JPS58144736A - Gas detecting element - Google Patents

Abstract

PURPOSE:To improve reliability and to facilitate manufacture of an alarm device, by constituting an element such that it is of a solid thermal conduction system formed by combination of a platinum film resistance, trimmed into a appropriate resistance, and a semiconductor layer. CONSTITUTION:A platinum film is formed on a fine alumina tube, and is adjusted into an appropriate resistance by trimming. An insulating protection film layer having an excellent thermal conduction is then placed thereon, and a solid thermal conduction type gas detecting part A forming a semiconductor layer is formed thereon. Meanwhile, a humidity-sensitive part B is formed on the insulating protection film layer in a similar manner. A bridge circuit consists of the parts A and B, and a voltage is applied. A response is improved through utilization of a self-heating of a platinum film resistance by means of a voltage applied to a bridge, gas sensitivity characteristics are regulated through adjustment of the voltage applied to a bridge, and the influence exercised by humidity can be completely eliminated by the humidity-sensitive part.

Description

[Detailed Description of the Invention] S■O2, Z■O, which are the main components of semiconductor gas sensors,
V2O5 and the like are often used in humidity sensors. Therefore, it is a well-known fact that it is as sensitive to humidity as it is to gas, or more sensitive than it is to gas.

City gas, L. P. The following points are required for alarm devices for G, CO gas, etc.

(1) Must be reproducible and reliable.

Even if external conditions change, an alarm will always sound at a constant gas concentration.

(2) Do not issue false alarms.

Also, for safety, alarms should be possible at as low a concentration as possible.

(3) It can be used stably for a long period of time (3 to 5 years).

(4) It is convenient to handle, consumes little power, and can be used at low temperatures. In particular, since there is an alarm, conditions (1) to (3) must be completely satisfied.

Alarm devices that use semiconductor sensors currently on the market often give false alarms due to humidity, alcohol, and other factors. P. G. Used in city gas.

The element temperature is set to 350-450 to improve gas adsorption and desorption.
A built-in heater is used to heat the product to ℃. This alone consumes 1 watt of power.

Alarm using catalytic combustion sensor.

There are no false alarms and the reproducibility is good within a short period of time, but over a long period of time the catalyst evaporates and the sensitivity decreases, and it is poisoned by organosilicon compounds and the gas sensitivity completely disappears and the width becomes small. It has some potentially dangerous flaws. This sensor also requires heating the element to 400 to 500°C, and the voltage consumed for this is about 0.5W to 0.7W.

Since the product of the present invention uses a solid heat conduction method that combines a platinum film and a semiconductor layer, it uses Joule heat from the bridge voltage without heating the device, so the device temperature is around 60 to 100℃, which may cause false alarms. The effect of humidity is canceled out by using a humidity sensor in the compensator, and the gas sensitivity is determined by changes in the humidity resistance of the platinum membrane, creating a linear relationship, which is convenient when used in automatic control circuits. .

Example 1 Platinum is applied to a film thickness of about 800 to 1500 Å by sputtering or other methods on a magnetic layer of about 0 mm × 3 mm or 2.0 mm × 6 mm. This is thermally edged to stabilize it and at the same time adjust the humidity coefficient. Next, the platinum film is trimmed to a resistance value of about 50 to 150 cm, and platinum wire leads are attached to both ends. An insulating protective film layer such as beryllia cement or alumina cement with good heat conductivity is formed on the entire surface of this platinum film and baked. Next, a metal oxide semiconductor suitable for the purpose of the gas to be pumped out is painted with an appropriate inorganic bonding agent, and the paint is baked onto the insulating film to form a gas sensing section. On the other hand, LiNbO3 is baked onto the insulating film using a similar method to create a humidity sensing section.

Assemble the gas sensing section and humidity sensing section into a bridge circuit and apply an appropriate bridge voltage. The platinum film resistance of each element is 10
When 6V is applied at 0■, the element humidity becomes 6 due to Joule heat.
0-62℃ 75-78℃ at 8V, 98-10 at 10V
The temperature will be around 0℃.

L. P. G. The present invention and a semiconductor sensor were manufactured using S O2 semiconductors used for city gas.
Methane sensitivity was measured and compared at 20°C 65%, 25°C 75-76%, and 30°C 85%.

As can be seen from the measured values, the resistance value of semiconductor sensors changes greatly depending on the temperature and humidity, so 20℃ 65% 400
If you set the alarm to sound at 0 PPM, it will be 30℃85%.
Then, the alarm will sound at around 800 PPM. It can be seen that the gas sensitivity of the product of the present invention is hardly affected by temperature and humidity.

Furthermore, the element temperature and gas sensitivity can be adjusted by the bridge voltage.

Also, the current flowing through the element 6V approximately 30mA 8V approximately 40mA 10V approximately 50mA and compared with other gas sensors There are very few It is a characteristic.

Using this method, it is possible to easily produce an alarm that does not give false alarms about humidity due to alcohol, by coexisting with LiNO3 a material such as CuO, which is sensitive to alcohol and insensitive to methane, in the compensator.

[Brief explanation of drawings]

FIG. 1 shows the structure of each sensing part of the product of the present invention. A is a gas sensing part, B is a humidity sensing part, (1) is a trimmed platinum film, (2) is an insulating protective film with good thermal conductivity such as an alumina cement layer (3) is S ■O
The semiconductor film (4), such as 2-based Z■O-based material, is a crystalline layer of LiNbO3. FIG. 2 shows a practical structure in which the gas sensing section and the humidity sensing section are integrated. FIG. 3 shows a circuit used in the product of the present invention.

Claims (1)

[Claims] An insulating layer such as alumina cement is placed on the platinum film, and a semiconductor layer of S O2, ZO, V2O5, etc. is formed on top of the insulating layer. Place an insulating layer such as alumina cement on the upper layer and place L on top of it.
It consists of a solid thermal conductivity type humidity detector composed of three layers of NBO, and two elements are assembled into a bridge circuit to improve the humidity response due to self-heating of the platinum film by the bridge voltage. A gas sensing element characterized by adjusting the sensitivity and completely eliminating the influence of humidity by using a humidity sensing part.