JP5457700B2 - Lubricating oil deterioration monitoring device - Google Patents

Description

  The present invention relates to a lubricant deterioration monitoring device. More specifically, the present invention relates to an apparatus for optimizing the light transmitted through the lubricating oil so as to best determine the degree of deterioration of any lubricating oil and determining the degree of deterioration of the lubricating oil by detecting the light.

  To accurately and continuously monitor the degree of deterioration of lubricating oil used in various equipment, various engines, machine drive parts, such as automotive lubricating oil and industrial lubricating oil, it is necessary to replace the lubricating oil when necessary This makes it possible to change the lubricant systematically. This not only saves the resources of the lubricating oil, but also extends the machine life.

  When determining the degree of deterioration of lubricating oil, it is generally performed by collecting the lubricating oil in use and measuring various physical properties such as color, viscosity, acid value, and amount of impurities in another laboratory. . In these methods, it is possible to comprehensively judge the degree of deterioration of the lubricating oil, but since it takes a lot of time and manpower, it is currently performed only in industrially important devices or expensive devices. It is. On the other hand, the fact is that such measures are not taken for many machines, including automobiles that exist in general, and many of these machines deteriorate according to driving time and mileage based on past experience. The current situation is that the lubricating oil is changed by assuming the situation or by simple visual inspection.

  Among the many deterioration monitors, apparatuses that are most likely to achieve both accuracy and price include a method by measuring transmitted light and a method by measuring electrical characteristics. Other methods are expensive or have problems with accuracy. The method based on electrical characteristics is very attractive because the structure of the device is simple and the cost can be kept low. However, this method has a problem that the measurement value varies depending on the measurement environment, and has a drawback that the change in the measurement value from the initial use to the middle period is small for industrial lubricating oil.

  On the other hand, the color determination method using light is characterized in that the color change of the lubricating oil always changes little by little with the use time, and the measurement value itself is very accurate. A simple apparatus is commercially available that uses this method to measure the transmittance of visible light to determine deterioration. However, with this simple method, even if the transmittance changes during the use of the lubricating oil, the deterioration degree and the transmittance are not in a linear relationship depending on the type of the lubricating oil, so the determination of the deterioration degree can be uniquely determined. Has the disadvantage of not.

  As a countermeasure against the difference in coloring tendency depending on the type of lubricating oil, a method of measuring transmitted light separately for RGB is known (see, for example, Patent Document 1). However, in this method, since the deterioration pattern differs depending on the type of lubricating oil, it is necessary to deal with each oil type, and it is difficult to determine a general-purpose deterioration degree. In this way, when the visible region is measured by dividing it into monochromatic light, it is necessary to select it or calculate it with an appropriate formula. Moreover, it becomes information only about the wavelength of the selected light, and it is assumed that it is difficult to cope with many types of lubricants or usage conditions. In addition, in order to measure transmitted light separately for RGB, it is necessary to use three types of RGB light emitting elements and one light receiving element, or one light source and three types of RGB light receiving elements.

  Further, the deterioration of the lubricating oil is determined from one of the tristimulus values of transmitted light and the chromaticity coordinates x and y obtained from the tristimulus values and constants A, B, C and D set in advance according to the type of the lubricating oil. There is known a method of obtaining a judgment score by calculation. (For example, see Patent Document 2). However, in this method, since it is necessary to obtain four constants for each oil type in advance, there remains a problem in versatility. Further, since three sensors are required, there is a problem that the cost becomes high.

  Furthermore, there is known an apparatus that uses at least two types of monochromatic light sources having different wavelengths and determines the degree of oil degradation based on a difference in light absorption loss between two wavelengths (see, for example, Patent Document 3). However, in this method, since the optimal monochromatic light is different for each oil type, there remains a problem in reliability in dealing with many oil types.

Japanese Patent Laid-Open No. 06-034541 Japanese Patent Laid-Open No. 05-223729 Japanese Patent Laid-Open No. 11-235097

  As described above, the conventional lubricant deterioration monitoring device includes a method using absorption of transmitted light or light of a specific wavelength, a method using absorption of infrared light or ultraviolet light, electrical characteristics such as capacitance, electrical resistance, dielectric constant, or electrodes. Various methods such as a method based on electromotive force measurement, a method based on physical properties such as viscosity or density, a method based on a particle counter or a method of measuring insoluble matter from the amount of light transmission have been proposed. However, none of them has been widely used due to reasons such as a problem in accuracy and reproducibility as an index for determining deterioration, or even if there is no problem, the device is expensive. In order to be applied to many machines, both improvement in accuracy as an index for determining deterioration and low price have been required.

  The object of the present invention is to solve such problems, and is highly accurate with respect to a wide range of oil types and a wide use environment, and can reduce costs and enable simple measurement. It is an object of the present invention to provide a lubricating oil deterioration monitoring device that can be used.

  Here, as a result of intensive research, the inventors have been able to more accurately grasp the deterioration of the lubricating oil by measuring transmitted light having a specific wavelength width instead of monochromatic light, and having a specific wavelength. It was found that the width can be easily set by devising a filter.

  Therefore, the lubricant deterioration monitoring device according to the present invention transmits visible light generated from a single light source to the lubricant oil, receives the light with a single light receiving element, converts it into an electrical signal, and detects the deterioration of the lubricant oil. A single or a plurality of filters having a predetermined center wavelength and a half width are arranged between the light source and the light receiving element.

  According to this lubricating oil deterioration monitoring device, a single or a plurality of filters having a predetermined center wavelength and a half width are arranged between the light source and the light receiving element. Therefore, the measurement can be performed with a wavelength range, and the degree of deterioration of the lubricating oil can be accurately grasped. That is, by measuring with a wavelength range instead of monochromatic light, it is possible to measure the transmitted light as a value obtained by averaging the differences even if there are differences in the oil type and the deterioration state. Furthermore, since only the light source, the filter, and the light receiving element are required, the apparatus itself can be made extremely small and measurement can be performed easily. In addition, if there is a single light source such as a halogen lamp and a single light receiving element, the deterioration of the lubricating oil can be measured, so that the device can be manufactured at a lower cost and installed in more machines. become. As described above, it is possible to achieve high accuracy with respect to a wide range of oil types and a wide use environment, reduce costs, and enable simple measurement.

  In the lubricant deterioration monitoring device according to the present invention, it is preferable that a plurality of filters be arranged in parallel on the optical path of visible light. Accordingly, one optical path can pass through a plurality of filters at respective area ratios, and light having the area ratio can be received by one light receiving element, so that an arithmetic circuit can be dispensed with. Furthermore, by arranging the filters in a balanced manner with respect to the cross-sectional area of the optical path, the accuracy can be further improved and versatility can be increased.

  In the lubricant deterioration monitor according to the present invention, specifically, the center wavelength of the visible region is 500 nm or more and less than 600 nm between the light source and the light receiving element, and the half width is 30 nm or more and less than 120 nm. There is a single filter having a total wavelength range of 350 nm or more and less than 750 nm. In addition, between the light source and the light receiving element, a first filter having a center wavelength in the visible range of 400 nm to less than 500 nm and a half width of 30 nm to less than 100 nm, and a center wavelength in the visible range of 500 nm to less than 575 nm And the ratio of the area occupied by the second filter having a half width of 30 nm or more and less than 100 nm in the cross-sectional area of the first filter and the second filter on the optical path is 0 to 80%, 20 to 100%, respectively. It arrange | positions so that it may become. In addition, between the light source and the light receiving element, a first filter having a center wavelength in the visible range of 400 nm to less than 500 nm and a half width of 30 nm to less than 100 nm, and a center wavelength in the visible range of 500 nm to less than 575 nm And a second filter having a half width of 30 nm or more and less than 100 nm, and a third filter having a center wavelength in the visible region of 575 nm or more and less than 650 nm and a half width of 30 nm or more and less than 100 nm. It arrange | positions so that the ratio of the area which occupies for the cross-sectional area on the optical path of a 1st filter, a 2nd filter, and a 3rd filter may be 0-80%, 20-100%, and 0-60%, respectively.

  ADVANTAGE OF THE INVENTION According to this invention, while being highly accurate with respect to a wide kind of oil and a wide use environment, cost can be reduced and simple measurement can be performed.

It is a figure which shows the structure of the lubricating oil deterioration monitoring apparatus which concerns on embodiment of this invention. It is the figure which looked at the filter of the filter unit from the optical path direction. It is a diagram which shows the result of Experimental example 1. FIG. It is a diagram which shows the result of Experimental example 2. FIG. It is a diagram which shows the result of Experimental example 3. It is a diagram which shows the result of Experimental example 4.

  Hereinafter, a preferred embodiment of a lubricant deterioration monitoring device according to the present invention will be described in detail with reference to the drawings.

  First, the configuration of the lubricant deterioration monitoring device 100 according to the embodiment of the present invention will be described. FIG. 1 is a diagram showing a configuration of a lubricant deterioration monitoring apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the lubricant deterioration monitoring apparatus 100 includes a single light source 3 that irradiates the lubricant 1 to be inspected with visible light, and a filter unit 4 that allows the visible light transmitted through the lubricant 1 to pass. A single light receiving element 5 that receives and detects visible light transmitted through the lubricant 1 and the filter unit 4, an ADC / MPU 6 that processes an electric signal output from the light receiving element 5, and a process performed by the ADC / MPU 6 The display 7 for displaying the received data and the personal computer 8 for processing the data are provided. The lubricating oil 1 is stored in a measurement location 2 such as a tank. In actual measurement, the light source 3, the filter unit 4, and the light receiving element 5 are immersed in the lubricating oil 1 as the measuring unit 10. However, the measurement may be performed by filling the sample cell with the lubricating oil 1 and arranging the sample cell between the light source 3 and the filter unit 4.

  As the lubricating oil 1, various kinds of lubricating oils used for various devices such as automobile lubricating oil and industrial lubricating oil, various engines, driving parts of each machine, and the like can be applied. Multipurpose oil, hydraulic working oil, industrial general purpose oil, etc. can be measured.

  The light source 3 is composed of a single light source that emits visible light. The light source 3 is composed of one capable of continuous projection such as a tungsten lamp or a halogen lamp, or one capable of instantaneous projection such as a pulsed xenon lamp. Has been. The light source 3 may be either a continuous projection type or an instantaneous projection, and the wavelength is not limited. The light receiving element 5 has a function of receiving light irradiated from the light source 3 and transmitted through the lubricating oil 1 and the filter unit 4, converting the light into a voltage, and outputting the voltage to the ADC / MPU 6. This light receiving element 5 is composed of a single element, and any commercially available photodiode can be used as an optical sensor.

  The ADC / MPU 6 includes an A / D converter for A / D converting the signal input from the light receiving element 5 and a microprocessor (MPU) for performing arithmetic processing. There are square root processing, cubic root processing, logarithmic processing, etc. as the arithmetic processing by the microprocessor. By performing these arithmetic processing, it is possible to improve the measurement sensitivity of the lubricating oil that is highly colored and darkly colored. It becomes. The calculation result by the microprocessor is output to the display 7 and the personal computer 8. Note that the A / D converted signal may be directly output to the display 7 and the personal computer 8.

  The measurement by the lubricant deterioration monitoring device 100 is started by an operation that simply turns on the power switch of the light source 3, the light receiving element 5, the A / D converter and display 7 and the personal computer 8. It is desirable to read the data into the personal computer 8 and plot the change over time. When the measured value is about 20% to 30% of the new oil, it can be judged as the standard for replacement of the lubricating oil. It is desirable to make a comparison with physical and chemical properties.

In addition, the lubricant deterioration monitoring device 100 of the present invention can be made extremely small because the only members required as the measurement unit 10 are the light source 3, the filter unit 4, and the light receiving element 5. Since this measurement unit has simple constituent members, the sensor portion of the light receiving element 5 can have a diameter of 3 mm to 15 mm. As a result, the measurement unit 10 can be attached to every part of the machine such as a pipe, a tank, a cooler, and an actuator. A glass fiber (referred to as f ₁ ) heading from the light source 3 to the filter unit 4 and a glass fiber that is disposed on the light source 3 side so that one end thereof faces the end of the glass fiber f ₁ and is attached to the filter unit 4. (Referred to as “f ₂ ”) and a glass fiber (referred to as “f ₃ ”) attached between the filter unit 4 and the light receiving element 5 may be arranged to connect the optical paths with each glass fiber. The light from the light source 3 is guided to the filter unit 4 and the light receiving element 5 by these glass fibers. Then, the measurement can be performed by filling the case containing the light source 3, the glass fiber f ₁ , the glass fiber f ₂ , the filter unit 4, the glass fiber f ₃ , and the light receiving element 5 with the lubricating oil 1. Alternatively, the measurement may be performed by filling the lubricating oil 1 in a case including a part of the glass fiber f ₁ , the glass fiber f ₂ , the filter unit 4, the glass fiber f ₃ , and the light receiving element 5. Alternatively, the measurement may be performed by filling the lubricating oil 1 in a case including a part of the glass fiber f ₁ , the glass fiber f ₂ , the filter unit 4, and a part of the glass fiber f ₃ . Further, the measurement may be performed by filling the lubricating oil 1 in a case including a part of the glass fiber f _{1 and only} a part of the glass fiber f ₂ , and in this case, only the glass fiber is immersed in the lubricating oil 1. . Each case can guide light between the light source 3, the filter unit 4, and the light receiving element 5 with each glass fiber.

  In measurement, the measurement place 2 where the measurement unit 10 of the lubricant deterioration monitoring apparatus 100 according to the present embodiment is installed may be any place that touches the lubricant 1 such as a machine oil tank, oil pan, or pipe. Further, it may be placed in a place where it does not come into contact with the lubricating oil 1 at normal times and inserted into a tank or the like every time measurement is performed. In addition, although it is necessary to devise in terms of equipment, it is also possible to perform measurement by keeping the lubricant 1 out of contact during normal times and introducing the lubricant 1 during measurement. By adopting such a configuration, the device can be prevented from being contaminated by the lubricating oil 1.

  If the measurement unit 10 of the lubricant deterioration monitoring device 100 is immersed in the lubricant 1 for several years, dirt of the lubricant 1 may adhere to the sensor portion of the light receiving element 5 of the measurement unit 10. It is necessary to wipe off the dirt of the lubricating oil 1. Various methods can be considered for wiping off the dirt. If a simple wiper is installed, automatic wiping is possible, and it is conceivable to periodically replace only dirty parts. Alternatively, it is possible to electrically cancel the dirt once taken out into the air.

  Next, the filter unit 4 of the lubricant deterioration monitoring device 100 according to this embodiment will be described in detail. The filter unit 4 is configured by arranging 1 to 3 filters having a predetermined center wavelength and a half-value width between the light source 3 and the light receiving element 5. The filter constituting the filter unit 4 can achieve its purpose with only one filter F1, but the combination of two filters F1 and F2 is good, and three filters F1, F2 and F3 are visible. By arranging each filter in parallel on the optical path of the light beam, that is, in a direction perpendicular to the optical path, more accurate measurement is possible. The position of the filter unit 4 is not particularly limited as long as it is on the optical path, and may be before or after passing through the lubricating oil 1.

  A filter installation pattern of the filter unit 4 will be described with reference to FIG. FIG. 2 is a view of the filter of the filter unit 4 as viewed from the optical path direction. As shown in FIG. 2A, the filters F1 to F3 are arranged radially from the center of one circle, and are 40%, 50%, and 10%, respectively, with respect to the optical path areas of the filters F1, F2, and F3. It is divided by. Note that the present invention is not limited to the example shown in FIG. 2A, and the circle may be divided vertically or horizontally in order to simplify the production. Also, the number of filters is not three, but may be one or two, and the area ratio may be changed. Further, as shown in FIG. 2B, the filters F1 and F2 are arranged by vertically dividing one rectangle, and the filters F1 and F2 are divided into 30% and 70%, respectively, with respect to the optical path area. doing. Note that the present invention is not limited to the example shown in FIG. 2B, and the rectangle may be divided horizontally, or may be divided radially from the center position, and the number of filters is not two but 1 , May be three, and the area ratio may be changed.

  When the filter unit 4 is composed of a single filter F1, the filter F1 has a center wavelength in the visible range of 500 nm or more and less than 600 nm and a half-value width of 30 nm or more and less than 120 nm, and the entire wavelength range to be measured When the thickness is 350 nm or more and less than 750 nm, the effect of the present invention can be obtained.

  When the filter unit 4 is constituted by two filters F1 and F2, the center wavelength in the visible region of the filter F1 is not less than 400 nm and less than 500 nm, the half width is not less than 30 nm and less than 100 nm, and the filter F2 The center wavelength of the visible region is 500 nm or more and less than 575 nm, the half width is 30 nm or more and less than 100 nm, and the filter F1 and the filter F2 are arranged in parallel on the optical path of visible light, It is preferable that the ratio of the area to the cross-sectional area is 0 to 80% and 20 to 100%, respectively.

  When the filter unit 4 is constituted by three filters F1, F2 and F3, the center wavelength in the visible region of the filter F1 is 400 nm or more and less than 500 nm, and the half width is 30 nm or more and less than 100 nm, The center wavelength in the visible region of the filter F2 is 500 nm or more and less than 575 nm, the half width is 30 nm or more and less than 100 nm, the center wavelength in the visible region of the filter F3 is 575 nm or more and less than 650 nm, and the half width is 30 nm. The filter F1, the filter F2, and the filter F3 are less than 100 nm and are arranged in parallel on the optical path of visible light, and the ratio of the area to the cross-sectional area on the optical path is 0 to 80% and 20 to 100%, respectively. , Preferably arranged to be 0 to 60%The ratio of the light receiving area is preferably 0 to 20%, 40 to 80%, 20 to 60%, and more preferably 0 to 10%, 40 to 60%, and 40 to 60%.

  Next, the operation and effect of the lubricant deterioration monitoring device 100 according to the embodiment of the present invention will be described.

  First, as a result of intensive research, the inventors have been able to more accurately grasp the deterioration of the lubricating oil by measuring transmitted light having a specific wavelength width instead of monochromatic light, and having a specific wavelength width. It was found that the setting of can be easily achieved by devising the filter.

  Furthermore, the present inventors have found that the reason why the deterioration of the lubricating oil can be grasped more accurately by measuring transmitted light having a specific wavelength width is as follows. The visible light transmittance of the lubricating oil is small on the short wavelength side and large on the long wavelength side. Further, the degree of decrease in the transmittance accompanying the deterioration of the lubricating oil tends to be large on the short wavelength side and small on the long wavelength side. For this reason, when measuring over the entire visible range, information on the long wavelength side, which has a large transmittance and a small change, is mainly used, and therefore the degree of change in the light transmittance accompanying the deterioration of the lubricating oil becomes small. .

  According to the lubricating oil deterioration monitoring device 100 according to the embodiment of the present invention derived in view of the above viewpoint, since the light in the visible range is divided and measured with a wavelength range, The degree of deterioration can be accurately grasped. That is, by measuring with a wavelength range instead of monochromatic light, it is possible to measure the transmitted light as a value obtained by averaging the differences even if there are differences in the oil type and the deterioration state. Further, in the lubricant deterioration monitoring apparatus 100 according to the present embodiment, light having a wavelength near the center of the visible range is the main target of measurement. This is because the transmittance on the short wavelength side is small in addition to the fact that the degree of change is large, so the transmittance may reach zero at the early stage of deterioration, and the change in transmittance is too small on the long wavelength side. This is because the change detection accuracy is low at the early stage of deterioration of the lubricating oil. Therefore, the lubricant deterioration monitoring device 100 according to the present embodiment can perform measurement with high accuracy even if there is a difference in deterioration state due to a difference in oil type or use environment.

  Furthermore, since the lubricant deterioration monitoring apparatus 100 according to the embodiment of the present invention includes only the light source 3, the filter unit 4, and the light receiving element 5 other than the ADC / MPU 6, the display device 7, and the personal computer 8, The device itself can be made extremely small and measurement can be performed easily. Further, if a single light source such as a halogen lamp is used as the light source 3 and a single sensor is used as the light receiving element 5, the deterioration of the lubricating oil can be measured. Can be installed on machines. As described above, it is possible to achieve high accuracy with respect to a wide range of oil types and a wide use environment, reduce costs, and enable simple measurement.

  The wavelength range to be measured may be only near the center, but by combining light with a wide wavelength range, it can be applied to more oil types and degradation conditions. Two or more wavelength ranges can be measured by combining two or more filters in parallel.

  In the lubricant deterioration monitoring device 100 according to the embodiment of the present invention, a plurality of filters F1 to F3 are arranged in parallel on the optical path of visible light. Accordingly, one optical path can pass through a plurality of filters at respective area ratios, and light with the area ratio can be received by one light receiving element 5, so that an arithmetic circuit can be dispensed with. Furthermore, by arranging the filters in a balanced manner with respect to the cross-sectional area of the optical path, the accuracy can be further improved and versatility can be increased.

  Hereinafter, experimental examples performed according to the present embodiment will be described.

[Experimental Example 1]
Deterioration degree index (cubic root calculated by MPU), which is the result of monitoring the deterioration of air compressor oil using the lubricating oil deterioration monitoring device 100 of the present invention equipped with one filter (center wavelength: 600 nm, half width: 80 nm) (Value) is shown in FIG. Further, the deterioration index and the remaining life data are plotted in FIG. The remaining life shown by the solid line in FIG. 3 (b) is obtained separately in the laboratory for various properties of the deteriorated oil (viscosity, acid value, color, amount of impurities, residual amount of additives, etc.) The life is determined. Degradation index obtained from visible light transmittance is relatively consistent with the remaining life determined from a lot of data, and can be used as an index of degradation if the degradation behavior of each device is known. I understand.

[Experiment 2]
Lubricating oil of the present invention in which the filter F1 (center wavelength: 450 nm, half width: 80 nm) and the filter F2 (center wavelength: 550 nm, half width: 80 nm) are combined at a filter area ratio (F1; 40%, F2; 60%) FIG. 4A shows a deterioration degree index (square root value calculated by MPU), which is a result of forced deterioration of industrial multipurpose oil in a laboratory using the deterioration monitoring apparatus 100 and monitoring the deterioration degree. Further, the degradation index and the remaining life data are plotted in FIG. It can be seen that there is a good agreement with the determination result taking into account all the data indicated by the solid line in FIG.

[Experiment 3]
Lubricating oil deterioration of the present invention in which the filter F1 (center wavelength: 450 nm, half width: 80 nm) and the filter F2 (center wavelength: 550 nm, half width: 80 nm) are combined at a filter ratio (F1; 40%, F2; 60%) FIG. 5A shows a deterioration degree index (a value of a square root calculated by MPU), which is a result of monitoring the deterioration degree of industrial general-purpose oil in an actual factory using the monitor device 100. Further, the deterioration index and the remaining life data are plotted in FIG. As can be seen from FIG. 5 (b), the results agree well with the determination result taking into account all the data indicated by the solid line.

[Experimental Example 4]
Filter F1 (center wavelength; 450 nm, half width; 80 nm), filter F2 (center wavelength; 550 nm, half width; 80 nm), and filter F3 (center wavelength; 600 nm, half width; 80 nm) are filter area ratios (F1; 30 %, F2; 60%, F3; 10%) The deterioration degree index (MPU) is the result of monitoring the degree of deterioration by forcibly degrading the hydraulic fluid in the laboratory using the lubricating oil deterioration monitoring apparatus 100 of the present invention. FIG. 6A shows the value of the square root calculated by (1). Further, the deterioration index and the remaining life data are plotted in FIG. It can be seen that the results agree well with the determination results taking into account all the data indicated by the solid line in FIG.

  DESCRIPTION OF SYMBOLS 1 ... Lubricating oil, 2 ... Measuring place, 3 ... Light source, 4 ... Filter unit, 5 ... Light receiving element, 6 ... ADC / MPU, 7 ... Display, 8 ... Personal computer, 10 ... Measuring unit, 100 ... Lubricating oil deterioration monitor Device, F1, F2, F3 ... filter.

Claims (2)

By transmitting visible light generated from a single light source to lubricating oil, receiving it with a single light receiving element and converting it to an electrical signal, converting that signal into a square root or cubic root value, and calculating a degradation index, Detecting deterioration of the lubricating oil,
A plurality of filters having a predetermined center wavelength and a half width are arranged between the light source and the light receiving element,
A plurality of the filters are arranged in parallel on the optical path of the visible light,
Between the light source and the light receiving element, a first filter having a center wavelength in the visible range of 400 nm to less than 500 nm and a half width of 30 nm to less than 100 nm, and a center wavelength in the visible range of 500 nm to less than 575 nm And the ratio of the area occupied by the first filter and the second filter in the cross-sectional area on the optical path of the second filter having a half width of 30 nm or more and less than 100 nm is 80% or less and 20%, respectively. Lubricating oil deterioration monitoring device, which is arranged as described above.   Between the light source and the light receiving element, a third filter having a center wavelength in the visible range of 575 nm or more and less than 650 nm and a half width of 30 nm or more and less than 100 nm, the first filter and the second filter, 2. The lubricant deterioration monitor according to claim 1, wherein the ratio of the area occupied by the third filter to the cross-sectional area on the optical path is 80% or less, 20% or more, and 60% or less, respectively. apparatus.

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