JP2014132241A - Gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detector capable of supplying the amount of electric power necessary for a resistor for a heater even when a battery voltage varies while a pulse voltage is being applied to the resistor for a heater.SOLUTION: A gas detector includes: a gas sensitive body 20 in which a value of resistance changes according to gas concentration; a resistor 21 for a heater which heats the gas sensitive body 20; a heater drive part 13 which supplies a pulse voltage to the resistor 21 for a heater with a battery 14 being a power source; a gas detection part 10c; a voltage measurement part 10b; and a control part 10a. The voltage measurement part 10b measures the pulse voltage applied to the resistor 21 for a heater. Based on the voltage value measured by the voltage measurement part 10b while the pulse voltage is being applied to the resistor 21 for a heater, the control part 10a controls time width of the pulse voltage applied to the resistor 21 for a heater next time in such a manner that the amount of electric power supplied to the resistor 21 for a heater becomes constant.

Description

  The present invention relates to a gas detection device.

  Conventionally, the battery voltage applied to the heater resistance wire is measured, and the pulse application time of the pulse voltage applied to the heater resistance wire is set so that the amount of power supplied to the heater resistance wire is constant based on this voltage value. There was a battery-driven gas detection alarm to be controlled (see, for example, Patent Document 1).

JP-A-11-248659

  The gas detection alarm described above controls the pulse application time of the pulse voltage based on the battery voltage applied immediately before the heater resistance wire.

  By the way, the output voltage of the battery drops as the internal resistance increases due to an increase in energy consumption. Therefore, the amount of power supplied to the heater resistor by the battery may be lower than the amount of power required to heat the heater resistor to a predetermined temperature.

  If a predetermined amount of electric power is not supplied to the heater resistor, the gas sensitive body is not heated to the target temperature, which affects the gas sensitivity characteristics.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide power necessary for the heater resistor even if the battery voltage fluctuates while the pulse voltage is applied to the heater resistor. An object of the present invention is to provide a gas detection device capable of supplying a quantity.

  The invention of claim 1 includes a gas sensitive body, a gas detection unit, a heater resistor, a heater driving unit, a voltage measurement unit, and a control unit. The resistance value of the gas sensitive body changes according to the gas concentration. The gas detection unit detects gas from a resistance value of the gas sensitive body. The heater resistor heats the gas sensitive body. The heater driving unit supplies a pulse voltage to the heater resistor. The voltage measuring unit measures a pulse voltage applied to the heater resistor. Based on the voltage value measured by the voltage measuring unit while a pulse voltage is being applied to the heater resistor, the control unit controls the heater power so that the amount of power supplied to the heater resistor is constant. Controls the time width of the next pulse voltage applied to the resistor.

  According to a second aspect of the present invention, in the first aspect of the invention, the heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source, and the voltage measuring unit applies a pulse being applied to the heater resistor. The voltage value of the voltage is continuously measured. The continuous measurement means that the voltage measuring unit constantly measures the voltage value of the pulse voltage or measures at a constant time interval while the heater driving unit is applying the pulse voltage. .

  According to a third aspect of the present invention, in the first aspect of the invention, the heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source, and the voltage measuring unit applies a pulse being applied to the heater resistor. The voltage value of the voltage is measured at the start and end of application of the pulse voltage.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source, and the voltage measuring unit applies a pulse being applied to the heater resistor. The voltage value of the voltage is measured when half of the application time has elapsed.

  According to the first aspect of the present invention, even when the power supply voltage gradually changes, the control unit determines the time width of the pulse voltage to be applied next time based on the voltage value of the pulse voltage being applied to the heater resistor, and drives the heater. By operating the unit, the power source supplies the heater resistor with the amount of power necessary to heat the gas sensitive body to a predetermined temperature.

  According to the invention of claim 2, the voltage measuring unit continuously measures the battery voltage being applied to the heater resistor, and the time width for applying the next pulse voltage to the heater resistor based on the measured voltage value is determined. When the control unit estimates more accurately and operates the heater driving unit, the battery power supply reliably supplies the electric power necessary for heating the gas sensitive body to a predetermined temperature to the heater resistor.

  According to the invention of claim 3, the voltage measuring unit measures the battery voltage at the start and end of application of the pulse voltage, and the control unit determines the time width of the pulse voltage based on the measured two voltage values. decide. Compared with the case where the time width is obtained from the multipoint voltage values, the processing of the measurement values can be simplified, and the power consumption required for driving the measurement unit can be suppressed.

  According to the invention of claim 4, the battery voltage is measured at the time when half of the application time of the pulse voltage has elapsed, and the control unit estimates the voltage drop of the battery voltage based on the voltage value at this time, and the pulse voltage Determine the time span. Since the battery voltage may be measured once, the processing of the measured value can be further simplified as compared with the case where the time width is obtained from the two voltage values, and the power consumption required for driving the measuring unit can be further suppressed.

It is a schematic circuit diagram of this embodiment. It is sectional drawing of the package which accommodated the gas sensitive body used for the same as the above. It is the perspective view which fractured | ruptured a part of the state in which the package used for the same was stored in the outer case. The application time and measurement time of the battery voltage are shown, (a) is the operation timing of the heater drive unit 13, (b) is the voltage V2 applied to the heater resistance, and (c) to (e) are voltage measurement units. It is a figure which shows the voltage value Vh output to the timing which 10b measures the voltage V2, and the control part 10a. It is a time chart explaining operation | movement same as the above, (a) is a figure which shows the change of resistance value Rs of a gas sensitive body, (b) is a figure which shows the timing of alerting | reporting output.

  Hereinafter, an embodiment in which the present invention is applied to a gas alarm that issues a gas leak alarm when the concentration of combustion gas (for example, methane) exceeds an alarm level will be described with reference to FIGS. Needless to say, the gas detection device according to the present invention is not limited to a gas alarm, and may be applied to a device that detects the degree of air contamination or a device that detects odor gas.

  FIG. 1 is a block diagram of a gas detection device. The gas detection device includes a gas sensitive body 20, a heater resistor 21, a center electrode 22, a switching element Q1, a signal processing circuit 10, a notification circuit 11, And a voltage stabilizing circuit 12.

The gas sensitive body 20 is made of, for example, a sintered body of a metal oxide semiconductor such as tin oxide (SnO ₂ ), and the electrical resistance, which is an electrical characteristic value, changes in response to the sensitive gas in the atmosphere. As the concentration of the combustion gas increases, the electric resistance of the gas sensitive body 20 decreases due to the oxidation-reduction reaction of the gas sensitive body 20. In this type of gas sensitive body 20, the temperature range in which the gas sensitivity is high depends on the type of gas. For example, in a relatively high temperature range around 400 ° C., the sensitivity of methane, which is a combustion gas, is sufficiently high compared to the sensitivity of carbon monoxide, which is an incomplete combustion gas. From the resistance value change in this temperature range, It is possible to selectively detect methane. In addition, in the relatively low temperature range around 80 ° C., the sensitivity of carbon monoxide, which is an incomplete combustion gas, is sufficiently high compared to the sensitivity of methane, which is a combustion gas. From the resistance value change in this temperature range, It is possible to selectively detect carbon monoxide. It should be noted that the temperature range sensitive to the gas is the required gas detection accuracy, the composition of the gas sensitive body 20, the type of gas, and the concentration at the time of gas detection assumed for that gas (that is, the alarm judgment level). (Concentration) and the like.

  The metal oxide semiconductor that is the material of the gas sensitive body 20 preferably supports a catalyst that reduces the sensitivity to various gases. Examples of such catalysts include palladium (Pd), tungsten (W), platinum (Pt), rhodium (Rh), cerium (Ce), molybdenum (Mo), vanadium (V), and the like. One type of these catalysts may be used alone, or two or more types may be used in combination. In particular, when Pd is used as the catalyst, the responsiveness of the gas sensitive body 20 is improved. That is, as the gas concentration increases, the time required for the electric resistance to stabilize after the electric resistance of the gas sensitive body 20 starts to change is shortened.

  The heater resistor 21 is formed by winding a noble metal wire (for example, platinum wire) in a coil shape and is embedded in the gas sensitive body 20, and both ends thereof are exposed to the outside of the gas sensitive body 20. The heater resistor 21 is connected between both ends of the battery 14 via the switching element Q1.

  The center electrode 22 is made of a rod-like noble metal wire (for example, platinum wire) and is embedded in the gas sensitive body 20 so as to penetrate the center of the heater resistor 21 formed in a coil shape, and both ends thereof are gas sensitive bodies. 20 are exposed to the outside. One end of the center electrode 22 is connected to the input terminal T3 of the signal processing circuit 10 and to the output terminal of the voltage stabilizing circuit 12 via the load resistor R1 and the transistor Q2. The base of the transistor Q2 is connected to the output terminal T2 of the signal processing circuit 10. An equivalent circuit of the gas sensitive body 20 is shown in FIG. 1, and the resistance value of the gas sensitive body 20 between one end of the heater resistor 21 and the center electrode 22 is Rs.

  The switching element Q1 is composed of, for example, an FET (Field Effect Transistor), and its gate electrode is connected to the output terminal T1 of the signal processing circuit 10 and is switched on / off according to the output signal from the signal processing circuit 10. Here, the heater drive unit 13 is configured by the switching element Q1 and a control unit 10a of the signal processing circuit 10 described later.

  The signal processing circuit 10 is composed of a microcomputer, and a control unit 10a, a voltage measurement unit 10b, and a gas detection unit 10c are realized by executing a control program whose calculation function is built in.

  The voltage measuring unit 10b takes in the voltage V2 applied to the heater resistor 21 from the input terminal T4, performs A / D conversion, and outputs the voltage value Vh to the signal processing circuit 10a.

  In accordance with the voltage value Vh output by the voltage measuring unit 10b, the control unit 10a determines the time width of the pulse voltage applied to the heater resistor 21 so that the gas sensitive body 20 is heated to a predetermined temperature. The control unit 10a outputs the duty signal having the determined time width from the output terminal T1 to the gate electrode of the switching element Q1, so that the amount of electric power necessary to heat the gas sensitive body 20 to a predetermined temperature is supplied to the battery power source. Is supplied to the heater resistor 21. For example, in the case of a combustion gas such as methane, the sensitivity of the gas sensitive body 20 becomes higher than the sensitivity to other gases when the temperature of the gas sensitive body 20 is about 400 ° C. Therefore, the power consumption of the heater resistor 21 is reduced. The signal processing circuit 10a determines the time width of the pulse voltage so as to be about 150 mW according to the voltage value Vh, and turns on the output of the output terminal T1.

  The gas detection unit 10c turns on the transistor Q2 by the output signal from the output terminal T2, and applies the voltage V1 input to the input terminal T3 in a state where a constant voltage is applied to the series circuit of the load resistor R1 and the gas sensitive body 20. A / D convert and capture. Here, when the electric resistance of the gas sensitive body 20 changes according to the gas concentration, the voltage division ratio between the load resistance R1 and the gas sensitive body 20 changes, and the voltage V1 of the center electrode 22 changes. For example, in the case of a combustion gas such as methane, when the gas concentration increases, the electric resistance of the gas sensing body 20 decreases, so that the voltage V1 of the center electrode 22 decreases due to the change in the partial pressure ratio. The gas detection unit 10c obtains the resistance value Rs of the gas sensitive body 20 from the voltage V1 input to the input terminal T3, and obtains the gas concentration from the resistance value Rs.

  The voltage stabilization circuit 12 includes a diode D1 and a capacitor C1, and the battery 14 charges the capacitor C1 to a constant voltage via the diode D1. The voltage stabilizing circuit 12 supplies a constant voltage to the signal processing circuit 10 and the like.

  The notification circuit 11 includes a speaker that outputs a notification sound (alarm sound) such as a buzzer sound or a voice message, for example, and outputs a predetermined notification sound according to an output signal from the signal processing circuit 10.

  As shown in FIG. 2, a heater resistor 21 and a center electrode 22 are embedded in the gas sensitive body 20. The center electrode 22 is disposed so as to penetrate the center of the heater resistor 21 formed in a coil shape.

  As shown in FIGS. 2 and 3, the gas sensitive body 20 is housed in a package 30 including a base 31 and a case 32. The base 31 is formed in a disc shape with an insulating resin, and three lead terminals 33a, 33b, 33c are provided so as to penetrate the base 31 in the thickness direction. Both ends of the heater resistor 21 are welded to the lead terminals 33a and 33b, respectively, and one end of the center electrode 22 is welded to the lead terminal 33c. The case 32 is integrally provided with a cylindrical tube portion 32a and an upper plate portion 32b provided so as to project inward from the upper end portion of the tube portion 32a, using a metal material. A ventilation through hole 32c is provided at the center of the upper plate portion 32b, and a stainless steel wire mesh 34, for example, is attached to the through hole 32c in order to suppress entry of dust and dirt.

  The package 30 is housed in an outer case 40 made of synthetic resin. The outer case 40 includes a cylindrical tube portion 40a having an inner diameter slightly larger than the outer diameter of the tube portion 32a, and an upper plate portion 40b provided so as to project inward from the upper end portion of the tube portion 40a. Is integrated. An opening 40c for ventilation is provided in the center of the upper plate portion 40b, and a stainless steel wire mesh 41 is attached to the opening 40c. The package 30 is housed inside the outer case 40 with the through hole 32c facing inward, and a filter 42 is disposed in the gas flow path between the through hole 32c and the opening 40c. The filter 42 is formed of, for example, activated carbon, silica gel, or the like, or may be formed of a material combining activated carbon and silica gel. When the filter 42 is provided, miscellaneous gas (for example, NOx, vapor of organic solvent such as alcohol) or poisonous gas (for example, silicon vapor) contained in the gas flowing into the outer case 40 from the opening 40c is filtered. 42 is removed. Thereby, since miscellaneous gas and poisonous gas flowing into the package 30 are reduced, erroneous detection due to miscellaneous gas is suppressed, and the gas sensitive body 20 is not easily poisoned by poisonous gas.

By the way, the above-mentioned gas sensitive body 20 is produced by an appropriate method. For example, when the oxide semiconductor contained in the gas sensitive body 20 is SnO ₂ , SnO ₂ powder prepared by an appropriate technique is used. For example, an aqueous solution of SnCl ₄ is hydrolyzed with NH ₄ to prepare a stannic acid sol. The stannic acid sol is air-dried and then baked in an air atmosphere at 550 to 700 ° C. for 0.5 to 3 hours. When the SnO ₂ lump obtained by this firing is pulverized, SnO ₂ powder is obtained. To the powdered SnO ₂ is supported palladium (Pd) is impregnated with an aqua regia solution of Pd in the SnO ₂ powder, calcined 1 hour at for example 500 ° C. in air atmosphere. The amount of Pd supported can be 1.7% by mass with respect to SnO _2, for example. In addition to Pd, tungsten (W) may be supported at 5% by mass with respect to SnO ₂ . In addition to Pd and W, SnO ₂ contains one or more of platinum (Pt), rhodium (Rh), cerium (Ce), and molybdenum (Mo) at about 0.5 mass% with respect to SnO ₂ . It may be supported. When aggregate is used, SnO ₂ powder and aggregate powder such as alumina (α-alumina) are mixed. When an organic solvent such as polyethylene glycol, glycerin or terpineol is added to this mixture, a paste-like mixture is prepared. When this paste-like mixture is applied around the heater resistor 21 and the center electrode 22 supported by the lead terminals 33a to 33c and baked in an air atmosphere at 500 ° C. for 1 hour, for example, the gas sensitive body 20 is formed. It is formed.

  The gas sensitive body 20 can be formed in an appropriate shape such as a flat plate shape or a spherical shape (including an elliptical spherical shape), and the size of the gas sensitive body 20 is also designed appropriately. In this embodiment, as shown in FIG. 2, the gas sensitive body 20 is formed in an elliptical shape having a diameter in the longitudinal direction of about 0.5 mm and a diameter in the short side direction of about 0.3 mm. When the gas sensitive body 20 is formed in a spherical shape, the gas sensitive body 20 can be reduced in size as compared with the case where the gas sensitive body 20 is formed in a flat plate shape or a cylindrical shape. The heat capacity can be reduced. In the present embodiment, the heater 21 and the center electrode 22 are embedded in the spherical gas sensitive body 20, and the gas sensor 20 that directly heats the gas sensitive body 20 with the heater resistance 21 is described as an example. The gas sensor may be a gas sensor in which a gas sensitive body is disposed on an insulating substrate such as alumina and the gas sensitive body is indirectly heated by a heater disposed on the back surface of the insulating substrate.

  The gas detection device of this embodiment has the above-described configuration, and the operation thereof will be described below.

  When the battery 14 is connected to the circuit and a voltage is supplied from the voltage stabilization circuit 12 to the signal processing circuit 10, the signal processing circuit 10 performs an initialization operation and then starts detection of combustion gas.

  In the initial operation, the control unit 10a sets the time width T of the pulse voltage applied to the heater resistor 21 as an initial value, and outputs a duty signal from the output terminal T1 so that the ON period becomes the time width T, thereby switching the switching element Q1. Is turned on, and the battery voltage is applied to the heater resistor 21.

  While the battery voltage is being applied to the heater resistor 21 by the heater driving unit 13, the voltage measuring unit 10b takes in the voltage V2 from the input terminal T4 and supplies the voltage value Vh obtained by A / D conversion to the control unit 10a. Output. FIG. 4 shows the take-in timing of the voltage V2 and the voltage value Vh.

  FIG. 4A shows the operation timing of the heater driving unit 13.

  FIG. 4B shows the transition of the voltage V2 applied by the heater driving unit 13, and the battery voltage is gradually decreased due to the increase in internal resistance accompanying energy consumption, and the voltage V2 is gradually decreased accordingly. .

  As shown in FIG. 4C, the voltage measurement unit 10b takes in the battery voltage V2 a plurality of times every time a predetermined measurement interval dt elapses. The voltage values Vh taken in by the voltage measuring unit 10b are respectively output to the control unit 10a as voltage values vi (i = 1, 2,..., N−1, n), and the voltage values vi and the heater resistance 21 are output. The control unit 10a estimates the amount of power supplied to the heater resistor 21 by time-integrating the power obtained from the resistance value.

  When the controller 10a obtains the amount of power actually supplied to the heater resistor 21 based on the voltage value Vh output from the voltage measuring unit 10b, the controller 10a supplies the heater resistor 21 with a predetermined amount of power. A necessary application time Tr is determined, and this application time Tr is set as a time width T of a pulse voltage to be applied next time.

  As described above, the control unit 10a determines the time width T of the pulse voltage to be applied next time from the result of measuring the voltage V2 every time the pulse voltage is applied to the heater resistor 21, and the heater resistor 21 has a predetermined width. The amount of electric power is supplied, and the gas sensitive body 20 is heated to a predetermined temperature.

  Here, as the measurement interval dt is shorter, the number of times of taking in the battery voltage V2 increases, so that the control unit 10a can estimate the fluctuation of the battery voltage and the amount of power supplied to the heater resistor 21 more accurately. The voltage measurement unit 10b measures the voltage V2 every time a predetermined measurement interval dt elapses. However, the voltage measurement unit 10b may be configured by an analog circuit to constantly measure the voltage V2.

  As described above, when a predetermined amount of electric power is supplied to the heater resistor 21 and the gas sensitive body 20 is heated to a predetermined temperature, the gas detection unit 10c determines the gas concentration based on the resistance value Rs of the gas sensitive body 20. Measure. The operation of the gas detector 10c will be described with reference to the time chart of FIG. FIG. 5A shows the resistance value Rs of the gas sensitive body 20, and FIG. 5B shows the notification output. After heating the gas sensitive body 20, the control unit 10a turns off the switching element Q1, and the gas detection unit 10c takes in the voltage V1 with the transistor Q2 turned on, and obtains the resistance value Rs from the voltage V1. As the gas concentration increases, the resistance value Rs of the gas sensitive body 20 decreases. When the resistance value Rs falls below the alarm determination level LV1 at time t1, the gas detection unit 10c determines that the gas concentration has exceeded the alarm level, and notifies the user. The circuit 11 is caused to perform a notification operation. Thereafter, when the gas concentration decreases and the resistance value Rs exceeds the alarm determination level LV1 at time t2, the signal processing circuit 10 determines that the gas concentration has fallen below the alarm level, and causes the notification circuit 11 to stop the notification operation.

  In the above description, the voltage measuring unit 10b continuously measures the battery voltage. However, as shown in FIG. 4D, the voltage measuring unit 10b is a voltage at the start of pulse voltage application and at the end of pulse voltage application. You may make it take in V2 as voltage value vs and voltage value ve, respectively. In this case, based on the voltages vs and ve input from the voltage measurement unit 10b to the control unit 10a, the control unit 10a estimates that a voltage drop occurs at a constant rate from the voltage value vs to the voltage value ve. The control unit 10a estimates that the average voltage value of the pulse voltage applied to the heater resistor 21 in the time width T is (vs + ve) / 2, and the heater value is determined from the voltage value and the resistance value of the heater resistor 21. The amount of power supplied to the resistor 21 is obtained. Since only two voltage measurements are required at the start and end of application of the pulse voltage, the processing of the control unit 10a can be simplified as compared with the case of performing voltage measurement three or more times.

  Further, as shown in FIG. 4E, the voltage measurement unit 10b takes in the voltage V2 at the time when half of the time width T determined at the previous application from the start of application of the pulse voltage as a voltage value vm, and the control unit You may output to 10a. In this case, the controller 10a estimates that a voltage drop has occurred at a constant rate from the start of pulse voltage application. The control unit 10a estimates that the voltage value vm when half of the time width T has elapsed from the start of application of the pulse voltage becomes the average voltage during the application period, and based on this voltage value vm and the resistance value of the heater resistor 21. The amount of power supplied to the heater resistor 21 is obtained. As described above, since the amount of electric power applied to the heater resistor 21 can be estimated by measuring the voltage value only once, the processing of the control unit 10a can be simplified as compared with the case where the voltage measurement is performed a plurality of times.

10 Signal processing circuit (control unit, voltage measurement unit, gas detection unit)
DESCRIPTION OF SYMBOLS 12 Voltage stabilization circuit 13 Heater drive part 14 Battery 20 Gas sensitive body 21 Resistance for heaters 22 Center electrode Q1 Switching element (heater drive part)
Q2 Transistor R1 Load resistance

Claims (4)

A gas sensitive body whose resistance value changes according to the gas concentration;
A gas detector for detecting gas from the resistance value of the gas sensitive body;
A heater resistance for heating the gas sensitive body;
A heater driving section for supplying a pulse voltage to the heater resistor;
A voltage measuring unit for measuring a pulse voltage applied to the heater resistor;
The heater driving unit is configured to provide a constant amount of power to be supplied to the heater resistor based on a voltage value measured by the voltage measuring unit while a pulse voltage is applied to the heater resistor. A control unit for controlling the time width of the pulse voltage to be applied next to the resistor;
A gas detection device comprising: The heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source,
2. The gas detection device according to claim 1, wherein the voltage measurement unit continuously measures a voltage value of a pulse voltage being applied to the heater resistor. The heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source,
2. The gas detection device according to claim 1, wherein the voltage measurement unit measures a voltage value of a pulse voltage being applied to the heater resistor at the start and end of application of the pulse voltage. The heater driving unit supplies a pulse voltage to the heater resistor using a battery as a power source,
2. The gas detection device according to claim 1, wherein the voltage measurement unit measures a voltage value of a pulse voltage being applied to the heater resistor at a time when half of the application time has elapsed.

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