JPH1114583A - Smoothing device for changing reference values - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the discontinuity in output due to the change in a reference value by performing smoothing so that an output concentration changes nearly smoothly to the output concentration that is obtained by the reference value after changing from the output concentration being obtained from the reference value before modification transiently after changing the reference value. SOLUTION: A thermistor 20 is heated to, for example, approximately 100 deg.C by receiving heat from a CO2 sensor 2. The thermistor 20 where temperature fluctuates while being linked to an ambient temperature measures the fluctuation in temperature. In a microcomputer 30, a temperature correction part 36 stores a reference temperature for correcting temperature, performs the temperature correction of the electromotive force of the CO, sensor 2 with the output of the thermistor 20 as a temperature-corrected electromotive force (EMF*). A memory 38 stores the histogram of EMF*. A reference value generation means 42 searches the histogram from a side where the CO2 concentration is lower and generates a reference value using the EMF* of the first peak. A smoothing part 44 smoothes the display of the CO2 concentration of a display part 48 when the reference value is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to smoothing when a reference value is changed, and more particularly to smoothing an output when a reference value of a sensor signal is changed, for example, in detecting CO2, turbidity of water, and air quality.

[0002]

2. Description of the Related Art In a CO2 sensor, a turbidity sensor, an oxygen deficiency sensor and the like, a sensor signal has a drift with time, and the drift is corrected using a reference value. For example, in Japanese Patent No. 2507079, the maximum value (corresponding to the lowest CO2 concentration) of the daily electromotive force of the solid electrolyte CO2 sensor is set as a reference value corresponding to the CO2 concentration in the atmosphere, and the CO2 concentration is determined by a difference from the reference value. Suggest to ask.

When the reference value is changed, the output density changes discontinuously. This is unnatural. However, the prior art does not consider the discontinuity of the output density due to the change of the reference value.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to make the output density change almost smoothly when the reference value is changed.

[0005]

According to the present invention, a sensor for measuring the concentration of a substance to be detected in an environment is provided, a signal of the sensor is learned to generate a reference value, and a signal of the sensor is corrected based on the reference value. The smoothing device of the device configured to output the concentration of the detection target substance, wherein after the change of the reference value, intermittently, the concentration of the detection target substance obtained from the reference value before the change is changed. Smoothing means is provided for changing the output concentration of the detection target substance almost smoothly to the concentration of the detection target substance obtained by the later reference value.

[0006] The sensor is the solid electrolyte or ND used in the embodiment.
In addition to a CO2 sensor such as IR (non-dispersive infrared), a water quality sensor, an oxygen deficiency sensor, or the like is used, and the CO2 sensor is preferably used. The reference value includes the minimum value, the maximum value, and the average value of the sensor signal in the past one hour to about one month, or the peak of the histogram of the sensor signal in the past one hour to one month. Use values, etc. Many correction methods are already known for correcting a sensor signal using a reference value, for example, using a difference or a ratio from the reference value.

There are, for example, three methods of smoothing. 1) Smoothing is regarded as a problem of the change speed of the reference value, and when the reference value is changed, the reference value gradually changes from the reference value before change to the reference value after change. Generate an effective reference value and determine the output concentration of the target substance based on the effective reference value.2) Change the output concentration of the target substance after the change of the reference value, considering smoothing as the continuity of output. Limit the speed.3) Smoothing is regarded as an internal part of the density obtained by the reference value before the change and the density obtained by the reference value after the change, and the internal division ratio is gradually biased toward the reference value before the change. To the side biased toward the reference value after the change.

[0008]

According to the present invention, after the reference value is changed, the output density is almost smoothly changed from the output density obtained by the reference value before the change to the output density obtained by the reference value after the change. Smoothing to change to As a result, the discontinuity of the output due to the change of the reference value is eliminated.
5).

The third to fifth aspects of the present invention provide a specific method for changing the output density almost smoothly, and the configurations of the third and fourth aspects are particularly excellent because the amount of calculation in smoothing is small.

[0010]

1 to 7 show an embodiment using a solid electrolyte CO2 sensor 2. FIG. The type of the CO2 sensor is arbitrary, and in addition to the solid electrolyte CO2 sensor 2 used in the embodiment, an NDI
An R (non-dispersive infrared) CO2 sensor or a CO2 sensor using the resistance value or capacitance of a metal oxide semiconductor may be used. In addition to the detection of CO2, the present invention can also be applied to the case of inspecting water quality using a turbidity sensor, or detecting oxygen deficiency using a ZrO2 oxygen sensor or the like.
Each of these sensors has a signal drift and needs to be corrected by a reference value. When the reference value is changed, smoothing is required.

FIG. 2 shows the structure of the CO 2 sensor 2.
Is a sodium ion conductor, 6 is a working electrode made of a mixture of gold and an alkali carbonate or a mixture of gold and an alkaline earth carbonate, and 8 is a reference electrode made of gold or the like. Reference numeral 10 denotes an alumina substrate, 12 denotes a heater such as a platinum heater, and 14 denotes sealing glass for sealing the reference electrode 8. This CO2 sensor 2 is known.

Returning to FIG. 1, reference numeral 20 denotes a thermistor for correcting the ambient temperature. The thermistor 20 is controlled by the CO2 sensor 2 so that the response does not shift between the CO2 sensor 2 and the thermistor 20.
The sensor 2 is disposed inside a housing (not shown). As a result, the thermistor 20 receives heat from the CO2 sensor 2 and is heated to, for example, about 100.degree. The temperature of the thermistor 20 fluctuates in conjunction with the ambient temperature, and the fluctuation of the ambient temperature is measured by the thermistor 20. 22 is a buffer amplifier for amplifying the output of the CO2 sensor 2 (electromotive force between the electrodes 6/8), and 24 is a differential amplifier. 26 may not be a sensitivity adjustment amplifier, and 30 is a microcomputer for signal processing.

In the microcomputer 30, 32
Is a bus, 34 is an A / D converter, 36 is a temperature correction unit, which stores a reference temperature TSTD for temperature correction, temperature-corrects the electromotive force EMF of the CO2 sensor 2 with the output of the thermistor 20, and generates a temperature-corrected temperature. Power EMF *. The temperature correction is performed for the temperature difference ΔT from the reference temperature TSTD, and the reference temperature TS
The TD changes each time the reference value changes. Reference numeral 38 denotes a memory for storing a histogram of EMF *, for example, a histogram of EMF * for the past day. The sampling interval of EMF * used for the histogram is, for example, 20 minutes.
The interval may be increased or decreased according to the capacity of the memory 38. In addition, the histogram memory 38 may store an EMF * histogram for the past week, for example, instead of the past one day. Reference numeral 40 denotes a D / A converter, which applies a reference voltage C for differential amplification to the positive input side of the differential amplifier 24, and determines the difference between the output of the CO2 sensor 2 and the reference voltage C by the A / D converter
Is subjected to A / D conversion.

Reference numeral 42 denotes a reference value generating means which searches the histogram from the side having a lower CO2 concentration and finds the EMF * of the first peak.
Is used to generate a reference value EMF * STD. Further, an offset is added to the reference value to obtain a reference voltage C output from the D / A converter 40. Note that the maximum value of the electromotive force of the past day or the like may be used as the reference value. A smoothing section 44 smoothes the display of the CO2 concentration on the display section 48 when the reference value is changed. Numeral 46 denotes a CO2 detecting unit which obtains the CO2 concentration and displays it on a display unit 48, and generates a control signal such as ventilation.

3 to 7 show the operation of the embodiment, and FIG. 3 shows a control algorithm. The electromotive force of the CO2 sensor 2 is unstable for about several hours from the start of the operation of the heater 12, and waits for eight hours after the power is turned on. After 8 hours, for example, the temperature of the thermistor 20 at that time is set to the reference temperature T
STD, and the temperature-corrected electromotive force EMF * at that time is set as a reference value. Next, clear the histogram memory 38,
Start creating a histogram.

The D / A converter 40 is EMF * STD +
A reference voltage C is generated as a small constant J 1, the difference between the reference voltage C and the output of the CO 2 sensor 2 is differentially amplified by the differential amplifier 24, A / D converted by the A / D converter 34, and the electromotive force EMFAD is generated. And Next, the EMFAD is restored to the EMF by the temperature correction unit 36 by the expression (1), and the temperature is corrected by the expression (2) using the difference ΔT between the thermistor temperature and the reference temperature TSTD at that time, and the temperature is corrected. An electromotive force EMF * is obtained. Due to the differential amplification, for example, the accuracy of A / D conversion is improved by about 16 times. EMF = EMFAD + (CK) (1) EMF: An electromotive force obtained by restoring the A / D converted electromotive force EMFAD to the original electromotive force using a reference voltage C and a constant K EMF * = EMF−A · △ T (2) EMF *: EMF obtained by temperature correction of EMF A: Primary temperature coefficient of electromotive force ΔT: Temperature T of thermistor 20 and reference temperature T
Difference from STD

The histogram is, for example, EMF every 20 minutes.
It is created by correcting the frequency of the histogram memory 38 according to the value of *, and the reference value is changed every day. Except when creating the histogram (every 20 minutes), CO2 is calculated according to equation (3).
The density is obtained and displayed on the display unit 48. EMF * STD−EMF * = B · Ln (PCO2 / PCO2STD) (3) EMF * STD: Reference value after temperature correction B: Conversion coefficient between electromotive force and CO2 concentration PCO2: CO2 concentration PCO2STD: Reference CO2 concentration (400 ppm )

FIG. 4 shows an example of a histogram. The vertical axis represents the frequency, and the horizontal axis represents the temperature-corrected electromotive force EMF *. Then, the reference value generating means 42 searches the histogram from the side where EMF * is large, samples the first peak of EMF *, and obtains a new reference value by equation (4). EMF * STDNew = EMF * + A · △ (TSTDnew−TSTDOld) at peak (4) EMF * STDNew New reference value TSTDNeW: New reference temperature (average temperature of previous day) TSTDOld: Old reference temperature

Here, when the reference value is changed, the displayed CO2 concentration on the display unit 48 is changed almost smoothly by the smoothing unit 44. The accuracy of the display unit 48 is ± 10 ppm.
If the display density is changed by 10 ppm, the display density is changed smoothly. Further, the change in the output density due to the change in the reference value is generally ± 80 ppm or less. In the embodiment, the timer is started when the reference value is changed, and the operation time of the timer is determined by converting the difference between the old reference value and the new reference value into the CO2 concentration, and the reference value is set to 1 every two minutes.
When the value is changed by the amount corresponding to 0 ppm, it is determined that the output concentration is changed to the value based on the new reference value when the timer expires. An effective reference value is a value obtained by changing the old reference value to a new reference value by an amount equivalent to 10 ppm every two minutes,
The CO2 concentration is determined based on the effective reference value.

The display condition of the CO2 concentration in the embodiment is as shown in FIG. 5. When the reference value is changed, the reference value shifts discontinuously as shown by a dashed line in the figure, but the effective reference value is 10 pp for 2 minutes.
The output CO2 concentration changes almost smoothly by m. Here, a value obtained by changing the reference value by 10 ppm is used as the effective reference value. For example, the old reference value and the new reference value are internally divided, and the internal division ratio is 9: 1 at first, and 8: For example, the effective reference value may be shifted to a new reference value while gradually changing the internal division ratio, for example, 7: 3. However, this method requires internal calculation every time.

The smoothing of the output density can be treated as a pure display problem. For example, the speed of changing the output density from the density before the change of the reference value has an upper limit and a lower limit (here, ± 1).
0 ppm / 2 min or more change is prohibited). FIG. 6 shows the operation in such an example. The shaded area in the figure is the allowable change range of the output CO2 concentration after the change of the reference value, and the output CO2 concentration exceeds this area with the change of the reference value. Try to change, limit within the area. Architecturally, the CO2 concentration before the change is stored, the time from the change of the reference value is detected, the permissible constant of the concentration change per time is stored, and an upper limit of the smoothing time such as 10 minutes is provided. I just need.

As shown in FIG. 7, the smoothing of the output CO2 concentration can be treated as a problem of the internal division between the CO2 concentration based on the old reference value and the CO2 concentration based on the new reference value. That is, the timer is started by changing the reference value, and the internal ratio is gradually changed according to the value of the timer. During this time, the CO2 concentration based on the old reference value and the CO2 concentration based on the new reference value are internally divided by the internal ratio. , Output CO2 concentration. However, in this method, it is necessary to obtain two CO2 concentrations each time, and it is necessary to calculate the inner portion each time.

In the embodiment, specific smoothing conditions such as 10 ppm every two minutes are shown, but the present invention is not limited to this.

[Brief description of the drawings]

FIG. 1 is a block diagram of a reference value generator according to an embodiment.

FIG. 2 is a cross-sectional view of a CO2 sensor used in an embodiment.

FIG. 3 is a flowchart showing a control algorithm according to the embodiment.

FIG. 4 is a characteristic diagram showing an example of a histogram of a CO2 sensor.

FIG. 5 is a characteristic diagram showing an operation of the embodiment.

FIG. 6 is a characteristic diagram showing an operation of a modified example.

FIG. 7 is a characteristic diagram showing the operation of the second modification.

[Explanation of symbols]

 2 CO2 sensor 4 sodium ion conductor 6 working electrode 8 reference electrode 10 alumina substrate 12 heater 14 sealing glass 20 thermistor 22 buffer amplifier 24 differential amplifier 26 sensitivity adjustment amplifier 30 microcomputer 32 bus 34 A / D converter 36 temperature correction unit 38 Histogram memory 40 D / A converter 42 Reference value generating means 44 Smoothing section 46 CO2 detection section 48 Display section

──────────────────────────────────────────────────の Continuing on the front page (51) Int.Cl. ⁶ Identification symbol FI G01N 27/406 G01N 27/58 Z (72) Inventor Takaharu Saegusa 2-12-19 Shibuya Shibuya-ku, Tokyo Yamatake Ha Newel Co., Ltd. (72) Inventor Kazuyuki Otsuka 1-3-5 Senba-Nishi, Minoh City Inside Figaro Giken Co., Ltd. (72) Inventor Takashi Yamaguchi 1-3-5 Senba Nishi, Minoh City Inside Figaro Giken Co., Ltd. (72 Inventor Takeshi Nakahara 1-3-5 Senba Nishi, Minoh City Inside Figaro Giken Co., Ltd.

Claims (5)

[Claims] A sensor for measuring the concentration of a substance to be detected in an environment is provided, a signal of the sensor is learned to generate a reference value, and a signal of the sensor is corrected by the reference value. A smoothing device of a device for outputting a concentration of a detection target substance, wherein the reference value after the change is obtained from the concentration of the detection target substance obtained with the reference value before the change, after the change of the reference value. A smoothing device for changing a reference value, wherein a smoothing means is provided for substantially smoothly changing the output concentration of the detection target substance to the concentration of the detection target substance obtained in (1). 2. The smoothing device according to claim 1, wherein the sensor is a CO2 sensor. 3. The smoothing means is configured to generate an effective reference value that gradually changes from a reference value before change to a reference value after change when the reference value is changed, based on the effective reference value. 2. The method according to claim 1, wherein the output concentration of the substance to be detected is determined. 4. The smoothing method according to claim 1, wherein said smoothing means comprises means for limiting a change speed of the output concentration of the detection target substance after the change of the reference value. 5. The method according to claim 1, wherein the smoothing means internally divides the concentration of the detection target substance obtained from the reference value before the change and the concentration of the detection target substance obtained from the reference value after the change, and The output concentration of the target substance is determined, and the internal division ratio is gradually changed from the side biased toward the reference value before the change to the side biased to the reference value after the change. 2. The smoothing method according to claim 1, wherein the reference value is changed.