JP3999891B2 - Gas detection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas detection method and apparatus for detecting a gas having a malodorous component with a small amount of power consumption in general household and industrial fields.
[0002]
[Prior art]
_2. Description of the Related Art Conventionally, semiconductor gas detection elements and hot-wire gas sensors using a gas sensitive body mainly composed of SnO ₂ have been used as household gas leak alarms for city gas and propane.
[0003]
The most mainstream gas detector using a semiconductor gas detecting element is to heat the gas sensitive body of the semiconductor gas detecting element with a heater so that the temperature is constantly kept at a relatively high temperature. The target gas is detected when the resistance value falls below a certain value.
[0004]
In addition, two types of high and low power are alternately supplied to the heater at regular intervals, the high temperature period and the low temperature period are alternately set, and the resistance value of the gas sensor at a certain point in the low temperature period is constant. The target gas is detected based on whether or not the following occurs.
[0005]
Since these semiconductor gas sensors change the resistance value even in the humidity in the atmosphere and the alcohol component generated during cooking, it has been a problem to make a false report with so-called miscellaneous gases.
[0006]
[Problems to be solved by the invention]
Gas with bad odor as in the above case, for example, sulfur compounds such as H ₂ S and CH ₃ SH, ammonia such as NH ₃ and CH ₃ NH ₂ , amine compounds, and aldehyde compounds such as HCHO and CH ₃ CHO The same applies to the case of detecting a gas represented by (hereinafter referred to as an odor component). However, if the resistance value of the semiconductor gas detection element is below a certain resistance value, the detection method for detecting the presence of odorous components has a problem that it is impossible to distinguish between humidity, miscellaneous gases, and odorous components. In particular, when detecting a trace amount of odor components, the sensitivity of alcohol was high, so the detection accuracy of only the odor components was poor.
[0007]
In view of the above-described problems, the present invention provides a gas detection method and apparatus capable of reliably detecting a target gas without being affected by various gases such as humidity and alcohol.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, a semiconductor gas detection element having a gas sensitive body mainly composed of SnO ₂ and a heater for heating the gas sensitive body is used, and the temperature of the gas sensitive body is set to a high temperature by controlling energization of the heater. The high temperature period and the low temperature period to be low temperature are alternately set at a predetermined cycle, and the low temperature period starts during the low temperature period and the gas sensitive body exhibits a large resistance change due to the presence of combustible gas, alcohol, and humidity. After a certain period of time has elapsed, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to determine the ratio between the two sampling values. A target gas having a component is detected.
The invention according to claim 2 is characterized in that, in the invention according to claim 1, the temperature during the high temperature period is 300 ° C. to 450 ° C., and the temperature during the low temperature period is 100 ° C. to 200 ° C.
According to a third aspect of the present invention, there is provided a semiconductor gas detection element having a gas sensitive body mainly composed of SnO ₂ and a heater for heating the gas sensitive body, and the temperature of the gas sensitive body is set to a high temperature by controlling energization of the heater. Temperature control means for alternately setting a high temperature period to be performed and a low temperature period to be a low temperature in a predetermined cycle, and the gas sensitive body exhibits a large resistance value change due to the presence of combustible gas, alcohol, and humidity during the low temperature period. After a certain period of time has elapsed from the start of the low temperature period, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to determine the ratio between the two sampling values, and the value of the ratio obtained is less than the certain value. And a gas detection means for detecting a target gas having an odor component.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0010]
FIG. 1 shows a circuit configuration of a gas detector used in the present invention. In the circuit shown in this figure, the voltage of an AC commercial power supply AC is stepped down by a step-down transformer Tr, and the stepped down voltage is converted to diode bridges DB ₁ and DB _2. Each of the diode bridges DB ₂ rectified voltage is smoothed by a smoothing capacitor C ₁ , stabilized at a predetermined voltage by a three-terminal regulator IC ₁ , and the voltage of the heater 2 of the semiconductor gas detection element 1 In addition, the power source of the 4-bit microcomputer 3 that controls the detection voltage and the control and detection is obtained.
[0011]
In the semiconductor gas detection element 1, the heater 2 is connected to the output terminal of the three-terminal regulator IC ₁ via the PNP transistor Q ₁ , and the heater 2 is energized when the transistor Q ₁ is turned on, and the heater 2 generates heat. A gas-sensitive body having an outer dimension of 0.8 mm or less and having a substantially spherical SnO ₂ as a main component, and a heater combined electrode made of coiled platinum embedded in the gas-sensitive body The heat capacity is very small.
[0012]
Test knowledge output terminal of the addition the semiconductor gas sensing element 1 of the gas-sensitive body, the detection voltage application and the control of the transistor Q ₂₁ for the series circuit and sense the voltage application control of the load resistor R ₂₁ transistors Q ₂₂ and the load resistor R ₂₂ Are connected to the output terminal of the three-terminal regulator IC ₁ via the diode D _{1 and} to the input port I ₁ of the microcomputer 3.
[0013]
The microcomputer 3 connects the base of the output port _O of the base of the transistor _{Q 1} via a resistor _1, and the output port _{O 21,} the _{O 22} via the resistor transistor _{Q 21, Q 22.}
[0014]
Further, the cathodes of the display light emitting diodes LED _{1 to} LED ₃ are connected to the output ports O _{3 to} O ₅ , respectively, and the light emitting diodes L ₁ and L _{2 of the} photocouplers PH ₁ and PH ₂ are connected to the output ports O ₆ and O _7. The cathode is connected. The light emitting diodes LED _{1 to} LED ₃ and the anodes of L ₁ and L ₂ are connected to the output terminal of the three-terminal regulator IC ₁ via a current limiting resistor.
[0015]
The photocouplers PH ₁ and PH ₂ are used as switch elements for outputting a gas detection signal corresponding to the concentration of the detection gas as a voltage signal.
The series control type stabilization circuit 4 is a circuit for outputting the voltage signal, and is connected to both ends of a smoothing capacitor C ₂ for smoothing the rectified output of the diode bridge DB ₁ , and is connected to the base of the series control transistor Q ₃ . The reference voltage to be connected is switched by turning on / off the phototransistors PT ₁ and PT ₂ of the photocouplers PH ₁ and PH ₂ .
[0016]
Reference voltage has become so obtained by dividing the voltage across the Zener diode ZD connected through a resistor R ₄ to both ends of the smoothing capacitor C ₂ by the resistors R ₁₁ to R _13, the phototransistor PT ₁ is the time of the on-resistance The voltage across the series circuit of R _{11 to} R ₁₃ , that is, the voltage across the Zener diode ZD is applied as a reference voltage to the base of the transistor Q ₃ , and when the phototransistor PT ₂ is on, the resistors R ₁₁ , R ₁₂ and R ₁₃ the divided voltage with the series circuit is applied as the reference voltage to the base of the transistor Q _3, a voltage signal corresponding to each of the reference voltage is output to the outside as the gas detection signal.
[0017]
A pull-up resistor R ₂ is connected between the emitter and base of the transistor Q ₁ , and a transistor Q ₄ is connected to both ends of the pull-up resistor R ₂ .
[0018]
The transistor Q ₄ constitutes the protection circuit 5 for the heater 2 together with the comparator CP and the like.
[0019]
That is, the protection circuit 5 connects the series circuit of the resistors R ₆ and R ₇ to the output terminal of the three-terminal regulator IC ₁ via the diode D ₁ to divide the output voltage and to set the voltage dividing point to the inverting input of the comparator CP. On the other hand, a series circuit of a resistor R ₈ and a capacitor C ₀ is connected between the output port O ₁ of the microcomputer 3 and the ground, and the midpoint of the series circuit is connected to the non-inverting output terminal of the comparator CP. The output terminal of the comparator CP is connected to the base of the transistor Q ₄ via the resistor R ₉ .
[0020]
Note that the buzzer 6 is a piezoelectric buzzer, and two comparators CP ₁ and CP ₁ that alternately output “L” and “H” by signals alternately output from the output ports O ₈ and O _{9 of the} microcomputer 3. _{At 2,} the polarity of the applied voltage is alternately reversed, and an alarm sound is oscillated and output. In the figure, reference numeral 7 is a reference clock oscillation circuit for supplying a reference clock to the microcomputer 3, and IC ₂ is a reset IC for resetting the microcomputer 3 when the power is turned on.
[0021]
Therefore, under normal conditions, when the output port O ₁ of the microcomputer 3 is at “H” level, the capacitor C ₀ is charged through the resistor R ₈ , and the charging voltage is at the connection point between the resistors R ₆ and R ₇ . When the voltage exceeds the voltage, the output of the comparator CP becomes “H” level, and the transistor Q ₄ is turned off.
[0022]
Then, a control signal of “L” level is output from the output port O ₁ of the microcomputer 3 at a predetermined period (8 msec) for a predetermined time (eg, 500 μsec in the high temperature period and 8 μsec in the low temperature period), and the transistor Q ₁ is turned on during the predetermined time. Then, the heater 2 of the semiconductor gas detection element 1 is energized. On the other hand, when the output port O ₁ of the microcomputer 3 becomes “L” level, the electric charge of the capacitor C ₀ of the protection circuit 5 is discharged through the resistor R _8, and the voltage at both ends thereof decreases, but the resistor R ₈ and the capacitor C the time constant of _0, until the predetermined time has elapsed, without the voltage of the capacitor C ₀ is below the voltage at the connection point of the resistors R _6, R _7, the output is "L of the comparator CP even Therefore during a predetermined time period The transistor Q ₄ is kept in the off state.
[0023]
At the normal time, when the predetermined time ends, the microcomputer 3 returns the output port O ₁ to the “H” level and turns off the transistor Q ₁ . By turning off, the energization of the heater 2 of the semiconductor gas detection element 1 is stopped.
[0024]
In this way, by performing duty control in which the heater 2 is energized for a predetermined time in a predetermined cycle, a high temperature period in which the gas sensitive body is at a high temperature and a low temperature period in which the gas sensitive body is at a low temperature are alternately set.
[0025]
Here, the present inventors use the above circuit configuration in order to distinguish and detect odor components and alcohol, humidity, and combustible gas, and the resistance of the gas sensitive body of the semiconductor gas detection element 1 under each atmosphere. It was actually measured how the value changed with time from the start of the low temperature period.
[0026]
That is, in the above circuit, the operation was set so that the high temperature period was set to, for example, 8 seconds and then the low temperature period of 300 seconds was set, and the change in resistance value of the gas sensitive body was measured after switching from the high temperature period to the low temperature period.
[0027]
FIG. 2 (a) shows a case where a low temperature period (A) is set a plurality of times in a clean air of 20 ° C. and humidity is set to 65%, and the gas sensitive body in each low temperature period (A) is set. The resistance value change is shown, and as can be seen from this measurement result, the width of the resistance value from the switching of the low temperature period to the end of the period is not so large in any low temperature period (A). A period during which the resistance value of the gas sensitive body changes greatly in an atmosphere of a combustible gas (that is, a predetermined time from the switching time at which the temperature of the gas sensitive body does not decrease so much, in the case of the semiconductor gas sensing element 1, less than about 20 seconds). ) Sampling each resistance value at two points after the elapse (for example, 20 seconds (indicated by an upward arrow in the figure) and 200 seconds (indicated by a downward arrow in the figure)), and resistance values at both points When the value of the ratio Rsa / Rsb is obtained, the value is almost unchanged.
[0028]
FIG. 2 (b) shows the case where the ambient temperature is set to 65%, 65%, 80% and 40% under clean air at temperatures of 20 ° C., 30 ° C., 40 ° C. and 0 ° C., respectively. The change in resistance value of the gas sensitive member during each low temperature period (A) is shown, and also in this case, the value of the resistance value ratio Rsa / Rsb of the two points is almost unchanged.
[0029]
On the other hand, when 10 ppm ethanol (alcohol) is added to clean air at a temperature of 20 ° C. and a humidity of 65% as shown in FIG. 3A, and 30 ppm ethanol (alcohol) is similarly added to the air. ), The change in resistance value of the gas sensitive body during each low temperature period (A) was measured. When ethanol was present, the change in resistance value from the switching of the low temperature period to about 20 seconds was large. The width of the resistance value change after that is small, indicating that the value of the resistance value ratio Rsa / Rsb at the two points hardly changes regardless of the ethanol concentration.
[0030]
On the other hand, as shown in FIG. 3 (b), the resistance value of the gas sensitive body is measured when 10 ppm, 30 ppm, and 100 ppm of odorous component H ₂ S are added to air at a temperature of 20 ° C. and humidity of 65%. As shown in the figure, it was found that the temperature changed with a large gradient from the switching point to the end point in the low temperature period (b) corresponding to each concentration, and the change width varied depending on the concentration. The low temperature period (A) in the figure shows a case of clean air with a temperature of 20 ° C. and a humidity of 65%.
Therefore, it has been found that the concentration of H ₂ S can be determined by distinguishing alcohol, humidity, or combustible gas by obtaining the value of the ratio Rsa / Rsb of the two resistance values.
[0031]
Then, when the resistance value change was measured by changing the humidity and temperature of the air to which the same concentration of H ₂ S was added, the result shown in FIG. 3C was obtained. In the figure, a is clean air at 20 ° C. and 60% humidity, b is 10 ppm of H ₂ S in air at 20 ° C. and 60% humidity, and c is H _{2 in} air at 30 ° C. and 65% humidity. When 10 ppm of S is added, d shows the case where 10 ppm of H ₂ S is added to air at 40 ° C. and 80% humidity.
[0032]
In this case, the curves indicating changes in the resistance values after the elapse of 20 seconds are substantially parallel to each other. Therefore, the value Rsa / Rsb of the above two resistance values is affected by humidity and temperature. It shows that it is almost the same. That is, if the value of the resistance value ratio Rsa / Rsb is known, the concentration of H ₂ S is known.
[0033]
In addition to the above, other odorous components such as sulfur compounds such as CH ₃ SH, ammonia such as NH ₃ and CH ₃ NH ₂ , amine compounds, and aldehyde compounds such as HCHO and CH ₃ CHO are also measured as described above. As a result, the same tendency was found.
[0034]
Therefore, the value of the resistance value ratio Rsa / Rsb corresponding to a plurality of concentrations of the odor component is obtained in advance through experiments or the like, and the value of Rsa / Rsb corresponding to each concentration is used as a reference value for concentration detection. In addition, the resistance value ratio Rsa / Rsb corresponding to the concentration at which an alarm is generated is registered in advance in the same manner, and the sampling points are set as 20 seconds after the low temperature period and 200 seconds after the high temperature period. Was set to 8 seconds and the low temperature period was set to 300 seconds.
[0035]
Thus, the microcomputer 1 performs duty control in which the heater 2 is energized for a predetermined time in a predetermined cycle, thereby alternately setting a high temperature period in which the gas sensitive body is at a high temperature and a low temperature period in which the gas sensor is at a low temperature. At the time of sampling during the period, the output port O ₂₁ (or O ₂₂ ) is set to “L” level to turn on the transistor Q ₂₁ or Q ₂₂ , whereby the semiconductor gas sensing element is connected via the load resistor R ₂₁ (or R ₂₂ ). A sampling voltage is applied to one gas sensitive body, the voltage across the gas sensitive body of the semiconductor gas sensing element 1 is taken into the input port I ₁ during the application period, and a sampling operation is performed to determine the presence or absence of odorous components, To detect the resistance of the gas sensitive body. When the sampling at the second point (at 200 seconds) during the low temperature period is completed, the resistance value R sb sampled and detected at the first point (at 20 seconds) and the resistance value R sa detected at the second sampling point The value of the ratio Rsa / Rsb is obtained, the value of this ratio is compared with the registered reference value to detect the concentration, and any one of the output ports O _{3 to} O ₅ is set to the “L” level according to the detected concentration. Then, any one of the light emitting diodes LED _{1 to} LED ₃ connected thereto is turned on. Further, the output port O ₆ or O ₇ is set to the “L” level according to the detected density, the corresponding photocoupler P H ₁ or P H ₂ is turned on, and a predetermined voltage signal is sent from the stabilization circuit 4 to the outside. Output. When the detected concentration exceeds the alarm concentration, when the resistance value ratio obtained as the reference resistance value ratio falls below the output value of the output ports O ₈ and O ₉ , the buzzer 6 is turned over alternately. Sounds an alarm. In the circuit configuration of the present embodiment, when the microcomputer 3 runs away due to external noise or the like and the output port O ₁ of the microcomputer 3 is fixed at the “L” level, the charge of the capacitor C ₀ is discharged in the protection circuit 5. Eventually, the voltage of the capacitor C ₀ becomes lower than the voltage at the connection point of the resistors R ₆ and R ₇ , and as a result, the output of the comparator CP is inverted from the “H” level to the “L” level, and the transistor Q ₄ is turned on. It is turned on, forcibly turned off the transistors Q ₁ lifting the base voltage of the transistor Q ₁ to the supply voltage.
[0036]
That is, even if the microcomputer 3 runs away, the heater 2 of the semiconductor gas detection element 1 is not energized more than necessary, and disconnection of the heater 2 can be prevented.
[0037]
As described above, in this embodiment, the heater disconnection due to the runaway of the microcomputer 3 can be easily prevented by appropriately setting the time constants of the capacitor C ₀ and the resistor R ₈ .
[0038]
The setting of the load resistance connected in series to a gas-sensitive material of the semiconductor gas sensing element 1 is made possible by selectively turns on either transistor Q ₂₁ or Q _22, the gas sensing device subject The load resistance to be connected is programmed in advance according to the target gas type.
[0039]
In addition, the time setting of the high temperature period and the low temperature period is of course set to an appropriate value depending on the heat capacity of the semiconductor gas detecting element 1 used, and is not particularly limited to the above value. The low temperature period is set in the range of about 200 seconds to 300 seconds from 8 seconds to several seconds. Of course, the first point to be sampled is set after it is not affected by the combustible gas.
[0040]
【The invention's effect】
The invention according to claim 1 uses a semiconductor gas detection element including a gas sensitive body containing SnO ₂ as a main component and a heater for heating the gas sensitive body, and controls the energization of the heater to increase the temperature of the gas sensitive body. The low temperature period in which the gas sensitive body exhibits a large change in resistance value due to the presence of flammable gas, alcohol, and humidity. After a certain period of time has elapsed from the start time, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to determine the ratio of both sampling values, and the value of the ratio obtained is less than a certain value, The target gas with odorous components is detected, so that the target gas with odorous components can be reliably detected without being affected by flammable gas, alcohol, or humidity, and the gas sensitive body is heated to a constant temperature. Since there is no need to continue, there is an effect that it is possible to suppress the power consumption.
[0041]
In the invention of claim 2, in the invention of claim 1, the temperature of the high temperature period is 300 ° C. to 450 ° C., and the temperature of the low temperature period is 100 ° C. to 200 ° C. Can be less.
[0042]
According to a third aspect of the present invention, there is provided a semiconductor gas detection element having a gas sensitive body mainly composed of SnO ₂ and a heater for heating the gas sensitive body, and the temperature of the gas sensitive body is set to a high temperature by controlling energization of the heater. Temperature control means for alternately setting a high temperature period to be performed and a low temperature period to be a low temperature in a predetermined cycle, and the gas sensitive body exhibits a large resistance value change due to the presence of combustible gas, alcohol, and humidity during the low temperature period. After a certain period of time has elapsed from the start of the low temperature period, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to determine the ratio between the two sampling values, and the value of the ratio obtained is less than the certain value. And gas detection means that detects target gases with odorous components, so that it is possible to reliably detect target gases with odorous components without being affected by flammable gas, alcohol, or humidity. We can provide that equipment.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating the principle of the above.
FIG. 3 is a diagram illustrating the principle of the above.
[Explanation of symbols]
1 Semiconductor Gas Detection Element 2 Heater 3 Microcomputer

Claims (3)

A high temperature period in which a gas sensitive body comprising SnO ₂ as a main component and a semiconductor gas detecting element having a heater for heating the gas sensitive body is used to control energization of the heater to increase the temperature of the gas sensitive body, and a low temperature The low temperature period is alternately set at a predetermined cycle, and a certain period of time has elapsed from the start of the low temperature period during which the gas sensitive body exhibits a large resistance change due to the presence of flammable gas, alcohol, and humidity. Later, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to determine the ratio between the two sampling values, and the target gas having an odor component is obtained when the ratio value obtained is less than a certain value. The gas detection method characterized by detecting. The gas detection method according to claim 1, wherein the temperature in the high temperature period is 300 ° C. to 450 ° C., and the temperature in the low temperature period is 100 ° C. to 200 ° C. A semiconductor gas sensing element having a gas sensitive body containing SnO ₂ as a main component and a heater for heating the gas sensitive body, a high temperature period during which the temperature of the gas sensitive body is increased by controlling the energization of the heater, and a low temperature. Temperature control means for alternately setting the low temperature period at a predetermined cycle, and a certain time from the start of the low temperature period during which the gas sensitive body exhibits a large resistance change due to the presence of flammable gas, alcohol, and humidity. After the lapse of time, the resistance value of the gas sensitive body is sampled at two points at a predetermined time interval to obtain the ratio of both sampling values, and the object having an odor component when the ratio value obtained is less than a certain value. A gas detection device comprising gas detection means for detecting gas.

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