JPH0375918B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a gas leak alarm,
The object is to provide a small gas leak alarm that is equipped with an output circuit insulated from a high voltage circuit, has a simple power supply circuit configuration, and is less likely to malfunction.

Conventionally, this type of gas leak alarm has been constructed as shown in Figs. 1 and 2, where 1 is a metal oxide semiconductor such as SnO ₂ between the heater H and the resistance detection electrode P. This is a gas sensor equipped with a sintered body, and the resistance value between the heater H and the electrode P changes (decreases) when combustible gas comes into contact with it while being heated by the heater H. There is.
2', a change in the resistance value of the gas sensor 1 is determined by a comparator CP ₁ consisting of an operational amplifier, and a gas detection signal V _G is outputted via a signal processing circuit 2a consisting of comparators CP ₂ and CP ₃ . The gas detection signal V _G is input to an output circuit 4' via a photocoupler 3 consisting of a light emitting diode LD and a phototransistor PT. This output circuit 4' is formed by transistors Q ₁₀ and Q ₁₁ and Zener diodes ZD ₁₀ and ZD ₁₁ ,
Outputs an external output signal VG' consisting of a voltage level signal of 12V when a gas leak is detected and 6V when no gas is detected. Note that the signal processing circuit 2a prevents malfunctions when the power is turned on. 5' is an operational amplifier
An alarm circuit consisting of OP ₁ , transistors Q ₆ , Q ₇ , Q ₉ , light emitting diode LD ₁ and buzzer BZ,
When the gas detection signal V _G is obtained, the buzzer BZ sounds and the light emitting diode LD ₁ flickers to issue a gas leak alarm.
By the way, in such a conventional example, the power transformer 7' that supplies power to each circuit has a primary winding N ₁ ,
2 o'clock windings N ₂ a, N ₂ b and a heater winding N ₃ are formed, and a voltage across the heater winding N ₃ is applied to the heater H of the gas sensor 1.
A commercial power supply 6 is applied to the series circuit of the voltage dividing resistors R ₁ and R ₂ , and the output of the rectifying voltage dividing circuit consisting of the diode D ₁ and the resistors R ₃ and R ₄ is input to the comparison terminal of the comparator CP ₁ . The secondary winding N ₂ a voltage of the power transformer 7' is applied to the power supply circuit 8a of the gas detection circuit 2' and the alarm circuit 4'.
On the other hand, an external output signal is generated based on the gas detection signal V _G.
Another secondary winding N ₂ b voltage of the power transformer 7 was applied to the power supply circuit 8b of the output circuit 4' forming V _G '. That is, the power supply circuit 8a of the gas detection circuit 2' and the alarm circuit 5' to which the commercial power supply 6 is applied, and the power supply circuit 8b of the output circuit 4' that forms the external output signal V _G ' are formed separately. By inputting the gas detection signal V _G to the output circuit 4' via the photocoupler 3, high voltage is prevented from being output as the external output signal V _G ' even if the circuit fails.
However, in such a conventional example, the power supply circuit 8a of the high voltage circuit such as the gas detection circuit 2'
and a power supply circuit 8b of a low voltage circuit such as the output circuit 4'.
are formed separately, so two secondary windings N ₂ a,
A power transformer 7' having N ₂ b is required, which increases the size of the power transformer 7' and complicates the circuit configuration.
Also, since the alarm circuit 5' through which intermittent current or large current flows, such as the buzzer BZ, and the gas detection circuit 2' are supplied with power from the same power supply circuit 8a, the gas detection circuit 2' may malfunction due to fluctuations in the power supply voltage. The drawback was that it was easy to do. The present invention has been made in view of the above points.

Examples will be described below using figures. 3 and 4 show an embodiment of the present invention, in which 1 is a gas sensor similar to the conventional example described above, 2
are transistors Q ₁ , Q ₂ , rectifier diode D ₁ ,
This is a gas detection circuit consisting of D ₂ and a Zener diode ZD ₁ for voltage regulation. When the resistance value of gas sensor 1 decreases and the voltage across resistor R ₄ becomes larger than the pace emitter voltage of transistor Q ₁ , transistor Q ₁ and _Q2 are turned on, and a gas detection signal V _G is output via the photocoupler 3. This gas detection signal V _G is input to the output circuit 4 and the alarm circuit 5 via a signal processing circuit 9 consisting of NAND circuits NA ₁ to _{NA 3} and a CR time constant circuit CR ₁ . This signal processing circuit 9 generates a gas detection signal for a certain period of time after the power is turned on.
This prevents V _G from being input to the output circuit 4 and alarm circuit 5 to prevent false alarms when the power is turned on. The output circuit 4 includes a reverse current blocking diode _D3 , a Zener diode _ZD2 for output voltage setting,
ZD ₃ , a control transistor Q ₃ and a short-circuit protection transistor Q ₄ , and the Zener voltage of the Zener diode ZD ₂ is set to 6V.
Now, when the output of the NAND circuit NA ₃ of the signal processing circuit 9 becomes H level (approximately the power supply voltage), that is, in the normal state when the gas detection circuit 2 does not output the junk detection signal V _G , the Zener diode
Current flows through ZD ₂ and resistor R ₅ , and the potential at point A becomes the value obtained by subtracting the Zener voltage of Zener diode ZD ₂ from the power supply voltage, and the voltage of external output signal V _G ' (voltage applied to external load 10) is the potential difference between the power supply voltage and point A, that is, the Zener voltage of Zener diode _ZD3 is 6V. On the other hand, when the NAND circuit NA ₂ output goes to L level, that is, when detecting a gas leak when the gas detection signal V _G is output from the gas detection circuit 2, the potential at point A becomes 0, so the external output signal V The voltage of _G ′ becomes the power supply voltage. However, R ₅ is several kilohms, and R ₆ is several + ohms. The Zener diode ZD ₃ also has a noise absorption function. Also, if output terminals T ₁ and T ₂ are shorted,
The voltage across resistor R ₆ increases, transistor Q ₄ turns on, and a short-circuit current flows through resistor R _5. Since R ₅ ≫ _{R 6} , transistor Q ₃ turns off. This is designed to prevent Transis Q ₃ from being destroyed. in this case,
Since the resistance value of resistor R ₅ is relatively high, no large short circuit current will flow.

On the other hand, the alarm circuit 5 is formed of an operation display section 5a consisting of a NAND circuit _NA4 , a transistor _Q5 and a light emitting diode _LD1 , and an acoustic alarm section 5b consisting of transistors _Q6 , _Q7 and a buzzer BZ. The display section 5a displays a light emitting diode LD ₁ during non-gas detection when the gas detection signal V _G is not output.
lights up continuously to indicate the standby state, and when gas detection signal V _G is output and gas is detected, light emitting diode LD ₁ flickers to indicate a gas leak. ing. Further, the acoustic alarm section 5b is activated when a gas leak is detected and issues a gas leak alarm by sounding a buzzer BZ. by the way,
In the embodiment, the power transformer 7 that supplies power to each circuit is the secondary winding of the conventional power transformer 7'.
It is a small type that omits N ₂ b, and directly applies the primary winding N ₁ voltage of the power transformer 7, that is, the commercial power supply 6, to the gas sensor 1 and the gas detection circuit 2,
The secondary winding N ₂ a voltage of the power transformer 7 is applied to a power supply circuit 8a that supplies power to the signal processing circuit 9, the output circuit 4, and the alarm circuit 5.
Therefore, since the power transformer 7 is miniaturized, the overall size of the alarm is reduced, and only one power supply circuit 8a is required, making the circuit configuration simpler than in the conventional example. In addition, the gas detection circuit 2, which is a high voltage circuit to which the commercial power supply 6 is applied, and the external output signal
Since the output circuit 4 that forms V _G ' is insulated by the power transformer 7 and photocoupler 3, even if the circuit fails, high voltage will not be output as the external output signal V _G ', improving safety. In addition to improving the power supply, the alarm circuit 5 and the gas detection circuit 2, through which a large current flows intermittently, have separate power supplies.
The gas detection circuit 2 will not malfunction due to fluctuations in power supply voltage.

The present invention is configured as described above, and applies commercial power to the gas sensor and gas detection circuit, and also applies the secondary winding voltage of the power transformer that steps down the commercial power to the output circuit and the power circuit of the alarm circuit. Compared to the conventional example, the power transformer is smaller and the power supply circuit configuration is simpler, making it possible to provide a small and inexpensive gas leak alarm. Since the power supply is provided in a separate system, the gas detection circuit does not malfunction due to fluctuations in the power supply voltage during operation of the alarm circuit, and there is an advantage that false alarms are less likely to occur.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a conventional example, FIG. 2 is a specific circuit diagram of the same, FIG. 3 is a block circuit diagram of an embodiment of the present invention, and FIG. 4 is a specific circuit diagram of the same. 1 is a gas sensor, 2 is a gas detection circuit, 3 is a photocoupler, 4 is an output circuit, 5 is an alarm circuit, 6 is a commercial power supply, 7 is a power transformer, and 8a is a power supply circuit.

Claims (1)

[Claims] 1. A gas sensor whose resistance value changes when combustible gas comes into contact with it, a gas detection circuit that detects the change in resistance value of the gas sensor and outputs a gas detection signal when the resistance value reaches a preset value, and a photocoupler. It consists of an output circuit that forms an external output signal based on the gas detection signal input through the gas detection signal, and an alarm circuit equipped with a buzzer that operates based on the gas detection signal, and applies commercial power to the gas sensor and the gas detection circuit. At the same time, a commercial response power source is applied to the primary winding, and a secondary winding voltage of a power transformer that steps down the commercial power source is applied to the output circuit and the power circuit of the alarm circuit.