OPTICAL FLUID LEVEL SENSOR

Abstract: The present invention is related to a sight glass (10) that utilizes both reflected light at a glass to air interface (40) as well as the light transmitted through a glass to fluid to glass interface (44) to form a light pattern that is indicative of the true fluid level. By requiring that light always appear in either an "air" or "fluid" channel (42, 46), any absence of light is assumed due to film coated surfaces or to other abnormal conditions. An absence of light is a signal that maintenance is required.

Description: This invention relates to optical fluid level sensors. Sight glasses are used to provide a visual indication of a fluid level. A sight glass uses the reflection of light caused by a glass to air interface, and the absence of reflection caused by a glass to fluid interface, to provide the visual indication of fluid level. Some fluids, such as gearbox oil, can form a heavy film on sight glass interface surfaces thereby giving a false fluid level reading. The absence of reflected light in such a case may cause one to assume erroneously that fluid levels are adequate. Equipment failure may result. In helicopter pre-flight inspection, it is required that the fluid levels of various rotor gearboxes be at normal levels. The levels are checked by using a flashlight to examine the appearance of a commercial sight glass that is mounted on the side of each gearbox. Such a procedure may be difficult to perform due to the location of the sight glasses, may be complicated by adverse weather or sea conditions, and may result in false readings. New methods and apparatus of checking for fluid levels are sought. DE-A-3 614 130 discloses an optical sensor for detecting the level of a fluid. Said sensor comprises a first passageway (waveguide 1) for conducting a signal beam, a second passageway (through the waveguide 3) for conducting said signal beam such that the signal may be detected, a third passageway (through the surface 13c) for conducting said beam such that it may be detected, a first means for conducting said beam from said first passageway (reflection at 14b) to said second passageway if said fluid level is too high, and a second means(reflection at the surface 13b) for conducting said beam from said first passageway to said third passageway if said fluid level is relatively low. US-A-2 240 988 discloses a liquid level indicator based on the principle of total reflection of light from the interface of two transparent mediums of different indices of refraction when a light beam passes to such interface at an angle greater than the critical angle. The liquid is contained in a chamber having parrallel walls, said chamber being formed at the interface of two prisms formed of transparent material. WO-A-86/07446 discloses an optical liquid detector comprising a first transparent rod connected at one end through an optical collecting system to a light conductor and a second optical rod connected at one end through an optical light expander to a second light conductor. Both light rods are provided with an interface surface arranged at an angle to their common longitudinal axis and being opposite and parallel to each other. When the detector is immersed into a liquid a light beam may pass through it from the second to the first light conductor. When the detector is emersed, no light beam passes between the optical conductors, but is instead reflected by said interface surfaces. The object of the invention is to provide an improved optical sensor for detecting fluid level which also indicates when maintenance is required. This object is achieved according to the invention by an optical sensor for detecting a fluid level comprising: a first passageway for conducting an incident light beam in a first direction into said sensor, second and third passageways for guiding said beam out of the sensor for being detected in a direction opposite to said first direction, a first interface having a planar surface for allowing said incident beam to pass therethrough from said first passageway to said third passageway if the fluid level is above a certain level, and to be reflected at said interface surface towards said second passageway if the fluid level is below said level, and a second interface having a planar surface located at substantially the same level as said first interface and in close proximity thereto characterised in that the faces of said interfaces are located with respect to each other such that when only a thin film of fluid coats both said surfaces no light is detected via either of said second or third passageways. Advantageous embodiments of the invention are claimed in the dependent claims. The optical sensor or sight glass of the invention utilizes both the reflected light at a glass to air interface as well as the light transmitted through a glass to fluid to glass interface to form a light pattern that is indicative of the true fluid level. By requiring that light always appear in either an "air" or "fluid" channel, any absence of light is assumed due to fluid coated surfaces or to other abnormal conditions. An absence of light is a signal that maintenance is required. According to a further aspect of the invention, a signal beam is directed down a first channel and then detected in either a second or third channel depending on whether the fluid level is high or low. If the signal beam is not detected in either of the second or third channels, maintenance is required and the fluid level must be detected by other means. These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings, wherein: Fig. 1(A-C) is a schematic view of an embodiment of a fluid level sensor of the invention; Fig. 1D is a top view of the sensor of Fig. 1(A-C), the sensor having been rotated forward 90° and disposed within a body of fluid; Fig. 2(A-C) is a schematic view of a further embodiment of a fluid level sensor of the invention; Fig. 2D is a top view of the sensor of Fig. 2(A-C), the sensor having been rotated forward 90° and disposed within a body of fluid; Referring to Fig. 1A, a side view of an embodiment of the fluid level sensor 10 is shown. The sensor has a flat top portion 12, a left side portion 14 and right side portion 16, each side portion extending downwardly at 90° angle from the top portion, and a left bottom portion 18 and right bottom portion 20. The left bottom portion 18 extends at an angle of about 135° from the left side portion 14. The left bottom portion intersects the right bottom portion at a 90° angle. The right bottom portion 20 extends at about 135° angle from the right side portion 16. A left opaque member 22 and right opaque member 24 each extend downwardly from the top portion. The right bottom portion is broken by a first channel 26 and a second channel 28 which extend to the left and right members 22, 24 respectively. The sensor 10 is made of a transparent material such as glass. A mirrored surface 30, such as aluminum, coats each bottom portion. Both mirrored surfaces are coated with glass 32, by conventional means, to protect them from interacting with the fluid being measured. The opaque members may be any compatible, non-transmissive material, such as an epoxy. The fluid level sensor is adapted to extend into a body 34 of fluid (see Figs. 1B and 1D). If the body is full or partially full of fluid, the fluid will extend up the channels 26, 28 to form a signal beam transmissive glass to fluid to glass interfaces, as will be discussed infra. Referring to Fig. 1A, where the fluid level is not high enough to extend up the channels, a signal beam 36, such as incandescent light, is directed down a middle passageway 38 formed between the two opaque members 22, 24. The light reaches a glass to air interface 40 between the passageway and the channel 26 and is reflected at a 90° angle to the mirrored surface 30 on the right bottom portion 20 and back out a right passageway 42. The light is reflected at the interface 40 because the fluid level does not extend up channel to form a beam transmissive glass to fluid to glass interface. Referring to Fig. 1B, where the fluid level 34 is high enough to extend up the channels, the signal beam is directed down the middle passageway 38 and passes through the glass to fluid to glass interface 44. The beam is reflected from the right 20 to the left bottom surfaces 18 and out the left passageway 46. In this way, a true fluid level is obtained. Referring to Fig. 1C, a signal beam 36 directed down the middle passageway 38 cannot pass to either the left 18 or right bottom portion 20 because of the fluid coating 48 within the channels. Light is lost within a fluid to glass to air interface 50 in the first channel 26 and within a similar fluid to glass to air interface in the second channel 28. If no light is passed through either the left 46 or right passageways 42, a problem, such as low fluid levels, is indicated and maintenance is required. Referring to Fig. 1D, a top view of the sensor 10 is shown. The sensor is rotated forward on its side within the fluid. The signal beam directed down the middle passageway 38 is reflected up a portion of the left passageway 46 disposed below the level 34. The signal beam is reflected out a portion of the right passageway 42 above the fluid level 34. Referring to Fig. 2A, a second embodiment of the sensor is shown. The sensor is basically similar to the sensor of the first embodiment. However, the sensor has only one channel 52 which extends from the right bottom portion 20 to the right opaque member 24. A right triangular notch 54 is machined into the left side portion 14 at a roughly 45° angle. As before, the bottom surfaces are mirrored. Referring to Fig. 2A, if the fluid level 34 does not fill the notch 54, a signal beam directed down the left passageway 46 is reflected at the glass to air interface 56 at the notch 54 to the mirrored surface 30 at the right bottom portion 20 and out the right passageway 42. Referring to Fig. 2B, when fluid level 34 fills the notch 54, the signal beam passes down the left passageway 46 through the glass to oil to glass interface 58, and reflects from the left bottom portion 16 to the right bottom portion 20 and out the middle passageway 38. Referring to Fig. 2C, with fluid film 48 coating the interfaces, the signal beam passes into the left passageway and is lost in the glass to fluid to air interfaces 60 in the notch 54 and in the channel 52. As a result the signal beam is not transmitted out either of the middle or the right passageways. Referring to Fig. 2D, a top view of the sensor of Figs. 2A-C is shown rotated forward 90° and disposed in the fluid at level 34. The signal beam 36 directed into the left passageway 46 is reflected out a portion of the middle passageway 38 disposed below the fluid level therein and is reflected out of a portion of the right passageway 42 above the fluid level 36. Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without depating from the scope of the invention as defined in the appended claims. Specifically, one of ordinary skill in the art may utilize other types of signal beams, such as lasers or light emanating from fiber optics. One may also utilize optical pick-ups so that the entire fluid level check may be performed automatically. By automatically checking the fluid level, the problems associated with inconveniently placed sight glasses and bad weather or sea conditions may be minimized.

Claims: An optical sensor for detecting a fluid level comprising: a first passageway (38;46) for conducting an incident light beam (36) in a first direction into said sensor, second and third passageways (42;42 and 46;38) for guiding said beam out of the sensor for being detected in a direction opposite to said first direction, a first interface (26;56) having a planar surface for allowing said incident beam to pass therethrough from said first passageway to said third passageway if the fluid level is above a certain level, and to be reflected at said interface surface towards said second passageway (42;42) if the fluid level is below said level, and a second interface (28;52) having a planar surface located at substantially the same level as said first interface and in close proximity thereto characterized in that the faces of said interfaces are located with respect to each other such that when only a thin film of fluid coats both said surfaces no light is detected via either of said second or third passageways. The optical sensor of claim 1 wherein said first interface (26,56) comprises an opening extending into said first passageway (38;46). The optical sensor of claim 2 wherein said second interface means (28,52) comprises an opening extending into said second passageway (42;42). The optical sensor of claim 3 wherein said first and second interface means (26,28;56,52) do not conduct or reflect, respectively, said signal beam if obstructed incomplete by fluid or air. The optical sensor according to any one of the claims 1 to 4, wherein said first to third passageways (38,42,46;46,42,38) are provided in a single body of transparent material, the first and second passageways (38,42;46,48) being separated by a first opaque element (24) and the first and third passageways (38,46;46,38) being separated by a second opaque element (22). The optical sensor according to any one of the claims 1 to 5, wherein said first to third passageways (38,42,46;46,42,38) are concentrically arranged.

Inventors: BULLIS ROBERT H, WIEGAND WALTER J JR, BULLIS, ROBERT, H., WIEGAND, WALTER, J., JR.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1989
Main classification: G01F23
IPC codes: G01F23