JPH08136492A - Water-in-liquid measuring apparatus - Google Patents

Abstract

PURPOSE: To smoothly replace a sensor with a new sensor with excellent compartibility even if the former sensor becomes out of order by composing a sensor side assembled body, which sends out a standardized signal independently of the differences of sensor characteristics, separately from a main body side. CONSTITUTION: In a sensor side assembled body 10 which is composed separately from a main body side assembled body 200, a capacitance type water sensor detects water in an oil and sends out capacitance C. A CR oscillating circuit of a sensor signal processing part changes the output frequency F corresponding to the change of the capacitance C. A computing circuit of a computation processing apparatus 20A which receives the output frequency computes a standardized signal H from the frequency F independently of the differences of the characteristics of sensors and sends out the signal H. An assembled body 200 which receives the signal H through a transmission cable 300 converts 20B into the water concentration L and shows 30 the concentration. Consequently, in the case a sensor S becomes out of order, the sensor S is replaced and the signal H is corrected, so that an assembled body 100 provided with a new sensor S with excellent compartibility can be connected and determination can be carried out immediately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the amount of water contained in various liquids such as insulating oil, lubricating oil for refrigerators, solvents, petroleum products such as fuels and petrochemical raw materials, that is, water concentration. The present invention relates to a measuring device (hereinafter, referred to as "liquid moisture measuring device") for detecting the.

[0002]

2. Description of the Related Art For example, since electrically insulating oil is reluctant to contain water in oil, it is dehydrated by an appropriate means such as a dehydrating agent or a vacuum oil purifier at the time of shipping at an oil refinery. , We are monitoring the water content. Also, in electric equipment such as oil-filled transformers and oil-filled transformers used in substations, power plants, etc., moisture monitoring is an important item for preventive maintenance of the electric equipment.

Further, the lubricating oils used in refrigerators, air conditioners for automobiles, etc. are inevitably changed with refrigerants in the background of the regulation of CFC gas. For this reason, conventional mineral oils are replaced with synthetic ester lubricants. And PAG (polyalkylene glycol). It is known that these synthetic lubricating oils have a higher hygroscopicity than mineral oils, and when they absorb moisture excessively, they are hydrolyzed or oxidatively deteriorated to lower their lubricity, thereby hindering normal operation of machines. Also, for example, for jet fuel, when an aircraft flies in the stratosphere,
It is known to freeze when it contains water and clog the fuel line.

For these reasons, there is an increasing need to detect the amount of water contained in lubricating oil and other various petroleum products.

Conventionally, such detection of water content in liquid has been
The coulometric titration method represented by the Karl Fischer method is the mainstream.

However, since the conventional coulometric titration method such as the Karl Fischer method is a batch-type measurement method, a fixed amount of oil is sampled on site, and it is transported to a test room and measured by an analyzer. There is a problem that it is not possible to respond promptly at the site, and further there is a problem that continuous monitoring is not possible.

To solve such a problem, an on-line type water content measuring device is desired, but there is no full-scale product available in the market which can sufficiently satisfy such a demand.

Another problem is that a wet analyzer such as the above-mentioned coulometric titrator has a large shape and is inconvenient to carry. For this reason, a so-called portable type water content measuring device that is small and portable is desired, but a product suitable for this purpose and having sufficient performance cannot be found in the market.

[0009] On the other hand, technically, aluminum anodic oxide film type moisture sensors have been studied as sensors suitable for such products. The feature of this sensor is that it is small and can be placed directly in the liquid.

The detection principle of the aluminum anodic oxide film type moisture sensor is based on the fact that when the sensor is placed in the liquid to be detected, the moisture is adsorbed on the interface between the sensor and the liquid to generate an electric capacitance. Since the capacitance corresponds to the amount of water molecules adsorbed, and the amount of adsorption corresponds to the water concentration in the liquid,
This sensor can be used to detect water in liquid.

The present inventors have proposed an apparatus for measuring water content in liquid using such a sensor. As shown in FIG. 2, the whole structure of this in-liquid moisture measuring apparatus has a capacitance type moisture sensor S such as an aluminum anodic oxide film type moisture sensor for detecting moisture in the liquid, and this moisture sensor S.
Sensor signal processing unit 10 having a CR oscillating circuit in which the output frequency F changes in accordance with the change of the electrostatic capacitance C, and calculation processing for converting the output frequency F from the sensor signal processing unit 10 into the water concentration L. Processing device 20 including a unit
And a display device 30 having a moisture value display circuit for displaying the moisture concentration from the arithmetic processing device 20 are integrally configured.

[0012]

In such an apparatus for measuring moisture in liquid, when the moisture sensor S fails, it needs to be replaced. However, the moisture sensor S has variations in its characteristics, and it is not necessary to simply replace only the portion of the moisture sensor S, and it is necessary to adjust the sensor signal processing unit 10 according to the characteristics of the moisture sensor S. , It will be extremely complicated work. Therefore, in actuality, when the moisture sensor S fails, the in-liquid moisture measuring device itself must be replaced with a new one. This is a processing unit 2 that is still fully usable.
0, the display device 30 is also discarded, which causes a problem in saving resources and economically.

As shown in FIG. 1, the present inventors output an in-liquid moisture measuring device according to (A) a capacitance type moisture sensor S and a change in the capacitance C of this moisture sensor S. The sensor signal processing unit 10 having a CR oscillation circuit in which the frequency F changes and the output frequency F from the sensor signal processing unit 10 calculates and outputs a standardized signal Θ that does not depend on the difference in sensor characteristics. First arithmetic processing unit 20A
And a sensor-side assembly 100 in which
(B) with a second processing unit 20B that the output signal Θ from the first processor 20A is converted into the water concentration L, and water display circuit for displaying the water concentration L from the processing unit 20B The display device 30 is divided into a main body side assembly 200 integrally configured, and both the assemblies 100 and 200 are
For example, it has been found that the problem that the apparatus for measuring moisture in liquid having the above-mentioned configuration can be solved by adopting a configuration in which the connection is made by an electrical connection means such as the transmission cable 300.

In other words, if the moisture sensor S fails, the moisture sensor S of the sensor side assembly 100 is replaced and the output signal Θ from the first arithmetic processing unit 20A is corrected to ensure compatibility. It is possible to connect the sensor side assembly 100 equipped with the new sensor to the main body side assembly 200 in the same manner as described above and immediately use it for measurement.

Therefore, the object of the present invention is to replace a new sensor with good compatibility even if the sensor fails, to eliminate the difference in characteristics between sensor solids, and to immediately measure the water content in the subject with high accuracy. An object of the present invention is to provide an apparatus for measuring water content in liquid that can be used for quantity detection measurement.

Another object of the present invention is to provide an apparatus for measuring water content in a liquid capable of detecting the water content in a sample with high accuracy by eliminating the difference in characteristics between sensor solids and the temperature dependence of the sensor itself. Is to provide.

[0017]

The above object is achieved by the apparatus for measuring water in liquid according to the present invention. In summary, the present invention comprises a capacitance-type moisture sensor for detecting moisture in a liquid, and a CR oscillating circuit whose output frequency changes according to a change in the output of the capacitance-type moisture sensor. The signal processing unit and the standardized signal (Θ) that does not depend on the difference in the characteristics of the sensor based on the output frequency from the signal processing unit are expressed by the following arithmetic expressions (1), (2), (3), ( 4) a first arithmetic processing unit that calculates and outputs, and further, from the output signal (Θ) from the first arithmetic processing unit to the water concentration ( L ) in oil by the following arithmetic expressions (5) and (5a). An in-liquid moisture measuring device comprising: a second arithmetic processing device for conversion and a moisture display device for displaying the moisture concentration output from the second arithmetic processing device. Θ = X _C / X _S (1) However, 0 ≦ Θ ≦ 1 X _C ≦ X _S , and X _C is the moisture sensor S whose temperature is corrected.
_Is an increment with respect to the base capacitance X _B and is expressed by the following equations (2) and (3). _{X C = C- X B (2} ) X B = f (T) = X BD + (∂ X B / ∂T) (T-T D) + △ A (3) where, X _BD is submerged Reference temperature T _D when the water concentration is 0
It is the actually measured capacitance of the moisture sensor S at, that is, the base capacitance. T is the temperature actually measured when measuring the water content in the liquid, and ΔA is a correction term. ∂ X _B / ∂T is the temperature coefficient of the base capacitance.

Further, the above-mentioned X _S is a saturated value of X _C and is represented by the following equation.

[0019]

[Equation 2] Is.

Further, L = Θ / ((1-Θ) K) (5) or Θ = 1 / (1 + 1 / L * K) (5a), and the above K is determined by the combination of the liquid and the sensor. And is an equilibrium constant that fluctuates depending on the temperature of the liquid, and K = κ (T) (6).

According to another aspect of the present invention, the following formula (7) can be used instead of the above formulas (5) and (5a). Θ = 1− {σ / ( L * K)} + δ (7) where σ and δ are correction coefficients.

According to a preferred embodiment of the present invention, the capacitance type moisture sensor, the signal processing unit and the first arithmetic processing unit are integrated to form a sensor side assembly,
The second arithmetic processing unit and the moisture display unit are integrated to form a main body side assembly, and the sensor side assembly and the main body side assembly are connected by an electrical connecting means such as a transmission cable.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus for measuring water content in liquid according to the present invention will be described in more detail below with reference to the drawings, taking the case of measuring water content in oil as an example. The apparatus for measuring moisture in liquid of the present invention is configured to connect a sensor side assembly 100 and a main body side assembly 200 with a transmission cable 300, as schematically shown in FIG.

The sensor-side assembly 100 includes a capacitance type moisture sensor S, such as an aluminum anodic oxide film type sensor, for detecting the amount of moisture in oil, and an electrostatic capacitance type moisture sensor S. A sensor signal processing unit 10 including a CR oscillation circuit whose output frequency changes according to a change in capacitance, and a standardized signal based on an output frequency F from the sensor signal processing unit 10 that does not depend on a difference in sensor characteristics. A first arithmetic processing unit 20A that calculates and outputs Θ is integrally configured. Further, the main assembly 200 displays the second arithmetic processing unit 20B that converts the output signal Θ from the first arithmetic processing unit 20A into the water concentration L and the water concentration L from this arithmetic processing unit 20B. The display device 30 including the moisture value display circuit is integrally configured.

Next, in the in-liquid moisture measuring apparatus of the present invention, the sensor signal processing unit 10 for converting the capacitance C of the moisture sensor S into an electric signal which can be easily handled thereafter, that is,
The conversion circuit will be described.

In order to change the capacitance C of the moisture sensor S into an electric signal that can be easily handled thereafter, several kinds of conversion circuits are conceivable, for example, conversion into frequency, conversion into voltage, phase difference. An electric circuit or the like for converting into

The present inventors have examined a method of converting electrostatic capacity into frequency as a conversion circuit. In this system, a voltage of a constant level, for example, a pulse voltage with a wave height of 5 V is output as an output, and the frequency thereof corresponds to the electrostatic capacitance. This method has an advantage that an output form with a good S / N ratio can be secured. As an example, a sensor signal processing unit 10 having a conversion circuit to which a Schmitt circuit is applied is shown in FIG.

The conversion circuit of the sensor signal processing section 10 shown in FIG. 3 is a CR oscillation circuit in principle. In this embodiment, for example, a C-MOS type Schmitt inverter 11 is used.
A fixed resistor R which is a pulse frequency determining element connected between the input and output of the inverter 11 (feedback circuit);
Capacitance element C ′ connected to the input side of the inverter 11
And an electrostatic capacitance sensor S, which is another pulse frequency determining element connected in series between the electrostatic capacitance element C ′ and the input side of the Schmitt inverter 11, A pulse signal whose frequency (F) fluctuates in response to a change in the electrostatic capacitance (C) of the sensor S caused by the amount of water is output. The resistor R ′ connected in parallel with the sensor S is for preventing a DC voltage component from being applied to the sensor S. Since a sensor made of aluminum oxide or the like is usually used as the moisture sensor S, when a DC voltage component is applied, deterioration of the sensor characteristics easily occurs due to polarization, dielectric breakdown, etc., and this is to prevent this. . The pulse signal from the pulse generation circuit is output to the first arithmetic processing unit 20A as an output voltage of the same frequency with the pulse waveform thereof being inverted by the second C-MOS type Schmitt inverter 12.

The relationship between the frequency F output from the conversion circuit 10 and the electrostatic capacitance C in this embodiment is expressed by the following equation (8).

[0030]

(Equation 3) Where F: output frequency C: capacitance of moisture sensor (C = X _C + X _B ) X _C : component that changes depending on moisture concentration X _B : intrinsic component of moisture sensor (base capacitance) C ′: circuit constant ( Capacitance) R: Circuit constant (resistance) k: Characteristic coefficient of circuit

Further, according to the present invention, in order to correct the temperature dependency of the moisture sensor S, the measurement ambient temperature (T) at the time of measurement is measured. Although any temperature measuring method and device can be used, in the present embodiment, the temperature detecting circuit 10 _{T which} is basically a CR oscillation circuit is used like the sensor signal processing unit, that is, the moisture detecting circuit 10. It That is, the temperature detection circuit 10 _T is a C-MOS type Schmitt inverter 31 and a resistance change such as a thermistor which is a pulse frequency determining element connected between the input and output (feedback circuit) of the inverter 31. CR which generates a square wave pulse signal related to temperature by a temperature sensor R _{T of the} formula and a fixed capacitance element C ₀ which is another pulse frequency determining element connected between the input side of the inverter 31 and the ground. The output frequency (F _T ) of the CR oscillator circuit is formed by the resistance of the temperature sensor R _T , which is an element for determining the pulse frequency, which changes in accordance with the temperature.
Corresponding to the oscillation output, that is, the square wave pulse signal, the waveform thereof is inverted by the second C-MOS type Schmitt inverter 32, and then the first arithmetic processing unit 20
It is input to A and the temperature corresponding to the frequency ( _FT ) is calculated.

In the apparatus for measuring water content in liquid of the present invention, the first arithmetic processing unit 20A determines the output frequency (F) from the sensor signal processing unit 10 according to a predetermined arithmetic expression regardless of the characteristic of the sensor. An arithmetic processing unit for converting the signal into a standardized signal (Θ) is provided.

The signal (Θ) from the first arithmetic processing unit 20A is an electrical connection means such as a transmission cable 300.
Via the second arithmetic processing unit 2 of the main assembly 200
Sent to OB. The signal (?) From the first arithmetic processing unit 20A is converted into an oil moisture concentration ( L ) according to a predetermined arithmetic expression in the arithmetic processing unit of the second arithmetic processing unit 20B. The moisture concentration output from the arithmetic processing unit 20B is displayed as a moisture value (%) on a display device 30 equipped with a moisture value display circuit.

To further explain, the arithmetic expression used in the first arithmetic processing unit 20A is as shown in the following expression (9). Θ = X _C / X _S (9) However, 0 ≦ Θ ≦ 1 X _C ≦ X _S.

Here, X _C is the base capacitance of the temperature-corrected moisture sensor S as understood from FIG.
It is an increment with respect to X _B and is expressed by the following equations (10) and (11). _{X C = C- X B (10} ) X B = f (T) = X BD + (∂ X B / ∂T) (T-T D) + △ A (11) In addition, X _BD is submerged water It is the measured capacitance of the moisture sensor S at the reference temperature T _D when the concentration is 0, that is, the base capacitance. T is the temperature actually measured when measuring the water content in the liquid, and ΔA is a correction term. ∂ X _B / ∂T is the temperature coefficient of the base capacitance.

As described above, the reason why the above correction is performed on X _C is that X _B is different between sensor solids and that the sensor itself has a temperature characteristic.

X _{S in the} above formula (9) is a saturation value of X _C , and a monomolecular film is formed at the interface between the sensor and the liquid when the water concentration in the liquid increases. Means the X _C value. In other words, X _S is represented by the following equation.

[0038]

[Equation 4]

In the present invention, the above-mentioned Θ and X _C and X _{S which} are the calculation bases thereof may be obtained by any method, for example, it can be obtained by actual measurement using an LCR meter for precise measurement. In the sensor signal processing unit 1
Since a frequency oscillator is used at 0, it will be described in connection with this.

The above Θ and X _C , X _S can be basically obtained by using the above-mentioned equation (8). That is,
From Expression (8), C can be rewritten as the following expression. C = 1 / (RkF-1 / C ') (13) where, F: output frequency C: capacitance of the moisture sensor _{(C = X C + X B} ) X C: components varying the water concentration X _B unique component moisture sensor (base capacitance) C ': circuit constant (electrostatic capacitance) R: circuit constants (resistance) k: characteristic coefficient above X _B of the circuit, C when the water concentration in the liquid was 0 It is calculated from the value using the above equation (13).

Of course, in the equation (13), it is possible to correct the actual calculated C value in order to match the actual measured value with, for example, an LCR meter.

As described above, the output frequency (F) from the sensor signal processing unit 10 is standardized by the arithmetic processing unit of the first arithmetic processing unit 20A in accordance with a predetermined arithmetic expression, regardless of the difference in sensor characteristics. Signal (Θ).

Next, a method for obtaining the water concentration L in oil by the second arithmetic processing unit 20B from the standardized signal Θ will be described.

First, the principle of measuring the amount of water in oil according to the present invention will be described. The output capacitance (C) of the moisture sensor in oil is determined by the in-liquid moisture measuring device (LCR).
According to the measurement by the meter), as shown in FIG. 4, it rises from the low concentration region and gradually approaches a constant value gradually. This phenomenon is completely different from moisture detection in the gas phase.
It is considered that this is because multi-molecule adsorption is carried out in the gas phase on the sensor surface, whereas mono-molecule adsorption is carried out in the oil.

Based on this idea, the following equation (1
4) is established.

[0046]

(Equation 5) Here, n: number of adsorption sites occupied by one oil molecule when one water molecule occupies one adsorption site M: one oil molecule P: one adsorption site on the sensor surface N ₀ : oil Number of adsorption sites occupied by molecules A ₁ : Activity of moisture in oil N ₁ : Number of adsorption sites occupied by water molecules A ₂ : Activity of oil Since the above formula (14) is in equilibrium,

[0047]

(Equation 6) Where N: total number of adsorption sites K: equilibrium constant

In the above equations (14) and (15), A ₂ is
It is the activity level of oil, but since it is in large quantity, it is set to 1,
A ₁ is the activity of water in the oil, but since the water concentration is low, it can be replaced with the concentration L 1.

Based on this premise, the above equations (15), (1
From equation (6), the following equation (17) is obtained.

[0050]

(Equation 7) In the above formula (17), N ₁ / N corresponds to the surface coverage (θ).

[0051]

(Equation 8) Is.

When the above equation (18) is expressed using the surface coverage (θ),

[0053]

[Equation 9] Therefore, this equation (19) has the same form as the Langmuir-type adsorption isotherm.

The standardized signal Θ from the first arithmetic processing unit 20A is the surface coverage θ shown by the above equation (18).
Is a parameter that is expressed more accurately according to the actual measurement. Based on the above formula (19), Θ and the water moisture concentration L
The relationship with and is expressed by the following equation (20) or (21). L = Θ / ((1-Θ) K) (20) or Θ = 1 / (1 + 1 / L * K) (21) where K = κ (T) (22) The above equation (20) or (21) ), The water concentration L in the liquid is obtained. At this time, K is a parameter determined by the combination of the liquid and the sensor, and is expressed by the above equation (1
It is determined by the reaction shown in 4), and is represented by the above formula (15) in the mathematical formula, which means an equilibrium constant.

In the equation (20) or (21), the equilibrium constant K changes depending on the temperature of the liquid and therefore needs to be corrected by the temperature. Therefore, K in the equation (15) is K = κ. It is necessary to express it as (T).

[0056] Incidentally, the above theta, equation submerged water concentration L is the idea when the approximate expression of the low density, theta = 1-a {σ / (L * K) } + δ (23), the water concentration L It is also possible to calculate.

Here, σ and δ in the above equation (23)
Is a correction coefficient, which is arbitrarily determined so that the actually measured moisture value by analysis and the measurement by the in-liquid moisture detector according to the present invention match the actual data.

Specifically, in the second arithmetic processing unit 20B, in order to obtain the water content in the liquid by using the above equation (20), as is apparent from this equation, κ (T) can be obtained by this equation. It is necessary to input it, but this can be obtained by an experiment by the following method.

[0059] That is, in equation (24) of the form obtained by modifying the equation (20), kappa (T) is determined as the reciprocal by plotting the L / theta with respect to L. L / Θ = L + 1 / κ (T) (24) By experimentally performing this at each temperature to obtain κ (T), and storing it in the ROM or RAM of the second arithmetic processing unit 20B, As long as the moisture sensor S and the first-stage arithmetic processing unit 20A output Θ, the second-stage arithmetic processing unit 20B can automatically output a signal of the moisture value L.

Of course, the output signal of the water content value L may be of any form as long as it corresponds to it, for example, the pulse number (frequency), analog current / voltage, etc. can be used.

When calculating the water content, the above equation (20) can be applied only when the equilibrium constant K has temperature dependence.

However, in reality, it is necessary to consider the case where the dielectric constant of the adsorption film of water molecules changes with temperature. The reason for this is that, in reality, the inventors have confirmed a phenomenon such as "the capacitance of the moisture sensor changes depending on the temperature even at the same moisture concentration in the liquid".

Taking this into consideration, the electrostatic capacitance generated by the moisture sensor S can be expressed in more detail by the following assumptions as in the following equations (25) and (26).

That is, (1) the dielectric constant of the adsorbed film changes with temperature. (2) The dielectric constant of the adsorption film when the monomolecular film is formed, that is, when Θ = 1 is represented by a function ε (T) of ε. T is the temperature. (3) ε for an arbitrary adsorption amount (Θ = 1 or less) is proportional to Θ. Assuming that and, the following is assumed: X _C = Θ * ε (T) * ξ (25) X _S = ε (T) * ξ (26) where ξ is a constant and the moisture sensitivity of the moisture sensor It corresponds to S / d when the part is regarded as a parallel plate capacitor. S is the plate area,
d is the distance between the electrode plates, which is invariable.

In this case, Θ = X _C / X _S , which is the same as equation (9), the coefficient of the dielectric constant with respect to temperature is eliminated, and by simply using Θ, the water content in the liquid can be calculated from equation (20). The concentration is required.

When the dielectric constant of the adsorption film behaves differently from the above (2) and (3), the following assumptions are made. (1) The dielectric constant of the adsorption film changes with temperature. (2) The dielectric constant of the adsorption film when the monomolecular film is formed, that is, when Θ = 1 is represented by a function ε1 (T) of ε. T
Is the temperature. (3) ε at an arbitrary adsorption amount (Θ = 1 or less) is a function temperature ε2 (T) different from the above (2). T is the temperature.

In this case, it is assumed that the following equations (27) and (28) hold. X _C = Θ * ε2 (T) * ξ (27) X _S = ε1 (T) * ξ (28) From equations (27) and (28), X _C / X _S = Θ * ε2 (T) / ε1 (T) (29) For the sake of simplicity, if ε2 (T) / ε1 (T) = Φ (T) (30) is set, the following equation (31) is obtained from equations (20), (29) and (30). obtain. L = 1 / ((Φ (T) / Θ-1) * κ (T)) (31) As can be seen from the above formula (31), in this case, the water concentration calculated from Θ changes with temperature. become.
As a solution to this, the following formula (3
Φ (T) and κ (T) are experimentally obtained from 2), and equation (3
It may be applied to 1). L / Θ = L / Φ ( T) + 1 / (Φ (T) * κ (T)) (32) i.e., L / theta for L at each temperature and each concentration of several points
By finding the slope and intercept from the plot of
Φ (T) and κ (T) are obtained. Then, by putting these into the equation (31), the water concentration L in the liquid is obtained by the calculation by the calculation processing device 20B.

As described above, according to the in-liquid moisture measuring apparatus of this embodiment, it is possible to accurately know the water concentration in the liquid.

Tables 1 and 2 show the results of measuring the water content in the ester type lubricating oil and the electric insulating oil by the apparatus for measuring the water content in the liquid of the present invention, and the measurement results by the Karl Fischer method.
It can be said that both measurement results are substantially in agreement.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

As described above, the apparatus for measuring moisture in liquid according to the present invention comprises (A) a capacitance-type moisture sensor S,
The sensor signal processing unit 10 including a CR oscillation circuit whose output frequency F changes according to the change in the capacitance C of the moisture sensor S, and the output frequency F from the sensor signal processing unit 10 determines the characteristics of the sensor. A first arithmetic processing unit 20 for calculating and outputting a standardized signal Θ that does not depend on the difference.
A sensor side assembly 100 in which A and A are integrally formed;
(B) with a second processing unit 20B that the output signal Θ from the first processor 20A is converted into the water concentration L, and water display circuit for displaying the water concentration L from the processing unit 20B The display device 30 and the main body side assembly 200 that are integrally configured are provided.
Since it is configured to be connected by an electrical connection means, for example, a transmission cable 300, even if the sensor fails, it can be replaced with a new sensor with good compatibility, eliminating the difference in characteristics between sensor solids, and further Can eliminate the temperature dependency of the sensor itself and can be immediately used for detection and measurement of the water content in the subject with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment of a device for measuring water content in liquid of the present invention.

FIG. 2 is a diagram showing an overall configuration of a conventional apparatus for measuring water content in liquid.

FIG. 3 is a circuit configuration diagram according to an embodiment of the apparatus for measuring water content in liquid of the present invention.

FIG. 4 is a diagram showing an example of a relationship curve between water concentration in liquid and capacitance.

[Explanation of symbols]

10, 10 _T sensor signal processing unit 20A, 20B first and second arithmetic processing device 30 moisture display device 100 sensor side assembly 200 main body side assembly 300 electrical connection means

Claims (3)

[Claims] 1. A signal processing comprising a capacitance type moisture sensor for detecting moisture in a liquid, and a CR oscillation circuit whose output frequency changes in accordance with a change in the output of the capacitance type moisture sensor. Section and a signal (θ) that is standardized based on the output frequency from the signal processing section and does not depend on the characteristic of the sensor, the following equations (1), (2), (3),
A first arithmetic processing device for performing arithmetic operation according to (4) and outputting;
Further, a second arithmetic processing unit for converting the output signal (Θ) from the first arithmetic processing unit into an oil moisture concentration ( L ) by the following arithmetic expression (5) or (5a), and the second arithmetic operation. An apparatus for measuring water content in a liquid, comprising: a water content display apparatus for displaying the water content output from the processing apparatus. Θ = X _C / X _S (1) However, 0 ≦ Θ ≦ 1 X _C ≦ X _S , and X _C is the moisture sensor S whose temperature is corrected.
_Is an increment with respect to the base capacitance X _B and is expressed by the following equations (2) and (3). _{X C = C- X B (2} ) X B = f (T) = X BD + (∂ X B / ∂T) (T-T D) + △ A (3) where, X _BD is submerged Reference temperature T _D when the water concentration is 0
It is the actually measured capacitance of the moisture sensor S at, that is, the base capacitance. T is the temperature actually measured when measuring the water content in the liquid, and ΔA is a correction term. ∂ X _B / ∂T is the temperature coefficient of the base capacitance. Further, the above-mentioned X _S is a saturation value of X _C and is represented by the following equation. [Equation 1] Is. Further, L = Θ / ((1-Θ) K) (5) or Θ = 1 / (1 + 1 / L * K) (5a), and the above K is determined by the combination of the liquid and the sensor. An equilibrium constant that varies with the temperature of the liquid, and K = κ (T) (6). 2. Instead of the above formula (5) or (5a),
The following formula (7) is used, The moisture measuring device in liquid of Claim 1 characterized by the above-mentioned. Θ = 1− {σ / ( L * K)} + δ (7) where σ and δ are correction coefficients. 3. The capacitance type moisture sensor, the signal processing unit, and the first arithmetic processing unit are integrated into a sensor side assembly, and the second arithmetic processing unit and the moisture display unit are 3. The apparatus for measuring moisture in liquid according to claim 1 or 2, wherein the body side assembly is integrally formed, and the sensor side assembly and the body side assembly are connected by an electrical connecting means.