TW487802B - A thermal conductivity gas analyzer - Google Patents

Abstract

The purpose of the present invention is to provide a thermally conductivity gas analyzer, wherein the component concentration ratio of a dually-mixed gas is measured by the different thermal conductivities of the dually-mixed gas with the reference gas. The Wheaston bridge is fabricated on the silicon chip by MEMS technology for the gas sensor of the present invention. The gas analyzer fabricated by the present invention has the advantage of small volume, light weight, easy for use and cheap cost, etc., which can be applied widely in analyzing the purity of gas, detecting leakage and gas component, etc.

Description

487802

V. Description of the invention 〇) 1. Background of the invention There are three states of matter, of which gas is omnipresent and has the closest relationship with daily life. It will fill any container, and different gases can be mixed in any proportion to form a homogeneous phase. Therefore, it is necessary to know the composition of the gas no matter it is environmental protection, medical facilities, home safety, chemical analysis, industrial production, etc. There are several methods for measuring gas components: (1) Gas chromatography, (2) Mass spectrometer, (3) Optical spectrometer (including body sensors, etc.) The first three types of accurate full-function analysis can only be effective, simple and effective, and the price is low. Multi-gas composition analysis needs to find a modest function that is based on this concept, thinking about the results of construction, and can simply lock in Binary analysis of the percentage of its components. It belongs to the precise price and is also quite used. The fourth 'but the lack of precision is often between, the price is also suitable for the known gas reference commonly used gas spectrum and other types of instruments, can be expensive, and There is only a single degree of accuracy, there is no gas between the two, the gas analysis equipment and gas composition analysis of the gas composition must have professional training-gas detection, leaf volume function. So I have to analyze Instrument. The principle of this sensor is analyzed in real life, and the sensitivity of work is sufficient for the purpose of the invention.

487802 V. Description of the invention (2)-~-III. Characteristics of the invention There are expensive full-function instruments for gas detection and composition analysis, and there are also sensors dedicated to single gas detection. The characteristic of the present invention lies between the two, 'Using the sensitivity of a gas sensor' to measure the one hundred and eighty ratio of the composition of the mixed gas. The principle of the gas sensing can use the conventional thermal conductivity sensor, and the knife is limited to the thermal conductivity sensor. When different component gases flow through the sensor, the size of the driver w varies, and the percentage of the component can be obtained after proper correction. The content of the invention. There is a heat transfer of matter through the heat transfer of gas. The heat transfer of gas is inversely proportional; the latter, such as the heat transfer of fluid (low) temperature, also changes due to contact with the gas. The relationship between heat transfer and heat convection is as follows: the former, such as the solid coefficient is roughly the square root of its molecular weight, the heat transfer rate and flow velocity are different from the archetype, and the heat dissipation rate is different. The resistance of the heating wire varies with the degree of :: is the temperature coefficient of resistance ’g) This is measured by electrical resistance. In terms of resistance, it is temperature or milk. For metal materials, the hot wire is affected by the gas heat conduction system dr, and the larger it is, the more gas sensors are handled accordingly, and the resistance will also change with it. Report etc. ’, He Li was born, such as flow meter, vacuum gauge

The formula for calculating the heat conduction of a simple gas is I. However, in daily life, a mixture of τ that can be deduced from aerodynamics can be regarded as a binary mixture.

487802

Aiki. For mixed gas, its thermal conductivity is more complicated. It is not obtained by adding the thermal conductivity of individual gases, but it is related to the mean free path of the mixed gas. Its thermal conductivity can be expressed as follows (1 ): In = λ " U + a12 (vXi)] + and 2 / 〔i (Χι " 2)] where λ! And 2 are the thermal conductivity of the respective gases, and χ and χ2 are the Mo of the respective gases. Ear fraction, Alz, a21 are calculated based on the molecular radius of each gas, the molecular mass, and the mutual attraction between molecules. From this formula, the percentage of different components can be calculated. Therefore, through the detection of the gas heat conduction sensor, we can measure the percentage of the binary mixture gas. It can be seen that the thermal conductivity varies with the composition of the gas. If the heating wire is placed in a binary mixture, the heat dissipation rate will also vary with the composition of the gas. The most sensitive and easy way to measure resistance is the Wyeth bridge. The principle is shown in Figure 1. When the bridge is in equilibrium, that is, R () Ri = Κ2Κ3, the current does not pass through the potentiometer of 206. When the sense resistance is changed, the Wyeth bridge balance is broken. The potentiometer senses the passage of current, and the change in resistance can be measured. Based on the above principles, this creation proposes the concept of a gas sensing element as shown in Figure 2. As shown in Figure 2, 201 ~ 204 are the four resistors of the Wyeth Bridge. The resistors are plated on a 2 0 5 adiabatic substrate with thin film technology (Figure 3); 221 ~ 228 are the leads of the resistors for the Wyeth Bridge For wiring and current input, 214 is an atmospheric channel, 21 5 is a closed air chamber, and a reference gas of about 1 atmosphere is passed. When the electric bridge heating current reaches a certain temperature, 2 1 and 2 2 become gas

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20 3 and 2 ° 4 are reference resistances. Due to the difference in the exothermic rate of the gas produced at different concentrations, 001 and 002 are the changes in birth and lice resistance, and the bridge is thus out of balance ... = 0 and 204 electrical measurements, rice, ge χ β / The concentration of the potential of the signal from the Wyeth bridge. 2 You can measure the resistance of the volatile substances in the air on the heart's perimeter bridge. Only two samples can be set up. A sample can be used. The above 2 〇 1 ^ η 9 and " Supported sensing gas M ♦ i and Both two resistors are used for detection, which can double the fastness, as shown in Figure 4. 『』 Another article of Jiawu is the part of the heat-conducting gas sensing element for the gas to be tested, and the part where the lice is closed has the same structure (not shown). In the figure, 21 8 is a silicon single crystal material. The lower and upper 205 of the sensing element are materials that are heat-resistant and low in thermal conductivity, and are generally materials such as silicon dioxide and '= polyimide. Because Shi Xijing is good: f ... conductor, in order to avoid heat dissipation through silicon crystal conduction, the area of the 217 lower cover contacting the heart ridge bridge needs to be made into a 21 6 cavity structure by anisotropic etching to reduce heat dissipation. Function: The upper cover plate 218 needs to be etched with the gas channel 214 and the closed air chamber 215 in advance, and then aligned with the lower cover plate 217 to complete the micro-electromechanical processing heat conduction sensing element. Figure 5 is a schematic diagram of the design of a simple gas composition analyzer, which is mainly composed of 2 2 i filter elements, 2 2 2 sample concentrators, 2 2 3 gas sensing elements, and 2 2 4 micropumps. The gas to be measured is driven by a 2 2 3 micropump and enters the sensing analysis system through the 2 2 0 inlet. Among them, 225 is a capillary flow channel. After removing the solid particles through the 221 transition element, it is analyzed by the 223 gas sensing element, and finally discharged to the atmosphere from the 226 outlet. Sometimes in order to detect low-concentration gases, a 222 concentrator can be added behind the sample inlet to test the gas.

Description of the invention (5) When the body is temporarily adsorbed to the degree of concentration, the temperature is increased by 2 °. When the cumulative amount of the gas to be measured reaches a certain concentration, the design diagram of the concentrator is used to desorb the sample gas. Figure 6 shows the sample. Attach a layer and coat the inner wall of the H25 capillary outside the tube! -Layer 227 suction ° 卩 Install 2 2 8 heating sleeve. Implementation method 4 The person uses this guide to measure the amount of another gas in the air, the target, especially the trauma, and other standards to prepare a series of known concentrations. The sum of the gas = the potential difference is made into a calibration curve as shown in Figure 7. The known concentration: gas I # ^ wheel ^ micro-processing crystal moon storage. When measuring the formula in the air, = # I bucket%, the micro-processing chip can directly convert the potential difference value on the potentiometer into the degree based on the calibration curve and interpolation method. Diagram description: Figure 1 Schematic diagram of Wyeth bridge Figure 2 Design of Wyeth bridge using microfabrication technology Figure 3 Design of heat conduction gas sensing element Figure 4 Schematic diagram of Wyeth bridge of thermal conduction gas element Figure 5 Design of simple gas composition analyzer Schematic diagram Fig. 6 Schematic diagram of sample concentrator design Fig. 7 Schematic diagram of binary mixed gas concentration correction curve

Ro, Ri, R2, R3 Four resistors on the Wyeth bridge.

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Page 8 487802 V. Description of the invention (6) 2 (Π ~ 2 04 The four resistors on the Wyeth bridge are made using thin-film technology. 2 0 6 potentiometer. 2 2 1 ~ 2 2 8 The leads of the resistor on the Wyeth bridge. 214 Atmospheric passage. 21 5 Closed air chamber. 205 Insulating low heat transfer coefficient material. 216 Cavity. 21 7, 2 1 8 Silicon material · As the lower cover of the sensor. 220 Inlet of gas to be measured 221 Filter element 222 Sample concentrator 223 Gas sensing element 2 24 Micro pump 225 Capillary tube 226 Gas outlet to be tested 2 2 7 Adsorption layer 228 Heating sleeve

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Claims (1)

487802 VI. Scope of patent application A thermally-conducting two-one pedestal is mounted on a pedestal and is provided with a gas flow channel and analyzer channels at both ends. The upper cover enters the gas through an outlet of a sample concentrator and is connected to a closed gas. The room test is binary and separated. The reference gas on the heat-sensing level is reduced. The reference gas and the gas-conducting conductive gas are produced in an electric test room. There is a gas-to-be-tested hot room, not to be compared with the Wyeth room of the upper sensing element. The number of phases in the test chamber is different. 5 Tiger gas source analysis instrument for processing signal source, including: Upper cover and lower cover made of silicon single crystal material; This base is the path for the gas to be measured and is an etched opening. The tube is used to guide the dual gas plate to be measured and is discharged after analysis by the gas sensing rigid element = The gas channel is connected in series with a filter element from the inlet end. Ϋ ΐ Ϊ ΐ ΐ ΐ is connected, and M is connected by the gas. After recognizing the animal pond, the exit end of the accessible gas channel is a closed air chamber etched on the upper cover, and the joint history is equal to 3: the thermal conductivity coefficient of the gas is ΐ. One touch, the two groups of the lower cover are empty. Acupoint Covered reference gas chamber and gas g, heat source of the measuring element: sensing to the corresponding, it's made of-a low-thermal-conductivity insulated bridge, the Wyeth bridge's _ pairs and decay materials should be, the Hui The other part of the J-bridge-pair resistance; bit = 2 to the gas to be measured, "% of Chengxin's bridge unevenness, to sense the second; circuit system, used to raise and process the oxygen mine circuit: its: The results are obtained in parallel; the device is a farm that generates direct current, using 4 power supplies D: \ micro-gc \ micro-gc \ Patent 4. ptd Page 10 487802 6. Scope of patent application Electricity required for binary gas composition analysis instrument. 2. If the thermal conductivity type binary gas composition analysis instrument of item 1 of the application scope, wherein a pair of resistances of the sensing element is located in the reference gas chamber and another pair of resistances is located in the gas sensing chamber, the sensing sensitivity can be increased. Times. 3. The thermal conductivity binary gas composition analysis instrument as described in item 1 of the application scope, wherein the filter element is used to remove solid particles in the gas to be measured. '' 4. The thermal conductivity type binary gas composition analysis instrument of item 1 of the application scope, wherein the sample concentrator is located between the filter element and the sensing element, and is coated with an adsorption layer on the inner wall of a capillary tube, and outside the capillary tube. A heating sleeve is installed to condense the gas to be measured to improve the resolution of the sensing element. 5. If the thermal conductivity type binary gas composition analysis instrument of item 1 of the application scope, the power generator may be a battery device. D: \ micro-gc \ micro-gc \ patent 4.ptd page 11