JP2006023097A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the sensing stability of carbon monoxide especially at the time of low temperature in a gas sensor using a semiconductor gas sensing element. <P>SOLUTION: The gas sensing element is repeatedly driven heretofore at a constant cycle determined by a high-temperature drive period Ta and a low-temperature drive period Tb as shown by Fig. (a) and, for example, methane is sensed in timing of t1 and carbon monoxide is sensed in timing of t2 but, since the time to sense gas to be sensed becomes generally long, for example, when the ambient temperature lowers, in a case that carbon monoxide of predetermined concentration or above is sensed, the low-temperature drive period is instantaneously made long (Tb'>Tb) like Tb' of Fig. (b) and a drive cycle is made long from T to T1 to perform the stable sensing of carbon monoxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a gas detection device using a semiconductor type gas detection element whose electric resistance changes in response to a gas component to be detected, particularly a means for controlling the heating temperature of the gas detection element. The present invention relates to a gas detector capable of detecting a plurality of gases by changing a temperature.

  Gas alarms that detect incomplete combustion gas components associated with incomplete combustion of city gas and propane gas equipment and warn of gas leakage and incomplete combustion are well known. In such a gas alarm device, a single gas detection element is used to operate a combustible gas component such as methane as a detected gas component indicating a gas leakage state, CO as a detected gas component indicating an incomplete combustion state, and the operation thereof. A device has been devised in which the temperature is controlled to the high sensitivity temperature range of each detected gas component and detected separately.

FIG. 4 shows an example of a gas alarm device disclosed in Patent Document 1, for example.
In the figure, 1 is a constant voltage circuit, 2 is a gas sensor such as a semiconductor type gas detection element, 3 is a microcomputer (also called a microcomputer), 4 is a display lamp, 5 is an alarm output unit, 6 is a speaker / buzzer, and Tr1 is Transistor, R3 is a sensor disconnection detection resistor, R4 is a sensor output resistor, and the gas sensor 2 is periodically driven from the microcomputer 3 via the transistor Tr1 at low and high temperatures. When the temperature is high, combustible gas components such as methane, Sometimes CO is detected.

  FIG. 5 shows temperature characteristics of a gas sensor, particularly a semiconductor type gas detection element, which is generally used in the gas alarm device. As is apparent from FIG. 5, the semiconductor gas sensing element changes its electric resistance (sensor resistance) depending on the concentration of the detected gas component methane or CO, and its value depends on the operating temperature of the semiconductor gas sensing element. And change greatly. In the case of methane, when comparing the case of clean air (methane concentration 0) and methane concentration 1000 ppm, it can be seen that there is a large difference in sensor resistance at high temperatures (eg, 420 ° C.), and that methane can be detected with high sensitivity. . Further, in the case of CO, when comparing the case of clean air (CO concentration of 0) and CO concentration of 100 ppm, a large difference occurs in sensor resistance at low temperatures (for example, 80 ° C.), and CO detection is possible with high sensitivity. I understand that.

Therefore, the gas alarm usually has a heater for controlling the operating temperature of the gas detection element to an appropriate temperature. For example, using the microcomputer 3 in FIG. 4, a high temperature state (420 ° C., 5 seconds) and a low temperature state ( By performing heater driving that periodically displaces at 80 ° C. for 10 seconds, methane and CO are periodically detected.
JP 2000-221151 A

  By the way, in a gas detection device such as a gas leak alarm, the semiconductor type gas is a cycle in which a voltage is applied to a heater or a sensor, and is a sum of a period driven at a high temperature and a period driven at a low temperature. Obviously, it is advantageous that the driving cycle of the detection element is short in view of the purpose of detecting gas leakage and incomplete combustion. In the gas alarm device as described above, the cycle for detecting the gas to be detected by the gas detection element is synchronized with the drive cycle described above, so that both methane and CO have a cycle of 15 seconds.

  On the other hand, for the purpose of reliably detecting gas, the gas detection period, which is a period for taking in the output of the gas detection element and judging the concentration of the gas, is determined from the time when the gas detection element can stably detect the gas. Although it is necessary, the gas detection of the semiconductor gas detection element utilizes the adsorption reaction phenomenon of the gas to be detected on the element surface, so the adsorption reaction rate becomes slow at low temperatures, and the gas can be detected stably. Time tends to be longer compared to high temperature conditions.

  In addition, when the temperature of the gas detection element is controlled by the electric power supplied to the heater, control that compensates for the ambient temperature is often not performed. Therefore, a change in the ambient temperature causes a change in the element temperature. When the temperature is low, the gas adsorption reaction rate is slow, and the time during which gas can be stably detected tends to be long. As a result, in the conventional gas detection device having a constant driving cycle, there is a high possibility that CO cannot be detected stably when the ambient temperature is low, and the reproducibility of gas detection in a low temperature state is deteriorated. is there.

  In addition, a catalyst such as a noble metal is widely added to a semiconductor gas detection element in order to enhance the sensitization action and response to the gas to be detected, and the gas detection element for detecting CO gas also has a sensitization action. In order to improve responsiveness, a noble metal catalyst is added. As a problem of this catalyst, the operating state of the gas detection element is different from that of a normal electronic device, and there is a problem of stability with time due to a very high temperature. In general, since the catalytic activity changes in a decreasing direction, problems such as a slow rate of adsorption of the gas to be detected also occur in the gas detector.

In other words, the conventional gas detection device having a constant driving cycle has a problem that the possibility of not being able to detect CO stably with time increases, and the reproducibility of gas detection in a state of change with time deteriorates.
Therefore, an object of the present invention is to improve the CO detection stability while keeping the driving cycle appropriate.

The invention of claim 1 includes a semiconductor gas detection element and driving means for periodically driving the semiconductor gas detection element between two types of high temperature and low temperature, and is combustible at high temperature. In gas detectors that detect carbon monoxide at low temperatures,
When carbon monoxide is detected at a predetermined concentration or more during low-temperature driving, the driving cycle of the semiconductor type gas sensing element is immediately matched with the output of the semiconductor type gas sensing element, and the carbon monoxide does not reach the predetermined concentration. It is characterized in that it is longer than the driving cycle of the semiconductor gas detection element at that time.

The invention of claim 2 includes a semiconductor gas detection element and driving means for driving the semiconductor gas detection element by periodically changing between two types of temperatures, high temperature and low temperature, and is combustible at high temperature. In gas detectors that detect carbon monoxide at low temperatures,
When carbon monoxide is detected at a predetermined concentration or more during low-temperature driving, the carbon monoxide is predetermined for a period during which the semiconductor-type gas sensing element is driven at a low temperature, immediately corresponding to the output of the semiconductor-type gas sensing element. When the concentration does not reach, the semiconductor gas detection element is made longer than a period of driving at a low temperature.

  In the first or second aspect of the invention, when carbon monoxide is detected at a predetermined concentration or more during the low temperature driving, the driving of the semiconductor gas sensing element is immediately associated with the output of the semiconductor gas sensing element. The period can be changed in the range of 10 seconds or more and 30 seconds or less (Invention of Claim 3).

  According to the present invention, it is possible to improve CO detection stability while maintaining an appropriate driving cycle, and to prevent a gas leak accident and a CO poisoning accident with high accuracy.

FIG. 1 is an explanatory diagram for explaining an embodiment of the present invention. FIG. 1 (a) shows a gas when CO gas is not detected, and FIG. 1 (b) shows a gas when CO gas is detected. The timing chart of the heater drive of a detection element is shown, respectively. As the gas detection element (gas sensor), a well-known one, for example, one described in Japanese Patent Application Laid-Open No. 07-198644 can be used. In addition, the present invention can be easily implemented by using the above-mentioned Patent Document 1.
In FIG. 1, Ta indicates a time for keeping the heater at a high temperature, and Tb indicates a time for keeping the heater at a low temperature. The driving cycle T is the sum of the Ta + Tb, that is, T = Ta + Tb. Further, t1 represents the methane detection timing during the Ta period, and t2 represents the CO detection timing during the Tb period.
Note that the detection timings of t1 and t2 are generally set near the end of the Ta and Tb periods, for example, 0.5 seconds before the end of the Ta and Tb periods. Thus, the driving cycle T and the gas detection cycle that actually takes in the output of the gas detection element are substantially equal.

  Here, in the conventional gas detection device, the gas driving cycle T is always constant. On the other hand, in the present invention, when the output of the gas detection element is detected at time t2 and reaches the output value for judging the presence of gas, for example, the CO concentration for issuing a CO alarm, that is, the output of about 100 ppm ( When an output (O50) corresponding to a concentration (50 ppm) of half (50 ppm) of O100) is detected, the heater driving cycle is changed from Tb to Tb ′ (Tb ′> Tb) immediately so that the heater driving cycle is shown in FIGS. Change as follows. Instead of changing Tb to Tb ′ and changing the driving cycle T to T1, the driving cycle T1 may be changed to include the time Ta. At this time, the drive period to be changed can be changed according to the output of the gas detection element.

  Then, when the output at the next detection timing t2 'exceeds O100, which is the CO concentration at which a CO alarm is issued, an alarm is issued. During the period when the CO alarm is issued, the low temperature driving time is kept at Tb ′, the CO concentration in the atmosphere decreases, and when the output at timing t2 ′ falls below O100, the driving cycle is shown in FIG. As in 1a. In this example, for example, Ta is 5 seconds, Tb is 10 seconds, and Tb 'is 20 seconds, but it is needless to say that these values are not restrictive.

  FIG. 2 explains the ambient temperature dependence of the CO output in the case of 10 conventional gas detection devices (see FIG. 2 (a)) and 10 gas detection devices of the present invention (see FIG. 2 (b)). It is explanatory drawing. Here, the CO gas concentration which issued the alarm when the ambient temperature is changed from 0 ° C. to 50 ° C. in the gas detector that issues the alarm at room temperature (20 ° C.) and CO concentration of 100 ppm is shown. Note that the temperature dependence of the output of the gas detection element is compensated by detecting the ambient temperature in both the conventional gas detection device and the gas detection device of the present invention.

As shown in FIG. 2, it can be seen that in the conventional gas detection device, the lower the ambient temperature, the worse the reproducibility of the concentration at which an alarm is issued, but the reproducibility of the gas detection device of the present invention is good. You can see (in Fig. 2 you can't clearly distinguish each of the 10 cars, but it's enough if you know roughly).
FIG. 3 is an explanatory diagram for explaining the ambient temperature dependence of the CO output as in FIG. 2. Here, except that, for example, 10 conventional gas detectors that have passed for 5 years are used as FIG. This is the same as in the case of FIG.

  That is, as shown in FIG. 3, in the conventional gas detection device, the lower the ambient temperature, the worse the reproducibility of the concentration that gives an alarm, and the higher the temperature at which the reproducibility starts to deteriorate compared to FIG. I understand that. This can be said to indicate that the catalytic function of the gas detection element deteriorates with time. On the other hand, the reproducibility of the gas detector of the present invention can be said to be good in the entire temperature range as shown in FIG.

  In the above, for comparison with the conventional gas detection device, Ta and Tb in FIG. 1 are set to have the same time as that of the conventional gas detection device. In this case, it can be shortened to Tb shorter than, for example, about Ta (that is, about the same as the driving cycle of 5 seconds in a high temperature state). Even in this case, it is preferable to make Tb ′ as long as possible in order to obtain good reproducibility. However, when applied to a gas leak alarm, it is necessary to reliably alarm gas leak (methane) within one minute. It is convenient to have two or more measurement cycles per minute. Therefore, it is desirable that the driving cycle T be 10 seconds or more and 30 seconds or less.

Explanatory drawing explaining embodiment of this invention Graph explaining ambient temperature dependence A graph explaining the ambient temperature dependence of a time-lapse product Configuration diagram showing a conventional example of a gas alarm Example of temperature characteristics of gas detection element

Explanation of symbols

T, T1 ... drive cycle, Ta ... high temperature holding period, Tb, Tb '... low temperature holding period, t1, t2 ... detection timing.

Claims (3)

A semiconductor type gas detection element and a driving means for driving the semiconductor type gas detection element by periodically changing between two kinds of temperatures, high temperature and low temperature, and combustible gas components at low temperature In gas detectors that detect carbon monoxide,
When carbon monoxide is detected at a predetermined concentration or more during low temperature driving, the semiconductor gas sensing element is driven at a high temperature and at a low temperature immediately corresponding to the output of the semiconductor gas sensing element. A gas detection device characterized in that a driving cycle of the semiconductor type gas detection element, which is a sum of a period of time and a period of time, is longer than a driving cycle of the semiconductor type gas detection element when carbon monoxide does not reach a predetermined concentration. A semiconductor type gas detection element and a driving means for driving the semiconductor type gas detection element by periodically changing between two kinds of temperatures, high temperature and low temperature, and combustible gas components at low temperature In gas detectors that detect carbon monoxide,
When carbon monoxide is detected at a predetermined concentration or more during low-temperature driving, the carbon monoxide is predetermined for a period during which the semiconductor-type gas sensing element is driven at a low temperature, immediately corresponding to the output of the semiconductor-type gas sensing element. A gas detection device characterized in that the semiconductor gas detection element is made longer than a period during which it is driven at a low temperature when the concentration is not reached. When carbon monoxide is detected at a predetermined concentration or more during the low temperature driving, the driving cycle of the semiconductor gas sensing element is set to 10 seconds or more and 30 seconds or less immediately corresponding to the output of the semiconductor gas sensing element. The gas detection device according to claim 1, wherein the gas detection device is changed within a range.

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