JPS59218936A - Remote spectrum analyzer - Google Patents

Abstract

PURPOSE:To obtain a remote spectrum analyzer which is economically effective, capable of highly accurate measurement by removing an error factor by providing said device with a light transmitting optical fiber, light branching means, by- pass optical fiber, photocoupling means, and a spectrum analyzing part. CONSTITUTION:Light as a light pulse is transmitted from a light source 1 to a place where a gas case 4 to be measured is arranged through the light transmitting optical fiber 2. The light from the light source 1 is branched by a light branching element 3 placed immediately before the case 4; one is passed through gas and outputted as signal light selectively absorbed at wavelength lambda1 and the other is guided to the by-pass optical fiber 5 and outputted as reference light which is not absorbed by the sample gas. These light beams are guided to the same light returning optical fiber 6 by a wave composing photocoupler 3'. The light returned to an observing point through the fiber 6 is transmitted to the spectrum analyzing part 12 consisting of a spectroscope 7, photodetectors 8, 8', amplifiers 9, 9', and a data processor 10 and electric signals corresponding to the signal light pulse and the reference light pulse are independently detected by the time sharing method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spectroscopic analyzer that quantitatively and remotely measures, for example, trace gas components in an atmosphere, moisture in a sample, etc. using changes in light absorption.

In a spectroscopic analyzer that remotely measures trace gas components in the atmosphere, moisture in a sample, etc., highly accurate measurement that eliminates error factors, a simple configuration, and high reliability are desired.

After transmitting an optical signal to a distant point using an optical fiber, it is passed through the object to be measured, and then sent back to the observation point using an optical fiber for two-spectrum measurements.

By measuring the absorption of light at specific wavelengths,
Examples of spectroscopic analyzers that quantitatively and remotely measure specific substances include methane gas sensors and moisture sensors.

Generally, gases and moisture absorb light of specific wavelengths based on their unique molecular structure.

When light of these wavelengths is passed through the atmosphere or sample to be measured, the light energy is absorbed depending on the amount of gas or moisture contained therein, so the amount of attenuation of this amount of light indicates the substances contained therein. You can know the amount of For example, as shown in Figure 1, when light from an InGaAsP light emitting diode is passed through methane gas, the distance is 1331 μm.
Absorption shear occurs at wavelengths of 324 μm, ], 322 μm. Although it is possible to measure the concentration of methane gas only from the amount of absorbed light, the amount of received light fluctuates due to factors other than the gas concentration, such as fluctuations in the intensity of the light source, resulting in errors.

The method of determining the gas concentration based on the amount of light received only at the absorption wavelength is vulnerable to disturbances.

Therefore, in order to eliminate the influence of such disturbance, for example, in addition to the absorption wavelength λ1 shown in FIG.

From this ratio of received light amounts, which are considered to be affected by disturbances at the same rate, it is possible to determine the gas concentration without being affected by disturbances. That is, in this measurement method,
i('At the light transmitting point, as shown in the figure.

An optical branching element 20 branches an optical signal from a light source].

Further, the light was separated by a spectroscope 21 to measure the intensity level of the light source at each wavelength λ1, ]2.

The light that has passed through the gas to be measured in the sample gas container 4 is:

This is sent back to the observation point using the optical fiber 6 for return light, and then separated into spectra by the spectrometer 7 to find the ratio of the intensity level at the wavelength λ and ]2. Measurements of gas concentration were made by comparing the ratio of intensity levels at these wavelengths measured at the same location. In addition.

22 and 22' are photodetectors, and 23 and 23' are amplifiers.

8 and 8' are photodetectors, 9 and 9' are amplifiers, 10 is a data processing device for calculating the gas concentration, and 11 is a measurement result display/recording device.

In this conventional method, a spectrometer 21 is used to separate the light from the light source 1, and a spectrometer 7 is used to separate the light that has passed through the gas to be measured and is returned. A set of spectrometers and a photodetector and amplifier attached to each spectrometer are required, which makes the equipment complex and expensive, and the difference in spectral characteristics between the two sets of spectrometers can become a source of error. Conceivable. Furthermore, if there is wavelength-dependent absorption or scattering due to causes other than the gas to be measured in the transmission path, there is a drawback that this also becomes a cause of measurement error.

An object of the present invention is to provide a remote spectroscopic analysis device that eliminates the above-mentioned drawbacks, has a relatively simple configuration, is economically advantageous, and enables highly accurate measurement without error factors. be.

According to the present invention, there is provided a light transmitting optical fiber at one end which receives a light pulse from a light source, and a light transmitting optical fiber located at the other end of the light transmitting optical fiber, which branches the output light of the light transmitting optical fiber into two. a bypass optical fiber that receives the other light branched by the optical branching means; and a bypass optical fiber that receives the other light branched by the optical branching means, and the light that has passed through the object to be measured and the bypass light. an optical coupling means for guiding the light from the fiber to the same optical fiber for returning light; and an optical coupling means for receiving the output light of the optical fiber for returning light and for the optical pulse passing through the object to be measured. A spectroscopic analysis unit that uses the time delay of the light/waves passing through the fiber to time-divisionally differentiate the electrical signals corresponding to these lights/waves and performs predetermined signal processing. A remote spectroscopic analysis device is obtained.

That is, in the present invention, the light from the light source is branched immediately before being guided to the object to be measured, one branch is passed through the object to be measured, and the other is split after passing through the optical fiber/N+ for , and again guide them into the same optical fiber and send them to the observation point, and detect the light/gusrus that has passed through the object to be measured. Using the time delay of the optical pulses that have passed through the bypass optical fiber, the corresponding electrical signals after detection are distinguished by a time division method.

It is designed to perform predetermined signal processing.

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 3, a light absorption sensor according to one embodiment of the present invention is shown. It is assumed that the output light of the light source 1 includes at least two wavelengths, λ and ]2. It is assumed that the light with the wavelength λ1 is selectively absorbed by the gas to be measured, but the light with the wavelength λ2 is not absorbed.

Light is transmitted in the form of optical pulses from a light source 1 via a light transmitting optical fiber 2 to a location where an f/s container 4 to be measured is installed. Here, the light from the light source 1 is branched by the light branching element 3 placed just before the container 4, and one of the lights passes through the gas and is selectively absorbed at the wavelength λ1 (hereinafter signal light On the other hand, the reference light (hereinafter referred to as reference light) is guided to the bypass optical fiber 5 and is not absorbed by the sample gas. These signal light and reference light are guided to the same optical fiber 6 for return light by an optical coupling element 3' for two-way multiplexing. By appropriately selecting the length of the bypass optical fiber 5, the pulses, such as pulses P1 and pulses P2, in the light transmission optical fiber 2 shown in FIG. As shown in FIG. 4(B), the signal light/gurus P1 and P2 pass through the gas to be measured.

The reference light pulse p passes through the bi/os optical fiber 5.
, / and P2', for example, by a time interval t1. The light sent back to the observation point via the return light optical fiber 6 is passed through a spectrometer 7 common to the signal light and reference light.
After the light intensity level at wavelengths λ and λ2 are detected by photodetectors 8 and 8', converted into electrical signals and sent to data processing device 10 through amplifiers 9 and 9'. In the data processing device 10, electric signals corresponding to the signal light pulses and the reference light beam at wavelengths λo and λ2 are detected separately by a time division method, and the wavelength λ! and λ
The intensity ratio of 2 is required. Furthermore, in the data processing device]0, the amount of absorption by the sample gas of the absorption wavelength λ2 is determined from the intensity ratio of the wavelengths λ1 and λ2 in the signal light pulse and the intensity ratio of the wavelengths λ1 and λ2 in the reference light pulse, and the concentration of the gas is determined. Calculate. That is, 2 spectrometers 7. photodetectors 8 and 8';
It is displayed and recorded by the amplifier 9 and the display/recording device 11.

From the above, according to the present invention, the spectral detection portion is not common for the signal light that has been absorbed by the object to be measured and the reference light that has not been absorbed.

The configuration of the device is simple and economical, and error factors caused by wavelength-dependent losses due to causes other than those caused by the object to be measured can be eliminated. optical path (excluding the part to be measured)
It can be removed by passing it through, which has the effect of improving measurement accuracy and reliability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the absorption shear torque of methane gas near 1.331 Lm. The wavelength that is selectively absorbed is represented by λl (here, for example, 1331 μm), and the wavelength that is not absorbed is represented by λ2. FIG. 2 is a diagram showing the configuration of a conventional gas sensor. FIG. 3 is a diagram showing the configuration of an embodiment of the present invention. Figures 4 (A) and (B) show the state of the light in the optical fiber for light transmission in Figure 3;・Chi v −l・. 1...Light source, 2...Optical fiber for light transmission, 3...
Optical branching element, 3'... Optical coupling element, 4... Sample gas container, 5... Optical fiber for binder gas, 6... Optical fiber for returning light. 7... Spectrometer, 8, 8'... Photodetector + 9
+9′...Amplifier. 10... Data processing device, 11... Display/recording device. 12... Spectroscopic analysis section, 20... Optical branching element, 21.
・・Spectrometer p 22 + 22' ・・Photodetector + 2
3 + 23'...Amplifier.

Claims (1)

[Claims] 1. A light transmitting optical fiber that receives a light pulse from a light source at one end, and a light transmitting optical fiber located at the other end of the light transmitting optical fiber, which branches the output light of the light transmitting optical fiber into two, and one of the two branches. a bypass optical fiber that receives the other light branched by the optical branching means; and a bypass optical fiber that receives the other light branched by the optical branching means, and a light that has passed through the measurement target and light from the bypass optical fiber. an optical coupling means for guiding the optical fiber to the same optical fiber for returning light; and an optical coupling means that receives the output light of the optical fiber for returning light and connects the optical pulse that has passed through the optical fiber for piracy with respect to the optical pulse that has passed through the object to be measured. 1. A remote spectroscopic analysis device comprising: a spectroscopic analysis section that time-divisionally distinguishes electrical signals corresponding to these optical pulses using the time delay of the optical pulses, and performs predetermined signal processing.