JPH02304341A - Measuring device for concentration of ozone - Google Patents

Abstract

PURPOSE:To measure the concn. of ozone over a wide range at the rapid speed of response by calculating the concn. of ozone from the degree of rise of resistance value when the degree of rise exceeds the preset value in a thin film type ozone sensor of an n-type semiconductor. CONSTITUTION:The resistance of an n-type semiconductor ozone sensor 1 changes by the concn. of ozone. The change in the resistance value is measured in a measuring circuit 3 and A/D-converted 4 and inputted to a CPU 6 constituted of a microcomputer. The CPU 6 detects that ozone is attracted to a sensor 1 and the resistance value starts to be raised. The concn. of ozone is calculated by the degree of increase in the resistance at every constant short time while keeping both the resistance value and the time as a reference. Further when the resistance value reaches equilibrium, the concn. of ozone is calculated on the basis of this resistance value. Thereby the measured value of the concn. of ozone in a wide range is obtained at the rapid speed of response.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ozone concentration measuring device for detecting ozone concentration in an atmosphere.

[Prior Art] Ozone has been used in various ways, for example, it is known to be used to eliminate odors from refrigerators.

This is a method in which a deadlight is installed inside the refrigerator, and the ultraviolet light it emits generates ozone inside the refrigerator, and this ozone removes odors inside the refrigerator. In such use of ozone, it is necessary to control the amount of ozone generated in consideration of the toxicity of ozone, and for this purpose, it is possible to detect the ozone concentration with a sensor and control the amount of ozone generated.

There is a means of using a semiconductor thin film as an ozone sensor that is necessary in such a case.

Figure 5 shows, for example, the n
FIG. 2 is a front view of a semiconductor thin film ozone sensor. Further, FIG. 6 is a sectional view taken along line A--A shown in FIG. 5.

In Figures 5 and 6, (101) is A I 20
(102) is a pair of sensor electrodes printed in a comb shape on the substrate (101), and (103) is an n-type semiconductor thin film formed on the surface of the substrate. It is an ozone-sensitive membrane. Note that (105) is a heating element attached to the back side of the substrate (101) to heat the ozone-sensitive film (103), and (106) is its electrode.

An ozone-sensitive film (1
03) has a property that its electrical resistance increases when it adsorbs a strongly oxidizing gas such as ozone, so the resistance value between the pair of sensor electrodes (102), which increases according to the ozone concentration, is measured by the lead wire (104). ) The ozone concentration can be detected by measuring the ozone concentration. In addition to the above-mentioned InO, the ozone-sensitive film (103) also contains SnO.
An n-type semiconductor such as 2 (tin oxide) may also be used.

[Problems to be Solved by the Invention] The relationship between the ozone concentration and the sensor resistance value of the n-type semiconductor ozone sensor as described above is the relationship between the elapsed time after ozone comes into contact with the sensor and the sensor resistance value as shown in Fig. 7. As shown in the diagram, the resistance value increases greatly as the ozone concentration increases, and in an atmosphere with a relatively high ozone concentration, the resistance value becomes so large that it cannot be measured. Generally, when the insulation resistance of a circuit board or the like decreases due to moisture absorption, the resistance value of the sensor becomes higher than these resistance values, making it impossible to accurately measure ozone concentration. In this case, by increasing the film thickness of the sensor, the resistance value of the sensor corresponding to the ozone concentration can be lowered, but on the other hand, the response of the sensor becomes slower and it takes a longer time for the resistance value to reach the value corresponding to the ozone concentration. The relationship between the resistance value change and the resistance value change is slower and gentler than that shown in FIG. Therefore, the conventional ozone concentration measuring device using this sensor has a problem in that measurement accuracy and response speed at high concentrations are not compatible with each other.

This invention was made to solve the above-mentioned problems, and aims to provide an ozone concentration measuring device that has a quick response and a wide measurement range.

[Means for Solving the Problems] The ozone concentration measuring device according to the present invention is provided with an n-type semiconductor ozone sensor and a circuit for determining its resistance value, and a microcomputer is used to increase the measured resistance value. It is equipped with a means for recognizing a time point, using the time and resistance value at this time as a reference, recognizing the rate of increase in the resistance value at regular intervals thereafter, and measuring and displaying the ozone concentration by calculation each time. be.

[Function] In this invention, the arithmetic unit detects that ozone is adsorbed to the sensor and its resistance value starts to rise, and the sensor detects the resistance value and the resistance value at regular intervals after a certain short period of time. The ozone concentration is detected by the rate of increase in the resistance value. ,
Furthermore, when the resistance value reaches equilibrium, the calculation is switched to detect the ozone concentration based on the resistance value.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an ozone concentration measuring device according to an embodiment of the present invention, and FIG. 2 is a diagram showing a measurement circuit of a sensor. In Figures 1 and 2, (1) is an ozone sensor, which uses a semiconductor gas sensor element using, for example, an In2O3-based n-type semiconductor, and is similar to the conventional device shown in Figures 4 and 5 above. be. (2) is the DC current g for the sensor, (3) is the measurement circuit, and (4) is the ozone sensor (1
) to convert the output voltage from analog to digital signal A
/D converter, (5) is an input circuit that processes the output signal of the A/D converter (4), and (6) has an internal clock function and processes the signal from the input circuit (5). Central processing unit (
CPU), (7) is the DC power supply of the central processing unit (6), (
8) is an output circuit that converts the output signal from the central processing unit (6) into an input signal to the next stage circuit, etc., and (9) is a memory that stores the output signal obtained from the central processing unit (6). (device), (10) is a concentration display section that displays ozone concentration by an output circuit (8).

Based on the above configuration, the operation will be explained with reference to a flowchart showing the operation flow of the ozone concentration detection device according to one embodiment of FIG. 3.

First, when you start measurement in the measurement start step (L2),
A prescribed voltage is applied to the ozone sensor (1), and the initial value of Rs - ■ is set as the initial value of the reference resistance Rs of the ozone sensor (1).
is set in the arithmetic circuit.

Next, after waiting W seconds (here W-1) in a standby step (14), the process proceeds to an Rm measurement step (15) to measure the resistance value Rm of the ozone sensor (1).

In the Re setting step (IB), Rm/Rs is set to Re, and the process proceeds to the determination step (17), where it is determined whether or not Re is greater than 1.1. If NO, the Re setting step (1
Proceed to step 8), reset Rs to the same value as Rm, and use the general formula C-A+BIog Rm (A and B are constants)
In the concentration calculation step (19) using the formula (1), R
The ozone concentration C is calculated from the value of m, and the concentration display step (
20) to display this. Next, in the reference time setting step (21), the time of the internal clock is set to 1 (W) seconds, and the process returns to the standby step (14).

As described above, in step (17) Re > 1. If it is not L (when there is almost no ozone), the loop ■ from step (14) to step (21) is approximately 1 (
W) It operates on a second cycle, and the ozone concentration is measured and displayed each time.

Next, the operation when the ozone sensor (1) in this state is placed in an atmosphere with an osmosis/concentration of 1 ppm, for example, will be described. Immediately after that, the resistance of the ozone sensor (1) itself changes as shown in FIG. If the answer is YES in (17), the process proceeds to the conditional setting step (22) for T, and the previous T-1 (W
) is changed to T-2, and if W>2, it is not necessary to reset T, and in the concentration calculation step (23), C-exp (A
The ozone concentration C is calculated from the equation (2) of log Re/log T) /B, and is displayed in the concentration display step (24). Next, in the standby step (25), TmT+W is set by waiting W (1) seconds through the standby step (2B), and the ozone sensor (1) is set in the Rn measurement step (27).
) and set this value as Rn. This Rn is R
In the n judgment step (28), it is judged whether or not it is infinite (the maximum measurable resistance value, here 100 MΩ-Roo), and as shown in Figure 7, the Since Rn is less than R-, select YES and set Rn/
Proceed to Rm determination step (29). Rn/Rm in Rn/Rm determination step (29) is 1.03
If the rate of increase in resistance is large, YES is selected in the T determination step (30), and T is 6.
If the result of the determination is YES, Rm-Rn is set in the Rm determination step (31), and the process returns to the Re setting step (16), whereupon the steps in loop (2) are repeatedly executed. Also, as shown in Figure 7, this ozone sensor (
1), Rn will change to the temporarily set R after 18 seconds.
Since oo exceeds 100MΩ, Rn judgment step (2
8), the concentration C calculated 1 (W) seconds ago is displayed in the concentration display step (24), and the loop continues until the value of Rn becomes smaller than measurable R==0.
Execute repeatedly.

The rate of increase in the resistance value of the ozone sensor (1) becomes smaller and Rn
If the value of Rm becomes 1.03 times or less the value of Rm measured 1 (W) seconds ago, Rn/Rm determination step (29)
If NO is selected in the step, the process proceeds to the Rm setting step (32), sets Rm and Rn equally, and then sets the Re setting step (18).
) to calculate the ozone concentration CJE: according to the concentration calculation step (19) in which the general concentration is calculated.
This concentration C is displayed in the concentration display step (20), and Re
Loop I is repeatedly executed until the value exceeds 1.1 according to the determination step (17).

Further, when Rn exceeds RoO and NO is selected in the Rn determination step (28), the display of the concentration C continues until Rn decreases in the procedure of loop (3).

Also, if Rn/Rm is 1603 or more, Rn/Rm
Even if the determination step (29) selects YES, T is 80 (
If the time exceeds 60xW) seconds, it is considered that a new concentration change occurred while loop ■ and loop ■ were repeated, so the T determination step (30) causes the Rm setting step (32) to be performed. via the Re configuration step (
18), execute loop I and Rm.

Newly set Rs and T, and Re is the determination step (17)
A decision is made as to whether or not normal concentration calculation using loop I is appropriate.

Taking the curve showing the relationship between elapsed time and sensor resistance in FIG. 7 as an example, C-exp (Alog Re/logT)/
A-1,643 as a constant in formula (2) denoted by B,
Since B-252 is obtained, Cmexp(1,643l
FIG. 4 shows the results of calculating the ozone concentration (corrected concentration) at each concentration and time in the figure using og Re / log T ) / 252. That is, according to the concentration calculation using the above formula and the flowchart in FIG.
By setting , B to appropriate values, even if the ozone sensor response is slow as shown in Figure 7, or the resistance value is so high that the true resistance cannot be measured, the response is fast and highly accurate. It becomes possible to perform DI determination.

In the above embodiment, the concentration correction calculation and its judgment were explained only when the resistance value increases, but it is possible to accurately display the concentration using the same steps even when the resistance value decreases.

Furthermore, the present invention can be applied to a measuring device that detects ozone concentration by a change in the color of a redox indicator, and converts this change into a change in resistance (output voltage) of a light receiving element.

[Effects of the Invention] As described above, according to the present invention, in ozone concentration detection using a slow-response n-type semiconductor sensor, even when the ozone concentration in the atmosphere is high or, for example, when there is a sudden change, Since the change in the sensor resistance value is detected and the ozone concentration is calculated and displayed sequentially from the rate of change, it is possible to obtain measured values of the ozone concentration over a wide range with a fast response speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an ozone concentration measuring device according to an embodiment of the present invention, FIG. 2 is a diagram of an ozone detection circuit used in the present invention, and FIG. 3 is a flowchart for explaining the present invention in detail. , FIG. 4 is a diagram showing the relationship between ozone concentration (corrected concentration) obtained by the present invention and elapsed time, FIG. 5 is a front view showing an example of a normal ozone sensor, and FIG. The cross-sectional view and FIG. 7 are diagrams showing the relationship between resistance value, time, and concentration in each ozone concentration atmosphere of a conventional ozone sensor. In the figure, (1) is the ozone sensor, (3) is the measurement circuit, (4) is the A/D converter, (5) is the input circuit, and (6)
is the central processing unit (CPU), (8) is the output circuit, (9
) is the memory, (10) is the density processing section, (15), (2
7) is the resistance measurement step of the ozone sensor (1), (17)
). (29) is a determination step that compares the resistance value W seconds ago and the current resistance value, (101) is the substrate, (102) is the electrode, (
103) is an ozone-sensitive film, (105) is a heating element for heating the entire body, and (106) is an electrode of the heating element. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Patent Attorney Muneharu Sasaki Figure 1 Figure 2 Figure 5 Figure 7 Figure 4

Claims (1)

[Claims] An n-type semiconductor thin film ozone sensor, a calculation device that detects the resistance value of this ozone sensor and periodically calculates the ozone concentration, and when the rate of increase in the resistance value within the period exceeds a set value. and an arithmetic device that calculates the ozone concentration by detecting the rate of increase at each cycle based on that point in time.