JP3918588B2 - Gas detector control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for detecting carbon monoxide and leaked gas.
[0002]
[Prior art]
As a conventional gas detection device of this type, for example, there has been a configuration described in JP 2000-346825 A as a configuration of a carbon monoxide detection device. FIG. 10 shows a conventional carbon monoxide gas detection device described in the publication.
[0003]
In FIG. 10, 1 is a solid electrolyte plate, 2 and 3 are electrodes, 4 is a carbon monoxide oxidation catalyst, and 5 is a heater, which are formed on a ceramic plate 6. By energizing the heater 5, a voltage corresponding to the carbon monoxide concentration is output between the electrodes 2 and 3, the carbon monoxide concentration is known from the output voltage, an alarm is issued, and a carbon monoxide poisoning accident is prevented in advance. It was that.
[0004]
[Problems to be solved by the invention]
However, in the conventional configuration, when a voltage is intermittently applied on the pulse to the heater for heating installed close to the gas detector, the temperature of the heater rises rapidly, the heater is disconnected, or due to a difference in thermal expansion. The heater may peel off from the substrate, and the heater may not be properly heated, and the gas concentration may not be detected correctly.
[0005]
The present invention solves the above-described conventional problems, and the gas detector is heated intermittently, and a voltage that raises the set temperature stepwise is also applied to the heater even when a voltage is applied. The purpose is to improve the detection accuracy and reliability of the gas detector by giving the gas detector the optimum temperature for gas concentration detection without impairing the performance of the heater involved. It is.
[0006]
[Means for Solving the Problems]
In order to solve the above-described conventional problems, a gas detection unit that detects a gas concentration, a heating element that heats the gas detection unit, a power supply unit that supplies power to the heating element, and a heating element A voltage control means for intermittently applying a plurality of stepped pulse voltages is provided.
[0007]
As a result, the thermal shock to the heating element is reduced, and the gas detector can be improved in reliability and power saving.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, when heated to a constant temperature, a power supply means for supplying power to a heating element that heats a gas detection unit that detects a gas concentration and intermittently applying a plurality of stepped pulse voltages to the heating element. It has a voltage control means for switching, and has a time constant switching means for switching the time constant of the filter for each applied pulse , reducing the thermal shock to the heating element, improving the reliability of the gas detector and saving power In addition, it is possible to select an appropriate rising operation according to the control voltage, that is, the set temperature.
[0017]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
Example 1
FIG. 1 is a configuration diagram of a control device for a gas detector in the first, third, fourth, fifth, and ninth embodiments of the present invention.
[0019]
Reference numeral 7 denotes voltage control means, 8, 9, 10 are analog switches, and control signal lines 15, 16, 17 of the microcomputer 14 using the control voltages 11, 12, 13 (13 is ground potential) as signal voltage output means. Is applied to the + terminal of the operational amplifier 18. The output of the operational amplifier 18 is directly subjected to the impedance-converted voltage at the + terminal and is input to the + terminal of the operational amplifier 22 through the resistor 20 and the capacitor 21 of the filter 19. The PNP transistor 23, the NPN transistor 24, and the DC power supply 25 constitute power supply means 26 for the heater 5.
[0020]
In this configuration, the current flowing from the DC power supply 25 through the emitter-collector of the PNP transistor 23 and flowing into the heater 5 is determined by the base current of the PNP transistor 23. The base current of the PNP transistor 23 is controlled by the base voltage of the NPN transistor 24, that is, the output voltage of the operational amplifier 22. By operating so that the − terminal and the + terminal of the operational amplifier 22 are at the same potential, the current flowing into the heater 5 is determined, and the fluctuation of the resistance value due to heat generation reaches an equilibrium state, so that the temperature balance of the heater 5 is also achieved. The
[0021]
FIG. 2 shows the resistance-temperature characteristics of the heater 5. As the temperature rises, the resistance value increases and the voltage at the negative terminal of the operational amplifier 22 increases. When the voltage difference from the + terminal becomes small, the base current of the NPN transistor 24 is reduced, and accordingly, the base current of the PNP transistor 23 is also reduced, the current flowing into the heater 5 is also reduced, and a voltage corresponding to the control voltage is applied to the heater 5. Will be applied. The temperature of the heater 5 is controlled to a constant value. If the control voltage is changed, the temperature of the heater 5 also changes accordingly. Therefore, if a control voltage with a constant pulse width is output at the first stage, and the first stage voltage is cut off, then a voltage different from the first stage is output with a constant pulse width at the second stage, the temperature control of the heater 5 in two stages becomes possible. Similarly, if the control is repeated, multi-stage heater temperature control becomes possible.
[0022]
FIG. 3 is a time chart showing the applied control voltage and the heater 5 voltage. (A) shows the passage of time of the control voltage, and (B) shows the passage of time of the heater voltage.
[0023]
When the control voltage is intermittently applied, the voltage of the heater 5 rises up to the control voltage with a filter time constant. In this case, the pulse width is 10 to 20 msec, and the control temperature is 200 ° C. in the first stage and 450 ° C. in the second stage. The period is 10 to 30 seconds.
[0024]
FIG. 4 is a perspective view showing the configuration of the gas detection unit. The detection gas is carbon monoxide gas. In FIG. 4, reference numeral 1 denotes a solid electrolyte plate having oxygen ion conductivity at a high temperature of 400 ° C. to 500 ° C., and a pair of electrodes 2 and 3 are provided on the surface thereof. It is formed by vapor deposition, sputtering, or thick film printing. A platinum electrode is usually used as the electrode.
[0025]
Reference numeral 4 denotes a carbon monoxide oxidation catalyst layer impregnated and held with a carbon monoxide oxidation catalyst (shown in the drawing with a part cut away), and has air permeability and covers the electrode 2. A heater 5 is formed on the surface of the ceramic plate 6 by vapor deposition or printing, and heats the solid electrolyte plate 1 and the carbon monoxide oxidation catalyst layer 4 to operate as a carbon monoxide sensing element. A voltage corresponding to the carbon monoxide concentration is output between the electrodes 2 and 3. The carbon monoxide oxidation catalyst layer 4, the electrodes 2 and 3, and the solid electrolyte plate 1 constitute a gas detection unit 27. About the gas detection part comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.
[0026]
First, the operation of detecting carbon monoxide with the above configuration will be described. When heated to a certain temperature, the carbon monoxide gas that has passed through the carbon monoxide oxidation catalyst layer 4 is oxidized when passing through the carbon monoxide oxidation catalyst layer 4 and does not reach the electrode 2. Accordingly, in the vicinity of the electrode 2 in the solid electrolyte plate 1, oxygen atoms adsorbed on the electrode 2 are ionized by the reaction represented by the formula (1).
[0027]
O + 2e ⁻ → O ²⁻ formula (1)
On the other hand, in the vicinity of the electrode 3, in addition to the reaction represented by the formula (1), since the carbon monoxide gas arrives, the reaction represented by the formula (2) also occurs.
[0028]
CO + O ²⁻ → CO2 + 2e ⁻ Formula (2)
A potential difference is generated between the electrodes 2 and 3 due to a difference in reaction between the electrodes 2 and 3 of the solid electrolyte plate 1. That is, the potential difference changes according to the concentration of carbon monoxide, and the device operates as a carbon monoxide sensing element.
[0029]
The heater 5 is a heat source for heating the solid electrolyte plate 1 and the carbon monoxide oxidation catalyst layer 4 to a constant temperature so that the reactions of the formulas (1) and (2) occur stably. Heating is realized.
[0030]
As described above, in this embodiment, by applying a pulse voltage in which the control voltage of the heater 5 is changed, heating of the heater 5 can be realized without giving a large thermal shock to the heater 5, and carbon monoxide detection is performed. It is possible to improve the reliability as a container and stabilize the characteristics.
[0031]
Here, an example of carbon monoxide detection has been described as an example of a gas detection device, but the present invention is also effective for a gas detection device that detects flammable gases such as methane gas and propane gas by heating the detection unit. Needless to say.
[0032]
(Example 2)
FIG. 5 is a configuration diagram of the control device for the gas detector according to the second embodiment of the present invention. The voltage of the DC power supply 25 is resistance-divided by the variable resistor 28 and the fixed resistor 29 and is input to the analog switch 8. Further, the voltage of the DC power supply 25 is resistance-divided by the variable resistor 30 and the fixed resistor 31 and is input to the analog switch 9. The variable resistor 28 and the fixed resistor 29, and the variable resistor 30 and the fixed resistor 31 constitute reference voltage setting means. The analog switches 8, 9, and 10 constitute reference voltage switching means.
[0033]
According to this configuration, the control voltage of the heater 5 can be set by setting the resistance value with the variable resistors 28 and 30, and the temperature of the heater 5 can be easily changed and set to an optimum value. .
[0034]
(Example 3)
In FIG. 1, control voltages 11, 12, and 13 are switched by analog switches 8, 9, and 10 and input to the + terminal of the operational amplifier 18. The analog switches 8, 9, and 10 are selected by setting the potential of the control signal lines 15, 16, and 17 of the microcomputer 14 to high, and the time for setting the potential of each signal line to high determines the pulse width. According to this configuration in which the reference voltage switching means is an analog switch, the analog switches 8, 9, and 10 can be switched at a speed of 1 millisecond or less at a much higher speed than when switching by an electromagnetic relay contact or the like. There is little generation of noise associated with opening and closing the door. In addition, there is little contact leakage, and there is little interference with control voltage. Therefore, the control voltage can be switched at high speed stepwise.
[0035]
Example 4
In FIG. 1, a high resistance 32 (1 MΩ to 2 MΩ) is connected between the + terminal of the operational amplifier 18 (the output portion of the control voltage switching means) and the ground. The high resistance 32 keeps the potential of the + terminal of the operational amplifier 18 close to the ground potential when the power is turned on, and prevents the heater 5 from being destroyed by applying an abnormal voltage to the heater 5 when the apparatus is in a transient state. If the resistance value is low, the control voltage is affected and the effect of stabilizing the potential too high is lost. Therefore, the range of 1 MΩ to 2 MΩ is an appropriate resistance range.
[0036]
With this configuration, an abnormal voltage is prevented from being applied to the heater 5 when the apparatus is in a transient state such as when the power is turned on, and the heater 5 is prevented from being destroyed.
[0037]
(Example 5)
In FIG. 1, there is a filter 19 at the output of the voltage control means 7, and the pulse voltage rises at a time constant determined by a product CR of the resistance value and the point, which is constituted by a resistor 20 and a capacitor 21. Since the rounded voltage is input to the + terminal of the operational amplifier 22, the voltage of the heater 5 connected to the − terminal rises as shown in FIG. 3. Therefore, as compared with the case where the pulse voltage is directly applied to the + terminal of the operational amplifier 22 without the filter 19, the thermal shock applied to the heater 5 is greatly relieved, and a defect associated with the thermal shock of the heater 5 can be prevented.
[0038]
(Example 6)
FIG. 6 is a diagram showing the heater voltage and heater temperature in Example 6 of the present invention.
[0039]
(A) is the heater voltage, and (B) is the heater temperature. The heater temperature of the first stage is set to 250 ° C., the heater temperature of the next stage is set to 450 ° C., and the pulse width is set to 20 msec for both the first stage and the next stage. Thus, through the steps, the heater is set to a predetermined heater temperature, thereby preventing the heater from being defective due to thermal shock.
[0040]
(Example 7)
FIG. 7 is a configuration diagram of a control device for a gas detector in Embodiment 7 of the present invention.
[0041]
The output section of the voltage control means 7 includes resistors 20, 33, 34, a capacitor 19, and analog switches 35, 36, 37 as time constant switching means. The analog switches 35, 36, 37 are connected to the control signal line 15 of the microcomputer 14. , 16 and 17 are set to high so that the resistors 20, 33 and 34 are selected (at the same time as selecting the pulse voltage), and the time constant is switched.
[0042]
With such a configuration, a time constant can be set for each individual pulse voltage. When the temperature is raised from room temperature to about 200 ° C., the pulse width is narrowed, the time constant is reduced, and the time constant is increased. In order to increase from 450C to 450C, the pulse width is wide and the time constant can be increased to start up slowly, and the thermal shock can be mitigated.
[0043]
(Example 8)
FIG. 8 is a time chart showing the applied control voltage and the heater 5 voltage according to the eighth embodiment of the present invention.
[0044]
(A) shows the passage of time of the control voltage, and (B) shows the passage of time of the heater voltage. If the pulse voltage width of the first stage is 10 msec, the control temperature is set to 200 ° C., and the time constant is about 3 msec, the pulse voltage width of the next stage is set to 25 msec, the control temperature is set to 450 ° C., and the time constant is set to about 10 msec. The rising speed is fast, and the rising speed is controlled slowly at high temperatures, and temperature control with less thermal shock to the heater 5 can be realized.
[0045]
Example 9
FIG. 9 is a time chart showing signal voltages of the control signal lines 15, 16, and 17 of the microcomputer 14 according to the ninth embodiment of the present invention.
[0046]
The control signal line 15 and the control signal line 16 are output while individual pulse voltages are output, and the control signal line 17 is output when the signals of the control signal line 15 and the control signal line 16 are not output. In FIG. 1, when the control signal line 17 is output, the + terminal of the operational amplifier 18 is maintained at the ground potential by the analog switch 10 and the voltage applied to the heater 5 is also 0V. The control signal line 17 is reliably output when the pulse voltage is not output, and in order to reliably maintain the potential of the heater 5 at the ground potential, it is possible to realize a highly reliable device that is resistant to disturbance noise. it can.
[0047]
【The invention's effect】
As described above, according to the present invention, the voltage applied to the heater for heating of the gas detection unit is applied in a pulsed manner to save power and the voltage application to the heater is performed stepwise to the heater. It is possible to reduce the rapid thermal shock of the gas detector and improve the reliability of the gas detector.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a control device for a gas detector in Examples 1, 3, 4, 5, and 9 of the present invention. FIG. 2 is a resistance-temperature characteristic diagram of a heater in Example 1 of the present invention. FIG. 4 is a perspective view showing a configuration of a gas detection unit in the first embodiment of the present invention. FIG. 5 is a gas detection in the second embodiment of the present invention. FIG. 6 is a diagram showing a heater applied voltage and a heater temperature in Embodiment 6 of the present invention. FIG. 7 is a block diagram of a gas detector controller in Embodiment 7 of the present invention. FIG. 9 is a time chart showing the control voltage and heater voltage of the eighth embodiment of the present invention. FIG. 9 is a time chart showing the signal voltage of the microcomputer control signal line in the ninth embodiment of the present invention. Configuration diagram of detector [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Solid electrolyte board 2, 3 Electrode 4 Carbon monoxide oxidation catalyst 5 Heater 6 Ceramic board 7 Voltage control means 8, 9, 10 Analog switch (reference voltage switching means)
11, 12, 13 Control voltage 14 Microcomputer (signal voltage output means)
15, 16, 17 Control signal line 19 Filter 20, 33, 34 Resistor 22 Operational amplifier 25 DC power supply 26 Power supply means 27 Gas detector 28, 30 Variable resistor 29, 31 Fixed resistor 32 High resistance 35, 36, 37 Analog switch (Time constant switching means)

Claims (1)

Power supply means for supplying power to a heating element that heats a gas detection unit that detects a gas concentration by being heated to a constant temperature, and voltage control means for intermittently applying a plurality of stepped pulse voltages to the heating element And the voltage control means includes time constant switching means for switching the time constant of the filter for each applied pulse .

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