JP2003004635A - Fluorescence type oxygen analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen analyzer which can be automatically calibrated in a use environment and has high stability and reliability for a long time. SOLUTION: The fluorescence type oxygen analyzer has a transparent substrate or optical fiber where a light-shielding layer having oxygen transmission properties and a fluorescent layer are layered, a light-emitting element, an optical filter for selectively separating the fluorescence generated from the fluorescent layer, a light-receiving element, an amplifier and a signal processing part. In the oxygen analyzer, regions to be illuminated by the light-emitting element are set mutually independently within the same measurement environment to the fluorescent layer on the substrate or optical fiber. A fluorescence signal obtained by illuminating a specific region among the regions with the light for only a short time is made a reference value, and a fluorescence signal obtained by illuminating a part other than the specified region with the light is made a measured value. The measured value is corrected by a relative value to the reference value. An oxygen concentration is displayed accordingly.

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a correction method for a fluorescent oximeter that measures oxygen concentration in a gas or liquid using light. Heretofore, the Clark-type oxygen electrode method has been well known as a typical method for measuring oxygen in a gas or a liquid. The basic structure of the device according to this method consists of a cathode, an anode, an electrolyte and an oxygen-permeable membrane. The principle is that oxygen permeating the membrane reaches the cathode surface and is electrochemically reduced. Since the flowing current is proportional to the oxygen partial pressure, the oxygen concentration can be measured from the current value. There are two types of electrochemical reduction methods: constant potential electrolysis with an external power supply and a battery reaction without using an external power supply. The former is called a polarographic method, and the latter is called a galvanic cell method. [0003] The Clark-type oxygen electrode method is simple and suitable for a portable type. However, since oxygen is electrochemically treated and consumed, it is necessary to supply oxygen through the oxygen-permeable membrane to the cathode surface. In addition, the liquid to be measured must be constantly stirred. In addition, the use of a liquid electrolyte requires replacement of the membrane and the electrolyte, which means that it cannot withstand long-term use without calibration, and that measurement errors due to contamination of the membrane surface and the attachment of organisms increase. It was not suitable as a sensor for remote sensing. On the other hand, recently, a fluorescent oximeter utilizing the quenching action of fluorescent light by oxygen has appeared. This emits fluorescent light when illuminating a fluorescent substance containing polycyclic aromatics or aromatic hydrocarbons, and this fluorescent light reacts with the excited fluorescent molecules in the presence of oxygen molecules to temporarily form a complex. However, it utilizes the fact that the quenching phenomenon occurs in proportion to the collision probability between oxygen molecules and fluorescent molecules. Here, the emission intensities of the fluorescence in the anoxic state and the aerobic state are represented by I ₀ and I
Then, the emission intensity ratio (I ₀ / I) is the oxygen concentration (partial pressure)
Is linearly proportional to Therefore, the oxygen concentration can be determined by measuring the relative emission intensity. FIG. 3 shows a specific configuration of a sensor section (conventional example) which is a main section of a fluorescent oximeter. 1 is a light shielding layer, 2
Is a fluorescent layer and has oxygen permeability. Reference numeral 3 denotes a glass or transparent plastic plate, but an optical fiber may be used in some cases. 4 is an optical filter, 5 is a light receiving element such as a photodiode, 6c is a light emitting element such as an LED, 25 is excitation light, and 26 is fluorescence. Excitation light 25 from the light emitting element 6 excites a fluorescent substance fixed inside the fluorescent layer 2 to generate fluorescence 26. This light has a longer wavelength than the original excitation light, and is filtered by an optical filter. The light is converted into an electric signal by the light receiving element 5. The converted electric signal is output as data indicating the oxygen concentration via an amplifier and a signal processing unit. As described above, the fluorescent oximeter utilizing fluorescence emission does not use an electrolytic solution as in the Clark-type oxygen electrode method, and does not require replacement or replenishment of the electrolytic solution, and is excellent in maintainability. In addition, since the method basically does not consume oxygen, it can be measured even in a stationary liquid and does not require stirring. Also, the measurement value hardly fluctuates even with the attachment of dirt and the like, and the handling is simple. However, the fluorescence intensity changes with time, and the fluorescence intensity decreases with time, affecting accuracy.
This is considered to be a phenomenon of deterioration in light resistance in which dye fading occurs when the fluorescent substance is irradiated with light for a long time. [0007] As described above, in a device using the Clark-type oxygen electrode method or an existing fluorescent oximeter, when measured for a long period of time, the measured value may change due to a change or deterioration in the characteristics of the sensor. There was a problem of durability that fluctuated. When these devices are used for a short period of time for research or research, it is sufficient to calibrate before the start of measurement in air in which the oxygen concentration (partial pressure) is stable at 20.9%. . However, in remote sensing applications where it is necessary to periodically measure dissolved oxygen at many points, the sensor is installed in the liquid, calibration in the air is difficult, and a long-term stable oxygen concentration meter is required. Was. An object of the present invention is to solve the above-mentioned problems and to provide an oxygen concentration meter having high stability and reliability over a long period of time. [0008] In order to achieve the above object, an oxygen concentration meter of the present invention comprises a transparent substrate or optical fiber in which a light shielding layer having an oxygen permeability and a fluorescent layer are laminated, a light emitting element, An optical filter for selectively separating fluorescence emitted from the fluorescent layer, a light-receiving element, and a fluorescent oximeter having an amplifier and a signal processing unit, wherein the fluorescent layer on the substrate or the optical fiber includes: Areas to be irradiated with light are provided independently of each other, and a fluorescence signal obtained by irradiating a specific area of the specific area only for a short time is used as a reference value, and a fluorescence obtained by irradiating a part other than the specified area is irradiated with light. The signal is a measured value, and the measured value is corrected by a relative value with respect to the reference value to display the oxygen concentration. FIG. 1 is a schematic view of a sensor which is a main part of the present invention. As described below, this structure has a configuration in which a calibration channel is added to the structure of FIG. 3 of the conventional embodiment in the same measurement environment. 1 is a light shielding layer, and 2 is a fluorescent layer, both of which have oxygen permeability. Reference numeral 3 denotes a transparent glass plate or plastic plate on which the light-shielding layer 1 and the fluorescent layer 2 are laminated. When an optical fiber is used, the optical fiber coated with the light-shielding layer 1 and the fluorescent layer 2 can be independently measured. And for calibration. Reference numeral 4 denotes an optical filter, and reference numeral 5 denotes a light receiving element (photodiode). Reference numerals 6a and 6b denote light-emitting elements (LEDs) of a measurement channel and a calibration channel, respectively, which emit excitation light 20 and excitation light 22 surrounded by solid arrows as shown in FIG. Irradiation is performed on regions that do not interfere with each other to generate fluorescent light 21 and fluorescent light 23 surrounded by an arrow dotted line. Note that the light emitting elements 6a and 6b are driven with a time lag, and the fluorescent lights 21 and 23 can be similarly extracted from the same light receiving element 5 as signals that can be temporally identified. When the sensor is placed in a gas or liquid measurement environment, oxygen enters and exits through the light-shielding layer 1 and the fluorescent layer 2 to increase or decrease the intensity of fluorescence generated from the fluorescent substance fixed in the fluorescent layer. FIG. 2 shows a system diagram of an electronic circuit for driving the present sensor. Reference numeral 11 denotes a light emission control circuit for the light emitting elements 6a and 6b, which is sampled or continuously driven. 12 is a light receiving element (photodiode), 13 is an amplifier, 14 is an A / D conversion circuit, 15 is an arithmetic processing unit, and 16 is a display unit or a data transmission unit. The light emitting elements 6a and 6b respectively emit the excitation light 2
0 and 22 are radiated to different regions on the fluorescent layer, and the fluorescent light 21 of the measurement channel and the fluorescent light 23 of the calibration channel are independent of each other in a close place. Although the fluorescent light 21 and the fluorescent light 23 may be received by independent light receiving elements, in the present embodiment, the light emission control circuit 11 controls the light emission timing of the light emitting elements 6a and 6b. Receiving signal, amplifier 13, A / D conversion circuit 14
Is output to the arithmetic processing unit 15 through The arithmetic processing unit 15 includes the fluorescent light 21 and the fluorescent light 23 in an anoxic state in advance.
Intensity I ₀₁ and I ₀₂ , and fluorescence intensity ratio (I ₀ / I)
The oxygen concentration characteristic value (calibration curve) is stored as operation data, and the fluorescence intensity I ₁ measured in the measurement environment is measured.
I ₀₁ / I ₁ is calculated from the above, and the oxygen concentration can be obtained from this and the calibration curve data. [0012] Incidentally, the fluorescence intensity I treated as the calculation data is a function of temperature because it is an amount that varies with temperature, taking separate temperature data in the measurement, I ₀₁ in which the correction
Must be used. The calibration is performed manually in the air when it can be operated in the air. In applications such as remote sensing, since the sensor is installed in the environment to be measured for a long time, it cannot be taken out into the air and calibrated in the air. Is operated briefly the light emitting element 6b calibration channel in air in preparation for measurement in this case to seek a fluorescent output I _2, then,
The light output _{I 1} by the light emitting element 6a of the measurement channel is _measured, previously obtained the _I 1 _/ I 2 = N. N is an initial fluorescence intensity ratio of the measurement channel and the calibration channel at the time of calibration in air. The calibration is performed, for example, by operating the calibration channel once a day for 5 seconds. The fluorescence output of the calibration channel at this time is i ₁
And if the fluorescence output of the measurement channel is i ₂ , i ₁ / i
₂ = n is the fluorescence intensity ratio after a lapse of a certain time, and n / N is a change from the initial value of the fluorescence intensity ratio, and represents a decrease rate of the fluorescence intensity due to dye fading due to long-time light irradiation. . Therefore, the correction is based on the fluorescence intensity I of the measurement channel.
The value obtained by multiplying the N / n to ₁ as the new I _1, the I _{01 /} I ₁ as described above was calculated, it is possible to determine the correct oxygen concentration from which the calibration curve data. As described above, calibration is usually performed in an environment where the oxygen concentration is known, for example, in anoxic condition or in air. However, in an application where such an environment cannot be obtained, an independent calibration area is provided on the fluorescent layer in an adjacent place separately from the measurement channel area as in the present embodiment, and a short-circuiting area which is not affected by dye fading or the like is provided. The original state is maintained by the time operation, and the correction is automatically performed with the relative value to the output of the measurement channel in which the fluorescence intensity gradually decreases with the fluorescence intensity as a reference value. According to the present invention, a calibration channel is provided separately from a measurement channel at a close place in the same measurement environment, and sensitivity deterioration due to dye fading or the like is automatically corrected in a short time operation, and a long-term operation is performed. To realize a stable oxygen concentration meter. Providing the calibration channel region close to the measurement channel region has the effect of eliminating and receiving normal changes such as oxygen concentration and temperature in common. This is to avoid the influence on the quality of the device such as the light emission sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a sensor as a main part of the present invention. FIG. 2 is a system diagram of an electronic circuit for driving the sensor of the present invention. FIG. 3 is a configuration diagram of a sensor unit of a fluorescent oximeter according to a conventional example. DESCRIPTION OF SYMBOLS 1: Shielding layer 2: Fluorescent layer 3: Transparent glass or plastic plate 4: Optical filter 5: Light receiving element 6a: Light emitting element 6b of measurement channel: Light emitting element 6c of calibration channel: Conventional example Element 11: emission control circuit 12: light receiving element 13: amplifier 14: A / D conversion circuit 15: arithmetic processing unit 16: display unit or data transmission unit

Claims (1)

Claims: 1. An optical filter for selectively separating a transparent substrate or an optical fiber in which a light-shielding layer having oxygen permeability and a fluorescent layer are laminated, a light-emitting element, and fluorescent light emitted from the fluorescent layer. And a light receiving element, a fluorescent oximeter having an amplifier and a signal processing unit, wherein a region irradiated by the light emitting element on the fluorescent layer on the substrate or the optical fiber is mutually independent in the same measurement environment. The fluorescence signal obtained by irradiating a specific area of the light for a short time as a reference value, and the fluorescence signal obtained by irradiating a portion other than the specified area as a measurement value is used as a measurement value. A fluorescent oximeter, wherein the oxygen concentration is displayed by correcting with a relative value to the reference value.