JP3432026B2 - Limit current type gas sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type gas sensor with a heater for detecting gas concentrations such as oxygen concentration and humidity.

[0002]

2. Description of the Related Art As a conventional technique of this kind, Japanese Patent Application Laid-Open No. 5-9
The technique disclosed in Japanese Patent No. 3706 is known. This technology discloses a limiting current type gas sensor in which a sensor element with a heater is attached to the tip of a probe, the periphery thereof is covered with a stainless protector, and the periphery thereof is covered with a porous filter. In addition, the protector is provided with a vent hole around which gas flows in and out so that the gas flowing into the filter is introduced into the protector.

[0003]

During the operation of such a limiting current type gas sensor, the inside of the protector such as the sensor element becomes high temperature due to the function of the heater. Then, when the operation of the limiting current type gas sensor is stopped and the heater is turned off, the temperature inside the protector gradually decreases, and when the measured atmosphere gas temperature falls below the dew point temperature, water vapor in the gas condenses abnormally inside the protector. There is a case.

The protector is provided with a vent hole, but the vent hole is usually provided at a position apart from the detecting portion of the sensor element so that the flow velocity of the gas does not affect the measurement result.
Therefore, depending on the installation direction of the limiting current type gas sensor, the dew condensation generated in the protector does not flow out of the protector but accumulates in the protector, and the sensor element may be submerged in the dew condensation water. Specifically, in the technique disclosed in the above-mentioned publication, since there are four ventilation holes provided on the probe side, when the sensor element is installed downward with respect to the probe, it is generated inside the protector. The condensed water does not flow out of the protector but collects in the protector, and the sensor element is submerged in the condensed water.

When the limiting current type gas sensor is operated, the sensor element operates at a high temperature (500 to 6) in a short time due to the function of the heater.
The temperature is raised to 00 ° C. When the sensor element is submerged in dew condensation water and the limiting current type gas sensor is operated,
Due to the water attached to the sensor element, a thermal shock may be applied to the sensor element, and the sensor element may be broken, causing an accident such as breakage.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a limiting current type gas sensor in which a sensor element is not damaged by the influence of dew condensation water.

[0007]

The limiting current type gas sensor of the present invention employs the following technical means. [Means for Claim 1] A limiting current type gas sensor includes a sensor element for detecting a gas concentration, a heater element for generating heat upon receiving energization and heating the sensor element to a sensor operating temperature, the sensor element and the heater element. And a probe base for installing in the gas to be measured and attached to the base in a state of covering the sensor element and the heater element, and having a bottomed container shape having a vent hole on the base side and in the periphery. And a protector. The protector is provided with the vent hole near the probe base, and has a tubular body that covers the sensor element and the heater element and is formed of an airtight material, and an end portion of the tubular body. It is attached and comprises a porous end filter permeable to water in the barrel.

[Means for Claim 2] In the limiting current type gas sensor according to claim 1, the heater element is provided with a heater energizing circuit for applying a voltage to the heater element.
A low voltage is applied to the heater element for a predetermined time so as to generate heat at a temperature lower than the sensor use temperature for a predetermined time, and then a high voltage is applied to the heater element so that the heater element generates heat at the sensor use temperature. Apply.

[0009]

[Operation and effect of the invention]

[Operation and Effect of Claim 1] In the limiting current type gas sensor, when the sensor element is installed on the upper side of the base, the dew condensation water condensed in the protector is discharged from the vent hole located on the lower side to the outside of the protector. leak. Further, when the sensor element is installed horizontally with respect to the base, the dew condensation water that has condensed in the protector flows out of the protector through the ventilation holes provided around the protector. Further, when the sensor element is installed on the lower side of the base, the dew condensation water that has condensed inside the protector flows out of the protector from the porous end filter located on the lower side.

As described above, the condensed water generated in the protector is irrespective of the installation direction of the limiting current type gas sensor.
Since it flows out of the protector, it is possible to prevent the sensor element from being submerged by dew condensation water as in the conventional case. Therefore, when the limiting current type gas sensor is operated, even if the sensor element is heated to a high temperature (sensor operating temperature) by the action of the heater, it is possible to prevent the sensor element from being damaged due to thermal shock.

[Operation and Effect of Claim 2] When the limiting current type gas sensor is operated, by the heater energizing circuit,
A low voltage is applied to the heater element for a predetermined time, and heat is generated at a low temperature for a predetermined time. As described above, by heating at a low temperature for a predetermined time, water attached to the heater element evaporates. Although the energization is started in a state where water is attached to the heater element, since the heating is performed at a low temperature, the thermal shock applied to the sensor element is small and the sensor element is not damaged. Then, after a lapse of a predetermined time, a high voltage is applied to the heater element by the heater energizing circuit to raise the temperature of the heater element to the sensor operating temperature.

As described above, when the limiting current type gas sensor is operated, the temperature of the sensor element is raised to a high temperature (sensor operating temperature) after the water adhering to the sensor element is evaporated, so that the sensor element is caused by thermal shock. It is possible to prevent the problem of damage. Also, Ru used in conjunction with the invention of claim 1
As a result , various problems caused by the condensation of water vapor can be completely eliminated.

[0013]

EXAMPLE An example of a limiting current type gas sensor adopting claims 1 and 2 will now be described with reference to FIGS. [Structure of Embodiment] As shown in FIGS. 1 and 2, a limiting current type gas sensor 10 is fixed to a round bar-shaped probe 20 (an example of a probe base) and a state in which it projects from the tip surface of the probe 20. The sensor main body 30, the protector 40 that accommodates the sensor main body 30, and the protector 4
And a porous storage filter 50 that stores 0.

(Description of Probe 20) The probe 20 is
It is a means for disposing the sensor main body 30 in the measurement atmosphere, and is a hollow round bar made of heat-resistant metal such as stainless steel. At the tip of the probe 20, the sensor body 3
A hole (not shown) for fixing 0 is provided, and fitting portions 21 and 22 for fitting the protector 40 and the accommodation filter 50 are formed around the hole.

(Description of Sensor Body 30) Sensor Body 30
As shown in FIG. 3, a plate-shaped sensor element 60 and a plate-shaped heater element 70 are joined by glass.

(Description of Sensor Element 60) Sensor Element 60
Is for detecting the gas concentration (oxygen concentration, humidity, etc.), and is provided by embedding a positive electrode 62 and a negative electrode 63 in a stabilized zirconia plate 61. The zirconia plate 61 is a solid electrolyte with good oxygen ion conductivity, which is provided by firing zirconium oxide to which yttrium oxide is added as a stabilizer. The external dimensions of the zirconia plate 61 in this embodiment are, for example, 23 mm in length and 5 m in width.
A rectangular opening 64 is formed inside the ceramic plate having a thickness of m and a thickness of 0.3 mm.

The zirconia plate 61 has a positive electrode 62.
A gas outlet hole 65 is formed to release the gas taken out from the zirconia plate 61 to the outside. The gas outlet hole 65 is a hole for exposing the detection electrode of the positive electrode 62 to the outside, and is a round hole in the present embodiment, but any shape can be used as long as it is a hole for exposing the detection electrode of the positive electrode 62 to the outside. Or size.

The positive electrode 62 and the negative electrode 63 are both porous platinum electrodes having a thickness of several tens of μm (for example, 20 μm), and are provided in the zirconia plate 61 so as to face each other. Specifically, from the side (upper side in FIG. 3) different from the side fixed to the probe 20, the detection electrode 62 having a width of 2 mm is used.
a, 63a, narrow extension electrodes 62b, 63b, and sensor wires 62c, 6 to which platinum wires 66, 67 are joined.
3c and.

Further, the negative electrode 63 is provided with a gas introducing portion 63d which branches from the extension electrode 63b of the negative electrode 63 and is exposed to the outside from the side surface of the zirconia plate 61. Like the other negative electrode 63, the gas introducing portion 63d is a porous platinum electrode and acts as a gas diffusion limiting means 63e that limits diffusion of the introduced gas together with the extension electrode 63b of the negative electrode 63.

(Description of Heater Element 70) Heater Element 70
Is the detection portion A of the sensor element 60 (detection electrodes 62a, 63
This is for locally heating the (a side) to the sensor operating temperature (for example, 500 to 600 ° C.), and as shown in FIG. 4, a heater electrode 72 is embedded and provided in an alumina plate 71. Similar to the zirconia plate 61 of the sensor element 60, the alumina plate 71 has an outer dimension of 23 mm in length, 5 mm in width, and 0.3 mm in thickness, and has a rectangular opening 73 formed therein.

The heater electrode 72 is an electrode made of platinum, and has a narrow line width and is provided in a substantially M-shape to heat the detecting portion A of the sensor element 60 locally.
A lead electrode 72b having a slightly wider line width for energizing the heat generating portion 72a, and heater connection electrodes 72c and 72d to which the platinum wires 74 and 75 are joined.

(Manufacturing Method of Sensor Main Body 30) Here, a manufacturing method of the sensor main body 30 will be described. First, a method of manufacturing the sensor element 60 will be described. Using a material containing zirconium oxide as a main component to which yttrium oxide is added, a plate-shaped solid electrolyte green sheet having holes to be openings 64 after firing and holes to be gas outlet holes 65 is formed (first step) ). Next, a platinum paste, which will become the positive electrode 62 and the negative electrode 63 after firing, is printed on the surface of the formed green sheet (second step). Next, the platinum wires 66 and 67 are placed on the ends of the green sheet, and the platinum paste that becomes the sensor connection electrodes 62c and 63c after firing and the platinum wires 66 and 67
67 is contacted (third step).

Next, a solid electrolyte green sheet formed in the same manner as in the first step is laminated on the surface of the green sheet on which the platinum paste is printed (fourth step). The green sheet used in this fourth step is the heater element 7.
If it is the side to be joined with 0, the positive electrode 62 and the negative electrode 6
Other materials may be used as long as 3 can be sealed and fired. Further, when the green sheet used in the fourth step is the side to be joined to the heater element 70, the hole serving as the gas outlet hole 65 may not be provided. Then, the stacked green sheets are integrally fired at about 1500 ° C. (fifth step). The sensor element 60 is completed through the above steps.

Next, a method of manufacturing the heater element 70 will be described. A plate-shaped green sheet having holes to be openings 73 after firing is formed from a material containing alumina powder as a main component (sixth step). Next, a platinum paste to be the heater electrode 72 after firing is printed on the surface of the formed green sheet (seventh step). Next, the platinum wires 74 and 75 are placed on the ends of the green sheet, and the platinum paste that becomes the heater connection electrodes 72c and 72d after firing and the platinum wires 74 and 7 are used.
And 5 are brought into contact with each other (8th step). Next, a green sheet formed in the same manner as in the sixth step is laminated on the surface of the green sheet on which the platinum paste is printed (ninth step). Then, the stacked green sheets are integrally fired at about 1500 ° C. (10th step). Through the above steps, the heater element 70 is completed.

Then, sealing glass or the like is applied between the sensor element 60 and the heater element 70 manufactured as described above,
Heat to about 800 ° C. (11th step). In the eleventh step, the sensor element 60 and the heater element 70 are joined to complete the sensor body 30.

The protector 40 (Description of the protector 40) is intended to adopt claims 1 and 2, as shown in FIGS. 1 and 2, the end filter and the cylindrical body 41, secured to the distal end in a bottomed cylindrical container made from 42, one end fitted into the fitting portion 21 provided in the probe 20 is secured to the probe 20 by the inorganic adhesive.

The tubular body 41 is made of a metal such as stainless steel that is heat-resistant and highly airtight, and has a tubular shape that covers the periphery of the sensor body 30, and the periphery of the side where the probe 20 is fitted to the fitting portion 21. And a ventilation hole 41a. The vent hole 41a protects the gas in the storage filter 50 from the protector 40.
In order to guide the gas inside and to discharge the gas inside the protector 40 to the outside, in this embodiment, holes with a diameter of about 1 mm are arranged at 90 ° intervals around the base end surface of the probe 20.
Is formed.

The end filter 42 is a porous member (pore diameter of about 70 μm) that allows water in the cylindrical body 41 to permeate and has excellent wettability.
In m), it is desirable to use a metal sintered body having excellent heat resistance such as stainless steel. The end filter 42 has a disk shape, is mounted inside the tip of the tubular body 41, and is fixed to the tip of the tubular body 41 by caulking.

(Explanation of the accommodation filter 50) The accommodation filter 50 greatly reduces the flow velocity of the gas that enters the inside, guides the surrounding gas into the accommodation filter 50 by removing dust and the like, and A porous member (bore diameter of about 70
μm), which is made of a metal sintered body having excellent heat resistance, such as stainless steel, which has the same quality as the above-mentioned end filter . The housing filter 50 has a bottomed cylindrical shape, and the open end has the probe 20.
It is fitted in the fitting portion 22 provided on and secured to the probe 20 by the inorganic adhesive.

(Description of Electric Circuit 80) As shown in FIG. 5, an electric circuit 80 is connected to the limiting current type gas sensor 10 provided as described above. This electric circuit 80 is
A heater energizing circuit 81 for energizing the heater element 70 to heat the heater element 70 and a measuring circuit 82 for measuring the gas concentration (oxygen concentration, humidity, etc.) are provided.

(Description of Heater Energizing Circuit 81) The heater energizing circuit 81 is a circuit for energizing the heater element 70 as described above, and has a high voltage (indicates a voltage higher than a low voltage described later) to the heater element 70 during steady operation. To apply the heater element 70
The heat generating portion 72a of the
Is a circuit for heating the sensor to a sensor operating temperature (500 to 600 ° C.).

The heater energizing circuit 81 employs claim 2, and when energizing the heater element 70, a low voltage is applied for a predetermined time (for example, about 60 seconds) as shown in FIG.
The sensor body 30 is applied with a low temperature (for example, about 80 to 250).
The sensor body 30
Low voltage applying means 8 for evaporating water (condensation water) attached to the
1a is provided. Then, the heater energizing circuit 81
When a predetermined time has passed after the start of energization, the heater element 7
0 is applied with a predetermined high voltage, and the detection unit A of the sensor element 60 is
Is maintained at the sensor operating temperature (500 to 600 ° C.).

(Explanation of Measuring Circuit 82) The measuring circuit 82 is
Constant voltage circuit 82a for applying a predetermined voltage to the sensor element 60
And an ammeter 8 for measuring the current value flowing through the sensor element 60.
2b, and detects the gas concentration (oxygen concentration, humidity, etc.) from the current value measured by the ammeter 82b. The constant voltage circuit 82a may be provided so that the applied voltage can be switched between V1 to V2 and V3 to V4 described later.

(Description of Operating Principle) Here, the operating principle of the limiting current type gas sensor 10 will be described with reference to FIG. When a voltage is applied to the sensor element 60 in a state where the sensor element 60 is arranged in a constant gas atmosphere and the detection unit A of the sensor element 60 is heated to the sensor operating temperature, the detection electrodes 62a of the positive electrode 62 and the negative electrode 63 are detected. , 63a is ionized, oxygen is pumped from the detection electrode 63a of the negative electrode 63 to the detection electrode 62a of the positive electrode 62, and as a result, a current flows through the sensor element 60.

The voltage applied to the sensor element 60 is 0 to V1.
If it is increased to 1, the pumping amount of oxygen from the detection electrode 63a of the negative electrode 63 to the detection electrode 62a of the positive electrode 62 increases. Then, oxygen in the measurement atmosphere is diffused and introduced into the negative electrode 63 from the gas introduction part 63d that is not sufficiently heated to exhibit oxygen ion conductivity. At this time, since the amount of oxygen introduced is relatively small, the amount of oxygen introduced increases as the applied voltage increases, and the current value flowing through the sensor element 60 also increases.

The voltage applied to the sensor element 60 is V1 to V
When it is increased to 2, the amount of oxygen diffused and introduced from the gas introduction part 63d into the negative electrode 63 is determined by the gas diffusion limiting means 63.
The introduction amount is limited by e. Therefore, the amount of oxygen introduced from the gas introducing portion 63d becomes constant, and the current value flowing through the sensor element 60 also becomes the constant current value I1. That is,
When the voltage applied to the sensor element 60 is increased to V1 to V2, the amount of oxygen introduced is limited and the constant current value I1
It becomes flat F1 of.

The voltage applied to the sensor element 60 is V2 (V
2 = 1.2 V) or more, water vapor in the introduced gas is electrolyzed, and oxygen ions generated by the electrolysis are pumped to the positive electrode 62. Therefore, when the applied voltage is increased to V2 to V3, the amount of electrolysis of water vapor in the introduced gas is increased, and the detection electrode 63a of the negative electrode 63 is increased.
The amount of oxygen pumped from the positive electrode 62 to the detection electrode 62a increases, and the current value flowing through the sensor element 60 increases again.

The voltage applied to the sensor element 60 is V3 to V
When it is increased to 4, the amount of water vapor diffused and introduced from the gas introduction part 63d into the negative electrode 63 is the gas diffusion limiting means 6
The introduction amount is limited by 3e. Therefore, the amount of water vapor diffused and introduced from the gas introduction portion 63d becomes constant, and the current value flowing through the sensor element 60 also becomes the constant current value I2.
That is, when the voltage applied to the sensor element 60 is increased to V3 to V4, the amount of water vapor introduced is limited, and the flat current F2 has a constant current value I2.

[Operation of the Embodiment] Next, the operation when the limiting current type gas sensor 10 is used for humidity detection in the atmosphere will be described. In the description of the operation, the limiting current type gas sensor 10 in which the sensor body 30 is installed downward with respect to the probe 20 is shown as an example.

(Start of Operation) When the limiting current type gas sensor 10 is operated, first, the low voltage applying means 81a of the heater energizing circuit 81 is operated, and as shown in FIG.
Then, a predetermined low voltage is applied for a predetermined time (for example, about 60 seconds). Then, the sensor body 30 is heated at a low temperature (for example, about 80 to 250 ° C.) for a predetermined time, and the water attached to the sensor body 30 evaporates. Then, a predetermined time (for example, about 6
0 seconds), the heater energizing circuit 81 applies a predetermined high voltage (voltage higher than the above-mentioned low voltage) to the heater element 70 as shown in FIG.
Is heated to the sensor operating temperature (500 to 600 ° C.).

On the other hand, the measuring circuit 82 is a constant voltage circuit 82a.
The sensor element 60 to a predetermined voltage (for example, V3 to V3).
Voltage between 4). Then, as explained in the operating principle, when the applied voltage is V3 to V4, the gas introduction part 6 is
Since the amount of oxygen diffused and introduced into the negative electrode 63 from 3d and the amount of water vapor diffused and introduced into the negative electrode 63 from the gas introduction part 63d are limited by the gas diffusion limiting means 63e, depending on the humidity of the measurement atmosphere. Then, as shown by the solid line in FIG. 8, the value of the current flowing through the sensor element 60 changes. Then, this current value is read by the ammeter 82b of the measuring circuit 82. That is, the humidity of the measurement atmosphere can be read from the numerical value of the ammeter 82b.

When the constant voltage circuit 82a applies a predetermined voltage between V1 and V2 to the sensor element 60, as shown by the broken line in FIG. Since the flowing current value changes, the humidity of the measurement atmosphere may be read from the numerical value of the ammeter 82b.

(Stopping the operation) When the operation of the limiting current type gas sensor 10 is stopped, the temperature inside the protector 40 gradually decreases, and when the temperature of the measurement atmosphere gas falls below the dew point temperature,
The water vapor in the measurement atmosphere that has entered the protector 40
Condensation may form inside the protector 40.

When dew condensation occurs, the water condensed on the inner surface of the cylindrical body 41 of the protector 40 is guided to the upper surface of the porous end filter 42 located below, and then the end filter 4
It passes through 2 and is discharged downward. Then, the water discharged from the end filter 42 falls into the accommodation filter 50, then passes through the accommodation filter 50 and is discharged downward.
That is, the water condensed on the inner surface of the tubular body 41 of the protector 40 passes through the end filter 42 and the accommodation filter 50, and is discharged to the outside of the limiting current type gas sensor 10.

In the description of the operation, the example in which the sensor main body 30 is installed downward with respect to the probe 20 is shown. However, when the sensor element 60 is installed above the base, the protector 40 is installed inside the protector 40. The condensed water that has condensed is discharged to the outside of the protector 40 through the ventilation hole 41a located on the lower side, and then passes through the accommodation filter 50 to be discharged to the outside of the limiting current type gas sensor 10. Further, when the sensor element 60 is installed horizontally with respect to the base, the condensed water that has condensed in the protector 40 is discharged from any of the four ventilation holes 41a provided around the protector 40 at 90 ° intervals. After being discharged to the outside of the protector 40, it passes through the accommodation filter 50 and is discharged to the outside of the limiting current type gas sensor 10. That is, regardless of the orientation of the limiting current type gas sensor 10, the dew condensation water that has condensed in the protector 40 is discharged to the outside of the limiting current type gas sensor 10.

[Effects of the Embodiment] In the limiting current type gas sensor 10 of the present embodiment, the condensed water generated in the protector 40 is generated by the limiting current type gas sensor 1 as described above.
Limiting current type gas sensor 10 regardless of the installation direction of 0
The sensor body 30 is not submerged by dew condensation water as in the conventional case, because it flows out to the outside. Further, when operating the limiting current type gas sensor 10, even if the sensor body 30 is heated at a low temperature for a predetermined short time, a small amount of water attached to the sensor body 30 is surely evaporated.

As described above, in this embodiment, the sensor body 3
Since the sensor element 60 can be heated to the sensor operating temperature (high temperature) after preventing water submersion of 0 and surely evaporating the water adhering to the sensor body 30 in a short time, the sensor element 60 is included. The thermal shock applied to the sensor body 30 can be suppressed to a small level, and the damage such as the sensor body 30 being cracked can be eliminated.

[Modification] Although the sensor element 60 in which the positive electrode 62 and the negative electrode 63 are provided on the same surface of the zirconia plate 61 is shown in the above-mentioned embodiment, as shown in FIGS. 9 and 10, zirconia is used. Board 61
Sensor element 6 having positive electrode 62 and negative electrode 63 on both sides of
You may use 0. The sensor element 60 shown in FIG. 9 has a structure in which the negative electrode 63 is covered with a box 91 to form a void 92, and the measurement atmosphere and the void 92 are communicated with each other by a micro hole 91 a provided in the box 91. Is. Further, the sensor element 60 of FIG. 10 is obtained by forming the box 91 of FIG. 9 with a porous member and eliminating the minute holes 91a.

In the above embodiment, the heater element 70 is provided in substantially the same shape as the sensor element 60 and bonded to the sensor element 60. However, the heater element 70 is bonded to a part of the sensor element 60, Conversely, the sensor element 60 may be joined to a part of the heater element 70. In the above embodiment, the end filter 42 is made of a porous metal sintered body having excellent heat resistance and wettability such as stainless steel. However, the gas flow rate is suppressed and heat resistance is improved. Ceramics are mentioned as being excellent in wettability and capable of transmitting water. In the above embodiment, an example in which the limiting current type gas sensor 10 detects the humidity in the measurement atmosphere has been described. It can also be applied to the detection of.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a limiting current type gas sensor (Example).

FIG. 2 is a cross-sectional view of a limiting current type gas sensor (Example).

FIG. 3 is a perspective view of a sensor body showing a structure of a sensor element (Example).

FIG. 4 is a perspective view showing a structure of a heater element (Example).

FIG. 5 is an electric circuit diagram of a limiting current type gas sensor (Example).

FIG. 6 is a graph showing the relationship between time and temperature for explaining the operation of the low voltage applying means in the heater energizing circuit (Example).

FIG. 7 is a graph showing a relationship between an applied voltage value and a detected current value showing an operating principle of a limiting current type gas sensor (Example).

FIG. 8 is a graph showing a relationship between humidity and a detected current value (Example).

FIG. 9 is a sectional view of a sensor element (modification).

FIG. 10 is a sectional view of a sensor element (modification).

[Explanation of symbols]

10 Limiting current type gas sensor 20 probes (probe base) 30 sensor body 40 protector 41 cylinder 41a Vent hole 42 Edge filter 50 storage filters 60 sensor elements 70 heater element 81 Heater energizing circuit 81a Low voltage applying means

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-93706 (JP, A) JP-A-62-129754 (JP, A) Actually opened 61-189259 (JP, U) Actually opened 5- 66553 (JP, U) International publication 94/016371 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/41 G01N 27/409

Claims (2)

(57) [Claims] 1. A sensor element for detecting a gas concentration, a heater element which generates heat when energized and heats the sensor element to a sensor operating temperature, and the sensor element and the heater element are installed in a gas to be measured. Limiting-current-type gas sensor including a probe base for protecting the sensor element and the heater element, and a protector in the form of a bottomed container that is attached to the base in a state of covering the sensor element and the heater element and that has a vent hole around the base side. In the protector, the protector is provided with the vent hole in the vicinity of the probe base, and has a tubular body formed of an airtight material that covers the sensor element and the heater element, and an end portion of the tubular body. A limiting current type gas sensor, which is attached and comprises a porous end filter that allows water in the cylinder to pass therethrough. 2. The limiting current type gas sensor according to claim 1.
There are, the heater element comprises a heater energization circuit for applying a voltage to the heater element, the heater energizing circuit, at the start of energization, so that a predetermined time heating at a lower temperature than the sensor operating temperature, the heater element A limiting current type gas sensor characterized in that a low voltage is applied for a predetermined time, and then a high voltage is applied to the heater element so that the heater element generates heat at the sensor operating temperature.