a system for measuring contaminant level in accordance with the present invention may be used to measure the amount of contaminant particles in any oil including lubricating oil . an embodiment for measuring contamination level of lubricating oil will be described . the measurement system of the present invention can measure the amount of paramagnetic and non - magnetic contaminant particles separately . it determines the level of contaminant including wear debris produced in the oil and impurities introduced from outside by measuring the change of light transmitted through the oil . in the present invention , a predetermined amount of oil is sampled and the oil sample is put to a cylindrical container . then , light is transmitted through the container by using light sensors , where a infrared (&# 34 ; ir &# 34 ;) light emitting diode (&# 34 ; led &# 34 ;) may be used as a light emitter and a photodiode may be used as a light receptor . by measuring the change of optical density , i . e ., the amount of light transmitted through oil sample in the container , the contamination level in the oil can be quantitatively determined . generally , wear debris generated in the lubricating oil consists of paramagnetic or ferromagnetic particles . therefore , magnetic properties of these wear debris are different from those of the impurities externally provided to the oil . to utilize this difference , strong magnetic field is applied around the cylindrical oil container in the present invention . when the magnetic field is applied to the oil sample , lines of magnetic force are formed vertically in the container and magnetic particles are arranged along the magnetic lines . therefore , when the magnetic field is applied , the intensities of light transmitted through the oil increase . by measuring the optical density before and after the magnetic field is applied , the ratio between magnetic wear debris and non - magnetic impurities can be determined . optical lenses are used to make the light passing through the container coherent . to compensate for the temperature characteristic of the diodes , the light emitted from the led is measured and , by feedback control , a constant amount of light is directed to the oil sample . in addition , optical fiber is used to make the characteristic of the light emitting and receiving diodes independent of temperature and to separate an amplifier including the light emitting and recepting diodes from a sensing device including the oil container . fig1 illustrates a sensing device 310 for measuring contaminant level in accordance with the present invention . the device 310 includes a cylindrical container 10 where the oil sample is provided and circulated for on - line measurement through an inlet 20 and an outlet 30 . the device 310 also includes an optical fiber l40 for delivering ir light generated by from an infrared (&# 34 ; ir &# 34 ;) led ( not shown ), an light - inputting optical lens 50 which converts the light delivered by the optical fiber to a coherent light and directing it into the oil sample , an light - receiving optical lens 60 for collecting the light attenuated while transmitted through the oil sample and focusing the collected light to another optical fiber l70 , the optical fiber l70 which deliver the collected light to a photodiode ( not shown ), a solenoid coil 80 for applying magnetic field to the oil sample in the container 10 , members 90 , 95 for fixing the optical fibers l40 , l70 and the optical lenses 50 , 60 , and a case 100 for protecting the interior of the sensing device 310 . generally , intensity of light transmitted through a medium is represented as follows : where i 1 is the intensity of light transmitted through the medium , i 0 is the intensity of incident light , x is the length through which the light travels , σ is an attenuating factor which is proportionally related to the concentration of contaminant particles in the medium . therefore , logarithm of the light intensity transmitted through the medium is proportional to the concentration of contaminant particles , by using the above relationship , change of optical density of the oil due to the contaminant particles depends upon the contamination level and the strength of the magnetic field and is represented as follows : ## equ1 ## where j 1 is the optical density of unused oil , j 2 is the optical density of used oil , j 3 is the optical density of the used oil after the magnetic field is applied , j 4 is the optical density of the used oil after the magnetic field is removed , thus , the change of optical density , d 1 , is determined by measuring the optical densities j 1 and j 2 of the unused and used oil , respectively . amount of contaminant particles in the oil corresponding to the determined d 1 value is obtained by referring a graph ( as shown in fig4 and 5 ) representing values of d 1 versus contaminant level which are experimentally predetermined by measuring d 1 values for various standard contaminant levels . when a magnetic field is applied to the container 10 , paramagnetic contaminant particles are arranged along the magnetic lines so that the optical density changes from j 2 to j 3 . from eq . ( 3 ), relative contaminant level due to the paramagnetic particles alone can be determined . the amount of paramagnetic particles may be determined by referring the result of an experiment conducted before the measurement . after the magnetic field is removed , small particles among those arranged along the magnetic lines are dispersed back into the oil . as a result , the optical density is decreased a little to j 4 . thus , j 4 may be used to determine the contaminant level due to the small particles . fig2 shows an oil circulation system 500 which includes the sensing device 310 in accordance with the present invention , parts for providing the oil from an oil tank 200 to the sensing device 310 , and parts for vacuuming which remove bubbles from the oil . a trochoid pump 110 , functioning as an oil circulating pump , provides he oil from the oil tank 200 to the sensing device 310 under the control of an input air pressure valve 210 and an output air pressure valve 220 . a pressure switch 410 is provided to ensure safety by controlling a solenoid valve 270 with a signal from the switch 410 against a case where oil pressure in tube exceeds a predetermined value . the parts for vacuuming include a solenoid valve 230 for applying the vacuum from a vacuuming pump 120 , a solenoid valve 240 for returning to the ambient air state from the vacuum state , an air pressure valve 250 for controlling the circulation of the oil and the vacuum , a chamber 420 for preventing the oil from flowing backwards to the vacuum line during the vacuum state and also acting as a buffer to remove the air bubbles from the oil , an oil trap 430 for collecting vaporized oil and backward - flowing oil and draining out the collected oil . the circulation system 500 depicted in fig2 can be operated in two ways . it can be used both for manual measurement of the contamination level or real - time measurement . the procedure for manual measurement is as follows : 3 ) stop the oil circulating pump 110 after the oil has been sufficiently circulated . operate the vacuuming pump 120 to remove bubbles from the oil . 4 ) put the air in the oil in the vacuum state and the ambient air state alternately until the air bubbles are completely removed . 5 ) stop the vacuuming pump 120 when the bubbles are removed . return to the ambient air state and measure the optical density j 2 of the used oil . 6 ) apply power to the electromagnetic coil 80 of the sensing device 310 . 60 seconds after the power is applied , measure optical density j 3 of the used oil . turn off the power and , after 60 seconds , measure optical density j 4 of the used oil . 7 ) open the valves to drain out the oil sample from the container 10 . 8 ) from the measured values j 2 , j 3 , and j 4 , determine a total contaminant level and contaminant levels due to paramagnetic and non - magnetic particles by referring contaminant level values predetermined by experiments . the circulation system 500 in accordance with the present invention can also be used for real - time measurement of contaminant level of lubricating oil in industrial fields . for this purpose , the air pressure and solenoid valves are automatized by using a programmable logic controller (&# 34 ; plc &# 34 ;) so that the oil can be sampled automatically . moreover , an independent measurement system is provided where the measurement results are analyzed in a computer which is connected to an external communication network for data transmission . fig3 shows a real - time measurement system including the circulation system 500 shown in fig2 a plc for controlling the solenoid and air pressure valves and pumps , a computer 520 for controlling the circulation system and processing , storing and displaying data obtained from the measurement and an amplifier 530 for generating light to be provided to the sensing device 310 , receiving light collected from the sensing device 310 , and providing a magnetic field to the oil . in response to instructions from the computer 510 , the plc 520 operates to control the pumps 110 , 120 and valves 210 to 270 . light is generated at an light emitting device , e . g ., infrared led , in the amplifier 530 which is displaced from the sensing device 310 and then conveyed through the optical fiber l40 to the sensing device 310 . light transmitted through the oil is provided via the optical fiber l70 back to an light recepting device , e . g ., photodiode , in the amplifier 530 . in this system , the measuring procedure explained above is repeated at regular intervals . measurement results are converted to digital values by using an analog / digital converter ( not shown ). the digitized measurement values are inputted to the computer 510 , stored therein and displayed on the monitor of the computer . fig4 depicts values of optical density change d 1 of lubricating oil measured by the sensing device of the present invention as the contamination level of the oil is changed by using acmtd particles . the concentration of the contaminant particles in the oil is set to 100 , 200 , 400 , 600 , 800 , 1000 , and 1500 ppm . it is observed that the optical density increases linearly as the contamination level ( in ppm ) increases . the inclination of the linear increase is 0 . 00168 , the regression coefficient is 0 . 995 , and the standard deviation is 0 . 11652 . thus , the observed relationship between the optical density and the contamination level is nearly linear . fig5 depicts values of values optical density change d 1 and d 2 of lubricating oil measured by the sensing apparatus of the present invention using carbonyl iron powder as the contaminant . the concentration of the contaminant particles in the oil is set to 100 , 200 , 400 , 600 , 1000 , 1300 and 1500 ppm . it is observed that both d 1 and d 2 increase linearly as the contamination level ( in ppm ) increases . for d 1 , the inclination of the linear increase is 0 . 00168 , the regression coefficient is 0 . 999 , and the standard deviation is 0 . 02217 and for d 2 , the inclination of the linear increase is 0 . 000577 , the regression coefficient is 0 . 992 , and the standard deviation is 0 . 04281 . thus , the observed relationship between d 1 , or d 2 and the contamination level is nearly linear . by using the on - line measurement system of contaminant level in accordance with the present invention , the contaminant level in lubricating oil can be qualitatively measured on a real - time basis . moreover , since the contaminant particles can be qualitatively analyzed , parts of a mechanical system where severe wear occurs can be identified . while the present invention has been described with respect to the particular embodiments , it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims .