JP2002318221A - Gas detector - Google Patents

Abstract

(57) [Problem] To provide a gas detection device of the present invention, since a constant voltage is constantly applied to a heater for raising the temperature of a sensor element, it takes a very long time to raise the temperature. It is assumed that. SOLUTION: It has a sensor element 2, a constant voltage circuit 4 for raising the temperature of a heater 3, a control means 5 and a current detection means 6 for detecting a current flowing through the heater 3, and the control means 5 detects gas. Is controlled so that the heater 3 is energized only when
The output voltage of the constant voltage circuit 4 is configured to have a voltage value higher than a minimum voltage value required to maintain a temperature required for the sensor element 2 to detect gas.
Since the voltage is applied to the heater 3 to control the temperature by turning on and off the voltage of the constant voltage circuit 4 based on the detection result of the current detecting means 6, the temperature can be raised accurately in a shorter time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to heating control of a gas detector.

[0002]

2. Description of the Related Art A conventional gas detector for detecting carbon monoxide has a heater provided in the detector as disclosed in Japanese Patent Application Laid-Open No. 63-78059, and operates stably. I am trying to do it. Further, Japanese Unexamined Patent Publication No.
As in JP-A-6816, heating is controlled in two temperature regions by applying a pulsed voltage. Further, a method of applying a pulse-like voltage only when detecting gas to reduce power consumption has been considered. This is shown in FIG.
11 will be described with reference to FIG.

First, the sensor element 2 will be described with reference to FIG. In this example, a solid electrolyte thin film 9 such as stabilized zirconia showing oxygen ion conductivity is laminated on a heat-resistant insulating substrate 7 such as alumina. On this stabilized zirconia thin film 9, a pair of thin film platinum electrodes 10a, 10a
b is stacked by, for example, a sputtering method, and a platinum catalyst 11 is stacked on one of the platinum electrodes 10b. Also,
On the back surface of the heat-resistant insulating substrate 7, a heater thin film 3 formed by sputtering platinum is formed. Then, the sensor element 2 detects carbon monoxide.

Next, the operation and operation of the sensor element 2 for detecting carbon monoxide will be described. On the platinum electrode 10b side of the sensor element 2 on which the platinum catalyst 11 is laminated, carbon monoxide reacts with oxygen gas by the action of the platinum catalyst 11 to become carbon dioxide gas and is consumed and disappears, so that the oxygen partial pressure increases. On the other hand, on the side of the platinum electrode 10a, the oxygen partial pressure is relatively low because the carbon monoxide gas and the oxygen gas coexist.
For this reason, the partial pressure of oxygen gas is higher in the platinum electrode 10b than in the platinum electrode 10a, and oxygen ions move in the stabilized zirconia 9 to generate an electromotive force. This electromotive force has a value substantially proportional to the logarithmic value of the concentration of carbon monoxide.

As shown in the block diagram of FIG. 9, the gas detector 14 comprises a sensor element 2, a constant voltage circuit 15, and a control circuit 16, and the constant voltage circuit 15 applies a voltage to the heater 3 and Is heated. And the sensor element 2
Is 400 by the heater 3 in order to obtain a stable electromotive force.
The temperature is controlled at a temperature of from 500C to 500C, preferably 450C.

As shown in FIG. 10, when detecting gas, a pulse-shaped rectangular wave is applied to the heater 3. As a result, the heater draws a curve as shown in FIG. The voltage value is set in advance so that the temperature becomes approximately 450 ° C. when a sufficient time has elapsed and the temperature has reached the temperature equilibrium state.

[0007]

However, the above conventional gas detector has a problem that it takes a long time to reach a temperature at which the sensor can detect carbon monoxide gas, that is, about 450 ° C.

[0008]

According to the present invention, there is provided a heat-resistant insulating substrate, a solid electrolyte thin film laminated on the heat-resistant insulating substrate, and a pair of platinum electrode thin films laminated on the solid electrolyte thin film. And a platinum catalyst laminated on one of the platinum electrode thin films, and a sensor element composed of a thin film of a heater laminated on a heat-resistant insulating substrate to raise the temperature of the platinum electrode, the platinum catalyst and the solid electrolyte. A constant voltage circuit for raising the temperature of the heater, and control means for controlling a voltage application time of the constant voltage circuit, wherein the constant voltage circuit is controlled to raise the temperature of the heater when gas is detected, The temperature of the heater is controlled by turning the circuit on and off a plurality of times, and the voltage value of the constant voltage circuit is lower than the minimum voltage value required to maintain the temperature required for the sensor element to detect gas. High And configured to the voltage value.

According to the above invention, the temperature can be raised in a shorter time because a high voltage is applied during the temperature rise and the temperature is raised.
In addition, since the control is performed by switching on and off when the temperature becomes appropriate, the temperature of the heater does not excessively increase.

[0010]

DETAILED DESCRIPTION OF THE INVENTION A gas detector according to claim 1 of the present invention comprises a heat-resistant insulating substrate, a solid electrolyte thin film laminated on the heat-resistant insulating substrate, and a pair of platinum electrodes laminated on the solid electrolyte thin film. A thin film, a platinum catalyst laminated on one of the platinum electrode thin films, and a sensor element composed of a heater thin film laminated on a heat-resistant insulating substrate to raise the temperature of the platinum electrode, the platinum catalyst and the solid electrolyte. A constant voltage circuit for raising the temperature of the heater, and control means for controlling a voltage application time of the constant voltage circuit, wherein the constant voltage circuit is controlled to raise the temperature of the heater when gas is detected, By controlling the temperature of the heater by turning on and off the circuit several times,
Further, the voltage value of the constant voltage circuit is configured to be higher than a minimum voltage value required for maintaining a temperature required for the sensor element to detect gas.

[0011] Since a high voltage is applied at the time of heating to raise the temperature, the temperature can be raised in a shorter time. In addition, since the control is performed by switching on and off when the temperature becomes appropriate, the temperature of the heater does not excessively increase.

According to a second aspect of the present invention, there is provided a gas detecting device having current detecting means for detecting a current flowing through a heater, calculating a temperature of the heater from the detected current value, and calculating an off time of the constant voltage circuit from the calculated value. Is determined.

[0013] Since the ON / OFF of the constant voltage source can be switched and controlled within an appropriate temperature range, the temperature of the heater does not rise excessively.

According to a third aspect of the present invention, there is provided a gas detecting device comprising a second constant voltage circuit and a second current detecting means for detecting a current flowing through the heater, and a second constant voltage circuit for detecting an off time of the first constant voltage circuit. A weak voltage is applied to the heater by the second constant voltage circuit, and the temperature is calculated from a heater resistance value obtained from the voltage value and the current value at that time. The circuit is controlled to be turned on.

Further, since the heater temperature is detected by the second constant voltage circuit and the second current detecting means even while the first constant voltage circuit is off, the heater temperature can be controlled more accurately. Can be.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a side sectional view of a sensor element 2 of a gas detection device 1 according to Embodiment 1 of the present invention, FIG. 2 is a block diagram, and FIG. 3 is a diagram showing a voltage applied to a heater 3. 4
3 is a diagram showing a temperature rise curve of the heater 3. FIG. In addition,
In this embodiment, a description of the same operation and operation as in the conventional example will be omitted.

The output voltage of the constant voltage circuit 4 shown in FIG. 2 is set to a higher value so that the temperature becomes 450 ° C. or more when the voltage is constantly applied to the heater 3.

When the temperature of the heater 3 is raised from the normal temperature, the control means 5 first turns on the constant voltage circuit 4 and the heater 3
Continue applying voltage until it reaches 0 ° C. Thereafter, the heater 3 is controlled to be maintained at about 450 ° C. by turning on and off the constant voltage circuit 4. At this time, the current flowing through the heater 3 is detected by the current detecting means 6, and the heater resistance value is calculated from the voltage value applied to the heater 3 and the current value flowing through the heater 3. Since the heater 3 is a platinum resistor, its resistance has a positive temperature characteristic, and the heater temperature can be determined from the calculated heater resistance. The temperature of the heater 3 is, for example, 450 ° C. ±
It is controlled within a range of about 10 ° C. At that time, heater 3
The constant voltage circuit 4 is controlled to be turned off when the temperature reaches 455 ° C. and to be turned on when the temperature reaches 445 ° C. At this time, the time for turning off the constant voltage circuit 4 is 4
The calculation shall be made in consideration of heat radiation by natural cooling in which the temperature is reduced from 55 ° C. to 10 K. FIG. 3 shows a voltage waveform applied to the heater 3 at that time, and a pulse-like rectangular wave is applied to the heater. At this time, the temperature rise curve of the heater 3 continuously rises from room temperature to 455 ° C. as shown in FIG. 4, and thereafter rises and falls between 455 ° C. and 445 ° C. according to the ON / OFF of the voltage pulse in FIG. Is controlled. The detection of gas is performed while the temperature of the heater 3 is controlled to about 450 ° C.

Therefore, as described above, since a high voltage is applied at the time of heating to increase the temperature, the temperature can be increased in a shorter time. In addition, since the control is performed by switching on and off when the temperature becomes appropriate, the temperature of the heater 3 does not rise excessively.

In this embodiment, an example in which the temperature of the heater is controlled in a range of, for example, about 450 ° C. ± 10 ° C. has been described. However, the present invention is not limited to this. It may be finely controlled to be in the range of about 2 ° C.

As shown in FIG. 5, a sensor element in which a heater thin film 3, a heat resistant insulating thin film 8, a solid electrolyte thin film 9, platinum electrode thin films 10a and 10b, and a platinum catalyst 11 are stacked in this order on a heat resistant insulating substrate 7 is also used. It is needless to say that the same effect can be obtained by controlling.

The constant voltage circuit 4 described here is, for example, a battery, a three-terminal regulator, one set, a DC-DC converter, a combination of an AC power supply and a DC conversion circuit, and the like.

(Embodiment 2) Embodiment 2 of the present invention is different from Embodiment 1 in that, as shown in FIG.
And that a weak voltage is applied to the heater 3 while the first constant voltage circuit 4 is off. At this time, the voltage value applied by the second constant voltage circuit 12 is sufficiently smaller than the voltage value A by the first constant voltage circuit 4 and small enough not to contribute to the temperature rise of the heater 3 as shown in FIG. B. For example, assuming that a voltage of about 3 to 5 V is applied by the first constant voltage circuit, the applied voltage by the second constant voltage circuit 12 is preferably 1 V or less, particularly about 0.1 V.

Thus, the temperature of the heater 3 can be detected even while the first constant voltage circuit 4 is off. The method of detecting the temperature of the heater 3 is the same as that described in the first embodiment, in which the second current detecting means 13 is provided, and the resistance value is obtained from the voltage value and the current value.

Therefore, since the temperature of the heater 3 can be detected not only when the first constant voltage circuit 4 is turned on but also when it is turned off, the temperature of the heater 3 can be more accurately controlled.

[0027]

As described above, the gas detecting device according to the first aspect of the present invention increases the temperature by applying a high voltage when the temperature is raised, so that the temperature can be raised in a shorter time. Further, since the control is performed by switching on and off when the temperature reaches an appropriate temperature, there is an effect that the temperature of the heater does not excessively increase.

The gas detector according to the second aspect can control the constant voltage source by switching on and off within an appropriate temperature range.

In the gas detector according to the third aspect, the temperature of the heater can be detected not only when the first constant voltage circuit is turned on but also when the first constant voltage circuit is turned off, so that the temperature of the heater can be more accurately controlled.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a gas detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of the gas detector.

FIG. 3 is a diagram showing a voltage applied to a heater of the gas detection device.

FIG. 4 is a diagram showing a temperature rise of a heater of the gas detection device.

FIG. 5 is a side cross-sectional view of another example of the gas detection device according to the first embodiment.

FIG. 6 is a block diagram of a gas detection device according to a second embodiment.

FIG. 7 is a diagram showing a voltage applied to a heater of the gas detector.

FIG. 8 is a side sectional view of a conventional gas detector.

FIG. 9 is a block diagram of a conventional gas detection device.

FIG. 10 is a diagram showing a voltage applied to a heater of a conventional gas detector.

FIG. 11 is a diagram showing a temperature rise of a heater of a conventional gas detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas detector 2 Sensor element 3 Heater 4 Constant voltage circuit 5 Control means 6 Current detecting means 7 Heat resistant insulating substrate 9 Solid electrolyte thin film 10 a, 10 b platinum electrode thin film 11 Platinum catalyst 12 Second constant voltage power supply 13 Second current Detection means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsuhiko Uno 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Kunihiro Tsuruta 1006 Kadoma, Kazuma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Takahiro Umeda 1006 Odaka, Kazuma Kadoma, Osaka Pref. BF05 BF07 BJ03 BK04 BL08 BM04

Claims (3)

[Claims] 1. A heat-resistant insulating substrate, a solid electrolyte thin film laminated on the heat-resistant insulating substrate, a pair of platinum electrode thin films laminated on the solid electrolyte thin film, and a platinum catalyst laminated on one of the platinum electrode thin films. A sensor element composed of a thin film of a heater laminated on a heat-resistant insulating substrate to raise the temperature of the platinum electrode, the platinum catalyst, and the solid electrolyte, and a constant voltage circuit for raising the temperature of the heater, Control means for controlling the voltage application time of the constant voltage circuit, the temperature of the heater is controlled by turning on and off the constant voltage circuit a plurality of times, when the gas is detected, the temperature of the heater is controlled. In addition, the voltage value of the constant voltage circuit is configured to be a voltage value higher than a minimum voltage value required to maintain a temperature required for the sensor element to detect the gas, and the carbon monoxide gas is detected. Do Gas detector. 2. The gas detection device according to claim 1, further comprising current detection means for detecting a current flowing through the heater, calculating a temperature of the heater from the detected current value, and determining an off time of the constant voltage circuit from the calculated value. . And a second current detecting circuit for detecting a current flowing through the heater, wherein the second constant voltage circuit detects a weak voltage when the first constant voltage circuit is turned off. And applying a control to turn on the first constant voltage circuit when the temperature of the heater is lowered, wherein the temperature is calculated from a heater resistance value obtained from the voltage value and the current value at that time. Gas detector.