KR870001052B1 - Gas detecting apparatus - Google Patents

Abstract

The appts. comprises a sensor (10) with a current limiting resistor (12) in series with it, across a DC, with potential from a battery source. A voltmeter (22) connected across the current limiting resistor (12) provides indication of the change in sensor resistance. The sensor (10) comprises a heater (18) of platinum film, formed by vapour deposition on the outer periphery of a heat resisting, electically insulating tubular support (24).

Description

Heat Linear Semiconductor Gas Detector

1 is an enlarged front view showing the configuration of a thermoforming semiconductor element used in the present invention.

2 is a circuit diagram showing a first embodiment of the present invention.

(A), (b) is a top view which shows 2nd Example of this invention, and sectional drawing by X-X line.

4 is an equivalent circuit diagram of FIG.

5 to 7 are for explaining the third embodiment of the present invention,

5 shows the relationship between the Rh content and the specific resistance.

6 shows the relationship between the Rh content and the resistance temperature coefficient α with respect to Pt.

FIG. 7 is a diagram showing the relationship between the ratio between 300 ° C. and 400 ° C. of the resistance value of the metal wire coil with respect to the Rh content as in FIG. 6.

8 to 10 are for explaining the fifth embodiment of the present invention,

8 shows a change in electrical resistance with respect to the temperature of a metal oxide semiconductor used in a noble metal and a gas sensitive semiconductor.

9 is an equivalent circuit diagram when the heating element and the gas-sensitive semiconductor are electrically connected in parallel.

FIG. 10 shows a change in electrical resistance with respect to the temperature of the equivalent circuit of FIG.

11 shows a specific example of the fifth embodiment and is a perspective view of a part which is partially broken.

12 and 13 are perspective views of a part broken in part showing another example of the fifth embodiment.

FIG. 14 is a sectional view showing another example of the fifth embodiment similarly to FIG.

15 and 16 show an example of a circuit using the heat linear semiconductor element shown in FIG.

FIG. 17 is a diagram showing the relationship between the power supply voltage and the output voltage as an example of experimental data according to the fifth embodiment.

18 and 19 are views for explaining a sixth embodiment of the present invention.

18 is a waveform diagram of the relative concentration of the bridge output and H ₂ gas.

19 is a waveform diagram for explaining the change in the time-lapse of the bridge output.

20 and 21 are gas sensor circuit diagrams showing another embodiment of the sixth embodiment, respectively.

* Explanation of symbols for main parts of the drawings

1: metal wire 2: metal oxide semiconductor

3: heat linear semiconductor element 3 ': compensation element

4: lead wire (metal pin) 10: detection means

20 gas detection element 21 substrate

22 electrode 23 gas detection layer

24: lead wire 30: heat linear semiconductor element

31 support 32 heating body

33: gas sensitive semiconductor 34: lead wire

35: lead wire 41: support

42: heating body 43: gas-sensitive semiconductor

44: lead wire 45: lead wire

The present invention relates to a highly reliable gas detection apparatus using a heat linear semiconductor element.

Various gas detection elements for gas detection have been proposed in the related art, and among them, the contact combustion type and the semiconductor type have been commonly used.

The catalytic combustion method is a sintered catalyst in a platinum coil. When the air containing combustible gas comes into contact with the catalytically active surface (maintained at about 300 ° C), even if the concentration is lower than the lower explosion limit, The flammable gas reacts with oxygen to generate heat of reaction, the temperature of the platinum coil rises and the resistance increases, so that the change in resistance is detected by a bridge circuit or the like to detect the gas.

This contact combustion gas detection element has linearity of sensitivity characteristics, but is inferior to semiconductor gas elements in terms of long-term stability.

On the other hand, the semiconductor gas detection element is a sintered metal oxide, for example, SnO ₂ , ZnO, or the like between a pair of electrodes, so that one electrode is formed in a coil state, and is commonly used as a heater and combined electrode.

The heater combined electrode is maintained at a temperature of 300 ° C. to 400 ° C. and detects that the conductivity of the semiconductor is increased by gas adsorption and the resistance between the two electrodes is lowered.

This semiconductor gas detection element has a longer lifespan than the contact combustion type, is superior in long-term stability, is superior to the contact combustion type against poisons, and consumes more power, so that the capacity of a power supply unit such as a power transformer is large. It becomes expensive.

In addition, compared with the heat linear semiconductor element described later, since the voltage dependence is large, the constant voltage circuit is required when the performance is to be improved, but the power consumption is large, and the value of the electrostatic circuit becomes expensive.

In addition, the heat capacity of the gas sensor is large, it takes a long time to stabilize, thereby requiring a long time to adjust, instability, poor productivity, and also depend on the temperature and humidity, which requires a temperature compensation circuit There was a problem such as.

This invention is made | formed in view of the above fault, and an object of this invention is to provide the heat linear semiconductor gas detection apparatus which has small power consumption, and can detect gas with small size reliably.

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, in order to achieve the said objective, a metal oxide semiconductor is closely attached to the metal wire used as a heating heater and an electrode for electric resistance value change detection, and a heat linear semiconductor element is comprised and this load is loaded with By connecting to a constant voltage power supply through the gas, the conductivity of the heat linear semiconductor element is increased during gas adsorption, the temperature is lowered and the resistance thereof is lowered, so that the heating deterioration of the heat linear semiconductor element is not caused. It is to provide a heat linear semiconductor gas detection device capable of performing.

An embodiment of the present invention will be described in detail with reference to the drawings.

Example 1

1 shows the configuration of a heat linear semiconductor element used in the present invention, where (1) is a platinum wire coil-shaped metal wire serving as a heater for heating and an electric resistance change detection electrode, and (2) the metal wire (1). ) Is a metal oxide semiconductor such as SnO ₂ , ZnO, etc., and the heat linear semiconductor element 3 is formed.

(4) is a metal pin for both a lead wire and a support, and both ends of the metal wire 1 are welded and supported.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention, in which Rb is a resistor, 3 'is a light-receiving element, and constitutes a bridge circuit like the heat linear semiconductor element 3.

The compensating element 3 'has the same shape as the heat linear semiconductor element 3 in FIG. 1, but does not react with gas.

E is a constant voltage power supply, Rl is a variable resistor for signal detection, and the detection means 10 of resistance value change is comprised as these.

The operational effects of such a device will be described as follows.

When the gas to be detected comes into contact with the heat linear semiconductor element 3, the metal oxide semiconductor 2 has a high conductivity and a good thermal conductivity, so that the temperature decreases.

Therefore, the resistance value of the metal wire 1 also goes down.

In other words, the resistance value of the heat linear semiconductor element 3 becomes low, and the balance of the bridge circuit is disturbed, and this appears as an output (sensor output) at both ends of the variable resistor Rl.

In the future, you can use this output to drive an alarm or a fan.

According to this structure, the temperature of the heat linear semiconductor element 3 is lowered by gas adsorption, and deterioration by heat does not occur.

In addition, compared with the conventional semiconductor gas detection element requiring at least three electrode terminals, the heat linear semiconductor element 3 of the present invention has a two-terminal type, so that there are few lead wires and the power supply can be used as one. Therefore, miniaturization and power reduction are achieved.

Example 2

(A) and (b) of FIG. 3 are a plan view showing a second embodiment of the present invention and a cross-sectional view taken along line XX, FIG. 4 is an equivalent circuit diagram of FIG. 3, and (20) shows the entire gas detection element. (21) is a substrate having heat resistance and electrical insulation such as alumina, (22) is a heating element and gum electrode formed as a pattern by a platinum deposition film on the surface of the substrate 21, (23) Is a gas detection layer serving as a semiconductor of a metal oxide such as SnO ₂ , and covers the entire surface of the electrode 22. Reference numeral 24 is a lead wire connected to both ends of the gas detection layer 23.

When explaining the effect on this is as follows.

An electric current flows through the lead wire 24, and the whole gas detection element is maintained at 300 to 500 degreeC.

This is to shorten the time for the adsorption and desorption of gas molecules to the gas detection layer 23 to reach an equilibrium state, and to correct the response of the gas detection element to the gas.

As described above, the gas detection layer 23 has the electrical conductivity increased by adsorbing gas molecules on its surface, and the resistance Rc of the electrode 22 and the intrinsic resistance of the gas detection layer 23 are appropriate. Select to be ratio.

As shown in FIG. 4, the current path of the gas detecting element includes a passage flowing through a portion of the electrode 22, and a passage flowing through a gas detecting layer 23 distributed in parallel at each portion of the electrode 22; The resistance value Rc of the portion of the electrode 22 hardly changes due to the contact of the gas, while the distribution resistance R's of the portion of the gas detection layer 23 is in contact with the gas. By this, it is largely changed and becomes a superficial parallel resistance Rs in which the distribution resistance R's of the gas detection layer 23 is combined, and can be used stably as a gas detection element.

In addition, according to this embodiment, integration technology can be used, and mass production is easy.

Example 3

Although the Pt wire is normally used for the metal wire 1 of the heat linear semiconductor element 3 of FIG. 1, this Pt wire has the disadvantage that it is small in specific resistance, weak in mechanical strength, and expensive.

Here, the present invention does not change the heat resistance and corrosion resistance so much using an alloy wire,

① detect the presence of detection gas more sensitively,

(2) The change in power consumption of the heat linear semiconductor element 3 in the gas atmosphere can be suppressed.

This embodiment is described below.

(1) Specific resistance of metal wires.

In FIG. 1, the resistance value of the coil-shaped metal wire 1 is defined as Rc, and the resistance value (hereinafter referred to as semiconductor resistance value for simplicity) is regarded as the resistance of the metal oxide as effectively the parallel resistance of the resistance value Rc of the metal wire. When it is set as Rs, the element resistance value R of the heat linear semiconductor element is represented by the parallel synthesis resistance of Rc and Rs.

It is preferable that Rs be smaller than Rc in order to make the change in the effective resistance value Rs other than the metal oxide part by the gas to be detected as the change in the element resistance value R as large as possible.

However, it is not so easy to reduce the resistance of the metal oxide semiconductor 2, and in order to balance Rc and Rs properly, it is necessary to increase Rc as much as possible.

For this purpose, the wire diameter of the coil-shaped metal wire 1 may be thinned or the number of windings may be increased, but there is a limit to this.

Thus, if an alloy wire containing Ph is used instead of the pure Pt wire, as shown in Fig. 5, the specific resistance ρc of the wire rod at 400 ° C is 25% or more of the pure Pt when the Rh content is 5-30%. At 10-20%, we see a 40% increase.

Therefore, when Pt-Rh alloy wire of suitable Rh content is used, the presence of a detection gas can be taken out as a sensor output more efficiently.

The thing mentioned above is a case of Pt-Rh alloy wire, but other alloy wires, such as Pt-Ir and Pt-Ni, can also be used.

The following table summarizes and shows the specific resistance p of the Pt alloy wire used in the present invention.

Table 1 (10 ^-6 Ωcm)

(2) Resistance temperature coefficient of metal wires.

In the case where the change in the element resistance value R is generally detected by applying a constant voltage to the gas detection element or by applying a constant current, the power consumption of the gas detection element changes in response to the change in the element resistance value R, Causes a change in temperature.

In order to suppress this change in temperature and to reduce the change in power consumption, it is good to make Rc smaller than Rs, but if it is too small, as is clear from the foregoing description, the R due to the change of Rs caused by the detection gas is determined. The change is small, so that the sensitivity of the so-called gas detection element is lowered, so that Rc cannot simply be reduced.

In addition, when Rc is moderately large, the larger the resistance temperature coefficient of Rc, the larger the influence on the magnitude of power consumption of the gas detection element.

Therefore, it is preferable to use the wire material which has a small temperature coefficient for the coil-shaped metal wire 1.

However, the resistance temperature coefficient of Pt is much larger than that of heating elements such as nichrome wire (non-metal wire such as nichrome wire cannot be used in terms of corrosion resistance).

Thus, in order to reduce the resistance temperature coefficient α without changing the corrosion resistance or the like, it is effective to use a Pt-Rh alloy wire containing Rh as the wire rod of the alloy wire coil.

As in FIG. 6, at the same time as the content of Rh to Pt increases, the resistance temperature coefficient α decreases initially and then increases again.

At a content of 5-70%, the value of α is about 55% of the net Pt line, and at a content of 10-60%, it is 50% or less of the net Pt line.

If the temperature of the gas detection element is used at 400 ° C. and the temperature is lowered by 100 ° C. (ie, 300 ° C.), the resistance value Rc of the metal wire 1 decreases as shown in FIG. 7. (In the city, denoted as Rc 300 ° C / Rc400 ° C)

If it is a pure Pt line | wire, it is a decrease of 15.4%, but the Rh content is about 11.5% in 5-65% Pt-Rh line | wire, and in content 10-50%, it is suppressed within about 10%.

Therefore, by using the Pt-Rh line with an appropriate Rh content, it is possible to suppress a change in the temperature of the gas detection element due to the presence of the detection gas.

The above description is the case of the Pt-Rh alloy wire, but other alloy wires such as Pt-Ir and Pt-Ni may be used.

Table 2 shows the resistance temperature coefficient α of the Pt alloy wire used in the present invention.

Table 2 (X10 ^-4 / ℃)

It is considered that 5-30% of the practical range of the content is considered in view of the fact that the workability becomes poor when the advantages described in the above (1) and (2) and the Rh content exceed 30%.

In addition, about the same effect was acquired also in the Pt alloy wire which made Pt-Ir and Pt-Ni containing 5-30%.

Example 4

As described above, the resistance value of the Pt line has a large resistance temperature coefficient, and if the temperature change occurs in the metal wire 1 for some reason, the resistance value Rc changes, and in response, the element resistance value R also changes. There is a problem.

The reason why the element resistance value R changes is as follows.

It is said that the semiconductor gas detector was operating in the atmosphere where no gas to be detected exists. (Hereinafter referred to as gas atmosphere operation)

At this time, the temperature of the metal wire 1 and the metal oxide semiconductor 2 shown in FIG. 1 are generated by the electric power applied to the heat linear semiconductor element 3 and the heat conduction through the metal wire 1. It will be a constant value determined in accordance with the state relationship by the heat dissipation relationship through the atmosphere.

By the way, the metal oxide semiconductor 2 is fixed to a support (for example, the metal pin 4) by the arm of a thin metal wire, and when a mechanical shock is applied from the outside, the position will be displaced, The staggering of these positions causes a change in the relative distance from the metal fin 4, the metal oxide semiconductor 2, and the container covering the entire metal fin 4, etc., so that the heat dissipation condition is changed, so that the metal wire 1 and the metal oxide semiconductor ( Temperature change occurs in 2).

As a result, the resistance value Rc of the metal wire 1 and the resistance value Rs of the metal oxide semiconductor 2 change. The output may be instructed even if there is no gas because the fluctuation of the element resistance R during the gas standby operation exceeds the allowable range.

This is a fatal flaw in stable use as a gas sensor.

T(℃) 만큼 변화하였다고 가정한다.(여기에서 간단하게 하기 위하여 금속 산화물 반도체(2)의 저항치 Rs의 온도에 의하는 변화는 무시할 수 있는 것으로 한다)For example, a mechanical shock causes displacement in the nasal position, causing the temperature of the nasal passage to

It is assumed that the change is as much as T (° C.)

T(℃)분 만큼 변화하여, 소자저항치 R가 R'로 되었다고 하면, 소자 저항치 R"는,Temperature change of resistance Rc of metal wire (1)

If it changes by T (degreeC) minutes and the element resistance value R becomes R ', the element resistance value R "is

………(1)

… … … (One)

It becomes

In Formula (1), α is the resistance temperature coefficient of the Pt line, and is approximately 3.92 × 10 ⁻³ / ° C.

Ro로 하면, 제 (1)식의 R'는,Here for simplicity of calculation Rs = Rc

If it is Ro, R 'of Formula (1) is

………(2)

… … … (2)

It becomes

T가 수 10도 (℃)로 되는 경우도 있고, 이때의 소자저항치 R'의 변화율 γ는 수 %에도 이른다.As a practical example, in (2) meals

T may be several degrees (degrees C), and the change rate (gamma) of the element resistance value R 'at this time reaches several%.

Where the rate of change γ is

If it is displayed, it becomes like 3rd table | surface.

3rd table

As shown in Table 3, the change rate γ of the element resistance value is very large considering that the change in the element resistance value R due to the presence of the gas to be detected as a practical gas concentration is about 20%.

As described above, in the thermal linear semiconductor element using the Pt line for the metal wire 1, the variation in the element resistance value R due to a given mechanical impact or the like cannot be ignored, which is one of the obstacles in the stable use of the concentration detection.

Example 4 of the present invention has been made in view of the above-mentioned point, and is a wire rod of a metal wire 1 used as a heater and an electrode, and has heat resistance and corrosion resistance as compared with pure Pt, and the contact resistance with a semiconductor is not changed so much. It is an object of the present invention to provide a heat linear semiconductor device which does not cause a change in output due to a staggered position by using a line made of a metal having a small resistance temperature coefficient compared to the net Pt.

The present invention will be described as follows.

The 4th table is a table according to the ratio of the mixed metal of the resistance temperature coefficient (alpha) of the alloy wire containing Pt or Pd which shows Example 4 of this invention.

X in Table 4 is% of content.

As can be seen from this fourth table, each alloy wire has a smaller value than the resistance temperature coefficient α = 3.9 × 10 ⁻³ / ° C. of the pure Pt wire.

For some of the alloy wires in the fourth table, the fluctuations that the temperature fluctuations give to the element resistance value R are obtained by the formula (2), and the comparison with the alloy wire (1) of the Pt wire is shown in the following fifth table.

T는 -20℃로한 경우인 것이다.However, temperature fluctuations

T is the case where it is set to -20 degreeC.

4th table (X10 ^-3 / ° C)

5th table

In Table 5, the rate of change γ (%) of the device resistance is -1.73% and -1.32% in Pt-Rh ₁₀ or Pt-Ir ₁₀ and only -0.40% in Pt-Ag ₁₀ , respectively.

In the alloy wires in the table, all of them are considerably smaller than the pure Pt wires (γ = 4.08%).

Thus, by using the alloy wire which has a resistance temperature coefficient smaller than pure Pt, the change of the element resistance value according to the temperature change of a sensor can be made quite small.

On the substrate-type semiconductor gas detection element, that is, a substrate having heat resistance and electrical insulation, one electrode pattern is formed of a conductive material, and a gas-sensitive semiconductor is coated on the substrate on the same side as the electrode pattern to form a heating body and In the structure formed in close contact with each other, and also when the electrode pattern is used as a heating heater and an electrode for detecting electric resistance change of the semiconductor, a material having a lower resistance temperature coefficient than the pure Pt as the material of the electrode pattern, for example, a noble metal alloy By using the material, the change in the element resistance (that is, the synthetic resistance between the electrode pattern and the applied gas-sensitive semiconductor) with respect to the temperature fluctuation of the electrode pattern portion caused by a certain cause is compared with the case of the electrode pattern based on the pure Pt. Of course, it has a merit which can be suppressed small.

As described above, the fourth embodiment is a heating heater and an electrode for detecting electric resistance change of a heat linear semiconductor element, and is constructed by using a metal wire having a resistance temperature coefficient smaller than that of pure platinum wires. As a result, the measurement error is small and the S / N ratio is large, so that high sensitivity can be achieved, and high reliability and high sensitivity can be obtained.

Example 5

By the way, in the conventional semiconductor gas detection device which requires three or more electrode terminals,

① heating by heating element (heater),

(2) The sensor is maintained at a constant high temperature state by both the joule heating by the current flowing through the sensor itself, so that the element resistance value in the so-called gas atmospheric state is determined, and the corresponding electrical output value (base value of the sensor output). ) Is determined.

In addition, ① and ② are not independent of each other, the sensor temperature changes due to the change of ①, the element resistance changes (that is, the base value changes), and as a result, the Joule heating of ② also changes.

Variation of the base value with such temperature fluctuation is a large cause of fluctuation of the output in the gas of constant temperature.

The cause of the fluctuation of ① is a fluctuation in the heater voltage, and the cause of the fluctuation of ② is a fluctuation in the humidity of the temperature change of the environment.

In the conventional three-terminal or four-terminal structure element, as described above, there is a drawback that the variation in the base value due to the power supply voltage variation and the output value in a gas of a constant concentration is large.

The fifth embodiment is made to solve the above-mentioned shortcomings, and a two-terminal structure is provided by covering a gas-sensitive semiconductor having a negative resistance temperature coefficient on a heating body having a positive resistance temperature coefficient. It is an object of the present invention to provide a heat linear semiconductor element having a simple structure and small temperature fluctuation of the base.

The fifth embodiment will be described below.

First, the principle will be explained.

The gas detection element according to the fifth embodiment differs from the conventional three-terminal or four-terminal semiconductor sensor in that the precious metal resistor, which is a heater, has a function of detecting a signal.

In other words, it can be considered that the resistance of the heater (the value of R _A ) and the resistance of the metal oxide semiconductor (the value of R _B ) constitute a parallel circuit.

Thus schematically (模式的) with the combined resistance R _R and in a circuit, its second terminal both sides L _1, L _2, as in FIG. 9 is the may display the food.

The variation by gas adsorption is R _B.

Next, the variation of the synthetic resistance R _{R due} to the change in temperature will be described.

In the noble metal used for a heating body in general, the change of the electrical resistance value R _A with respect to temperature changes linearly as shown by the straight line i of FIG.

R _A = R _AO (1 + ATc)

You can get closer to

Here, R _Ao is a resistance value at 0 ° C, A is a positive resistance temperature coefficient, and Tc is a temperature (° C: ° C).

In addition to the metal oxide semiconductor used for the semiconductor gas reaction, the change in the electrical resistance R _B in treating temperature, and changes as indicated in the eighth-degree curve (ii).

And in the stable region T ', the temperature dependence of the resistance becomes close to that of the intrinsic semiconductor,

The resistance temperature coefficient is negative.

However, R _BO and B are positive integers and TB is absolute temperature (° K).

In the temperature change of the synthesis resistance R _R , the resistance of the precious metal wire is large in the low temperature region, and the resistance temperature coefficient is positive.

In addition, in the temperature region, the resistance of the metal oxide semiconductor works largely, and the resistance temperature coefficient becomes negative as shown in FIG.

Therefore, by appropriate combination of four parameters R _AO , A, R _BO , and B, as shown in FIG. 10, it is possible to make the temperature dependence of R _R in the region T 'almost superficially zero.

In the region T ', a gas detection element without fluctuations in the base can be obtained for both the fluctuations in the heater power supply voltage and the fluctuations in the ambient temperature.

Referring to the gas detection device formed by the above principle is as follows.

11 is a perspective view showing a specific example of Embodiment 5 of the present invention, wherein 31 is a cylindrical or columnar support having heat resistance and electrical insulation, and 32 is a platinum on the outer circumference of the support 31. A heating body formed of a vapor deposition film and also serving as an electrode, trimmed in a spiral shape to a predetermined resistance value.

Reference numeral 33 denotes a gas-sensitive semiconductor that is in contact with the outer circumference of the heating body 32 and is covered with a metal oxide semiconductor such as SnO ₂ , and 34 and 35 respectively represent the heating body 32 and the gas-reactive semiconductor 33. Lead wires connected at both ends of the

12 shows another example of the fifth embodiment, in which 41 is a flat support, 42 is a heating body, 43 is a gas-sensitive semiconductor, and 44 is a lead wire. to be.

FIG. 13 shows yet another example of the fifth embodiment, in which there is no support, and the gas-sensitive semiconductor 43 in the shape of an ellipse is covered on the coil-shaped heater 42.

14 is a cross-sectional view showing yet another example of the fifth embodiment, and its appearance is the same as that of FIG. 12, and the same reference numerals as those of FIG. 12 denote the same parts, but the heating body 42 and the gas reaction semiconductor 43 Is contacted at both ends, and the middle part is electrically insulated by the insulator 46.

In addition, the thing of the same material as FIG. 12 is used for each part of FIG.13 and FIG.14.

15 and 16 show an example of a circuit using the heat linear semiconductor element shown in FIG.

In these illustrations, reference numeral 30 denotes a thermal linear semiconductor element, E denotes a constant voltage power supply (indicative of the power supply voltage), V denotes an output detector (also indicates output voltage), and R ₁ , R ₁ , and R ₂ Is the load resistor and R ₃ is the zero point variable resistor. Others and the same reference numerals in Fig. 11 denote the same parts.

Also, the same circuit can be obtained by using the heat linear semiconductor elements shown in FIGS.

FIG. 17 shows an example of experimental data according to the fifth embodiment, showing the relationship between the power supply voltage E (corresponding to temperature) and the output voltage V, curve a is H ₂ gas, and curve b is CO. : H ₂ = 2: 1 mixed gas, curve C is ETOH gas, curve d is CO gas, curve e is CH ₄ gas, curve f represents base (air), and each gas is It is 100 ppm, The ten used thermal linear semiconductor elements were used, and the average value was floated and each curve was obtained.

As can be seen from this figure, there is almost no fluctuation above the power supply voltage of 2.6 V, which indicates that the output voltage does not fluctuate with temperature fluctuations.

If it is configured as a heating body having such a positive resistance temperature coefficient and a gas sensitive semiconductor having a negative resistance temperature coefficient, and the operating temperature is selected such that the resistance temperature coefficient of the heating body and the resistance temperature coefficient of the gas sensitive semiconductor cancel each other, In addition, a gas detector element having a small output variation with respect to a change in temperature can be obtained.

Example 6

When the thermal linear semiconductor element 3 having the configuration shown in FIG. 1 is used in bridge contact as shown in FIG. 2 in a high concentration gas, for example, 20% of H ₂ , the bridge output is unstable and an alarm is generated. In some cases, the material used for the element material of the thin Pt wire coil having a diameter of about 20 µφ may be stopped. As described later, the compensation element 3 'is disconnected and the alarm does not stop even when the H ₂ gas is removed. have.

The reason for this is due to the characteristics of the heat linear semiconductor element 3 having the property of significantly lowering the electrical resistance in a high concentration gas, and the electrical resistance is reduced by contact with the gas as in the contact combustion type device. In the case of an increasing device, the above problem does not occur.

In the heat linear semiconductor element 3, the conductivity of the oxide semiconductor is increased by gas adsorption, and the element resistance and the element temperature are lowered in the high concentration gas.

On the other hand, in contrast to this, the resistance of the semiconductor element decreases, conversely, the voltage applied to the compensation element 3 'increases, the power consumption of the compensation element 3' increases, and the resistance increases at the same time as the temperature rises. This becomes large, and the voltage and temperature applied to the compensation element 3 'rise again.

That is, a problem arises in that the temperature rise due to Joule heat generation in the compensating element 3 'and the positive feedback of the resistance value increase occur. For this reason, the bridge output in the constant high concentration gas fluctuates in the range shown by the broken lines I _a and I _b in FIG. 18, and becomes very unstable.

In addition, during the first 18, and the horizontal axis shows the (Vol.%) H ₂ gas concentration, and the vertical axis represents the bridge output P _1.

In addition, as the temperature of the compensating element 3 'rises, contact combustion occurs on the surface of the heat linear semiconductor element 3, whereby the oxide semiconductor deteriorates and the bridge output is sometimes zero.

In addition, solid line II in FIG. 18 is demonstrated later.

Embodiment 6 is made in view of the same point as above, and an object of this invention is to provide the heat linear semiconductor type gas detection apparatus which operates stably in high concentration gas.

In the sixth embodiment, a resistor is used in place of the compensation element 3 'in the circuit of FIG. 2, and the circuit is shown in FIG.

That is, instead of the compensating element 3 ', due to Joule heat generation, for example, nickel, chromium, tin oxide or the like, which has a resistance value equivalent to the operating resistance of the heat linear semiconductor element 3, An electric resistor R ₅₀ capable of ignoring the change in resistance value is used, and others are the same as in FIG.

The resistor R ₅₀ is combined in a bridge circuit connected to the constant voltage power supply E in the same manner as the two resistors R _b and the heat linear semiconductor compact 3 to constitute the gas detecting device of the present invention.

When the heat linear semiconductor element 3 starts to detect gas, the balance of a bridge circuit will be disturbed and a bridge output will be output corresponding to gas concentration.

The detailed description of this operation is as follows.

The bridge output P ₁ of the conventional apparatus and the bridge output P ₂ of the present invention for the passage of time in 20% of H ₂ will be described with reference to FIG. 19.

In this illustration, the horizontal axis represents time (minutes) and the vertical axis represents bridge output (V).

In addition, the solid line shows the bridge output Ⅲ P _2, and a broken line _a Ⅳ, Ⅳ one-dot chain line _b indicates the bridge output P _1. In the conventional device, Ⅳ the case of displaying the output characteristic as shown in _a or _b and Ⅳ, the bridge output P ₁ is very unstable and is greatly changed over time.

On the other hand, the bridge output P ₂ (solid line III) is stable even in 20% of H ₂ (0-60 minutes), quickly returns to the normal value after the gas is removed (after 60 minutes), and also has excellent reproducibility. Do.

In addition, when the heat generated by the electrical resistor R ₅₀ causes contact combustion on the surface of the heat linear semiconductor element 3 described above, which may deteriorate the accuracy of the gas concentration indication, the heat linear semiconductor element 3 By adding Pb, As, Sb, P, Si, S, Cl, Se, Te, etc. as a combustion inhibitor to the material, stability can be obtained even in a higher concentration of gas.

In addition, although the bridge circuit is shown as the gas sensor circuit in the above embodiment, it is not always necessary to be a bridge circuit, and as shown in FIG. An electrical resistor R ₅₀ having a small resistance temperature coefficient (such as a resistance temperature coefficient of ± 500 ppm / ° C. or less) may be connected in series, and both ends of the electrical resistor R ₅₀ may be used as output terminals.

The output terminal may be provided at both ends of the heat linear semiconductor element 3, and eventually, the connection point of the heat linear semiconductor element 3 and the electric resistor R ₅₀ becomes one output terminal, and the other output terminal is a reference potential. It is good to be connected to point.

In this manner, the sixth embodiment connects the heat linear semiconductor element 3 and the electric resistor R ₅₀ capable of ignoring the change in resistance caused by Joule heating in series with the constant voltage power supply E, and the connection point between the heat linear semiconductor element and the resistor. Since the reference potential point and the output terminals are respectively used, the gas concentration can be detected with good reproducibility with stability from the low concentration region to the high concentration region.

It also eliminates the need for compensating elements, making it simple and inexpensive to manufacture and miniaturizing the entire device.

Claims (6)

A heat linear semiconductor element formed by bringing a metal oxide semiconductor into close contact with a metal wire serving as a heating heater and an electric resistance change detection electrode is connected in series with a constant voltage source via a load, so as to absorb gas from the hot linear semiconductor element. And a means for extracting a change in resistance value as a detection signal. The heat linear semiconductor gas detection device according to claim 1, wherein the metal wire is formed on a substrate having heat resistance and electrical insulation in a required pattern of conductive material. The heat linear semiconductor gas detection device according to claim 1 or 2, wherein the metal wire is made of a Pt alloy wire containing at least one of Rh, Ir, and Ni in a range of 5-30%. The heat linear semiconductor gas detection device according to claim 1 or 2, wherein the metal wire is made of a metal having an electrical resistance temperature coefficient smaller than that of pure platinum. 3. The heat linear semiconductor gas detecting device according to claim 1 or 2, wherein the metal wire has a positive resistance temperature coefficient, the metal oxide semiconductor has a negative resistance temperature coefficient, and the resistance temperature coefficients are selected to cancel each other. . The heat linear semiconductor gas detection device according to claim 1, wherein the load is a resistor capable of ignoring a change in resistance caused by Joule heat generation.

Images