JPH07159358A - Air quality detector - Google Patents

Abstract

PURPOSE:To accurately obtain a standard signal for sensor signals for detecting the fouling of indoor air. CONSTITUTION:Signals from a sensor 1 for detecting the fouling of air inside a room is sampled with a constant interval of time by a sampling means 2 and the obtained sensor signals are processed to obtain their change quantity by a signal storage means 3 where N pieces of sensor signals are stored from the past upto now and a change-quantity calculation means 4. Based on the change quantity, an output drop judgement means A5a, change quantity integration means 6 and cleanliness judgement means 7 judge whether or not the sensor signal reaches the clean outdoor-air level. If judged that it reaches the level, the sensor signal is stored as being at a clean level in a clean level storage means 8. A fouling quantity calculation means 9 calculates the fouling quantity on the basis of the sensor signals referring to the clean level as a standard and an output means 10 outputs the results to the outside, thereby accurately detecting the sensor signals in a clean outdoor air state as the standard value and precisely detecting the fouling of indoor air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting dirt in indoor air of a building air conditioner, a house, and the like, and a detector equipped with the sensor.

[0002]

2. Description of the Related Art In recent years, energy saving has progressed in houses and buildings.
However, airtightness is improved to improve the efficiency of air conditioning.
On the other hand, such airtightness is caused by smoking, for example.
Dust, H ₂Formed from gases such as CO, CO, and building materials
Aldehyde, volatile organic gas (VOC gas), stove
CO, NO generated from combustion appliances such as_X, SO_X, CO₂etc
Gas, CO generated by human breathing₂, Also cigarettes
Smells such as odors, body odors, rotten odors, and bad odors may remain indoors.
It pollutes the indoor air and adversely affects the occupants. Bill
In which, CO₂Based on concentration
Despite the standard ventilation, the above V
Sick building syndrome caused by OC gas etc. is a problem
It has become. Therefore, such contaminated air in the room
While maintaining both energy saving and comfort, the ventilation and air purifier
Therefore, it is required to be discharged and removed.

There is also a demand for measurement using human odor sensation as an index of indoor air quality pollution.

Therefore, it is known that indoor air pollution is detected by using a CO ₂ concentration and a gas sensor to perform ventilation and air cleaning.

Conventionally, this type of air quality detecting device has generally been constructed as shown in Japanese Patent Application Laid-Open No. 1-181026. The configuration will be described below with reference to FIG.

As shown in the figure, the carbon monoxide sensor 101
A, the hydrogen sensor 101B, the propane sensor 101C, the oxygen sensor 101D, and the smoke sensor 101E respectively output analog signals to the comparators 102A to 102E. Comparator 1
Nos. 02A to 02E have a reference level set in advance, and when the indoor air pollution increases and the sensor output exceeds the reference level, the output becomes, for example, "H".

Further, the outputs of the comparators 102A to 102E are
It is input to the arithmetic means 103. The operation means 103 performs an OR operation and outputs one of the outputs of the sensors 101A to 101E.
If the reference level is exceeded at any time, a signal is output to the output means 104 to operate the ventilation fan.

[0008]

In such a conventional air quality detecting device, when setting the reference level and obtaining the sensor output, the reference value is obtained from the sensor signal and the difference between the reference value and the sensor output is used. As the reference value, a sensor signal in clean outside air is generally used.

However, in the room to be measured,
As compared with clean outside air, there is gas generated from building materials, furniture, etc. as a background. For example, hydrocarbons such as methane, alcohols, VOC gas, aldehydes, etc. High concentrations of these gases impair health, but they exist at low concentration levels that pose no health problems, and their concentrations and components differ from room to room. Therefore, there is a problem that the sensor signal in the clean outside air can be obtained only when the window is opened or the ventilation fan is operated in the house, and in the office building when a large amount of the outside air is introduced in the middle of spring or autumn.

Further, many of the sensors used in the air quality detecting device are semiconductor type gas sensors, and the output and sensitivity of these sensors change with time and depending on the temperature and humidity of the atmosphere. Therefore, there is a problem that the reference value must be updated and the temperature and humidity must be corrected.

The present invention is to solve the above-mentioned problems. The inside of the room is detected by detecting that the inside of the room is approaching the clean outside air level by introducing the outside air from the change amount of the sensor signal and obtaining the sensor signal in the clean outside air as a reference value. The first purpose is to accurately measure the degree of air pollution.

A second object is to obtain the sensor signal of the clean outside air level more accurately by adding the sensor signal in the background state of the room to the determination of the clean outside air level.

A third object is to erroneously obtain the clean outside air level by always monitoring the minimum value of the sensor signal after obtaining the reference value of the clean outside air level and setting the minimum value as the reference value. However, after that, correction is made and the value closest to the clean outside air level is automatically obtained.

A fourth object is to reliably detect the clean outside air level obtained in the intermediate period of spring and autumn as a reference value by monitoring the minimum value of the sensor signal for more than half a year.

The fifth object is to correct the obtained reference value by temperature and humidity, so that even if the reference value is obtained in a season when the climate is completely different, the change in the pollution state of indoor air is not affected by the temperature and humidity. Is to detect with high accuracy.

[0016]

The first means for achieving the first object of the present invention is to provide one or more sensors for detecting dirt in the air in a room and a signal of the sensors for a predetermined time. A change amount of the sensor signal is calculated from a signal sampling means for sampling for each time, a signal storage means for storing a plurality of sensor signals sampled by the sampling means from the past to the present, and N sensor signals stored in the signal storage means. A change when the output is reduced from the output decrease determination unit A and the output decrease determination unit A that compare the change amount output from the change amount calculation unit and the change amount output from the change amount calculation unit to determine whether the sensor output is decreased. Whether the current sensor signal is the output value in the clean air from the change amount integrating means for integrating the amount and the integrated change amount output from the change amount integrating means Whether or not the cleaning level is determined based on the result of the cleanness determination means and the result of the cleanness determination means, and the output value of the cleanness level storage means is used as a reference value to compare with the output of the sensor. The configuration includes a stain amount calculating means for calculating the stain amount and an output means for outputting the stain amount to the outside.

Second aspect for achieving the second object of the present invention
Means for monitoring the stability of the amount of change based on the amount of change in the sensor signal and determining whether the sensor signal is stable, and the output when the sensor signal is stable from the output of the stability monitoring unit and the stability monitoring unit. The background level storage means for storing as a ground level, the change amount, and the output reduction determination means B for determining whether or not the sensor signal is lower than the background level which is the output of the background level storage means are the first aspect of the present invention. It is configured in addition to the means.

Third aspect for achieving the third object of the present invention
Means for comparing the sensor signal with the output value stored in the cleaning level storage means, storing the smaller value, and outputting the reference value storage means to the contamination amount calculation means as the first and second means of the present invention. This is an additional configuration.

A fourth object for achieving the fourth object of the present invention.
The means is one or more sensors for detecting dirt in the room, sampling means for sampling the signal of the sensor at regular time intervals, and a sensor signal sampled by the sampling means for one day or more and half a year or less. From the minimum value calculation means for calculating the minimum value of the signal of the sensor during the period, the minimum value storage means for storing the minimum value which is the output of the minimum value calculation means for at least half a year, and the minimum value stored in the minimum value storage means. Clean level calculating means for obtaining the output of the sensor in clean air; dirt amount calculating means for calculating the amount of dirt in the indoor air by comparing the output value of the clean level calculating means with a signal of the sensor; The configuration is such that an output means for outputting the quantity to the outside is provided.

A fifth aspect for achieving the fifth object of the present invention.
In the fourth means of the present invention, the means is a temperature / humidity sensor for detecting the temperature and humidity of indoor air, and a reference value correction means for correcting the output value of the cleaning level calculation means from the temperature and humidity output from the temperature / humidity sensor. This is an additional configuration.

[0021]

According to the present invention, by the structure of the above-mentioned first means, it is detected from the change amount of the sensor signal that the indoor air is changed to the clean outside air level due to the ventilation or the introduction of the outside air, and the change amount is integrated from the start of the change. Since it is determined that the value reaches the clean outside air level based on the value, the sensor signal of the clean outside air level that is the reference value of the sensor signal can be obtained.

Further, by the constitution of the second means, the sensor signal for the gas existing as the background in the room is judged by the stability of the sensor signal obtained from the change amount of the output, and the background level is set to the clean outside air level. Since it is determined whether or not the indoor air has changed by comparing the amount of change, the sensor signal, and the background level, the clean outside air level can be accurately obtained.

Further, by the configuration of the third means, the level of the clean outside air obtained as the reference value is compared with the sensor signal, and when the sensor output becomes lower than the reference value, the sensor output is set as the reference value. Even when the level is used as the reference value, the correct clean outside air level can be obtained after that when the clean outside air level is reached.

Further, by the constitution of the fourth means, the minimum value of the sensor signal for the past half a year or more is memorized and used as the reference value, so that the standard of the clean outside air level always obtained in the intermediate period of spring or autumn. The value can be obtained.

Further, by the constitution of the fifth means, the temperature and humidity environment when the reference value is obtained by correcting the reference value with the temperature and the humidity obtained by the temperature and humidity sensor and the temperature and humidity at the time of measurement. It is possible to obtain an accurate clean outside air level even in different cases.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, a plurality of sensors 1 for detecting dirt in indoor air output sensor signals to sampling means 2. The sampling means 2 samples the sensor signal at regular intervals and outputs the sensor signal to the signal storage means 3, the cleaning level storage means 8 and the contamination amount calculation means 9. The signal storage means 3 stores n sensor signals sampled by the sampling means 2 from the past to the present, and discards the oldest signal when the latest sensor signal is stored.
The change amount calculation means 4 calculates the change amount of the sensor signal from the n sensor signals stored in the signal storage means 3 and outputs it to the output decrease determination means A5a and the change amount integration means 6. The output decrease determination means A5a compares the amount of change with a preset determination value to determine whether the sensor signal has dropped to the clean outside air level, and if it determines that the sensor signal has dropped to the clean outside air level, the change amount integrating means. The judgment result is sent to 6. Change amount integrating means 6
When the determination result is received from the output reduction determination unit A5a, the integrated output amount of the change amount calculation unit 4 is integrated and output to the cleanliness determination unit 7. The cleaning determination means 7 compares the integrated value of the change amount output from the change amount integration means 6 with a preset cleaning level determination value, and when it determines that the cleaning level has been reached, outputs the determination result to the cleaning level storage means 8. . When the cleaning level storage means 8 receives the determination result of the change amount integration means 6, the cleaning level storage means 8 stores the sensor signal output from the sampling means 2 and outputs the sensor signal to the contamination amount calculation means 9. The dirt amount calculation means 9 uses the output of the clean level storage means 8 as a reference value and compares it with the sensor signal which is the output of the sampling means 2 to calculate the dirt amount. The calculated dirt amount is output to the output unit 10. Output means 10
Outputs the amount of dirt, which is the output of the dirt amount calculating means 9, to an external device such as an LED or a panel meter display, a ventilation device, or an air cleaning device.

As the sensor 1, various types of sensors can be used as long as they are sensitive to pollutants which represent the polluted state of the indoor air to be detected. For example, when detecting smoking, a hydrogen sensor or a CO sensor as a tobacco sensor, or an alcohol sensor when detecting VOC gas,
A carbon dioxide sensor is used to detect a person or combustion, and a hydrogen sulfide sensor or an ammonia sensor is used as an offensive odor sensor to detect a bad odor. The number of the sensors 1 may be one or more depending on the detection target.

Here, the sensor signal is ventilation (ventilating fan operation,
When the window is opened and the outside air is introduced) or the load such as cigarettes, it moves as shown in Fig. 2. The sensor signal shows a signal of a clean level when ventilating operation is performed and the outside air is introduced. When the ventilation operation is stopped, the sensor 1 detects gas existing as a background in the room and shows a signal of background level. It changes according to the pollution of.

The gas existing as the background is mainly hydrocarbon type, alcohol type and organic solvent type, and the total concentration is several tens to several hundreds of PPb level, which is a level that does not pose any problem to human health. Existing.

Next, the operation will be described with reference to FIG.
In steps 19 and 20, the sensor signal Vs is sampled in the sampling means 2 at intervals of T seconds. The sampled sensor signal Vs is stored in the signal storage means 3 in step 21,
22 processing is performed. Step 21 stores n sampled sensor signals Vs from past to present (X1 to Xn), and when a new sensor signal is sampled, X2 is obtained.
Data of Xn to Xn are sequentially stored in X1 to Xn-1, and a new sensor signal Vs is stored in Xn. Next, in step 22, the total of a pieces of data from X1 to Xa is set to A,
The total of (na) pieces of data from Xa + 1 to Xn is B
And Next, the change amount calculating means 4 performs the process of step 23. In step 23, (BA) is multiplied by a constant K to calculate the amount of change DV. Next, the output reduction determining means 5 performs the process of step 23. In step 23, the change amount DV is set in advance and compared with the change amount DVair when the sensor signal is changing to the clean outside air level, and if it is determined that the change is to the clean outside air level, step 26, otherwise step Go to 25. In step 26, DV is integrated in the change amount integrating means 6 to obtain a change amount integrated value SDV, and the process proceeds to step 27. Step 25 is a change amount integrated value SDV
Is cleared and the process proceeds to step 27. In step 27, the change amount integrated value SDV in the cleanliness determination means 7 is compared with the change amount integrated value SDVa obtained when the sensor signal reaches the preset clean outside air level, and it is judged that the clean outside air level has been reached. Step 28, otherwise Step 2
Proceed to 9. In step 28, the cleaning level storage means 8 stores the sensor signal Vs in the cleaning level Va. Step 29
In the dirt amount calculation means 9, the dirt amount is calculated from the sensor signal Vs with reference to the clean level Va. In step 30, the amount of dirt is output to the outside in the output means 10.

With the above configuration, it is possible to determine whether the indoor air is at the clean outside air level or not based on the change amount of the sensor signal and the integrated value of the change amounts, so that the sensor signal at the clean outside air level can be used as the reference value.

As described above, according to the air quality detecting apparatus of the first embodiment of the present invention, it is possible to detect the amount of dirt in the room air with reference to the clean outside air level.

Next, the second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. The same parts as those of the conventional example and the first embodiment of the present invention are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 4, the sampling means 2 outputs a sensor signal to the background level storage means 12, the clean level storage means 8 and the contamination amount calculation means 9. The stability monitoring unit 11 obtains the stability of the sensor signal from the change amount output from the change amount calculation unit 4, and outputs the determination result as to whether the sensor signal is stable to the background level storage unit 12. Background level storage means 12
Receives the determination result that the sensor signal is stable from the stability monitoring means 11, stores the sensor signal which is the output of the sampling means 2 as the background level and outputs it to the output reduction determination means B5b. Output decrease determination means B5
b is a determination result based on the change amount of the sensor signal output from the change amount calculation unit 4 and the background level output from the background level storage unit 12 to determine whether or not the sensor signal is reduced to the clean outside air level. Is output to the variation amount integrating means 6.

Next, the operation will be described with reference to FIG. Since steps 19 to 23 are the same as those in the first embodiment of the present invention, they are omitted. In steps 31, 32 and 33, the stability of the sensor signal is determined in the stability monitoring means 11. The step 31 compares the absolute value of the change amount DV obtained in the step 23 with the change amount DVb when the preset sensor signal is stable at the background level. If it is smaller than DVb, the process proceeds to step 33, otherwise. If so, proceed to step 32. Step 33 is a counter A for stability determination.
Count T and proceed to step 34. In step 32, the counter AT is cleared and the process proceeds to step 36. Step 3
Reference numerals 4 and 35 determine whether or not the counter AT in the background level storage means 12 is longer than a preset stable duration Cb. If it is larger, the routine proceeds to step 35, and if it is smaller, the routine proceeds to step 36. Step 35 is Step 34
When it is determined that the stable state of the sensor signal continues longer than the set time (Cb), it is determined to be the background state, the sensor signal Vs is stored in the background level Vbg, and the process proceeds to step 36. In step 36, if it is determined that the output has dropped to the clean outside air level by comparing the amount of change DV with a preset DVair in the output drop determination means B5b, and if the sensor signal Vs is smaller than the background level Vb, step 26 is entered. move on. Otherwise, go to step 25. Steps 25 to 30 below
Are omitted because they are the same as the first embodiment of the present invention.

As described above, according to the air quality detecting apparatus of the second embodiment of the present invention, the clean outside air level determination is performed by setting the sensor signal in the background state of the indoor air as the background level and adding it to the determination of the clean outside air level. Can be prevented from malfunctioning.

Next, the third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. The same parts as those of the conventional example and the embodiment of the present invention are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 6, the sampling means 2 outputs sensor signals to the reference value storage means 13, the clean level storage means 8 and the dirt amount calculation means 9. The cleaning level storage means 8 outputs the stored cleaning level sensor signal to the reference value storage means 13. The reference value storage means 13 compares the sensor signal output from the sampling means 2 with the clean level output from the clean level storage means 8, stores the one with the lower value as the reference value, and outputs it to the dirt amount calculation means 9.

Next, the operation will be described with reference to FIG. Since steps 19 to 27 are the same as those in the first embodiment of the present invention, the description thereof will be omitted. In step 37, when it is determined in step 27 that the clean outside air level has not been reached, the clean level Va is compared with the sensor signal Vs, and when the sensor signal Vs becomes lower than the clean level Va, the process proceeds to step 28, otherwise step 29. Proceed to. In step 28, the sensor signal Vs is stored in the cleaning level Va and the process proceeds to step 29.

As described above, according to the air quality detecting apparatus of the third embodiment of the present invention, even if the clean outside air level is erroneously determined, the clean outside air level can be automatically fetched as the reference value thereafter.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those of the conventional example and the embodiment of the present invention are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 8, the minimum value calculation means 14 calculates the minimum value of the sensor output for a certain period from the output of the sampling means 2 and outputs it to the minimum value storage means 15. The minimum value storage means 15 stores the minimum value output from the minimum value calculation means 14 for half a year or more (for example, when the minimum value calculation means 14 calculates the minimum value of the sensor signal for one week, the minimum value storage means 15). Stores the minimum value of 53 or more). The clean level calculation means 16 calculates a sensor signal of the clean outside air level from the minimum values stored in the minimum value storage means 15, and outputs it as a clean level to the dirt amount calculation means 9.

With the above configuration, the minimum value of the sensor signal for at least the past half year is stored, and the clean level is obtained from the minimum value group, so that the clean outside air level obtained in the middle of spring or autumn is always used as a reference. It can be used as a value.

As described above, according to the air quality detecting apparatus of the fourth embodiment of the present invention, the clean outside air level serving as the reference value of the sensor signal is obtained from the minimum value of the past half a year or more and is obtained by introducing the outside air in the intermediate period. Since the clean outside air level is used as the reference value, the degree of pollution of the indoor air can be accurately obtained.

Next, the fifth embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The same parts as those of the conventional example and the embodiment of the present invention are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 8, the temperature / humidity sensor 17 measures the temperature and humidity in the room and outputs the room temperature and humidity to the reference value correction means 18. The cleaning level calculating means 16 outputs the cleaning level to the reference value correcting means 18. The reference value correction means 18 corrects the clean level, which is the output of the clean level calculation means 16, by the room temperature / humidity, which is the output of the temperature / humidity sensor 17, and outputs it as a reference value to the dirt amount calculation means 9.

According to the above configuration, the sensor signal of the clean level can be temperature / humidity corrected and used as the reference value.

As described above, according to the air quality detecting apparatus of the fifth embodiment of the present invention, since the temperature and humidity of the reference value are corrected, the temperature and humidity when the reference value is updated and the temperature and humidity at the time of measurement are different. Even in this case, the contamination level can be accurately determined.

[0050]

As is apparent from the above embodiments, according to the present invention, it is judged from the change amount of the sensor signal whether the measurement atmosphere is approaching the clean outside air level, and the clean outside air level is determined from the integrated value of the change amount. The sensor signal when the room changes to clean outside air can be used as the reference value by determining whether or not the ambient temperature has reached, and since the sensor signal can be measured based on the reference value, the indoor air pollution can be accurately measured. Can be measured.

Further, by deriving the sensor signal in the background state in the room and starting the integration of the variation from the time when the sensor signal becomes lower than the background level, it is possible to prevent the malfunction of the clean outside air level judgment, and thus it is possible to more accurately In addition, it is possible to provide an air quality detection device which is effective in making the clean outside air level the reference value of the sensor signal.

Furthermore, in addition to updating the reference value by the clean outside air level judgment, the reference value is updated by the minimum value of the sensor signal, and when the reference value cannot be updated by the clean outside air level judgment or the reference value is updated by mistake. Even in such a case, it is possible to provide an air quality detection device that is effective in correcting the reference value to a correct value.

Further, by setting the minimum value of the sensor signal in the last half year as the reference value, it is possible to always have the clean outside air level obtained by introducing a large amount of outside air in the intermediate period of spring or autumn as the reference value. An effective air quality detection device can be provided.

Furthermore, by correcting the reference value with the room temperature and humidity obtained by the temperature and humidity sensor, even if the temperature and humidity at the time when the reference value is updated and the temperature and humidity at the time of measurement are different, the indoor air is accurately polluted. It is possible to provide an air quality detection device that has an effect of being able to detect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an air quality detection device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a trend of a sensor signal of the air quality detection device according to the first embodiment of the present invention.

FIG. 3 is a chart showing the operation of the air quality detection device of the first embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an air quality detection device according to a second embodiment of the present invention.

FIG. 5 is a chart showing the operation of the air quality detection device of the second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an air quality detection device according to a third embodiment of the present invention.

FIG. 7 is a chart showing the operation of the air quality detection device of the third embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of an air quality detection device according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of an air quality detection device according to a fifth embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a conventional air quality detection device.

[Explanation of symbols]

 1 sensor 2 sampling means 3 signal storage means 4 change amount calculation means 5a output reduction determination means A 5b output reduction determination means B 6 change amount integration means 7 cleaning determination means 8 clean level storage means 9 contamination amount calculation means 10 output means 11 stable Degree monitoring means 12 background level storage means 13 reference value storage means 14 minimum value calculation means 15 minimum value storage means 16 clean level calculation means 17 temperature / humidity sensor 18 reference value correction means

Claims (5)

[Claims] 1. One or a plurality of sensors for detecting contamination of air in a room, a signal sampling means for sampling a signal of the sensor at regular time intervals, and a sensor signal sampled by the sampling means from past to present N The signal output means for calculating the change amount of the sensor signal from the signal storage means for individually storing and the change amount of the sensor signal from the plurality of sensor signals stored in the signal storage means and the change amount output from the change amount calculation means are compared to obtain the sensor output. Based on the output decrease determination means A for determining whether or not the output is decreased, and the change amount integration means for integrating the change amount when the output is decreased based on the determination results of the output decrease determination means A and the integrated change amount which is the output of the change amount integration means. Based on the result of the cleanliness judging means and the cleanliness judging means for judging whether or not the current sensor signal is the output value in the clean air, Clean level storage means for storing the sensor signal, a dirt amount calculation means for calculating the dirt amount of the indoor air by comparing the output value of the clean level storage means with the output of the sensor as a reference value, and the dirt amount externally. An air quality detection device comprising: 2. The stability monitoring means for monitoring the stability of the variation based on the variation of the sensor signal to determine whether or not the sensor signal is stable, and the output when the sensor signal is stable from the output of the stability monitoring means. A background level storage means for storing as a background level, an amount of change, and an output reduction determination means B for determining whether or not the sensor signal is lower than the background level which is the output of the background level storage means. 1. The air quality detection device according to 1. 3. The reference value storage means for comparing the sensor signal with the output value stored in the cleaning level storage means, storing the smaller value and outputting it to the dirt amount calculation means. Air quality detector. 4. One or more sensors for detecting dirt in the room, sampling means for sampling a signal of the sensor at regular intervals, and one or more days and a half year or less from the sensor signal sampled by the sampling means. Minimum value calculation means for calculating the minimum value of the signal of the sensor for a fixed period, minimum value storage means for storing at least half a year the minimum value output from the minimum value calculation means, and minimum value stored in the minimum value storage means A clean level calculating means for obtaining an output of the sensor in clean air; and a dirt amount calculating means for calculating a dirt amount of the indoor air by comparing the output value of the clean level calculating means with a signal of the sensor, An air quality detection device having an output means for outputting the amount of dirt to the outside. 5. A temperature / humidity sensor for detecting the temperature and humidity of indoor air, and a reference value correction means for correcting the output value of the cleaning level calculation means from the temperature and humidity output from the temperature / humidity sensor. Air quality detector.