JPH1073551A - Co detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the prevention of errors and the increase in CO sensitivity in the high-temperature, high-humidity atmosphere by setting the period, the width and the semiconductor temperature in pulsating heating for a metal oxide semiconductor and the sampling period after the end of the heating in the respective ranges. SOLUTION: After the end of pulse heating to a metal oxide semiconductor, the temperature dependency of a CO sensor becomes small during the period of 100-250 milliseconds, and the relatively high sensitivity for CO is obtained. Then, the output of the CO sensor is sampled during this period and the effect of humidity is decreased. Furthermore, the temperature dependency is decreased when the width of the heating pulse is increased, the pulse period is shortened or the maximum temperature of the metal oxide semiconductor at the pulse heating is increased. Then, the heating pulse width is set at 10-30 milliseconds, and the pulse period is set at 200-500 milliseconds. Furthermore, the maximum temperature of the metal oxide semiconductor in pulse heating is set at 320 deg.C or more. Thus, the temperature dependency of the device is decreased, and the prevention of the erroneous report in the high-temperature, high-humidity environment and the increase in CO sensitivity can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CO detecting apparatus for detecting a CO by heating a metal oxide semiconductor in a pulsed manner.

[0002]

2. Description of the Related Art The applicant has developed a CO sensor in which a heater is provided on an alumina substrate via a heat insulating film, and an insulating film and a SnO2 film are stacked on the heater. The CO sensor is provided with a filter of activated carbon or the like, and the heater generates pulses of heat at a rate of, for example, about 10 msec per second. SnO2 for sensor material
Is added with Pd or Pt (JP-A-5-340910). In this case, the power consumption of the CO sensor becomes extremely small, and a CO detection device with low power consumption is obtained.

[0003] However, the inventors have found that this CO detection device has a remarkable humidity dependency, and in an extreme case, an alarm is generated despite the absence of CO in a high-temperature and high-humidity atmosphere.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the humidity dependency of a CO detector to prevent false alarms in a high-temperature, high-humidity atmosphere.
Another object of the present invention is to increase the CO sensitivity in a high humidity atmosphere.

[0005]

According to the present invention, there is provided a CO detecting apparatus in which a metal oxide semiconductor having a resistance value changed by a gas is heated in a pulsed manner to detect CO, and 80 to 400 ms after the completion of the pulse heating. A means for sampling the resistance value of the metal oxide semiconductor and a means for detecting CO from the resistance value obtained by this means.

[0006] Preferably, the temperature of the metal oxide semiconductor at the time of sampling is from room temperature + 30 ° C to room temperature, and more preferably, the sampling is performed for 100 ms to 25 minutes after the completion of pulse heating.
This is performed during 0 ms.

[0007] The CO sensitivity of the sensor after the end of the pulse heating is:
It increases with the maximum heating temperature during pulse heating and increases with the width of pulse heating. For this reason, the pulse heating width is preferably set to 10 ms or more, and the maximum temperature of the metal oxide semiconductor during the pulse heating is set to 320 ° C. or more. Since the CO sensitivity after the completion of the pulse heating increases as the pulse cycle is reduced, the pulse heating cycle is preferably set to 200 ms to 5 ms.
00 ms.

The present invention also provides a CO detection device in which a metal oxide semiconductor having a resistance value changed by a gas is heated in a pulsed manner to detect CO, wherein the pulse heating cycle is set to 200 ms to 500 ms. Means for sampling the resistance value of the metal oxide semiconductor at a pulse heating width of 10 ms to 30 ms, and for 100 ms to 250 ms after the end of the pulse heating, and a metal oxide obtained by the means. Means for detecting CO from the resistance value of the semiconductor.

Although the structure and material of the gas sensor used here are arbitrary, it is preferable that the gas sensor has a thickness of about 2 to 30 μm.
2 thick film is used. Preferably, a heater film is laminated on an insulating substrate of alumina, silica, titania, zirconia, etc. via a heat insulating glass film, and the above-mentioned SnO2 film is laminated on this heater film via an insulating film. . S
Pt is preferably used as an additive for the nO2 film,
It is preferable to add 3 to 5 parts by weight of Pt per 100 parts by weight of O2. Hereinafter, in this specification, SnO21
The amount of Pt added is indicated by the added parts by weight per 00 parts by weight,
Unless otherwise specified, the characteristics of the O sensor indicate the characteristics after the end of the pulse heating. Although the sampling time of the output of the CO sensor is indicated by the time from the end of the pulse heating, the start time of the pulse heating is indicated as time 0 in the embodiment, and the value obtained by subtracting the width of the heating pulse from this time is the pulse heating end. It will be a later time.

[0010]

The present inventor has found the following about the pulse heating type metal oxide semiconductor CO sensor. 1) The CO sensitivity of the sensor during pulse heating is significantly affected by humidity, causing false alarms in a high-temperature, high-humidity atmosphere. 2) There is a period in which the humidity dependency of the CO sensor becomes small after the end of the pulse heating.
This is a period of 400 msec, especially 100 m-250 msec.
In this period, relatively high sensitivity to CO is obtained. Therefore, if the output of the CO sensor is sampled during this period, the influence of humidity can be reduced. 3) The humidity dependency of the CO sensor decreases when the width of the heating pulse is increased, the pulse period is shortened, or the maximum temperature of the metal oxide semiconductor during pulse heating is increased. From these facts, the width of the heating pulse is set to 10 m or more, particularly 10 msec to 30 msec, and the pulse cycle is set to 200 msec to 500 msec.
Preferably, it is m seconds. The maximum temperature of the metal oxide semiconductor during pulse heating is preferably 320 ° C. or higher.

In this way, the humidity dependency of the CO detector is reduced, and false alarms in a high-temperature, high-humidity atmosphere can be prevented. In addition, CO sensitivity in a high humidity atmosphere increases, and C
The quantitativeness of O detection is improved.

[0012]

1 to 13 show an embodiment and its characteristics.
Note that the sensor characteristics are indicated by an average value of 10 sensors, and measurement of the characteristics was started after the CO sensor immediately after manufacturing was energized for 3 days under pulse driving conditions.

1 to 3 show the structure of a CO sensor. In the figure, 2 is a sensor body, 4 is an SnO2 film, 6 is a heater film, 8 is an alumina substrate, and may be a substrate made of zirconia or titania, or a heat-resistant insulating substrate. Reference numeral 10 denotes an insulating film which insulates the SnO2 film 4 from the heater film 6;
Is a heat insulating film for insulating the heater film 6 from the alumina substrate 8. Here, the thickness of the SnO2 film 4 is about 15 μm, preferably 2 to 30 μm. Pt is added to SnO2, and the amount of Pt is 3 to 5 parts by weight based on 100 parts by weight of SnO2. Pt was added as chloroplatinic acid, but the addition form is arbitrary. Here, a RuO2 film having a thickness of 15 μm is used as the heater film 6, but a Pt film or the like may be used instead. The heat insulating film 12 has a thickness of 50 μm.
A glass film having a thickness of about 1.
A glass film of about 5 μm was used. MgO in insulating film 10
Since the film contaminates the SnO2 film 4 and changes its characteristics, it is preferable that the insulating film 10 is free of MgO. FIG. 2 is a plan view of the sensor main body 2, in which a heat insulating film 12 is provided on the entire surface of an alumina substrate 8, a heater film 6 is provided thereon, and the insulating film 10 is covered.
This shows that the SnO2 film 4 is laminated. SnO2 film 4
Each pair of electrodes is connected to the heater film 6 and connected to an external lead from an electrode pad provided at an end of the alumina substrate 8 by, for example, wire bonding.

FIG. 3 shows the entire structure of the gas sensor 14.
Reference numeral 16 denotes an activated carbon filter, which is obtained by crushing coconut palm activated carbon (trade name “Shirasagi”, Shirasagi is a trade name of Takeda Pharmaceutical Co., Ltd.). In order to narrow the particle size distribution of the activated carbon, activated carbon that does not pass through 32 meshes in an 8 mesh pass was used. The amount of activated carbon used is 130 mg per sensor. Instead of the activated carbon filter 16, a filter such as silica gel, activated clay, or a resin-based gas-selective permeable membrane may be used. Reference numerals 18 and 20 denote wire meshes above and below the activated carbon filter 16. In this case, a double wire mesh of 100 mesh stainless steel is used for the wire mesh 18.
A 100 mesh stainless steel single wire net was used.

FIG. 4 shows a driving waveform of the CO sensor 14. The CO sensor operates at a cycle of 250 ms, of which 14
A 5 V heater pulse is applied to the heater 6 using m seconds, and S
Heat nO2 to a maximum temperature of about 340 ° C. The temperature of the SnO2 film 50 ms after the end of the pulse heating is room temperature + about 3
0 ° C., after 100 ms, room temperature + 10-20 ° C., 150 ° C.
After m seconds, the temperature is from room temperature to room temperature + 10 ° C. As a result, in the range 80 to 236 ms after the end of the pulse heating, SnO2
The temperature of the film is between room temperature and room temperature + 30 ° C.

In FIG. 4, pulse heating is performed at a cycle of 250 ms so that sensor output can be sampled during an arbitrary period of 80 ms to 236 ms after the completion of pulse heating. May be times. The width of the pulse heating and the maximum heating temperature are arbitrary. The maximum heating temperature is preferably 320 to 500 ° C., and the width of the pulse heating is preferably 10 to 30 msec. The cycle of the pulse heating is preferably 200 to 500 msec.

FIG. 5 shows a circuit of the CO detection device. In the figure, reference numeral 20 denotes a microcomputer, a CO sensor 1
An AD converter 22 reads a sensor signal from the voltage of the load resistor 46, and is used for the control of 4 and the detection of CO. The AD converter 22 reads a temperature compensation signal from a temperature compensation circuit using the thermistor 48 and the resistor 50, and reads an alarm threshold value of CO determined by the resistors 52 and 54.
Reference numeral 24 denotes a heater control unit which controls the transistor 42,
The heater film 6 generates heat in a pulsed manner. A sampling control unit 26 applies a detection voltage to the SnO2 film 4 and the load resistor 46 during the sampling period using the transistor 44.
Reference numeral 28 denotes a timer, which controls the AD converter 22 and the heater control unit 2.
4, the operation timing of the sampling control unit 26 is controlled, and 30 is an arithmetic and logic operation unit.

Reference numeral 32 denotes a CO detection unit, which is an alarm threshold value obtained from the voltage at the voltage dividing point of the resistors 52 and 54, for example, CO200p.
pm, an alarm threshold corresponding to low-concentration CO of 60 ppm is generated, and the resistance value of the SnO2 film 4 is obtained from the sensor signal read by the AD converter 22.
Compare with two alarm thresholds corresponding to pm and 60 ppm. The CO detection unit 32 also assumes that the relative humidity is constant from the temperature compensation signal read by the AD converter 22,
The ambient temperature dependence of the SnO2 film 4 is compensated. Therefore, the change in the relative humidity directly becomes an uncompensated error factor.
The CO detection unit 32 detects, for example, that
When a CO is present for more than 60 minutes or when CO of 60 ppm or more is present for, for example, 15 minutes or more, a detection signal of CO is generated. With this signal, the alarm control unit 34 issues an alarm using the buzzer 62 and the LED 64 via the driver 60. 4
0 is a constant voltage power supply.

[0019]

[Characteristics] Chloroplatinic acid is added to SnO2 obtained by hydrolyzing an aqueous solution of SnCl4 with ammonia and calcining, followed by calcining.
Pt was loaded. The method of adding Pt is arbitrary. For example, even if Pt is added with Pt resinate, platinum octylate, tetraammineplatinum (2) bis (2-ethylhexanoic acid) or the like instead of chloroplatinic acid, the characteristics are almost the same. . Therefore, the characteristics when Pt is added as chloroplatinic acid are shown below. The driving conditions of the CO sensor 14 are as shown in FIG. 4 unless otherwise specified. A heating pulse having a width of 14 ms is applied four times per second, and the maximum heating temperature of the SnO2 film 4 is set to about 34.
0 ° C.

FIGS. 6 and 7 show that 6 wt% of Pt is added to SnO 2.
Shows the characteristics after the completion of the pulse heating when is added. The heating conditions were a pulse width of 14 ms, a cycle of 1 second, and SnO2.
6 shows the characteristics of a standard atmosphere at 20 ° C. and a relative humidity of 65%, and FIG. 7 shows the characteristics of a high temperature and high humidity atmosphere at 50 ° C. and a relative humidity of 90%. In a standard atmosphere, the sensitivity to CO 60 ppm during pulse heating, that is, the ratio of the resistance value between air and CO 60 ppm is about 3,
This decreases to about 1.5 in high temperature and high humidity. In high-temperature, high-humidity air, the resistance during pulse heating decreases significantly,
For this reason, even if CO does not exist, an alarm may be issued.

Focusing on the characteristics after the completion of the pulse heating, in a standard atmosphere, the resistance value in air at a time of 50 ms to 600 ms is extremely high, and the CO sensitivity is high. Even in a high-temperature and high-humidity atmosphere, CO sensitivity is obtained in a period of about 100 ms to 400 ms, which is higher than the CO sensitivity during pulse heating.
From this, 80 msec to 400 m after the end of pulse heating
It can be seen that the effect of humidity can be reduced by sampling the sensor signal in seconds, more preferably in 100 ms to 250 ms.

FIGS. 8 and 9 show the characteristics when 1.0 wt% of Pt is added to the SnO2 film and operated under the driving conditions of FIG. The resistance during pulse heating in 60 ppm CO (standard atmosphere) is about 20 to 30 kΩ. On the other hand, in a high-temperature, high-humidity atmosphere, the resistance value during pulse heating is lower than 30 kΩ even in the absence of CO. Therefore, if the sensor resistance is sampled during the pulse heating, an erroneous report occurs in a high-temperature, high-humidity atmosphere. However, FIGS. 8 and 9 show that a large CO sensitivity is obtained around 150 ms. This is the same as in FIGS.

FIGS. 10 and 11 show that 4.0 wt.
5 shows characteristics when Pt is added and the device is operated under the driving conditions shown in FIG. At 4.0 wt% Pt, C after pulse heating
The O sensitivity further increases, and accordingly, the humidity dependency of the CO sensor 14 decreases, and the CO concentration dependency increases.

FIG. 12 shows the change in CO6 due to the change in the amount of Pt added.
The graph shows the sensitivity to 0 ppm and the change in resistance value at high temperature and high humidity. The operating conditions were as shown in FIG. 4, and sampling was performed at a time of 150 ms. The CO sensitivity is indicated by the ratio of the resistance value in air in each atmosphere to the resistance value in 60 ppm of CO, and the numbers shown in the figure are the resistance values of the SnO2 film 4. The atmosphere is a standard atmosphere of 20 ° C. and a relative humidity of 65%,
Two types of high-temperature and high-humidity atmospheres having a temperature of 50 ° C. and a relative humidity of 90% were used. The resistance in a high-temperature and high-humidity environment (the line indicated by △) indicates the resistance value in the air in this atmosphere.
If the concentration exceeds the line (ppm line) in ppm, no false report due to the high-temperature and high-humidity atmosphere occurs, and if it is below this line, a false report due to the high-temperature and high-humidity atmosphere occurs. It can be seen that when the amount of Pt added is 3 to 5 wt%, the resistance value in air at high temperature and high humidity can be made sufficiently larger than the resistance value at 60 ppm CO in a standard atmosphere, and false reports due to the high temperature and high humidity atmosphere can be prevented. The difference in the CO sensitivity between the standard atmosphere and the high-temperature and high-humidity atmosphere (the interval between ■ and ◇) indicates a decrease in the CO sensitivity due to humidity.
It can be seen that the reduction in sensitivity can be reduced.

FIG. 13 shows the relationship between the amount of Pt added and the CO concentration dependence of the sensor. This characteristic is obtained when the sensor output at the time of 150 msec is sampled under the driving conditions of FIG. The important thing here is α (60-200)
This is the ratio of the resistance values in 60 ppm CO and 200 ppm CO. And the Pt addition amount is 3 to 5 wt%
Then, α (60−200) becomes 1.36 or more,
1.25 with Pt addition of 2 wt% and Pt addition of 6 wt%
Is larger than 1.26.

In order to examine the sensor characteristics after 250 ms, it was considered to apply a heating pulse having a width of 14 ms at 500 ms intervals twice per second. In this case, time 100m
The CO sensitivity in the second to 250 ms was smaller than that in the example, and after the time 250 ms, the CO sensitivity gradually decreased as in FIGS. The CO sensitivity after 250 ms is
For example, when Pt 4% by weight was added to SnO2, the ratio between the air at high temperature and high humidity and the resistance at 60 ppm of CO changed as shown in Table 1. Table 1 shows that the sampling of the sensor output is preferably performed 80 ms to 400 ms after the completion of the pulse heating, and more preferably 100 ms to 25 ms.
0 ms later.

[0027]

[Table 1] Sampling time and CO sensitivity sampling 100 114 150 200 264 400 500 Time (msec) CO sensitivity 3.2 4.8 6.5 6.2 5.8 2.8 1.5 (60 ppm in air and CO) * Ratio of Pt 4.0 wt% added to SnO2 film 4 * Pulse heating twice per second, 14 msec width

The relationship between the maximum heating temperature of the SnO 2 film 4 and the CO sensitivity was examined, and the results shown in Table 2 were obtained. From this table, the maximum heating temperature is preferably 320 ° C. or higher, particularly 320 to 500 ° C.
It turns out that C is preferable.

[0029]

Table 2 Maximum heating temperature and CO sensitivity Maximum heating temperature (° C) 300 340 410 460 Rair / Rco60 1.5 2.8 6.5 8.0 * The measurement conditions are as follows: pulse heating cycle is 500 ms, The heater pulse width is 14 ms, 14 ms / 500 ms, the SnO2 film 4 contains 6.0 wt% Pt, the measurement atmosphere is a high humidity atmosphere at 50 ° C. and 90% relative humidity, and the resulting Rair / Rco60 is in air. Indicates the ratio of the resistance value to that in 60 ppm of CO. Sampling of the sensor resistance is 136 ms after the end of pulse heating.

The relationship between the width of the heating pulse and the CO sensitivity was examined, and the results shown in Table 3 were obtained. From this table, it is understood that the width of the heating pulse is preferably 10 ms to 30 ms. When the width of the heating pulse is set to 14 ms for the same sensor, CO at 60 ppm at high temperature and high humidity at 150 ms is used.
The sensitivity to was as follows. That is, the pulse heating cycle was 4.4 at 250 ms, 2.8 at 500 ms, and 2.0 at 1 second.

[0031]

Table 3 Width of heating pulse and width of CO sensitivity heating pulse (msec) 814 20 30 Rair / Rco60 1.2 2.8 4.5 6.0 Maximum heating temperature (° C) 250 340 410 480 * The measurement conditions are as follows: pulse heating cycle is 500 ms, SnO2 film 4 contains 6.0 wt% Pt, measurement atmosphere is high humidity atmosphere at 50 ° C and relative humidity 90%, and the resulting Rair / Rco60 is in air and CO 60 ppm. 136 ms after the end of pulse heating.

Although the SnO2 film 4 is used as a metal oxide semiconductor in the embodiment, In2O3 or the like may be used instead of SnO2, and the heating pulse may be applied as a single pulse.
Alternatively, it may be added as an aggregate of many sub-pulses.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a CO sensor used in an embodiment.

FIG. 2 is a plan view of a main part of a CO sensor used in Examples.

FIG. 3 is a cross-sectional view of a CO sensor used in Examples.

FIG. 4 is a characteristic diagram showing a driving waveform of the CO sensor in the embodiment.

FIG. 5 is a circuit diagram of the CO detection device according to the embodiment.

FIG. 6 shows the relationship between the value of SnO2 / Pt6 wt%
Characteristic diagram in standard atmosphere when driven for 4 ms / 1 second

FIG. 7 shows the results of a SnO 2 / Pt 6 wt% sensor.
Characteristic diagram in a humid atmosphere when driven for 14 ms / 1 second

FIG. 8 shows the relationship between the value of SnO2 / Pt1 wt%
Characteristic diagram in standard atmosphere when driven for 4 ms / 250 ms

FIG. 9 shows the relationship between the value of SnO2 / Pt1 wt%
Characteristic diagram in a humid atmosphere when driven for 4 ms / 250 ms

FIG. 10 shows the relationship between the value of SnO2 / Pt4 wt%
Characteristic diagram in standard atmosphere when driven for 4 ms / 250 ms

FIG. 11 shows a graph of 1 in a sensor of SnO2 / Pt4 wt%.
Characteristic diagram in a humid atmosphere when driven for 4 ms / 250 ms

FIG. 12 is a characteristic diagram showing a relationship between Pt concentration and humidity dependency of a CO sensor.

FIG. 13 is a characteristic diagram showing a relationship between Pt concentration and CO concentration dependency of the CO sensor.

[Explanation of symbols]

2 Sensor Body 20 Microcomputer 4 SnO2 Film 22 AD Converter 6 Heater Film 24 Heater Control Unit 8 Alumina Substrate 26 Sampling Control Unit 10 Insulating Film 28 Timer 12 Thermal Insulating Film 30 Arithmetic Logic Operation Unit 14 CO Sensor 32 CO Detection Unit 16 Activated Carbon Filter 34 Alarm controller 18, 20 Wire netting 40 Constant voltage power supply 42, 44 Transistor 46 Load resistance 48 Thermistor 50, 52, 54 Resistance 60 Driver 62 Buzzer 64 LED

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akihisa Ishida 1-3-5 Senba Nishi, Minoh City Inside Figaro Giken Co., Ltd. (72) Inventor Toru Nomura 1-3-5 Senba Nishi Mino City, Figaro Giken Inside the corporation

Claims (6)

[Claims] 1. A CO detection device configured to detect CO by heating a metal oxide semiconductor having a resistance value changed by a gas in a pulsed manner, wherein the semiconductor is 80 ms to 400 ms after the completion of the pulse heating. A CO detection device comprising: means for sampling a resistance value; and means for detecting CO from the resistance value obtained by the means. 2. The CO detection device according to claim 1, wherein the temperature of the metal oxide semiconductor at the time of sampling is between room temperature + 30 ° C. and room temperature. 3. Sampling is performed 10 hours after the completion of pulse heating.
2. The CO detection device according to claim 1, wherein the detection is performed between 0 ms and 250 ms. 4. The CO detection device according to claim 1, wherein a width of the pulse heating is 10 ms or more, and a maximum temperature of the metal oxide semiconductor during the pulse heating is 320 ° C. or more. 5. A pulse heating cycle of 200 msec to 500 m
The CO detection device according to claim 1, wherein the time is set to seconds. 6. A CO detection device configured to detect a CO by heating a metal oxide semiconductor having a resistance value changed by a gas in a pulsed manner, wherein a cycle of the pulse heating is 200 ms to 500 ms.
Means for sampling the pulse heating width from 10 ms to 30 ms, and sampling the resistance value of the metal oxide semiconductor 100 ms to 250 ms after the end of the pulse heating, and CO from the resistance value obtained by this means. A CO detection device, comprising: means for detecting.