JP2524883B2 - Contact combustion type CO gas sensor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a wire material for each coil of an active part and a compensating part using Fe-P.
Contact combustion CO using d alloy wire or Fe-Pd-Co alloy wire
Regarding a gas sensor.

[Conventional technology]

It has been reported that more than 80% of the fatalities at the time of a fire occur due to CO poisoning as well as the fatalities caused by CO that have been generated by incomplete combustion of combustion equipment, reverse flow of exhaust gas, or use of ondol. However, as a countermeasure, even though highly reliable and highly sensitive CO sensors are widely desired overseas, the CO sensors disclosed so far have problems in their sensitivity, mass productivity, workability, etc. However, in the present situation, no one having sufficient performance has appeared.

Even the present inventors have been working on CO sensors since 1970,
We have released various improved CO sensors and have reached the present day, but until now, we still have to solve the industrially significant CO sensors that satisfy various conditions such as sensitivity, mass productivity, and workability. There were various problems.

Various types of CO sensors have been announced that can be put to practical use, but the important ones will be mentioned.

(I) Semiconductor CO sensor of SnO ₂ , ZnO, etc. Although this sensor has the advantage that it is sensitive to low-concentration CO, it has poor gas selectivity and has many unstable elements, and reproducibility is low. There are some disadvantages. For this reason, an O-floating circuit is used, or an appropriate filter is also used in combination, but since it has high sensitivity to humidity and alcohol gas, it cannot detect CO. Unreliable. Experiments of solid-state heat conduction type have been attempted to improve selectivity, safety, etc., but it was difficult to put them to practical use.

(Ii) CO sensor using Pt wire or Pt alloy wire This is a wire rod that the present inventor has used for many years. With the 20μ line,
A CO sensor with a bridge voltage of 6 V and a sensor temperature of 180 to 200 ° C and excellent selectivity and reproducibility has been completed. Further, various studies have been conducted on the catalyst coated on the upper surface of the coil, and the sensitivity at CO500ppm is 5 to 7 mV. However, even if other gas was present, the CO sensor had almost no sensitivity to the gas and had good reproducibility.

However, in order to obtain the above sensitivity at the mass production stage, Pt
When manufacturing a coil with a diameter of 0.8φ and a diameter of 42 to 45 from a 20μ wire, it is difficult to maintain the uniformity of the coil, and as a result, the product yield is poor and commercialization is delayed. Met.

In order to improve this, Pt alloy wire was examined, and as a result, the specific resistance and hardness became large, and workability was improved considerably, but CO
The temperature coefficient that influences the sensitivity is much smaller than that of the Pt line, which causes problems such as not being suitable for manufacturing a highly sensitive CO sensor.

The table below shows the specific resistance and temperature coefficient for Pt wire and Pt alloy wire.

[Problems to be Solved by the Present Invention] Generally, the performance required for a CO sensor is as follows.

(I) High sensitivity CO is 200ppm and headache occurs when breathing for 2-3 hours, 500ppm
It is said that breathing for 1 to 2 hours causes headache and nausea, and death at 2 hours at 1,600 ppm, death at 10 to 15 minutes at 3,200 ppm, and death at 5 to 10 minutes at 6,500 ppm.

Therefore, even if the concentration is relatively low, 200 to 500 ppm, it is strongly required to be able to detect it completely.

(Ii) No sensitivity to other gases, etc. No false alarms due to moisture or alcohol gas. This is extremely important when used as an alarm.

(Iii) Withstand continuous use. Even if the surrounding high temperature or temperature change is large, it can withstand enough and there is little change over time.

(Iv) Good reproducibility.

(V) The device is downsized and can be supplied at a low price.
Must be mass-produced.

In response to such a request, as a material for the coil,
The inventors have learned that the Fe-Pd alloy wire and the Fe-Pd-Co alloy wire according to the present invention are most suitable, and have completed the present invention.

In the contact type CO sensor according to the present invention, (Where ΔV is the gas sensitivity, ΔR is the coil resistance change value when CO touches the coil, R is the active part coil resistance value, and V _i
Is the bridge voltage, α is the temperature coefficient of the wire, a is a constant, m is the gas concentration, Q is the heat of molecular combustion, and c is the heat capacity of the sensor. ) Although theoretical equation of is established, in order to increase the gas sensitivity ([Delta] V), the bridge voltage (V _i) and or to the large temperature coefficient α of the wire, or, except for the small heat capacity c of the sensor There is no way.

Although it has already been successful to change V _i from 2 V to 6 V, higher values are not preferable because they increase the sensor temperature and adversely affect other electric parts of the circuit. Therefore, it is a metal with a higher specific resistance than conventional Pt (the number of turns of the coil is small, it is hard and workability is improved, the sensor is downsized and the heat capacity c is small), and the temperature is higher. Various metals with a large coefficient were examined, and as a result, as a coil material
The present invention finds a Fe—Pd alloy wire according to the present invention and a similar Fe—Pd—Co alloy wire in place of the Pt wire or its alloy wire.

[Means for solving problems]

Thus, the developed Fe-Pd alloy wire has various properties suitable for the contact-type CO sensor according to the present invention. First, a. Depending on the composition, the specific resistance and temperature coefficient are Figure 2 shows the temperature coefficient (ppm / ppm) based on the composition of Fe-Pd.
(C) change is shown.

b. Next, the Fe-Pd or Fe-Pd-Co alloy wire is stable with no phase transformation at 400 ° C or lower.

c. The workability was poor because the Pt wire had a Viccus hardness (H _v ) of 50, which was soft, but the Fe-Pd wire had a workability of 100 to 300, so workability was extremely good.

The temperature-resistance characteristic of d.Fe-Pd (75 wt%) changes almost linearly from 0 ° C to 230 ° C as shown in Fig. 3, which is R _t = R _o (Hαt + βt ² ) α = 8625, β = 3.75 (where R _t is the characteristic at t ° C., R _o is the characteristic at 0 ° C., α and β are constants). Therefore, the reliability of the measured value becomes great.

By obtaining such a wire rod, i) In the Pt 20 μm wire, since the specific resistance ρ is 10.6 μΩcm, the diameter of 0.8φ is wound 45 turns to finally obtain the resistance value 45Ω for having an appropriate CO sensitivity. On the other hand, Fe-Pd
Since the (75 wt%) wire has a specific resistance of 43 μΩcm in the 30 μm wire, a desired resistance value of 45Ω can be obtained by winding 24 turns with a 0.8φ diameter. Also with that aforementioned Vickers hardness is 150H _v, workability is significantly improved, uniformity of the coil, mass productivity becomes very good.

ii) However, since it is a metal that is relatively easily oxidized, sintering of the Al ₂ O ₃ catalyst on the upper surface of the coil must be performed by completely dehumidifying it in a N ₂ stream, and Pd
The same process cannot be applied to PdO attached by a thermal decomposition process such as an aqueous solution of Cl ₂ or an aqueous solution of Pd (NO ₃ ) _2, so it is necessary to use PdO purified by oxidizing metallic palladium.

iii) The temperature coefficient of Pt is 3,800 ppm / ° C, whereas the maximum is 8,500 ppm / ° C in the alloy of the present invention. Then, with the alloy wire of the present invention, it was estimated that a sensitivity of 5 to 7 × 8,500 / 3,800 = 11 to 15, that is, 11 to 15 mV was obtained, but in an actual machine, it was 15 to 18 mV, 15 to 18 mV, 18 to 25 mV. Good results were obtained in sequence. This is considered to be due to the fact that the heat capacity c of the sensor has become considerably small and the difference between the new PdO catalyst.

As described above, CO500ppm is 18 to 25 mV, and 200 ppm gives a sensitivity of 8 to 10 mV, which is 4 to 5 times higher than the sensitivity of a conventional CO sensor using a Pt 20 μm wire of 5 to 7 mV. Since the resistance and hardness are large, it is possible to easily manufacture a coil having uniform properties and mass-produce a sensor with high reliability.

〔Example〕

 The manufacturing method of this sensor will be described below.

First, in manufacturing the coils of the active part and the compensating part, which are the core of the sensor, Fe-Pd (40 to 85 wt%) 20 μm wire was accepted, and it was made into a coil of 0.8φ diameter 24 turns, and the stem (separate type After welding to TO-5) and washing, a fine powder of Al ₂ O ₃ in the resin liquid is electrodeposited on the surface of the coil, and the resin component is expelled and sintered in a N ₂ stream. Up to this point, it is common to both active and compensation parts.

Next, the coil to be the active part was electrodeposited with a resin solution of PdO and Al ₂ O ₃ which was obtained by strongly heating metallic palladium to oxidize it, followed by natural drying and vacuum drying, followed by baking in an N ₂ gas furnace. After the conclusion
After applying a protective film and aging, the required cap is put on the product. On the other hand, the compensator is electrodeposited with a resin solution of Ni ₂ O ₃ and Al ₂ O ₃ , and after natural drying and vacuum drying, it is sintered in an N ₂ gas furnace, and then a protective film is applied and aged. After that, the required cap is put on and completed.

Obtain the resistance value (also called cold resistance value) at 20 ° C and the resistance value when applying D.C3V close to the usage conditions for each of the completed active parts and compensation parts. That is, resistance value at 20 ℃ Active part (S) R _S1 , R _S2 … (R _S ) Compensation part (D) R _D1 , R _D2 … (R _D ) Resistance value when 3V is applied Active part (S) R ′ _{S1 , R 'S2 ... (R'} S) compensator _{(D) R 'D1, R} ' D2 ... (R 'D) _{wherein, R' S R 'D,} R' S / R S ≒ R 'D / R _The active part and the compensating part satisfying the condition of _D are combined to form a pair. Ideally, R _S = R _D and R _'S = R ' _D , but it is difficult to obtain the exact same one, so select a resistor with a slightly large resistance in the compensator and insert a trimming resistor in parallel. ′ _S ≈ R ′
Make a _D.

In this way, the coils of the active section and the compensating section thus completed are incorporated into a circuit as shown in FIG. Active part 1
And the compensator 2 are arranged in series, and bridge resistors r ₁ , r ₂ and r ₃ are arranged in series on the opposite side. A sensitivity meter 4 for displaying a voltage value (mV) is provided between the intermediate point 3 between the active portion 1 and the compensating portion 2 and the resistance r _3, and a DC voltage is applied to the active portion, the compensating portion and the bridge resistor. It is formed by arranging a bridge power supply 5 that operates. Further, T _r is a trimming resistor inserted as necessary. The active part 1 and the compensating part 2 have respective resistance values.
R _S and R _D are equal and R _S = R _D = R. (In reality, there is no choice but to make a slight difference.) In the Fe-Pd alloy or Fe-Pd-Co alloy 30 μm line used for each coil of the active part 1 and the compensating part 2, the temperature coefficient of each is the former. Is 8263ppm / ℃,
The latter was 9462 ppm / ° C.

This wire rod is finished as a coil of 14 turns with a winding diameter of 1.2φ. The total length of the coil is about 2.3 mm. The active part 1 and the compensating part 2 are separated and attached to the stem respectively. The operating temperature of the sensor is 160 ° C to 170 ° C.

Each coil is subjected to Al ₂ O ₃ electrodeposition finish, and the resin component of the electrodeposition liquid is expelled and sintered in a N ₂ stream.

Next, the respective coils of the active section and the compensating section are processed differently. The active coil is impregnated with PdO, Pt-black and Al ₂ O ₃ electrodeposition liquid mixed in the resin liquid, and the electrodeposition liquid is sufficiently adhered to the inner part of the coil wire by electrodeposition. After that, after sintering in N ₂ gas flow, Snow-Tix or alumina sol is applied to form a protective film, and after finishing, it is aged for 4 to 5 days.

In this case, PdO is attached to both sleeves of the compensation circuit, especially when it is required to remove the H ₂ sensitivity. The H ₂ sensitivity is that the internal temperature of the cap that is put on the coil when energized is 50
It can be removed at ~ 60 ° C.

Finally, the coils of the active part and the compensating part, the bridge resistors of r ₁ , r ₂ , r ₃ and the bridge power source of 6VDC are combined to form the CO sensor of the present invention.

In a real machine, it has a preferable sensitivity of 20 mV or more at 500 ppm CO and is incorporated in an alarm device to make alcohol (C ₂ H ₅ OH).
False sensitivity does not occur when the sensitivity is 5 mV or less. In addition, the zero drift is within the range of 20 ℃ ± 20 ℃, and a good result of less than 2mV is obtained.
The power consumption was 34mA ± 1mA at 6VDC.

〔The invention's effect〕

As described above, in the CO sensor according to the present invention, the coils for the active part and the compensating part have the Fe-Pd alloy wire or the similar Fe-Pd-Co wire.
Alloy wires are used.Since these alloy wires have high specific resistance and hardness, the coil uniformity and mass productivity are significantly improved compared to conventional Pt wires. And again
CO sensitivity in the sensor is large and is especially required
CO in the range of 200 to 500 ppm can be sufficiently detected by reducing the influence of other gases, and since the temperature coefficient is large, zero drift stops within the minimum range and the temperature-resistance characteristic is good. Since the temperature is almost linear from 0 ℃ to 230 ℃, the reliability of the measured value becomes remarkably large.
Since various characteristics required for the sensor can be almost completely satisfied, this is a very useful invention.

[Brief description of drawings]

FIG. 1 is a circuit diagram of the CO sensor according to the present invention, and FIG. 2 is a temperature coefficient (ppm / ppm) based on the composition of the Fe—Pd alloy wire according to the present invention.
℃), Fig. 3 is a graph showing temperature-resistance characteristics of Fe-Pd (75wt%), and Fig. 4 is Fe-Pd (75wt%).
%) CO concentration of each sensor and Pt (platinum) sensor (ppm)
3 is a graph showing the sensitivity (mV) in FIG. 1 ...... active portion coil 2 ...... compensator coil, 3 ...... midpoint, r _1, r _2, r ₃ ...... bridge resistors, 4 ...... sensitivity meter, T _r ......
Trimming resistance, 5 ... DC power supply

Claims (5)

(57) [Claims] 1. A catalytic combustion type CO in which each coil forming an active part and a compensating part is arranged in series, and a bridge resistance is provided so as to face the respective coils via a gas sensitometer and a power source is incorporated to form a circuit. In the gas sensor, a wire rod for each coil is a Fe-Pd alloy wire, and a contact combustion type CO gas sensor. 2. The Fe-Pd alloy wire contains 15 to 60 wt% Fe and 40 to 85 Pd.
The catalytic combustion type CO gas sensor according to claim 1, which has a composition of wt%. 3. The catalytic combustion type CO gas sensor according to claim 1, which is used at a sensor temperature of 200 ° C. or lower. 4. A catalytic combustion type CO in which each coil forming an active part and a compensating part is arranged in series, and a bridge resistance facing each coil via a gas sensitivity meter is provided and a power source is incorporated to form a circuit. In the gas sensor, the contact combustion type CO gas sensor, wherein each of the coil wires is an Fe-Pd-Co alloy wire. 5. A Fe-Pd 30 μm wire with a winding diameter of 1.2φ for 14 turns and a coil length of about 2.3 mm, which is made into an active part and a compensating part, is electrodeposited with Al ₂ O ₃ and then sintered in a N ₂ stream. Furthermore, PdO-Pt black-Al ₂ O ₃ was electrodeposited on the coil for the active part and sintered and aged in a N ₂ stream, and the required coil for removing alcohol sensitivity was charged on the coil for the compensating part. After arriving, it is sintered and aged in N ₂ air flow, and the active part and the compensating part, which are each coil attached to the stem, are arranged in series, and a bridge resistor is provided to oppose each of these parts through a gas sensitivity meter. A method for manufacturing a catalytic combustion CO gas sensor in which a circuit is built by incorporating a.