JPH01219997A - Detecting device - Google Patents

Abstract

PURPOSE:To raise detecting resolution and to exactly execute a detecting operation by generating a current being in inverse proportion to a variation of a resistance and detecting an abnormal state, based on a variation of this current. CONSTITUTION:A semiconductor gas sensor 3 contains a heater coil and constituted so that the higher the gas concentration becomes, the lower its resistance value becomes. To both terminals of the semiconductor gas sensor 3, a prescribed voltage which has subtracted a base-emitter voltage of a transistor 10 from a constant-voltage of a Zener diode 11 is applied. When the resistance value of the semiconductor gas sensor 3 is varied in accordance with the gas concentration, a current being in inverse proportion to this variation flows to the semiconductor gas sensor 3. Subsequently, a voltage across a resistance 4 caused by this current is inputted to a comparator 7, compared with a reference voltage and a detecting operation is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a detection device that detects abnormal situations such as gas leakage using, for example, a semiconductor gas sensor.

(Prior Art) An example of this type of detection device is a gas alarm device that detects leaked gas. This gas alarm device uses a semiconductor gas sensor whose resistance changes as the concentration of gas leaking into the surrounding area increases. FIG. 4 is a circuit diagram of such a conventional gas alarm device.

In FIG. 4, a semiconductor gas sensor 203 has a built-in heater coil 202, and a constant voltage is applied to the heater coil 202 by a constant voltage circuit 201. The semiconductor gas sensor 203 is connected in series with a resistor 204 and supplied with power at a voltage 1, and the connection point with the resistor 204 is connected to one input of a comparator 207. The other input of the comparator 207 is connected to a resistor 205°20 connected in series to the power supply of voltage 1 and forming a voltage dividing circuit.
The connection points between 6 are connected. A speaker 208 constituting an alarm means is connected to the output of the comparator 207.

In such a configuration, the semiconductor gas sensor 203 is
As shown in FIG. 5, the resistance value R1l+ changes as the concentration of gas leaking into the surroundings increases, for example, the concentration of CO gas. This change in the resistance value Rg of the semiconductor gas sensor 203 appears as a change in the current flowing through the semiconductor gas sensor 203 and the resistor 204, and this change in current is applied to one side of the comparator 207 as a leak gas 111 degree detection voltage consisting of a voltage drop across the resistor 204. and the other input of the comparator 207.
．． 206 is compared with a reference voltage from a voltage divider circuit. When the leakage gas concentration detection voltage becomes higher than the reference voltage, the comparator 207 operates the speaker 208 to generate an alarm.

In such an operation, the resistance value Rg of the semiconductor gas sensor 203 changes as shown in FIG. As shown in the following equation (1), it is obtained by dividing the power supply voltage 1 by the resistance value RQ of the semiconductor gas sensor 203 and the resistance value RI04 of the resistor 204, and changes as shown in FIG. .

l04 Vd = V+ ・−−11−−−−−− (1)
RQ 10R+ 04 (Problem to be solved by the invention) In the conventional detection device described above, the semiconductor gas sensor 203
The leakage gas concentration detection voltage V obtained according to the change in resistance of
Since d is influenced by the resistance value RI04 of the resistor 104 as shown in the above equation (1), the amount of change is small as shown in FIG.

In particular, for example, changes in high concentration gases, including gas concentrations (2001)l)m, which correspond to the alarm level of CO gas sensors for kerosene stoves, are extremely small, resulting in extremely poor gas concentration detection resolution, resulting in malfunctions and accurate detection. There is a problem that a detection operation cannot be performed.

The present invention has been made in view of the above, and an object of the present invention is to provide a detection device capable of performing an accurate detection operation with a large gas concentration detection resolution.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the detection device of the present invention is a detection device that detects an abnormal situation by a change in resistance, and in which the detection device detects an abnormal situation by a change in resistance. The gist of the present invention is to include a current generating means for generating a current, and a detecting means for detecting an abnormal situation based on a change in the current generated from the current generating means.

(Function) The detection device of the present invention generates a current that is inversely proportional to a change in resistance, and detects an abnormal situation based on the change in the current.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram of a detection device according to an embodiment of the present invention. The detection device shown in the figure detects leakage gas, for example,
It constitutes a so-called gas alarm device that generates an alarm when the leakage gas concentration exceeds a predetermined concentration, and uses the semiconductor gas sensor 3 to detect the leakage gas and also to generate the alarm. I am using speaker 8.

The semiconductor gas sensor 3 has a built-in heater coil 2, and the heater coil 2 includes a transistor 15. ．． A constant voltage is supplied from a voltage source 1 consisting of a resistor 16 and a resistor 17, 18, which enables operation at high temperatures. As shown in FIG. 5, the semiconductor gas sensor 3 increases the resistance value R as the detected gas concentration, for example, the CO gas concentration increases.
The Q is now lower.

One end of the semiconductor gas sensor 3 is connected to a power supply of voltage 1, and the other end is connected to the emitter of a transistor 10. The collector of the transistor 10 is connected to a reference potential such as ground via a resistor 4, and is also connected to a comparator 7.
is connected to one input terminal of the In addition, the power supply voltage
A series circuit consisting of a Zener diode 11 and a resistor 12 and a voltage dividing circuit consisting of resistors 5 and 6 are connected between the Zener diode 11 and the reference potential, and a connection point between the Zener diode 11 and the resistor 12 is connected to the base of the transistor 10. ,
The connection point between resistors 5 and 6 is connected to the other input terminal of comparator 7.

In the structure as described above, a Zener diode 11 is connected to the base of the transistor 10 whose emitter is connected to the semiconductor gas sensor 3, specifically between the base and the other end of the conductive gas sensor 3. A constant voltage of the Zener diode 11 is supplied. Therefore,
Zener diodes 11 are connected to both ends of the semiconductor gas sensor 3.
A constant voltage v3 obtained by subtracting the base-emitter voltage Vbe of the transistor 10 from the constant voltage is applied.

The voltage Vbe between the base and emitter of the transistor 10 is negligibly small compared to the constant voltage of the Zener diode 11, and its fluctuation is also very small, so the voltage 3 applied across the semiconductor gas sensor 3 is Almost constant voltage. As a result, a current IO shown by the following equation (2), which is the constant voltage (3) divided by the resistance value Pa of the semiconductor gas sensor 3, flows through the semiconductor gas sensor 3.

10=V3/R(J...(2) Therefore, when the resistance value Rq of the semiconductor gas sensor 3 changes as shown in FIG. flows to

This current lo flows from the semiconductor gas sensor 3 as an emitter current of the transistor 10, and a collector current IC almost opposite to this emitter current flows through the transistor 10.
Flows from to resistor 4. This collector current 1c is a current 1o
is equal to the base current of the transistor 10 minus the base current of the transistor 10. However, since the base current is so small that it can be ignored, if it is calculated as being approximately equal to the current IO flowing from the semiconductor gas sensor 3, it will be generated across the resistor 4. Voltage vO
If the resistance value of resistor 4 is R4, then the following equation is obtained.

VO=IO・R4=V3・R4/Rf3”-(
3) That is, in this equation, the voltage V3 is a constant voltage and the resistance value R4 is also constant, so the voltage vO across the resistor 4 changes in inverse proportion to the resistance value R17 of the semiconductor gas sensor 3. FIG. 2 is a graph showing this voltage VO with respect to the CO gas concentration, which shows a large change and higher resolution than the conventional leakage gas concentration detection voltage Vd shown in FIG. 6 described above. Therefore, this voltage (0) is supplied to one input of the comparator 7 as the leakage gas concentration detection voltage, and compared with the reference voltage Vr from the voltage dividing circuit consisting of the resistor 5.6, which is supplied to the other input. Therefore, an accurate detection operation can be performed with greater resolution.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

In the embodiment shown in FIG. 1, an NPN transistor 11 is used instead of the transistor 10 in the embodiment shown in FIG.
0, the positions of the semiconductor gas sensor 3 and the resistor 4 are connected inversely to the voltage, and a transistor 111 and resistors 112, 113, 114 are used instead of the constant voltage circuit consisting of the Zener diode 11 and the resistor 12.
The only difference is that a constant voltage circuit consisting of the following is used, and the other configurations, functions, and effects are the same as those of the embodiment shown in FIG.

[Effects of the Invention] As explained above, according to the present invention, a current that is inversely proportional to a change in resistance is generated, and an abnormal situation is detected based on the change in the current, so that changes in resistance can be directly detected. Since it can be extracted as a change in current and is not affected by the resistors connected in series as in the conventional case, the gas temperature detection resolution is higher than in the conventional case, and an accurate detection operation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a detection device according to an embodiment of the present invention, FIG. 2 is a graph showing changes in leakage gas concentration detection voltage 0 with respect to detected gas concentration in the detection device of FIG. 1, and FIG. A circuit diagram of another embodiment of the present invention, FIG. 4 is a circuit diagram of a conventional detection device, and FIG. 5 is a detection gas 11 of a semiconductor gas sensor.
FIG. 6 is a graph showing changes in leakage gas concentration detection voltage Vd with respect to detected gas concentration in the detection device of FIG. 4. 3... Semiconductor gas sensor 4... Resistor 7... Comparator 11... Zener diode

Claims (1)

[Claims] A detection device that detects an abnormal situation based on a change in resistance, comprising a current generating means that generates a current that is inversely proportional to the change in resistance, and a detection device that detects an abnormal situation based on the change in the current generated from the current generating means. A detection device comprising means.