JPH08101156A - Sensing device for atmospheric gas - Google Patents

Abstract

PURPOSE: To determine the gas quantity in the a atmosphere without being influenced by the ambient temp. and without nullifying the sensor sensitivity for the surrounding gas. CONSTITUTION: The terminal voltage of a sensor Rs changes in response to the surrounding gas when a specified current is fed, and currents I1 -In having different wave heights corresponding to the types of atmospheric gases to be determined are fed to the sensor Rs, and the reaction values of the sensor Rs for each atmospheric gas quantity are previously determined as a presumption equation. The sensor Rs is placed under the condition CH of the atmospheric gas to be determined, and currents I1 -In having different wave heights are fed, and the reaction value of the sensor Rs is determined and substituted into the presumption equation so that the solution is drawn. The quantity of gas to be determined is sensed and displayed on a DISP.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an atmospheric gas detection device, and more particularly, to an atmospheric gas detector such as nitrogen, oxygen,
The present invention relates to an atmospheric gas detection device that detects atmospheric gas such as argon, carbon dioxide, and water vapor.

[0002]

2. Description of the Related Art Conventionally, a platinum thin-film resistor (a platinum thin-film resistor will be described below as an example of the sensor, the sensor in the present invention is not limited to the platinum thin-film resistor). In order to detect atmospheric gas using, there are many methods of detecting only specific atmospheric gas. For example, in the case of detecting water vapor, a platinum thin film resistor (hereinafter, if necessary, a resistor or a temperature detection sensor) is used. , A water vapor detection sensor, or simply a sensor) responds to both temperature and water vapor. (1) Use two sensors, a temperature detection sensor and a water vapor detection sensor that have the same temperature sensitivity, and subtract the reaction amount of both. By doing so, the amount of water vapor is obtained by comparing the remaining amount of reaction with the reference amount of reaction. (2) By using two sensors, a temperature detection sensor and a water vapor detection sensor having different temperature sensitivities, and detecting the temperature with the temperature detection sensor, the reaction amount with respect to the temperature of the water vapor detection sensor is removed, and the remaining water vapor detection sensor The amount of water vapor is obtained by comparing the amount of reaction with the reference amount of reaction. However, in (1), it is difficult to manufacture a temperature detection sensor and a water vapor detection sensor having the same temperature sensitivity in terms of manufacturing. In (2), since the temperature detection sensor is also affected by the water vapor, an error occurs depending on the amount of the water vapor, and in particular, when the temperature increases, the water vapor amount rapidly increases, which is strongly affected by this. There were drawbacks such as.

FIG. 3 is a diagram showing the relationship between the terminal voltage of the platinum thin film resistor and the amount of gas in the atmosphere or the atmospheric temperature when a constant current is applied to the platinum thin film resistor using the current as a parameter. 3A shows the relationship between the amount of water vapor in the atmosphere and the terminal voltage of the resistor, and FIG. 3B shows the relationship between the helium concentration in the atmosphere and the terminal voltage of the resistor. ) Shows the relationship between the atmospheric temperature and the terminal voltage of the resistor. As is clear from these figures, when a current is applied to the platinum thin film resistor,
The gas concentration in the atmosphere or the atmospheric temperature can be detected.

[0004]

[Problems to be Solved by the Invention]

(1) In the humidity detection using the platinum thin film resistor, the resistor itself is also affected by the temperature.
The temperature change of the resistor had to be removed.
Therefore, it is necessary to prepare separate sensors for temperature detection and humidity detection. (2) By using the temperature detection sensor and the humidity detection sensor having the same temperature sensitivity, the difference in temperature can be removed by calculating the difference between the output voltages, so that the humidity is obtained from the remaining humidity change. However, it is difficult to manufacture a temperature detection sensor and a humidity detection sensor having the same temperature sensitivity in terms of manufacturing. (3) When using a temperature detection sensor and a humidity detection sensor that have unequal temperature sensitivities, first find the temperature with the temperature detection sensor, and then use that temperature value to remove the temperature effect of the humidity detection sensor. , The humidity is calculated from the remaining value. However, the temperature detection sensor loses its thermal equilibrium when humidity is applied, and a correct temperature cannot be obtained. This tendency is likely to be affected because the absolute amount of humidity increases as the temperature rises. (4) A self-temperature compensation method in which temperature detection is performed by a humidity detection sensor is also considered, but this principle is established by adjusting the current at the point where the humidity sensitivity becomes zero. However, it is difficult to adjust the humidity sensitivity of the humidity detection sensor to zero, and the zero point shifts when the ambient temperature changes.

[0005]

In order to solve the above-mentioned problems, the present invention has (1) a sensor having a terminal voltage which changes in response to ambient gas when a predetermined constant current is passed through the sensor. Depending on the number of kinds of atmospheric gas desired to be obtained, the reaction value of the sensor for each amount of atmospheric gas is applied as an estimation formula by applying currents with different peak values, and the sensor is placed under the conditions of the desired atmospheric gas. Characterizing that the reaction value of the sensor is obtained by applying currents having different peak values, the reaction value is substituted into the estimation formula to obtain the solution, and the amount of atmospheric gas to be obtained is detected thereby. And further (2)
There are at least as many sensors as the atmospheric gas that the terminal voltage changes in response to the ambient gas when a predetermined constant current is applied, and currents with different peak values are applied to each sensor at the same time. The reaction value of the sensor with respect to is obtained as an estimation formula, the sensor is placed under the conditions of the atmospheric gas to be obtained, currents with different peak values are simultaneously applied to each sensor to obtain the reaction value of each sensor, and the reaction The value is substituted into the above estimation formula to obtain the solution, and the amount of the atmospheric gas to be obtained is detected by the solution, and further, (3) the terminal voltage reacts with the ambient gas when a predetermined constant current is applied. When a single sensor that changes is used and only one kind of atmospheric gas is desired, by utilizing the property of the sensor to react to the ambient temperature,
A current having different peak values is applied twice to the sensor to obtain a reaction value with respect to the atmospheric gas and ambient temperature as an estimated value, and the current having different peak values is applied under the conditions of the atmospheric gas for which the sensor is desired. Then, the reaction value is obtained, the reaction value is substituted into the estimation formula to obtain the solution, and the amount of the atmospheric gas is obtained from the solution.

[0006]

[Function] When a current is applied to the platinum thin film resistor, a voltage is generated in response to temperature or humidity, and when the current applied to the platinum thin film resistor is changed, the degree of reaction changes and the voltage changes. , The platinum thin-film resistors are arranged in two directions of temperature and humidity, currents with different peak values of two factors (temperature and humidity) are added, and the voltage change in that case is obtained as an estimation formula, Give orthogonality to those estimation formulas, and obtain an unknown number from the estimation formula (in this case, the currents with different peak values are in the current range applied to the humidity detection sensor, and if the reaction current value is obtained,
Any value). By doing so, the temperature or humidity can be obtained with one humidity detection sensor, and the current at zero humidity sensitivity, which is difficult for the self-temperature compensation method to perform humidity detection with one humidity detection sensor, is unnecessary.

[0007]

EXAMPLES The present invention shows that when a current is applied to a platinum thin film resistor, it reacts with atmospheric gases such as nitrogen, oxygen, argon, carbon dioxide, and water vapor, and by changing the peak value of the current, Utilizing the property that the degree of reaction changes,
Currents with different peak values are applied to the resistor for the number of types of atmospheric gas desired in advance, and the reaction value of the resistor with respect to the amount of atmospheric gas is obtained as an estimation formula. , The reaction values of the resistors when different currents with different crest values are applied are substituted into the above estimation formula and are made simultaneous, and the solution of the estimation formula is obtained to determine the amount of atmospheric gas to be obtained. It's something I got directly.

To simplify the explanation, water vapor, helium, temperature, etc. will be described as an example. When a current is applied to the platinum thin film resistor, the platinum thin film resistor will show the vapor and helium in the atmospheric gas. It exhibits the characteristics as shown in FIG. 3 with respect to the concentration or the temperature. From this, it is possible to obtain the amount or temperature of atmospheric gas (water vapor, helium) by arranging the amount or temperature of atmospheric gas in multiple ways, giving orthogonality to the estimation formulas, and connecting the respective estimation formulas simultaneously. become. Here, an example will be described in which the Chebyshev orthogonal polynomials shown in (Equation 1) and (Equation 2) in which the orders of the two variables of water vapor and temperature are made linear are used to obtain the estimation equation.

[0009]

[Equation 1]

Here, I _1, I ₂ : current applied to the resistor [A] V _1, V ₂ : terminal voltage of the resistor at I ₁ and I ₂ [V] dH: change of water vapor amount, H -H _b [g / m ³ ] H: Water vapor amount [g / m ² ] H _b : Average value of water vapor amount [g / m ³ ] dT: Change in temperature, T−T _b [° C.] T: Temperature [° C.] T _b : average value of temperature [° C.] m ₁ : terminal voltage of the resistor at I _1, H _b and T _b [V] h ₁ : coefficient of linear equation [v] / of H at I ₁ [G /
m ³ ] t ₁ : coefficient [v] / [° C.] of the linear expression of T at I ₁ m ₂ : terminal voltage of the resistor at I _2, H _b and T _b [V] h ₂ : H at I ₂ Coefficient of linear equation [V] / [g /
m ³ ] t ₂ : The coefficient [V] / [° C.] of the linear expression of T in I ₂ The coefficients m _1, h _1, t _1, m _2, h ₂ and t ₂ are described in mathematical formulas, etc. It can be easily obtained from the table of Chebyshev's orthogonal polynomials. As a result, dH and dT can be obtained by giving V ₁ and V ₂ .

FIG. 1 is a diagram for explaining an example of a detection circuit for obtaining water vapor and temperature using the above-mentioned (Equation 1) and (Equation 2) as an embodiment of the atmospheric gas detection apparatus according to the present invention. In the figure, in the figure, I _{1 to} In are constant current circuits (and constant current), Rs is a platinum thin film resistor, CH is the desired environment,
A / D is an analog / digital conversion circuit, ALU is an arithmetic circuit, DISP is a display device, and CONT is a control circuit.

In FIG. 1, first, a platinum thin film resistor Rs
In the environment where it is desired to obtain, the currents I ₁ and I ₂ having different peak values are sequentially applied, and the terminal voltages V ₁ and V ₂ of the platinum thin film resistor Rs generated at this time are converted into analog / digital converter A. / D to the arithmetic circuit ALU. The arithmetic circuit ALU incorporates the determinant solution program shown in (Equation 3), and the average value H _{b of} water vapor and the average value T of temperature T are included in the obtained amount of change dH of water vapor and amount of change dT of temperature. _The amount of water vapor H and the temperature T are calculated by adding _b . The control circuit CONT operates the switch SW for switching the current value, and at the same time, supplies the voltage appearing in the analog / digital converter A / D to the arithmetic circuit ALU in order. In addition, the display circuit DISP
Indicates the amount of water vapor H and the temperature T. The above example is for two unknowns, water vapor and temperature,
Even if there are three or more, this unknown can be obtained by performing the same procedure.

FIG. 2 is a diagram for explaining the current application method, and FIGS. 2 (a) and 2 (b) are diagrams showing the detection method when one detection sensor is used. As described above, the currents I _{1 and} I ₂ having different crest values are applied at different times, and the pulse width of each current may be about 50 ms. Further, FIG. 2C is a diagram in the case of obtaining a plurality of types of atmospheric gas, and in the case of obtaining a plurality of types of atmospheric gas in this way, the detection state is delayed in time, which causes an error. If atmospheric currents having different peak values are simultaneously applied to these, atmospheric gas can be detected at high speed.

[0014]

As is apparent from the above description, according to the first aspect of the invention, a single sensor can be used to detect a plurality of types of atmospheric gases without being affected by ambient temperature. . Further, according to the invention of claim 2, since the reaction values of all the sensors are detected within the same time by using a plurality of sensors, it is possible to detect the case where the atmospheric gas changes with time. Even if there is, the atmospheric gas can be detected without causing a time lag. Further, according to the invention of claim 3, even if the number of the atmospheric gas to be obtained is one, the atmospheric gas can be detected without being affected by the ambient temperature by utilizing the reaction to the ambient temperature. .

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an atmospheric gas detection device according to the present invention.

FIG. 2 is a diagram for explaining the timing of a current applied to the atmospheric gas detection device according to the present invention.

FIG. 3 is a diagram showing an example of reaction characteristics of a sensor used in the present invention.

[Explanation of symbols]

I _{1 to} In ... Constant current circuit, Rs ... Platinum thin film resistor, CH
... ambient atmosphere, A / D ... analog / digital conversion circuit, ALU ... arithmetic circuit, DISP ... display device, CONT
... control circuit.

Claims (3)

[Claims] 1. A sensor having a terminal voltage that changes in response to ambient gas when a predetermined constant current is applied, and currents having different peak values are applied to the sensor by the number of kinds of atmospheric gas desired. The reaction value of the sensor for each atmospheric gas amount is obtained as an estimation formula, the sensor is placed under the conditions of the atmospheric gas desired to obtain the reaction value of the sensor by applying currents with different peak values, and the reaction An atmospheric gas detection device, characterized in that a value is substituted into the estimation formula to obtain a solution thereof, and the amount of atmospheric gas to be obtained is detected by the solution. 2. A sensor in which the terminal voltage changes in response to ambient gas when a predetermined constant current is applied is provided for at least as many kinds of atmospheric gases as desired, and currents having different peak values are simultaneously applied to each sensor. Then, the reaction value of the sensor for each atmospheric gas amount is obtained as an estimation formula, and the sensor is placed under the condition of the atmospheric gas desired to be obtained, and the currents having different peak values are simultaneously applied to the respective sensors to obtain the reaction value of each sensor. And the reaction value is substituted into the estimation formula to obtain a solution thereof, and the amount of the atmospheric gas desired to be obtained is detected thereby. 3. An ambient temperature of a sensor, which has a single sensor whose terminal voltage changes in response to an ambient gas when a predetermined constant current is applied, and which has only one type of atmospheric gas to be obtained. Utilizing the property of reacting, currents having different peak values are applied twice to the sensor, and a reaction value with respect to the atmospheric gas and ambient temperature is obtained as an estimated value, and the sensor is measured under the atmospheric gas conditions. An atmospheric gas detection device, characterized in that a reaction value is obtained by applying currents having different peak values, the reaction value is substituted into the estimation formula to obtain a solution thereof, and the amount of the atmospheric gas is obtained therefrom.