JP6551052B2 - Apparatus and method for measuring moisture content in powder - Google Patents

Description

  The present invention relates to a moisture content measuring device and a moisture content measuring method in powder, and in particular, there are powdery materials, intermediates, and products used in the fields of food, chemistry, medicine and the like. The present invention relates to an apparatus for measuring moisture contained in these powders by microwave resonance and a moisture measuring method. In the present specification, unless the term "moisture" is specifically described as "moisture content", "moisture content" refers to all possible moisture to be measured, including the moisture content and the water content.

There are various needs in each industrial field regarding the measurement of moisture in powders. As a measuring means of water | moisture content, the Karl-Fisher method and the moisture meter of the infrared system are used conventionally conventionally.
The Karl-Fisher method is the only method that can directly measure moisture, and is widely used because it can measure with high accuracy. However, since this method is a kind of redox titration, it is mainly used at the laboratory level due to the measurement principle and cannot be measured in real time. It is difficult to apply to on-line measurement that sees In addition, it is necessary to prepare and manage reagents suitable for the sample, and there is a problem that it takes time and labor to prepare for measurement.

  The infrared method can be measured in real time and can be used for on-line measurement in the process, so that it has been widely used. However, they are easily affected by disturbances such as color and ambient heat sources, and when measuring by reflection, only information on the surface can be obtained. Moreover, they are easily influenced by things behind the object to be measured. Weaknesses have been pointed out. On the contrary, in the case of measurement by transmission, if the thickness of the sample is large, the attenuation of the intensity of the transmitted infrared light becomes large and the measurement becomes difficult. Since the infrared method sees resonance absorption mainly based on vibration of the OH group of water, the absorbed energy is weak and hence susceptible to disturbances, so the measurement accuracy of the infrared method is generally not so high The point is that it can not be denied in terms of measurement principle and is well known in the field. Nevertheless, the reason why it has been widely used conventionally is that infrared light sources and light receiving elements are relatively inexpensive, and they have many advantages such as being applicable to on-line measurement due to their high measurement speed.

As another method, the method of drying and measuring the weight of bone-drying is often used conventionally, but there is a problem that measurement accuracy is high but it takes time for measurement. It is also well known that when temperature is applied, depending on the sample, something other than water may evaporate or vaporize, and an accurate water content may not be measured.
In addition, although various moisture meters for powder using microwaves are known, these are those using traveling waves of microwaves, and attenuation of microwaves which are simply irradiated to the sample and transmitted through the sample The amount is being measured.
Also, the inventors of the present invention invented a method and apparatus for measuring a minute amount of water contained in a sheet-like sample such as paper using a microwave cavity resonator (see Patent Documents 1 and 2).

Patent No. 4321525 International Publication Number WO2013 / 022104 published brochure

In the conventional moisture measuring method using the microwave cavity resonator described above, a sheet-like sample is used. In the case of laboratory applications, a sheet-like sample such as paper or film is placed on the sample holder or sandwiched and inserted together with the sample holder into a slit with a width of about 4 to 10 mm at the center of the microwave cavity. It was Further, in the case of the on-line application, the sheet was installed on a sheet production line, and the sheet passed through the center of the slit portion of the microwave cavity resonator as in the laboratory application. For this reason, powder could not be set in the measurement unit.
For this reason, the conventional method using a microwave cavity resonator has a problem that moisture in the powder cannot be measured.
The present invention provides an apparatus and method for measuring the moisture contained in powder.

The inventor uses a microwave cavity resonator, puts a powder sample into an elongated tube-shaped member, installs it in an appropriate position of the opening of the microwave cavity resonator, and shifts the resonance frequency shift amount (simply “ Hereinafter, the same shall apply in the present specification) and / or the amount of change in resonance peak level (sometimes referred to simply as “ΔP”. Hereinafter, the same applies in the present specification). It has been found that the moisture contained in the body can be measured easily, quickly and with high accuracy.
Here, placing the powder sample in the tubular member also includes flowing the powder sample in the tubular member. This is the same throughout the present specification.
In addition, the term “opening” is a term including all open structures provided in a waveguide, which enables the above-mentioned tubular member to be installed in a microwave cavity resonator. An example of such an open structure can include at least one slit and / or hole. Of course, the present invention is not limited thereto. For example, as shown in FIG. 15, the holes include elongated holes elongated along the periphery of the cross section of the waveguide. Further, the long hole includes a partial slit portion extending in the circumferential direction of the waveguide and partially surrounding the periphery of the waveguide.

The present invention has the following aspects.
(1) The apparatus for measuring moisture in powder according to the present invention comprises a microwave cavity resonator including a waveguide provided with an opening, and a tube provided in the opening and capable of holding the powder airtight. , A control unit for controlling the measurement sensitivity of the resonance frequency or the resonance peak level by changing the position of the tubular member, measurement means for measuring the resonance frequency or the resonance peak level, and the measured resonance Calculating means for calculating moisture contained in the powder from the frequency and / or resonance peak level.
(2) Here, the tube-shaped member is constituted by a continuous tube-shaped member through which the powder passes continuously through the inside or a one-end sealed tube-shaped member into which the powder is stored.
When the tube-like member is configured to allow powder to pass continuously, a so-called tubular structure is formed so as to penetrate the waveguide and becomes a continuous tube-like member. Further, the structure in which the powder is stored is the structure of the one-end sealed tube-like member, and means a state in which one side of the tube-like member is sealed. The sealing portion may be configured to be inside or outside of the waveguide. More preferably, the opposite end of the sealing portion has a tapered shape.
(3) Further, the tubular member may be installed in the waveguide so that the intensity of the electric field formed inside the tubular member becomes substantially uniform.
(4) Moreover, the said tubular member can be inserted and installed substantially parallel to the direction of gravity.
(5) Moreover, the tubular member may be directly or indirectly connected to the vibration device. By the vibration of the vibrating device, the powder can be smoothly passed through the tubular member or can be smoothly filled in the tubular member without adhering or staying on the inner wall of the tubular member.
(6) Further, the tube-like member may be connected to a powder feeding device for filling or continuously feeding the tube-like member with powder.
(7) Moreover, the cross section of the said microwave cavity resonator can be made into a rectangle.
(8) Further, to change the position of the tubular member in the control unit , slits are provided in at least one surface of the waveguide or in at least one pair of opposing surfaces parallel or perpendicular to the tube length direction, the members can be performed by moving the inserted direction substantially perpendicular along the slit.
(9) Moreover, the said calculation means shall calculate the moisture content of the water | moisture content contained in the said powder.
The method according to any one of claims 1 to 8, wherein when calculating the water content, the calculation means calculates the water content of the water contained in the powder according to the following formulas A and B: Moisture measuring device in powder.
Δ f = α · BD + β · WC (A)
ΔP = ω · WC (B)
The shift amount Δf of the resonance frequency and the change amount ΔP of the resonance peak level refer to the difference between the values when the powder sample is present and absent in the tubular member, respectively.
The weight of the dry part of the powder is BD, and the weight of water is WC.
α = K1 · (ε'1-1) / a (C)
β = K1 · (ε'2-1) / b (D)
ω = K2 ・ ε ”2 / b (E)
The dielectric constant of the dry part of the powder is ε'1
The dielectric constant of water is ε'2 and the dielectric loss factor is ε "2
a and b are proportional constants, K ₁ and K ₂ are proportional constants (10), and the hole or slit may be provided at a position where the electric field strength in the waveguide is maximized or maximized. The maximum or maximum here means that a hole or the like is preferably provided in the vicinity of the position where the electric field strength is maximum in the waveguide, and it is not necessarily required to be the maximum. It also means that it is good.
(11) Further, the tube-like member can be made of a material that absorbs and reflects less microwaves.
(12) According to another aspect of the present invention, in the method of measuring the moisture content in powder according to the present invention, at least the inside of the waveguide is filled with holes or slits provided in the waveguide. A method of measuring the moisture content in a powder using a waveguide type microwave resonator, in which a tube-shaped member capable of holding or passing therethrough is inserted, wherein the position of the tube-shaped member is changed Controlling the measurement sensitivity of the resonance frequency or the resonance peak level, measuring the resonance frequency and the resonance peak level in the absence and presence of powder in the tubular member, and the measurement Calculating a moisture content of moisture contained in the powder from a resonance frequency and a resonance peak level.

  According to the present invention, the moisture contained in the powder can be easily, quickly, and rapidly obtained from the relationship between the ratio or amount of water contained in the powder and the amount of resonance frequency shift or resonance peak change that is a measured value. It can measure with high accuracy.

It is a figure which shows the structure of the moisture content measuring apparatus in the powder which concerns on 1st Embodiment of this invention. It is a block diagram showing functional composition of a network analyzer concerning a 1st embodiment of the present invention. It is a figure which shows the relationship between the resonance curve which concerns on embodiment of this invention, the dielectric constant of a sample, and a dielectric loss factor. It is a figure which shows the structure of the moisture measuring apparatus in the powder which concerns on 2nd Embodiment of this invention. It is a figure which shows the example of the electromagnetic field distribution inside the microwave cavity resonator which concerns on embodiment of this invention. It is a figure which shows the powder model for deriving the formula which calculates | requires the moisture content of powder. It is a figure showing a sample container for powder concerning an embodiment of the present invention. It is a graph which shows correlation with (DELTA) P and water content which were measured in Example 1 of 2nd Embodiment of this invention. It is a graph which shows the relationship between BD (weight of an absolutely dry part) measured by the absolute dry method in Example 1 of 2nd Embodiment of this invention, and measured BD. It is a graph which shows the relationship between the moisture content measured by the absolutely dry method in Example 1 of 2nd Embodiment of this invention, and the moisture content computed from (DELTA) P. It is a graph which shows the relationship between the moisture content measured in Example 1 of 2nd Embodiment of this invention, and the moisture content obtained by actual measurement by the absolutely dry method. FIG. 3 is a schematic perspective view of a cavity resonator in which holes are also formed in the top and bottom surfaces of a waveguide according to an embodiment of the present invention. It is a schematic perspective view of the cavity resonator which opened the long hole (Z direction) in the waveguide waveguide concerning 3rd Embodiment of this invention. It is a schematic perspective view of the cavity resonator which opened the long hole (X direction) in the waveguide which concerns on 4th Embodiment of this invention. It is a graph which shows correlation with (DELTA) P and water content which were measured in Example 2 of embodiment of this invention. FIG. 21 is a schematic perspective view of a cavity resonator in which a long hole Eh is formed to extend to a side surface of the cavity as a modification of the third and fourth embodiments of the present invention. It is the schematic which shows the structure of an example of the moisture measuring apparatus in the powder provided with the vibration apparatus based on 5th Embodiment of this invention. It is a figure which shows the structure of an example of the moisture measuring apparatus provided with the powder supply apparatus based on 6th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
First Embodiment
FIG. 1 shows an example of the configuration of a moisture measuring device in powder according to the first embodiment of the present invention. A moisture measuring device 100 in powder includes a microwave cavity resonator 102 provided inside a measurement unit, a network analyzer 104, a computer 105, a control unit 1610, and a drive unit 1608 provided outside the measurement unit. Configured The microwave cavity resonator 102 is composed of a pair of waveguides A and B. The network analyzer 104 performs microwave oscillation and detection. The computer 105 processes the signal sent from the network analyzer 104.

A tube 106, which is an example of a tubular member, is configured to be capable of holding the powder in an airtight manner. Here, it is desirable that the material of the tube 106 be low in absorption and reflection of microwaves. As a material satisfying such requirements, for example, a fluororesin is desirable. As the fluorine resin, Teflon (registered trademark) is most preferable. For example, Teflon (registered trademark) PFA tube manufactured by Freon Industrial Co., Ltd., code no. F-8011-02 can be used. Besides, for example, the following Teflon (registered trademark) material can be used. A powder feeding device (not shown) is connected to the upper side of the tube 106 in the figure.
· Fully fluorinated resin polytetrafluoroethylene (tetrafluorinated resin, abbreviation: PTFE)
・ Partially fluorinated resin Polychlorotrifluoroethylene (trifluorinated resin, abbreviation: PCTFE, CTFE), polyvinylidene fluoride (abbreviation: PVDF), polyvinyl fluoride (abbreviation: PVF)
・ Fluorinated resin copolymer PFA, tetrafluoroethylene / hexafluoropropylene copolymer (abbr .: FEP), ethylene / tetrafluoroethylene copolymer (abbr .: ETFE), ethylene / chlorotrifluoroethylene copolymer Combined (abbreviation: ECTFE)

Here, PFA has a molecular weight of several hundred thousand to several million, a viscosity of 10 ⁴ to 10 ⁵ poise (380 ° C.), a melting point of 300 ° C. to 310 ° C., and a maximum continuous use temperature of 260 ° C. PFA has properties comparable to PTFE, and is excellent in surface smoothness and permeation resistance. Moreover, it can be melt-molded and is often used in the semiconductor field.

In addition, FEP has a molecular weight of several hundred thousand to several millions, a viscosity of 10 ⁴ to 10 ⁵ poise (380 ° C.), a melting point of 250 ° C. to 270 ° C., and a maximum continuous use temperature of 200 ° C. FEP is slightly inferior in heat resistance to PTFE, but other properties are almost the same as PTFE. Moreover, it can be melt-molded and is often used as a wire covering material.

  Examples of materials after Teflon (registered trademark) include polyethylene, polypropylene, polystyrene, and polyphenylene oxide. The tube may be, for example, 7 mmφ in outer diameter, 6 mmφ in inner diameter, and 12 cm in length.

  A slit 110 as one of the openings is provided between the pair of waveguides A and B. The 4 GHz band microwaves oscillated from the network analyzer resonate in the waveguide, and resonance energy is detected by the network analyzer 104.

  FIG. 2 is a block diagram schematically showing an example of a functional configuration of the present embodiment. In the network analyzer 104, no powder exists in the tube 106 based on the swept microwaves sent from the oscillation unit 202 that oscillates microwaves in the 4 GHz band, the reception unit 204 that receives resonance energy, and the network analyzer 104. Resonant peak level detection unit 206 for detecting resonant peak levels in the state and the existing state, and in the absence and presence of powder in the tube 106 based on the swept microwaves sent from the network analyzer 104 as well A resonance frequency detector 208 that detects the resonance frequency is included. The computer 105 stores data such as a data holding unit 212 that holds a calibration curve, which will be described later, data measured by the resonance peak level detection unit 206 and / or the resonance frequency detection unit 208, and mathematical expressions, coefficients, and the like as necessary. A calculation unit 210 that calculates the moisture contained in the powder from the data held in the unit 212 is included.

  The control unit 1610 can control the installation position of the tube 106 based on the measurement value or the like of the resonance peak level detection unit 206 and / or the resonance frequency detection unit 208. The drive unit 1608 can drive the tube 106 based on a control signal from the control unit 1610 to determine the installation position of the tube 106. These control units and drive units are not essential components, but are preferably installed when it is required to automatically adjust the moisture detection sensitivity. In the case where the tube 106 is fixed at the optimum detection sensitivity position, usually the highest sensitivity position, these controls and drivers are not necessary.

  The apparatus 100 for measuring moisture in powder according to the present embodiment uses a microwave cavity resonator 102, puts a powder sample into an elongated tube 106, and places it in an appropriate position of the slit portion 110 of the microwave cavity resonator 102. The moisture content contained in the powder is measured from the shift amount (Δf) of the resonance frequency and the change amount (ΔP) of the resonance peak level. Specifically, a correlation between the percentage (%) of water contained in the powder and the measured value Δf or ΔP is obtained in advance as a calibration curve, so that the measured value Δf or ΔP is used as the powder. The moisture content in the body is measured. In a measurement method in which the influence of the powder volume described later can be ignored, a coefficient in a specific relational expression can be obtained, and the moisture content can be obtained using an approximate expression.

As described above, it can be assumed that the state in which the powder moves in the tube 106 is measured in a state in which the powder flows in the air flow generated by the powder supply device configured by a blower or the like. It is also possible to create a flow of powder by gravity. Such an embodiment will be described later. When the tube-like member is configured to allow powder to pass continuously, a so-called tubular portion penetrates the waveguide to form a continuous tube-like member.
On the other hand, it is conceivable that the powder is measured in a state of being filled, stored and fixed in the tubular member. The structure in which the powder is stored is the structure of a one-end sealed tubular member, which means that one side of the tubular member is sealed. Such an embodiment will be described later. Storage and filling are almost synonymous, but storage is broader and includes filling. In addition, it is considered that the filling is more meaningful as the powder is forcibly packed in the tube and in the container.

Next, a specific method for measuring Δf or ΔP will be described.
Basically, the resonance frequency (= f0) and the resonance peak level (= P0) in the blank state (only the tube corresponding to the sample container) without the powder sample are measured in advance. Next, for the cylindrical container containing the powder sample, the resonance frequency (= fS) and the resonance peak level (= PS) are similarly measured at the same position. As a result, a peak frequency shift amount Δf (= f0−fS) and a peak level change amount ΔP (= P0−PS) are obtained.

  FIG. 3 shows the relationship between the microwave frequency (Hz) and the transmitted microwave intensity. When a powder sample is present in a tube installed in the slit portion of the waveguide, the resonance curve shifts toward the low frequency side (left side in the figure) and the peak level decreases. The vertical axis represents transmitted microwave intensity, but strictly speaking, it is generally represented by a decibel value calculated by the following equation.

Decibel value = 10 x Log (input / output) (1)
Here, the output means microwave power (W) output from the network analyzer, and the input means microwave power (W) returned to the network analyzer after passing through the cavity. The resonance curve is a collection of the above decibels when frequency is swept and plotted against the frequency on the horizontal axis, and the vertical axis is displayed in decibels to display on the same screen to a minute level Is possible.

  The shift amount (Δf) of the resonance frequency is proportional to (dielectric constant-1) × volume of the powder sample. Further, the amount of change ΔP (W) of the resonance peak level changes in proportion to the dielectric loss factor × volume of the powder sample. Here, ΔP (W) is the case where the vertical axis in FIG. 3 is expressed in linear, that is, in watt (W) unit, and when expressed in decibel unit by equation (1), it is expressed as ΔP (dB) I assume. Hereinafter, when the above distinction is necessary, any notation will be used according to the above definition.

  In order to determine the moisture content in a powder sample, as with almost all moisture meters except the Karl Fischer method, a method of measuring the moisture content after previously determining the coefficients used in the calibration curve or calculation formula Take. The calculation formula and how to obtain the coefficient will be described later.

  Moreover, as an example of the powder supply apparatus not shown in the figure, there is a granular air transport apparatus that transports powder by air. The air flow is generated by a blower, a compressor or the like, and the powder flows in a floating state in the air flow. Further, as an example of another powder supply apparatus, there is a powder fixed quantity supply system as shown in FIG. In such a system, the quantified powder is continuously supplied batchwise in the system by quantitative 枡 etc. The powder itself falls in the tubular member 106 by gravity, and measurement is made while passing through the cavity resonator to obtain the shift amount Δf of the peak frequency and the change amount ΔP of the peak level. That is, the powder falls in the tubular member according to gravity. In this state, moisture can be measured while passing through the cavity resonator.

Second Embodiment
FIG. 4 shows an example of the configuration of a moisture measuring device in powder according to the second embodiment of the present invention. The members given the same reference numerals as in FIG. 1 are the same as those in FIG.
In FIG. 4, there is one waveguide forming the microwave cavity 102a. This waveguide is provided with a hole as one of openings at the center of one side. A cylindrical container 106a capable of holding powder inside is inserted into the hole. The cylindrical container is one of the one-end sealed tubular members whose one end is sealed. Hereinafter, although a hole, a long hole, etc. are one of the opening parts, description of each time is omitted.

  Here, the material similar to the tube 106 demonstrated previously is used for the material of a cylindrical container. Further, as the cylindrical container, for example, one having an outer diameter of 10 mmφ, an inner diameter of 8 mmφ, and a length of 3 cm can be used. As can be seen from the figure, the cylindrical container has a funnel-shaped upper part, which is not an absolutely necessary part, and is more preferable because it is less likely to spill when the powder is put into the container. is there. If the powder is supplied in a tubular shape thinner than the tubular portion inserted in the waveguide, such a funnel-shaped portion is not necessary. That is, the funnel-shaped portion may be replaced with a tubular portion.

  Among powder samples, various powders are assumed such as those having a large or small amount of microwave absorption. In this case, the microwave absorption amount is expressed as ΔP (W). However, if the microwave frequency and the electric field strength are constant, ΔP (W) is proportional to the product of the dielectric loss factor and the volume of the powder. If moisture is contained, the amount of microwave absorption increases, and ΔP (W) increases. This is because the dielectric loss rate of water is 4 GHz, about 13 at room temperature, which is very large compared to other materials, for example, about 0.012 for PET film and about 0.001 for polyethylene. In PET films and the like, the molecular chains in the crystal part do not move to the external electric field of the microwave, so the dielectric loss factor is generally said to be approximately zero. The dielectric loss factor is caused by the phase difference δ caused by the delay of the electrical displacement due to the dipole of the substance that cannot follow the fast alternating electric field of the microwave, so it excludes most conductors such as metals. In the case of the above powder, it is considered that in the absolutely dry part excluding water, the molecules hardly move with respect to the electric field of the microwave or there is no large dipole moment, and therefore the dielectric loss rate is considered to be extremely small. Food is heated in a microwave oven because of the moisture contained in the food, and the dielectric loss rate of this moisture consumes microwave energy and generates heat.

  As the waveguide used for the cavity resonator, various shapes such as a cylindrical shape and a prismatic shape can be used, but here, the prismatic waveguide is mainly described as an example. As shown in FIG. 5, a hole is provided in the center portion Cu in the Z direction and the X direction in the rectangular parallelepiped (waveguide constituting the microwave cavity resonator). FIG. 5 shows the electromagnetic field distribution inside a microwave cavity comprised of a waveguide having a rectangular cross section as shown in FIG. 4, ie, a prismatic waveguide. FIG. 5A shows the structure of the waveguide, and FIG. 5B shows the electric field intensity distribution in each cross section of the waveguide. The electromagnetic field distribution of the microwave cavity resonator according to this embodiment is formed as shown in FIG. 5B, and the electric field strength is not uniform inside. Antennas are provided at both ends in the z direction of the microwave cavity resonator of FIG. A cylindrical container (corresponding to 106a in FIG. 4) containing a powder sample is inserted into a hole provided in the central portion Cu and set. Here, it is sufficient that at least one hole is provided. In addition, the smaller the inner diameter of the hole is, the better it is. That is, in at least a rectangular cavity resonator, if an opening is generally provided, microwaves leak from the opening, making it difficult to obtain a sharp resonance curve (high Q value). When the Q value (the sharpness of the resonance) decreases, the resonance curve becomes broad, making it difficult to detect the peak, but when measuring a powder containing a large amount of water, the peak tends to be more difficult to detect.

  As to the shape of the hole, there is no problem even if it is an ellipse or a polygon such as a pentagon or a hexagon other than a circle. In addition, the shape of the cylindrical container for containing the powder sample can be measured in a long and narrow container such as a square pole as well as a cylinder, and there is no problem with a pentagonal column and a hexagonal column. It is preferable that the gap between them is small.

  Here, it should be noted that the electric field distribution in the microwave cavity resonator changes depending on the cross-sectional shape of the waveguide constituting the microwave cavity resonator. For example, when the cross-sectional shape of the waveguide is circular, the electric field distribution is generally radial or looped. On the other hand, a rectangular parallelism creates a neatly arranged parallel electric field, so the measurement sensitivity is effective by adjusting the insertion position of the cylindrical container where the powder sample to be measured exists, depending on the electric field distribution. It is possible to adjust to Therefore, when the measurement sensitivity of the resonance peak level and the resonance frequency is controlled by changing the position of the cylindrical container, the cross-sectional shape of the waveguide is preferably rectangular.

  In order to appropriately control the measurement sensitivity, the inventor passes the powder sample or stores the powder sample (hereinafter referred to simply as “pass through”) based on the electromagnetic field distribution in the microwave cavity resonator described above. Both the storage and storage were considered together with the position and direction of inserting the tubular member including the cylindrical container "including the powder sample".

As shown in FIG. 5B, the y component E _y of the electric field intensity changes in a sine curve in the x direction, and is maximum at the center of the cross section. The electric field strength is preferable because the change in the maximum portion is less. The y component E _y of the electric field strength changes in the sine curve also in the z direction, and the electric field strength is maximum at three locations in the waveguide. Here, from the viewpoint of stabilizing and improving the sensitivity, in the usual case, it is preferable that the tubular members be disposed at the central portions Cu and Cs.
If a tube-shaped member is inserted so as to include a powder sample in a place where the electric field strength is high, the interaction between the electric field and the powder increases, so the measured values ΔP and Δf increase even with a small amount of moisture, and therefore the measurement is performed. The sensitivity is increased. On the other hand, when a tube-shaped member containing a powder sample is inserted in a place where the electric field strength is small, the measured values ΔP and Δf become smaller even with the same amount of water, and the measurement sensitivity becomes smaller. In the latter case, instead of decreasing the measurement sensitivity, the change width of ΔP can be afforded, so that it is possible to deal with a sample having a larger amount of moisture, that is, a powder sample having a large microwave absorption.

  Further, since the tubular member is inserted in the y-axis direction, an almost constant electric field Ey is always applied inside the tubular member, and the powder is almost anywhere in the y-axis direction in the tubular member. Since the same electric field strength is applied, it is not affected by differences in powder location. In this case, it is preferable that the cross-sectional area of the tubular member is relatively small because it is less susceptible to the difference in electric field strength depending on the position on the xz plane. That is, the same measurement result can be obtained wherever the powder is in the y-axis direction in the cylindrical container. This is the reason for using a tubular tubular member (cylindrical container) instead of a flat tubular member.

Next, the principle of controlling the shift amount (Δf) of the resonance frequency and the change amount (ΔP) of the resonance peak level will be described.
In the microwave cavity resonator, it is assumed that the eigenmode in the microwave cavity resonator when no powder sample is inserted is a mode, and the natural angular frequency is ωa, and the electric field and the magnetic field are Ea and Ha, respectively. . Now, if a sample of volume ΔV is inserted into the hole and the complex natural angular frequency of the microwave cavity becomes ω, the following perturbation theory equation holds.

However,

Also,
P + J / jωa = ε ₀ (χer−jχei) E (4)
ε '= 1 + χer (5)
ε ′ ′ = χei (6)

Here, ω = 2πfs, ωa = 2πf ₀ , V is the volume of the cavity, ΔV is the volume of the sample, P is the electrical polarization of the sample, J is the conduction current density, μ ₀ is the permeability of vacuum, and M is the magnetization , H: magnetic field strength, ε: dielectric constant of air, ε ₀ : dielectric constant of vacuum, 真空: proportional constant between polarization density and electric flux density, 束 er: real part of χ, χei: imaginary part of χ, ε ′ represents the dielectric constant of the sample, ε ′ ′ represents the dielectric loss factor of the sample, and ^* represents a complex number.
The resonance frequency shift amount Δf and the resonance peak level change amount ΔP (W) are proportional to the volume integral of the inner product of the electric field E, the dielectric constant ε ′, and the dielectric loss factor ε ″ inside the resonator. It is derived from (2) of the perturbation theory.

  Moreover, it is also derived from the perturbation theory expressed by the equation (2) that the measurement sensitivity changes depending on where the tube-shaped member is inserted in the waveguide constituting the microwave cavity resonator. This is because Δf and ΔP depend on the electric field strength if the dielectric constant, dielectric loss factor and volume of the sample are the same.

Therefore, the strength of the electric field can be adjusted by the electric field distribution at the measurement position, and the volume integral can be adjusted by the volume of the powder to be measured. These two factors make it possible to set the measurement sensitivity freely and widely. .
In addition, changing the cross-sectional area cut by the surface perpendicular | vertical to the length direction of a tube-shaped member as an example which adjusts the volume of powder is mentioned.

Next, a method of creating a calibration curve will be briefly described.
First, a plurality of powder samples of various water contents are created by leaving the powder to be measured in a constant humidity atmosphere for several specific times. Next, Δf and ΔP are measured for each sample, and the relationship of Δf or ΔP to the moisture content is determined. The preparation of the sample containing constant moisture is the same as the sample preparation in Example 1 described later.

  At this time, it was difficult to obtain a good calibration curve. As a result of repeating the test many times, it was found that the measurement value largely depends on the conditions such as the atmosphere and the pressure of filling when packing each powder sample in the measurement container. Therefore, it took much labor to find the optimum and stable conditions. A good calibration curve can be obtained by making various conditions such as the pressure at the time of powder filling, the procedure at the time of filling, the atmosphere and the like optimally optimal. It has been found that there is a problem that it is very time-consuming in reality because it is necessary to search for optimum conditions each time the type, composition, shape, etc. of the sample changes.

  Therefore, the inventors examined a method capable of stably measuring the water content in the powder regardless of the filling condition of the powder and the like. As a result, by introducing a formula as described below, it came to obtain a measurement method which can neglect the influence by the filling condition etc., that is, essentially the volume of the powder.

First, the introduction of an equation for obtaining the moisture content of the powder from the measured values Δf and ΔP, and the four coefficients used therein will be described.
Generally, when a dielectric sample such as powder is inserted into a cavity resonator, as shown in FIG. 3, the resonant frequency is in proportion to the (dielectric constant-1) × volume of the sample, and the low frequency side Since the resonance peak level decreases in proportion to the dielectric loss factor of the sample × volume, when the frequency shift amount is Δf and the peak level change amount is ΔP (W), both are expressed as follows. Be done.

Where ε ′ represents the dielectric constant of the sample, ε ′ ′ represents the dielectric loss factor of the sample, V represents the volume of the sample, and K ₁ and K ₂ represent proportional constants.

Then, the volume V of the powder sample as in FIG. 6, be divided into a volume V ₂ of the volume (volume excluding water) V ₁ and water portion of the bone dry parts of the powder. Here, when the dielectric constant of the absolutely dry portion of the powder is ε ′ ₁ , the dielectric loss factor is ε ″ ₁ , the dielectric constant of water is ε ′ ₂ , and the dielectric loss factor is ε ″ ₂ , the absolutely dry portion and the water portion (7) and (8) can be expressed as two sums as shown in equations (9) and (10), since each contributes to .DELTA.f and .DELTA.P (W).

Assuming that the weight of the dry portion of the powder is BD, and the weight of water is WC, BD and WC are proportional to their respective volumes V ₁ and V ₂ and can be expressed as follows.

Here, a and b represent proportional constants.
Substituting the equations (11) and (12) into the equations (9) and (10) and collecting the constants, equations (13) and (14) are obtained.

However,
α = K ₁ · (ε ′ ₁ −1) / a (15)
β = K ₁ · (ε ′ ₂ −1) / b (16)
γ = K ₂ · ε ′ ′ ₁ / a (17)
ω = K ₂ · ε ” ₂ / b (18)

  If the constants α, β, γ, and ω are known, the BD and WC can be obtained by solving the simultaneous equations (13) and (14) using the measured values Δf and ΔP (W).

Therefore, the moisture content M (%) is obtained by the following equation using BD and WC.
M = WC × 100 / (BD + WC) (19)

The feature of this method is that the moisture content of the powder can be measured from two measured values (Δf, ΔP), and can be measured regardless of the weight or volume of the powder.
It goes without saying that the present method is applicable to either of the embodiments regardless of the shape of the tubular member shown in the first and second embodiments described above.

  Next, based on the above basic idea, a concrete procedure for actually obtaining the moisture content and how to find the constants α, β, γ and ω will be described. In addition, this procedure is described about the case where one end sealing tube-shaped member is applied in 2nd Embodiment.

(Step 1)
In equation (17), γ (= K ₂ · ε ′ ′ ₁ / a) is a constant resulting from the dielectric loss factor ε ′ ′ ₁ of the dry part of the powder, but in most dielectrics it does not contain water The dielectric loss factor of the absolutely dry part can be regarded as almost zero. This is because, in general, the molecules or molecular chains of the powder do not move with respect to the external microwave electric field, or move slightly, or they may be regarded as almost zero because the dipole moment is small. For example, in the case of a polymer film, since the molecule does not move in the crystal part, the dielectric loss factor can be regarded as zero. Accordingly, since γ in equation (17) can be regarded as zero, equation (14) can be rewritten as the following equation.
ΔP = ω · WC (20)
Although this equation means that the measured value ΔP (W) is proportional to the water content WC, in practice the relationship between ΔP (dB) and WC is because ΔP is measured in decibels as described above. Can be approximated by a cubic equation passing through the origin as follows.
WC = a · ΔP ³ + b · ΔP ² + c · ΔP (21)
However, a, b and c are coefficients of a cubic approximation.

(Step 2)
Prepare samples of the same kind of powder sample with various volumes and moisture contents, measure the powder weight for each, put the powder sample in the tube-like member immediately after that, and put it in the cavity resonator. Measure Δf and ΔP (dB). Thereafter, the powder sample is put in a dryer and sufficiently dried, and then the dry weight is measured. The bone dry weight BD is measured for each sample, and the water content WC is calculated.

(Step 3)
For all powder samples having different volumes and moisture percentages, by plotting the moisture content WC on the Y-axis and ΔP (dB) on the X-axis and performing approximate calculation, the coefficients a, b, and c in the equation (21) are calculated. Ask for It is clear from the above measurement theory that even if the powder volume and moisture content are changed, the same kind of powder will be on one approximate curve.

(Step 4)
Substituting the measured bone dry weight BD and the water content WC into the equation (13), the shift amount Δf (= Δfcal) in calculation is calculated.
Δfcal = α · BD + β · WC (13)
At this time, α and β are searched for all samples having different volumes and moisture ratios so that the calculated Δf (= Δfcal) and the actually measured Δf are as close as possible to each other. Specifically, α and β are found that minimize the sum of the squares of the differences between the calculated value Δfcal and the actually measured value Δf. In practice, finding the best α and β using the solver function in Microsoft software "Excel" is one way.

(Step 5)
Once α and β of the powder to be measured are determined, the bone dry weight BD can be calculated from the following equation using WC calculated using the measured ΔP (dB) and equation (21) and using Δf also measured calculate.
BD = (Δf−β · WC) / α (22)

(Step 6)
Since the moisture content WC and the absolute dry weight BD of the powder were found, the moisture content M (%) is expressed by the following equation.
M = WC × 100 / (BD + WC) (23)

Example 1
Hereinafter, Example 1 using the second embodiment of the present invention will be described.
A powder of polyvinyl alcohol (Kuraray's Klarepovar (5-98); sometimes simply described as "PVA"; hereinafter the same in the present specification) is prepared, and adjusted to a temperature of 20 ° C and a humidity of 90%. Moisture was applied by leaving it in a humid chamber for a certain period of time. The size of the PVA powder sample was observed by a microscope with a wide distribution width of about 10 μm to about 500 μm in maximum diameter of the particles. In addition, although the shape of particle | grains was also square, it comprised various shapes, such as substantially spherical shape, prismatic shape, and column shape. The standing time was changed by six steps to change the moisture content by six levels, and PVA samples having different moisture content from about 4.2% to about 10.3% were prepared.

  Three types of cylindrical crucibles with different volumes are prepared for each volume, and the obtained powder samples are placed in each of three types of containers to make the volume approximately constant at every three levels of volume (1507, 1005 and 502 cubic mm) Then, it is transferred to the Teflon (registered trademark) sample container shown in FIG. 7A, that is, an end-sealed tubular member, and it has a cavity resonance with a 10.5 mmφ hole on only one side as shown in FIG. The sample was inserted into a vessel, and Δf and ΔP were measured. In this state, the bottom of the sample container was inserted at such a position that the bottom of the sample container would not contact the inner wall of the cavity resonator. Immediately after the powder sample was taken out and weighed, it was transferred to an aluminum container and then placed in an oven at 105 ° C., taken out after about 4 hours and measured for absolute dry weight to obtain a moisture content. As for the number of samples of powder, a total of 54 samples of 6 levels of moisture, 3 levels of volume and 3 N number are made, and for all samples, Δf, ΔP, moisture amount WC, absolute value as above The dry weight BD was measured.

The relationship between ΔP and the water content WC is as shown in FIG. 8, and is found to be expressed by equation (24).
WC = 0.00011214 × (ΔP) ² −0.00043420 × ΔP (24)
Origin can be approximated by a quadratic curve passing through the correlation coefficient R ² was found to be highly correlated with 0.9790.

Next, Δf on calculation was calculated for 54 powder samples using the equation (13).
Δfcal = α · BD + β · WC (13)
Here, actual values are used for BD and WC, and provisional values are used for α and β.

  Next, α and β were selected such that the difference between the measured Δf and the Δfcal calculated by the equation (13) was as small as possible for all 54 powder samples. Specifically, α and β were searched for such that the sum of the squares of the differences between Δf and Δfcal is minimized. More practically, α and β were obtained by using the solver function of Microsoft spreadsheet software “Excel”. As a result, it was found that when α was 39.333 and β was 180.41, the calculated value Δfcal and the measured value Δf were statistically closest to each other. That is, the eigenvalues α and β of this PVA powder were determined.

Next, the dead weight BD was calculated from the following equation using the α, β and WC determined by the equation (24) and Δf measured.
BD = (Δf−180.41 · WC) /39.333 (25)
Since BD and WC were known, the moisture content M (%) was calculated using the following equation.
M = WC × 100 / (BD + WC) (26)

FIG. 9 is a graph showing the correlation between the solid content BD (weight after absolute drying) measured by this method and the solid content BD measured by the absolute drying method for the 54 samples measured. The correlation coefficient R ² was found to be highly correlated with 0.9976, which can be approximated by a straight line passing through the origin with a slope of 0.9995 X and Y 0.9995X.

Next, FIG. 10 shows the relationship between the moisture content calculated from ΔP and the moisture content obtained by the absolutely dry method for 54 samples. It was found that Y = 0.9964X, and the inclination was 0.9964, and it could be approximated by a straight line passing through the origin. Further, it was found to be highly correlated with the correlation coefficient ^{R 2} is also 0.9791.

Next, the correlation between the water content measured using this method and the water content measured using the bone-dry method is shown in FIG. 11 for all of the measured powder samples. From this graph, the relationship between the water content measured by the present method and the water content measured by the bone-drying method has a linear relationship of Y = 0.986 X, and the correlation coefficient R ² also has a high correlation with 0.899. I understood it. The fact that the slope of the first-order approximation straight line passes through the origin almost at 1 means that the calculated moisture percentage directly corresponds to the true moisture percentage. It means that the moisture content is established with high correlation at least over about 4% to about 10%. One of the reasons for the fact that the correlation coefficient is not completely 1.000 and the slope of the first-order approximation is not completely 1.00 is the accumulation of various measurement errors during the experiment. Although it is conceivable, basically, it was confirmed that the present method was a method capable of instantaneously measuring the moisture content of the powder regardless of the weight and volume of the powder.

Example 2
Next, a specific example 2 of the present invention will be described.
In Example 2, a test was conducted in exactly the same manner as in Example 1 except that a cavity resonator 102b having holes 10.5 Hf and Hb on both sides as shown in FIG. 12 was used. That is, the sample container used what was shown to FIG. 7 (A).
In the same manner as in Example 1, Δf, ΔP, water content WC, and absolute dry weight BD were measured for 54 samples.

It was found that the relationship between ΔP and the amount of water WC was expressed by equation (27).
WC = 0.00010421 × (ΔP) ² −0.00011880 × ΔP (27)
It can be approximated by a quadratic curve passing through the origin, and it was found that the correlation coefficient R ² has a high correlation of 0.9875.

Next, the calculated Δf was calculated using equation (13), and α and β were determined in the same manner as in Example 1. As a result, α was 33.106 and β was 199.34. Next, the absolute dry weight BD was calculated in the same manner as in Example 1 using α and β.
The correlation between the BD measured with this device and the measured BD for solid content (weight after bone-drying) is Y = 0.99996X, and the slope can be approximated by a straight line passing through the origin of 0.9996, and the phase relationship The number R ² was found to be highly correlated with 0.9900. Also, regarding the water content, when the relationship between the result calculated from ΔP by this method and the actual measurement value by the absolute drying method is obtained, Y = 0.9978X, which is also approximated by a straight line passing through the origin with a slope of 0.9978. It turned out that it can be done. Further, it was found that the correlation coefficient R ² also has high correlation with 0.9876.

Next, since BD and WC were found, the moisture content was calculated from equation (26). With respect to the prepared 54 powder samples, the relationship between the water content obtained from the above calculation and the water content measured by the bone-dry method was obtained.
From the results, the relationship between the measured moisture content in the process and actually measured absolute dry Method moisture content is in a linear relationship Y = 1.027X, a high correlation with a correlation coefficient R ² also 0.9051 I understood it. In the second embodiment, as in the first embodiment, it was found that the inclination is approximately 1, and the approximation is made by a straight line passing through the origin. Similar to Example 1, the accumulation of various experimental errors is considered to be the cause of the fact that the correlation coefficient is not completely 1.000 and the slope of the first-order approximation is not completely 1.000. However, the results were almost similar to those of Example 1.

  The difference between the first embodiment and the second embodiment will be considered. The difference between the two embodiments is that the holes 10.5 Hf and Hb provided in the cavity resonator are either one on one side or two on both sides. From the above results, although there are variations due to measurement errors etc., it was confirmed that almost the same results were obtained, so that there is almost no difference between the two cavity resonators.

  When measuring physical properties such as moisture and dielectric constant using a cavity resonator, it is ideally desirable to measure in a sealed state, that is, without an opening such as a hole or a slit. This is because if there is an opening such as a hole, microwaves may leak from the opening and a theoretical electromagnetic field distribution may not be obtained. However, in the cavity resonator, the sum of the energy due to the electric field and the energy due to the magnetic field is always constant, so that the magnetic field is minimized at the place where the electric field is maximized, and the magnetic field is maximized at the place where the electric field is minimized. Since the electric field corresponds to the voltage and the magnetic field corresponds to the current, the current is minimized at the place where the magnetic field is minimum, and almost no current flows. Therefore, even if an opening is provided there, the microwave does not leak. On the contrary, in the place where the electric field is minimum, the maximum current flows, so the opening functions as an antenna and microwaves leak to the outside.

  Based on such theory and knowledge, the inventor provided a hole at a place where the electric field is maximum, but this time, the result of Example 2 in which two holes were provided yielded the same result as Example 1 with one hole. It is confirmed that the above theory is correct. The positions where the holes are provided are the positions of Cu and Cs as shown in FIG.

  Since the same result as in the sealed state was obtained even when two holes were opened, when measuring while continuously passing the powder, holes were made on both sides as shown in FIG. A penetration type cavity resonator can be used, and a powder sample container having no bottom as shown in FIG. 7B can be used. Such a powder sample container without a bottom is a form of the continuous tubular member itself described above rather than a container. The moisture content of the powder can be measured continuously and in real time while continuously passing the powder downward from the upper part of the continuous tubular member. The reason is that the method of the present embodiment can measure the moisture content of the powder regardless of the weight and volume of the powder and the position of the powder in the tubular member. As shown in FIG. 5, it is very important to provide two holes at positions Cu and Cs where the electric field is maximum and to arrange the cavity resonator so that the tubular member penetrates, in order to increase the sensitivity of moisture measurement. Preferred. However, as shown in FIG. 1 above, it is also possible to divide the cavity resonator into two parts and provide a slit portion between them, and a tube-like member can pass between them. In that case, when emphasizing the sensitivity, it is preferable that the tubular member passes between the central portion of the slit portion, that is, between Cu and Cs in FIG. The same applies when a long hole is provided instead of the slit.

(Third and fourth embodiments)
FIG. 13 shows the configuration of a microwave cavity according to a third embodiment of the present invention.
By providing an Eh elongated hole parallel to the Z-axis direction, the cylindrical container can be moved to any position, and by adjusting the measurement sensitivity, various samples ranging from a large amount of microwave absorption to a small amount of sample can be obtained. It is possible to measure the moisture content of

  Moreover, the structure of the microwave cavity resonator which concerns on 4th Embodiment of this invention was shown in FIG. By providing Eh oblong holes parallel to the X-axis direction, the tube-like member 106 can be similarly moved to an arbitrary position, and by adjusting the measurement sensitivity, from samples with large microwave absorption to small samples It becomes possible to measure the moisture content of various samples. By making the insertion direction parallel to the Y-axis, the electric field strength Ey always remains constant regardless of the position of the powder sample in the tubular member 106. Measurement can be performed without being affected by the position at. The actual powder sample is assumed to have a wide target range from one containing almost no water to one containing a lot of water. For this reason, it is desirable to change the insertion position of the tubular member 106 according to the amount of microwave absorption of the powder sample, and the optimum measurement sensitivity can be obtained by changing the insertion position.

Of course, the tubular member 106 in the third and fourth embodiments may be a continuous tubular member, or may be a one-end sealed tubular member.

  Further, as a modified example of the third and fourth embodiments, an example in which the long hole is very long is shown in FIG. In FIG. 15, since the elongated hole Eh is formed so as to wrap around to the side surface portion of the cavity resonator, the tube-like member 106 is moved to the external position of the cavity resonator, and another tube-like member whose view is omitted is replaced instead. Move to the same position and switch sample measurement and measurement when there is no sample in a short time, or when performing measurement to change the type of sample, switch the tubular member itself that passes or stores the sample in a short time It has the advantage of being able to switch between multiple samples in a short time.

Fifth Embodiment
FIG. 16 shows a configuration of an example of a moisture measuring device in powder provided with a vibration device according to the fifth embodiment of the present invention.
The tube-like member (powder sample container) 106a or 106b (see FIG. 7) inserted in the microwave cavity resonator 102b is connected to the vibration device 107, and the powder sample container 106a or 106b vibrates by vibration. The powder sample 108 can be appropriately stored inside the sample container 106a while preventing the powder sample 108 from remaining in or near the inlet of the sample container 106a or 106b or adhering to the inside of the sample container. Alternatively, it can pass through the sample container 106b. The vibration device 107 vibrates the vibration part 107a in the direction of arrow m in the figure by a motor or solenoid not shown.

Sixth Embodiment
FIG. 17 shows a configuration of an example of a moisture measuring device provided with a powder supply device according to a sixth embodiment of the present invention.
The powder sample 108 can be stably and quantitatively supplied to the tubular member 106 b inserted in the microwave cavity resonator by the powder quantitative supply device 109. In particular, when the moisture content is measured while continuously passing through the powder sample, the powder sample can be efficiently supplied by supplying an appropriate amount without interruption of the powder sample and without overflowing the sample container. The moisture content can be measured. Such powder quantitative supply devices are provided by each manufacturer. For example, as an example, a parts supply apparatus using SANDEX FEEDER technology manufactured by Sankyo Seisakusho Co., Ltd. enables quantitative transfer of powder by elliptical vibration transfer technology performed by two sets of cam mechanisms.
It goes without saying that the plurality of embodiments described above can be used in combination of two or more of each form in a timely manner.

  Industrial fields in which this moisture meter may be used include food, snacks, milk powder, coffee, cocoa, czechrate, biscuits, flour, sugar, nuts, noodles, bread crumbs, powdered cheese, wakame, starch, There are rice bran, soy flakes, nori, tea, salt, seasoning, seeds, food ingredient powder, buckwheat flour, soy flour, pepper powder, pepper, chili powder, powdered wasabi, citric acid, anhydrous glucose, dog food and so on. In the fiber and fiber related fields, there are cotton, rayon, acetate, tire cord, soft cotton, glass fiber, vinylon, acrylic and the like. In the field of chemistry, there are resin pellets, pesticides, salt, sodium bicarbonate, silica sand, ABS powder, PVC powder, detergent (powder), plastic pellets and the like.

Reference Signs List 100 moisture measuring apparatus 102 microwave cavity resonator 104 network analyzer 105 computer 106 tube 202 oscillating unit 204 receiving unit 206 resonant peak level detecting unit 208 resonant frequency detecting unit 210 computing unit 212 data holding unit

Claims (12)

A microwave cavity resonator comprising a waveguide provided with an opening;
A tubular member provided at the opening and capable of holding the powder in an airtight manner;
A controller that controls the measurement sensitivity of the resonance frequency or the resonance peak level by changing the position of the tubular member;
Measuring means for measuring the resonant frequency or resonant peak level;
And a calculation means for calculating water contained in the powder from the measured resonance frequency or resonance peak level.   2. The tubular member according to claim 1, wherein the tubular member is a continuous tubular member through which powder continuously passes or a single-end sealed tubular member in which powder is stored. Moisture measuring device in powder.   3. The powder according to claim 1, wherein the tubular member is installed in the waveguide so that the strength of an electric field formed inside the tubular member is substantially uniform. Moisture measuring device.   The apparatus for measuring moisture in powder according to any one of claims 1 to 3, wherein the tubular member is installed substantially parallel to the direction of gravity.   The apparatus for measuring moisture in powder according to any one of claims 1 to 4, wherein the tubular member is directly or indirectly connected to a vibration device.   The powder according to any one of claims 1 to 5, wherein the tubular member is connected to a powder supply device in order to fill or continuously supply the powder to the tubular member. Moisture measuring device.   The apparatus for measuring moisture in powder according to any one of claims 1 to 6, wherein a cross section of the microwave cavity resonator is rectangular. The change of the position of the tubular member in the control unit is a slit in which the opening is provided in at least one surface of the waveguide or in at least one pair of opposing surfaces in parallel or perpendicular to the tube length direction. moisture measuring device in the powder according to any one of the Jo member claims 1 and performing by moving the inserted direction substantially perpendicular along the slit 7. The apparatus according to any one of claims 1 to 8, wherein the calculating means calculates the moisture content of the water contained in the powder according to the following formulas A and B.
Δf = α · BD + β · WC (A)
ΔP = ω · WC (B)
The shift amount Δf of the resonance frequency and the change amount ΔP of the resonance peak level refer to the difference between the values when the powder sample is present and absent in the tubular member, respectively .
The weight of the dry part of the powder is BD, and the weight of water is WC .
α = K1 · (ε'1-1) / a (C)
β = K1 · (ε'2-1) / b (D)
ω = K2 · ε ”2 / b (E)
The dielectric constant of the dry part of the powder is ε'1
The dielectric constant of water is ε'2, and the dielectric loss factor is ε "2.
a and b are proportional constants, and K ₁ and K ₂ are proportional constants. 10. The opening according to claim 1, wherein the opening is a hole or a slit, and the hole or the slit is provided at a position where the electric field formed in the waveguide is maximized or maximized. Moisture measuring device in powder.   The device for measuring moisture in powder according to any one of claims 1 to 10, wherein the tubular member is made of a material that absorbs and reflects less microwaves. A powder using a waveguide type microwave resonator provided with a tube-like member capable of holding or passing powder in an airtight manner at least inside the waveguide at an opening provided in the waveguide. Is a method of measuring water content in
Controlling the measurement sensitivity of the resonance frequency or the resonance peak level by changing the position of the tubular member;
Measuring the resonant frequency and the resonant peak level in the absence and presence of powder in the tubular member;
Calculating the water content of the water contained in the powder from the measured resonance frequency and resonance peak level.