JPH05249073A - Carbon dioxide concentration detection apparatus - Google Patents

Abstract

PURPOSE:To enhance the accuracy of a carbon dioxide concentration detection apparatus by improving the latching treatment of a reference value when the carbon dioxide concentration detection apparatus is calibrated. CONSTITUTION:The maximum value within a prescribed time (a) of signals from a carbon dioxide sensor 101 is stored in a maximum-output-value storage means (a) 102; the maximum value is stored in a maximum-output-value storage means (b) 1 only for a prescribed time (b). A group of maximum values which have been stored in the maximum-output-value storage means (b) 1 are weighted respectively by their dispersion; they are weighted by the difference from a reference value; the reference value is computed in a reference-value computation means 2. Thereby, the accuracy of the reference value is enhanced. In addition, when the maximum value is latched into the maximum-output-value storage means (a) 102, the stability of outputs is detected by using a sensor-output-stability detection means 6 so that the latching accuracy of the maximum value is enhanced. In addition, the state of a measuring atmosphere is known from the outputs of the sensor by using a sensor-output-value- dispersion monitoring means 7. Thereby, the proper maximum value is latched. In addition, the maximum value is monitored by means of dispersion degree and the reference value by using a maximum-value storage and monitoring means 8. Thereby, the reference value can be renewed stably.

Description

Detailed Description of the Invention

[0001]

The present invention relates to facility horticulture, environmental hygiene,
The present invention relates to a carbon dioxide gas concentration detector using a solid electrolyte carbon dioxide gas sensor used in a place for measuring and controlling carbon dioxide gas concentration for disaster prevention, industrial use, and the like.

[0002]

2. Description of the Related Art As a sensor for detecting carbon dioxide concentration,
There is a carbon dioxide gas sensor of a solid electrolyte that electrochemically detects the carbon dioxide gas concentration in an atmosphere using a solid electrolyte.

However, this sensor has some drawbacks, and the output tends to gradually decrease with time as shown in FIG. Therefore, it is necessary to correct the change with time of the output in the process of processing the output of the sensor.

For this reason, generally, the fact that a clean atmosphere (concentration of carbon dioxide gas is about 350 ppm) is constant is used to correct the change with time by utilizing the sensor output in the atmosphere.

A conventional carbon dioxide concentration detector will be described below with reference to FIGS. 9 and 11.

In the solid electrolyte carbon dioxide sensor, the sensor output is proportional to the logarithm of the carbon dioxide concentration as shown in the characteristic of FIG. 11, and the lower the concentration, the larger the output. Using this characteristic, the output was corrected in the normal environment where the carbon dioxide concentration is the lowest in the clean atmosphere, that is, the maximum value of the output is used as the reference value. FIG. 8 shows an example of a block diagram of a conventional carbon dioxide concentration detector.

In the figure, the carbon dioxide sensor 101 sends a signal to the maximum output value storage means 102 and also sends it to the concentration calculation means 103. Maximum output value storage means 102 receives a signal from carbon dioxide sensor 101, updates and stores the maximum value within a predetermined time, and sends the maximum value to concentration calculation means 103. The concentration calculating means 103 takes in the signal of the carbon dioxide sensor 101 and the maximum value of the maximum output value storing means 102 to calculate the carbon dioxide concentration, and sends the carbon dioxide concentration to the concentration outputting means 104. The concentration output means 104 outputs the carbon dioxide concentration to the outside. Here, according to the carbon dioxide concentration calculation method in the concentration calculation means 103, the relationship between the output of the carbon dioxide gas sensor and the carbon dioxide concentration is V = A + BLOG (CO ₂ ) where V is the sensor output and A is the reference. The value, B is the sensitivity of the sensor, and CO ₂ is the carbon dioxide concentration (ppm).

Among these, B is a value specific to the sensor and is a constant. The maximum value obtained by the maximum output value storage means 2 is C
Sensor output V and carbon dioxide concentration C at O2 = 350ppm
The O ₂ relationship is uniquely determined.

[0009]

However, when updating and storing the maximum output value in the maximum output value storage means, when the carbon dioxide concentration does not reach the concentration calculation standard of 350 ppm as shown in FIG. When the output value is the maximum output value, or when the extreme sensor output value such as noise is the maximum output value as shown in FIG.
As shown in FIG. 4, even if the output value of the sensor when the output value of the sensor moves improperly due to the influence of the interference gas or the like becomes the maximum output value, that value is stored as the maximum output value. There is a problem that the maximum output value is updated as a reference value with the passage of time.

The present invention solves such a problem, and the concentration of carbon dioxide gas in the atmosphere within a predetermined time is set to a standard value of 35.
A first object of the present invention is to provide a carbon dioxide gas detection device capable of updating the reference value with an error suppressed even when it does not reach 0 ppm.

A second object of the present invention is to provide a carbon dioxide detecting device capable of preventing the update of an erroneous reference value due to an illegal signal such as noise and monitoring the stability of the sensor output.

A third object of the present invention is to provide a carbon dioxide detecting device which monitors the state of air from the output change of the sensor and prevents the wrong reference value from being updated when the carbon dioxide concentration is high.

A fourth object is to provide a carbon dioxide detecting device capable of monitoring the stability of the sensor by monitoring the update of the reference value.

[0014]

The first means for achieving the first object of the present invention is a carbon dioxide gas sensor for detecting carbon dioxide gas, and a signal of the carbon dioxide gas sensor which is constantly received within a predetermined time a. Maximum output value storage means a for storing the maximum value of
A maximum output value storage means b capable of storing the maximum value obtained by the maximum output value storage means a for a predetermined time b, and carbon dioxide gas from a maximum value group stored in the maximum output value storage means b. Reference value calculation means for calculating a reference value necessary for obtaining the concentration, reference value storage means for updating and storing the reference value calculated by the reference value calculation means, and a signal of the carbon dioxide sensor during carbon dioxide detection And a reference value stored by the reference value storage means for calculating a carbon dioxide concentration from the signal and the reference value, and a concentration for outputting the carbon dioxide concentration received from the concentration calculating means to the outside. And output means.

The second means for achieving the second object is the maximum output value storage means a of the first means of the present invention.
The past output value storage means for always storing the signal of the carbon dioxide sensor for the past several minutes, the sensor output value stability detection means for detecting the stability of the sensor output value stored in the past output value storage means, Receiving the signal of the sensor output value stability detecting means and the signal of the carbon dioxide gas sensor, from the signal of the carbon dioxide gas sensor and the signal of the sensor output value stability detecting means, the maximum value is updated if it is stable, and if not stable, the maximum value is It is configured by including maximum value update determination means for determining not to update.

The third means for achieving the third object is the maximum output value storage means a of the first means of the present invention.
In addition, the sensor output value variation degree monitoring means for monitoring the variation of the sensor output value stored in the past output value storage means, the sensor output value variation degree monitoring means signal and the carbon dioxide gas sensor signal are received. From the signal of the gas sensor and the signal of the sensor output value variation degree monitoring means,
The maximum value update determination means for determining that the maximum value is not updated when the variation degree is large and the maximum value is updated when the variation degree is small is provided and configured.

A fourth means for achieving the fourth object is the maximum output value storage means c or the maximum output value storage means described in the second means of the present invention or the third means of the present invention. The means d calculates the maximum value update ratio by counting the number of maximum value update permission times from the signal of the sensor output value stability detecting means or the signal of the sensor output value variation degree monitoring means for the predetermined time a. Further, the signal from the maximum output value storage means a is fetched, the determination of storage of the maximum value sent from the maximum output value storage means a is determined from the maximum value update rate, and the maximum output value storage means e The maximum value storing and monitoring means for storing the signal from is stored only for a predetermined time b.

[0018]

The present invention has the configuration of the first means described above, and when the reference value is calculated from the maximum value group stored in the maximum output value storage means b by the reference value calculation means, the maximum output value storage means b is used. A variance weighting value obtained from the variance value and a difference weighting value obtained from the difference between the reference value and each maximum value are added to the respective maximum values stored in. That is, when the maximum value fluctuates and when it is far from the reference value, it is processed so as not to be used for the calculation of the reference value, so that the carbon dioxide concentration is 350 ppm of the reference concentration.
Even if the output value when it has not reached is stored as the maximum value, its influence can be reduced.

With the configuration of the second means, when the maximum output value is stored in the maximum output value storage means a, the stability of the output value of the carbon dioxide sensor for the past several minutes is detected by the sensor output value stability determination means. Since it is possible to know the sensor output or the stability of the carbon dioxide concentration of the atmosphere,
It is possible to stably update the reference value.

With the configuration of the third means, when the maximum output value is stored in the maximum output value storage means a, the sensor output variation degree detecting means detects the variation degree of the output value of the carbon dioxide gas sensor in the past several minutes. Since it is possible to know the state of the air from the variation of the sensor output,
The maximum output value can be prevented when the air is not clean, and the stable reference value can be updated.

With the configuration of the fourth means, the maximum output value storage means c of the second means or the maximum output value storage means d of the third means is provided with a maximum value update monitoring means, and the maximum output value storage means is provided. When the maximum value is stored in f, the maximum value to be stored is monitored to prevent erroneous update of the reference value due to temporary stabilization of the sensor output, and stable update of the reference value can be performed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.
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 the figure, the carbon dioxide sensor 101 is
A signal is sent to the maximum output value storage means a102. And a signal to the concentration calculation means 103. Maximum output value storage means a1
02 receives the signal from the carbon dioxide sensor 101, updates and stores the maximum value within a predetermined time a, and sends it to the maximum output value storage means b1. The maximum output value storage means b1 stores the signal from the maximum output value storage means a1 for a predetermined time b and sends it to the reference value calculation means 2 after the predetermined time b has elapsed.
The reference value calculation means 2 takes in the signal from the maximum output value storage means b1 and, for each maximum value stored in the maximum output value storage means b1, the dispersion weighting value obtained from the dispersion value, and the reference value, and the respective reference values. Calculate the weighted value of the difference obtained from the difference with the maximum value, that is, when the maximum value varies and is far away from the reference value, it is processed so that it is not used in the calculation of the reference value, and the reference value is calculated. And sends it to the reference value storage means 3. The reference value storage means 3 takes in the reference value sent from the reference value calculation means 2, updates and stores the reference value, and sends the reference value to the density calculation means 103. The concentration calculation means 103 takes in the signal from the carbon dioxide gas sensor 101 and the reference value of the reference value storage means 3, calculates the carbon dioxide concentration, and sends the carbon dioxide concentration to the concentration output means 104. Concentration output means 10
4 sends the carbon dioxide concentration to the outside.

Next, the operation will be described. In FIG. 2, when the carbon dioxide detection device is turned on and the carbon dioxide sensor is warmed up, and then the carbon dioxide detection device is placed in a normal measurement atmosphere, the operation from step 401 to step 408 is cut off. Is repeated until. The operation from steps 401 to 408 will be described. First, the maximum output value storage means a102 determines whether or not the fixed time a (30 minutes) of step 401 has elapsed, and if so, the process proceeds to step 403. .. If it has not elapsed, the process proceeds to step 402, and the larger one of the maximum value stored in the maximum output value storage means a102 and the signal received from the carbon dioxide sensor is stored as a new maximum value. When the process proceeds to step 403, the maximum value stored in the maximum output value storage means a102 is stored in the maximum output value storage means b1, and in step 404, the constant value b
Whether or not (4 hours) has elapsed is judged, and if it has elapsed, the routine proceeds to step 405, where the reference value calculation means 2 stores the maximum value stored in the maximum output value storage means b1 (in 30 minutes). One maximum value is stored for 4 hours), and the variance weighting value of the maximum value is calculated from the variance values obtained from the maximum value group, and the difference between each maximum value and the current reference value is calculated. The weighted value of each difference obtained is calculated, and the respective dispersion weighted value and the weighted value of the respective difference are added to the respective maximum values to calculate the reference value, and in step 406, the reference value storage means 3 is used. Update and store the reference value. If it has not elapsed, the maximum value for calculating the reference value is not available, so the reference value is not updated. Steps 402.40.4
Upon completion of 06, in any case, the operation proceeds to the operation of step 407, the carbon dioxide concentration is calculated from the difference between the reference value and the signal received from the carbon dioxide sensor 101 in the concentration calculating means 103, and from the concentration outputting means 104 in step 408. The carbon dioxide concentration is output to the outside.

After that, the process returns to the step 401. Hereinafter, embodiments of the second, third, and fourth carbon dioxide concentration detectors of the present invention will be described with reference to FIGS. 3 to 8. The description of the first carbon dioxide concentration detector of the present invention will be given below. The same parts as those shown in FIGS. 1 and 2 used in FIG.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. As shown in the figure, the carbon dioxide sensor 101 sends a signal to the past output value storage means 4 and also determines the maximum value update determination means 5 and the concentration calculation means 103.
Send a signal to. The past output value storage means 4 receives the signal from the carbon dioxide gas sensor 101, updates and stores the signals for the past several hours, and sends the signals for the past several hours to the sensor output value stability detecting means 6. The sensor output value stability detecting means 6 is shown in FIG.
As shown in FIG. 4, the signal for the past several hours is received from the past output value storage means 4, and it is detected whether the output signal of the carbon dioxide gas sensor 101 is stable or not from the difference between the maximum value and the minimum value in the past, and the maximum value update determination means 5 is detected. Send stability signal to. The maximum value update determination means 5 takes in the signal of the carbon dioxide gas sensor 101 and the stability signal of the sensor output value stability detection means 6, and if the value of the stability signal is stable, stores the signal of the carbon dioxide gas sensor 101 in the maximum output value storage means a102. If the value of the feed stability signal is unstable, the signal of the carbon dioxide sensor 101 is changed to the maximum output value storage means a10.
Make a decision not to send to 2. Maximum output value storage means a102
Is the carbon dioxide sensor 1 that has passed through the maximum value update determination means 5.
Upon receiving the signal from 01, the maximum value within a predetermined time a is updated and stored, and the maximum output value storage means b1 is sent.

Next, the operation will be described. In FIG. 4, first, the maximum output value storage means a2 determines whether or not the fixed time a (30 minutes) of step 401 has passed, and if it has passed, the process proceeds to step 403. If it has not elapsed, the routine proceeds to step 601, where the signal of the carbon dioxide gas sensor 101 is taken into the past output value storage means 4 and the signal of the past several hours (16 minutes) is updated and stored. The sensor output value stability detecting unit 6 detects the stability of the signal of the carbon dioxide gas sensor for the past 16 minutes from the signal output in the past output value storage unit 4 for the past several hours. If the detection result is unstable, the process proceeds to step 407. .. If stable, step 4
In step 02, the maximum output value storage means a102 stores the maximum value. After that, the operations from steps 403 to 408 are the same as those of the first carbon dioxide detection device of the present invention.

Next, a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. As shown in the figure, the carbon dioxide sensor 101 sends a signal to the past output value storage means 4 and also determines the maximum value update determination means 5 and the concentration calculation means 103.
Send a signal to. The past output value storage means 4 receives the signal from the carbon dioxide gas sensor 101, updates and stores the signals for the past several hours, and sends the signals for the past several hours to the sensor output value variation degree monitoring means 7. Sensor output value variation degree monitoring means 7
Receives signals for the past several hours from the past output value storage means 4, monitors the variation of the output signal of the carbon dioxide sensor 101, and the output signal of the sensor varies proportionally when the air becomes dirty as shown in FIG. Therefore, the state of air is sent to the maximum value update determination means 5 as a dispersion degree signal. The maximum value update determination means 5 takes in the signal of the carbon dioxide gas sensor 101 and the variation degree signal of the sensor output value variation degree monitoring means 7, and sends the signal of the carbon dioxide gas sensor 101 to the maximum output value storage means a102 if the variation degree signal is small, If the variation degree signal is large, it is determined that the signal of the carbon dioxide sensor 101 is not sent to the maximum output value storage means a102. The maximum output value storage means a102 receives the signal from the carbon dioxide gas sensor 101 that has passed through the maximum value update determination means 5, updates and stores the maximum value within a predetermined time a, and sends it to the maximum output value storage means b1.

Next, the operation will be described. In FIG. 6, first, the maximum output value storage means a2 determines whether or not the fixed time a (30 minutes) in step 401 has passed, and if it has passed, the process proceeds to step 403. If it has not elapsed, the routine proceeds to step 701, where the signal of the carbon dioxide gas sensor 101 is taken into the past output value storage means 4, and the signal of the past several hours (16 minutes) is updated and stored. The sensor output value variation degree detection means 7 monitors the variation of the signal of the carbon dioxide gas sensor for the past 16 minutes, and the signal captured in the past output value storage means 4 is monitored by the sensor output value variation degree detection means 7 and the signal indicates that the person is in the room or burns. If there are variations due to the influence, proceed to step 407. If it is stable, the process proceeds to step 402, and the maximum output value storage means a102 stores the maximum value. After that, the operations from steps 403 to 408 are the same as those of the first carbon dioxide detection device of the present invention.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. As shown in the figure, the carbon dioxide sensor 101 sends a signal to the past output value storage means 4 and also determines the maximum value update determination means 5 and the concentration calculation means 103.
Send a signal to. The past output value storage means 4 receives the signal from the carbon dioxide gas sensor 101, updates and stores the signals for the past several hours, and sends the signals for the past several hours to the sensor output value variation degree monitoring means 7. Sensor output value variation degree monitoring means 7
As shown in FIG. 16, a signal for the past several hours is received from the past output value storage means 4, the degree of variation of the output signal of the carbon dioxide sensor 101 is monitored, and a variation degree signal is sent to the maximum value update determination means 5, and at the same time the maximum value is determined. A variation degree signal is sent to the value storage monitoring means 8. Whether the maximum value update determination means 5 takes in the signal of the carbon dioxide gas sensor 101 and the variation degree signal of the sensor output value variation degree monitoring means 7 and sends the signal of the carbon dioxide gas sensor 101 to the maximum output value storage means a102 according to the value of the variation degree signal. judge. Maximum output value storage means a1
02 receives and receives a signal from the carbon dioxide sensor 101 that has passed through the maximum value update determination means 5, updates and stores the maximum value within a predetermined time a, and sends the maximum value to the maximum value storage monitoring means 8. The maximum value storage monitoring means 8 fetches and updates / stores the reference value sent from the reference value storage means 3 when the reference value storage means 3 updates / stores the reference value, and also the maximum value of the maximum output value storage means a102. Then, the variation degree signal of the sensor output value variation degree monitoring means 7 is fetched, the variation degree signals are integrated, and the maximum value of the predetermined time a is determined by the integrated value. The maximum output value storage means b1 is the maximum value storage monitoring means 8
The signal from is stored for a predetermined time b and is sent to the reference value calculating means 2 when the predetermined time b has elapsed. Further, the reference value storage means 3 takes in the reference value sent from the reference value calculation means 2, updates and stores the reference value, and the reference value is calculated by the density calculation means 10.
3 and the maximum value storage monitoring means 8.

Next, the operation will be described. In FIG. 8, first, the maximum output value storage means a2 determines whether or not the fixed time a (30 minutes) in step 401 has passed, and if it has passed, the process proceeds to step 1002. If it has not elapsed, the routine proceeds to step 701, where the signal of the carbon dioxide gas sensor 101 is taken into the past output value storage means 4, and the signal of the past several hours (16 minutes) is updated and stored. The sensor output value variation degree detection means 7 monitors the variation of the signal of the carbon dioxide gas sensor for the past 16 minutes, and the signal captured in the past output value storage means 4 is monitored by the sensor output value variation degree detection means 7 and the signal indicates that the person is in the room or burns. If there are variations due to the influence, proceed to step 1001. If it is stable, the process proceeds to step 402, the maximum output value storage means a102 stores the maximum value, and the process proceeds to step 1001. Step 1001
Is a predetermined time a (30 minutes) according to a signal from the sensor output value variation degree monitoring means 701 by the maximum value update monitoring means 8.
During this period, it is monitored whether the signal of the carbon dioxide sensor 101 is stable. When the process proceeds to step 1002, the predetermined time a obtained by the maximum value storage monitoring means 8 in step 1001
During the period, the maximum value storage monitoring means 8 monitors the maximum value update from the stability of the signal of the carbon dioxide sensor 101. If the stability indicates stable, the maximum value stored in the maximum output value storage means a102 at that time is sent to the maximum output value storage means b1. When the stability is unstable, the value of the reference value currently stored in the maximum value storage monitoring means 8 is sent to the maximum output value storage means b1. further,
When the reference value storage means 3 updates and stores the reference value, the maximum value storage monitoring means 8 fetches and updates the value and stores it.
When the reference value storage means 3 in step 406 updates and stores the reference value, the value is sent to the maximum value update monitoring means 8.

After that, the operation from step 403 to step 408 is the same as that of the first carbon dioxide detecting device of the present invention.

[0033]

As is apparent from the above embodiments, according to the present invention, when the reference value calculation means calculates the reference value from the maximum value group stored in the maximum output value storage means b, The respective dispersion weighting values calculated from the dispersion values obtained from the maximum value group to the respective maximum values of the maximum value group, and the respective weighting values of the differences obtained from the difference between the current reference value and the respective maximum values are respectively described above. A carbon dioxide detection device is provided that has the effect of reducing the effect of the output value when the carbon dioxide concentration does not reach the standard concentration of 350 ppm by being added to the maximum value of it can.

Further, when storing the maximum output value in the maximum output value storage means a, the stability of the output value of the carbon dioxide sensor for the past several minutes can be detected by the sensor output value stability determination means, and the sensor output and Since it is possible to know the stability of the carbon dioxide concentration in the atmosphere, it is possible to provide a carbon dioxide detector which is effective in updating the reference value in a stable manner.

Further, when the maximum output value is stored in the maximum output value storage means a, the variation degree of the output value of the carbon dioxide gas sensor in the past several minutes can be detected by the sensor output variation degree detecting means, and the state of the air Since it can be known from the dispersion of the sensor output, by providing the carbon dioxide detection device with the effect that the stable reference value can be updated by not taking the maximum output value when the carbon dioxide concentration is high. it can.

Further, according to the configuration of the fourth means, the maximum output value storage means c of the second means or the maximum output value storage means d of the third means is provided with maximum value storage monitoring means, and the maximum output value storage means is provided. When storing the maximum value in f, by monitoring the stored maximum value, it is possible to prevent erroneous updating of the reference value due to temporary stabilization of the sensor output and to perform stable updating of the reference value. A gas detector can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of a first carbon dioxide concentration detector according to the present invention.

FIG. 2 is a chart showing the operation of the first carbon dioxide concentration detecting device of the present invention.

FIG. 3 is a block diagram of a second carbon dioxide concentration detector according to the present invention.

FIG. 4 is a chart showing the operation of the second carbon dioxide concentration detecting device of the present invention.

FIG. 5 is a block diagram of a third carbon dioxide concentration detector according to the present invention.

FIG. 6 is a chart showing the operation of the third carbon dioxide concentration detecting device of the present invention.

FIG. 7 is a block diagram of a fourth carbon dioxide concentration detector according to the present invention.

FIG. 8 is a chart showing the operation of the fourth carbon dioxide concentration detecting device of the present invention.

FIG. 9 is a block diagram of a conventional carbon dioxide concentration detector.

FIG. 10 is a diagram showing a change with time of a carbon dioxide sensor.

FIG. 11 is a diagram for explaining a method of calculating carbon dioxide concentration.

FIG. 12 is a diagram showing changes in carbon dioxide concentration over time.

FIG. 13 is a diagram showing noise of a signal from a carbon dioxide sensor.

FIG. 14 is a diagram showing the influence of interference gas on the signal of the carbon dioxide sensor.

FIG. 15 is a diagram for explaining the stability of the signal of the carbon dioxide sensor.

FIG. 16 is a diagram for explaining the state of air depending on the degree of dispersion of signals of a carbon dioxide sensor.

[Explanation of symbols]

 1 maximum output value storage means b 2 reference value calculation means 3 reference value storage means 4 past output value storage means 5 maximum value update determination means 6 sensor output value stability detection means 7 sensor output value variation degree monitoring means 8 maximum value storage monitoring Means 101 Carbon dioxide sensor 102 Maximum output value storage means a 103 Concentration calculation means 104 Concentration output means

Claims (4)

[Claims] 1. A carbon dioxide gas sensor for detecting carbon dioxide gas, a maximum output value storage means a for always receiving a signal from the carbon dioxide gas sensor, and storing a maximum value within a predetermined time a, and the maximum output value storage means a. The maximum value obtained by
A maximum output value storage means b capable of storing only a minute, a reference value calculation means for calculating a reference value necessary for obtaining the carbon dioxide concentration from the maximum value group stored in the maximum output value storage means b, and the reference value The reference value storage means for updating and storing the reference value calculated by the calculation means, the signal of the carbon dioxide sensor during the detection of carbon dioxide concentration and the reference value stored by the reference value storage means, and the signal And concentration calculating means for calculating the carbon dioxide concentration from the reference value,
A carbon dioxide concentration detecting device comprising a concentration output means for outputting the carbon dioxide concentration received from the concentration calculation means to the outside. 2. The maximum output value storage means a detects past output value storage means for always storing the signal of the carbon dioxide sensor for the past several minutes, and the stability of the sensor output value stored in the past output value storage means. When the sensor output value stability detecting means receives the signal of the sensor output value stability detecting means and the signal of the carbon dioxide gas sensor, the maximum value is obtained from the signal of the carbon dioxide sensor and the signal of the sensor output value stability detecting means if stable. 2. The carbon dioxide concentration detecting device according to claim 1, further comprising maximum value update determining means for determining whether or not the maximum value has been updated if it is updated. 3. A maximum output value storage means a, a past output value storage means, a sensor output value variation degree monitoring means for monitoring a variation degree of the sensor output values stored in the past output value storage means, and the sensor output. When the variation of the value of the carbon dioxide sensor and the signal of the sensor output value variation monitoring means is large, the maximum value is not updated and the variation is small. 2. The carbon dioxide concentration detecting device according to claim 1, further comprising a maximum value update determining means for making a determination to update the maximum value. 4. The number of updates of the maximum value is counted for a predetermined time a from the signal of the sensor output value stability detecting means or the signal of the sensor output value variation degree monitoring means according to claim 2 or 3. Then calculate the maximum update rate,
Further, after a lapse of a predetermined time a, the maximum value sent from the maximum output value storage means a is fetched, and the storage of the maximum value sent from the maximum output value storage means a is judged from the maximum value update rate. 2. The carbon dioxide concentration detecting device according to claim 1, further comprising a maximum value storage monitoring means for making a determination and sending a signal from the maximum output value storage means a to a maximum output value storage means b for storing a predetermined time b.