JPH10111270A - Correction method for signal base line value of carbon dioxide gas measuring unit and carbon dioxide gas measuring unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a carbon dioxide gas measuring unit simple and compact by monitoring a signal value of the concn. of carbon dioxide detected by a detection means and correcting a signal base line value when the signal value is less than a corrected set concn. value during a definite period. SOLUTION: A detection means A1 containing a solid electrolyte type carbon dioxide gas sensor, a power supply necessary for driving the same, various temp. compensation circuits or signal amplifying circuits detects the concn. of carbon dioxide. A correction and calibration means A2 corrects a signal base line value when the signal value of the concn. of carbon dioxide gas detected for the definite period by the detection means A1 is not less than a corrected set concn. value. The definite period is pref. about one week or more and usually one - several months. The concn. data of carbon dioxide corrected and calibrated by the correction and calibration means A2 is inputted to the ventilation judging means B1 of a ventilation unit B and compared with separately determined required ventilation concn. and, if necessary, ventilation is started by a ventilation means B2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide gas having detection means for detecting the concentration of carbon dioxide, and correction and calibration means for correcting and calibrating a signal value detected by the detection means and converting it to a carbon dioxide concentration value. Related to the measurement unit. This is, for example, connected to a display unit to serve as a carbon dioxide concentration measuring device, connected to a ventilation unit to function as a ventilation monitor, and connected to an alarm unit to constitute a carbon dioxide alarm device.

[0002]

2. Description of the Related Art A carbon dioxide gas ventilation monitor has a carbon dioxide gas sensor such as a solid electrolyte type sensor or an infrared sensor as a carbon dioxide gas detecting means, and a signal value sent from the detecting means is preset. Compared to the alarm required concentration, if the value is higher than that value, it is assumed that an abnormality has been detected and the ventilation unit is activated to perform ventilation, and it is used for applications related to combustion heating equipment such as water heaters, boilers, etc., or for safety or security. Widely used for purposes.

[0003] As the detection means of the above-mentioned carbon dioxide gas alarm, NASICO has good sensitivity at low concentration and responsiveness to concentration change, and can be made compact.
A concentration cell type carbon gas sensor in which a carbonate is attached to a solid electrolyte such as N is widely used as a detection unit. Since the concentration cell type oxygen sensor generates an electromotive force corresponding to the concentration of carbon dioxide in the gas to be measured, the concentration of carbon dioxide can be known from the potential difference.

However, during long-term use, the electromotive force tends to decrease. When used as an apparatus, the baseline of the output of the detection means may drift without the correction means, and ventilation may be required even when ventilation is unnecessary. Here, the output of the concentration cell type carbon dioxide gas sensor is the electromotive force E (mv), and the output of the high impedance circuit is considerably high. FIG. 1 shows the relationship between the actual elapsed days and the amount of change in the base electromotive force. For the correction and calibration of the base electromotive force, automatic calibration performed by introducing outside air can be considered, but the equipment and circuits are complicated and the size is increased, and the cost is increased. It becomes difficult to apply to fields such as ventilation monitors.

Japanese Patent Laid-Open Publication No. 7-270315 has proposed a correction / calibration means for automatically performing correction / calibration. In this technique, two detection means are provided, and correction and calibration are performed on the assumption that the outputs of the two detection means have the same baseline drift. However, it is unlikely that a plurality of detection means will have completely equal baseline drifts, and therefore have low reliability.
In addition, since a plurality of detection means are provided, it is difficult to reduce the size of the apparatus, and the cost is increased.

On the other hand, as a simple method of correcting the baseline value, there is known a method in which the concentration of carbon dioxide in the atmosphere is kept constant. That is, since the concentration of carbon dioxide present in normal air is considered to be about 400 ppm, this method is a method of correcting this value to match the baseline.

[0007] However, it has been found that the output corresponding to the baseline of the sensor in the air changes depending on the daily atmospheric environment. That is, FIG. 2 shows the result of examining the history of the carbon dioxide concentration of the air in a certain room over one week. In this figure, the carbon dioxide concentration on the fourth day is high, which is the effect of the rainy day. Such a carbon dioxide concentration is, for example, 400
When the baseline value is corrected on the basis of ppm, and a sample gas containing 1000 ppm of carbon dioxide is measured, a large measurement error as shown in FIG. 3 occurs. In particular, according to the correction of the rainy day on the fourth day, an error of more than 30% occurs and cannot be overlooked.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, that is, a signal baseline value of a carbon dioxide gas measuring unit suitable for a field requiring simplification and compactness such as a ventilation monitor. It is an object of the present invention to provide a correction method of the above and a carbon dioxide measurement unit.

[0009]

According to a first aspect of the present invention, there is provided a method for correcting a signal baseline value of a carbon dioxide gas measuring unit, wherein a signal value of a carbon dioxide gas concentration detected by a detecting means is monitored and a constant value is obtained. When the signal value does not fall below the correction set density value during the period, the signal baseline value is corrected.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the zero level concentration value is the concentration of carbon dioxide present in the ordinary atmosphere, which is 330 ppm in the Chemical Handbook (Revised 3rd Edition).
The science chronology (1996 version) states that it is 320 ppm. Any of the values described in the literature such as these or their average values may be used, but since these values are not normally observed today due to the recent increase in atmospheric carbon dioxide, etc., they may be slightly higher. , For example, 360 ppm is desirably used as the reference concentration.

On the other hand, the standard level concentration value is the lowest concentration of carbon dioxide in the place where the carbon dioxide gas measuring unit is installed, and is therefore a value higher than the zero level concentration value. Here, it is usually desirable to use 500 ppm, which is the lowest value in an environment where humans enter and exit, as the standard level concentration value. The correction set density value is a standard value for performing the correction, and is set to a value higher than the standard level density value. Since the range between the correction set density value and the standard level density value is a measure of an allowable error width, the maximum error is 20%.
Usually, it is desirable to set the value to about 600 ppm.

Although it has been described above that the base electromotive force of the concentration cell type carbon dioxide gas sensor changes as shown in FIG. 1 over a long period of use, it eventually deteriorates and the sensitivity lowers. That is, FIG. 4 shows the results obtained by using the concentration cell type carbon dioxide sensor for a long period of time and examining the change in sensitivity during that period. In FIG. 4, the horizontal axis represents the amount of change in the base electromotive force that has changed as a result of use, and the vertical axis represents the amount of change in the sensor output with respect to air containing 2000 ppm of carbon dioxide. From FIG. 4, it can be seen that the sensitivity is not significantly deteriorated during the period when the amount of change of the base electromotive force is about −50 mV. Therefore, this period can be used only by correcting the baseline value, but thereafter, since the sensitivity itself has changed, accurate measurement cannot be performed only by correcting the baseline value. Therefore, the correction by correcting the signal baseline value can be performed until the correction amount becomes about -50 mV in terms of electromotive force in practical use.

Since the change of the signal baseline is relatively slow as shown in FIG. 1, the certain period in the present invention is preferably about one week or more, usually one month to several months. However, at the time of initial startup after startup, this period is short as several seconds to several hours,
An optimal signal baseline can be obtained by initializing the signal baseline.

In the signal baseline correction method of the present invention, the correction width can be arbitrarily determined. However, for example, the signal baseline value may be corrected so that the minimum value of the signal value during the certain period matches the zero-level density value. The correction width of the baseline value is the difference between the standard level density value and the correction set density value (the standard level density value is 500 ppm, and the correction set density value is 600 ppm).
100 ppm).

When the correction of the signal baseline value is too large and the measured value becomes less than the zero level density value (for example, 360 ppm) in the subsequent measurement, the signal value is immediately replaced with the zero level density value. If the signal baseline is corrected (hereinafter, referred to as “reverse correction”) so as to match the above, overcorrection can be prevented. It should be noted that this inverse correction must not be performed when the carbon dioxide gas measurement unit is used in an environment with extremely low carbon dioxide gas concentration (such as in an artificial atmosphere).

Here, an example of the method of correcting the signal baseline value of the carbon dioxide measuring unit of the present invention will be described with reference to the model diagram of FIG. In this model, the standard level density value is 5
00 ppm, the correction set density value is 600 ppm, and the zero level density value is 360 ppm. The place where the carbon dioxide measuring unit is used is usually in the atmosphere, and the unit has been operating stably since a long time has passed since the power was turned on. The sensor output gradually increases due to the drift of the signal baseline. In the first period and the second period, the signal value in each period is the correction set concentration value (600 ppm)
Therefore, no correction is made.

In the third period, since the lowest value of the signal value in that period does not become lower than the correction set density value (600 ppm), the signal baseline is corrected simultaneously with the start of the fourth period. In this example, the correction of 100 ppm, which is the difference between the correction set density value and the standard level density value, is performed. However, since the above correction is overcorrection, the correction value may be less than the zero level density value in the fourth period. Therefore, reverse correction of the signal base line is performed so as to match the zero level density. As the sensor output increases thereafter, the necessity of reverse correction is eliminated. The correction value is the correction set concentration value (600 ppm) in the fifth term.
Since it does not become the following, the signal baseline is corrected at the same time as the start of the sixth period. In this model, a correction of 100 ppm was performed.
Various corrections are possible, such as performing correction so as to match pm.

FIG. 6 is a block diagram showing an example of a ventilation monitor using the carbon dioxide measuring unit of the present invention.
Reference numeral A1 in the drawing denotes detection means (including a solid electrolyte type carbon dioxide sensor and a power supply required for driving the same, various temperature compensation circuits, a signal amplification circuit, and the like) for detecting the concentration of carbon dioxide. .

On the other hand, what is indicated by reference numeral A2 is that the signal value of the carbon dioxide concentration detected by the detecting means falls below the signal value of the carbon dioxide concentration detected by the detecting means A1 for a certain period of time. If there is no correction value, the correction correction means corrects the signal baseline value and reversely corrects the signal baseline so that the signal value of the carbon dioxide gas does not fall below the zero level concentration value. The measurement unit A is constituted by the detection means A1 and the correction calibration means A2.

The carbon dioxide concentration data corrected / calibrated by the correction / calibration means A2 of the measurement unit A is input to the ventilation determination means B1 of the ventilation unit B, and is compared with a separately determined required ventilation concentration. Thus, ventilation is started by the ventilation means B2. The display unit C displays the signal value corrected by the correction configuration unit, that is, the measured value. If the ventilation unit B is not provided, the carbon dioxide measurement unit A is not a carbon dioxide ventilation monitor but a carbon dioxide concentration measurement device.

Hereinafter, an example of a ventilation monitor using the carbon dioxide measuring unit according to the present invention (when the carbon dioxide concentration is 2000
(ventilation at over ppm) will be described in more detail. FIG. 7A is a circuit diagram of a ventilation monitor using the carbon dioxide measuring unit according to the present invention. Reference numeral 1 denotes a detection unit, which includes a concentration cell type carbon gas sensor, an impedance conversion circuit, a temperature correction circuit, an amplification circuit, and other accessory circuits.

In FIG. 7A, the output of the detector 1 is A
An input port 2 ia with a / D converter is taken into a microprocessing unit (hereinafter, referred to as “MPU”) 2 and converted into a numerical value corresponding to an output in the input port 2 ia (obtained by the input port 2 ia). The value thus obtained is hereinafter referred to as “sensor output”).

The MPU 2 has, in addition to the input port 2ia, an output port 2oa for transmitting a control signal of a ventilation fan as the ventilation means 3, an output port 2ob for transmitting a measurement result to the LCD display unit 4, and A control program; and
R storing a reference level value L (here, 2000 ppm) which is a threshold concentration of ON / OFF for controlling the ventilation means 3 and the like.
OM2ro (see FIG. 7 (b)), time data of elapsed time since power-on (hereinafter referred to as "timer T1"), time data of elapsed time during initial correction (hereinafter "timer T2")
), Time data for a certain period of time during measurement (hereinafter, referred to as "timer T3"), a signal baseline value K which is a signal baseline value, and A which temporarily holds a sensor output. , And RA storing various data of Amin that holds the lowest sensor output within a certain period.
M2ra (see FIG. 7 (c)), a central processing unit (hereinafter referred to as "CP") for executing the above program.
U ") is built in.

Ventilation means is connected to the output port 2oa of the MPU 2. When a signal ON is output to the output port 2oa, the ventilation means is activated, and when a signal OFF is output, the ventilation means is stopped. Has become. The LCD display unit 4 is connected to the output port 2ob. When the carbon dioxide concentration corrected by the signal baseline value K is output to the output port 2ob, it is displayed on the LCD display unit 4. As will be described later, the LCD display unit displays a measured value without correction for 5 minutes after the power is turned on, and thereafter displays the corrected measured value. Therefore, if there is no change in the carbon dioxide concentration during this time, the signal baseline value, that is, the magnitude of the correction amount can be determined from the difference between the display value after the switch is turned on and the corrected display value thereafter, and as a result, the sensor Deterioration status can be known.

The operation of the ventilation monitor will be described with reference to flowcharts (FIGS. 8 and 9). The operation of the ventilation monitor can be divided into three stages after the power supply is introduced. That is, the initial display stage, the initial correction stage, and the steady stage. The initial display stage is a stage in which the temperature rise by the heater attached to the sensor for maintaining the solid electrolyte at an appropriate temperature is started and stabilized, and is set to 5 minutes in the following example. Also,
During this period, the measured value without correction is displayed, so that the deterioration state of the sensor can be grasped as described above.
This step corresponds to steps S1 to S4 in FIG.

In this embodiment, the initial correction stage is from 5 minutes after the power supply is introduced to 1 hour. At this stage, the signal baseline value is corrected every minute to make it appropriate immediately. This step corresponds to steps S5 to S17 in FIG. In the next steady stage, the carbon dioxide concentration is measured by the signal baseline obtained in the initial correction stage, the ventilation means is controlled as necessary, and the signal value of the carbon dioxide concentration detected by the detection means. Is monitored, and if the signal value does not fall below the correction set density value during a certain period, the signal baseline value is corrected. This step corresponds to steps S18 to S32 in FIG.

In the following example, the standard level density value is 5
00 ppm, the correction set density value is 600 ppm, and the zero level density value is 360 ppm. The place where the carbon dioxide measuring unit is installed is usually in the atmosphere. The correction range is to correct the signal baseline value so that the minimum value of the signal value during the above-mentioned fixed period matches the standard level density value.

First, as shown in FIG. 8, when the power is turned on, the control program starts, the values in the RAM 2ra are initialized, and then, as shown in step S1, the timer T
1 starts. The sensor output at that time, that is, the value of the input port 2ia is output to the output port 2ob,
It is displayed on the display unit 4 (steps S2 and S3). Steps S2 and S3 are repeated for 5 minutes in step S4. After a lapse of 5 minutes, the initial display stage ends, and the initial correction stage starts. First, the timer T2 starts.
Ami that holds the minimum sensor output within the period in step S6
Initialize n.

Step S7 is a step for monitoring the end of the initial correction stage. In this step S7, until one hour elapses after the power is turned on, steps S6 to S1 are performed.
7 is repeated. If the value of the timer T2 is not 1 minute or more in step S8, the process proceeds to step S9. In step S9, the value of the input port 2ia is assigned to A in the RAM. In step S10, the value of Amin is compared with the value of A. If the value of Amin is large, the value of Amin is determined in step S11.
The value of A is substituted for the value of Amin, and the value of Amin keeps the minimum value of the period, and the process proceeds to step S12. If the value of Amin is less than the value of A, the process immediately proceeds to step S12.

In step S12, it is checked whether or not the density obtained by correcting the sensor output value with the signal baseline value K (initial value is 0) is less than the standard level density value. The signal baseline value K that becomes the standard level density is corrected (step S13), and the process proceeds to step S14. In step S15, the corrected measured value is output to the output port 2ob and displayed on the LCD display unit 4. Such steps S6 to S14 are repeated, and when the value of the timer T2 exceeds one minute,
The process proceeds from step S8 to step S15.

In step S15, the value of the timer T2 is reduced by one minute. In step S16, the value obtained by correcting the minimum value Amin of the signal value for one minute before that by the signal baseline value K is 6
It is checked whether it is more than 00 ppm.
If not less than m, it is determined that the baseline is not stable, and in step S17, the signal baseline value K is corrected so that the value obtained by correcting Amin with the signal baseline value K becomes 500 ppm, and the process returns to step S6. When the concentration becomes 600 ppm or less, step S6 is immediately performed.
And the steps S6 to S17 are repeated in this manner until one hour after the power is turned on. One hour after the power is turned on, the process proceeds from step S7 to step S18 (see reference numerals in FIGS. 8 and 9), and a steady state is reached.

FIG. 9 shows a flow chart at the steady stage. In step S18, the timer T3 starts. Step S1
In step 9, Amin holding the minimum sensor output within the period managed by the timer T3 is initialized. Step S20 is a step for monitoring a cycle of a certain period (10 days in this example). If the value of the timer T3 does not exceed 10 days, steps S220 to S29 are repeated.

In step S21, the value of the input port 2ia is assigned to A in the RAM. In step S22, the value of Amin is compared with the value of A. If the value of Amin is large, the value of A is substituted for Amin in step S23, and the value of Amin keeps the minimum value of the period. If the value is equal to or less than the value of A, the process proceeds to step S24.

In step S24, it is checked whether or not the density corrected from the sensor output value by the signal baseline value K (initial value is 0) is less than the zero level density value (360 ppm). Is corrected to the zero level density (step S25), and if it is equal to or higher than the zero level density, the process proceeds to step S26. In step S26,
The measured value corrected by the signal baseline value K is output to the output port 2ob and displayed on the LCD display unit 4.

In step S27, the corrected measured value is compared with a reference level L (2000 ppm in this example),
If it is higher than the reference level L, a signal ON is output to the output port 2oa and the operation of the ventilation means is started. If it is lower than the reference level L, a signal OFF is output to the output port 2oa and the operation of the ventilation means is stopped. And then step S2
Returning to 0, steps S20 to S29 are repeated.

If the value of the timer T3 exceeds 10 days, which is a fixed period in this example, the process proceeds from step S20 to step S30. In step S30, 10 days are subtracted from the value of the timer T3, and the process proceeds to step S31. In step S31,
A value obtained by correcting the lowest output value of the sensor output during the certain period by the signal baseline value K is the correction set density value 600.
It is checked whether it is more than 600 ppm. If this value does not fall below 600 ppm, it is determined that the signal baseline has changed, and Amin is changed to the signal baseline value K in step S32.
The signal baseline value K is corrected so that the corrected value becomes 600 ppm. When the corrected value becomes 600 ppm, the process returns to step S19 and the steps S19 to S32 are repeated. In addition, MP of this ventilation monitor
U2 corresponds to the correction configuration unit A2 and the ventilation determination unit B1 in the block diagram of FIG. 6, and the LCD display unit 4 corresponds to the display unit c.

FIG. 10 shows the correspondence between the sensor output (electromotive force E) and the carbon dioxide concentration when the ventilation monitor is actually used, that is, the change in the calibration curve. At this time, the displacement between the reference position (the output value for the air containing 360 ppm of carbon dioxide one hour after the power was turned on) and the corrected position after 420 days is 17 mv. It can be seen that this sensor has a practically sufficient life.

[0038]

The carbon dioxide measuring unit of the present invention monitors the signal value of the carbon dioxide concentration detected by the detecting means, and if the signal value does not fall below the correction set concentration value during a certain period, the signal is monitored. Since the configuration for correcting the baseline value is provided, the correction of the signal baseline value of the carbon dioxide gas measuring unit can be easily performed by one detecting unit.

[Brief description of the drawings]

FIG. 1 is a diagram showing a base electromotive force change amount during long-term use.

FIG. 2 is a diagram showing the results of examining the history of the concentration of carbon dioxide in air for one week in a certain room.

3 is a diagram showing a measurement error that occurs when the baseline value is corrected by assuming that the concentration of carbon dioxide in the indoor air shown in FIG. 2 is 400 ppm.

FIG. 4 is a diagram showing a result of examining a change in sensitivity during use of a concentration cell type carbon dioxide sensor for a long period of time.

FIG. 5 is a model diagram illustrating an example of a method of correcting a signal baseline value of the carbon dioxide measuring unit according to the present invention.

FIG. 6 is a block diagram showing an example of a ventilation monitor using the carbon dioxide measuring unit of the present invention.

FIG. 7A is a circuit diagram of a ventilation monitor using the carbon dioxide measuring unit according to the present invention. (B) It is explanatory drawing which shows the content of ROM2ro. (C) It is explanatory drawing which shows the content of RAM2ra.

FIG. 8 is a flowchart showing the operation of a ventilation monitor using the carbon dioxide measuring unit according to the present invention.

FIG. 9 is a flowchart showing the operation of a ventilation monitor using the carbon dioxide measuring unit according to the present invention.

FIG. 10 is a diagram showing a correspondence relationship between a sensor output (electromotive force E) and a carbon dioxide gas concentration, that is, a change in a calibration curve when a ventilation monitor according to the present invention is actually used.

[Explanation of symbols]

 A Carbon dioxide measuring unit A1 Detecting means A2 Correcting and calibrating means B Ventilating unit B1 Ventilation determining means B2 Ventilating means C Display means 1 Detecting unit 2 MPU 2cp CPU 2ia Input port 2oa, 2ob Output port 2ra RAM 2ro ROM 3 Ventilation means 4 LCD display Department

Claims (8)

[Claims] 1. A method for monitoring a signal value of a carbon dioxide gas concentration detected by a detecting means, and correcting a signal baseline value when the signal value does not fall below a correction set concentration value within a predetermined period. A method for correcting a signal baseline value of a carbon dioxide gas measuring unit, characterized in that: 2. The signal base according to claim 1, wherein a signal baseline value is corrected so that a minimum value of the signal value during the certain period matches a standard level density value. Line value correction method. 3. The method according to claim 1, wherein the signal baseline is corrected by a difference between a standard level density value and a correction set density value. 4. The signal base of the carbon dioxide measuring unit according to claim 1, wherein the signal base line is inversely corrected so that the signal value does not fall below a zero level density value. Line value correction method. 5. A detecting means for detecting a carbon dioxide concentration, and correcting a signal baseline value when a signal value of the carbon dioxide concentration detected by the detecting means during a certain period does not fall below a correction set concentration value. A carbon dioxide gas measurement unit, comprising: 6. The carbon dioxide gas according to claim 5, wherein the correction calibration means corrects the signal baseline value so that the minimum value of the signal value during the certain period matches the standard level density value. Measurement unit. 7. The carbon dioxide measurement unit according to claim 5, wherein the correction range of the baseline value performed by the correction calibration means is a difference between the standard level density value and the correction set density value. 8. The signal correction method according to claim 5, wherein the correction calibration means performs reverse correction of the signal baseline so that the detected signal value of the carbon dioxide gas does not become less than the zero level concentration value. A carbon dioxide gas measurement unit according to any one of the above.