JPH11190710A - Method and sensor for detecting oxygen concentration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a concentration of oxygen gas, by detecting by means of an oxygen gas detection thermistor a temperature of an oxygen ambiance based on a reference temperature, i.e., temperature of a space not influenced by the oxygen ambiance for the purpose of temperature correction, and detecting an output difference of detected temperatures when a concentration of the other gas is known or is not affected. SOLUTION: A humidity sensor having an absolute humidity measurement thermistor is utilized. A pair of thermistors is used to measure a concentration of oxygen under a condition without being affected by the other gas or that a concentration of the other has is known. A humidity detector of the thermistor detects as a reference temperature a temperature of a space isolated from the outside. A measured absolute humidity is outputted with the use of the humidity detector and a bridge circuit used also for a temperature compensation. When the humidity sensor is used as an oxygen concentration detection sensor, the humidity detector becomes an oxygen detector and a compensator is used as an oxygen concentration detection sensor. The sensor has an oxygen detector 2 and a compensator 3 set at a holder 1 and is connected by an external wiring 6. An oxygen concentration can be detected stably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an oxygen concentration by installing it in a high-concentration oxygen atmosphere, and a sensor for detecting the oxygen concentration used for the measurement.

[0002]

2. Description of the Related Art As a method for continuously measuring the oxygen concentration in an atmosphere, for example, the oxygen in exhaust gas, a magnetic method and an electrochemical method are conventionally known.

[0003] The magnetic method utilizes an absorption force generated when paramagnetic oxygen molecules are magnetized in magnetism, and the electrochemical method utilizes an electrochemical oxidation-reduction reaction of oxygen. As the oxygen concentration meter currently used for the process, there are many magnetic systems and zirconia systems.

The magnetic type has a high selectivity and a simple structure, but has a disadvantage that it is easily affected by pressure. On the other hand, in the zirconia method, zirconia is made conductive to oxygen ions at a high temperature of several hundred degrees Celsius, and when gases having different oxygen partial pressures are introduced to both ends of zirconia, due to the difference in oxygen partial pressure, This utilizes the phenomenon that the action of an oxygen concentration cell occurs (see P447, published by Toyo Keizai Shimposha, New Product Edition, Toyo Keizai Shinposha, a new product dictionary of modern products).

[0005]

The above-mentioned oximeter has the following features.
The oxygen concentration is measured by selectively extracting oxygen gas from a mixed gas containing various components such as exhaust gas.

On the other hand, as a so-called gas sensor, there are a contact combustion type using a platinum wire as a catalyst and a semiconductor type gas sensor utilizing a change in the electric resistance of a semiconductor due to a gas. Although such a gas sensor can be used easily, it has no selectivity for the detection gas and detects the concentration of the total amount of gas containing various components. For this reason, when used for gas leak detection or fire detection of city gas or propane gas, the power can be exhibited.

An object of the present invention is to provide a method for measuring the oxygen concentration under a specific use by using a so-called gas sensor having no selectivity for a detection gas and an oxygen concentration detection sensor used in the method. .

[0008]

In order to achieve the above object, the present invention provides an oxygen concentration measuring method for measuring the oxygen concentration of an atmosphere using a pair of thermistors. Is for detecting oxygen gas, the other thermistor is for temperature compensation, and is not affected by other gas, or the temperature of oxygen atmosphere is supplied to the thermistor for oxygen gas detection under the condition that the concentration of other gas is known. , The temperature compensating thermistor detects the temperature of the space unaffected by the oxygen atmosphere as a reference temperature, and outputs the oxygen gas concentration as a positive voltage change from the output difference between the detected temperatures of both thermistors.

An oxygen concentration detection sensor having a pair of thermistors, wherein one of the pair of thermistors is for detecting oxygen gas and the other thermistor is for detecting oxygen gas.
For temperature compensation, both thermistors are built into a bridge circuit and generate heat, and the oxygen gas detection thermistor detects the temperature change in the environment that is in contact with the oxygen gas atmosphere and occurs in proportion to the oxygen gas concentration. The temperature compensating thermistor detects the temperature of a space isolated from the environment as a reference temperature.

An oxygen concentration detection sensor having an oxygen detector and a temperature compensator on a holder, wherein the oxygen detector and the temperature compensator each house a thermistor in a cap attached to the holder. One of the caps is hermetically sealed, the other cap has a small hole that communicates with the outside air, the oxygen detector contains a thermistor in the cap that communicates with the outside air, The lead wire of the thermistor is drawn out through the holder, the temperature compensator accommodates the thermistor in a hermetically sealed cap, and the lead wire of the thermistor is drawn out through the holder to detect oxygen. The vessel and the cap of the temperature compensator are arranged close to each other.

Further, the oxygen detector and the temperature compensator are housed in the explosion-proof structure.

The present invention provides an absolute humidity sensor having a pair of thermistors that has been used for measuring absolute humidity, to provide an oxygen concentration sensor under conditions that are unaffected by other gases or whose concentrations are known. It is used for the measurement of The absolute humidity sensor has the following configuration. That is, each having a pair of thermistors housed in a hollow case or cap, the case or cap forms one and the other chamber separated or isolated from each other, one chamber is hermetically sealed, the other chamber Has a hole that communicates with the outside air, the pair of thermistors are for humidity sensing and temperature compensation, and the humidity sensing unit is a case where the thermistor is housed in a chamber or a cap that communicates with the outside air. The temperature compensator detects the temperature in a space isolated from the outside as a reference temperature, in which the temperature compensator contains a thermistor in another room of an airtightly sealed case or cap. Is what you do.
The measured value of the absolute humidity is output using a bridge circuit including a humidity sensor and a temperature compensator. When the absolute humidity sensor is used as an oxygen concentration detection sensor for measuring oxygen concentration, the humidity sensor is an oxygen detector, and the temperature compensator is also a temperature compensator when used as an oxygen concentration detection sensor. Is unchanged.

An embodiment of the oxygen concentration detecting sensor used in the present invention will be described below, but the oxygen concentration detecting sensor used in the present invention is not limited to the following embodiment.

In FIG. 1, an oxygen concentration detecting sensor according to the present invention comprises an oxygen detector 2 and a temperature compensator 3 in a holder 1.
And the oxygen detector 2 and the temperature compensator 3 are covered with a hood 4 if necessary, and a cover 5 is attached to the back surface of the holder 1. It is electrically connected to the temperature compensator 3.

In the present invention, as shown in FIG. 2, the oxygen detector 2 and the temperature compensator 3 contain a thermistor 8 in a cap 7, and the cap 7 is locked by a base 9. , The base 9 is provided with a pair of lead wires 10, 10. In this embodiment, a glass-sealed microchip thermistor is used as the thermistor 8. The thermistor 8 has a pair of platinum wires as terminal wires 11, and the platinum wires are drawn out in opposite directions from both ends of the thermistor 8, and each terminal wire 11 is a pair held at both ends in the longitudinal direction of the base 9. Are connected to the lead wires 10, 10, respectively.

The cap 7 is a substantially rectangular parallelepiped hollow container having curved edges at both ends, and has an opening on the lower surface. The opening edge is engaged with the base 9 to seal the thermistor 8 in the cap 7. It is stopped.

The cap 7 used for the oxygen detector 2 includes:
A small hole 12 is opened in a part thereof to communicate the inside of the cap 7 with the outside air. However, the cap 7 used for the temperature compensator has no small hole and is hermetically sealed by the base 9. Although it is convenient for the holder 1 to be welded to the cap, it is desirable to use a metal plate having excellent thermal conductivity as much as possible. A pair of insertion holes 13 into which the lead wires 10 and 10 of the oxygen detector 2 and the temperature compensator 3 are to be inserted are opened close to each other on the plate surface of the holder 1, and the oxygen detector 2 and the temperature compensator Reference numerals 3 denote respective lead wires inserted into the insertion holes 13 and arranged close to each other, and are fixed to the plate surface of the holder 1 by welding.

The oxygen detector 2 and the temperature compensator 3
Is that the lower surface of each base 9 is welded to the plate surface of the holder 1, but when the weldability between the base 9 and the plate surface of the holder 1 is poor, the plate surface of the holder to which the base is to be welded is Hit the part with a punch etc., and the protrusion 1 due to the dent
4 is added to increase the joining strength by welding. Spot welding is sufficient, but if the entire circumference of the base 9 is seam-welded, it can be more reliably fixed.

FIG. 3 shows the lead wires 10 and 1 of the oxygen detector 2 and the temperature compensator 3 drawn out from the lower surface of the holder 1.
0,... And connection with the external wiring 15 having an output line and a common line.

In the present invention, each lead wire 10 of the oxygen detector 2 and the temperature compensator 3 is connected to the external wiring 15 via a lead frame 16. FIG.
2A, the oxygen detector 2 and the temperature compensator 3 each have two lead wires 10 on the back surface of the holder 1.
(Hereinafter, distinguished as 10a, 10b, 10c, and 10d) are drawn out, each one being an output terminal and the other being a common terminal.

When the holder 1 on which the oxygen detector 2 and the temperature compensator 3 are mounted is carried into the carrying line of the lead frame 16, the holder 1 is moved in the carrying direction of the line indicated by the arrow.
When the directions of the oxygen detector 2 and the temperature compensator 3 are inclined by about 45 °, the three segments 16a to 16
16c, one lead wire 10a, 2
One lead wire 10b, 10c and one lead wire 10d correspond to each other.

In FIG. 3B, each of the lead wires 10a to 10a
The terminal of 10d is bent at a right angle in the direction of the segments 16a to 16c, and the bent portion is welded to the corresponding segment, and each segment 16a to 16c is separated from the tie bar 17 at its base as shown in FIG. And then external wiring 1
The crimping elements of the fifth output terminal wires 15a and 15b and the common terminal wire 15c are fixed to the respective segments 16a to 16c by welding or ultrasonic bonding.

That is, in FIG. 3C, three segments 16a, 16b and 16c are sequentially arranged in the first and second stages.
In the third and third stages, for example, the first output terminal line 15a of the external wiring 15 is connected to the first stage segment 16a to which one lead wire 10a serving as the output terminal of the oxygen detector 2 is attached. The common terminal line 15b of the external wiring 15 is connected to the second stage segment 16b to which the two lead wires 10b and 10c serving as common terminals of the oxygen detector 2 and the temperature compensator 3 are attached. The second output terminal line 15c of the external wiring 15 is connected to the third segment 16c to which one lead wire 10d serving as the output terminal 3 is attached.

Next, as shown in FIG. 4, a cover 5 is provided on the back side so as to cover the connection between the lead wire 10 and the external wiring 15.
Is attached to complete the oxygen sensor. However, as shown in FIG. 5, a hood 4 may be attached to the upper surface side of the holder 1 so as to cover the oxygen detector 2 and the temperature compensator 3. On the upper surface of the hood 4, a number of small holes 18, 18,... Are opened to maintain air permeability inside and outside the hood.

In the above embodiment, the thermistor 8
When the combination of the oxygen detector 2 and the temperature compensator 3 is installed on the holder 1, the thermistor 8 of the oxygen detector 2 is used.
And the thermistor 8 of the temperature compensator 3 can be arranged very close to each other, so that the installation environments of the thermistors 8 and 8 can be matched, and the measurement accuracy can be improved. In addition, since the oxygen detector 2 and the temperature compensator 3 are separate units, the combination of the two units can be freely selected and thermistors 8, 8
Characteristics can be matched.

FIG. 6 shows a circuit for detecting the oxygen concentration. In the figure, an oxygen detector 2 and a temperature compensator 3 and a resistor R1,
A bridge circuit 18 is formed by combining R2 and a control device 19 is connected to an output terminal of the bridge circuit 18 to detect a change in output characteristics inherent to oxygen gas. Thermistor-type absolute humidity sensor used as the oxygen concentration detection sensor of the present invention has a positive output change with respect to air when detecting hydrogen gas, methane gas, ammonia gas, etc., as shown in FIG.
Freon gas, argon gas and carbon dioxide gas have negative output changes. When the atmospheric pressure of the environment where the sensor is placed changes, the heat dissipation constant of the sensor changes, and the output changes. However, the amount of change is a change of about 10 mPascal and a change of 0.01 mV level, which is not a problem in a normal living area. The control device stores the output change characteristic of oxygen and measures the oxygen concentration of the environment from the value of the output voltage obtained by the detection circuit. Bridge circuit 18
Is adjusted by the resistor VR, but the output of the bridge circuit 18 is adjusted to 0 V in the air containing no oxygen.

The oxygen concentration detecting sensor according to the present invention is used for measuring the oxygen concentration of an oxygen-enriched air producing machine (concentrator) shown in FIG. 8, for example.
Converts the outside air taken in from the air inlet 21 into the oxygen concentrator 2
2 and passed through a gas separation membrane to increase the oxygen concentration in the air, store the resulting oxygen-enriched air in a compression storage container 23, take out the oxygen-enriched air when necessary, and remove the humidification filter 24. Through the oxygen outlet 25 via
The oxygen / oxygen concentration detection sensor 31 according to the present invention is installed in an air supply line 26 for oxygen-enriched air from the compression storage container 23 to the humidification filter 24, and is provided in the oxygen-enriched air sent from the oxygen outlet 25. Is used to measure the oxygen concentration of the sample.

(Examples) Examples of the present invention will be described below.
When using the oxygen concentration detection sensor of the present invention in an oxygen-enriched air production machine, the following tests examined the adaptability of oxygen concentration detection.

1. Test Method (1) Using a humidity generator, output characteristics are measured while changing the mixture ratio of nitrogen gas / oxygen gas. The number of samples was five, and a glass type absolute humidity sensor (04AHN2-GR-0600) manufactured by Oizumi Seisakusho was used as an oxygen concentration detection sensor. FIG. 9 shows the apparatus used for the test. This device connects an oxygen cylinder 27 and a nitrogen cylinder 28 to a mixer 29,
The mixed gas of nitrogen gas / oxygen gas is introduced into the humidity generator 30, the oxygen concentration is measured by the oxygen concentration detection sensor 31, and the data is recorded on the recorder 32.

The nitrogen is dry nitrogen (99.99%), and the oxygen is medical oxygen (99.9%). The flow rate is as shown in Table 1 below. However, it is 5 liters based on the flow meter of the humidity generator. Gas temperature control utilizes the controller of the humidity generator.

[0031]

[Table 1] * The TOTAL flow rate was set to 5 liters, and the flow rate from the mixer to the generator was used as a reference.

(2) Measurement temperature is +5, 10, 20, 3
0, 40, 60, 80, and 100 ° C. In addition, 40 ° C
The above measurement was performed by correcting the output zero point of the bridge circuit for each temperature at which only 0%, 50%, and 100% were measured.

(3) Considering the actual use condition of the sensor,
Air cylinder 1 because it is necessary to measure the output from the atmosphere
Zero the output with 0 liter and 100% nitrogen: 1
A measurement of 0 liter, oxygen: 100%: 10 liter was also performed.

2. Measurement results (1) Tables 2 to 10 show the relationship between oxygen concentration and output at each temperature. Table 11 shows the basic characteristics of the sensors used in this test with respect to humidity. In addition, + 10 ° C → + 40 ° C (3
The temperature characteristics of dry air (0 ° C. width) and oxygen 100% are also shown.

(2) FIG. 10 shows the oxygen concentration and the sensor output characteristics.
Shown in The oxygen concentration and the output have a substantially linear relationship. FIG. 11 shows only 10 ° C., 20 ° C., and 30 ° C.

(3) After zero-adjustment by flowing 10 liters of dry air at each of 10 ° C., 20 ° C., and 30 ° C., nitrogen 100%: 10 liters, oxygen 100%: 10 liters
FIG. 12 shows a measurement result of the sensor output which is stabilized by flowing liters sequentially. The approximate expression at 20 ° C. is as shown in FIG.

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

[0042]

[Table 7]

[0043]

[Table 8]

[0044]

[Table 9]

[0045]

[Table 10]

[0046]

[Table 11]

3. Discussion (1) Sensor output from the atmosphere (oxygen: 21%) is about 15
A large output is obtained as compared with mV (at 20 ° C., O2: 100%). (2) The variation in sensor output between five samples (10 to 30 ° C.) is about 0.76 mV. (3) The temperature characteristic at 10 ° C. to 40 ° C. in 100% oxygen is about 1 mV. (4) There is no difference in sensor output between 100% oxygen and flow rates of 5 liters and 10 liters. Further, even if the amount is changed every 1 liter from 1 liter to 10 liters, it is stabilized after only 2 to 3 minutes only by an instantaneous change. From the above results, it was found that the oxygen concentration can be detected by AHS-GR using the thermistor type absolute humidity sensor. It has been demonstrated that dry oxygen can be used as an oxygen concentration detection sensor.

In the above examples, the measurement was performed with nitrogen 100% as a reference (0%). As a result, an output of about 18 mV is obtained. 6 mV of humidity output (40 ° C, 35
g / m3), three times the output is obtained. This is considered to be easy to use as an oxygen concentration detection sensor. However, actually, the output from the atmosphere is detected. The amount of oxygen in the atmosphere is 20.
93% (volume percentage 23.01%) and the output is 15m
About V.

On the other hand, + 10 → + 40 ° C.
Temperature characteristics at 100% oxygen in a 30 ° C range are about ±
1 mV. Since the sensor has a temperature characteristic of 0.2% with a temperature characteristic of + 10 → + 40 ° C. at a humidity of 0% RH, the output is large,
Temperature characteristics have also increased.

The output of the oxygen concentration detection sensor is about 15 mV (O ₂ 10
0%) and the value is large, so that the temperature characteristic is ± 2 m
Even if there is about V, it is considered that there is no particular problem if the bridge adjustment is performed for each sensor.

The following points may be considered as problems to be considered when actually using the apparatus. That is, an error occurs in the case of oxygen containing water. Since a bridge circuit is used, adjustment to a standard at the time of shipment is required. Weak to vibration. It is necessary to correct the oxygen concentration for the temperature. Explosion proof structure is required. (For self-heating at 200 ° C.).

The oxygen-enriched air producing machine (concentrator) produces oxygen using zeolite for the gas separation membrane, and there is no problem in that all becomes dry oxygen. Has a track record as a humidity sensor.
Can be processed in a circuit. As shown in FIG. 6, a wire mesh 32 of # 100 mesh is used for an explosion-proof structure, and an oxygen detector of a sensor, a temperature compensator, especially an oxygen detector can be stored in the wire mesh 32 to prevent explosion.

[0053]

As is apparent from the above embodiments, a thermistor type humidity sensor is used as an oxygen concentration detection sensor, and is not affected by other gases or under the condition that the concentration of other gases is known. Can stably measure the concentration of oxygen gas from a low concentration to a high concentration. In particular, a sensor that can continuously detect high-concentration oxygen stably has never been considered. The present invention relates to an enriched oxygen production apparatus (concentrator)
Besides, it can be widely used for measurement of oxygen concentration in environments that are clearly formed by oxygen atmosphere such as incubators and respirators. However, the sensor of the present invention is installed in an environment where the oxygen concentration is a problem, for example, in a tunnel, in a place such as an underground parking lot, and compares the normal value with the current measured value to cause an abnormal situation. It can also be used as a sensor for determining whether or not.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram of an oxygen detector and a temperature compensator.

FIG. 3 is a diagram showing a procedure for connecting a lead wire to an external wiring.

FIG. 4A is a sectional side view showing an embodiment of the present invention, and FIG. 4B is a plan view thereof.

FIG. 5 is a cross-sectional side view showing another embodiment.

FIG. 6 is a diagram showing a circuit for detecting an oxygen concentration.

FIG. 7 is a diagram showing changes in output characteristics with respect to gas.

FIG. 8 is a diagram showing a configuration of an oxygen-enriched air producing machine.

FIG. 9 is a configuration diagram of a test apparatus.

FIG. 10 shows oxygen concentration and sensor output characteristics (+ 5 ° C. to 100
FIG.

FIG. 11 shows oxygen concentration and sensor output characteristics (+ 10 ° C. to +3).
0 ° C.).

FIG. 12 shows oxygen concentration and sensor output characteristics (+ 10 ° C. to 30 ° C.).
FIG.

FIG. 13 is a diagram showing an oxygen concentration and a sensor output characteristic (+ 20 ° C.) by an approximate expression.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Holder 2 Oxygen detector 3 Temperature compensator 4 Hood 5 Cover 6 External wiring 7 Cap 8 Thermistor 9 Base 10, 10a-10d Lead wire 11 Terminal wire 12 Small hole 13 Insertion hole 14 Projection 15 External wiring 16 Lead frame 16a-16c Segment 17 Tie bar 18 Bridge circuit 19 Controller 20 Oxygen-enriched air producing machine 21 Air intake 22 Oxygen concentrator 23 Compression storage container 24 Humidifying filter 25 Oxygen outlet 26 Air supply line 27 Oxygen cylinder 28 Nitrogen cylinder 29 Mixer 30 Humidity Generator 31 Oxygen sensor 32 Recorder 33 Wire mesh

Claims (4)

[Claims] 1. An oxygen concentration measuring method for measuring an oxygen concentration in an atmosphere using a pair of thermistors, wherein one of the thermistors is for detecting oxygen gas, the other thermistor is for temperature compensation, and the other thermistor is for the purpose of temperature compensation. Or the oxygen gas detection thermistor detects the temperature of the oxygen atmosphere under conditions where the concentration of other gases is not known or the temperature of the space not affected by the oxygen atmosphere is detected by the temperature compensation thermistor. An oxygen concentration measuring method, wherein the oxygen gas concentration is detected as a reference temperature and the oxygen gas concentration is output as a positive voltage change from the output difference between the detected temperatures of both thermistors. 2. An oxygen concentration detection sensor having a pair of thermistors, wherein one of the pair of thermistors is for detecting oxygen gas, the other thermistor is for temperature compensation, and both thermistors are a bridge. It is built into the circuit and generates heat, and the thermistor for oxygen gas detection touches the oxygen gas atmosphere,
Oxygen concentration detection for detecting a temperature change in the environment occurring in proportion to the oxygen gas concentration, wherein the temperature compensating thermistor detects the temperature of a space isolated from the environment as a reference temperature. Sensor. 3. An oxygen concentration detection sensor having an oxygen detector and a temperature compensator on a holder, wherein the oxygen detector and the temperature compensator each house a thermistor in a cap attached to the holder. One cap is hermetically sealed and the other cap is
The oxygen detector has a small hole that communicates with the outside air.The oxygen detector contains a thermistor in a cap that communicates with the outside air.The lead wire of the thermistor is drawn out through the holder, and the temperature compensator is airtight. The thermistor is housed in a sealed cap, the lead wire of the thermistor is drawn out through the holder, and the oxygen detector and the cap of the temperature compensator are arranged close to each other. An oxygen concentration detection sensor characterized by the above-mentioned. 4. The oxygen concentration detection sensor according to claim 3, wherein the oxygen detector and the temperature compensator are stored in an explosion-proof structure.