JPH06308008A - Method and apparatus for identifying mixed gas component - Google Patents

Abstract

PURPOSE:To correctly identify component gas and quantify concentration at a low cost. CONSTITUTION:A gas adsorbing film 2 is formed on a surface of a single crystal oscillator 2 placed in a measurement cell 1, and when sample is supplied from a gas supplier 8, a frequency counter 5 counts resonance frequency of the crystal oscillator oscillated by an oscillation circuit 4. A computer 6 compares a time constant of an exponential function included in a change with time of the resonance frequency measured by the frequency counter 6 with a time constant in the case of single gas of each component gas to identify a type of each component gas, also calculates a saturated adsorbed amount to the gas adsorbing film 2 to quantify concentration of the component gas, and displays results on a display device 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a crystal oscillator provided with a gas adsorption film on the surface thereof, and obtains a change in the resonance frequency of the crystal oscillator due to the adsorption of a gas to be detected on the gas adsorption film to achieve mixing. The present invention relates to a mixed gas component discrimination and quantification method and apparatus for identifying the type of each component gas in gas and quantifying the concentration.

[0002]

2. Description of the Related Art In a chemical sensing device for measuring a chemical substance, it is necessary to detect and discriminate a small amount of a target gas with high sensitivity by a simple and inexpensive structure. Conventionally, as such a gas discriminating method, there is a method using a crystal oscillator having a gas adsorption film (hereinafter simply referred to as an adsorption film) provided on the surface. This method uses the fact that when the gas molecules to be detected are adsorbed on this adsorption film, the resonance frequency of the crystal oscillator changes in proportion to the mass change of the adsorption film. The type and concentration of the gas to be detected are identified. In this method, a plurality of crystal oscillators are required unless the adsorption film is sensitive only to a specific gas, and a method such as pattern recognition is used from the saturated adsorption amount value of each crystal oscillator. I was identifying.

[0003]

The above-mentioned conventional mixed gas component determination method has the following drawbacks. That is, it is difficult to develop an adsorption film that is sensitive only to a specific gas, and usually a plurality of crystal oscillators are used. In that case, in order to identify each component gas in the mixed gas, first, it is necessary to prepare an adsorption film having at least the same number of different adsorption characteristics as the component gas, which increases the cost. In addition, it is necessary to prepare as a database the saturated adsorption amount of the crystal oscillator coated with each adsorption film for the mixed gas of which the type and concentration of the component gas are known, and to identify each component gas by pattern matching. At present, it is not possible to accurately discriminate the component gases in the mixed gas, because the patterns of the saturated adsorption amount of the gas and the quartz oscillator coated with the respective adsorption films do not correspond one-to-one. Furthermore, it is difficult to quantify each component gas.

An object of the present invention is to provide a single crystal oscillator provided with an adsorption film sensitive to a plurality of kinds of gas components, so that the kind of the component gas in the mixed gas can be surely identified and the concentration can be quantified. It is intended to provide a gas component discrimination and quantification method and apparatus.

[0005]

The method for discriminating and quantifying a mixed gas component according to the present invention uses one crystal oscillator provided with a gas adsorption film on the surface thereof, and is included in the time variation of the resonance frequency of the crystal oscillator. Procedure for detecting time constant of exponential function, time constant of exponential function included in time change of resonance frequency of crystal oscillator detected by the procedure, and time change of resonance frequency in case of individual gas of each component gas Is compared with the time constant of the exponential function and whether or not they match, the procedure for identifying the type of each component gas and the saturated adsorption amount of each component gas to the gas adsorption film are calculated for each component gas. And a procedure for quantifying the concentration of

A linear filter algorithm may be used to detect the exponential time constant included in the time change of the resonance frequency of the crystal oscillator.

A mixed gas component discriminating and quantifying apparatus of the present invention comprises a measuring cell in which a single crystal oscillator having a gas adsorption film on the surface is arranged, and a gas supplier for supplying a gas sample to the measuring cell. An oscillation circuit that oscillates at the resonance frequency of the crystal oscillator when a gas sample is supplied to the measurement cell, a frequency counter that counts the resonance frequency of the crystal oscillator oscillated by the oscillation circuit, and a display device. A gas sample supplied to the measuring cell, which detects the time constant of an exponential function included in the time variation of the resonance frequency of the crystal oscillator due to the adsorption of the gas sample to the gas adsorption film, which is counted by the frequency counter. Each component gas is identified by comparing it with the time constant of the exponential function that represents the time change of the resonance frequency in the case of a single component gas, and identifying the type of each component gas. The seeking saturated adsorption amount to the adsorption film performs quantification of the concentration of each component gas, and a computer which displays the results on the display device.

This includes one in which a fluorine-containing polymer thin film derived from plasma is used as the gas adsorption film of the crystal oscillator.

[0009]

By using a single crystal oscillator provided with an adsorption film, the time constant of an exponential function included in the time change of the resonance frequency of the crystal oscillator is detected, and the exponent of each component gas alone is detected. Since the type of each component gas is identified and the concentration is quantified by comparing with the time constant of the function, the apparatus is inexpensive and accurate results can be obtained.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the mixed gas component discriminating and quantifying device of the present invention, FIG. 2 is a flowchart of the processing of the computer 6 of FIG. 1, and FIG. 3 is the crystal oscillator 3 alone of FIG. FIG. 4 is a graph showing a specific example of the piezoelectric response with respect to the time change of the resonance frequency with respect to the gas and the mixed gas, and FIG. 4 is a graph showing the time constant and the saturated adsorption amount of the single gas and the mixed gas obtained from the piezoelectric response of FIG. .

The present invention has been made as a result of detailed examination of the adsorption process of the gas molecules to be detected on the adsorption film. Here, the examination result will be described.

Adsorption is formed as a film on the crystal oscillator by high frequency sputtering using both polyethylene and polytetrafluoroethylene as targets, and changes in the resonance frequency of the crystal oscillator due to the adsorption of gas molecules to be detected on the adsorption film. Examined. It is known that the resonance frequency of the crystal oscillator is proportional to the mass change of the adsorption film, that is, the mass of the adsorbed gas to be detected. As a result, when the gas to be detected is a normal organic compound such as various alcohols, aromatic compounds, and ketones, this adsorption film in a state in which the gas to be detected is not adsorbed is exposed to a gas having a certain concentration. However, the time change of the resonance frequency at the time (time k · Δt) sampled at every certain time Δt, that is, the adsorption amount m [k] is

[0014]

## EQU1 ## m [k] = a (1-exp (-k.Δt / τ))

Where exp is an exponential,
That is, with an exponential function, k is a variable (integer) representing time,
It is known that Δt represents the sampling time, a represents the saturated adsorption amount of the gas to be detected, and the time constant τ is deeply related to the type of gas to be detected.

It has been known that the time variation m [k] of the resonance frequency of the crystal oscillator with respect to the mixed gas (including n kinds of component gases) is represented by the sum of exponential functions as follows.

[0017]

[Equation 2] Here, since the time constant τ _j of each component gas does not change even in the mixed gas, the time constant is measured beforehand with respect to the standard sample of each component gas, and the above equation τ _j is calculated from the measurement data by the algorithm of the linear filter described later. That is, the type of each component gas can be identified by extracting the time constant of each component gas and a _j, that is, the saturated adsorption amount of each component gas and comparing with the time constant of the standard sample. If the concentration is the same, the saturated adsorption amount is the same for both the mixed gas and the single gas. Therefore, the concentration can be quantitatively determined from the saturated adsorption amount of each component gas.

Next, the mixed gas component discriminating and quantifying device of this embodiment will be described.

As shown in FIG. 1, this mixed gas component discriminating and quantifying device comprises a measuring cell 1, a crystal oscillator 3, an oscillating circuit 4, a frequency counter 5, a computer 6, a display device 7 and a gas supplier 8. To be done.

The gas supplier 8 has a suction function such as a pump and constantly supplies the gas sample to the measuring cell 1. One crystal oscillator 3 is arranged in the measurement cell 1, and an adsorption film 2 is provided on the surface of the crystal oscillator 3. Here, the adsorption film 2 is formed by sputtering polyethylene and polytetrafluoroethylene as targets to coat the surface of the crystal oscillator 3. For example, graphite, polyfluorotrifluoroethylene, or the like is used as a target. It may be another plasma-derived fluorine-containing polymer thin film formed as described above. The oscillator circuit 4 oscillates at the resonance frequency of the crystal oscillator 3. The frequency counter 5 counts the resonance frequency of the crystal oscillator 3 oscillated by the oscillation circuit 4.

The computer 6 tracks changes in the oscillation frequency of the oscillation circuit 4 measured by the frequency counter 5, and based on the changes in the resonance frequency of the crystal oscillator 3, the time constant of each component gas in the gas sample and the saturation adsorption. The amount is extracted, the type of the component gas in the measurement cell 1 is identified, and the concentration is quantified. Further, a display device 7 is connected to the computer 6, and displays the piezoelectric response of the crystal oscillator 3, the identification result of the component gas and the concentration.

The processing in the computer 6 will be described in detail below with reference to the flowchart of FIG.

First, the computer 6 obtains the saturated adsorption amount a and the time constant τ of each standard sample from the piezoelectric response curve of the crystal oscillator 3 for each standard sample (step 11). Since this response curve is expressed by an equation including one exponential function, it is easy to estimate the time constant and the saturated adsorption amount.

Next, when the mixed gas to be measured is introduced into the measuring cell 1, the piezoelectric response of the crystal oscillator 3 to the mixed gas is obtained (step 12). Here, the time constant τ _{j of} the exponential function and the saturated adsorption amount a _j included in the piezoelectric response curve are extracted according to the following linear filter algorithm (step 13).

That is, from time k · Δt to time (K-
P). The vector M consisting of the adsorption amount up to Δt is M = (m [k], m [k-1], ... M [k-P])
^T , (P + 1) × L matrix φ consisting of the adsorption amount from time (k−1) · Δt to time (k−P−L) · Δt

[0026]

[Equation 3] And P>L> n, (1) B = {φ ^T φ} ⁻¹ φ ^T M is calculated to obtain B = (b ₁ , b ₂ , ..., B _L ) ^T.

(2) Using b _j obtained in (1), X
Equation for

[0028]

[Equation 4] Solve This real solution

[0029]

[Equation 5] And

(3) Time constant τ _j = -Δt / log (r
_j ).

Of these values, the remaining time constant excluding the _one with the largest absolute value (tau ₁ ) is the time constant of each component gas. The vector A consisting of the saturated adsorption amount of each component gas is A = (a _1, −a ₂ , −a ₃ , ..., −a _{n + 1} ) ^T , the reciprocal of the real number solution obtained in (2) The matrix R of (P + 1) × (n + 1) obtained by using

[0032]

[Equation 6] Then, (4) the saturated adsorption amount a _j of each component gas is obtained from A = {R ^T R} ^-1 R ^T M.

The type of each component gas is identified from the time constant τ _j obtained by the above algorithm. That is, a certain time constant τ _j is compared with the time constant τ _i of gas i (step 1
4), if τ _j is not equal to τ _i , the gas i is not discriminated (step 16). After it is judged in step 14 that τ _j is equal to τ _i and the gas i is likely to be contained in the mixed gas, it is judged whether or not a _j is larger than the threshold value d _i (step 15). . d _i is an amount for determining whether or not a _j is due to noise, and is, for example, a saturated adsorption amount for a standard sample having a minimum concentration measured in advance. When a _j ≤d _i , the a _j is judged to be noise and is not judged to be gas i (step 16). a _j
When> d _i , gas i is discriminated (step 17), and its concentration is estimated from a _j (step 18).

Next, a method of using this mixed gas component discriminating and quantifying device will be described.

First, a gas sample containing a gas to be detected is sent into the measuring cell 1 from the gas supply device 8, and the gas inside the measuring cell 1 is replaced with the gas sample within a time that can be ignored compared to the measuring time. Then, the adsorption of the gas molecules to be detected to the adsorption film 2 of the crystal oscillator 3 is started, and the time change of the adsorption amount of the gas to be detected is converted into the piezoelectric response of the crystal oscillator 3, and the oscillation frequency of the oscillation circuit 4 is changed. The time change of the adsorption amount can be monitored by measuring with the frequency counter 5. The computer 6 samples the output of the counter 5 at regular intervals, traces the piezoelectric response of the crystal oscillator 3, and estimates the time constant τ _j and the saturated adsorption amount a _j of each component gas.

Thereafter, the computer 6 identifies each component gas by comparing it with the time constant obtained from the measurement performed on the standard sample, and also quantifies the concentration based on the saturated adsorption amount and displays it on the display device 7. indicate.

Next, a specific example of the mixed gas component discrimination and quantification according to this embodiment will be described.

FIG. 3 shows the piezoelectric response of the crystal oscillator 3 by the mixed gas component discriminating and quantifying device of this embodiment.
ppm methanol (a), 1110 ppm benzene (b), 580 ppm acetone (c) and 940 p
580 with pm methanol and 1110 ppm benzene
The piezoelectric response of the crystal oscillator 3 to a mixed gas (d) of ppm acetone is shown by a frequency change / time curve.

Here, the sampling time Δt by the computer 6 is set to 4 seconds. The adsorption film 2 was prepared by placing a polyethylene disk having a diameter of 80 mm on a polytetrafluoroethylene disk having a diameter of 135 mm, a sputtering power of 0.94 W / cm ^{2 on} average, and a sputtering time of 76 minutes. The height is 0.76 μm. The crystal oscillator 3 is AT-cut and has a thickness of 0.1 mm.
It is a disk with a diameter of 85 mm. FIG. 4 shows the time constant and the saturated adsorption amount estimated from the mixed gas (d) by using the above algorithm with L = 15.

In the graph of FIG. 4, ◯ marks 21, 22,
23 is a time constant and a saturated adsorption amount obtained from the piezoelectric response of the crystal oscillator 3 with respect to a single gas of methanol (a), benzene (b), and acetone (c), respectively. Also,
□, 31, 32, 33, 34 are methanol, acetone,
The time constant and the saturated adsorption amount obtained from the piezoelectric response to the mixed gas (d) of benzene. Four time constants were obtained from the mixed gas (d), but the saturated adsorption amount 33 for one of them was very small (0.7 Hz), and it was judged that this was due to noise. The remaining 31, 32,
It can be seen that the three gas numbers 34 are close to the time constants of the individual gases, and that the mixed gas contains the three gases of methanol, benzene, and acetone.

Further, since the saturated adsorption amount of each component gas is almost equal to the saturated adsorption amount in the case of a single gas, the concentration can be quantified from the saturated adsorption amount-concentration relational expression in the case of a single gas. In this case, the saturated adsorption amounts of the gases (a), (b) and (c) are 25.8 Hz, 55.1 Hz and 74.
6 Hz, and saturated adsorption amounts of methanol, benzene, and acetone in the mixed gas (d) are 22.3 Hz and 4 respectively.
At 5.7 Hz and 61.3 Hz, the saturated adsorption amount of each component gas is almost equal to the saturated adsorption amount in the case of a single gas, and therefore the concentration can be determined from the saturated adsorption amount-concentration relational expression in the case of a single gas. It is possible.

In the mixed gas component discriminating and quantifying apparatus of this embodiment, the type of the component gas can be identified by using a single crystal oscillator by a plurality of time constants obtained from the piezoelectric response to the mixed gas. Since the concentration can be quantified from the saturated adsorption amount, the cost is low and the accurate identification result can be obtained.

[0043]

As described above, the present invention uses a single crystal oscillator provided with an adsorption film on its surface, exposes the crystal oscillator to a gaseous sample, and changes the resonance frequency of the crystal oscillator. Each component gas is identified by extracting multiple time constants from the time change, and the concentration is quantified from the saturated adsorption amount of each component gas. The effect is that it can be done accurately.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment of a mixed gas component determination and quantification device of the present invention.

FIG. 2 is a flowchart of a process of a computer 6 of FIG.

FIG. 3 is a graph showing a specific example of piezoelectric response of the crystal oscillator 3 of FIG. 1 to a single gas and a mixed gas.

4 is a graph showing time constants and saturated adsorption amounts of a single gas and a mixed gas obtained from the piezoelectric response of FIG.

[Explanation of symbols]

1 Measuring cell 2 Adsorption film 3 Quartz oscillator 4 Oscillation circuit 5 Frequency counter 6 Computer 7 Display device 11, 12, ..., 18 Steps 21, 22, 23 ○ mark 31, 32, 33, 34 □ mark a of 940ppm Methanol b 1110 ppm benzene c 580 ppm acetone d 940 ppm methanol, 1110 ppm benzene and 580 ppm acetone mixed gas

Claims (4)

[Claims] 1. A component in a mixed gas is obtained by using a crystal oscillator provided with a gas adsorption film on its surface, and obtaining a change in resonance frequency of the crystal oscillator due to adsorption of a gas to be detected to the gas adsorption film. In a mixed gas component identification and quantification method for identifying the type of gas and quantifying the concentration, a single crystal oscillator provided with a gas adsorption film on the surface is used, and the resonance frequency of the crystal oscillator is included in the time change. A procedure for detecting the time constant of the exponential function, the time constant of the exponential function included in the time change of the resonance frequency of the crystal oscillator detected by the procedure, and the time change of the resonance frequency in the case of a single gas of each component gas. Is compared with the time constant of the exponential function, and the procedure for identifying the type of each component gas is determined, and the saturated adsorption amount of each component gas to the gas adsorption film is calculated to determine each component gas. The concentration of A method for discriminating and quantifying a mixed gas component, which comprises a step of performing an amount. 2. The method of discriminating and quantifying a mixed gas component according to claim 1, wherein a linear filter algorithm is used to detect the time constant of an exponential function included in the time change of the resonance frequency of the crystal oscillator. 3. A measurement cell in which a single crystal oscillator having a gas adsorption film provided on the surface thereof is arranged, a gas supplier for supplying a gas sample to the measurement cell, and a gas sample for supply to the measurement cell. An oscillation circuit that oscillates at the resonance frequency of the crystal oscillator, a frequency counter that counts the resonance frequency of the crystal oscillator that the oscillation circuit oscillates, a display device, the frequency counter, In the case of a single gas of each component gas of the gas sample supplied to the measurement cell, the time constant of the exponential function included in the time change of the resonance frequency of the crystal oscillator due to the adsorption of the gas sample to the gas adsorption film is detected. The type of each component gas is identified by comparing with the time constant of the exponential function that represents the time change of the resonance frequency, and it is determined whether the saturated adsorption amount of each component gas to the adsorption film is obtained. Perform quantification of the concentration of the minute gas, mixed gas component and a computer for displaying the result on the display device determination and quantification device. 4. The mixed gas component discriminating and quantifying device according to claim 3, wherein a fluorine-containing polymer thin film derived from plasma is used for the gas adsorption film of the crystal oscillator.