JP3466426B2 - Smoothing device for changing reference values - Google Patents

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, for detecting turbidity of CO2 or water and air quality.

[0002]

2. Description of the Related Art In a CO2 sensor, a turbidity sensor, an oxygen deficiency sensor, etc., a sensor signal has a drift over time, and the drift is corrected using a reference value. For example, in Japanese Patent No. 2507099, the maximum value of the electromotive force per day (corresponding to the lowest CO2 concentration) in the solid electrolyte CO2 sensor is set as the reference value corresponding to the CO2 concentration in the atmosphere, and the CO2 concentration is determined by the difference from this reference value. Suggests to seek.

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 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 the environment is provided, a signal of the sensor is learned to generate a reference value, and the signal of the sensor is corrected by the reference value. Then, the smoothing device of the device for outputting the concentration of the substance to be detected, transiently after the change of the reference value, from the concentration of the substance to be detected obtained by the reference value before the change, after the change It is characterized in that a smoothing means is provided for changing the output concentration of the substance to be detected almost smoothly to the concentration of the substance to be detected obtained by the reference value of.

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 preferably a CO2 sensor. As the reference value, the minimum value, the maximum value, or the average value of the sensor signal in the period of the past 1 hour to January, or the sensor signal with respect to the peak of the histogram of the sensor signal in the period of the past 1 hour to January, Use values etc. A large number of correction methods are already known for correcting the sensor signal based on the reference value, using, for example, a difference from the reference value or a ratio.

There are, for example, three methods for smoothing. 1) Taking smoothing as a problem of changing speed of the reference value, when the reference value is changed, the reference value before the change is gradually changed to the reference value after the change. Generate an effective reference value and determine the output concentration of the detection target substance based on the effective reference value. 2) Change the output concentration of the detection target substance after changing the reference value, considering smoothing as the continuity of output. Limit the speed, 3) Treat the smoothing as the internal content of the density obtained by the reference value before the change and the density obtained by the reference value after the change, and gradually divide the internal division ratio to the reference value before the change. There is a case to change to a side biased to the changed reference value.

[0008]

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

The inventions of claims 3 to 5 provide a concrete method for changing the output density almost smoothly. Particularly, the configurations of claims 3 and 4 are excellent because the amount of calculation in smoothing is small.

[0010]

EXAMPLE An example using a solid electrolyte CO2 sensor 2 is shown in FIGS. The type of CO2 sensor is arbitrary, and in addition to the solid electrolyte CO2 sensor 2 used in the embodiment, 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 CO2 detection, 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.
All of these sensors have signal drift and require correction with a reference value. Then, if the reference value is changed, smoothing becomes necessary.

The structure of the CO2 sensor 2 is shown in FIG.
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. Reference numeral 10 is an alumina substrate, 12 is a heater such as a platinum heater, and 14 is a 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 CO2 so that the response does not deviate between the CO2 sensor 2 and the thermistor 20.
The sensor 2 is arranged 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 ° C. The temperature of the thermistor 20 fluctuates in association with the ambient temperature, and the fluctuation of the ambient temperature is measured by the thermistor 20. Reference numeral 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 does not have to 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, and 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 the temperature-corrected start-up is performed. The power is EMF *. Temperature correction is performed for the temperature difference ΔT from the reference temperature TSTD, and the reference temperature TS
TD changes every time the reference value changes. 38 is a memory for storing the EMF * histogram, for example, the EMF * histogram for the past one 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. Further, the histogram memory 38 may store the EMF * histogram for the past one week 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 so that the difference between the output of the CO2 sensor 2 and the reference voltage C is A / D converter 34.
To be A / D converted.

Reference numeral 42 is a reference value generating means, which searches the histogram from the side where the CO2 concentration is low and 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 the reference voltage C output by the D / A converter 40. It should be noted that the maximum value of the electromotive force of the past day or the like may be used as the reference value. A smoothing unit 44 smoothes the display of the CO2 concentration on the display unit 48 when the reference value is changed. Reference numeral 46 denotes a CO2 detection unit, which determines the CO2 concentration and displays it on the display unit 48, and also generates a control signal for ventilation or the like.

The operation of the embodiment is shown in FIGS. 3 to 7, and the control algorithm is shown in FIG. The electromotive force of the CO2 sensor 2 is unstable for several hours after the heater 12 starts operating, and waits for 8 hours after the power is turned on. After the lapse of 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 as the reference value. Next, clear the histogram memory 38,
Start creating a histogram.

The D / A converter 40 is EMF * STD +
As a small constant J 1, a reference voltage C is generated, a differential amplifier 24 differentially amplifies the difference between the reference voltage C and the output of the CO 2 sensor 2, and an A / D converter 34 A / D converts the electromotive force EMFAD. And Next, in the temperature correction unit 36, EMFAD is restored to EMF by the equation (1), temperature is corrected by the equation (2) using the difference ΔT between the thermistor temperature and the reference temperature TSTD at that time, and the temperature is corrected. Obtain the electromotive force EMF *. The differential amplification improves the accuracy of A / D conversion by about 16 times, for example. EMF = EMFAD + (C−K) (1) EMF: A / D converted electromotive force EMFAD is restored to the original electromotive force by using the reference voltage C and the constant K. Electromotive force EMF * = EMF−A · Δ T (2) EMF *: EMF temperature-corrected EMF A: First-order temperature coefficient of electromotive force ΔT: Temperature T of thermistor 20 and reference temperature T
Difference from STD

The histogram shows the EMF every 20 minutes, for example.
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: Temperature-corrected reference value B: Conversion coefficient between electromotive force and CO2 concentration PCO2: CO2 concentration PCO2STD: Reference CO2 concentration (400ppm) )

An example of the histogram is shown in FIG. The vertical axis represents 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 having a larger EMF *, samples the first peak of EMF *, and obtains a new reference value by the equation (4). EMF * STDNew = peak EMF * + A ・ △ (TSTDnew−TSTDOld) (4) EMF * STDNew new reference value TSTDNeW: new reference temperature (average temperature of the previous day) TSTDOld: old reference temperature

Here, when the reference value is changed, the smoothing unit 44 changes the displayed CO2 concentration of the display unit 48 substantially smoothly. The accuracy of the display 48 is ± 10 ppm
Then, if the display density is changed by 10 ppm, the display density is smoothly changed. 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 2 minutes.
When the amount corresponding to 0 ppm is changed, when the timer expires, the output concentration will be changed to the one based on the new reference value. The old reference value is changed every 2 minutes by 10 ppm to the new reference value, and is changed to the effective reference value.
The CO2 concentration is calculated based on the effective reference value.

The display state of the CO2 concentration in the embodiment is as shown in FIG. 5, and the reference value shifts discontinuously as shown by the chain line in the figure by changing the reference value, but the effective reference value is 10 pp in 2 minutes.
The output CO2 concentration changes almost smoothly by shifting by m. Here, a value obtained by changing the reference value by 10 ppm is used as the effective reference value, but, for example, the old reference value and the new reference value are internally divided, and the internal division ratio is initially 9: 1 and then 8: The effective reference value may be shifted to the new reference value side by gradually changing the internal division ratio by setting the value to 2, and then to 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 change speed of the output density from the density before the change of the reference value has an upper limit and a lower limit (here, ± 1).
(Prohibit change of 0 ppm / 2 minutes or more) may be provided. When the operation in such an example is shown in FIG. 6, the shaded area in the drawing 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 due to the change of the reference value. Try to change and limit within the area. On the architecture, 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 the upper limit of the smoothing time such as 10 minutes is set. Good.

As shown in FIG. 7, the smoothing of the output CO2 concentration can be treated as a problem of the inner part of 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 division ratio is gradually changed according to the value of the timer. During this period, 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 division ratio. , Output CO2 concentration. However, with this method, it is necessary to obtain two CO2 concentrations each time, and it is also necessary to calculate the internal content each time.

In the embodiment, a specific smoothing condition such as 10 ppm every 2 minutes is shown, but the present invention is not limited to this.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a CO2 sensor used in the examples.

FIG. 3 is a flowchart showing a control algorithm of the embodiment.

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

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

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

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

[Explanation of symbols]

2 CO2 sensor 4 Sodium ion conductor 6 Working pole 8 reference pole 10 Alumina substrate 12 heater 14 Sealed glass 20 thermistor 22 Buffer amplifier 24 differential amplifier 26 Sensitivity adjustment amplifier 30 microcomputer 32 buses 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 detector 48 display

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification FI G01N 27/22 G01N 27/22 A 27/406 27/46 376 27/416 27/58 Z (72) Inventor Takaharu Saegusa Tokyo 2-12-19 Shibuya, Shibuya Yamatake Honeywell Co., Ltd. (72) Inventor Kazuyuki Otsuka 1-3-5 Senba West, Minoh City In-house Figaro Giken Co., Ltd. (72) Takashi Yamaguchi 1-chome, Senjo Nishi, Minoh No. 5-3 Figaro Giken Co., Ltd. (72) Inventor Takeshi Nakahara 1-5-3 Funaba Nishi, Minoh City No. 5 Figaro Giken Co., Ltd. (56) Reference JP-A-10-142192 (JP, A) JP Heihei 9-329559 (JP, A) JP-A-6-308073 (JP, A) JP-A-11-14586 (JP, A) JP-A-10-332615 (JP, A) JP-A-6-11477 (JP, A) A) JP-A-5-307018 (JP, ) Patent flat 5-249074 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) G01N 27/00 - 27/49 G01N 33/00 - 33/46 G01N 21/64

Claims (5)

(57) [Claims] 1. A sensor for measuring the concentration of a substance to be detected in the environment is provided, a signal of the sensor is learned to generate a reference value, and the signal of the sensor is corrected by the reference value, A smoothing device for an apparatus configured to output the concentration of a substance to be detected, which is transient after the change of the reference value, from the concentration of the substance to be detected obtained by the reference value before the change, and the reference value after the change. A smoothing device at the time of changing a reference value, which is provided with smoothing means for changing the output concentration of the substance to be detected almost smoothly to the obtained concentration of the substance to be detected. 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 the reference value before the change to the reference value after the change when the reference value is changed, and based on the effective reference value. The smoothing device for changing the reference value according to claim 1, wherein the output concentration of the substance to be detected is determined. 4. The smoothing device according to claim 1, wherein the smoothing means is constituted by means for limiting a changing speed of the output concentration of the substance to be detected after changing the reference value. 5. The smoothing means internally divides the concentration of the substance to be detected obtained with the reference value before the change and the concentration of the substance to be detected obtained with the reference value after the change, and after the reference value is changed. The output concentration of the substance to be detected is determined, and the internal division ratio is gradually changed from the side biased to the reference value before the change to the side biased to the reference value after the change. The smoothing device when changing the reference value according to claim 1.