JPS6123789Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gas detection device that selectively and individually detects each component gas in a mixed gas.

Conventionally, gas detection devices that use oxide semiconductors as gas detection elements have a configuration in which the temperature of the detection element during measurement is the same, and only the electrical conductivity of the detection element is extracted as output.
When a detection element comes into contact with a mixed gas whose main component is a sensitive gas, it is difficult to individually detect two or more types of each component gas.

Therefore, an object of the present invention is to provide a gas detection device that can individually detect each component gas in a mixed gas.

According to the present invention, the purpose of this is to periodically change the temperature of the gas detection element in at least two stages and detect the electrical conductivity in the high temperature region in synchronization with the temperature change. By calculating the temporal rate of change in electrical conductivity in a temperature range other than the high temperature range, and combining this temporal rate of change with the electrical conductivity above, each component gas in the mixed gas can be detected individually This is achieved by trying to obtain.

As a gas detection element, for example, stannic oxide,
When using an oxide semiconductor obtained by mixing a platinum metal or rare earth metal salt as a catalyst and glass powder as a binder, drying the mixture, and sintering it in an oxidizing atmosphere, the temperature of the element at the time of measurement and The way the element responds differs depending on the type of gas it comes into contact with.
That is, the temperature of the gas detection element is plotted on the horizontal axis of the equal scale, and the electrical conductivity ratio is plotted on the vertical axis of the logarithmic scale, based on the electrical conductivity in air.
As shown in the figure, even the same gas detection element has different characteristics as shown by characteristic lines a ₁ , b ₁ , and c ₁ depending on the types of gases A, B, and C in contact with it and the temperature of the gas detection element. It gets hot.

Also, as shown in Figures 2 and 3, where time is plotted on the horizontal axis and electrical conductivity ratio is plotted on the vertical axis,
Even at the same gas detection element temperature, the electrical conductivity ratio of the gas detection element changes depending on the type of gas it comes into contact with.
They differ as shown by characteristic lines a ₂ , b ₂ or a ₃ , c ₂ .
Note that FIG. 2 shows a characteristic curve at an element temperature of 150±50°C, and FIG. 3 shows a characteristic curve at an element temperature of 350±50°C. Characteristic line
a ₁ , a ₂ , a ₃ are for gas A, characteristic lines b ₁ , b ₂ are for gas B
In addition, characteristic lines c ₁ and c ₂ represent the characteristics of the gas detection element corresponding to gas c.

The present invention skillfully utilizes the above-mentioned characteristics to achieve the intended purpose.The measurement temperature range is divided into three stages, and the output is electrical conductivity in the high temperature range, and An example in which the temporal rate of change in electrical conductivity is measured in the low temperature region will be described in detail.

FIG. 4 shows an embodiment of the gas detection device according to the present invention. In this device, a heater element 2 is disposed in close contact with a gas detection element 1 whose main component is an oxide semiconductor, and a heater current controlled from a heating control circuit 3 is passed through the heater element 2. temperature is high,
It is controlled in three temperature ranges: medium and low. This temperature control is carried out by the timer circuit ₄ , as shown in _{FIG .
2.} This is performed by sequentially and periodically switching control to I _H3 corresponding to "low". Gas detection element 1
and a load resistor 5 connected in series constitute a voltage divider that divides the voltage of the power supply 6. The electrical conductivity of the gas detection element 1 increases in gas, so the low resistance value of the load resistor 5 increases relatively, and the voltage across the load resistor 5 increases. That is, an output voltage corresponding to the gas concentration can be taken out from both ends of the load resistor 5.
The voltage across the load resistor 5 is introduced into an amplification and differentiation circuit 7. This amplification and differentiation circuit 7 simply outputs an amplified value of the input voltage (see FIG. 5b) in synchronization with the temperature change of the gas detection element 1 in response to a switching signal from an output holding circuit 8 controlled by a timer circuit 4. or
The differential value (see Fig. 5c) is output.

The output signal of the amplification and differentiation circuit 7 is input to an output holding circuit 9. The output holding circuit 9 is the timer circuit 4
_{Due to the action} of timing _{signals from}
The output of the amplifying and differentiating circuit 7 immediately before switching is memorized and held, and thereafter, the stored contents are used at the corresponding switching point.
The memory is maintained while being updated one after another at T ₅ , T ₆ , T ₇ , and further at T ₈ , T ₉ , T ₁₀ , and so on. In that case, in the high temperature measurement performed at measurement time points T ₂ , T ₅ . . _. , for example, the change in electrical conductivity Va ( _5th
(see Figures b and d) and hold the output at the measurement point.
In medium and low temperature measurements performed at T ₃ , T ₆ ... and T ₄ , T ₇ ..., the differential value of electrical conductivity Vb
and Vc (see Fig. 5 c, e, and f).

Output values for each temperature range of the output holding circuit 9 are indicated to indicators 10a, 10b, and 10c, respectively.

From time t ₁ to t ₄ , the gas detection element 1 is placed in clean air, and its detection output is used as the reference for subsequent gas concentration measurements.From time t ₄ , gases A, B, and C are
If the electrical conductivity and its differential value of the gas detection element 1 when measured in contact with a mixed gas having as a component are those shown in FIG. 5 b and c, then high, medium, Low From each measurement value at each temperature, the detection output Va for gas A at time T ₂ and T ₅ , the detection output Vb for gas B at time T ₃ and T ₆ , and the detection output Vb for gas C at time T ₄ and T ₇ . The detection output Vc of the indicators 10a and 1
0b and 10c can be instructed. Since the detection outputs Va, Vb, and Vc are related to the concentrations of the gases A, B, and C, respectively, the indicators 10a, 10b, and 10c can selectively and individually indicate the concentrations of the component gases in the mixed gas. In addition to the indicator, an audible alarm may be provided to issue an alarm when the output exceeds a certain level.

As an example, in the above-mentioned high temperature range, combustible gas concentration around a few percent of the lower explosive limit is detected as electrical conductivity, and in medium temperature range, carbon monoxide gas concentration near the permissible concentration is detected as electrical conductivity. By detecting the temporal rate of change (differential value) of the gas temperature as an output, it is possible to simultaneously issue an explosion warning and a gas poisoning warning.

In the above embodiments, a method has been described in which the output of the amplification and differentiation circuit immediately before the heating condition is changed is stored and output, but the present invention is not limited thereto.

In an adsorbed gas atmosphere, the electrical conductivity of a gas detection semiconductor element and the transient characteristics of its rate of change over time vary significantly depending on the temperature in the temperature range corresponding to the gas to be detected. In other words, if the target gas is a mixture of two or more types and the temperatures in the temperature ranges corresponding to the component gases are close to each other, the target gas can be determined by the gas corresponding to the adjacent temperature range. output is affected.

Now, let A be a gas that is affected by a temperature range higher than the corresponding temperature range, and B be a gas affected by a lower temperature range than the corresponding temperature range.The output-concentration characteristics with the memory retention time as a parameter are shown in Figures 6 and 6, respectively. It will look like Figure 7. In both figures, both the vertical and horizontal axes are equal scales, and τ _A and τ _B
is the time in the temperature range corresponding to gas A or B (corresponds to t ₁ - _{t 2} , t ₂ - t ₃ , t ₃ - t ₄ , etc. in Fig. 5), and t _H is the time corresponding to each temperature range. The sampling time of the stored output is shown based on the start time of each temperature range.

In such cases, depending on the type of target gas,
By storing and storing the output at an appropriate fixed time specific to each temperature region within the time of each temperature region, good output-concentration characteristics can be obtained, making it possible to detect gases with a wider range of concentrations. Become.

Next, the electrical conductivity of a gas detection semiconductor element in an adsorbed gas atmosphere and the transient characteristics of its rate of change over time vary significantly depending on the type of target gas and its concentration. In particular, when the gas concentration changes over a wide range, the transient characteristic curve changes significantly. In such a case,
A wide range of gas concentrations can be detected by storing the maximum value or minimum value of the output within each temperature range time, or a linear combination value of the maximum value and the minimum value, such as an arithmetic average value, corresponding to that temperature range. It becomes possible.

Figures 8 to 10 show the maximum value (Figure 8), the minimum value (Figure 9), and the arithmetic average value of the maximum and minimum values (Figure 10) as output holding values. The concentration characteristics are shown as time-dependent characteristic curves of the outputs of gases A, B, and C within each temperature range, and each output retention value is indicated by a black circle.

In addition, in FIGS. 8 to 10, H, M, and L indicate the temporal characteristics of the output under high concentration, medium concentration, and low concentration gas atmospheres, respectively.

Furthermore, if there is a common index quantity for the target gas corresponding to each temperature range, for example, if the target gas is a flammable gas and the lower explosive limit concentration is known, then all of the index quantities Sometimes we want to obtain the total amount as an instruction output. In such a case, the output value stored for each temperature range is multiplied by the weight for each index quantity, added for each temperature range, and the sum is made to correspond to one measurement cycle including multiple temperature ranges. All you have to do is to store it in a new memory.

For example, if the target gas is a flammable gas, the lower explosive limit can be used as the output display unit by using the output sensitivity of the lower explosive limit concentration as a weight to be multiplied by the output value corresponding to each temperature range. It becomes possible to display.

As described above, according to the present invention, it is possible to provide a gas detection device that can individually detect each component gas in a mixed gas.

[Brief explanation of the drawing]

1, 2, and 3 are characteristic diagrams showing characteristic examples of the detection element used in the present invention, FIG. 4 is a block diagram showing an embodiment of the gas detection device according to the present invention, and FIG. Figures a to f are diagrams for explaining the detection principle of the device in Figure 4, Figures 6 and 7 are diagrams for explaining a modified example of the device of the present invention, and Figure 8.
FIGS. 9 and 10 are diagrams for explaining other modifications of the device of the present invention. 1...Detection element, 2...Heater element, 3
... Heating control circuit, 4 ... Timer circuit, 7 ...
Amplification differentiation circuit, 8...Output holding circuit.

Claims (1)

[Claims for Utility Model Registration] 1. A gas detection element made of a semiconductor element whose electrical conductivity changes in an adsorbed gas atmosphere, and a temperature control unit that periodically changes the temperature of the gas detection element in at least two stages; a detection circuit that detects the temporal change rate of the electrical conductivity of the gas detection element in a high temperature range and the electrical conductivity of the gas detection element in other temperature ranges in synchronization with temperature changes; and an output holding circuit that selectively and individually outputs an output signal corresponding to each component gas in the gas to be detected based on the combination of the electrical conductivity and the temporal rate of change detected by the sensor. Device. 2 Utility Model Registration Scope of Claims 1. In the gas detection device according to claim 1, the output holding circuit stores and outputs the output at a certain time specific to the temperature range within each temperature range time corresponding to that temperature range. A gas detection device characterized by: 3 Utility Model Registration In the gas detection device according to claim 1, the output holding circuit stores the maximum value or minimum value of the output within each temperature range time, or the linear combination value of the maximum value and the minimum value at each temperature. A gas detection device characterized in that it stores and outputs information corresponding to a region. 4. Utility Model Registration In the gas detection device according to any one of claims 1 to 3, the output holding circuit may store and hold each output signal corresponding to each of a plurality of temperature ranges during one measurement cycle. A gas detection device characterized in that it stores and outputs a new linear combination value of output values every cycle.