JPS59143947A - Gas leak alarming device - Google Patents

Abstract

PURPOSE:To obtain a gas leak alarming stably operated even if temp. dependence due to the kind of gas and the irregularity of heater 4 are not considered, by constantly controlling the temp. of a sensor 3 by providing the heater, a heater voltage control circuit and a thermocouple. CONSTITUTION:A thermocouple 16 for detecting the temp. of a sensor 3 is embedded in the sensor 3 and connected to a heater voltage control circuit 5 so as to constantly control the output thereof whereupon an element temp. is made constant regardless of a circumferential temp., voltage and high concn. gas. When combustible gas is contacted with the sensor 3, the potential at the connection point with a resistor 10 and, when it becomes higher than the potential at the connection point D of resistors 17, 18 each for applying a reference level, a voltage discriminating circuit 19 and a drive circuit 13 are operated to alarm the gas leakage by a lamp 14 and a buzzer 15.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a gas leak alarm.

The configuration of the conventional example and its problems The conventional example will be explained based on the drawings. Figure 1 is a block diagram of a conventional gas leak alarm using a gas sensing element made of an iron oxide-based metal oxide semiconductor sensitive material, where 1 is an h-current power supply, 2 is a gas sensing element, and 3 is an oxidation 4 is a heater for maintaining the sensitive body 3 at a predetermined temperature; 5 is a heater voltage control circuit that applies a constant voltage to the heater 4 in order to keep the power of the heater 4 constant; 6 is a A temperature compensation circuit compensates for the dependence of the sensitive body 3 on the ambient temperature. 7
~10 are resistors, 11.12 are voltage discrimination circuits, 1
3 is the lamp 14. This is a drive circuit that drives the buzzer 15.

When combustible gas comes into contact with the sensitive element 3, the resistance value of the sensitive element 3 decreases, the potential at point A rises, and the temperature compensation circuit 6 and the resistor 9
When the potential at point A becomes higher than the potential at point B, the voltage discrimination circuit 12 is inverted, and the drive circuit 13 of the lamp 14 and buzzer 15 is operated,
Lamp 14° and buzzer 15 warn of gas leakage.

Figure 2 shows the characteristics of the resistor resistance and the gas concentrations of methane, hydrogen, and inbutane. As is clear from this figure, when the gas concentration increases, in the case of hydrogen, isobutane, etc., the reactor undergoes thermal runaway due to the heat of reaction with the gas, and the resistance value rapidly decreases.

Since this phenomenon leads to deterioration of the sensitive body 3, the resistor 7.8 is provided in FIG. The voltage of the heater 4 is reduced by the heater voltage control circuit 5, and the l? I'll give you a boner C. In this way, thermal runaway in the reaction with hydrogen and isobutane is prevented.

The problem with the conventional example shown in FIG. 1 is that the temperature compensation circuit 6
Even if compensation is made for the ambient temperature, the temperature dependence differs depending on the gas, so the temperature characteristics differ depending on the gas. In addition, although the heating voltage is controlled to be constant in order to keep the temperature of the sensing element constant, the wetted surface of the sensing element varies due to variations in the heating voltage and distance from the sensing element, so the characteristics may vary. This causes variation in the Therefore, conventionally, it has not been possible to provide a gas leak alarm that operates stably.

OBJECTS OF THE INVENTION The present invention aims to provide a more stable gas leak alarm by eliminating the above-mentioned problems caused by fluctuations in the temperature of the sensitive body, high concentration protection circuits, and differences in temperature characteristics due to gas.

Structure of the Invention The present invention has a thermocouple buried inside the reactor body to detect the temperature, which is maintained at a high temperature by a heater, and when it comes into contact with a flammable gas, This heat'"↓L
By controlling the heater voltage to keep the output constant, a stable gas leak alarm can be provided.

DESCRIPTION OF EMBODIMENTS The present invention will be described in detail below with reference to FIG. In the same figure, 16 is embedded inside the sensitive body 3, and the sensitive body 3
By connecting the output of the thermocouple 16 to the heater voltage control circuit 6 and controlling the output of the thermocouple 16 to a constant value, the element temperature can be maintained regardless of the ambient temperature, voltage, or high concentration gas. is kept constant. When the combustible gas comes into contact with the sensitive element 3, the potential at the connection point A with the resistor 10 rises, and the resistor 17. which provides the reference level rises. When the potential becomes higher than the connection point '18, the voltage discrimination circuit 19 and the drive circuit 1
3, the lamp 14. A buzzer 15 is configured to warn of gas leakage.

As is clear from the above, according to the present invention, the temperature of the sensitive body 3 can be controlled to be constant using the thermocouple 16, so stable operation can be achieved without considering temperature dependence depending on the type of gas or variations in the heater 4. We can provide gas leak alarms. or,
In the present invention, since it is not affected by the ambient temperature, etc., a temperature compensation circuit is not required, and the entire circuit can have a single configuration. Furthermore, since a thermocouple is used in the present invention, thermal runaway caused by a sudden rise in temperature of the sensitive body 3 can be prevented.

Effects of the Invention According to the present invention, (1) There is no variation in the temperature of the sensitive body, and the variation in characteristics is reduced.

(Takumi) There is no need for a temperature compensation circuit, and there are no differences in temperature characteristics depending on the gas.

(3) Since the temperature of the sensitive body is controlled to be constant, thermal runaway due to reaction heat with high concentration gas is eliminated, and the high concentration protection circuit becomes unstable.

It has the following effects.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a characteristic diagram showing the relationship between gas concentration and sensing element resistance value in the conventional example, and FIG. 3 is a characteristic diagram showing the relationship between ambient temperature and sensing element resistance value. FIG. 4 is a circuit diagram showing one embodiment of the present invention. 3 Sensing body, 4 Heater, 6 Heater voltage control circuit, 16 Heat pair. Name of attorney: Toshio Nakao and 1 other person
1 Figure 5 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A metal oxide sensitive body whose resistance value decreases when it comes into contact with a flammable gas, a heater that maintains the sensitive body at a predetermined temperature, a detection circuit that detects a change in the resistance value of the sensitive body, and a A gas leak alarm comprising an embedded thermocouple and a heater control circuit that controls voltage to the heater to keep the thermocouple output constant.