JPH032654A - Carbon monoxide sensor - Google Patents

Abstract

PURPOSE:To improve accuracy by using two kinds of SnO2 semiconductors. CONSTITUTION:An active part 1 and a compensating part 2 comprising coils which have the approximately equal resistance value at the time of no gas are arranged in series. Bridge resistors r1, r2 and r3 are arranged in series at the opposite side. A sensitivity meter 4 wherein the sensitivity of CO gas is displayed with a voltage value is provided between the intermediate part between the active part 1 and the compensating part 2 and the resistor r2. A bridge circuit is formed of said parts and a bridge power source 5. One weight % of Pd and one weight % of Pt are loaded into SnO2 of an SnO2 semiconductor, and the semiconductor is baked for 1.5 hours at about 900 deg.C. The sensitivity for CO is enhanced. The SnO2 based semiconductor formed in this way is used for the active part 1. For the compensating part 2, general- purpose SnO2/Sn whose sensitivity is not enhanced is used. Thus the accuracy of the sensor can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention provides an active part and a compensation part containing SnO with different compositions.
□Relates to a carbon monoxide sensor of the Brifuji circuit type formed by incorporating a system semiconductor.

[Conventional technology]

In general, semiconductor sensors, including SnO-based semiconductor sensors, have extremely high sensitivity to low concentration gases, but on the other hand, a) they lack gas selectivity. That is, when various gases are mixed, the sensitivity of a specific gas is not good.

b. Sensitive in the atmosphere, especially characteristics when there is no gas (e.g.
zero point) is unstable and uncertain.

C1 reproducibility is poor.

d. Changes in the characteristics are observed due to changes in the environment, ie, changes in temperature and humidity.

Even with gas leak alarms for LPG, the alarm concentration for 1 ctH+o is 500 to 3000 pPta.
The actual situation is that false alarms often occur with C, H50H, etc. For this reason, even though SnO□-based semiconductors have good sensitivity to CO, applying conventional SnO□-based semiconductors to alarm devices has been unstable and sometimes even dangerous.

[Problems to be solved by the present invention]

In view of these circumstances, the present invention has been made through various studies on the relationship between the composition and temperature of SnO□-based semiconductors and the sensitivity characteristics of various gases of the sensor.
□Using a semiconductor to offset the sensitivity of other gases, extracting only the CO sensitivity and learning about the scales, and further considering various aspects with a focus on composition, we were able to improve the accuracy of the SnO□-based semiconductor sensor. be.

[Means for solving problems]

The present invention has the following features: (i) The active part 1 and the compensation part 2 are arranged in series and have approximately the same resistance value during no gas, and a predetermined bridge resistance rl+rZ+r is arranged in series in parallel on the opposite side thereof. , the intermediate point 3 between the active part 1 and the compensation part 2 and the bridge resistance r2
A sensitivity meter for displaying the CO gas sensitivity as a voltage value is installed between the bridge circuit and the bridge circuit, which is equipped with a bridge power supply valve that applies a DC voltage to the active section, compensation section, and each bridge resistor. (ii) The active part 1 contains 5nO sensitized only to the CO sensitivity.
z/Pd, Pt semiconductors are used, (iii) and a SnO2/Sn semiconductor whose CO sensitivity is not sensitized is used for the compensator 2, (iv)
The gist of this is a (v)-carbon oxide sensor that determines the CO sensitivity based on the resistance value difference that occurs between the active part 1 and the compensating part 2 in a Co atmosphere.

〔Example〕

Hereinafter, the present invention will be described based on examples with reference to the drawings.

FIG. 1 is a circuit diagram of a sensor according to the present invention.

First, the active part 1 and the compensation part 2 arranged in series are composed of coils having approximately the same resistance value when no gas is present, and a bridge resistor rI+r2°r3 is arranged in series in parallel on the opposite side thereof. A sensitivity meter 4 is provided between the midpoint between the active part 1 and the compensation part 2 and the bridge resistor r2, and the sensitivity meter 4 displays the CO gas anger level with an equivalent voltage value. A bridge circuit is formed by arranging a bridge power supply 5 that applies voltage.

The coils forming the active part 1 and the compensation part 2 both have a wire diameter of 1.
Platinum (Pt) wire or platinum alloy (Pt-
It is made by winding a wire (Pt-Ni, Pt-Rt, etc.) into a coil around a ceramic tube.

The 5nu2n halves used in the active part 1 were prepared by adding 1% by weight each of Pd and Pt to SnO□ and heating them at about 600°C for 1.
The one used is one whose CO sensitivity has been sensitized by firing for 5 hours, and the general-purpose SnO□/ whose sensitivity has not been sensitized is used in the compensation section 2.
Sn is used.

Semiconductor powder of each composition is finely ground, a sintering agent such as SiO□ colloidal solution is added to form a paint, and as shown in FIG. Coil 8, which is formed by winding a Pt wire to form a resistor and has a signal extraction lower 7, is coated and sintered at 650'' to 700°C for 1 to 1.5 hours, and then the hollow of the ceramic tube is A heating element 9 such as a Ni-Cr wire built into the part is attached.After the SnO-based semiconductor sensor is sintered, it is subjected to sufficient electrical aging.The voltage applied to the heating element 9 causes the sensor to heat up. The temperature is determined, i.e. the applied voltage is between 220' and 240' at DCIOV.
℃ and 12V, it becomes 300' to 320℃.

Using the sensor configured in this way, the sensitivity A (kΩ) of the above sensor and CO500 ppr in no gas state.
The sensitivity B (kΩ) of the sensor in a atmosphere was measured. The results are shown in Table 1.

From the above table, depending on the voltage applied to the heater, that is, the sensor temperature, at 10V the rate of change (average) of the active part is 61.7% Compensation part #24.3% Difference in the rate of change (average) 37.4% At 12V the active part The rate of change in the active part (average) is 62.7%, the compensation part is 45.7%, the difference in the rate of change (average) is 17.0%, but the difference between the active part and the compensation part is almost the same at the same concentration. Because it is hail, at 500 ppm of CO, 37
A sensitivity (kΩ) corresponding to % occurs. Therefore, at other concentration values, for example, 11000 pp, a change value of 74% will be measured.

Next, the present invention attempts to improve the stability of a semiconductor sensor whose resistance value is relatively unstable in the absence of gas by the following means. Now, when we examine the characteristics (Ro) of the conventional 5nOz semiconductor sensor when no gas is present for the heating element 10, the results are as shown in Table 2.

As shown in the table above, the relationship between the active part and the compensation part is always h.In many cases, the change values listed separately do not appear significantly, and the RO characteristics of the active part and the compensation part vary considerably. I can't escape it.

In order to solve this problem, the present invention employs an indirect heating type solid heat conduction method as described below.

FIG. 2 shows a semiconductor sensor with an active part and a compensation part manufactured by this method. First, the outer diameter is 1.2~
1.6φ, inner diameter 0.8 to 1.2φ, length about 4 to 6n, Pt wires of 20 to 25μm are placed at equal intervals on a ceramic tube with a resistance of 100 to 150Ω (at 20℃). On the coil wound like this, a SiO□ colloidal solution of the semiconductor powder used for the active part and the repair part is applied as a paint to a thickness of about 20 to 30 μm, as smooth as possible, and dried. 1-16 at 650-700℃
It was sintered in 5 hours.

Next, a Ni--Cr wire heater is placed inside the magnetic tube, and as shown in FIG. 3, the tubes are assembled and fixed to a holder (stem). In the figure, reference numerals 7° and 7' indicate signal output ports in the active section and compensation section, respectively, and 9 and 9' indicate terminals of the heater.

When the sensor is heated with a heater in this configuration, CO
The temperature becomes 1506 to 200°C, which is the optimum temperature for sensitivity, and the resistance of the Pt wire increases to, for example, about 1.5 to 1.6 times that of room temperature (20°C). When this method is applied to the bridge circuit according to the present invention, the Pt coil is
If the resistance of the wire is relatively high, the stability will be further improved.

With this indirectly heated structure, the resistance when no gas is present depends mainly on the resistance of the Pt coil, and the sensitivity v0 is stabilized. Also. Since it is a solid heat conduction type, when flammable gas touches the surface of the sensor and is absorbed, heat dissipation from the surface improves and the interior is cooled.

Therefore, the resistance of PtB decreases by ΔR in proportion to the gas concentration, and the fluctuation rate is somewhat smaller than when using PtB alone, but it is advantageous because it offsets the sensitivity of other gases than CO, such as H2.

Next, the CO in the active part and the compensation part in this sensor is
In order to further increase the difference in sensitivity, the invention has been devised as follows.

This is determined by determining the range of the resistance value of SnO, the system semiconductor, and the resistance value of the Pt coil in the solid-state thermal conductivity sensor mentioned above.
This increases sensitivity.

Now, the resistance value R of the fixed heat conduction sensor is considered to be a composite value of the resistance value r of the SnO2-based semiconductor and the resistance value rt of the Pt coil, and the two are in a parallel relationship as shown in Figure 4 (since they are in a parallel relationship, α is a constant value, and it becomes a constant value depending on the operating temperature.

Now, when we consider how the resistance value changes depending on the presence or absence of gas in cases where the resistance value r1 of the semiconductor is relatively small and relatively large, we find that when a and r are relatively small, For example, r, = lkΩ.

If rz=150Ω, the combined resistance R1 at no gas time is r, +r.

There is a relationship between

In addition, the resistance value r1 of the SnO2-based semiconductor is the SnO2-based semiconductor during sintering.
It was found that the composition of the O2 powder and the sintering agent (for example, 5iOz colloidal liquid) changes greatly, and in particular, as the amount of the sintering agent increases, the resistance value increases.

Furthermore, the resistance value of the Pt coil is Rt = R, (1+αt) ・ ・ ・ ・ (
2) However, R, and R are respectively at the temperature t'c and 0°C, but if the semiconductor comes into contact with CO gas and r changes to 50Ω, then r+'=50Ω.

rz=150Ω (unchanged), and the combined resistance R2 is as follows, and the difference value △R3 between R and R is 92.9Ω.
changes greatly.

b.On the other hand, if r is relatively large, e.g.

= 500 Ω and rz = 150 Ω, first, the combined resistance Rh when there is no gas is as follows. However, if the semiconductor comes into contact with CO gas and the resistance of rl decreases at the same rate as above, then it becomes 1000:50.
= 500000: x

From this, as shown in a, in the active region, if rl is selected so that the resistance value of the semiconductor is smaller than the resistance value of the Pt coil at the target CoWl level (for example, 500 ppm), the CO of the sensor will be reduced. Sensitivity is greatly increased.

For the compensation section, a component with almost no change in resistance due to CO is selected, so there is no problem as shown on the left; It is desirable that something is selected.

Hereinafter, specific examples will be described. SnO□ according to the present invention
The rate of change in resistance of a semiconductor due to cO gas is c.

At 500ppm, active part SnO2/Pd, Pt 60%
Compensation section Snug/Sn 20%, at 20°C, a Pt coil of approximately 100Ω will exceed the operating temperature (
220'~240℃), its resistance is 150~160
Ω, so the active part is c.

In order to have a resistance of 150Ω or less at 500ppm, it is sufficient to have a resistance value of about 375Ω when there is no gas.
The combination of the sintering agent may be determined so as to maintain this resistance value.

In addition, the resistance value of the compensation section changes by about 20% at 500 ppm of CO as mentioned above, so it is 375 Ω when no gas is present.
It can be seen that even if the resistance is mixed so that the resistance is about 300Ω, the resistance changes to 300Ω at most, and there is no problem.

In the actual machine, when there is no gas, the sensor becomes as follows in an atmosphere of 500 ppn+ CO, and the difference value △R of the combined resistance is △R=R,°-R,'=100-75=25 (Ω). Become.

When this active part and compensation part are applied to the bridge circuit shown in Fig. 1 and the bridge voltage is 6V, the gas sensitivity △■ is as follows: △R=25 (Ω), R=375 (Ω), V ,=
6 By substituting (V), △■ Z
x 6 = 0.1 (V) = 100(
An output of mV)X375 is obtained.

In addition, due to the adsorption of CO gas, the resistance of the Pt coil increases by 1
50-△RI°, 150Ω-△R2', and △
Since R,'>ΔR2', an even larger output may be obtained.

As described above, in the present invention, the resistance value of the SnO
Even for gases with low concentrations such as pm, the zero point remains stable at 1.
It is possible to manufacture a sensor that outputs an output of 00 mV or more.

In the present invention, a CO sensor is constructed by combining two types of SnO2 semiconductors with different compositions, and H
The sensitivity of other gases such as z + C2) ISOHI icJ+o is canceled out in the relationship between the active part and the compensation part, and it is possible to extract only the CO sensitivity.

However, the CO produced by the combination of semiconductor sensors
In sensors, it is quite difficult to make the resistance value the same when there is no gas, so it is inevitable that the yield will be poor.

As a means to solve this problem, the above-mentioned solid heat conduction method is introduced. Since the resistance of the sensor during no gas substantially depends on the resistance of the Pt coil, zero point adjustment is easy and it is easy to use. In particular, by manufacturing the semiconductor so that the resistance value is less than the resistance value of the Pt coil at a constant value of CO gas, the C
O? An output of at least 100 mV or more was obtained at M degrees. If it is too troublesome to make careful adjustments, use C0100ppIIl, 1OOIIlv, 200p.
A method of sorting for pm, 100 mV, etc. is also used.

Semiconductor sensors, unlike catalytic combustion type sensors, do not normally require a linear proportional relationship between gas concentration and sensitivity output, but if the high sensitivity characteristics at low concentrations according to the present invention are used, CO selection This improves the performance and can make it useful as an alarm device.

〔Effect of the invention〕

The present invention is based on the above-described configuration, and significantly improves the CO sensitivity of a semiconductor sensor, and greatly improves the lack of selectivity in conventional sensors. In particular, it adopts a solid heat conduction type. This makes it possible to fully use it as an alarm device, making it an extremely useful invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the bridge circuit according to the present invention, FIG. 2 is an explanatory diagram of the active part of the sensor according to the present invention, FIG. 3 is an explanatory diagram showing the connection state of the active part and the compensation part, FIG. 4 is an explanatory diagram showing the arrangement of the Pt coil resistance and the SnO□ semiconductor resistance in the solid heat conduction type. 1... Active part, 2... Compensation part, rl, r2. r3・
...Bridge resistance, 4...Sensitivity meter, 5...Bridge power supply, 6...Ceramic tube, 8...Pt coil, 9
...heating element.

Claims (1)

[Claims] 1. An active part 1 and a compensation part 2 are provided which are arranged in series and have approximately the same resistance value when no gas is present, and r_1, r_2, r_3 are connected to predetermined bridge resistances in parallel on the opposite side. A sensitivity meter 4 is arranged in series between the intermediate point 3 between the active part 1 and the compensation part 2 and the bridge resistor r_2, and the sensitivity meter 4 displays the CO gas sensitivity with an equal voltage value. This is a carbon monoxide sensor formed with a bridge circuit in which a bridge power supply 5 is arranged to apply a DC voltage to a compensating part 2, and the active part 1 is equipped with SnO_2/2, which has only the CO sensitivity sensitized.
Pd, Pt semiconductors are used, and the compensation section 2 is made of CO.
Carbon monoxide, characterized in that a SnO_2/Sn semiconductor whose sensitivity has not been sensitized is used, and the CO sensitivity is determined based on the resistance difference generated between the active part 1 and the compensation part 2 in a CO atmosphere. sensor. 2. The carbon monoxide sensor according to claim 1, wherein each semiconductor component is sintered in the active part and the compensation part, which are formed by fixing a Pt wire coil of the same resistance on a ceramic tube, and the ceramic tube has a built-in heating element. . 3. The combined resistance value of the Pt coil and semiconductor in the active region when no gas is present is greater than the resistance value of the Pt coil during use, and the resistance value of the semiconductor is smaller than the resistance value of the Pt coil in CO gas. In addition, each Sn
Claim 1, wherein the composition of the O_2-based semiconductor and the sintering agent is determined.
Carbon monoxide sensor as described in .