JP2005308404A - Hydrogen detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen detector for accurately detecting the concentration of gaseous hydrogen contained in gas by using a hydrogen storage alloy highly selective about hydrogen. <P>SOLUTION: This hydrogen detector 11 is equipped with a hydrogen absorbent material 12 for reversibly absorbing/discharging hydrogen, a temperature detection means 15 for detecting the temperature of the absorbent material, and a weight change detection means 14 with electrodes 13a and 13b disposed on both ends thereof in their thickness direction for detecting a weight change corresponding to the absorption/discharge of hydrogen of the absorbent material based on a frequency change of an AC current flowing through the electrodes with the absorbent material kept at a constant temperature. The detector 11 is characterized in that one 13a of the electrodes is disposed between the absorbent material 12 and the detection means 14, and the absorbent material 12 is heated by passing a DC current through one 13a of the electrodes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen detector that detects a hydrogen concentration in a gas.

Conventionally, as a hydrogen sensor that detects hydrogen using a hydrogen storage alloy, the hydrogen storage alloy is attached to one surface of the substrate and a crystal unit is attached to the other surface, and the weight when the hydrogen storage alloy stores hydrogen. There is known a hydrogen gas sensor (see, for example, Patent Document 1) that detects a frequency fluctuation of a crystal resonator caused by an increase and detects a hydrogen storage amount based on the magnitude of the detected frequency fluctuation. In this hydrogen gas sensor, the hydrogen concentration can be detected more accurately as the rate of change in weight increase according to the hydrogen storage amount is larger.
JP-A-2-110341

By the way, when the hydrogen storage alloy is used as a hydrogen sensor, it is necessary to keep the hydrogen storage alloy at a constant temperature. At this time, if the crystal resonator is incorporated in the heater, the accuracy of measuring the weight change amount of the hydrogen storage alloy by the crystal resonator is deteriorated due to an increase in the weight of the object to be vibrated. Therefore, in order not to increase the weight of the object to be vibrated, the heater is disposed separately below the crystal unit to indirectly heat the crystal unit. However, by indirectly heating the crystal unit with a heater, it becomes impossible to accurately control the temperature of the crystal unit.
The present invention has been made in view of the above circumstances, and provides a hydrogen detector capable of accurately detecting the concentration of hydrogen gas contained in a gas by using a hydrogen storage alloy having high selectivity to hydrogen. The purpose is to do.

The present invention employs the following means in order to solve the above problems. That is, a hydrogen detection device according to the invention described in claim 1 (for example, the hydrogen detection device 11 in the embodiment) includes a hydrogen absorbing material (for example, the detection element 12 in the embodiment) that reversibly absorbs and releases hydrogen, and the hydrogen. Temperature detecting means for detecting the temperature of the absorbent material (for example, the temperature sensor 15 in the embodiment) and electrodes (for example, the electrodes 13a and 13b in the embodiment) are arranged at both ends in the thickness direction to keep the hydrogen absorbent material at a constant temperature. Weight change detecting means (for example, the quartz crystal resonator 14 in the embodiment) for detecting a weight change according to the absorption and release of hydrogen of the hydrogen absorbing material based on the frequency change of the alternating current flowing through the electrodes in the state of being One of the electrodes is disposed between the hydrogen absorbing material and the weight change detecting means, and the hydrogen absorption is performed by applying a direct current to one of the electrodes. Characterized by heating the.
According to the present invention, one of the electrodes is disposed between the hydrogen absorbing material and the weight change detecting means, and one of the electrodes is heated by passing a direct current through the one of the electrodes, and the temperature is reduced to hydrogen. The hydrogen absorbing material is heated by being directly transmitted to the absorbing material. Thereby, the thermal efficiency at the time of transmission to the hydrogen absorbing material is improved, and temperature adjustment with excellent responsiveness is possible.
Further, since the hydrogen absorbing material is heated by one of the electrodes, there is no need to newly install a heater for heating the hydrogen absorbing material.
Furthermore, since one of the electrodes itself functions as a heater, it does not increase the weight of the weight change detection means, and therefore prevents deterioration in accuracy of measuring the weight change amount of the hydrogen absorbent by the weight change detection means. It becomes.

The hydrogen detector according to claim 2 is characterized in that the weight change detecting means is a crystal resonator.
According to the present invention, it is possible to accurately detect a change in weight that occurs in the hydrogen absorbing material in response to absorption and release of hydrogen as a frequency variation that occurs in the crystal resonator.

According to the hydrogen detector according to the first aspect of the present invention, temperature adjustment with excellent responsiveness is possible, so that the temperature control of the hydrogen absorbent can be easily performed. Moreover, since it is not necessary to newly install a heater for heating the hydrogen absorbing material, the number of components provided in the hydrogen detection device can be reduced. Furthermore, since the weight of the weight change detecting means does not increase, it is possible to prevent deterioration in accuracy of measuring the weight change amount of the hydrogen absorbent by the weight change detecting means, and the concentration of hydrogen gas contained in the gas. Can be detected with high accuracy.
In addition, according to the hydrogen detector according to the second aspect of the present invention, it is possible to accurately detect a change in weight generated in the hydrogen absorbent material in accordance with absorption and release of hydrogen.

Hereinafter, an embodiment of the hydrogen detector of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, for example, the hydrogen detection apparatus 11 according to the present embodiment includes a detection element 12 as a hydrogen absorbing material and a quartz crystal resonator as weight change detection means sandwiched from both sides by a pair of electrodes 13a and 13b. 14, a temperature sensor 15 as temperature detection means, and a control device 20.
And the inside of the box-shaped housing | casing 21 which has the opening part into which inspection object gas is introduce | transduced is formed as a gas detection chamber, and the detection element 12 and a pair of electrode 13a, 13b are provided in this housing | casing 21 inside. The crystal resonator 14 and the temperature sensor 15 are accommodated, and the control device 20 is disposed outside the housing 21.

Detecting element 12 is a flat plate made of a hydrogen storage alloy having a temperature change characteristic of a given hydrogen storage pressure, such as AB ₅ type hydrogen storage alloy having a fine space penetrates therein. In this detection element 12, the hydrogen storage pressure (for example, 0.005 atm) at a predetermined operating temperature (for example, 100 ° C.) is determined based on the relationship between the hydrogen partial pressure and the hydrogen concentration in the atmosphere. (For example, a hydrogen partial pressure of 0.005 atm corresponds to a hydrogen concentration of 0.5%).
Further, the detection element 12 changes in a state that occurs when hydrogen is occluded (for example, volume expansion, heat generation, weight increase, etc.) or changes in a state that occurs when the occluded hydrogen is released (for example, volume contraction, endotherm, (Weight reduction, etc.) is set to be a predetermined state change. For example, when the detection element 12 occludes hydrogen when the hydrogen partial pressure of the inspection target gas is equal to or higher than a predetermined partial pressure (for example, 0.005 atm), the weight increases by an increment Δm.
The detection element 12 is bonded onto the surface of the one electrode 13a by an appropriate bonding method having heat resistance such as sintering, pressure bonding, thermal spraying, and adhesion.

The temperature sensor 15 is provided above the detection element 12 and is energized via the control device 20. The control device 20 detects the temperature of the detection element 12 by detecting a change in the resistance value according to the temperature change of the temperature sensor 15.
The substantially plate-shaped crystal resonator 14 is sandwiched from both sides in the thickness direction by a pair of electrodes 13a and 13b for exciting the crystal resonator 14, that is, one electrode 13a is connected to the detection element 12 and the crystal vibration. It is arranged between the child 14. In this crystal resonator 14, by applying an alternating current to the electrodes 13 a and 13 b, a change in the resonance frequency of the crystal resonator 14 according to a change in the state of the detection element 12 is transmitted as an electrical signal via the pair of electrodes 13 a and 13 b. To the control device 20.

  Conductive wires 23 and 24 are attached to both ends of one electrode 13a, respectively. The conducting wires 23 and 24 are connected to an external power source P so that a direct current can be applied. The external power source P is connected to the control device 20 so that the temperature of the detection element 12 bonded on the surface of the one electrode 13a can be controlled.

The hydrogen detection device 11 according to the present embodiment has the above-described configuration. Next, the operation of the hydrogen detection device 11 will be described.
The hydrogen storage alloy constituting the detection element 12 suppresses the storage of hydrogen when the hydrogen partial pressure of the atmosphere inside the casing 21 serving as the gas detection chamber is lower than each hydrogen storage pressure corresponding to the temperature, and the hydrogen partial pressure is reduced. Starts to store hydrogen when each hydrogen storage pressure according to the temperature is reached. Since the hydrogen storage alloy increases in weight when storing hydrogen, a change in the resonance frequency of the crystal resonator 14 is detected by the control device 20.
In other words, when the temperature of the detection element 12 is controlled to be a predetermined operating temperature, the resonance of the crystal resonator 14 to be detected depends on whether or not the hydrogen storage alloy constituting the detection element 12 stores hydrogen. The frequency is different, and based on the change in the resonance frequency, it is possible to detect in which concentration range the hydrogen concentration of the atmosphere is.

  For example, in a state where the temperature of the detection element 12 is maintained at a predetermined operating temperature (for example, 100 ° C.), the hydrogen partial pressure of the atmosphere satisfies the hydrogen storage pressure (for example, 0.005 atm) of the detection element 12. In the case where there is not, the detection element 12 does not occlude hydrogen and the change in the weight of the hydrogen detection device 11 is zero, so the change in the resonance frequency of the crystal unit 14 is zero, and the hydrogen concentration in the atmosphere is 0.5. Detected to be less than%.

  And when the hydrogen partial pressure of atmosphere is more than the hydrogen occlusion pressure (for example, 0.005 atm) of the detection element 12, the detection element 12 occludes hydrogen and the weight of the hydrogen detection apparatus 11 increases by increment (DELTA) m. By detecting a change in the resonance frequency of the crystal resonator 14 according to the increase in weight, it is detected that the hydrogen concentration in the atmosphere is 0.5% or more.

  Moreover, in order to maintain the state where the temperature of the detection element 12 is maintained at a predetermined operating temperature (for example, 100 ° C. or the like) using one electrode 13a as a heater, the detection element 12 is used using the control device 20. To control the temperature. That is, as shown in the flowchart of FIG. 2, the temperature of the detection element 12 is detected by a temperature sensor to determine whether or not the temperature is below a predetermined operating temperature (for example, 100 ° C.) (step S11). When the temperature of the element 12 falls below a predetermined operating temperature (for example, 100 ° C. or the like) (“Yes” in step S11), the temperature of the detection element 12 reaches a predetermined operating temperature (for example, 100 ° C. or the like). The external power source P is operated until one electrode 13a is heated (step S12), and when the temperature of the detection element 12 has already reached a predetermined operating temperature (for example, 100 ° C.) (step S12). In S11, “No”), the operation of the external power supply P is stopped (step S13).

  Thereafter, it is determined whether or not the temperature of the detection element 12 is maintained at a predetermined operating temperature (for example, 100 ° C. or the like) (step S14), and the temperature of the detection element 12 is maintained (step S14). In S14, “Yes”), the process returns to step S11, and the temperature of the detection element 12 is detected by the temperature sensor to determine whether or not the temperature is lower than a predetermined operating temperature (for example, 100 ° C. or the like). When it is no longer necessary to maintain the temperature of the detection element 12 at a predetermined operating temperature (for example, 100 ° C. or the like) such as when the operation of the hydrogen detector 11 is stopped (“No” in step S14) ]), This flow is finished.

  As described above, according to the hydrogen detection device 11 of the present invention, one electrode 13a is arranged between the detection element 12 and the crystal resonator 14, and a DC current is supplied to the one electrode 13a from the external power source P. By flowing, one of the electrodes 13a is heated, the temperature is directly transmitted to the detection element 12, and the detection element 12 is heated. Thereby, the thermal efficiency at the time of transmission to the detection element 12 is improved, and when the heating of the one electrode 13a is adjusted, the temperature of the detection element 12 is quickly adjusted. That is, since temperature adjustment with excellent responsiveness is possible, temperature management of the detection element 12 can be easily performed.

Further, since the detection element 12 is heated by the one electrode 13a, it is not necessary to newly install a heater for heating the detection element 12, such as a Peltier element and a heat transfer body. Therefore, the number of components provided in the hydrogen detector 11 can be reduced.
Moreover, since one electrode 13a itself functions as a heater, an increase in the weight of the crystal unit 14 due to the incorporation of the heater in the crystal unit 14 can be avoided. Therefore, it is possible to prevent deterioration in accuracy of measuring the weight change amount of the detection element 12 due to an increase in the weight of the crystal resonator 14. Therefore, the concentration of hydrogen gas contained in the gas can be detected with high accuracy.
Further, by using the crystal resonator 14 to detect the weight change, the weight change generated in the detection element 12 in accordance with the absorption and release of hydrogen can be accurately detected as the frequency fluctuation generated in the crystal resonator 14. .

In the embodiment described above, the detection element 12 is not limited to be provided on the surface of the one electrode 13a, but may be provided on the surface of the other electrode 13b.
In the above-described embodiment, the temperature sensor 15 may be provided at any position as long as the temperature of the detection element 12 can be measured. Further, the temperature sensor does not need to be installed on the detection element 12 and may be arranged at a position separated from the detection element 12 as long as the temperature of the detection element 12 can be measured.
In the embodiment described above, the temperature control method for one electrode 13a is so-called ON-OFF control for turning on or off the external power supply P. However, the temperature of the one electrode 13a is controlled by chopper, PID control, or the like. Any temperature control method may be used as long as the control is effective for adjustment.

It is a block diagram of the hydrogen detection apparatus which concerns on one Embodiment of this invention. It is a flowchart which controls the temperature of one electrode of the hydrogen detection apparatus which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Hydrogen detection apparatus 12 Detection element (hydrogen absorption material) 13a, 13b Electrode 14 Crystal oscillator (weight change detection means) 15 Temperature sensor (temperature detection means)

Claims (2)

A hydrogen absorber that reversibly absorbs and releases hydrogen;
Temperature detecting means for detecting the temperature of the hydrogen absorbing material;
Based on the change in frequency of the alternating current flowing through the electrodes with the electrodes disposed at both ends in the thickness direction and the hydrogen absorber being held at a constant temperature, the hydrogen absorber absorbs and releases the weight according to the change in weight. A weight change detecting means for detecting,
One of said electrodes is arrange | positioned between the said hydrogen absorption material and the said weight change detection means, The said hydrogen absorption material is heated by sending a direct current through one of the said electrodes, The hydrogen detection apparatus characterized by the above-mentioned. The hydrogen detection apparatus according to claim 1, wherein the weight change detection means is a crystal resonator.

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