JP2013113778A - Dew point sensor and method for measuring dew point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dew point sensor which is highly accurate.SOLUTION: The dew point sensor includes a heating resistance element 1, a current supply device 2 for supplying current to the heating resistance element 1 so as to make a heat generation temperature of the heating resistance element 1 constant, a humidity detection element 3 maintaining constant temperature by being brought into contact with the heating resistance element 1, and an atmospheric temperature specification part for specifying the temperature of gas coming into contact with the humidity detection element 3 on the basis of the current supplied to the heating resistance element 1.

Description

  The present invention relates to a detection technique, and relates to a dew point sensor and a dew point measurement method.

  In refrigerated / freezer storage and food factories, desiccant air conditioners are used as air conditioning equipment to provide a low-humidity environment in order to suppress the generation of mold and germs due to condensation and frost formation on devices and products, or the generation of rust. Is being used. In such a low humidity environment, it is important to manage the dew point. Here, the dew point refers to a temperature at which condensation starts when air containing water vapor is cooled. In other words, the dew point is a temperature at which the relative humidity of air is 100%. The dew point can be accurately measured by, for example, a specular dew point meter, but the specular dew point meter is expensive. Therefore, for example, an inexpensive dew point meter (for example, see Patent Documents 1 to 4) including a temperature detection element and a capacitance type humidity detection element is widely adopted.

JP 2003-98141 A Japanese National Patent Publication No. 10-508096 JP 7-294469 A JP-A-1-295147

  However, the conventional capacitance type dew point meter has a problem that the dew point measurement accuracy is low because the response speed of the temperature detection element is different from the response speed of the humidity detection element. Therefore, an object of the present invention is to provide a dew point sensor and a dew point measuring method with high accuracy.

  According to an aspect of the present invention, (a) a heating resistor element, (b) a current supply device that supplies current to the heating resistor element so that the heating temperature of the heating resistor element is constant, and (c) a heating resistor element A dew point sensor is provided, comprising: a humidity detecting element that is kept at a constant temperature by contacting the temperature sensor; and (d) an air temperature specifying unit that specifies the temperature of the gas in contact with the humidity detecting element.

  According to the aspect of the present invention, (a) supplying a current to the heating resistor element so that the heating temperature of the heating resistor element is constant, and (b) bringing the humidity detecting element into contact with the heating resistor element, There is provided a method for measuring a dew point, comprising: maintaining a humidity detecting element at a constant temperature; and (c) specifying a temperature of a gas in contact with the humidity detecting element.

  According to the present invention, it is possible to provide a dew point sensor and a dew point measuring method with high accuracy.

It is a circuit diagram of a part of the dew point sensor according to the first embodiment of the present invention. It is a schematic diagram of a part of the dew point sensor according to the first embodiment of the present invention. It is a schematic diagram of the humidity detection element which concerns on the 1st Embodiment of this invention. It is a partial circuit diagram of the dew point sensor which concerns on the 2nd Embodiment of this invention. It is a partial circuit diagram of the dew point sensor which concerns on the 3rd Embodiment of this invention. It is a partial circuit diagram of the dew point sensor which concerns on the 4th Embodiment of this invention.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
As shown in FIG. 1, the dew point sensor according to the first embodiment includes a heating resistor element 1 and a current supply device that supplies current to the heating resistor element 1 so that the heating temperature of the heating resistor element 1 is constant. 2 and a humidity detecting element 3 that is kept at a constant temperature by being in contact with the heating resistor element 1. Furthermore, the dew point sensor according to the first embodiment includes an air temperature specifying unit 301 shown in FIG. 2 that specifies the temperature of the gas in contact with the humidity detecting element 3 based on the current supplied to the heating resistor element 1, and FIG. And a dew point specifying unit 303 for specifying a dew point based on the electrical characteristics of the humidity detecting element 3 shown in FIG. 2 and the gas temperature specified by the air temperature specifying unit 301 shown in FIG. The temperature specifying unit 301 and the dew point specifying unit 303 are included in, for example, a central processing unit (CPU) 300.

  A heating resistance element 1 shown in FIG. 1 is a thin wire made of a metal having a large resistance temperature coefficient such as platinum, tungsten, or platinum iridium. The resistance of the heating resistor element 1 decreases when the temperature of the surrounding gas in contact with the heating resistor element 1 decreases. Further, the resistance of the heating resistor element 1 increases as the temperature of the surrounding gas in contact with the heating resistor element 1 increases.

  The heating resistor element 1 forms part of a bridge circuit. The bridge circuit includes a first resistance element 11 connected in series to the heating resistance element 1 and second and third resistance elements 12 and 13 connected in parallel to the heating resistance element 1 and the first resistance element 11. And comprising. Each of the first to third resistance elements 11, 12, and 13 is made of, for example, a metal having a low resistance temperature coefficient. Each of the first to third resistance elements 11, 12, and 13 may be insulated from the gas in contact with the heating resistance element 1.

  A contact point between the first resistance element 11 and the third resistance element 13 forms an input terminal of the bridge circuit. The contact point between the heating resistor element 1 and the second resistor element 12 forms an output terminal of the bridge circuit. The output terminal of the bridge circuit is grounded, for example.

  The current supply device 2 includes an operational amplifier 20 including a first input terminal 21 that is an inverting input terminal (−), a second input terminal 22 that is a non-inverting input terminal (+), and an output terminal 23. A first input terminal 21 of the operational amplifier 20 is connected to a contact point between the heating resistor element 1 and the first resistor element 11. The second input terminal 22 of the operational amplifier 20 is connected to the contact point between the second resistance element 12 and the third resistance element 13. The output terminal 23 of the operational amplifier 20 is connected to the input terminal of the bridge circuit.

When the resistance of the heating resistor element 1 decreases due to a decrease in the temperature of the gas in contact with the heating resistor element 1, the heating resistor element 1 connected to the first input terminal 21 that is the inverting input terminal (−) of the operational amplifier 20 and the first one. The voltage at the contact of the first resistance element 11 also decreases. Then, the feedback current supplied from the output terminal 23 of the operational amplifier 20 to the bridge circuit increases. On the other hand, when the resistance of the heating resistor element 1 increases due to an increase in the temperature of the gas in contact with the heating resistor element 1, the voltage at the contact point between the heating resistor element 1 and the first resistor element 11 also increases. Then, the feedback current supplied from the output terminal 23 of the operational amplifier 20 to the bridge circuit decreases. Thus, in accordance with the variation of the resistance of the heating resistor element 1, because the feedback current is supplied to the heating resistor element 1, the heat producing temperature T _H of the heating resistor element 1 is kept constant.

  The dew point sensor according to the first embodiment further includes an ammeter 25 that is provided between the output terminal 23 of the operational amplifier 20 and the input terminal of the bridge circuit and measures the feedback current from the operational amplifier 20. The ammeter 25 is connected to the CPU 300 shown in FIG. A relation storage device 401 is connected to the CPU 300. As described above, the feedback current of the operational amplifier 20 shown in FIG. 1 correlates with the temperature of the gas in contact with the heating resistor element 1. The relationship storage device 401 illustrated in FIG. 2 stores the relationship between the temperature of the gas in contact with the heating resistor element 1 illustrated in FIG. 1 and the current measured by the ammeter 25, which is acquired in advance.

  The temperature specifying unit 301 illustrated in FIG. 2 reads the relationship between the temperature of the gas and the current from the relationship storage device 401. Further, when receiving the current measurement value from the ammeter 25 shown in FIG. 1, the temperature specifying unit 301 contacts the heating resistance element 1 and the humidity detection element 3 based on the received current measurement value and the relationship. Specify the gas temperature value. For example, the relationship read from the relationship storage device 401 shown in FIG. 2 is expressed by a function in which the temperature of the gas in contact with the heating resistor element 1 shown in FIG. 1 is a dependent variable and the current measured by the ammeter 25 is an independent variable. 2, the temperature specifying unit 301 shown in FIG. 2 substitutes the measured value of the current into an independent variable of the function, and calculates the temperature value of the gas in contact with the heating resistor element 1 and the humidity detecting element 3 shown in FIG. calculate.

  The humidity detecting element 3 is not limited as long as it has a hygroscopic film and detects changes in electrical characteristics such as the dielectric constant or impedance of the hygroscopic film due to the adsorption and desorption of water molecules. Here, the humidity detection element 3 will be described by taking the capacitance type as an example. As shown in FIG. 3, the capacitance-type humidity detecting element 3 includes an insulating substrate 31, a lower electrode 32 disposed on the substrate 31, a moisture absorption film 33 disposed on the lower electrode 32, And an upper electrode 34 disposed on the moisture absorption film 33.

  The insulating substrate 31 is made of glass or ceramic. Each of the lower electrode 32 and the upper electrode 34 is made of a conductor such as gold. The upper electrode 34 may have a mesh structure in order to ensure moisture permeability to the hygroscopic film 33. The hygroscopic film 33 is made of a cellulose / ester compound such as cellulose / acetate, a polymer such as polyvinyl / alcohol, polyacryl / amide, or polyvinyl / pyrrolidone, or aluminum oxide. The relative dielectric constant of the hygroscopic film 33 is changed by the adsorption and desorption of moisture contained in the gas in contact with the hygroscopic film 33, and the capacitance of the humidity detecting element 3 is changed. Therefore, the capacitance of the humidity detection element 3 correlates with the humidity of the gas in contact with the humidity detection element 3.

The heating resistance element 1 shown in FIG. 1 is provided in contact with the lower surface of the insulating substrate 31 of the humidity detection element 3 shown in FIG. 3, for example. The amount of heat Q supplied from the heating resistor element 1 to the humidity detecting element 3 is given by the following equation (1).
^{_{Q = I H 2 R H -H}} H = V H 2 / R H -H H ··· (1)
In Equation (1), I _H is a current flowing through the heating resistor element 1, R _H is a resistance of the heating resistor element 1, V _H is a voltage applied to both ends of the heating resistor element 1, and H _H is a voltage from the heating resistor element 1 to the surroundings. The amount of heat released to the gas.

The heat release amount H _C from the humidity detecting element 3 to the surrounding gas is given by the following equation (2).
H _C = (a + bU ^1/2 ) (T _C −Ta) (2)
In the formula (2), a and b are constants, U is the wind speed of the gas in contact with the humidity detection element 3, T _C is the temperature of the humidity detection element 3, and Ta is the temperature of the gas in contact with the humidity detection element 3. Since the heat generation temperature T _H is in contact with the constant heating resistance element 1, the temperature T _C of the humidity detection element 3 is also kept constant. The humidity detection element 3 tends to have a slower response speed as the temperature of the gas in contact with the humidity detection element 3 decreases. As a cause of the slow response speed, the adsorption speed of water molecules to the moisture absorption film 33 is slow. On the other hand, for example, the humidity detection element 3 is kept at the temperature T _{C at} which the response speed of the humidity detection element 3 is the highest by the heating resistor element 1.

The amount of heat Q supplied to the humidity detection element 3 from the heating resistance element 1 having a constant heat generation temperature _H and the amount of heat release H _C from the humidity detection element 3 to the surrounding gas are expressed by the following equation (3). In an equilibrium state.
Q = H _C (3)
Therefore, the heat capacity of the humidity detection element 3 can be regarded as substantially zero. Therefore, the response speed of the humidity detection element 3 can be improved.

  The relationship storage device 401 illustrated in FIG. 2 further stores the relationship between the humidity of the gas in contact with the humidity detection element 3 illustrated in FIG. 1 and the capacitance of the humidity detection element 3 that is acquired in advance. The CPU 300 illustrated in FIG. 2 further includes a humidity specifying unit 302. The humidity specifying unit 302 reads the relationship between the humidity of the gas and the capacitance from the relationship storage device 401. Further, when receiving the measurement value of the capacitance of the humidity detection element 3 shown in FIG. 1, the humidity specifying unit 302 contacts the humidity detection element 3 based on the received measurement value of the capacitance and the relationship. Specify the humidity value of the gas. For example, the relationship read from the relationship storage device 401 shown in FIG. 2 is expressed by a function in which the humidity of the gas in contact with the humidity detection element 3 shown in FIG. 1 is a dependent variable and the capacitance of the humidity detection element 3 is an independent variable. 2, the humidity specifying unit 302 shown in FIG. 2 substitutes the measured capacitance value into the function independent variable to calculate the humidity value of the gas in contact with the humidity detecting element 3 shown in FIG.

  As described above, the dew point specifying unit 303 calculates the dew point based on the electrical characteristics of the humidity detecting element 3 correlated with the humidity of the gas and the air temperature specified by the air temperature specifying unit 301. An input device 312 and an output device 313 are further connected to the CPU 300. As the input device 312, for example, a keyboard and a pointing device such as a mouse can be used. The relationship stored in the relationship storage device 401 is input from the input device 312, for example. As the output device 313, an image display device such as a liquid crystal display and a monitor, a printer, and the like can be used. For example, the output device 313 outputs the dew point specified by the dew point specifying unit 303.

In the conventional dew point sensor, when the temperature of the gas is low, the response speed of the humidity detection element tends to be slower than the response speed of the temperature detection element. Therefore, for example, when the dew point temperature rises, if the detection temperature of the temperature detection element at the time of detecting the electrical characteristics such as the capacitance of the humidity detection element is the dew point, the dew point temperature lower than the actual dew point is It may be specified as. On the other hand, in the dew point sensor according to the first embodiment, as described above, the heat capacity of the humidity detection element 3 can be regarded as substantially zero. Is fast. Therefore, it becomes possible to specify a dew point correctly. Further, the relationship between the capacitance of the humidity detecting element 3 and the humidity can change depending on the temperature of the gas. Therefore, the conventional humidity sensor needs to acquire the relationship between the capacitance and the humidity in advance under various temperature conditions. In contrast, in the dew point sensor according to the first embodiment, the humidity detecting element 3 is kept at a constant temperature T _C. Therefore, the relationship storage device 401 may store the relationship between the capacitance and the humidity at a certain temperature T _C.

(Second Embodiment)
The dew point meter according to the second embodiment includes a voltmeter 26 as shown in FIG. 4 instead of the ammeter 25 shown in FIG. The input terminal of the voltmeter 26 is connected to the output terminal 23 of the operational amplifier 20. The output terminal of the voltmeter 26 is grounded. Thereby, the voltmeter 26 measures the output voltage of the operational amplifier 20. The output voltage of the operational amplifier 20 is proportional to the feedback current of the operational amplifier 20. Therefore, in the second embodiment, the air temperature specifying unit 301 illustrated in FIG. 2 calculates the temperature value of the gas in contact with the heating resistor element 1 illustrated in FIG. 1 based on the output voltage of the operational amplifier 20. In this case, the relationship storage device 401 stores the relationship between the temperature of the gas in contact with the heating resistor element 1 shown in FIG. 4 and the voltage measured by the voltmeter 26, which is acquired in advance. As described above, in the present disclosure, specifying the temperature of the gas in contact with the heating resistor element 1 based on the current supplied to the heating resistor element 1 is based on the voltage applied to the heating resistor element 1. It includes specifying the temperature of the gas in contact with the resistance element 1. Since the other components of the dew point meter according to the second embodiment are the same as those of the dew point meter according to the first embodiment, description thereof is omitted.

(Third embodiment)
The dew point meter according to the third embodiment further includes an npn type bipolar transistor 40 as shown in FIG. The transistor 40 has a base connected to the output terminal 23 of the operational amplifier 20, a collector connected to the power supply 50, and an emitter connected to the input terminal of the bridge circuit. Thereby, when the feedback current of the operational amplifier 20 flows as the base current, the collector current flows from the collector to the emitter. Therefore, a larger current can be supplied to the heating resistor element 1. Since the other components of the dew point meter according to the third embodiment are the same as those of the dew point meter according to the second embodiment, description thereof is omitted.

(Fourth embodiment)
In the first to third embodiments, the contact point between the first resistor element 11 and the third resistor element 13 forms an input terminal of the bridge circuit, and the heating resistor element 1 and the second resistor element. The example in which the contact point 12 and the output terminal of the bridge circuit is formed has been described. On the other hand, as shown in FIG. 6, in the dew point meter according to the fourth embodiment, the contact point between the first resistance element 11 and the third resistance element 13 is the output terminal of the bridge circuit. None, the contact point between the heating resistor element 1 and the second resistor element 12 forms the input terminal of the bridge circuit.

  In this case, the contact point of the heating resistor element 1 and the first resistor element 11 is connected to the first input terminal 121 which is the non-inverting input terminal (+) of the operational amplifier 120. Further, the contact point of the second resistance element 12 and the third resistance element 13 is connected to the second input terminal 122 which is the inverting input terminal (−) of the operational amplifier 120.

  When the resistance of the heating resistor element 1 decreases due to a decrease in the temperature of the gas in contact with the heating resistor element 1, the heating resistor element 1 connected to the first input terminal 121 that is the non-inverting input terminal (+) of the operational amplifier 120 The voltage at the contact point of the first resistance element 11 rises. Then, the feedback current supplied from the output terminal 123 of the operational amplifier 120 to the bridge circuit increases. On the other hand, when the resistance of the heating resistor element 1 rises due to an increase in the temperature of the gas in contact with the heating resistor element 1, the voltage at the contact point between the heating resistor element 1 and the first resistor element 11 falls. Then, the feedback current supplied from the output terminal 123 of the operational amplifier 120 to the bridge circuit decreases.

Also in the circuit shown in FIG. 6, in accordance with the variation of the resistance of the heating resistor element 1, because the feedback current is supplied to the heating resistor element 1, the heat producing temperature T _H of the heating resistor element 1 is kept constant. Since the other components of the dew point meter according to the fourth embodiment are the same as those of the dew point meter according to the first embodiment, description thereof will be omitted.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, embodiments, and operation techniques should be apparent to those skilled in the art. For example, in the dew point meter according to the embodiment, when the wind speed of the gas in contact with the heating resistance element 1 and the humidity detection element 3 varies, the amount of heat released from the heating resistance element 1 and the humidity detection element 3 to the gas may vary. Therefore, a sintered metal filter or the like may be provided on a pipe or the like on which the dew point meter according to the embodiment is disposed, and the wind speed of the gas in contact with the heating resistance element 1 and the humidity detection element 3 may be made constant. Or you may make constant the wind speed of the gas which touches the heating resistance element 1 and the humidity detection element 3 using constant flow valves, such as a mass flow controller. Alternatively, if the gas wind speed in contact with the heating resistor element 1 and the humidity detecting element 3 cannot be made constant, a temperature measuring element is provided separately to measure the gas temperature Ta, and the capacitance of the humidity detecting element changes. The dew point may be calculated from the relationship between the output and the temperature Ta measured by the temperature measuring element. In this case, for example, the air temperature specifying unit 301 shown in FIG. 2 specifies the air temperature Ta measured by the temperature measuring element as the temperature of the gas in contact with the humidity detecting element. Thus, it should be understood that the present invention includes various embodiments and the like not described herein.

DESCRIPTION OF SYMBOLS 1 Heat generating resistive element 2 Current supply apparatus 3 Humidity detection element 11 1st resistive element 12 2nd resistive element 13 3rd resistive element 20, 120 Operational amplifier 21, 121 1st input terminal 22, 122 2nd input terminal 23, 123 Output terminal 25 Ammeter 26 Voltmeter 31 Substrate 32 Lower electrode 33 Hygroscopic film 34 Upper electrode 40 Bipolar transistor 50 Power supply 300 Central processing unit 301 Temperature specifying unit 302 Humidity specifying unit 303 Dew point specifying unit 312 Input device 313 Output device 401 Relational storage device

Claims (24)

A heating resistance element;
A current supply device for supplying a current to the heating resistor element so that the heating temperature of the heating resistor element is constant;
A humidity detecting element that is kept at a constant temperature by contacting the heating resistor element;
An air temperature specifying unit for specifying the temperature of the gas in contact with the humidity detecting element;
A dew point sensor.   2. The dew point sensor according to claim 1, wherein the temperature specifying unit specifies a temperature of a gas in contact with the humidity detecting element based on a current supplied to the heating resistor element. A temperature measuring element;
The dew point sensor according to claim 1, wherein the air temperature specifying unit specifies the air temperature measured by the temperature measuring element as a temperature of a gas in contact with the humidity detecting element.   The dew point specifying unit that specifies a dew point based on the electrical characteristics of the humidity detection element and the temperature of the gas specified by the air temperature specifying unit is further provided. Dew point sensor.   When the resistance of the heating resistance element decreases due to a decrease in the temperature of the gas in contact with the heating resistance element, the current supply device increases the current supplied to the heating resistance element, and the heat generation due to the increase in the temperature of the gas. The dew point sensor according to claim 1, wherein when the resistance of the resistance element increases, the current supplied to the heating resistance element is decreased.   The dew point sensor according to any one of claims 1 to 5, wherein the heating resistor element forms part of a bridge circuit.   The bridge circuit includes a first resistance element connected in series to the heating resistance element, and second and third resistance elements connected in parallel to the heating resistance element and the first resistance element. The dew point sensor of Claim 6 provided. The current supply device includes an operational amplifier including a first input terminal, a second input terminal, and an output terminal;
The first input terminal is connected to the contact point between the heating resistor element and the first resistor element, and the second input terminal is connected to the contact point between the second resistor element and the third resistor element. The dew point sensor according to claim 7.   The dew point sensor according to any one of claims 1 to 8, wherein the humidity detecting element detects humidity based on a change in capacitance.   The dew point sensor according to any one of claims 1 to 8, wherein the humidity detection element detects humidity based on a change in impedance.   The dew point sensor of any one of Claims 1 thru | or 10 with which the said humidity detection element is provided with the moisture absorption film which consists of a polymer or aluminum oxide.   The dew point sensor according to any one of claims 1 to 11, wherein the humidity detecting element is maintained at a temperature at which a response speed is fastest by the heating resistance element. Supplying a current to the heating resistor element so that the heating temperature of the heating resistor element is constant;
Bringing a humidity detection element into contact with the heating resistor element and keeping the humidity detection element at a constant temperature;
Identifying the temperature of the gas in contact with the humidity sensing element;
Dew point measurement method including   The dew point measurement method according to claim 13, wherein the temperature of the gas in contact with the humidity detection element is specified based on a current supplied to the heating resistor element.   The dew point measurement method according to claim 13, wherein the temperature of the gas in contact with the humidity detection element is specified using a temperature measurement element.   The method of measuring a dew point according to any one of claims 13 to 15, further comprising specifying a dew point based on an electrical characteristic of the humidity detection element and a temperature of the specified gas.   In supplying current to the heating resistor element, when the resistance of the heating resistor element is reduced due to a decrease in the temperature of the gas in contact with the heating resistor element, the current supplied to the heating resistor element is increased. The dew point of any one of claims 13 to 16, wherein the current supplied to the heating resistor element is reduced when the resistance of the heating resistor element increases due to an increase in the temperature of the gas. Measuring method.   The dew point measurement method according to any one of claims 13 to 17, wherein the heating resistor element forms part of a bridge circuit.   The bridge circuit includes a first resistance element connected in series to the heating resistance element, and second and third resistance elements connected in parallel to the heating resistance element and the first resistance element. The method for measuring a dew point according to claim 18.   A contact point between the heating resistor element and the first resistor element is connected to a first input terminal of an operational amplifier, and a contact point between the second resistor element and the third resistor element is connected to a second input terminal of the operational amplifier. The method for measuring a dew point according to claim 19, which is connected.   The dew point measurement method according to any one of claims 13 to 20, wherein the humidity detection element detects humidity based on a change in capacitance.   The dew point measurement method according to any one of claims 13 to 20, wherein the humidity detection element detects humidity based on a change in impedance.   The dew point measurement method according to any one of claims 13 to 22, wherein the humidity detection element includes a moisture absorption film made of a polymer or aluminum oxide.   The dew point measurement method according to any one of claims 13 to 23, wherein the humidity detecting element is maintained at a temperature at which a response speed is fastest by the heating resistance element.

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