JPS59218945A - Detector of gas component and humidity - Google Patents

Abstract

PURPOSE:To detect simultaneously humidity in atmosphere and the density of a gas component and to correct the influence of the atmospheric humidity exerting upon the detection of gas density by using only one sensor. CONSTITUTION:A gas component and humidity detecting sensor 1 consists of a gas sensitive/humidity sensitive element 11, heater 12, and a thermistor 13, etc. The gas sensitive/humidity sensitive element 11 is an element changing its resistance value in accordance with the humidity in the atmosphere and the concentration of the gas component and consists of a metallic oxide semiconductor such as SnO2. A sensor output (a) from the element 11 is guided to a reference voltage operation setting circuit 4, a humidity detecting circuit 5 and a gas detecting circuit 6 respectively. The heater 12 and the thermistor 13 are connected to a heater control circuit 2 respectively and the circuit 2 controls the temperature of the sensor 1 so that time interval between the detection of humidity and the detection of gas is alternately switched. Consequently, the humidity in the atmosphere and the density of the gas component can be simultaneously detected and the influence of the atmospheric humidity exerting upon the detection of the gas density can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an apparatus for detecting gas components and humidity in an atmosphere. The detection device according to the present invention is used, for example, when detecting harmful gas components generated by smoking in the interior of an automobile.

[Prior art]

In general, sensors made of metal oxide semiconductors have the property that when they come into contact with the atmosphere, their electrical conductivity, that is, their resistance value changes in response to the humidity and gas component concentration in the atmosphere, and the sensor's temperature and sound The humidity in the atmosphere or the gas concentration of the target component can be selectively detected.

This ↓ Una sensor is sensitive to the humidity in the atmosphere and its resistance value changes even at the sensor temperature (for example, 150°C to 400°C) when a single moxibustion gas is discharged, so only the gas concentration can be accurately measured. In order to output VC@, all effects of humidity must be corrected. To make this correction,
It would be possible to provide a humidity sensor and a gas sensor separately and use the humidity sensor output to correct the influence of humidity on the gas sensor output, but this would require many sensor manufacturing steps and would complicate sensor assembly. There is a problem that the cost also increases.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to simultaneously detect the humidity in an atmosphere and the concentration of a gas component using all of one sensor, and to correct the adverse effects of the atmospheric humidity on gas concentration detection. Gas component and humidity detection device? It's about getting.

[Structure of the invention]

In the present invention, a sensor made of a metal oxide semiconductor is provided, a heater attached to the sensor is controlled by a heater control circuit, and the temperature of the sensor is adjusted to the humidity measurement temperature by at least one step at predetermined time intervals. By switching to the gas measurement temperature of
A gas component detected by a sensor, and a reference level for comparison at the time of gas detection is calculated and set based on the output of the sensor at the time of humidity detection, so that a gas concentration corrected for the influence of atmospheric humidity is detected. and a humidity detection device.

〔Example〕

FIG. 1 is a block diagram showing a detection device according to an embodiment of the present invention. This device j11 detects the humidity and concentration of gases such as CO in the atmosphere inside an automobile, and when these become higher than a predetermined value. This is for controlling the humidity of the atmosphere or performing a gas purification process. In FIG. 1, reference numeral 1 denotes a gas/humidity sensing element 11, a heater 12. This is a sensor for detecting gas components and humidity, which includes a thermistor 13 and the like. The gas/humidity sensing element 11 is an element whose resistance value changes in response to the humidity and gas component concentration in the atmosphere, and is made of a metal oxide semiconductor such as 5NO2. The sensor output (a) from this gas/humidity sensing element 11 is output from the reference voltage calculation setting circuit 4. Humidity detection circuit 5. and gas detection circuit 6, respectively. The heater 12 and thermistor 13 are connected to the heater control circuit 2
This heater control circuit 2 is connected to
Control is performed to alternately switch the temperature of the sensor 1 between the temperature at the time of humidity detection and the temperature at the time of gas detection at certain time intervals. This temperature is, for example, id'30 degrees Celsius when detecting humidity, and @degrees which has the best sensitivity to the target gas when detecting gas.

For example, 200° C. is chosen for CO gas. The heater control circuit 2 is also connected to a detection timing calculation circuit 3, which outputs a timing output (C) indicating that the temperature of the sensor 1 is at the time of humidity detection.
and timing output (d) indicating that gas is being detected.
The signals are sent to the ffi gas detection circuit 6, respectively.

In the humidity detection circuit 5, the sensor output (a) from the gas/humidity sensing element 11 is branched into two branches, each of which is guided to one input terminal of an analog comparison circuit 51, 52. A reference voltage H setting circuit 53 for setting the lower limit humidity is connected to the other input terminal of the analog comparison circuit 51, and a reference voltage setting circuit 54 for setting the upper limit humidity is connected to the other input terminal of the analog comparison circuit 52. Connected. This analog comparison circuit 5
Each of the outputs of 1°52 is sent to one input terminal of AND circuits 55 and 56, and the timing output (c) is led to the other input terminal of AND circuits 55+56, respectively. Furthermore, each output of the AND circuits 55 and 56 is led to an actuator 7 for humidity control. Examples of the actuator 7 include an air conditioner, a humidifier, and the like.

In the reference voltage calculation setting circuit 4, the sensor output (a) from the gas/humidity sensing element 11 is sent to the sample hold circuit 4.
I am guided by 1. The timing output (c) from the detection timing calculation circuit 3 is guided to this sample and hold circuit 41 as a hold timing signal, and the output of this sample and hold circuit 41 is sent to a rendition circuit 42. The output of the arithmetic circuit 42 is sent to the gas detection circuit 6 as a comparison reference level output (f).

In the gas detection circuit 6, the sensor output (a) is led to one input terminal of an analog comparison circuit 61.

The comparison reference level output (f) from the L pressure calculation setting circuit 4 is led to the other input terminal.The output of this analog comparison circuit 61 is led to one input terminal of the AND circuit 62, and the The timing output (d) from the detection timing calculation circuit 3 is led to the other input terminal of the circuit 62. Furthermore, the output of the AND circuit 62 is led to the actuator 8 for gas purification. There are gas purifiers, gas exhaust blowers, etc.

2, 3, and 4 are diagrams showing the specific configuration of the sensor 1 in FIG. 1, and FIG. 2 is a plan view of the sensor 1,
FIG. 3 is a side view, and FIG. 4 is a back view. This sensor 1
Electrodes 15a, 15b, 15c made of gold, platinum, aluminum, etc. are formed on the surface of an insulating ceramic sensor substrate 14 made of alumina, etc.
Also, similar electrodes 15d and 15g are provided on the back surface, and between these electrodes 15a and 15b is a gas/moisture sensing element 11 made of a Kinjo oxide semiconductor mainly composed of 5N02, and between electrodes 15b and 15c. All the thermistors 13 are used to detect the temperature of the sensor board, and RuO2 and P are placed between the negative poles 15d and 15e.
The heaters 12 for heating sensors such as TO and carbon are respectively provided in a 'fc' configuration, and each of these members is manufactured by screen printing, sputtering, vapor deposition, etc. Further, lead wires 16a to 16e connected by aluminum bonding or the like are drawn out from each electrode 15a to 15e, respectively.

FIG. 5 is a detailed circuit diagram of the heater control circuit 2 in FIG. 1. In the figure, 21 is an oscillation circuit, the output of which is input to a counter 22, and the counter output (e) of the counter 22 is led to an analog switch 230 control input terminal. A high voltage Vh and a low voltage V°C are respectively guided to two fixed contact pieces of the analog switch 230, and the movable contact pieces are connected to a series resistor 24. It is grounded via the thermistor 13 of the work center 1. This movable contact piece is alternately switched to two fixed contacts according to the counter output (e). One end of the thermistor 13 is connected to the non-inverting input terminal of an operational amplifier 25, and the output of this operational amplifier 25 is
A current is supplied to the base of a power transistor 26 for supplying an operating current to the heater 12 in the sensor 1, one end of which is connected to the emitter circuit. It is grounded and connected to the inverting input terminal of the operational amplifier 25.

This heater control circuit 2 is a circuit that heats the sensor 1 using a sensor heating pattern as shown in FIG. The temperature of the sensor 1 is kept constant by controlling the transistor 26 to adjust the flow of 71 ml to the heater 12. Then, the counter output (e) from the counter 22 causes the analog switch 23 to
The movable contact piece is connected to the VA side or the cam connected to the Vh side, and the equilibrium temperature of sensor 1 is determined by the temperature at the time of humidity detection (
For example, 20°C to 30°C) and the temperature at the time of gas detection (for example, 20°C to 30°C).
00°C to 300°C).

FIG. 7 is a detailed circuit diagram of the detection timing calculation circuit 3 in FIG. 1. In the same figure, a part of the counter output (e) from the counter 22 shown in FIG. The signal is input to the integrating circuit 35 via 34. The output of the integrating circuit 31 is input to the one-shot multivibrator 33 via the buffer 32, and this one-shot multivibrator 33
It is output as a timing output (C) indicating the humidity detection timing. Similarly, the output cover buffer 36 of the integrating circuit 35. It is output as a timing output (d) indicating the gas detection timing via the one-shot Martino (ibrator 37).

Next, the operation of the apparatus of this embodiment configured as described above will be explained.

First, to explain the temperature control operation of the sensor 1 by the heater 12, the counter 22 of the heater control circuit 2
The analog switch 23 is controlled to be switched alternately, thereby switching the voltage applied to the thermistor 13.

The terminal voltage of this thermistor 13 is applied to the pace of the power transistor 26 via the operational amplifier 25. The time interval of the temperature heating pattern is determined by the oscillation circuit 21 and the output bit of the counter 22, but in consideration of tracking the sensor temperature, at least 20 seconds of counterfeiting is required.

Next, the operation of the detection timing calculation circuit 3 will be explained using the signal waveform diagram of each part shown in FIG. analog switch 23
Counter output (e) of counter 22 that controls
is also input to the detection timing calculation circuit 3Vc as temperature information of the sensor 1, and is processed there. This counter output (e) is a rectangular waveform output, which is branched into two,
One is input to the integrating circuit 31 and the other is input to the integrating circuit 35 via the inverter 34. The integrating circuits 31 and 35 form a delay circuit that delays the input signal by a certain period of time by integrating the input signal. Such a delay circuit is necessary because the sensor output (a) is not immediately stable with respect to the heater control output (b) of the heater control circuit 2 when the senna temperature is changed.

As shown in FIG. 8, timing detection is performed at a position where the sensor output (a) is stable during gas detection and humidity detection. next.

The outputs of the integrator circuits 31 and 35 are sent to buffers 32 and 3, respectively.
6, the waveform is returned to a rectangular wave, and the one-shot multivibrator 33.37 determines the detection time width, and outputs a timing output (c) that determines the humidity detection timing and a timing output (c) that determines the gas detection timing output. d) output.

Next, the processing operation of the sensor output (a) will be explained.

First, in the gas detection operation, a timing output (c) for humidity detection is manually inputted from the detection timing calculation circuit 3 to the reference voltage calculation setting circuit 4. This reference voltage calculation setting circuit 4 is for detecting the humidity immediately before gas detection is performed on the sensor 1, and for correcting the influence of the humidity on gas concentration detection, as shown in the flowchart of FIG. Perform the actions shown in . That is, the sensor output (a)
' at the timing of the timing output (c), the sample and hold circuit 41 samples it, and the arithmetic circuit 42
Yo! 7 Determine the humidity of the atmosphere from the value of the sensor output (a) sampled by the sample hold circuit 41. Furthermore, based on the determined humidity, the influence of the humidity on a predetermined gas concentration in the atmosphere (for example, 50 ppm of CO gas) is calculated, and the humidity-corrected comparison reference voltage level (f) for the gas concentration is calculated. Calculate and output. To explain this in more detail using figures, Fig. 10 is an example characteristic diagram showing the dependence of sensor output (a) on atmospheric humidity, where i yellow M is humidity and the vertical axis is sensor output (a). be. In the figure, ■ indicates the sensor output humidity dependence at a sensor temperature of 20°C, ■ indicates the sensor output humidity dependence at a sensor temperature of 200°C in the absence of gas, and ■ indicates the sensor output humidity dependence at a sensor temperature of 200°C. , shows the humidity dependence of the sensor output when 50 ppm of CO gas is present. To correct the influence of humidity during gas concentration detection vr, the sensor output at the time of humidity detection (
A) is obtained by using the gunf of the wet craftsman in the atmosphere, and the sensor output at the gas concentration of 50 ppm is determined using the Clan, and the reference voltage for all comparisons is It is output to the comparator circuit 61 as level (f).

Comparison circuit 61 completely compares the output (a) with comparison reference voltage level (f), and provides the comparison result to AND circuit 62. The AND circuit 62 outputs the comparison result to the total gas purification actuator 8 in synchronization with the gas detection timing of the sensor 1 using the Quiminck output (d). Therefore, when the sensor output (a) is thicker than the reference voltage level (f), the output of the AND circuit 62 becomes high level, and the sensor 1
It is detected that the detected gas concentration has become higher than a predetermined reference value, and the actuator 8 performs the necessary gas purification operation.

Next, referring to the humidity detection operation, the sensor output (a) fl from the sensor 1 is input to the analog comparison circuits 51 and 52, respectively. The analog comparison circuit 51 compares this output (,) with the lower limit reference voltage corresponding to the lower limit humidity of, for example, 50 inches from the reference voltage setting circuit 53.
The analog comparison circuit 52 compares the sensor output (,) with the upper limit reference voltage from the reference voltage setting circuit 54, which corresponds to the upper limit humidity of, for example, 60%. The comparison result output of each of these analog comparison circuits 51 and 52 is outputted to an AND circuit 5.
Further, in synchronization with the timing output (c) for humidity detection, it is sent from each AND circuit 55 and 56 to the actuator 7 for humidity control. Actuator 7
Based on these input signals, all controls are carried out so that the relative humidity of the atmosphere is maintained within a range of 50% to 60%.

Many variations of the embodiments described above are possible in carrying out the invention. For example, in this embodiment, a metal oxide semiconductor mainly composed of 5no2 was used as the gas/humidity sensitive element, but the present invention is not limited to this.

For example, MPOr 20a + Fe0r 20a +
Ni Cr z 04 *Mn0r204 HoUar
204 g C60r204 + Zn c,, 04
It is possible to use one mainly based on ror203 or the like.

In addition, in the above embodiment, a two-stage heating pattern for the humidity detection temperature and a gas detection temperature was used as the heating pattern for the sensor 1, but the present invention is not limited to this.For example, a three-stage heating pattern as shown in FIG. You can also use This is done in order to selectively detect the gas component that has the best sensitivity at each temperature by setting the sensor temperature at two levels during gas detection. High 00.
It detects gas sounds such as H2, and at 0 it detects all hydrocarbons such as propane and butane, which have high sensitivity at high temperatures. In this case as well, the influence of humidity is corrected and gas detection is performed in the same manner as in the previous embodiment.

Furthermore, instead of the humidity detection circuit 5 used in the above-mentioned embodiment, it is also possible to make a modification in which only one of the comparison circuits is used to detect only the upper or lower limit of humidity, and control is performed by the actuator 7. be.

〔Effect of the invention〕

As explained above, according to the present invention, the humidity and gas concentration in the atmosphere can be detected simultaneously with one sensor, and the negative effect of the atmospheric humidity on the gas concentration detection can be corrected, so that the gas concentration can be detected with high accuracy. This has the advantage of being able to detect. In addition, since only one sensor is required, the structure for compensating for waves becomes simple, making it possible to reduce the size and cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, and FIGS. 2 to 4 are examples of the sensor configuration in the apparatus shown in FIG. 1. FIG. 5 is a detailed circuit diagram of the heater control circuit in the device shown in FIG. 1, and FIG. 6 is a diagram showing the heater control circuit in the device shown in FIG. 7 is a circuit diagram of the detection timing calculation circuit in the device shown in FIG. 1; FIG. 8 is a diagram explaining the detection timing in the detection timing calculation circuit of FIG. 7; FIG. 9 The figure is a calculation flowchart of the basic LW voltage setting calculation circuit in Figure 1 and 2, Figure 10 shows the atmospheric humidity dependence in the apparatus shown in Figure 1, and Figure 11 shows a three-stage heating pattern. It is a figure showing a modification. DESCRIPTION OF SYMBOLS 1...Sensor, 2.Heater control circuit, 3..Detection timing calculation circuit, 4..Reference voltage Hama J (setting circuit, 5..
...Humidity detection circuit, 6...Gas detection circuit, 7.8...
・Actuator, 11...Gas/moisture sensing element, 12
... Heater, 13 ... Thermistor, 41 ... Sample hold circuit, 42 ... Arithmetic circuit, 51, 52.6
1...Analog comparison circuit, 53+54...J,
1. H quasi voltage setting circuit. Patent Applicant Co., Ltd. Japan Auto Parts Co., Ltd. Patent Application Representative Patent Attorney Akira Aoki Patent Attorney Kazuyuki Nishi Patent Attorney Takashi Kobayashi Patent Attorney Akira Yamaguchi Figure 7 Figure 10 A

Claims (1)

[Claims] 1.1. A sensor made of a metal oxide semiconductor is provided, a heater attached to the sensor is controlled by a heater control circuit, and the temperature U of the sensor is at least equal to the humidity measurement temperature at predetermined time intervals. By switching to one stage of gas measurement temperature, gas concentration and atmospheric humidity are detected by one sensor, and the output of this sensor when detecting humidity increases the ratio when detecting gas +1? The i reference level was calculated and set, so that the gas concentration corrected for the influence of atmospheric humidity was detected. Gas component and humidity detection device. (,2: The device ri0 according to claim (1), in which the gas measurement temperature at which the temperature of the sensor is switched is selected in two stages.