JPH09329559A - Correction method for signal baseline value in measuring unit for carbon dioxide, and measuring unit for carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a correction method in which a signal baseline value can be corrected by one detection means by setting the signal baseline value in such a way that the signal value agrees with the reference concentration when the signal value of the concentration of carbon dioxide is less than a reference concentration. SOLUTION: A detection means A1 which detects the concentration of carbon dioxide includes a carbon dioxide sensor, a power supply which is required to drive the sensor, various temperature compensation circuits and the like. On the other hand, when the signal value of the concentration of the carbon dioxide detected by the means A1 is less than a reference concentration, a primary correction which sets a signal baseline value in such a way that the signal value agrees with the reference concentration and the time, i.e., the lowest signal time, in which the signal value of the concentration of the carbon dioxide detected by the means A1 becomes lowest are investigated, the correction time on that day us decided, and a secondary correction in which the signal baseline value is corrected by a correction calibration means A2 is executed to the correction time so that the sigbal value of the carbon dioxide detected by the means A1 agrees with a second reference concentration.

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 form a carbon dioxide concentration measuring instrument, and connected to an alarm unit to form a carbon dioxide alarm.

[0002]

2. Description of the Related Art A carbon dioxide alarm has a carbon dioxide sensor such as a solid electrolyte type sensor or an infrared sensor as its carbon dioxide detecting means, and a signal value sent from the detecting means is preset. Compared with the required alarm concentration, if the concentration is higher than that value, an alarm is given by light (red lamp, etc.) or sound (buzzer, etc.), etc. to warn of safety or security or aerobic bacteria. It is widely used for aeration treatment control in wastewater treatment.

In such an alarm device, as a result of long-term use, the baseline of the output of the detection means may drift, so that no warning may be given or an erroneous alarm may occur even if necessary. Therefore, the alarm is periodically corrected. -Needs to be calibrated. However, the correction / calibration requires time and effort. In order to save these troubles and time, for example, Japanese Patent Laid-Open No. 7-
A correction / calibration means for automatically performing correction / calibration has been proposed in Japanese Patent No. 270315. This prior art has two detection means, and the correction / calibration is performed on the assumption that the baseline drifts of the outputs of these two detection means are equal.

However, in a plurality of detecting means,
It is difficult to completely equalize the drift of the baseline, and therefore the reliability is low, and it is difficult to make the device compact because it has a plurality of detection means. There was a need for a baseline correction method.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for correcting the signal baseline value of a carbon dioxide gas measuring unit which solves the above-mentioned problems of the prior art and can be easily performed by one detecting means. With the goal.

[0006]

In order to solve the above-mentioned problems, according to the present invention, when the signal value of the carbon dioxide concentration detected by the detecting means becomes less than the reference concentration, The signal baseline value is set so that the signal value matches the reference density.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Here, the reference concentration is the concentration of carbon dioxide gas in normal air, and in the present invention, it is usually assumed that the concentration of carbon dioxide gas in air does not fall below the reference concentration. To use. The standard concentration is the concentration of carbon dioxide present in normal air, and is 330 ppm in the Chemical Handbook (revised 3rd edition), science chronology (1996 edition).
Describes that it is 320 ppm. Although any of the values described in literatures such as these or their average value may be used, these values are not usually observed in the observation in a normal environment, and 350 p which is slightly higher than them.
It is desirable to use pm as the reference concentration. In this way, when the signal value from the detection means becomes less than the reference density, the signal baseline value is corrected and the signal value is set to the reference density (such correction will be referred to as "primary correction" hereinafter).
Therefore, when the concentration of carbon dioxide gas in the atmosphere actually measured by the detecting means reaches the required alarm concentration, an alarm can be surely issued.

In the above structure, the correction when the baseline drifts downward is possible, but it cannot be dealt with when the baseline drifts upward, and therefore the carbon dioxide concentration is actually low. Nevertheless, there is a possibility that an erroneous alarm will be issued because the alarm concentration is required. This problem can be solved as follows. That is, normally
In a room where people enter and leave (excluding a place where a chemical factory operates for 24 hours), the carbon dioxide concentration decreases at night. After conducting various studies in such a place,
It was found that the CO2 concentration, which became high during the daytime when people entered and exited, gradually decreased at night, but dropped to at least about 400 ppm (see Fig. 1). In the invention, it is called "second reference concentration").

Therefore, it has been found that by applying this fact, the baseline can be corrected more accurately than in the case of only the above-mentioned primary correction. As the correction method, it is possible to correct the signal baseline value so that the lowest value of the signal value from the detection means on the day becomes the second reference density determined in advance, but in this case, the maximum value is 50 to 80.
An error of ppm may occur. Therefore, as a result of various studies, it was found that the time at which the signal value from the detection means becomes the minimum (hereinafter referred to as the “minimum signal time”) is almost the same time every day (see FIG. 1), but there is a slight deviation. It has been found that it is possible to reduce the above error by utilizing this.

That is, the weight of the time when the detection means detects the lowest concentration on the previous day is set to 1, and the weight is multiplied by 1/2 for each one day before that. The "time" means "the time when the signal baseline value is corrected"), and the signal baseline value is corrected so that the signal value of the carbon dioxide concentration detected at this correction time matches the second reference concentration. (Such correction is hereinafter referred to as "secondary correction"). If this secondary correction is performed, even if a time that is significantly different from the normal time becomes the minimum signal time, it is less likely to be affected.

In the above correction, if there is a day when the decrease in the density is small, it is expected that the signal baseline value will be significantly deviated. However, the signal baseline value is deviated as follows. Or the corrected CO2 concentration value based on the signal baseline value is 350 ppm
When it becomes less than, it is corrected by the above-mentioned primary correction. By combining such secondary correction with the above-mentioned primary correction, it becomes possible to stabilize the measurement accuracy for a long term. When a carbon dioxide sensor is installed in a place where the carbon dioxide concentration may be maintained high all day long, such as in a hospital or a factory, and such secondary correction is performed, the secondary correction level is set to 500 to 600 ppm in advance. By doing so, it is possible to reduce the error.

An example of a carbon dioxide alarm device which implements the method of correcting the signal baseline value of the carbon dioxide measuring unit will be described. FIG. 2 shows a block diagram of an example of the carbon dioxide alarm device. In the figure, reference numeral A1 indicates a detecting means for detecting the carbon dioxide concentration. This includes a carbon dioxide sensor that is normally used, such as a solid electrolyte type carbon dioxide sensor or an infrared type carbon dioxide sensor, and a power supply necessary for driving the carbon dioxide sensor, various temperature compensation circuits, signal amplification circuits, and the like.

On the other hand, reference numeral A2 indicates a signal baseline value so that when the signal value of the carbon dioxide concentration detected by the detecting means A1 becomes less than the reference concentration, the signal value matches the reference concentration. Primary correction to set, and
The time when the signal value of the carbon dioxide concentration detected by the detection means A1 becomes the lowest, that is, the lowest signal time is checked, and the weighting of the lowest signal time of the previous day is set to 1, and the weight is multiplied by ½ every time one day before. The correction is performed at each minimum signal time, the correction time of the day is determined, and the signal baseline value is corrected so that the signal value of the carbon dioxide concentration detected by the detection means A1 at the correction time matches the second reference concentration. It is a correction / calibration means for performing secondary correction. The measuring unit A includes the detection means A1 and the correction / calibration means A2.
It consists of.

The carbon dioxide concentration data corrected / calibrated by the correction / calibration means A2 of the measurement unit A is input to the alarm determination means B1 of the alarm unit B, compared with the alarm concentration required separately, and if necessary, A warning is issued by the warning means B2. If the carbon dioxide measuring unit A is connected to a display unit (not shown) having a concentration displaying means instead of the alarm unit B, a carbon dioxide measuring instrument is formed instead of the carbon dioxide alarm.

Hereinafter, an example of a carbon dioxide alarm device using the carbon dioxide measuring unit according to the present invention will be described in more detail. FIG. 3A is a circuit diagram of a carbon dioxide alarm device using the solid electrolyte carbon dioxide sensor according to the present invention. Reference numeral 1 denotes a detection unit, which includes a sensor and its associated circuit. Reference numeral 1a is a sensor element of the solid electrolyte type carbon dioxide gas sensor, and reference numeral 1b is a heater portion of the solid electrolyte type carbon dioxide gas sensor, which keeps the sensor element 1a at a suitable measurement temperature. A solid electrolyte type carbon dioxide gas sensor is constituted by these 1a and 1b.

Reference numeral 1c is a voltage application circuit connected to the heater portion 1b of the sensor. This voltage application circuit 1c
Is for applying a two-stage voltage of a high voltage and a low voltage to the heater 1b of the sensor according to a change in the signal output to the output port 2oa of the microprocessing unit 2 described later. That is, Hi is output to the output port 2oa as an output signal.
Is output to the heater 1b, and when Lo is output to the output port 2oa as an output signal, a low voltage is applied to the heater 1b. The voltage application circuit 1c is specifically configured by combining a switch mechanism and a power supply circuit.

Here, the two levels of high and low voltages can be applied to the heater 1c for the following reason. A sensor element 1a of a solid electrolyte type carbon dioxide gas sensor has a structure in which two electrodes are arranged with a solid electrolyte membrane sandwiched therebetween.
The electromotive force generated by the difference in carbon dioxide concentration near each electrode is measured. In order to obtain sufficient sensor sensitivity, the sensor element of such a solid electrolyte type carbon dioxide gas sensor needs to be heated to 350 ° C. to 450 ° C. at which the fixed electrolyte has good conductivity due to carbonate ions. Of the voltages of the stages, the low voltage is for maintaining this temperature. However, water and other substances are adsorbed on the solid electrolyte membrane before the power is turned on, and immediately after the power is turned on, these adsorbed substances are desorbed, so the sensor element output rises sharply and the reference level, which is the output value at the time of zero signal, is exceeded. It will take several hours or days for the output value to return to the standard level.

Here, a high voltage is applied to the heater section 1b,
High temperature (470 ℃ to 550 ℃) that does not deteriorate the sensor element
By maintaining the temperature at (° C.), the time required for returning the sensor output to the reference level can be shortened to about several minutes by a process of rapidly releasing the adsorbed substance, that is, a so-called heat-up process. Note that the processing time of the heat-up processing largely influences the time required to return to the reference level. There is an optimum processing time for this heat-up processing,
It has been found that the effect of shortening the time required to stabilize the output of the sensor element 1a is small regardless of whether the processing time is shorter or longer than the optimum processing time.

Here, various examinations were conducted on the optimum processing time (y) of the heat-up processing, and the heater 1b
From the start of heating by the standard level (350ppm-400
It has been found that it can be obtained by the calculation ax + b from the time x required for exceeding (ppm) and the sensor-specific values a and b.

In FIG. 3A, the output signal of the sensor element 1a is the impedance conversion circuit 1d and the temperature correction circuit 1.
After being converted / corrected and amplified by the e and amplifier circuit 1f, it is taken into the micro processing unit (hereinafter referred to as “MPU”) 2 from the input port 2ia with an A / D converter, and is output at the input port 2ia. It is converted into a corresponding numerical value (the value obtained by this input port 2ia is hereinafter referred to as "sensor output").

In addition to the above-mentioned input port 2ia, the MPU 2 sends an input port 2ib for taking in the required alarm concentration set in the required alarm concentration setting switch 3 into the MPU 2 and a control signal for the voltage applying circuit 1c. Output port 2oa for outputting, and an output port 2ob for sending out a signal for controlling the LED notification unit 4 which is an alarm means, a ROM 2ro storing a control program, sensor constants a and b, reference level values, etc. 2 (b)), time measurement data for secondary correction (hereinafter referred to as "timer T1"), and time measurement data of elapsed time after power-on (hereinafter referred to as "timer T1").
2 "), time measurement data for heat-up processing (hereinafter referred to as" timer T3 "), time measurement data of elapsed time from an arbitrary start time (hereinafter referred to as" timer T4 "), or various types. RAM 2ra for storing control variables x, y, Tmin1 (minimum signal time) and Tmin2 (correction time), various data of signal baseline value Ba, etc.
As shown in FIG. 2 (c), a central processing unit (hereinafter referred to as "CPU") 2cp for executing the above program is incorporated.

The above-mentioned timer T1 is the time measurement data from 0 to 24 hours, and it will be timed again from 0 when the time exceeds 24 hours as will be described later. Twenty-four hours from when the timer T1 becomes 0 is treated as "one day". In other words, 24 hours after the power is turned on, the first day, more than 24 hours 4
Up to 8 hours is called the second day.

The alarm concentration setting switch indicated by reference numeral 3 in FIG. 3 is composed of a slide switch and is used to set the alarm concentration required. The required alarm concentration is 700 ppm, 1400 pp for this alarm device.
m or 2400 ppm can be set.
The LED notification unit 4 is connected to the output port 2ob of the MPU 2. The LED notification unit 4 has a green light emitting diode 4g and a red light emitting diode 4r. When the signal Gbl is output to the output port 2ob, the green light emitting diode 4g is blinked, and when the signal Gon is output. The green light emitting diode 4g is continuously turned on, while the red light emitting diode 4r is continuously turned on when the signal Ron is output.

A flow chart of the operation of the carbon dioxide alarm device (see FIG. 4).
7 to 7) and an explanatory diagram (FIG. 8). First, as shown in FIG. 3, the control program is started by turning on the power, and the signal Gbl is output to the output port 2oa as shown in step S1. As a result, the green light emitting diode 4g of the LED notification unit 4 blinks. (See FIG. 8), indicating that the carbon dioxide alarm has been turned on.

In step S2, timer T1 and timer T2
Then, the signal Hlo is output to the output port 2ob (step S3), a low voltage is applied to the heater 1b, and heating of the sensor element 1a is started. Step S4
After that state is held for 10 seconds, the signal Hhi is output to the output port 2ob in step S5, and the voltage applying means 1c is output.
As a result, a high voltage is applied to the heater 1b, and heat-up processing is performed (S5). The reason why the heat-up process is performed after the low voltage is once applied to the heater 1b is to prevent the sensor element 1a from being deteriorated or damaged due to a rapid temperature rise.

With the start of the heat-up process, step S
At 6, the timer T2 is started in order to obtain the optimum heat-up processing time. When the sensor output reaches the reference level L (400 ppm in this carbon dioxide alarm device) (step S7), the optimum processing time of the heat-up process is calculated from the value (x) of the timer T3 and the sensor-specific values a and b. y) is obtained (steps S8 and S9) until the heat-up processing time (value of the timer T2) reaches either the optimum processing time (y) or 120 seconds (step S10).
And step S11) heat-up processing is performed. In addition,
Here, the heat-up process is set to 120 seconds at the longest in order to prevent the sensor element 1a from being deteriorated if the heat-up process is performed for more than 120 seconds, and the deterioration is prevented.

When the time to finish the heat-up process is reached, the signal Hlo is output to the output port 2ob, and the heater 1b is output.
The voltage applied to is set to a low voltage (step S12). Next, as shown in FIG. 5, after 130 seconds have elapsed as the time until the sensor output is stabilized by the timer T4 (step S13, step S14), the measurement state is entered. here,
Since the baseline of the sensor output is not stable and its value is high, there is a possibility that an erroneous alarm will be issued at the moment when the measurement state is entered. Therefore, the sensor output when entering this measurement state is 4
When it is higher than 00 ppm, the signal baseline value Ba is corrected so that it becomes 400 ppm (steps S15 and S16), and then the signal Gon is output from the output port 2
This is output to ob (step S17), and the green light emitting diode 4g of the LED notification unit 4 is turned on to indicate that this carbon dioxide alarm is in the measuring state (see FIG. 8).

FIG. 6 shows a flowchart of the operation after the start of measurement. When the carbon dioxide concentration value obtained by correcting the sensor output with the signal baseline value Ba (hereinafter referred to as “corrected concentration value”) is less than the reference concentration (350 ppm in this embodiment), the signal baseline value Ba is set to Change to make the corrected concentration value equal to 350 ppm (step S
18 and step S19). These steps S18 and S19 are related to the primary correction.

The corrected concentration value is compared with the required alarm concentration set in the required alarm concentration setting switch 3 (input to the input port 2ia) (step S20). The signal Ron is output from the output port 2oa to the LED notification section 4 to turn on the red light emitting diode 4r (step S21). Instead of (or at the same time as) turning on the red light emitting diode 4r, a buzzer or the like may be used to notify that the concentration of carbon dioxide gas is equal to or higher than the required alarm concentration. Further, the alarm means may be linked to a separately provided ventilation means to give an alarm and to improve the detected atmosphere by ventilation.

If the corrected concentration value is less than the required alarm concentration in step S20, the signal Rof is output from the output port 2oa to the LED notification section 4 (step S2).
2) If the red light emitting diode 4r is on, turn it off. Next, the secondary correction will be described in steps S23 to S33. Step S23
Check whether the sensor output has reached the minimum value of the day, and if it has reached the minimum value, read the time from the timer T1 and save it as the minimum signal time Tmin1 (step S2).
4).

Next, as shown in FIG. 7, in step S25, it is checked whether or not 24 hours or more have passed since the power was turned on. If not, the value of the minimum signal time Tmin1 is copied to the correction time Tmin2 in step S26. After that, the process returns to step S18 (see FIG. 6) and the above step S1.
8 to step S26 are sequentially repeated, during which primary correction is performed as necessary, and an alarm is issued when the corrected concentration value reaches the required alarm concentration. In this way, for 24 hours (first day) after the power is turned on, steps S18 to S2 are performed.
Repeat step 6, but after that (from the second day onwards) step S
It progresses from 25 to step S27.

That is, if the value of the timer T1 is checked and it matches the above Tmin2 (correction time: the time when the sensor output on the first day becomes the minimum value in the case of the second day), the sensor at that time is determined in step S28. The baseline variable Ba is corrected (secondary correction) assuming that the output value is the second reference level (400 ppm in this embodiment). Step S2
When the timer T1 has a value of 24 hours or more in 9, it is considered that the date of one day has advanced, and 24 hours is subtracted from the value of the timer T1 in step S30, and then the minimum signal time Tmin1 of the previous day Value and correction time Tmi of the previous day
The arithmetic average with the value of n2 is performed, and the result is stored as the correction time Tmin2 of the day. By this arithmetic mean,
As for the correction time Tmin2, the weighting of the lowest signal time of the previous day is set to 1, and the weighting of ½ each time going back one day before that is performed on each minimum signal time to determine the correction time of the day. . Then, step S
18 (see FIG. 6), the above steps S18 to S31 are sequentially repeated to perform the secondary correction once a day, and the primary correction is performed if necessary. If the concentration is reached, give an alarm.

As is apparent from the above description, the carbon dioxide alarm device according to the present invention as described above has the detection unit 1 as the detection means A1 of the carbon dioxide measurement unit A shown in the block diagram of FIG.
The PU 3 and the alarm concentration setting switch correspond to the correction component A2 of the carbon dioxide measuring unit A and the alarm determination unit B1 of the alarm unit B, and the LED notification unit 4 corresponds to the alarm unit B2 of the alarm unit B.

[0034]

According to the carbon dioxide measuring unit of the present invention, when the signal value of the carbon dioxide concentration detected by the detecting means becomes less than the reference concentration, the signal baseline value is adjusted so that the signal value matches the reference concentration. Since it has a configuration to set,
Correction of the signal baseline value of the carbon dioxide measurement unit,
It can be easily performed with one detection means.

[Brief description of drawings]

FIG. 1 is a diagram showing a periodic change of carbon dioxide in a room where a person usually goes in and out.

FIG. 2 is a block diagram of an example of a carbon dioxide alarm device.

FIG. 3 is a circuit diagram of a carbon dioxide alarm device using a solid electrolyte carbon dioxide sensor.

FIG. 4 is a flowchart showing the operation of the carbon dioxide alarm device of the embodiment.

FIG. 5 is a flowchart showing the operation of the carbon dioxide alarm device of the embodiment.

FIG. 6 is a flowchart showing the operation of the carbon dioxide alarm device of the embodiment.

FIG. 7 is a flowchart showing the operation of the carbon dioxide alarm device of the embodiment.

FIG. 8 is an explanatory diagram of the operation of the carbon dioxide alarm device of the embodiment.

[Explanation of symbols]

 A1 detection means A2 correction calibration means 1 detection part 1a sensor element of solid electrolyte type carbon dioxide gas sensor 1b heater part of solid electrolyte type carbon dioxide gas sensor 1c voltage application circuit 1d impedance conversion circuit 1e temperature correction circuit 1f amplification circuit 2 MPU 2cp CPU 2ia input port 2ib Input port 2oa Output port 2ob Output port 2ra RAM 2ro ROM 3 Alarm concentration setting switch 4 LED notification section 4 4g Green light emitting diode 4r Red light emitting diode Ba Signal baseline value

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location G01N 27/26 381 G01N 27/26 381B 27/416 27/46 376

Claims (6)

[Claims] 1. A carbon dioxide gas characterized by setting a signal baseline value such that when the signal value of the carbon dioxide concentration detected by the detecting means becomes less than the reference concentration, the signal value matches the reference concentration. How to correct the signal baseline value of the measuring unit. 2. The time when the signal value of the carbon dioxide concentration detected by the detection means becomes the lowest, that is, the lowest signal time is examined, and the correction time for correcting the signal baseline value is determined from the lowest signal time, The signal baseline value of the carbon dioxide gas measuring unit according to claim 1, wherein the signal baseline value is corrected so that the signal value of the carbon dioxide concentration detected by the detecting means at the correction time matches the second reference concentration. Value correction method. 3. When determining the correction time, the weighting of the lowest signal time of the previous day is set to 1, and the weighting of 1/2 is multiplied at each previous day, and the weighting is performed at each lowest signal time of the day. The method for correcting the signal baseline value of the carbon dioxide measuring unit according to claim 2, wherein the correction time is determined. 4. A detecting means for detecting the carbon dioxide concentration, and a signal baseline value so that when the signal value of the carbon dioxide concentration detected by the detecting means becomes less than the reference concentration, the signal baseline value matches the reference concentration. A carbon dioxide gas measuring unit, comprising: a correction / calibration means for setting. 5. The correction / calibration means checks the time at which the signal value of the carbon dioxide concentration detected by the detection means becomes the lowest, that is, the minimum signal time, and determines the correction time for correcting the sensor output from the minimum signal time. 5. The carbon dioxide gas measurement according to claim 4, wherein the signal baseline value is corrected so that the signal value of the carbon dioxide gas concentration detected by the detection means at the correction time matches the second reference concentration. unit. 6. When determining the correction time, weighting of the lowest signal time of the previous day is set to 1, and weighting that is multiplied by 1/2 is traced back to one day before that day at each lowest signal time, and the weighting is performed at each lowest signal time. The carbon dioxide measuring unit according to claim 5, wherein the correction time is determined.