JPS6046479B2 - Detection device - Google Patents

Description

[Detailed description of the invention]
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The present invention aims to provide a device that can selectively detect various gases and smoke with a single detection element.

In recent years, with the rapid spread of gas appliances, accidents due to gas leaks have been occurring frequently, and methods to prevent these accidents are being studied from various angles.

As one method in particular, various types of gas leak alarms have been developed to detect flammable gas leaks.
Gas leak alarms that have been put into practical use can be roughly divided into two types based on their detection methods: semiconductor methods and catalytic combustion methods. The former is a semiconductor (generally a metal oxide semiconductor, SnO) heated to a high temperature (200-4000C).

, ZnO, Ni-Fe. O. etc.) takes advantage of the property that the electrical resistance value decreases when it comes into contact with flammable gas such as propane gas. In the latter method, a catalyst is placed on a platinum wire, etc., the platinum wire is energized to generate heat, gas is catalytically combusted on the catalyst, and the temperature rise due to combustion is detected as an increase in the electrical resistance of the platinum wire, etc. There is a way to do it.

Although this method has the advantage that the output changes linearly with the gas concentration, the output obtained as an electrical signal is smaller than the former method, and it is necessary to add an amplifier circuit or the like. A problem with these detection elements for gas leak alarms is that the detection elements themselves do not have gas selectivity.

A detailed explanation of the invention will be given below. In general, gas sensing elements cannot be sensitive to combustible gas, smoke, or other gases, and exhibit sensitivity characteristics unique to each individual sensing element.

For example, a certain sensing element is sensitive to alcohol, relatively sensitive to butane, but
There are also sensing elements that have properties such as extremely low sensitivity to methane, and the opposite characteristics. These characteristics must be fully understood in advance before turning them into alarm devices, but many of them are generally highly sensitive to alcohol, which can cause malfunctions when used at home. This is extremely dangerous because even if a flammable gas alarm is issued, the user cannot determine whether the alarm is due to evaporation of alcohol during cooking or smoke. This is not very useful as a gas leak alarm, no matter how highly stable it is. Research is currently underway in various fields regarding countermeasures to this problem.
No definitive method has yet been established.

Typical methods that have been proposed include adding various noble metal catalysts (generally platinum, palladium, etc.) to metal oxide semiconductors to control the sensing sensitivity to various gases, and controlling the heating temperature of the sensing element. There is a method of changing the sensing sensitivity to various gases by changing the . Regarding the former, the effects of precious metal catalysts have not been theoretically elucidated, and efforts are being made by repeatedly changing the type and amount of precious metal catalysts and measuring the characteristics of each.

Therefore, there are drawbacks such as the need to consider reliability such as lifespan accordingly. In the latter case, the heating temperature, or operating temperature. Depending on the temperature, the sensitivity to various gases changes, and the types of gases that are most sensitive to each temperature change.

In general, in semiconductor type devices, the sensitivity to alcohol is high at low operating temperatures, and as the temperature increases, the sensitivity to alcohol decreases, making it easier to detect gases such as methane and propane. The device of the present invention utilizes the fact that the various gases and smoke change depending on the heating temperature of the detection element, that is, the operating temperature, and periodically changes the operating temperature in a stepwise manner depending on the desired gas and amount. , identification of any gas,
Furthermore, it is possible to function not only as a gas detector but also as a smoke detector.

The configuration basically consists of a detection element, a power supply device that periodically changes the heater voltage in a stepwise manner to control its heating temperature, and a detection device that can detect arbitrary identification gases and smoke. A display device that indicates the presence of a certain type of gas or a notification/alarm device that alerts only to a given gas is added.

Below, examples thereof will be given and explained in detail.

Gamma type ferric oxide (r-Fe2O3) was used as a typical metal oxide semiconductor gas sensing element. This sensing element exhibits the characteristics shown in FIG. 1, and targets three types of gas: methane, propane, and alcohol. Figure 1A shows the relationship between operating temperature and resistance value for each gas.
Curve 1 is the electrical resistance value in clean air, and curves 2, 3, and 4 are for alcohol, propane, and methane at 1000 pp each.
This is the electrical resistance value in m. Figure B shows the characteristics shown in figure A in terms of sensitivity, that is, the ratio of the electrical resistance value in clean air to the electrical resistance value in an atmosphere of 1000 ppm of each gas, and curves 2, 3, and 4 are, respectively. Sensitivity for alcohol, propane, and methane. As is clear from the figure, the sensitivity to alcohol is high at relatively low temperatures, reaching a maximum at around 250°C.

Thereafter, as the temperature increases, the sensitivity decreases, and conversely, the sensitivity of propane increases. The sensitivity of propane becomes higher at around 350°C. At higher temperatures, the sensitivity of methane increases as well, becoming even higher at about 450°C. As described above, the sensitivity characteristics to each gas change depending on the operating temperature.

Specific gas sensitivity characteristics are shown in Tables 1 to 3.

Table 1 shows 1000 of various gases when the operating temperature is 250℃.
It shows the element resistance value in ppm, and Tables 2 and 3 show the characteristics at 350°C and 450°C, respectively. Next, the configuration of a device using this sensing element will be described in detail.

FIG. 2 shows a circuit configuration of an embodiment of the present invention.

First, a description will be given of the circuit that functions to periodically change the heater voltage stepwise. In this example, the temperature at three points is maintained in two [phases] each, and (1) seconds is set as one cycle. 11 is the timer circuit, which generates a signal every 2 seconds.

Reference numeral 12 denotes a signal conversion circuit, which is a circuit for converting a signal generated by the timer circuit 11 into a control signal to a control circuit 14 that controls the power supply 13. in particular,
A silicon controlled rectifier (SCR) is used as the control circuit 14, and the conversion circuit 12 is configured so that a phase control signal of the SCR is sequentially applied to the SCR by a timer circuit. In this way, if the AC power from the power source 13 is phase-controlled by the control circuit 14 and further rectified by the rectifier circuit 16, a step-like periodic voltage is applied to the heater portion of the sensing element 15. . This situation is shown in FIG. 3A.

In this case, the temperature corresponding to each heater voltage is 25
The temperatures are set to 00C, 350°C, and 450°C. Next, regarding the sensor section, in the same way, the switching circuit 17 is activated by the signal from the timer circuit 11, and it is automatically switched to the detection circuits 18, 19, and 20 corresponding to 2500C, 350C, and 4501C. It will be done. In each of the switching circuits 18, 19, and 20, a sensor resistance value for an arbitrary type of gas and its concentration is set (in this example, a resistance value of 415 kΩ for alcohol 1000 ppm at 250°C, and a resistance value of 415 kΩ for propane 1000 ppm at 350°C).
m resistance value 154kΩ, methane 1000 at 450℃
(ppm resistance value is set to 65 kΩ), and if the resistance value is lower than that, the alarm buzzers 21 and 22 and the display circuit 23 will operate. To explain this specifically, by periodically applying a heater voltage as shown in FIG. 3A to the sensing element 15, the sensing element 15 as shown in FIG. 3B is activated in clean air. 15 resistance values change periodically.

In this figure, each detection circuit 1 is indicated by a broken line.
8, 19, and 20 are the operating set points for alarms and displays.
In the state shown in this figure, at each operating temperature, the resistances of the sensing elements 15 are all above the alarm/display operation set point, and no alarm or display is performed. Next, FIG. 4 shows a case where the detection element 15 is installed in an atmosphere with an alcohol concentration of 1500 ppm.

FIG. 4A shows the change in the resistance value of the detection element 15 at that time. As is clear from the figure, the resistance is lower than the alarm and display setting value at the operating temperature of 250°C. As shown in FIG. 4B, only the alcohol detection circuit operates and issues an alarm or display, revealing the presence of alcohol. As the next example, the characteristics in an atmosphere with a methane concentration of 2000 ppm are shown in FIG.

In FIG. 5(A), it can be seen that there is almost no sensitivity at 250° C. and 350° C., and the resistance of the sensing element 15 falls below the set point only when operating at 450° C.
As a result, as shown in Figure 5B, the presence of methane is alerted.
Can be displayed/displayed. The details of the device of the present invention have been explained above, but if intermittent alarms are inappropriate, it is of course possible to add an appropriate circuit and set the alarm and display to continue, especially if the alarm is temporarily high. Even if a high concentration of gas comes into contact with the sensor, false alarms can be prevented with a high degree of accuracy by configuring the device to issue an alarm unless the contact continues for one cycle or more.

Additionally, if the concentration of any gas falls below a set value in a high-concentration gas atmosphere at each operating temperature, an alarm will be issued, but in reality, the concentration of the gas generally increases gradually. During the periodic repetition of the heater voltage, the sensing circuit corresponding to the gas should be the first to be sensitive. Furthermore, in the present invention, alcohol, propane, and methane have been described, but it goes without saying that it is possible to detect not only other gases but also smoke in the same way, and the gas detector has a smoke detection function. If the type of gas can be identified, the concentration of the gas can also be determined by changing the operating temperature over time.

Further, in this example, an r-Fe2O3 gas detection element was used, but other metal oxide semiconductors may be used.
Moreover, it does not apply to structures such as thick films or sintered types.

[Brief explanation of the drawing]

1A and 1B are diagrams showing the characteristics of the detection element used in the gas detection device according to the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the device of the present invention, and FIGS. 3A, B, Figure 4 A, B
5A and 5B are waveform diagrams for explaining the operation. 11...Timer circuit, 12...Signal conversion circuit, 13...Power supply, 14...Control circuit, 15...Detection element, 16... ... Rectifier circuit, 17... Switching circuit, 18, 19, 20...
...Detection circuit, 21, 22...Buzzer, 23
······display.

Claims (1)

[Scope of Claims] 1. A detection element sensitive to gas or smoke, a power supply device that periodically supplies a stepped voltage to a heater for heating the detection element, and a resistor connected to the detection element. and a set value corresponding to the concentration of the gas or smoke to be detected, the stepwise voltage supplied from the power supply device to the heater is applied to A detection device characterized in that the detection device is adapted to correspond to the operating temperature of the detection element exhibiting maximum sensitivity. 2. Supply voltage from the power supply to the heater corresponding to the operating temperature at which the detection element exhibits maximum sensitivity for each of the multiple gases and smokes to be detected, and 2. The detection device according to claim 1, wherein said detection element is selectively sensitive. 3. The power supply device includes an AC power source, a silicon-controlled rectifier, a control circuit and a timer circuit that periodically control the phase of the silicon-controlled rectifier, and a rectifier circuit connected to the output end of the silicon-controlled rectifier. A detection device according to claim 1 or 2, characterized in that: