JPH02284045A - Detection of concentration and pressure of gas with tunable etalon utilized therefor - Google Patents

Abstract

PURPOSE:To detect concn. of gas with high precision by resonating and modulating a tunable etalon wherein light passed through a gas cell is made incident and utilizing both total quantity of light of absorbed light and nonabsorptive light and absorption coefficient of absorbed light. CONSTITUTION:Light emitted from a light emission diode 3 is transmitted to an optical instrument bracket 6 provided with a gas cell 7 which is encapsulated with gas to be detected. This light is converged in a beam-shape by a lens 8and passed through the gas cell 7 and converged by a lens 9. Furthermore it is passed through an optical connector 11 and made incident on a subcase 12 and split into transmitted light L3 and reflected light L4 by an interference filter F1. When the former is made incident on a tunable etalon 2, both a first light having wavelength corresponding to the gas absorption spectrum and a second light having nonabsorptive wavelength are alternately passed by vibra tion of the etalon plates 21A, 21B. CPU 18 calculates the difference of a signal corresponding to the quantities of light of the first and second light. The concn. of gas in the gas cell 7 is calculated and detected on the basis thereof. Thereby the concn. of arbitrary gas is detected with high precision.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to the resonance of a tunable etalon having the characteristics of an optically narrow m1jffl filter depending on the absorption vector of the gas whose concentration (pressure) is detected. This invention relates to a method of detecting the fA degree (pressure) of any gas by modulating its wavelength.

[Prior Art] Conventionally, as means for detecting the concentration (pressure) of, for example, methane gas, there has been a circuit configuration as shown in FIG.

This is a process in which light transmitted through a gas cell filled with methane gas is partially transmitted and partially reflected by a half mirror 101, and the reflected light is used as a reference light and photoelectrically converted by a photodiode 102, and then the photoelectrically converted direct current The signal is amplified by an amplifier 103, and the amplified DC signal is applied to one input terminal of a differential amplifier 104, while the light transmitted through the half mirror 101 is passed to an interference filter 105 whose center wavelength matches the absorption spectrum of methane gas. The light that has passed through the interference filter 105 is converted into a measurement light by a photodiode 106, and then the photoelectrically converted DC signal is amplified by an amplifier 107, and the amplified DC signal is sent to the other input terminal of the differential amplifier 104. , the difference between the DC signal corresponding to the reference light and the DC signal corresponding to the measurement light is amplified in the differential amplifier 104, and the differential amplifier 1
Based on the signal output from 04, the degree of methane gas is detected.

[Problems to be Solved by the Invention] The conventional gas concentration (pressure) detection means described above is a half mirror.
101 divides the optical path into a reference light and a measurement light, and each electric circuit is made independent, so that, for example, the amplifier 103
．． When the electrical characteristics of the differential amplifier 107 and the differential amplifier 104 change due to changes in ambient temperature, the amplification factors of each amplifier vary slightly, and the DC signal corresponding to the reference light and the DC signal corresponding to the measurement light vary depending on the temperature. Since the concentration fluctuates, there is a problem in that accurate concentration detection cannot be performed. Conventionally, therefore, it was necessary to place the electric circuit in a constant temperature bath to stabilize the circuit characteristics against temperature. and 1 degree (pressure)
In order to increase detection accuracy, it was necessary to increase the accuracy of temperature control of the thermostatic chamber. However, there is a problem in that there is a technical limit to increasing the accuracy of temperature control 211 of the thermostatic oven, and thermostatic ovens with high temperature control accuracy are expensive.

Further, since it is a DC signal amplification method, it is difficult to remove noise, and even if a drift current is generated, it is extremely difficult to remove it.

Therefore, in the present invention, in order to solve the above problem, the light transmitted through the gas cell is passed through the A-light path without being split into two optical paths, the reference light and the measurement light, and this single optical path or the 4q k: of the gas cell is performed. The tunable etalon whose resonant wavelength can be tunable is controlled to slightly modulate the resonant wavelength around the absorption wavelength of the gas whose concentration (pressure) is detected. Feedback automatically adjusts to the absorption wavelength of light of the detected gas (pressure) it, I! The technical problem to be solved is to detect the n degree (pressure) of gas with high precision by controlling the temperature.

[Means for solving the problem] The technical means for solving the above problem is to transmit a beam-shaped light through a gas cell filled with a gas to be detected for concentration (pressure), and to convert the light transmitted through the gas cell into a tunable etalon. The tunable etalon is resonantly modulated at a predetermined timing while the tunable etalon is being incident on the gas, and a first light having a wavelength that is strongly absorbed by the concentration (pressure) detection gas and a second light having a wavelength that is not absorbed by the gas. At the same time, the total light R of the first light and the second light that has passed through the tunable ether O is monitored, and when this total light amount is attenuated to a predetermined amount or less, the above-mentioned light is transmitted based on the attenuated light amount. The first light and The absorption rate of the first light by the concentration (pressure) detection gas is calculated based on the first electric signal obtained by photoelectrically converting the second light and the second electric signal, and the absorption rate of the first light by the gas to be detected is calculated from the absorption rate. Concentration (pressure) This is to calculate the concentration (pressure) of the detected gas.

Alternatively, a tunable etalon disposed in an incident optical path for making a beam of light incident on a gas cell filled with a gas to be detected (pressure) may be resonantly modulated at a predetermined timing to detect the concentration (pressure). A first light with a wavelength that is strongly absorbed by the detection gas and a second light with a wavelength that is not absorbed by the detection gas are passed, and the sum of the first light and second light that has passed through the tunable etalon is obtained. The amount of light is monitored, and when the total amount of light is attenuated to a predetermined amount or less, the resonance modulation of the tunable etalon is corrected based on the attenuated amount of light, and the center of the modulation of the resonance wavelength of the tunable etalon is detected by the concentration (pressure). Feedback control is performed to match the absorption wavelength of the light of the gas, and the concentration (pressure) is ) Calculating the absorption and yield rate of the first light by the detection gas, and calculating the concentration (pressure) of the detection gas from the absorption rate.

[Function] With the above technical means, the light that has passed through the gas cell is not separated into reference light and measurement light as in conventional gas sensors, but is passed through the same optical path, and the light that has passed through the same optical path is The first light of the wavelength absorbed by the concentration (pressure) detection gas by the resonance modulation effect of the tunable etalon provided in the optical path after the gas cell or in the optical path before the gas cell, and A second light having a wavelength that is not absorbed by the detection gas is passed as a measurement light and a reference light, respectively, and feedback control is performed to align the center of the resonant wavelength of the tunable etalon with the absorption wavelength of the concentration (pressure) detection gas. Therefore, the function is to detect the concentration (pressure) of any gas with high precision based on the light intensity corresponding signal of the first light as the measurement light and the previous corresponding signal of the second light as the reference light. do.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an overall structural system diagram for realizing an embodiment of the present invention.

In FIG. 1, a constant current circuit 2 provided in the main case 1
Due to the constant current applied from the light emitting diode <LED
) 3 emits light having a wavelength in the 1.3 micrometer band, for example, and this light is transmitted to the optical equipment bracket 6 via the optical connector 4 and the optical fiber 5. This optical bracket 6 includes a target 8 for detecting concentration (pressure).
A gas cell is disposed in which, for example, methane gas is uniformly filled as a detection gas (pressure). The light transmitted to the light fixture bracket 6 is incident on the lens 8,
The light beam L1 is focused into a beam by the lens 8 and is transmitted through the gas self. The light beam L1 transmitted through the gas self is condensed by a lens 9 and connected to a multimode fiber 10.
It is returned to the main case 1 via the optical connector 11. The main case 1 has a built-in sub-case 12, and the gas cell transmitted light returned to the main case 1 is transmitted to the sub-case 12 through the sub-optical connector 13 connected to the optical connector 11.
is incident on the

Gas cell transmitted light L2 incident on the sub-case 12 is separated into transmitted light L3 and reflected light L4 by an interference filter F1 having a half-mirror characteristic capable of reflecting a portion of the incident light. Note that this interference filter F1 has a wavelength bandwidth of 20 nm (nanometers) as shown in FIG. The reflected light L4 is condensed by a lens 15, photoelectrically converted by a photodiode PDI, amplified by an amplifier 16, and then sent to an AD converter 17.
J3 is converted into a digital signal R1. The digital signal R1 corresponding to the amount of reflected light L4 is input to a microcomputer (CPU) 18. This digital signal R1 is sent to a microcomputer (CPU).
) 1B is the optical fiber 5, multimode? iba 10
In order to monitor the optical fiber optical path, the microcomputer 18 samples it at a predetermined timing, and if the digitization @R1 is not input at the sampling timing, or if the potential becomes extremely low, an abnormality occurs in the optical fiber optical path. The microcomputer 18 outputs an abnormality signal to the alarm output circuit 19.

On the other hand, the transmitted light L3 is incident on the tunable etalon 21. This tunable etalon 21 includes two opposing etalon plates 21△, 21B, and a dielectric reflective film is formed on the opposing surface of each etalon plate 21△, 21B to reflect incident light onto the etalon. Plate 21A, 2
The structure is such that multiple reflections are performed between the etalon plates 21Δ and 21B, and light having a wavelength corresponding to the distance between the etalon plates 21Δ and 21B is transmitted through resonance. Either of the etalon plates 21A, 21B, for example, the etalon plate 21B
For example, a piezo element (PZT) 22 is attached as a tunable etalon driving means for slightly changing the distance between the etalon plates 21Δ and 21B. Vibration width is controlled. In addition, this tunable etalon 21 is
A device with a band of 1 nanometer is used.

As shown in Figure 2, the first light has a wavelength corresponding to the absorption spectrum of methane gas, that is, 1.3312 micrometers, and the first light has a wavelength of 1.3772 micrometers, which is slightly shifted from this 1.3312 micrometer wavelength. Meter (
dλ=5 nm), which is the second wavelength that is not absorbed by methane gas.
A piezo driver (tunable etalon control means) 23 is provided to output a control signal to the piezo element 22 in order to vibrate the etalon plate 21B so as to pass the light (see FIG. 3) in an AC manner.

Through the vibration control described above, the first light having a wavelength of 1.3312 micrometers and the second light having a wavelength of 1.3372 micrometers, which is slightly shifted from the wavelength of 1.3312 micrometers, alternate on the etalon. When passing through,
These lights are separated into spectral lights N1 and N2 by a two-way spectrometer 24. As shown in FIG. 4, the spectral beam N1 passes through an interference filter F2 having a half-width of 4 nanometers, is focused by a lens 25, and is photoelectrically converted by a photodiode PD2. Photodiode PD2
The DC signal that is photoelectrically converted and output from the photodiode PD2 is amplified in the amplifier 26, and then
It is converted into an alternating current signal N3 by passing through a capacitor 27, and is input to a synchronous detection circuit 28.

On the other hand, the spectral light N2 is focused by the lens 30 and photoelectrically converted by the photodiode PD3.

The DC signal photoelectrically converted in the photodiode PD3 and outputted from the photodiode PD3 is amplified in the amplifier 31, and then converted to an AC signal N4 by passing through the capacitor 32, and the gain is further adjusted by the programmable gain amplifier 33 whose gain is adjustable. The alternating current signal N5 is input to the synchronous detection circuit 34.

An oscillation circuit (
The O20) 36 oscillates and outputs a 50112 sine wave signal, and this oscillation signal S1 is sent to the adder 37, and a similar oscillation signal S2 is sent to the phase control circuit 38.

The adder 37 outputs to the piezo driver 23 a tightening signal S4 obtained by tightening the oscillation signal S1 and a dunable etalon resonance control correction signal S3, which will be described later.

The phase control circuit 38 inputs the 50oz sine wave signal S2 and generates a pulse signal every time the 50H7 sine wave crosses Z1, and outputs 10011z rectangular wave pulse signals S5 and S6. The F pulse signal S5 is input to the Sonoki Doho detection circuit 28, and the other pulse signal S6 is input to the synchronous detection circuit 34.

The synchronous detection circuit 28 inputs the pulse signal S5 and the AC signal N3, and synchronously detects the AC signal N3 in synchronization with the pulse signal S5. The output signal S7 synchronously detected in the synchronous detection circuit 28 is input to a PID circuit (proportional integral, proportional differential circuit) 40. The synchronously detected output signal S7 is transmitted by the tunable etalon 21 to the piezo element 2.
2, the vibration width changes from a predetermined value for some reason, and the first light that zeros the wavelength of 1.3312 micrometers and the first light that slightly deviates from the wavelength of 1.3312 micrometers. This is a signal for correcting the vibration width to return it to a predetermined value so that the second light having a wavelength of 3372 micrometers is not impossible to obtain.This signal S7 is sent to the PID circuit (proportional integral, proportional differential circuit). ) 40 to make a more precise signal and apply it to the adder 37 as the tunable etalon resonance control correction signal $3. Therefore, the signal S4 outputted from the accumulator 37 to the piezo driver 23 is composed of the oscillation signal S1, the tunnosol etalon resonance control correction signal S3 as a kind of feedback signal for correcting the vibration width of the dunable etalon, and the oscillation signal S1. It becomes the Shinga that adds up.

Further, the synchronous detection circuit 34 inputs the pulse signal S6 and the AC signal N5, and synchronously detects the AC signal 9N5 in synchronization with the pulse signal S6. The output signal 88 synchronously detected in the synchronous detection circuit 34 is converted into a digital signal 89 by the AD converter 17 and then input to the microcomputer 18 .

The microcomputer 18 has the same 1!11 detection circuit 34.
When a digital signal S9 corresponding to the synchronous detection output signal S8 output from
The reliability corresponding to the light intensity of the first light having a wavelength of 12 micrometers, and the above-mentioned 1. which is not absorbed by methane gas.
The difference between the signal and the signal corresponding to the amount of second light having a wavelength of 3372 micrometers is calculated, and the concentration (pressure) of the methane gas in the gas self is calculated and detected based on the difference.

The calculated concentration (pressure) of methane gas is displayed on the LED display 42 by setting the keyboard 41.

As described above, resonance occurs between the wavelength corresponding to the absorption spectrum of the first light absorbed by the concentration (pressure) detection gas and the non-absorption wavelength of the second light that is slightly shifted from the wavelength corresponding to the absorption spectrum. The means for detecting the gas concentration (pressure) with high precision by modulating the tunable etalon 21 in this manner is not limited to the methane gas disclosed in this embodiment, but can detect and display the concentration (pressure) of any gas. It is also useful in cases where

Note that when the gas concentration (pressure) exceeds a preset reference value, an alarm signal can be output from the alarm output circuit 19 in order to issue an alarm.

Incidentally, as a modification of the above embodiment, the interference filter F2
Instead, by using a gas cell filled with a gas to detect the concentration (pressure) and transmitting the light beam N1 through this gas cell, the center of the modulation of the resonant wavelength of the tunable etalon 21 can always be used to detect the concentration (pressure). Feedback control may be performed to match the absorption wavelength of the gas.

Further, the position n of the tunable etalon 21 does not have to be immediately after the interference filter F1 as in the above embodiment, but may be, for example, immediately before or after the gas self, or any other effective position. good.

Furthermore, an optical coupler or beam splitter is disposed immediately after the gas self, and the light transmitted through the gas self is divided into two, one of the lights is made to enter the interference filter F1, and the other light is sent to the reference power measuring section. It is also possible to input light and monitor the optical fiber optical paths of the optical fiber 5 and multimode fiber 10. However, in this case, the interference filter F1 does not require a half mirror function.

[Effects of the Invention] As described above, according to the present invention, a beam-shaped light is transmitted through a gas cell filled with an arbitrary gas whose concentration (pressure) is to be detected, and the first wavelength of light absorbed by the gas is transmitted. When detecting the gas concentration according to the light absorption of A first light and a second light as a reference light having a wavelength that is not absorbed by the gas are passed through at a predetermined timing, and the total destination of the first light and second light that has passed through the tunable etalon is calculated. and feedback-controls the center of the modulation of the resonant wavelength of the tunable etalon to automatically match the absorption wavelength of the light of the concentration (pressure) detected gas according to the total light m. The absorption rate of the first light by the detected gas is estimated based on the first electric signal and the second electric signal obtained by photoelectrically converting the first light and the second light. Since the degree (pressure) of the concentration (pressure) of the gas to be detected can be extracted from the above, there is an effect that the concentration (pressure) of any gas can be detected with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the overall configuration of an embodiment of the present invention, and FIG. 2 is an absorption spectrum characteristic diagram of methane gas,
FIG. 3 is an explanatory diagram of the characteristics of the interference filter and the tunable etalon, and FIG. 4 is an explanatory diagram of the characteristics of another interference filter. Further, FIG. 5 is a structural diagram of a conventional gas concentration (pressure) detection signal. 3... Light emitting diode 7... Gas cell Fl, F2... Interference filter 18... Microcomputer 21... Tunable etalon 22... Piezo element 23... Piezo driver 24... Spectrometer 2G... MjIIA unit 27... Capacitor 28... Synchronous detection circuit PO2, PO2... Photodiode 31... Amplifier 32... Capacitor 34... Synchronous detection circuit 36... Launching circuit 37... ... Adder 38 ... Phase control circuit 42 ... LED display

Claims (2)

[Claims] (1) A beam of light is transmitted through a gas cell filled with a gas to detect the concentration (pressure), and the light transmitted through the gas cell is incident on the tunable etalon, and the tunable etalon is resonantly modulated at a predetermined timing. , passing a first light having a wavelength that is strongly absorbed by the concentration (pressure) detection gas and a second light having a wavelength not being absorbed by the gas, and the first light having passed through the tunable etalon. and the second light, and when this total light amount attenuates to a predetermined amount or less, the resonant modulation of the tunable etalon is corrected based on the attenuated light amount, and the resonant wavelength modulation of the tunable etalon is corrected. Feedback control is performed to align the center with the absorption wavelength of the light of the concentration (pressure) detection gas, and a first electrical signal and a second electrical signal are obtained by photoelectrically converting the first light and the second light. The tunable etalon is characterized in that the absorption rate of the first light by the concentration (pressure) detection gas is calculated based on the concentration (pressure) detection gas, and the concentration (pressure) of the concentration (pressure) detection gas is calculated from this absorption rate. Gas concentration pressure detection method using (2) Resonance modulation is performed at a predetermined timing on a tunable etalon disposed in the incident optical path for inputting a beam of light into a gas cell filled with a gas to be detected for concentration (pressure);
A first light having a wavelength that is strongly absorbed by the concentration (pressure) detection gas and a second light having a wavelength that is not absorbed by the detection gas are passed through the tunable etalon. Monitoring the total amount of second light, when the total amount of light attenuates to a predetermined amount or less, correcting the resonance modulation of the tunable etalon based on the attenuated amount of light;
Feedback control is performed so that the center of the modulation of the resonant wavelength of the tunable etalon is aligned with the absorption wavelength of the light of the concentration (pressure) detected gas, and the first electricity is generated by photoelectrically converting the first light and the second light. Calculating the absorption rate of the first light by the concentration (pressure) detection gas based on the signal and the second electric signal, and calculating the concentration (pressure) of the concentration (pressure) detection gas from this absorption rate. A method for detecting gas concentration and pressure using a tunable etalon.