JPH0333224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas leak detection device, which uses a pulse power source to heat the heater wire, and is capable of detecting disconnection of the heater wire at least during the period when voltage is applied to the heater wire. That is.

WO ₃ has traditionally been used as a substance that senses CO, methane, LPG, hydrogen, and other flammable gases.
Reduced semiconductors such as SnO, ZnO, CoO, NiO,
Oxidized semiconductors such as Cu ₂ O (hereinafter collectively referred to as metal oxide semiconductors) are known, and the conductivity or resistance value of these metal oxide semiconductors that occurs when gas is adsorbed is known. Using electrical changes caused by changes in gas, a gas detection element as shown below is fabricated as a single unit and used in a gas leak alarm system in combination with an alarm device. As shown in FIG. 1, this gas detection element is usually made by passing a heater wire 1a through the inside of the porcelain tube 1b, and then
metal oxide semiconductor layer or resistor layer 1c on the outer surface of
A so-called indirectly heated element is provided on which electrodes 1d ₁ and 1d ₂ are placed facing each other at an interval, and a heater wire also serves as one of the pair of electrodes 1d ₃ as shown schematically in FIG. 2. A directly heated element is used. Furthermore, as a modification of the case shown in FIG. 1, the gas detection element 1 may be provided outside the semiconductor layer or resistor layer 1c without passing the heater wire 1a through the ceramic tube 1b.
The reason why heater wires are used in these gas detection elements is that heating the aforementioned semiconductor to a high temperature of 100°C to 400°C accelerates the adsorption reaction of gas ions. This is to increase the detection sensitivity of the gas, but in some cases, the conductivity changes by adsorbing the gas at a low temperature without heating the heater wire. A heater wire is used to attach and detach from the element, and the present invention relates to the latter type in which the heater wire is intermittently heated.

Gas leak alarm systems using such gas detection elements require normal operation at all times, but disconnections often occur, so disconnections are detected by monitoring the current flowing through the heater wire that heats the gas detection element. It has been proposed to detect disconnection by monitoring the presence or absence of output from the gas sensing element due to damage to the gas sensing element, such as damage to the metal oxide semiconductor or poor electrode contact. It was unthinkable to detect and display the detection and display of electrode disconnection and gas detection element damage at the same time. Moreover, since the gas detection element has a relatively short lifespan, the operation of the gas detection element must be constantly monitored, and it is important to prevent the danger of non-operation in the event of a gas leak due to failure of the gas detection element.

Taking these points into consideration, the present invention has developed a gas detection element that can simultaneously detect and display element damage caused by disconnection of the heater wire of the gas detection element, damage to the semiconductor, or poor contact between the semiconductor and both electrodes. A leak alarm device is provided.

Furthermore, in the present invention, a pulse from a pulse generator is used as a heating power source for the heater wire, and this causes the sensing element to be in a high temperature state and a low temperature state, that is, to alternately heat and stop heating the heater wire, depending on the characteristics of the gas sensing element. It is carried out smoothly in accordance with a certain gas inspection period and gas discharge period, and at least during the heating period of the heater wire, a voltage drop is generated in a certain resistance using the current flowing through the heater wire. , to the first transistor to reliably detect a break in the heater wire. For this purpose, in some cases, the detection of disconnection of the heater wire is prohibited by the output of the pulse generator mentioned above during the period when the heater wire is not heated. Furthermore, in some cases, disconnection of the heater wire can be actively detected via the second transistor even during a period when the heater wire is not being heated.

Next, an embodiment of the present invention will be explained with reference to the drawings. Figure 3 is a circuit configuration diagram showing a case in which disconnection detection of the heater wire is prohibited by the output of the pulse generator during the period when the heater wire is not heated. Figure 4 shows the waveform of the pulse generator PG based on Figure 3. Heater wire 1a, inverter INV,
FIG. 3 is a response diagram of a resistor R ₂ , a transistor Q ₂ , a comparator COM ₂ , and a transistor Q ₃ .

In the figure, PG is a pulse generator, 1 is the gas detection element shown in Figure 1, and the conductivity or resistance value of the heater wire 1a and the semiconductor 1c (to be exact, the semiconductor connected between the electrodes 1d ₁ and 1d ₂₎ . ) and circuit connections for monitoring. One end of the heater wire 1a connected to the pulse generator PG is connected to the inverter INV through the resistor R ₁ and the diode D ₁ to the transistor Q ₂
connected to the base of The other end of the heater wire 1a is grounded through a resistor _R2 and connected to the base of a transistor _Q2 through a resistor _R3 . Further, one end of the semiconductor 1c of the gas detection element 1 is grounded through an electrode and a resistor _R4 , and is also connected to the + side input terminal of the comparator COM ₁ and the - side input terminal of the comparator COM ₂ . The other end side is connected to the + power supply terminal _B1 via the other electrode. Also + power supply terminal B ₁
is grounded through resistors R ₅ and R ₆ , the connecting part of resistors R ₅ and R ₆ is connected to one side input terminal of comparator COM ₁ , and the output side of comparator COM ₁ is connected to resistors R ₇ and R ₈ The connecting portion of resistors R ₇ and R ₈ is connected to the gate terminal of a gate-polarized semiconductor Q ₁ such as a transistor or a thyristor. The anode of the transistor Q ₁ is connected to the alarm signal terminal B ₂ from the alarm indicator light LED ₁ through the resistor R ₉ , and the cathode of the transistor Q ₁ is grounded. Also, resistor from + power supply terminal B ₁
It is connected to the collector of transistor Q ₂ through R ₁₀ and R ₁₁ , and the emitter of transistor Q ₂ is grounded.
The connection between resistors R ₁₀ and R ₁₁ is connected to the + side input terminal of comparator COM ₂ , and the output side of comparator COM ₂ is connected to the resistor
It is grounded through R ₁₂ and R ₁₃ , and the junction between resistors R ₁₂ and R ₁₃ is connected to the gate terminal of a gate-polarized semiconductor Q ₃ such as a transistor or a thyristor. The cathode of the transistor Q ₃ is grounded, and the
The anode side of Q ₃ is connected to the resistance R ₁₄ from the fault indicator LED ₂ .
and is connected to the fault signal terminal _B3 . In this embodiment, the resistor R ₂ serves as the first current detection means, the transistor Q ₂ and the comparator COM ₂ serve as the heater burnout determination means, the inverter circuit INV and the diode D serve as the inhibiting means, and the resistor R ₄ serves as the first current detection means. The resistors R ₁₀ and R ₁₁ and the comparator COM ₂ constitute the heater breakage determining means. By the way, although FIG. 3 shows a type that is connected to a receiver (not shown) and sends an alarm signal and a failure signal to the outside, it is of course applicable to a gas leak detector used at home.

Next, the operation of FIG. 3 will be explained with reference to the waveforms of FIG. 4. If the gas detection element is normal now, a predetermined current flows through both the heater wire 1a and the semiconductor 1c, so during the period when the pulse voltage V is applied to the heater wire, there is a resistance due to the current flowing through the heater wire 1a.
The voltage drop across R ₂ is applied to the base of transistor Q ₂ , transistor Q ₂ is turned on and the comparator COM ₂
A voltage obtained by dividing the power supply voltage from the +B ₁ power supply terminal with respect to ground E by resistors R ₁₀ and R ₁₁ is applied to the + side input terminal of the comparator COM ₂ , and a voltage flowing through the semiconductor 1c is applied to the - side input terminal of the comparator COM 2. A voltage drop across resistor _R4 due to current is added, and the voltage applied to the + side input terminal of comparator COM ₂ is normally set lower than the voltage applied to the - side input _terminal . No output is taken out, transistor Q ₃ is off, and fault indicator LED ₂ is not lit.
Also, during the period when no voltage is applied to the heater wire 1a, the output of the pulse generator PG is
The voltage inverted at INV is applied to the base of transistor _Q2 through diode _D1 , and is applied to heater wire 1a.
_Transistor Q ₂ remains on as in the case _where voltage is applied to . Next, when the heater wire 1a is disconnected, no current flows through the heater wire 1a and the voltage drop across the resistor R ₂ disappears, and the transistor Q ₂
is turned off, and the power supply voltage from the +B power supply terminal relative to ground E is directly applied to the + side input terminal of comparator COM ₂ , which becomes higher than the voltage applied to the - side input terminal of comparator COM ₂ , and the output Therefore, the gate voltage based on the resistors R ₁₂ and R ₁₃ is applied to the gate of transistor Q ₃ , transistor Q ₃ is turned on, the fault indicator LED ₂ lights up, and a fault signal is sent from the fault signal terminal B ₃ . The signal can be extracted and sent to the outside through a receiver (not shown). In addition, if the semiconductor 1c side is disconnected or has a poor contact, no current flows through the semiconductor 1c, and the voltage drop due to the resistor _R4 is drastically reduced.
The voltage applied to the negative input terminal of COM ₂ decreases compared to the voltage applied to the positive input terminal, resulting in an output from the comparator COM ₂ , which applies gate voltage to the transistor Q ₃ and turns on the fault indicator LED _2. will be lit and a failure signal will be sent to the outside. Also, when leaked gas is adsorbed by the gas detection element 1, the resistance value of the semiconductor 1c decreases, the voltage drop across the resistor _R4 increases, and the voltage applied to the + side input terminal of the comparator COM ₁ becomes the - side input. Since the voltage exceeds the terminal voltage and the output is taken from the comparator COM ₁ , the resistor
A voltage is applied to the gate terminal of transistor Q ₁ via R ₇ and R ₈ , turning on transistor Q ₁ , lighting up alarm indicator LED ₁ , and sending out an alarm signal from terminal B ₂ to activate a receiver (not shown). You can inform the outside world.

In this manner, in the embodiment shown in FIG.
By applying a pulse voltage to the heating of a, the heating period and heating stop period of the heater wire are alternately provided,
Furthermore, failure of the heater wire is detected during the heating period of the heater wire, and during the heating stop period, the output of the pulse generator is used to prohibit the detection of a break in the heater wire, thereby preventing a simulated break output.

Furthermore, FIGS. 5 and 6 show that the heater wire detection operation can be performed both during the heater wire heating period and during the heating stop period. In Figure 5, pulse generator PG, gas detection element 1, comparator COM ₁ ,
COM ₂ , alarm indicator LED ₁ , fault indicator LED ₂ ,
It is assumed that the same reference numerals as in FIG. 3 are used for convenience.

The heater wire 1a connected to the pulse generator PG through the diode D is connected to a series resistor from the + power supply.
They are connected through R ₁₄ and R ₁₅ , and the connection between resistors R ₁₄ and R ₁₅ is connected to the base of transistor Q ₄ . The other end of the heater wire 1a is grounded through a resistor _R16 and connected to the base of a transistor _Q5 through a resistor _R17 . One electrode side of the semiconductor 1c of the gas detection element 1 is grounded through the resistor _R18 and connected to the + side input terminal of the comparator COM ₁ and the - side input terminal of the comparator COM ₂ , and the other electrode side is +Power terminal B ₁
connected to. The collector of transistor _Q4 is connected to ground E through resistor _R20 and connected to NOR circuit NOR.
The collector of the transistor Q ₅ is connected to the + power supply terminal B ₁ through the resistor R ₁₉ and to the other terminal of the NOR circuit NOR through the inverter INV. The negative input terminal of comparator COM ₁ passes through resistor R ₂₁ to + power supply terminal B ₁ , and also connects to resistor R 21.
Ground through R ₂₂ . The output side of comparator COM ₁ is grounded through resistors R ₂₃ and R ₂₄ and connected to resistor R ₂₃ .
The connection part of _R24 is connected to the gate pole of a transistor or a semiconductor with a gate pole _Q6 , and this transistor _Q6
The anode of is connected to the alarm indicator LED ₁ and the alarm indicator terminal B ₂ via the resistor R ₂₅ , and the cathode of the transistor Q ₆ is grounded. Also, Noah circuit
The output side of NOR is connected to the + of comparator COM ₂ through resistor R ₂₆ .
This + side input terminal is connected to the + power supply terminal B ₁ via a resistor R ₂₇ . comparator
The output side of COM ₂ is grounded through resistors R ₂₈ and R ₂₉ , and the connection between resistors R ₂₈ and R ₂₉ is a transistor (or a semiconductor with a gate pole such as a thyristor) Q ₇
The anode of the transistor Q ₇ is connected to the fault indicator terminal B ₃ via the fault indicator light LED ₂ , and the cathode of the transistor Q ₇ is grounded.
Figure 6 shows the pulse voltage of the pulse generator PG, the heater wire 1a, the voltage drop of the resistor _R16 , the on/off of the transistors _Q4 and _Q5 , and the inverter circuit INV.
The waveforms for the inversion situation, the NOR circuit NOR, the output of the comparator COM ₂ as well as the output of the transistor Q ₇ are shown.

Next, the operation of the apparatus of the present invention will be explained with reference to FIG. 5 in conjunction with FIG. 6.

First, when the gas detection element 1 is normal, a voltage drop occurs across the resistor R ₁₆ and the transistor Q ₅ is turned on during the period when the voltage is applied to the heater wire 1a according to the pulse voltage from the pulse generator PG. However, transistor _Q4 is turned off and the NOR circuit NOR
The input on the transistor _Q4 side becomes L (low),
Also, transistor _Q5 is on and the inverter circuit INV
The other input of the NOR circuit NOR becomes H (high), and the output of the NOR circuit NOR is L and the comparator COM ₂
The power supply voltage is divided by resistors _R27 and _R26 and a voltage is applied to the + side input terminal of. Furthermore, if the current flowing through the semiconductor 1c is normal at the negative input terminal of the comparator COM ₂ , the voltage drop across the resistor _R18 is set in advance to be higher than the voltage at the positive input terminal, and the comparator COM ₂ outputs Transistor Q ₇ is off and fault indicator LED ₂
does not light up. Also, during the period when no voltage is applied to the heater wire 1a according to the pulse voltage from the pulse generator PG, there is no voltage drop across the resistor _R16 , and the transistor _Q5 is off, passing through the inverter circuit INV to one end of the NOR circuit NOR. is given L. Also, the transistor _Q4 is turned on by the voltage drop that occurs across the resistor _R14 when the pulse generator PG does not produce an output, and H is applied to the other end of the NOR circuit NOR, and the output of the NOR circuit NOR is L in this case. Comparator COM ₂ does not output any output, transistor Q ₇ remains off, and fault indicator LED ₂ does not light up.

However, if the heater wire 1a of the sensing element 1 is disconnected, the transistors Q ₄ and Q ₅ are always turned off, the output of the NOR circuit NOR becomes H, and the + side input terminal voltage of the comparator COM ₂ becomes high, and the comparator COM ₂ takes out the output, voltage is applied to the gate of transistor Q ₇ , transistor Q ₇ is turned on, failure indicator LED ₂ lights up, notifying the failure and giving a failure signal to the external receiver side. If the semiconductor 1c of the sensing element is disconnected, the voltage drop across the resistor _R18 will be approximately 0V and the comparator COM ₁ will not work, but the negative input terminal of the comparator COM ₂ will be connected to the resistance of the positive input terminal.
Since the voltage is lower than the voltage divided by R ₂₇ and R ₂₆ , the output of the comparator COM ₂ is taken out and the transistor Q ₇
Increase the gate voltage appropriately, turn it on, and turn on the failure indicator LED ₂ to indicate a failure.
When gas detection element 1 detects gas, as the resistance value of semiconductor 1c changes and decreases, the flowing current increases and the voltage drop across resistor _R18 increases, which is applied to the negative input terminal of comparator _COM1 . The voltage across the resistor R ₂₁ from the + power supply terminal is greater than the voltage and the comparator COM ₁
takes out the output and increases the gate voltage of transistor Q ₆ to turn it on and turn on the alarm indicator light.
This will light up LED ₁ .

Thus, in the embodiment shown in FIG. 5, it is possible to detect disconnection or damage to the element due to the heater wire 1a and semiconductor 1c of the gas detection element 1, and by applying a heating pulse voltage to the heater wire 1a, it is possible to heat the heater wire and stop the heating. This is done alternately, and disconnection of the heater wire can always be detected reliably during both the heating period and the heating stop period.

As can be seen from the above explanation, the gas leak detection device that uses the pulse power supply of the present invention to give the heater wire a heating period and a heating stop period, and alternately adsorbs and desorbs gas, Since the heating current does not flow in the heater wire, it is possible to prevent false alarms due to simulated disconnections and to reliably detect only disconnections in the heater wire, as well as to prevent disconnections due to damage to the metal oxide semiconductor and poor contact between the semiconductor and both electrodes. It is also possible to detect element damage accidents caused by such factors.

[Brief explanation of the drawing]

1 and 2 are a perspective view of a gas detection element according to one embodiment used in the present invention and a schematic diagram of another embodiment of the element, and FIGS. 3 and 5 are different embodiments of the present invention. The wiring diagrams of the main parts of the device, Figures 4 and 6, are shown in Figure 3.
6 is an operation waveform diagram of each part in FIG. 5. FIG. In the figure, 1 is the gas detection element, 1a is the heater wire, 1c
is a semiconductor, PG is a pulse generator, COM ₁ ,
COM ₂ is the comparator, INV is the inverter, LED ₁ is the alarm indicator, LED ₂ is the fault indicator, R ₁ - _{R 29} is the resistor,
_Q1 to _Q7 are transistors, and NOR is a NOR circuit.

Claims (1)

[Claims] 1. By providing a heating period and a heating stop period for the heater wire using a pulse power supply, and adsorbing gas in a low temperature state without heating the heater wire during the heating stop period, the conductivity or A gas leak detection device that detects a gas leak by using a change in resistance value, and issues a gas leak alarm by combining a gas detection element of the type that desorbs the gas from the element by heating a heater wire during the heating period with an alarm device. a first current detection means for detecting a heating current flowing through the heater wire; and a breakage signal for determining a break in the heater wire when the first current detection means no longer detects the heating current; heater breakage determining means for outputting a signal; inhibiting means for detecting the heating stop period by the pulsed power supply and prohibiting the operation of the heater breakage determining means during the heating stop period; a second current detection means for detecting a current; and when the current detected by the second current detection means drops below a predetermined value, a disconnection or poor contact is determined in the metal oxide semiconductor, and the disconnection is detected. A gas leak detection device comprising: semiconductor disconnection determination means that outputs a signal;