JPH0358461B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention is a method for controlling oxygen concentration to a predetermined dangerous value by the output of an oxygen sensor, such as a galvanic cell type oxygen sensor, which generates a voltage according to the oxygen concentration in the air. The present invention relates to an oxygen concentration detection device that detects a decrease in oxygen concentration.

[Prior Art] Conventionally, there have been devices of this type as shown in FIGS. 1 and 2. FIG. 1 is a block diagram showing a conventional oxygen concentration detection device, which was shown in the September 1980 issue of the monthly magazine Keiho, for example. In the figure, 1 is a galvanic cell type oxygen sensor, 2 is an amplifier, and 3 is a voltage comparator, 4 is a reference battery for alarm setting, 5 is an alarm buzzer,
6 is a solid state relay. FIG. 2 is a side sectional view showing the structure of the galvanic cell type oxygen sensor 1, in which 7 is a positive electrode material, 8 is a negative electrode material, and 9 is a negative electrode material.
is an electrolytic solution, 10 is a temperature compensation thermistor, 11 is a holder, 12 is a positive terminal, 13 is a negative terminal, 14
is the external resistance.

The galvanic cell type oxygen sensor 1 is constructed as shown in FIG. 2, and by inserting an external resistor 14 between the positive terminal 12 and the negative terminal 13, a voltage is generated across the external resistor 14, and this voltage is It changes depending on the oxygen concentration in the air. FIG. 3 shows an example of the characteristic, and as the oxygen concentration in the air increases, the terminal voltage V increases. In the figure, V ₁ is the output voltage value of sensor 1 at 20.6%, which is the normal oxygen concentration in the air, and V ₂ is the output voltage value of sensor 1 at 18.0%, which is the dangerous oxygen concentration.

An output voltage corresponding to the oxygen concentration in the air is outputted from the oxygen sensor 1, amplified by the amplifier 2 shown in FIG. A voltage from battery 4 is applied. The voltage value of this reference battery 4 is above
V ₂ , and therefore, when the oxygen concentration of the detected air drops to the dangerous range of 18.0%, the output of the voltage comparator 3 is inverted, which causes the alarm buzzer 5 and the solid state Relay 6 is driven and dangerous oxygen concentration detection operation is performed.

However, the above characteristics of the galvanic cell type oxygen sensor 1 change over time. Figure 4 shows an example of this characteristic variation, where A represents the characteristics of the initial product and B represents the characteristics of the initial product.
indicates the characteristics of a product that has deteriorated over time; when the oxygen concentration changes from a normal value of 20.6% to a dangerous value of 18.0%, V ₁ →V ₂ for an initial product and V ₁ ′ → for a deteriorated product.
V ₂ ′, the slope of the straight line changes, and the dangerous concentration detection voltage also decreases from V ₂ to V ₂ ′.

Therefore, if the voltage of the reference battery 4 in Fig. 1 is set to V ₂ for the initial product, if the sensor 1 deteriorates, it will detect, for example, around 19.5% as a dangerous state of oxygen deficiency, as shown in Fig. 4. This had the disadvantage of causing a malfunction in that it would issue an alarm.

[Summary of the invention]

This invention was made in order to eliminate the above-mentioned drawbacks, and is aimed at eliminating the drawbacks of oxygen sensors such as galvanic oxygen sensors.
Output voltage at hazardous oxygen concentration (18.0%) versus output voltage V ₁ at normal oxygen concentration (20.6%)
Focusing on the fact that the ratio of V ₂ is almost the same for both the initial product and the deteriorated product that has changed over time, this ratio is calculated using an A/D converter and central processing unit while measuring the output of the oxygen sensor, and the calculation is performed. It is an object of the present invention to provide a highly reliable oxygen concentration detection device that does not malfunction even over time by detecting when the value has decreased to a predetermined value or lower.

[Embodiments of the invention]

An embodiment of this invention will be described below. FIG. 5 is a block diagram showing a schematic configuration of an embodiment of the present invention. Reference numerals 1, 2, 5, and 6 indicate the same parts as those in FIG. 1, and 15 indicates the amplifier 2 of the oxygen sensor 1. A/D that converts the output voltage of the hete into a digital signal
Converter 16 is a central processing unit (hereinafter referred to as CPU) that processes the digital output of this A/D converter 15.
It is. The operation of the oxygen concentration detection device which is an embodiment of the present invention constructed as described above will be explained with reference to the flowchart shown in FIG. First, the output voltage of oxygen sensor 1 at a normal oxygen concentration of 20.6%
e ₀ is input to the A/D converter 15 via the amplifier 2 and converted into digital data, and the data is always cleared in the initial state of the CPU 16 (Step 21 in Figure 6). Optional writing section (hereinafter referred to as RAM) (Step 22), and initialize it in RAM as an initial value (Steps 23, 24). Next, the second and subsequent output voltages e ₂ , e ₃ , ..., e _o of the oxygen sensor 1 in the air to be detected are digitally converted and sent to the CPU 1.
The ratio of the written value to the initial value θ _o =e _o /e ₀ is calculated (step 25), and that value is set as the standard setting value θ _k =V set in advance in the CPU 16. If larger than ₂ /V ₁ , e ₂ ,
The values of e ₃ ,..., e _o are written to the CPU 16 each time (steps 26, 27), and when they become less than θ _k , writing is stopped, and the digital output signal of the CPU 16 drives the alarm buzzer 5 and the solid state relay 16. (Steps 26, 28, 29).

Regarding the case of deteriorated products, the relationship between _the output voltage values e ₀ and e _o of the oxygen sensor and _the oxygen concentration is as shown in _FIG . ₂ ′.

Therefore, by writing in advance the ratio of the terminal voltage value V ₂ /V ₁ to 20.6% of the oxygen concentration of 18.0% in the initial product of the galvanic cell type oxygen sensor 1 into the CPU 16 as the reference setting value θ _k , Since the voltage ratio V ₂ ′/V ₁ ′ in the degraded product is also equal to the reference setting value θ _k , the dangerous oxygen concentration in the air to be detected can be accurately detected.

To prevent malfunction, when setting the initial value to the CPU 16, the output voltage of the oxygen sensor 1 in normal air is written multiple times, and when the values match, it is written as the initial value. The value of e _o when θ _o becomes less than θ _k is 2
After writing ~3 times, the alarm buzzer 5 and solid state relay 16 are finally activated due to the matching of the values.
etc. may also be driven.

〔Effect of the invention〕

As described above, the present invention constantly calculates the ratio of the output voltage of the oxygen sensor in the detected air to the output voltage of the oxygen sensor in normal air, and detects when the value becomes less than a predetermined value. This has the effect of making it possible to obtain an accurate and highly reliable oxygen concentration detection device that does not malfunction even if the characteristics of the oxygen sensor deteriorate over time.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional oxygen concentration detection device, Fig. 2 is a side sectional view showing the structure of a galvanic cell type oxygen sensor, Figs. 3 and 4 are its operating characteristics, and Fig. 5 FIG. 6 is a block diagram showing a schematic configuration of an embodiment of the present invention, FIG. 6 is a flowchart for explaining its operation, and FIG. 7 is an operation characteristic diagram in the case of a deteriorated product. In the figure, 1 is a galvanic cell type oxygen sensor, 2 is an amplifier, 5 is an alarm buzzer, 15 is a D/A converter, 16
is the central processing unit (CPU). Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. In an oxygen concentration detection device that detects that the oxygen concentration has decreased to a predetermined dangerous value by the output of an oxygen sensor that generates a voltage according to the oxygen concentration in the air, the output of the oxygen sensor is An A/D converter that converts voltage into a digital signal and a central processing unit that processes the digital output of this A/D converter are provided, and the output voltage of the oxygen sensor in air with normal oxygen concentration is digitally converted by these. means for writing and setting the output voltage value in the air to be detected in the central processing unit as an initial value; means for digitally converting the output voltage value in the air to be detected and writing it in the central processing unit as a second or subsequent value; and calculating a ratio with respect to the initial value; It is characterized by comprising means for comparing the calculated value with a preset reference setting value, and means for driving an alarm when the calculated value becomes equal to or less than the reference setting value as a result of this comparison. Oxygen concentration detection device. 2. The oxygen concentration detection device according to claim 1, wherein the oxygen sensor is a galvanic cell type oxygen sensor. 3. The means for writing and setting the initial value is to digitally convert the output voltage of the oxygen sensor in air with normal oxygen concentration, write it multiple times, and when the values match, write and set it in the central processing unit as the initial value. The oxygen concentration detection device according to claim 1 or 2, wherein the oxygen concentration detection device is a means for detecting oxygen concentration. 4. The means for driving the alarm is such that the calculated value is equal to the reference setting value multiple times through this comparison;
Claim 1, characterized in that the device is a means for activating an alarm when the temperature reaches or below the
The oxygen concentration detection device according to item 2 or 3. 5. The reference set value is the ratio of the output voltage of the initial oxygen sensor in air with an oxygen concentration of 18.0% to the output voltage in air with an oxygen concentration of 20.6%. The oxygen concentration detection device according to any one of Items 1 to 4.