JPH0519101B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a gas detection device using a catalytic combustion type gas sensor and a compensation sensor.

[Background technology]

The conventional gas detection device, as shown in Fig. 4,
A series circuit of a catalytic combustion type gas sensor GS and a compensating sensor of the same type (compensating for temperature and humidity) GC is connected to a DC power supply E via a switching transistor Tr ₁ , and a pulse power supplied from the DC power supply E is connected. The oscillation circuit OSC drives the switching transistor Tr ₁ on and off at a constant cycle, applies a pulse voltage Vs to the series circuit of the gas sensor GS and the compensation sensor GC, and connects the detection output terminal TM to the connection point of the gas sensor GS and the compensation sensor GC. The sensor output voltage V ₀ is taken out by providing the sensor output voltage V 0 .

As shown in FIG. 5, the gas sensor GS is constructed by applying a catalyst 2 supported on a carrier such as alumina around a platinum wire heater 1. The compensation sensor GC also has the same configuration.

The pulse oscillation circuit OSC consists of an open collector comparator IC ₁ , resistors R ₁ to R ₅ , and a capacitor C.
and diodes _D1 and _D2 , the output of which is input to the base of the switching transistor _Tr1 via a resistor _R6 .

The operation of the gas detection device described above will be explained. When DC power supply E is turned on, capacitor C becomes resistor R ₃
However, while the voltage of capacitor C is lower than the divided voltage of resistors R ₁ and R ₂ , the comparator
IC ₁ is in an output open state, and switching transistor Tr ₁ is off. When the capacitor C is charged and the voltage of the capacitor C exceeds the divided voltage of the resistors R ₁ and R ₂ , the comparator IC ₁ becomes the output low level state and the switching transistor
Tr ₁ turns on and the charge on capacitor C is transferred to resistor R ₄
and is discharged through diode D ₁ , the voltage on capacitor C drops, and also comparator IC ₁
The voltage at the positive input terminal of the resistor _R1 also drops to the voltage divided by the resistors _R2 and _R5 . The discharge of capacitor C progresses, and the voltage of capacitor C increases to resistor R ₁ and resistor R ₂ ,
When it drops to the divided voltage with R ₅ , the comparator IC ₁
becomes the output open state, the switching transistor Tr ₁ is turned off, and the discharging of the capacitor C through the resistor R ₄ is stopped and the charging through the resistor R ₃ is resumed, and the positive input of the comparator IC ₁ The voltage at the end also rises to the divided voltage of resistors R ₁ and R ₂ . After that, repeat the above operation to complete the pulse oscillation circuit.
The OSC will generate pulse oscillation.

The pulse oscillation circuit OSC oscillates a pulse, and when this output switches the switching transistor Tr ₁ , the gas sensor GS and the compensation sensor
A pulse voltage Vs with a constant pulse width as shown in FIG. 6A is applied to the series circuit of the GC, and the series circuit of the gas sensor GS and the compensation sensor GC (the series circuit of two platinum wire heaters) is energized. A platinum wire heater generates heat and raises the catalyst to reaction temperature.

At the detection output terminal TM, a sensor output voltage _V0 , which is obtained by dividing the pulse voltage Vs by the resistance of the platinum wire heater of each of the gas sensor GS and the compensation sensor GC, appears. Under normal conditions, when there is no flammable gas, the platinum wire heater of the gas sensor GS has a resistance value that corresponds to the amount of heat generated by the supplied power, and the sensor output voltage V ₀ is a low value (Fig. 6B). period T ₁ ).

When flammable gas is present, the combustible gas is burned by the catalyst of the gas sensor GS, and the temperature of the catalyst increases, so the temperature of the platinum wire heater increases,
As a result, the resistance value of the platinum wire heater of the gas sensor GS increases and the sensor output voltage V ₀ rises (period T ₂ in Figure 6B), and it is detected that this sensor output voltage V ₀ exceeds a predetermined level. This means that gas detection has been performed.

When the combustible gas concentration becomes even higher, the catalyst temperature of the gas sensor GS becomes extremely high (800℃).
(above), therefore, the temperature of the platinum wire heater also rises, its resistance value increases, and the sensor output voltage V ₀ rises (period T ₃ in FIG. 6B).

After that, when the gas concentration decreases, the gas sensor GS
The catalytic reaction also decreases and the temperature decreases, so the resistance value of the platinum wire heater decreases and the sensor output voltage V ₀ also decreases (period T ₄ in FIG. 6B).

After that, when the combustible gas disappears, the temperature of the gas sensor GS further decreases, and the sensor output voltage V ₀ also becomes the same as the period T ₁ in FIG. 6B (period T ₅ in FIG. 6B).

However, if the catalyst temperature of the gas sensor GS rises abnormally, the catalyst performance changes (deteriorates), resulting in a shortened service life. Although it would be possible to use a material with extremely high heat resistance as the catalyst material for the gas sensor GS, there was a problem in that the cost would be extremely high.

[Purpose of the invention]

An object of the present invention is to extend the life of a gas sensor and provide an inexpensive gas detection device.

[Disclosure of the invention]

The gas detection device of the present invention includes a series circuit of a catalytic combustion type gas sensor and a compensation sensor, a switch element connected between the series circuit of the gas sensor and compensation sensor and a power supply, and a pulse oscillation device that drives the switch element on and off. A circuit, a detection signal output terminal provided at a connection point between the gas sensor and the compensation sensor, and a control circuit that narrows the output pulse width of the pulse oscillation circuit in accordance with an increase in the shared voltage of the gas sensor. Features.

With this configuration, it is possible to prevent the gas sensor from rising above a certain temperature, and therefore, even if the gas sensor uses an inexpensive catalyst with low heat resistance, its performance deterioration is small and its life can be extended.

An embodiment of the present invention will be described based on FIGS. 1 to 3. As shown in Figures 1 and 2, this gas detection device connects a series circuit of a catalytic combustion type gas sensor GS and a compensating sensor of the same type (compensating for temperature and humidity) GS to a switching transistor _Tr1. A pulse oscillation circuit OSC supplied with power from the DC power supply E drives the switching transistor Tr ₁ on and off at a constant cycle to apply a pulse voltage Vs' to the series circuit of the gas sensor GS and the compensation sensor GC. A detection output terminal TM is provided at the connection point of the gas sensor GS and the compensation sensor GC to take out the sensor output voltage V ₀ ', and the voltage at the connection point of the gas sensor GS and the compensation sensor GC, i.e. Pulse oscillation circuit depending on the level of sensor output voltage V ₀ ′
The OSC duty is changed in small and large steps.

The configurations of the gas sensor GS and compensation sensor GC and the configuration of the pulse oscillation circuit OSC are the same as in the conventional example.

The control circuit CT is composed of an open collector type comparator IC ₂ , resistors R ₇ to R ₁₀ and a diode D ₃ .

Next, the operation of this gas detection device will be explained in detail. The pulse oscillation circuit OSC oscillates pulses,
When switching transistor Tr ₁ is switched with this output, a pulse voltage Vs' as shown in FIG. 3A is applied to the series circuit of gas sensor GS and compensation sensor GC, and the series circuit of gas sensor GS and compensation sensor GC is When electricity is applied, the platinum wire heater generates heat, raising the catalyst to the reaction temperature as in the conventional example.

At the detection output terminal TM, a sensor output voltage V ₀ ', which is obtained by dividing the pulse voltage Vs' by the platinum wire heaters of each of the gas sensor GS and the compensation sensor GC, appears. Under normal conditions, when no flammable gas is present, the platinum wire heater of the gas sensor GS has a resistance value that corresponds to the amount of heat generated by the supplied power, and the sensor output voltage V ₀ ' is a low value (Fig. 3). B period
T ₁ ′).

If a flammable gas is present, the flammable gas will be burned by the catalyst of the gas sensor GS, thus increasing the temperature of the platinum wire heater, resulting in the gas sensor
If it is detected that the resistance value of GS increases (period T ₂ ' in FIG. 3B) and this sensor output voltage V ₀ ' exceeds a predetermined level, gas detection is performed. In this case, the oscillation duty of the pulse oscillation circuit OSC is determined by the charge from the resistor _R3 to the capacitor C and the charge from the capacitor C to the comparator _IC2 through the resistor _R4 .
It is determined by the discharge flowing into the area and remains constant.

When the combustible gas concentration becomes abnormally high, the catalyst temperature of the gas sensor GS increases, and the resistance value of the platinum wire heater of the gas sensor GS increases accordingly.
The sensor output voltage V ₀ ' increases. Sensor output voltage
When the level of V ₀ ' exceeds the voltage divided by resistors R ₇ and R ₈ , the output of comparator IC ₂ becomes low level,
Since the capacitor C is now discharged also through the resistor _R10 , the discharge time of the capacitor C is shortened, and the time during which the switching transistor _Tr1 is on is shortened, so that the pulse applied to the gas sensor GS and the compensation sensor GC is shortened. The duty of the voltage Vs' becomes smaller, and therefore the supplied power also decreases, the amount of heat generated by energizing the platinum wire heater decreases, the temperature of the catalyst of the gas sensor GS decreases, and the temperature of the platinum wire heater decreases. The resistance value of the heater decreases, and the sensor output voltage V ₀ ' decreases. When this sensor output voltage V ₀ ' becomes lower than the divided voltage of resistor R ₇ and the parallel circuit of resistors R ₈ and R ₉ , comparator IC ₂
Since the output of is in an open state, the charge of the capacitor C is no longer discharged through the resistor _R10 , the duty of the pulse voltage Vs' increases, the power supplied to the gas sensor GS and the compensation sensor GC increases, and the temperature of the gas sensor GS increases. increases, and the sensor output voltage V ₀ ' also increases. When the sensor output voltage V ₀ ' increases, the output of the comparator IC ₂ becomes low level again, and the duty of the pulse voltage Vs' becomes small. By repeating this operation, even when the gas concentration is high, the temperature of the gas sensor GS (temperature of the platinum wire heater and catalyst)
is kept constant, therefore the resistance value of the platinum wire heater becomes constant, and the sensor output voltage V ₀ ' also remains constant (does not rise above a certain point) as shown in period T ₃ ' in Figure 3, and the gas concentration gas sensor even if it is expensive
The temperature of GS does not become abnormally high and can be maintained at a relatively low temperature. In addition, the period shown in Figure 3B
At T ₃ ′, only the pulse voltage Vs′ with a narrow pulse width is shown, but in reality, narrow and wide pulse widths occur repeatedly depending on the sensor output voltage V ₀ ′, and the sensor temperature is held constant, that is, the sensor output voltage V ₀ ' is held constant.

After that, when the gas concentration decreases, the gas sensor GS
The catalytic reaction also decreases and the temperature decreases, so the resistance value of the platinum wire heater decreases, the sensor output voltage V ₀ ' decreases (period T ₄ ' in Figure 3), and the pulse voltage decreases.
The pulse width of Vs′ remains wide.

After that, when the combustible gas disappears, the temperature of the gas sensor GS further decreases, and the sensor output voltage V ₀ ' becomes the same as the period T ₁ ' in FIG. 3B (period T ₅ ' in FIG. 3B).

As a result of this configuration, when the gas concentration increases, the catalytic reaction becomes more intense, the temperature rises, and the sensor output voltage V ₀ ' increases, the pulse oscillation circuit OSC
Narrow the pulse width of the output pulse and reduce the pulse voltage
The duty of Vs′ can be reduced to reduce the power supply, the temperature of the gas sensor GS can be kept constant (not raised above a certain temperature), and the gas sensor uses an inexpensive catalyst with low heat resistance.
The lifespan of GS can be extended.

[Effects of the Invention] As described above, according to the gas detection device of the present invention, the electric power necessary for preheating can be supplied in a warning state where flammable gas is not present, and gas detection can be performed reliably and quickly. It can be carried out.

Moreover, since the power supplied to the gas sensor is suppressed in the gas detection state, it is possible to prevent the gas sensor from rising in abnormal temperature due to heat generated by the catalytic reaction, and it is possible to protect the gas sensor from overheating. In other words, in the gas detection state, when the gas concentration is high and the catalytic reaction becomes intense and the temperature of the gas sensor rises, the power supplied to the gas sensor is suppressed, which prevents abnormal temperature rises of the gas sensor and improves heat resistance. Even a gas sensor using an inexpensive catalyst with a low temperature can have a sufficiently long life.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a specific circuit diagram thereof, FIG. 3 is a waveform diagram for explaining its operation, FIG. 4 is a circuit diagram of a conventional gas detection device, and FIG. Figure 5 is a schematic diagram showing the configuration of the gas sensor.
FIG. 6 is a waveform diagram for explaining the operation. GS...Gas sensor, GC...Compensation sensor, OSC...Pulse oscillation circuit, CT...Control circuit.

Claims (1)

[Claims] 1. A series circuit of a catalytic combustion type gas sensor and a compensation sensor, a switch element connected between the series circuit of this gas sensor and compensation sensor and a power supply, a pulse oscillation circuit that turns on and off this switch element, and the gas sensor and compensation sensor. A gas detection device comprising: a detection signal output terminal provided at a connection point of a sensor; and a control circuit that narrows the output pulse width of the pulse oscillation circuit in accordance with an increase in the shared voltage of the gas sensor.