JPH0333225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas leak detection device, and in particular uses a pulse power source to heat a heater wire, and constantly detects a gas leakage between the heater wire during a period when a voltage is applied to the heater wire and during a period when a voltage is not applied to the heater wire. This makes it possible to detect wire breaks.

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 of these metal oxide semiconductors that occurs when gas ions are adsorbed is known. A gas detection element having the configuration shown below is made as a single unit by utilizing the electrical change caused by the change in value, and is used in combination with an alarm device for a gas leak alarm device. This gas detection element usually uses a heater wire 1a as shown in FIG.
is passed through the inside of the porcelain tube 1b, and a metal oxide semiconductor or resistor layer 1c is provided on the outer surface of the porcelain tube 1b, and electrodes 1d ₁ and 1d ₂ are placed thereon facing each other at intervals. An indirectly heated type element and a directly heated type element in which a heater wire also serves as one of a pair of electrodes _1d3 are used, as shown schematically in FIG. Further, as a modification of the case shown in FIG. 1, the gas detection element 1 can also 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, making it possible to detect trace amounts of gas. This is to increase the gas detection sensitivity, but in some cases, the conductivity changes by adsorbing the gas at a low temperature without heating the heater wire. In this case, the gas is A heater wire is used for attaching and detaching the wire, 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 the current flowing through the heater wire that heats the gas detection element must be monitored to prevent disconnections. It has been proposed to detect wire breakage 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 semiconductor or poor electrode contact. It was inconceivable to simultaneously detect and display the detection and display of heater wire breakage and gas detection element damage.
Moreover, since the gas detection element has a relatively short lifespan, it is necessary to constantly monitor the operation of the gas detection element, and it is important to prevent the danger of non-operation in the event of gas leakage due to failure of the gas detection element.

Taking these points into consideration, the present invention provides a gas leakage system that can 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. The present invention provides an alarm device.

Furthermore, in the present invention, a pulse voltage from a pulse generator is used as a heating power source for the heater wire, and this causes the sensing element to have a high temperature state and a low temperature state, that is, a heating period and a heating stop period. Gas detection and gas desorption, which are the characteristics of

By using a pulse voltage, a period during which no voltage is applied to the heater wire is used to lower the temperature of the gas detection element, but this is the same phenomenon as a disconnection in that no current flows through the heater. become.

The present invention reliably detects damage to the heater wire, semiconductor, etc. of the gas detection element even during a period when no voltage is applied to the heater, and issues a failure display/alarm.

Next, see the third section regarding the circuit configuration diagram of one embodiment of the present invention.
This will be explained with a diagram. Incidentally, FIG. 4 is a time diagram corresponding to the waveform of the pulse generator of the main part in FIG. 3.

In the figure, PG is a pulse generator, 1 is the gas detection element shown in Figure 1, and the heater wire 1a and the semiconductor 1c (more precisely, the conductivity or resistance value of the semiconductor connected between the electrodes 1d ₁ and 1d ₂ ). ) are included in the supervisory circuit connection. The heater wire 1a on the side connected to the pulse generator PG through the diode D is connected to the power supply through the series resistors R ₁ and R ₂ , and the connection between the resistors R ₁ and R ₂ is connected to the base of the transistor Q ₁ . Ru.
The other end of the heater wire 1a is grounded through a resistor _R3 and connected to the base of a transistor _Q2 through a resistor _R4 . 1 of the semiconductor 1c of the gas detection element 1
One electrode side is grounded through resistor _R5 and connected to the + side input terminal of comparator COM ₁ and the - side input terminal of comparator COM ₂ , and the other electrode side is connected to the + side input terminal of comparator COM 2.
Connected to B ₁ . The collector of transistor _Q1 is grounded through resistor _R7 and connected to NOR circuit NOR.
The collector of the transistor _Q2 is connected to the + power supply terminal _B1 through the resistor _R6 , and the NOR circuit NOR through the inverter INV.
Connected to the other terminal. The negative input terminal of comparator COM ₁ passes through resistor R ₄ to + power supply terminal B ₁ , and also connects to resistor R _9.
and ground E. In addition, the output side of the comparator COM ₁ is grounded through resistors R ₁₀ and R ₁₁ , and also connected to the resistor R ₁₀
The connection between R11 and _R11 is connected to the gate pole of a transistor (or a semiconductor with a gate pole such as a thyristor) _Q3 , and the anode of this transistor _Q3 is connected to the warning indicator LED ₁ resistor _R12 to the alarm display terminal. B ₂ and the cathode of transistor Q ₃ is grounded E. The output side of the NOR circuit NOR is connected to the + side input terminal of the comparator COM ₂ through the resistor R ₁₃ , and this + side input terminal is connected to the + power supply terminal B ₁ through the resistor R ₁₄ .
connected to. The output side of comparator COM ₂ is resistor R ₁₅ ,
It is grounded through R ₁₆ , and the connection between resistors R ₁₅ and R ₁₆ is connected to the gate of transistor (or semiconductor with a gate electrode such as a thyristor) Q ₄ , and the anode of transistor Q ₄ is connected to the fault indicator LED. ₂ to the failure indicating terminal _B3 , and the cathode of the transistor _Q4 is grounded. Figure 4 shows the heater wire 1a and resistance for the pulse voltage of the pulse generator PG.
Voltage drop of R ₃ , on/off of transistors Q ₁ and Q ₂ ,
Inversion status of inverter circuit INV, NOR circuit NOR,
The waveforms for the output of comparator COM ₂ as well as the output of transistor Q ₄ are shown.

Note that in this example, the resistor _R3 and the transistor
Q ₂ serves as the first current detection means for detecting the heating current, resistors R ₁ , R ₂ , transistor Q ₁ and diode D serve as the second current detection means, and the inverter circuit
INV and NOR circuit NOR are the heater burnout determination means.
The resistor R ₅ constitutes the third current detection means, and the comparator COM ₂ and the resistors R ₁₃ and R ₁₄ constitute the semiconductor disconnection determining means.

Next, the operation of the apparatus of the present invention will be explained with reference to FIG. 3 in conjunction with FIG. 4. First, when the gas detection element 1 is normal, a voltage drop across the resistor R ₃ occurs during the period when the voltage is applied to the heater wire 1a according to the pulse voltage from the pulse generator PG, and the transistor Q ₂ is turned on. However, transistor Q ₁ is turned off, and the input on the transistor Q ₁ side of the NOR circuit NOR becomes L (low), and the transistor Q ₂ side is on, and the other input of the NOR circuit NOR becomes H after passing through the inverter circuit INV. (High), the output of the NOR circuit NOR is L, and a voltage obtained by dividing the power supply voltage by resistors _R14 and _R13 is applied to the + side input terminal of the comparator _COM2 .
In addition, if the current flowing through the semiconductor 1c is normal at the negative input terminal of comparator COM ₂ , the voltage drop across resistor _R5 is set higher than the voltage at the positive input terminal, and comparator COM ₂ will output no output. However, transistor Q ₄ is off and failure 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, the resistance R ₃
There is no voltage drop, transistor _Q2 is off, and L is applied to one end of the NOR circuit NOR through the inverter circuit INV. Also, when the transistor _Q1 does not produce an output from the pulse generator PG, it is turned on due to the voltage drop generated across the resistor _R1 , and H is applied to the other end of the NOR circuit NOR.
The output of is L, and in this case as well, the comparator circuit COM ₂ does not output and the transistor Q ₄ remains off, and the failure indicator LED ₂ does not light up either.

However, when the heater wire 1a of the sensing element 1 is disconnected, both the transistors Q ₁ and Q ₂ are turned off, the output of the NOR circuit NOR becomes H, and the voltage at the + side input terminal of the comparator COM ₂ becomes high. COM ₂ takes out the output, voltage is applied to the gate of transistor Q ₄ , transistor Q ₄ 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 1 is disconnected, the voltage drop across the resistor _R5 will be approximately 0V and the comparator COM ₁ will not work, but the negative input terminal of the comparator COM ₂ will drop and the resistance at the positive input terminal will decrease. Since it is lower than the voltage divided by R ₁₄ and R ₁₃ , the output of comparator COM ₂ is taken out, and the gate voltage of transistor Q ₄ is increased appropriately, so it is turned on and the fault indicator LED ₂ is lit. Displays a fault. When detecting gas with the gas detection element, as the resistance value of the semiconductor 1c changes and decreases, the flowing current increases and the voltage drop across the resistor _R5 becomes large, resulting in a voltage of + applied to the negative input terminal of the comparator _COM1 .
The voltage across resistor R ₈ from the power supply terminal is greater than the voltage, so comparator COM ₁ takes out an output and increases the gate voltage of transistor Q ₃ , which turns it on and lights up alarm indicator LED ₁ , as well as transmits the alarm signal to the receiver. It is given to the other side.

Figure 5 is a circuit configuration diagram of an embodiment in which one of the heater and electrode of the gas detection element is used.It is of a gas detector type, unlike the receiver sending type as shown in Figure 3. It can also be used for receiver output types.

In Fig. 5, 1 is a gas detection element of the type shown in Fig. 2, _1d3 is a heater and one electrode, _1d2 is the other electrode with a semiconductor 1c interposed between them, a pulse generator PG, a comparator. COM ₁ , COM ₂ , NOR circuit NOR, alarm indicator LED ₁ , failure indicator
For convenience, the same reference numerals as in FIG. 3 are used for LED ₂ . First, from the pulse generator PG, the diode D is passed through the heater/one electrode _1d3 of the gas detection element 1, and then the resistor _R21 is connected to the + side terminal of the power supply _E1.The connection point of the resistor _R21 on the element 1 side is It is applied to the base of transistor _Q6 through resistor _R23 . Also, a diode D is passed from the pulse generator PG to the emitter of the transistor _Q5 , and then a diode D is connected to the emitter of the transistor Q5.
is grounded through resistors R ₁₈ and R ₁₉ , and is connected to resistor R ₁₈ and
The connection point of _R19 is connected to the base of transistor _Q5 , and the collector of transistor _Q5 is grounded through resistor _R20 and connected to one input terminal of NOR circuit NOR.

The other electrode 1d ₂ of the gas detection element 1 is grounded through a resistor R ₂₂ and connected to the + input terminal of the comparator COM ₁ and the - input of the comparator COM ₂ . The collector of the transistor _Q6 is grounded through a resistor _R24 and connected to the other terminal of the NOR circuit NOR.
The output of the NOR circuit passes through the resistor R ₃₀ to the comparator.
It is applied to the + side input terminal of COM ₂ , and the voltage of power supply E ₁ is applied to both ends _of series resistors R ₂₅ and R ₂₆ .
The connection between R26 and _R26 is connected to the negative input terminal of comparator _COM1 . The output of comparator COM ₁ is connected to resistors R ₂₇ and R ₂₈
The connection between resistors R ₂₇ and R ₂₈ is connected to a gate-polarized semiconductor Q ₇ such as a transistor or SCR.
The anode of the transistor Q ₇ is connected to the + terminal of the power supply E ₁ via the alarm indicator LED ₁ resistor R ₂₉ and its cathode is grounded. Comparator COM ₂
The + side input terminal of the comparator COM 2 is connected to the + power supply terminal through a resistor R ₃₁ , and the output side of the comparator COM ₂ is connected to ground through a resistor R ₃₂ and a failure indicator LED ₂ . Others _E2 is the power supply for the pulse generator PG. or,
Figure 6 shows the pulse generator PG in Figure 5.
heater wire/electrode 1d ₃ for transistor Q ₅ ,
Q ₆ , NOR circuit NOR, comparator COM ₂ , fault indicator light
3 is a response waveform diagram of LED _2. FIG. In addition, in this example,
The resistor R ₂₁ and the transistor Q ₆ serve as the first current detection means, the resistors R ₁₈ and R ₁₉ , the transistor Q ₅ and the diode D serve as the second current detection means, the NOR circuit NOR serves as the heater burnout determination means, and the resistor R ₂₂ constitutes third current detection means, and comparator COM ₂ and resistors R ₃₀ and R ₃₁ constitute semiconductor disconnection determination means, respectively. Next, we will explain the operation of the embodiment of the present device shown in FIG _. Transistor Q ₅ is turned off so that there is no voltage drop and resistor R ₂₀
In other words, one input of the NOR circuit NOR is L (low).
However, there is a resistor R ₂₁ at the base of transistor Q ₆ .
A predetermined voltage is applied due to the voltage drop of , which turns it on, the other input of the NOR circuit NOR becomes H, the output of the NOR circuit NOR becomes L, and the power supply voltage is connected to the + side input terminal of the comparator COM ₂ through the resistor R. The voltage divided by _{R 31} and R ₃₀ is applied, and the voltage across the resistor R ₂₂ applied to the negative input terminal is set higher than the voltage of the positive input terminal, so comparator COM ₂ does not output and fails. Indicator light LED ₂ does not light up. Also, when the pulse generator PG is not producing pulse output,
In other words, during the period when no voltage is applied to the heater, the transistor _Q6 is off and L is applied to one input terminal of the NOR circuit NOR, but the transistor _Q5 is turned on due to the voltage drop that occurs in the resistor _R18 , and the NOR circuit NOR is turned on. H is added to the other input terminal, and the output of the NOR circuit is L, indicating the failure indicator LED ₂ as described above.
does not light up. Next, when the heater wire 1d ₃ is disconnected, both transistors Q ₅ and Q ₆ are turned off,
L is added to the two inputs of the NOR circuit, and the output is H.
Then, the output of comparator COM ₂ is taken out and the failure indicator LED ₂ lights up to notify the failure. Furthermore, when the semiconductor 1c of the gas detection element is disconnected, the voltage across the resistor R ₂₂ becomes almost 0, and the negative input terminal of the comparator COM ₂ naturally becomes lower than the positive input terminal.
COM ₂ takes out the output and lights up the failure indicator LED ₂ to notify the failure. Furthermore, when the gas detection element is in a normal state and gas adsorption is performed, the resistance value of the semiconductor 1c decreases, the current increases, the voltage drop across the resistor _R22 increases, and the voltage applied to the + side input terminal of the comparator _COM1 increases. becomes large and output is taken from comparator COM ₁ ,
Increase the gate voltage of transistor Q ₇ to turn it on and turn on the alarm indicator LED ₁ .
Gas detection can be notified.

As described above, according to the present invention, disconnection of the heater and semiconductor of the gas detection element can be reliably detected and failure can occur, both during the period when voltage is applied to the heater wire of the gas detection element and during the period when the voltage is not applied. can display alarms.

[Brief explanation of the drawing]

1 and 2 are a perspective view of one embodiment of the gas detection element used in the present invention, a schematic diagram of another embodiment, and a third embodiment of the gas detection element used in the present invention.
5 is a circuit configuration diagram of a different embodiment of the present invention,
FIGS. 4 and 6 are response waveform diagrams for the pulse generator in the corresponding portions of FIGS. 3 and 5. In the figure, 1 is a gas detection element, 1a and _1d3 are heater wires 1c are semiconductors, _COM1 and _COM2 are comparators, PG is a pulse generator, _Q1 to _Q7 are transistors,
R ₁ to _{R 32} are resistors, LED ₁ and LED ₂ are indicator lights, INV is an inverter, NOR is a NOR circuit, D is a diode,
E ₁ is the power supply, E ₂ is the power supply for the pulse generator.

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 In 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 a type that is detached from the gas 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 supplying a current for detecting disconnection to the heater wire during a heating stop period by the pulsed power supply;
a second current detecting means for detecting the supplied current; and determining a break in the heater wire when both the first current detecting means and the second current detecting means no longer detect the current; heater disconnection determination means that outputs a disconnection signal; third current detection means that detects a current flowing through the metal oxide semiconductor; and when the current detected by the third current detection means decreases below a predetermined value. A gas leak detection device comprising: semiconductor disconnection determination means for determining whether the metal oxide semiconductor is disconnected or has poor contact and outputs a disconnection signal when the metal oxide semiconductor is disconnected. 2 The first current detection means includes a detection resistor that detects the current flowing in the heater wire, and a first transistor that is turned on by a voltage drop due to the heating current generated in the detection resistor, and The detection means includes a supply resistor that supplies a disconnection detection current to the heater wire in response to the output of the pulse power supply during the heating stop period, and a second transistor that is turned on by a voltage drop occurring in the supply resistor. and the first
2. The gas leak detection device according to claim 1, wherein the outputs of the second transistor and the second transistor are connected to heater disconnection determining means. 3. The heater disconnection determining means includes an inverter to which the output of the first transistor is connected, and a NOR circuit to which the output of the inverter and the output of the second transistor are connected. Gas leak detection device according to item 1.