JPH0411164Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a gas detection device using a metal oxide semiconductor gas sensor.

<Prior Art> As this type of gas detection device, there is a gas leak alarm for home use as shown in FIG. 5 of page 70 of "Sensor Technology", July 1983 issue.

The structure and operation of the main parts of such a gas leak alarm will be briefly explained based on FIG. 2.

In the figure, 1 is a gas sensor as a gas detection part using a metal oxide semiconductor, for example, S _{O 2}
A heater 2 which also serves as one electrode, and another electrode 3 corresponding to the heater 2 are buried in the sintered body. The heater 2 is provided for stabilizing the temperature of the sintered body. Since the conductivity of the S _{O 2} sintered body changes depending on the gas concentration, the resistance value between the heater 2 and the electrode 3 changes. 4
is a voltage dividing circuit connected in series with the gas sensor 1, which includes resistors R ₁ , R ₂ and a thermistor for temperature compensation.
It is composed of R _TH . In 5, the comparison voltage, that is, the voltage divided by the gas sensor 1 and the voltage dividing circuit 4, is input to the non-inverting input terminal (+ side terminal), and the reference voltage V _S is input to the inverting input terminal (- side terminal). A comparator serves as an input comparison circuit, and when the divided voltage becomes equal to or higher than the reference voltage V _S , its output becomes "H" level. Reference numeral 6 denotes a light emitting diode serving as an alarm unit that lights up when the transistor 7 becomes conductive.

In such a configuration, when gas enters the S _o O ₂ sintered body of the gas sensor 1 due to gas leakage, its conductivity changes and the resistance value between the heater 2 and the electrode 3 decreases.
R _T becomes _smaller . This allows the above
The potential at point a in the figure, which is determined by the voltage division ratio of R _T and the combined resistance value R _C of voltage divider circuit 4, increases, and the reference voltage V _S
When the temperature exceeds this level, the output of the comparator 5 changes from "L" to "H", turning on the transistor 7 and lighting the light emitting diode 6 to notify the gas leak.

On the other hand, when there is no gas leak, the divided voltage at point a is lower than the reference voltage V _S , so the output of comparator 5 is at "L" level, transistor 7 is OFF, and light emitting diode 6 is off. .

<Problems to be solved by the invention> However, in the case of such a gas detection device, a failure of the gas sensor 1 such as a disconnection of the heater 2 causes the R _T
is too high or the power supply voltage V _DC is not supplied, the potential at point a will not exceed V _S and the light emitting diode 6 will be turned off, and the voltage divider circuit 4 will turn off.
When the resistors R ₁ and R ₂ and the thermistor R _TH are disconnected, the potential at point a does not become lower than the reference voltage V _S and the light emitting diode 6 lights up.

Therefore, if the light-emitting diode 6 is lit, it can be said that it has a fail-safe function by determining that there is a gas leak and taking measures even if it is caused by a device failure, but if the light-emitting diode 6 is turned off, However, there was a problem in that even if a malfunction occurred in the equipment, it could not be recognized and it was determined that there was no gas leak.

This idea was made in view of the above circumstances.
The purpose of the present invention is to improve the reliability of a gas detection device by providing the gas detection device with a self-diagnosis function for diagnosing whether the device is normal or not.

<Means for solving the problem> For this reason, in this invention, between the power line and the ground,
A gas detection section whose resistance value decreases as the gas concentration increases and a voltage dividing circuit are connected in series, and the pressure is divided by the resistance value of the gas detection section and the resistance value of the voltage dividing circuit. A comparator circuit that inputs the midpoint voltage between the gas detection unit and the voltage dividing circuit that changes according to a change in the resistance value of the gas detection unit, compares it with a preset reference voltage, and outputs an output when the midpoint voltage is equal to or higher than the reference voltage. and an alarm unit that issues an alarm when the comparator circuit outputs an output, the gas detection device is equipped with: a gas detection device that is equipped with an alarm unit that issues an alarm when the comparator circuit outputs an output; A switching circuit is provided to periodically raise the midpoint voltage level above the reference voltage.

<Function> As a result, when there is no gas leak and the gas detection device is normal, the divided voltage input to the comparator circuit rises and falls around the reference voltage in synchronization with the disconnection/connection operation of the switching circuit, causing the light emitting diode to rise and fall. Make it blink.
In addition, in the event of equipment failure, the switching circuit can be disconnected or
Regardless of the connection operation, the light emitting diode will be either off or on and will no longer blink.
You can know whether the device is normal or not.

<Example> An example of the present invention will be described in detail below with reference to FIG. Incidentally, the same parts as in FIG. 2 are given the same reference numerals, and the description thereof will be omitted.

In FIG. 1, reference numeral 8 denotes a switching circuit composed of a transistor 9 inserted between the voltage dividing circuit 4 and ground, and an oscillator 10 which generates an output at a predetermined period to the base of the transistor 9.

Next, the effect will be explained.

First, a case where the gas detection device is normal will be described.

The transistor 9 is normally in an ON state, and is turned OFF at regular intervals by the output from the oscillator 10. When the transistor 9 is in the ON state, the voltage dividing circuit 4 is grounded, so the circuit configuration is the same as the conventional one, and the current supplied from the power source flows through the gas sensor 1 and the voltage dividing circuit 4 to the ground.
The voltage V at point a at this time is expressed by the following equation.

V=R _C・V _DC /(R _T +R _C )……(1) Here, R _T is the interelectrode resistance value of the gas sensor, R _C
is the combined resistance of the voltage divider circuit, and V _DC is the power supply voltage.
Furthermore, when the transistor 9 is turned off, current flows through the gas sensor 1 and the comparator 5 to ground. The voltage V at point a at this time is expressed by the following equation.

V=R _i ·V _DC /(R _T +R _i )...(2) Here, R _i represents the input resistance of the comparator.

Therefore, when there is no gas leak, the resistance value R _T of the gas sensor 1 is large when the transistor 9 is in the ON state, and V<V _S according to equation (1), and the output of the comparator 5 becomes "L" level and the transistor 7 is turned on.
When it is OFF, the light emitting diode 6 is turned off. Also,
When the transistor 9 turns OFF, in equation (2), since the input resistance R _i of the comparator 5 is large, V increases and V>V _S , and the output of the comparator 5 becomes “L”.
becomes “H”, transistor 7 turns on, and the light emitting diode lights up. In this manner, when the gas detection device is normal and there is no gas leak, the light emitting diode 6 blinks in response to the ON/OFF state of the transistor 9.

Further, when a gas leak occurs and the gas sensor 1 detects this, the resistance value R _T of the gas sensor 1 decreases and V increases. When the concentration exceeds a predetermined level, even if the transistor 9 is in the ON state, V
>V _S , the output of the comparator 5 changes from "L" to "H" and the light emitting diode 6 lights up. In this manner, if a gas leak occurs while the gas detection device is operating normally, the light emitting diode 6 lights up continuously to notify the gas leak.

Next, a case where the gas detection device fails will be explained.

For example, if the resistance value R _T of the gas sensor 1 becomes extremely high due to a disconnection of the heater 2, or if the power supply voltage V _DC
In the event of a failure where the voltage is not being supplied, the voltage V at point a will drop significantly regardless of whether transistor 9 is ON or OFF, and the reference voltage of comparator 5 will drop.
The voltage does not exceed V _S and the light emitting diode 6 remains off.

In addition, the resistors R ₁ and R ₂ of voltage divider circuit 4 and thermistor
When R _TH is disconnected, the combined resistance R _C of voltage divider circuit 4 becomes extremely large, so transistor 9
The voltage V is always higher than the reference voltage V _S regardless of whether it is ON or OFF, and the light emitting diode 6 remains lit. Furthermore, the transistor 9 and the oscillator 10
If the light emitting diode 6 fails, the light emitting diode 6 will not blink. In this way, when some kind of failure occurs in the gas detection device, the light emitting diode 6 is fixed to either a lit or unlit state.

In this way, the output of the comparator 5 can be inverted only when the gas detection device is normal, and this can be determined based on the state of the light emitting diode 6. In other words, if the light is blinking, you know that the device is normal and there is no gas leak, if the light is off, you know that the device is malfunctioning, and if it is lit, you know that the device is malfunctioning. Or it can be determined that a gas leak has occurred.

<Effects of the invention> As described above, according to the invention, the self-diagnosis function is built into the gas detection device itself, and the diagnosis result is notified by the alarm unit. It is possible to know whether the device is normal and capable of gas detection, or whether the detection device has failed and the gas detection function has been lost, and the failure diagnosis of the gas detection device can be performed, greatly increasing the reliability of the detection device. I can do it.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure shows a circuit diagram of a conventional example. DESCRIPTION OF SYMBOLS 1... Gas sensor, 4... Voltage dividing circuit, 5... Comparator, 6... Light emitting diode, 7... Transistor, 8... Switching circuit, 9... Transistor, 10... Oscillator.

Claims (1)

[Scope of utility model registration request] A gas detection section whose resistance value decreases as the gas concentration increases and a voltage dividing circuit are connected in series between the power supply line and the ground, and the resistance value of the gas detection section and the voltage dividing circuit are connected in series. The midpoint voltage between the gas detection section and the voltage dividing circuit, which is divided by the resistance value and changes according to the change in the resistance value of the gas detection section, is input and compared with a preset reference voltage to determine the midpoint voltage. In a gas detection device that includes a comparison circuit that outputs when the voltage is equal to or higher than a reference voltage, and an alarm section that issues an alarm when the comparison circuit outputs an output, a 1. A gas detection device comprising a switching circuit that periodically increases the intermediate point voltage level to a reference voltage or higher by periodically disconnecting the voltage.