperature sensor in addition to the liquid temperature sensor, and a liquid temperature / antenna that corrects a measurement error from a temperature difference between the measured liquid temperature and the antenna. Since the temperature difference correction table is created from the actually measured values, there is a problem that it is not uniquely determined and it takes time and effort to actually measure each time the measurement conditions change.

  The present invention has been made to solve such a conventional problem, and provides a microwave densitometer capable of reducing measurement errors with a simple configuration even when there is a sudden change in liquid temperature. For the purpose.

  In order to achieve the above object, a microwave densitometer according to the present invention is configured such that a microwave transmission antenna and a microwave reception antenna are inserted facing each other from the outer peripheral side surface of a measurement tube through which a liquid to be measured flows, and from the microwave transmission antenna A microwave densitometer for obtaining a concentration of the liquid to be measured from a change in propagation time from transmission of a microwave to reception by the microwave reception antenna, each of the microwave transmission antenna and the microwave reception antenna Is a synthetic resin member that is press-fitted into the opening from the outer wall of the measuring tube having a patch antenna and a pair of openings to which the patch antenna is attached, and is fixed in contact with the liquid to be measured; and the synthetic resin A fixing member for fixing the patch antenna provided in the vicinity of the synthetic resin member to the measurement tube from the rear side of the outer wall of the member; The patch antenna includes a circular dielectric substrate having a high dielectric constant, and the dielectric substrate includes a ground plane pattern formed on one surface on the outer side of the measurement tube and a linear antenna pattern formed on the other surface. And a coaxial connector fixed to the ground plane pattern, and further, the dielectric substrate is provided with a hole perpendicular to the ground plane pattern surface and inserted into the antenna pattern, and a coaxial cable is attached to the coaxial connector, A coaxial core of the coaxial cable is inserted into the hole and connected to the antenna pattern.

  As described above, according to the present invention, it is possible to provide a microwave densitometer that can reduce measurement errors with a simple configuration even when there is a sudden change in liquid temperature.

The block diagram of the transmission / reception antenna of the microwave concentration meter of this invention. Structure diagram of a patch antenna. The block diagram of the microwave densitometer of this invention.

  This will be described with reference to FIGS. First, the overall configuration of the microwave densitometer will be described with reference to FIG.

  The configuration shown in FIG. 1 is different from the conventional configuration shown in Patent Document 1 or the like. The microwave transmission antenna 4 and the microwave reception antenna 5 are patch antennas 4c, which will be described in detail later, and the liquid temperature is steep. The temperature correction calculation part 14 which performs the temperature correction calculation by the liquid temperature sensor 7 and the liquid temperature correction table 14a with respect to the change is provided.

  Next, an overall configuration according to the embodiment will be described with reference to FIG. FIG. 1A is a cross-sectional view of the microwave transmission antenna 4 as viewed from a direction orthogonal to the tube axis of the measurement tube 3, and FIG. 1B is a diagram of the patch antenna 4 c as viewed from the outer wall direction of the measurement tube 3. It is a side view which shows the position of the antenna pattern 4c3 and its coaxial core.

  In the figure, the configuration of the microwave concentration meter according to the present embodiment includes a detection unit 10 for flowing a liquid to be measured and a signal processing unit 20 for receiving a signal from the detection unit 10 and obtaining the concentration of the liquid to be measured. Become.

  The detection unit 10 is in contact with the liquid to be measured from the outer wall side of the measurement tube 3 that is usually formed of a metal tube, and faces each other on the inner surface of the measurement tube 3 in the direction perpendicular to the tube axis of the measurement tube 3. A microwave transmitting antenna 4 and a microwave receiving antenna 5 provided at positions, and a liquid temperature sensor 7 provided by inserting from the outside of the tube wall of the measuring tube 3 are also provided.

  Next, the signal processing unit 20 includes the microwave transmitter 1, the microwave transmitted from the microwave transmitter 1, the power splitter 2 that branches the signal into two systems, and the microwave transmitted from the power splitter 2. The microwave signal of one measurement system path transmitted via the microwave transmission antenna 4, the liquid to be measured, and the microwave reception antenna 5, and the microwave signal of the reference system path directly output from the other power splitter 2 A phase difference measurement unit 11 that measures a phase difference between the temperature difference, a temperature correction calculation unit 14 that performs a correction calculation of the phase difference due to the liquid temperature from the output of the phase difference measurement unit 11, and a temperature-corrected phase difference and concentration It comprises a density calculation unit 15 for obtaining the relationship.

  Furthermore, a converter 12 that receives a signal from the liquid temperature sensor 7 and outputs a temperature signal to the temperature correction calculation unit 14 is provided.

  Further, it is desirable that the signal processing unit 20 configured in this way has a structure integrated with the detection unit 10 in order to maintain the same temperature environment of the measurement system path and the reference path.

  Next, the details of the microwave transmission antenna 4 and the microwave reception antenna 5 will be described with reference to FIG. Since the microwave transmission antenna 4 and the microwave reception antenna 5 have the same configuration, only one microwave transmission antenna 4 will be described, and description of the microwave reception antenna 5 will be omitted.

  The microwave transmission antenna 4 is press-fitted into the opening A from the outer wall of the measurement tube 3 including a patch antenna (also referred to as a microstrip antenna or a microstrip patch antenna) 4c and a pair of openings A to which the patch antenna 4c is attached. A synthetic resin member 4a formed by plastic or the like fixed in contact with the measurement liquid, and a patch antenna 4c provided in proximity to the synthetic resin member 4a from the outer wall rear surface side of the synthetic resin member 4a are fixed to the measurement tube 3. And a fixing member 4b formed of a metal such as SUS.

  The fixing member 4b is divided into fixing members 4b1 and 4b2, but this may be integrally formed.

  Next, the details of the patch antenna 4c will be described with reference to FIG. 2A is a cross-sectional view of the patch antenna 4c (xx cross-sectional view of FIG. 2B), and FIG. 2B is a view of the patch antenna 4c as viewed from the inner surface direction of the measurement tube 3. 2 (c) is a side view of the measuring tube 3 viewed from the outer surface direction.

  The patch antenna 4c includes a circular dielectric substrate 4c1 having a high dielectric constant such as ceramics, a ground plane pattern 4c2 connected to a ground potential formed on one surface of the dielectric substrate 4c1 on the outer wall side of the measurement tube 3, and the other one. A linear antenna pattern (L × W) 4c3 formed on the surface and a coaxial connector 4d1 fixed to the ground plane pattern 4c2 are provided.

  The dielectric substrate 4c1 is provided with a hole Aa that is perpendicular to the surface of the ground plane pattern 4c2 and is inserted into the antenna pattern 4c3. A coaxial cable 4d that supplies a microwave signal is attached to the coaxial connector 4d1, and a coaxial core of the coaxial cable 4d is formed in the hole. Insert into Aa and connect to antenna pattern 4c3.

  The diameter d of the hole Aa is set to an allowable dimension capable of press-fitting the coaxial core, the hole Aa is provided at a position shifted by a distance S from the center position of the dielectric substrate 4c, and the inserted coaxial core is an antenna pattern. Solder to 4c3 and fix.

  The dielectric substrate 4c1 is formed by fixing a metal plate or metal plating on a ceramic substrate or by etching a metal foil.

  And between the surfaces where the synthetic resin member 4a and the patch antenna 4c face each other, even if the synthetic resin member 4a and the patch antenna 4c are deformed due to a change in ambient temperature, the antenna 4c is not subjected to mechanical stress. In addition, the fixing member 4a and the synthetic resin member 4b1 are previously formed to have a predetermined thickness so that a gap is provided so that the temperature of the liquid to be measured can be insulated.

  The fixing member 4b is fixed so that heat transmitted through the measurement tube 3 and the fixing member 4b can be insulated by sandwiching a heat insulating material such as synthetic resin on the surface that contacts the outer peripheral surface of the patch antenna 4c. Further, the fixing member 4b is made of metal and is formed so as to cover the ground plane pattern 4c2 of the dielectric substrate 4c, so that the microwave transmitted to the outside of the measuring tube 3 is not radiated.

  If the change range of the liquid temperature is light, only the dielectric substrate 4c may be used.

  The geometric shape of the microwave transmitting antenna 4 configured as described above is that the diameter Da and the thickness of the patch antenna 4c are determined by the microwave frequency f set in advance and the dielectric constant of the dielectric substrate 4c1 to be used. Then, the size (L × W) of the linear antenna pattern 4c3 is obtained.

  In addition, the size of the patch antenna 4c can be theoretically obtained, but an optimum value may be determined by measuring the transmitted microwave and performing cut and try.

  According to experiments, when the microwave frequency is set in the vicinity of 2 GHz, it is desirable that the relative dielectric constant is 30 or more ceramics, and the thickness is 5 mm or more.

  Further, the position of the hole Aa through which the coaxial core is inserted is provided by shifting the distance S from the center position of the diameter D of the opening A, but this is for increasing the radiation efficiency radiated from the opening A, It may be received by the microwave receiving antenna 5 and the optimum value may be adjusted.

  According to the embodiment as described above, even if the liquid temperature of the liquid to be measured changes suddenly, the amount of heat transfer is reduced in the patch antenna 4c formed on the dielectric substrate 4c1 formed of ceramics, and the patch antenna 4c. Therefore, the microwave transmission state does not change suddenly.

  Next, according to the microwave densitometer configured as described above, when the liquid temperature changes suddenly, the liquid temperature and the antenna can be obtained only by the liquid temperature correction by the conventional liquid temperature correction table 14a described in Patent Document 2. Measurement errors can be reduced without correcting for temperature differences.

  Further, since the patch antenna 4 has a circular flat plate shape, the measurement tube 3 can be easily processed when attached to the measurement tube 3, and the dimensions of the measurement tube 3 can be reduced.

  As described above, according to the structure shown in this embodiment, even if the liquid temperature of the liquid to be measured changes suddenly, the change is not transferred to the patch antenna 4c. It is possible to provide a microwave densitometer that does not have the risk of causing the above.

  The present invention is not limited to the above-described embodiments, and may be any one that can be thermally insulated and fixed using a patch antenna. The structure of thermal insulation is appropriately changed depending on the change range of the liquid temperature of the liquid to be measured. However, various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Microwave transmitter 2 Power splitter 3 Measuring tube 4 Microwave transmission antenna 4a Synthetic resin member 4b Fixing member 4b1, 4b2 Fixing member 4c Patch antenna 4c1 Dielectric board | substrate 4c2 Ground plane pattern 4c3 Antenna pattern 4d Coaxial cable 5 Microwave receiving antenna 7 Liquid temperature sensor 10 Detection unit 12 Converter 14 Temperature correction calculation unit 14a Liquid temperature correction table 15 Concentration calculation unit 20 Signal processing unit

Claims (4)

Propagation until a microwave transmitting antenna and a microwave receiving antenna are inserted facing each other from the outer peripheral side surface of the measuring tube through which the liquid to be measured flows, and the microwave is transmitted from the microwave transmitting antenna and received by the microwave receiving antenna A microwave densitometer for obtaining a concentration of the liquid to be measured from a change in time,
Each of the microwave transmitting antenna and the microwave receiving antenna is a patch antenna,
A synthetic resin member that is press-fitted into the opening from the outer wall of the measurement tube having a pair of openings for attaching the patch antenna, and fixed in contact with the liquid to be measured;
From the outer wall rear surface side of the synthetic resin member, comprising a fixing member for fixing the patch antenna provided close to the synthetic resin member to the measurement tube,
The patch antenna includes a circular dielectric substrate having a high dielectric constant,
The dielectric substrate includes a ground plane pattern formed on one surface on the outer side of the measurement tube and a linear antenna pattern formed on the other surface,
A coaxial connector fixed to the ground plane pattern,
Further, the dielectric substrate is provided with a hole that is perpendicular to the ground plane pattern surface and is inserted into the antenna pattern, a coaxial cable is attached to the coaxial connector, and a coaxial core of the coaxial cable is inserted into the hole to connect the antenna. Microwave densitometer connected to the pattern.   The microwave densitometer according to claim 1, wherein the dielectric substrate is made of ceramics, and the ground plane pattern and the antenna pattern are formed by fixing a metal plate or a metal foil.   The microwave densitometer according to claim 1, wherein the hole is provided by shifting a center position of the dielectric substrate.   2. The microwave densitometer according to claim 1, wherein the fixing member is made of metal, is formed so as to cover the ground plane pattern of the dielectric substrate, and is fixed to a surface in contact with the patch antenna via a synthetic resin insulator. .

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