JPH01265149A - Sensor of concentration detector for combustible gas and concentration detector for combustible gas - Google Patents

Abstract

PURPOSE:To enable the use of the sensor for detecting the concn. of a high- concn. combustible gas by printing a heating resistor on a substrate formed of ceramics and allowing the heating resistor to function as a catalyst and a resistor for detecting calorific value. CONSTITUTION:The sensor element 1 is constituted by printing the resistor 3 essentially consisting of platinum, rhodium or palladium, etc., by a paste printing method on a base plate 2 which is made of thin sheet-like ceramics formed by calcination of alumina or silica-alumina at about 1,500 deg.C. This element is energized as a heater in order to detect the concn. of the combustible gas and the combustible gas is burned by the catalytic effect of the platinum, rhodium or palladium printed as the resistor 3 on the base plate 2. The resistance value of the resistor 3 is then detected and the temp. thereof is controlled constant. The sensor element 4 has exactly the same constitution as the constitution of the sensor element 1 except that the catalytic function of the resistor 6 is eliminated.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a sensor and a combustible gas concentration detection device for detecting the concentration of combustible gas contained in gas, and particularly relates to a sensor for detecting the concentration of flammable gas contained in gas, and particularly to This is effective in detecting the concentration in the canister of an automobile.

[Prior Art] Conventionally, as shown in FIG. 8, a sensor for detecting the concentration of combustible gas has been used, in which a platinum wire 60 in a substantially coil shape is covered with ceramic black 1, and a platinum catalyst 62 is supported on the ceramic 61. 63 and the invention introduced in Japanese Unexamined Patent Publication No. 56-89049, a sensor is used in which a resistance wire is printed on the surface of a ceramic substrate and an oxidation catalyst is supported on a part of the resistance wire.

In the former case, as shown in FIG. 9, as a measurement circuit, a platinum wire 60 is provided as a heating resistor between F-0 of the bridge circuit 64, and the heat generated when the platinum wire 60 is energized , the combustible gas is combusted by the catalytic action of the platinum catalyst 62. At this time, the resistance value of the platinum wire 60 changes due to combustion heat, so the potential difference between point F and point H, which changes accordingly, is used as an output signal for concentration detection. On the other hand, when using the latter sensor, the resistance wire printed on the ceramic substrate surface is a heat-generating resistor, so the concentration is detected by a circuit equipped with a separate detection resistor to detect the amount of combustion. . In Fig. 9, 65 and 66 are fixed resistors, and 67 is a temperature-dependent resistor for compensating for changes in the resistance value of the platinum wire 60 due to outside temperature and air flow. This is platinum resistance wire.

[Problem to be solved by the invention] ゛ However, in a highly concentrated flammable gas such as in the canister of an automatic transmission, the amount of combustion tends to increase and the combustion temperature becomes high. When combustion begins, the catalytic function improves due to the heat of combustion and combustion is promoted, and the combustion temperature rapidly rises by 1, regardless of the current status of the platinum wire, etc., and so-called thermal runaway tends to occur.As a result, the output signal The platinum wire may drift, making it impossible to obtain accurate measurements, or the platinum wire itself may melt due to overheating.
It may become unusable. Also, in the circuit of Fig. 9,
Uramasa does not take into account changes in catalyst function when the temperature of the catalyst changes with combustion.

An object of the present invention is to provide a sensor for detecting the concentration of combustible gas that can be used to detect the concentration of combustible gas at a high concentration. It is an object of the present invention to provide a combustible gas concentration detection device that does not change and can accurately detect the concentration.

[Means for Solving the Problems] The present invention heats a heating resistor by applying electricity to burn the combustible gas by the action of a catalyst, and detects the amount of heat generated by the combustion to burn the combustible gas. In a sensor for a combustible gas concentration detection device that detects the concentration in a gas, the sensor consists of a substrate molded from ceramic and a heating resistor printed on the substrate, and the heating resistor has a catalytic function. The technical means is that the resistor has the following properties and is also used as a detection resistor for detecting the amount of heat generated.

Also, a flammable gas concentration detection device that heats a heating resistor with electricity, burns the flammable gas by the action of a catalyst, and detects the amount of heat generated by the combustion to detect the concentration of the flammable gas in the gas. A first heating resistor having a catalytic function and a second heating resistor not having a catalytic function are disposed in the gas, and the first heating resistor and the second heating resistor are controlled to a constant temperature based on their respective resistance values, and the concentration of the flammable gas is detected based on the power consumption of the first heating resistor and the power consumption of the second heating resistor. technical means to do so.

[Operation and Effects of the Invention] In the first invention, a heating resistor having a catalytic function is printed on a ceramic substrate. Therefore, since the heat generated during combustion can be dissipated to the ceramic substrate, it is possible to suppress an increase in the temperature of the heat generating resistor due to combustion. Furthermore, the combustion temperature of the combustible gas can be directly detected by the heating resistor, which is a catalyst. Therefore, the current value of the heating resistor can be quickly controlled based on the detected combustion temperature, and the combustion temperature can be easily controlled, so that the temperature field can be further suppressed. Therefore, the sensor does not overheat even when used to detect high concentrations of combustible gases, resulting in high IA1. It can also be used to detect the concentration of combustible gas.

In the second invention, the heat generation temperature of the first heat generating resistor with catalytic action is controlled to a constant temperature based on its resistance value, and the power consumption is controlled according to the temperature change of the combustible gas and the gas flow rate or temperature change. changes.

On the other hand, the heat generation temperature of the second heat generating resistor, which does not have a catalytic function, is also controlled to a constant temperature based on its resistance value, but the power consumption changes only according to changes in the gas flow rate and temperature. It does not change in response to changes in gas concentration. At this time,
Since the first heat generating resistor having a catalytic function is controlled to a constant temperature, the catalytic action does not change by temperature. Therefore, the concentration of flammable gas can be determined from the power consumption of the first heating resistor and the power consumption of the second heating resistor. can do. Therefore, highly accurate concentration detection can be performed.

[Example code] Next, the present invention will be explained based on examples.

1 to 3 show a first embodiment of a sensor of a combustible gas concentration detecting device according to the present invention.

The sensor element 1 shown in FIG. 1 is made of alumina or silica.
A resistor 3 whose main component is platinum, rhodium, palladium, etc. is printed on a ceramic substrate 2 in the form of a thin plate made of alumina fired at about 1550°C.
C is printed. This heater is energized to detect the concentration of combustible gas, and the combustible gas is burned by the catalytic action of platinum, rhodium, or palladium printed as a resistor 3 on the substrate 2, and the resistance value of the resistor 3 is is detected and its temperature is controlled to a constant temperature.

Further, the sensor element "F4" is composed of a substrate 5 and a low antibody 6 having exactly the same structure as the sensor element T-1, and a resistor 6.
was surface-treated in a lead atmosphere to eliminate its catalytic function. This sensor element 4 is used to compensate for temperature when the gas flow velocity or temperature changes, and the low antibody 6 is energized as a heater like the sensor element 1, and its resistance value The temperature is controlled at a constant temperature based on

Lead wires 7 and 8 for conducting current are connected to both ends of the resistor 3 of the sensor element 1 by soldering, brazing, etc., and one end of the resistor 3 is connected to one end of the resistor 6 of the sensor element 4. A lead wire 8 is connected to one fd11, and a lead wire 9 is connected to the other fd11.

As shown in Fig. 2, the sensor elements 1.4 are arranged at intervals so that each low antibody 3.6 faces the sensor elements 1.4, and are mounted using resin cement onto hexagonal bolts 10, etc. The same name is given by the fixing agent such as 1~, and it is used to avoid 75 winds,
It is covered with a wire mesh 11 to prevent combustion from spreading.

Alternatively, each sensor element 1.4 may be integrally arranged by aligning the surfaces of each substrate 2.5 on which the resistor 3.6 is not printed, as shown in FIG.

In this case, instead of providing two substrates, resistors may be printed on each of the front and back sides of one substrate. Furthermore, a can-shaped protector 12 is used instead of the wire mesh 11 that protects the board.
The protector 12 may be provided with ventilation holes 12a.

Next, a second embodiment of the sensor of the present invention is shown in FIGS. 4 and 6.

As shown in FIG. 4, two resistors 14 and 15 as platinum heaters are continuously printed on one side of a ceramic substrate 13 having the same composition as in the first embodiment. 14 is coated with a coating agent 16 made of alumina or mullite to form a porous protective layer, as shown in FIG.
In order to eliminate the catalytic function of No. 5, a coating material 17 mixed with glass is coated to form an airtight snow protection layer.

Each coating agent 16.17 has an average particle size of about 1.6[
, czm], alumina with a specific surface area of about 2n(/g), and the glassy material of the coating agent 17 is Si.

02, MgO, and CaO in an amount of 8% by weight.

After the lead wires 7.8.9 are connected, the substrate 13 coated with the coating agents 16, 17 having different properties is removed in the same manner as in the above embodiment, as shown in No. 6 [i'I]. The attachment is fixed to a hexagonal bolt 10 or the like of C using a bonding agent such as resin cement, and is protected by a protector 12.

Each sensor shown in the first and second embodiments described above is fixed, for example, in a canister of an automobile by a hexagonal bolt 10.

Each sensor having the above configuration is used as a sensor of a combustible gas alcohol level detection device 7I20 according to the present invention whose circuit is shown in FIG.

This concentration detection device 20 includes a combustion detection circuit 30, a compensation circuit 40, and an arithmetic circuit 50.

The combustion detection circuit 30 includes a resistor 31 which has a catalytic function and is also a heat generating element connected in series with a resistor 32, and a resistor 33.
A series circuit consisting of a resistor 34 and a resistor 34 are connected in parallel to form a bridge circuit Ii! 835 and control the potentials of the connection point A between the resistor 31 and the resistor 32 and the connection point B between the resistors 33 and 34 with respect to the ground electrode C to be the same using the operational amplifier 36 and the transistor 37. Resistor 31
control the temperature to a constant temperature.

In this combustion detection circuit 30, heat is generated by applying electricity to the resistor 31, and combustion occurs due to its catalytic action.
The energizing current is controlled according to the resistance value of the resistor 31, and the energizing current is controlled to decrease as the combustion amount increases.

Furthermore, since the resistor 31 is provided on the ceramic substrate, the heat generated during combustion is dissipated to the ceramic substrate, so that combustion will not be accelerated and temperature control will not become impossible. Here, the power consumption of the resistor 31 changes depending on the concentration of the detected combustible gas, and also changes depending on the gas flow rate or the change in temperature.

In the compensation circuit 40, a resistor 41 which is a heating element but does not have a catalytic function is connected in series with a resistor 42.
A bridge circuit 45 similar to the combustion detection circuit 30 is constructed by connecting a series circuit consisting of a resistor 41 and a resistor 44 in parallel in a parallel line, and a bridge circuit 45 similar to the combustion detection circuit 30 is constructed. The temperature of the resistor 41 is controlled to a constant temperature by controlling the potentials of the point p] to the ground electrode C to be the same by the operational amplifier 46 and the transistor 47.

Since the compensation circuit 40 controls the temperature of the resistor 41, which does not have a catalytic function, the power consumption changes only in accordance with changes in the gas flow rate or the temperature.

The arithmetic circuit 50 turns off each resistor 31 and 41 of the combustion detection circuit 30 and the compensation circuit 40! - Only the electric power generated by the flammable gas is determined from the applied voltages at the connection points A and D, which respectively indicate electric power. That is, when there is no flammable gas, the voltage applied to the resistor 31 and the voltage applied to the resistor 41 both change when the gas flow rate or temperature changes; body 3
Since the change in the voltage applied to the resistor 41 is different from the change in the voltage applied to the resistor 41, the concentration signal of the combustible gas 11 can be obtained from these signals.

In the arithmetic circuit 50, the operational amplifier 51 differentially amplifies the voltage difference between the connection point A and the connection point and outputs it as a C concentration detection signal.

In the concentration detection device 20, the resistor 31 and the resistor 41 correspond to the resistors 3 and 6, respectively, in the first embodiment of the sensor, and correspond to the resistors 14 and 6 in the second embodiment, respectively. This corresponds to the resistor 15.

The combustible gas concentration detection device 20 having the above configuration is as follows:
It works as follows.

When there is no change in the gas flow rate or temperature for which the concentration of flammable gas is detected, the power consumption of the resistor 41 remains unchanged regardless of whether flammable gas is present or not. On the other hand, the resistor 31 is heated by the heat generated by energization and the reaction heat generated by burning the combustible gas by the catalytic action.

However, in response to the heat generated during combustion, the current flowing through the resistor 31 is reduced ζ, and the resistance value of the resistor 31 is controlled to be constant. Temperature does not change. Therefore, since the catalytic function does not change due to temperature, a concentration detection signal can be obtained from the power consumption.

When there is a change in the flow rate or temperature of the gas whose concentration of combustible gas is detected, the power consumption of the resistor 41 changes.

On the other hand, the power consumption of the resistor 31 also changes depending on the gas flow rate or temperature change. Further, the power consumption of the resistor 31 changes depending on the concentration of combustible gas. Therefore, the power consumption of the resistor 31 that changes at this time includes a change due to the temperature change and a change due to the combustible gas. However, the change due to flow velocity or temperature change is
1, so only the change due to combustible gas (hi) can be found. At this time, the change in resistor 3
1 is maintained at a constant temperature, the catalytic action will take place at a constant temperature.

As described below, in the sensor of the present invention, platinum, which has a catalytic action, is printed on the ceramic substrate surface as a heating element and is also used as a detection resistor, so the amount of heat generated can be controlled based on the resistance value. You can also do
Even if combustion occurs due to catalytic action, the sensor temperature will not rise by -L.

Therefore, it can be used to detect the concentration of high-concentration combustible gas.

In the combustible gas concentration detection device of the present invention, the temperature of the catalyst that burns the combustible gas is controlled to be constant, so the catalyst temperature does not change depending on the combustible gas concentration and the catalytic performance does not change. Furthermore, since the influence of changes in flow velocity or temperature is detected by four independent compensation paths, highly accurate concentration detection signals can be obtained.

[Brief explanation of the drawing]

1 to 3 all show a first embodiment of the sensor of the present invention, and FIG. 1 shows the sensor substrate on the disassembled lower surface 1'threshold;
Figure 2 is a side view with a part cut away showing the state of the assembly, Figure 3 is a side view with a part cut away showing the state of other assemblies, and Figures 4 to 6 are Figures 4 and 5 are 1) side views showing the manufacturing process of the sensor board, and Figure 6 is a partially cutaway side view showing the assembled state. , FIG. 7 is a circuit diagram showing an i1 combustible gas concentration detection device according to the present invention, FIG. 8 is a diagonal PA diagram showing a conventional sensor, and FIG. 9 is a circuit diagram showing a conventional combustible gas concentration detection device. FIG. In the figure, 1... sensor element (sensor), 2... substrate,
3...Resistor (heating resistor, catalyst, detection resistor),
20...Concentration detection device (combustible gas concentration detection device),
31...Resistor (first heating resistor), 41...Resistor (second heating resistor).

Claims (1)

[Scope of Claims] 1) A combustible device that heats a heating resistor by applying electricity, burns a flammable gas by the action of a catalyst, and detects the amount of heat generated by the combustion to detect the concentration of the flammable gas in the gas. In a sensor for a concentration detection device for a toxic gas, the sensor includes a substrate molded from ceramic and a heating resistor printed on the substrate, and the heating resistor has a catalytic function and detects the amount of heat generated. A sensor for a combustible gas concentration detection device, characterized in that it is also used as a detection resistor. 2) A heat-generating resistor is electrically heated to burn the combustible gas by the action of a catalyst, and the amount of heat generated by the combustion is detected to determine whether the gas in the combustible gas has a catalytic function. A heating resistor and a second heating resistor having no catalytic function are arranged, and the first heating resistor and the second heating resistor are controlled to a constant temperature based on their respective resistance values. and the concentration of the flammable gas is detected based on the power consumption of the first heating resistor and the power consumption of the second heating resistor. .