GB1561668A - Device for determiningfluid density - Google Patents

Description

(54) DEVICE FOR DETERMINING FLUID DENSITY (71) We, GRUMMAN AEROSPACE COR- PORATION, a corporation organised under the laws of the State of New York, United States of America, of South Oyster Bay Road, Bethpage, New York 11714, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a device for determining fluid density by measuring the refractive index of the fluid.

Such a device is suitable for detecting the presence of contaminants, such as water, in fuel, and in particular, the fuel contained in the or each fuel tank of an aircraft. As described and claimed in co-pending application No. 49602/76 (Serial No. 1561667), the device of the present invention may be used in conjunction with a fluid level indicating means as described and claimed therein, so as to provide a device for indicating the weight of fuel remaining in each or all of the fuel tanks if, particularly, an aircraft.

According to the invention, there is provided a device for determining fluid density comprisrng a housing, a lens dividing said housing into first and second chambers, said housing being such that when the housing is immersed in a fluid, said second chamber is filled with the fluid, light transmitting means for radiating light into said first chamber to illuminate an end of said lens, light conducting means orientated relative to said lens so as to receive light reflected and refracted by said lens and electrical means responsive to light received by said light conducting means to provide at least one signal to a display means.

The light conducting means preferably comprises light pipe means, for example fibre optic bundles or one or more fibre optic tapes, mounted in at least one block. In a preferred arrangement, two blocks are provided, one adjacent the lens to receive reflected light, one adjacent an end of the second chamber to receive refracted light.

The portion of the lens exposed to the first chamber is preferably shaped so as to focus light falling thereon from the light transmitting means. The shaped portion of the lens is preferably aspherical so as to provide two focal planes, one on the face of the lens exposed to the second chamber and the other at an end of the lens which receives reflected light.

The only figure of the accompanying draw ing shows an embodiment of a device accordto the invention.

The device is in the form of an electrooptical densimeter/water detector for use in the fuel tank of an aircraft as more particularly described in co-pending application No. 49602/76 (Serial No. 1561667).

The densimeter/contaminant detector has an electronics-housing within which or to which a light source will illuminate a fibre optic element 178 and a semiconductor means sensitive to light being conducted by other fibre optic elements related thereto, such as elements 188, 190, 192, 196, 198, 200 and 202. Actually the conducting fibre optic elements may be of tape construction rather than the sheathed, tubular, individual bundles shown. The detector uses the principle of Snell's law of reflecting/refracting light at an inclined optical surface 164 of a clear elongate lens 166 having an aspherical end 168 within a housing 170, preferably a clear plastics housing. Lens 166 and its aspherical end cooperate with the walls of housing 170 to separate a liquid chamber 172 from an air chamber 174.As shown the housing is closed at one end by a block 176 that is formed, for example by boring, to receive a fibre optic bundle 178. Alternatively the block 176 could be slit to allow sunlight or any other light source to radiate into the air chamber 174.

The lens 166 is also provided with a block 184 that is bonded to a support frame 186 that mounts the bundles 188, 190 and 192 or a tape construction of fibre optic elements. Frame 186 curves about the other end of the housing 170 to support a block 194 supporting, in turn bundles 196, 198, 200 and 202 or a tape construction adjacent the end 204 of housing 170. With tape constructions it will be readily recognized by one skilled in the art that the exposed ends will be on the inside of blocks 184 and 194 as is the case with the bundles shown.

The bundle 178, when used as a means to transmit light, will transmit the light through the chamber 174 in a spherical radiation pattern indicated by arrows 206. In that the aspherical end 168 has one radius of curvature in the plane of the figure and another in the plane of surface 164, light received thereby will be directed to a focal point along the surface 164 andjor to a focal point adjacent the end of lens 166 with which the block 184 is associated, so that the light within the lens 166 is either reflected and/or refracted at surface 164 so as to illuminate bundles 188, 190 or 192 or a combination of same or bundles 196, 198, 200 or 202 or a combination of same, respectively.

Actually one block with a fibre optic ribbon tape can be used at a preselected pitch to the axis of lens 166 and the housing 170.

With such an arrangement one skilled in the art will be able to limit the digitizing error to pitch selected of detector elements. The housing 170 is provided with openings in any event to permit chamber 172 to receive fluid that is within the tank 88 at a limited distance above the bottom thereof. This will enable the probe to be effective indicating contaminants above an expected level. In any event the light received by the bundles 188, 190, 192, 196, 198, 200 and 202 will be indicative of density at one end of the bundles and contamination at the other so that appropriate summing circuitry will enable the proper electrical signal to show density, as at indicator 142, or warn of contamination such as too much water in the fuel, as at indicator 144.

With the above detector fluid density can be indicated without passing light through fuel. Therefore, shadings of fuel colours do not affect the system.

By providing a plurality of fibre optic bundles and individual light sensitive semiconductive means in the densimeter/contaminant probe not only is the failsafe features of this probe provided, but in addition, it is possible to trigger a warning of unmanageable contamination at a predetermined level of contamination on the surface 164 as well as triggering a density reading in units in that the angle of surface 164 will cause reflection of varied order as fuel density changes. That is to say certain of the optical fibres will be illuminated in blocks 184 and 194 as contaminant level in chamber 172 varies or as differing fuels are employed having different density or as the density varies because of changes in temperature.

The device of the invention, at least in its preferred embodiment, has the advantages of being passive, lightweight and inexpensive.

It is capable of providing adequate resolution and manageable signal levels. It is further easy to calibrate and is not susceptible to EMI interference problems. The detector is able to measure absolute density by accounting for variations in density of delivered fluid and changes in the temperature of the fluid.

WHAT WE CLAIM IS: 1. A device for determining fluid density comprising a housing, a lens dividing said housing into first and second chambers, said housing being such that when the housing is immersed in a fluid, said second chamber is filled with the fluid, light transmitting means for radiating light into said first chamber to illuminate an end of said lens, light conducting means orientated relative to said lens so as to receive light reflected and refracted by said lens and electrical means responsive to light received by said light conducting means to provide at least one signal to a display means.

2. A device as claimed in claim 1, wherein said light conducting means comprises light pipe means mounted in at least one block.

3. A device as claimed in claim 2, comprising a first block adjacent the lens and a second block adjacent an end of the housing for the second chamber.

4. A device as claimed in any preceding claim, wherein the portion of the lens exposed to the first chamber is shaped so as to focus light from said light transmitting means.

5. A device as claimed in claim 4, wherein said portion of the lens is aspherical.

6. A device as claimed in claim 4 or 5, wherein the light is focused on the face of the lens exposed to the second chamber.

7. A device as claimed in any of claims 4 to 6, wherein reflected light is focussed at an end of the lens opposite said shaped portion.

8. A device as claimed in any preceding claim, wherein said first chamber is a sealed chamber containing air.

9. A device for determining fluid density

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. be slit to allow sunlight or any other light source to radiate into the air chamber 174. The lens 166 is also provided with a block 184 that is bonded to a support frame 186 that mounts the bundles 188, 190 and 192 or a tape construction of fibre optic elements. Frame 186 curves about the other end of the housing 170 to support a block 194 supporting, in turn bundles 196, 198, 200 and 202 or a tape construction adjacent the end 204 of housing 170. With tape constructions it will be readily recognized by one skilled in the art that the exposed ends will be on the inside of blocks 184 and 194 as is the case with the bundles shown. The bundle 178, when used as a means to transmit light, will transmit the light through the chamber 174 in a spherical radiation pattern indicated by arrows 206. In that the aspherical end 168 has one radius of curvature in the plane of the figure and another in the plane of surface 164, light received thereby will be directed to a focal point along the surface 164 andjor to a focal point adjacent the end of lens 166 with which the block 184 is associated, so that the light within the lens 166 is either reflected and/or refracted at surface 164 so as to illuminate bundles 188, 190 or 192 or a combination of same or bundles 196, 198, 200 or 202 or a combination of same, respectively. Actually one block with a fibre optic ribbon tape can be used at a preselected pitch to the axis of lens 166 and the housing 170. With such an arrangement one skilled in the art will be able to limit the digitizing error to pitch selected of detector elements. The housing 170 is provided with openings in any event to permit chamber 172 to receive fluid that is within the tank 88 at a limited distance above the bottom thereof. This will enable the probe to be effective indicating contaminants above an expected level. In any event the light received by the bundles 188, 190, 192, 196, 198, 200 and 202 will be indicative of density at one end of the bundles and contamination at the other so that appropriate summing circuitry will enable the proper electrical signal to show density, as at indicator 142, or warn of contamination such as too much water in the fuel, as at indicator 144. With the above detector fluid density can be indicated without passing light through fuel. Therefore, shadings of fuel colours do not affect the system. By providing a plurality of fibre optic bundles and individual light sensitive semiconductive means in the densimeter/contaminant probe not only is the failsafe features of this probe provided, but in addition, it is possible to trigger a warning of unmanageable contamination at a predetermined level of contamination on the surface 164 as well as triggering a density reading in units in that the angle of surface 164 will cause reflection of varied order as fuel density changes. That is to say certain of the optical fibres will be illuminated in blocks 184 and 194 as contaminant level in chamber 172 varies or as differing fuels are employed having different density or as the density varies because of changes in temperature. The device of the invention, at least in its preferred embodiment, has the advantages of being passive, lightweight and inexpensive. It is capable of providing adequate resolution and manageable signal levels. It is further easy to calibrate and is not susceptible to EMI interference problems. The detector is able to measure absolute density by accounting for variations in density of delivered fluid and changes in the temperature of the fluid. WHAT WE CLAIM IS:

1. A device for determining fluid density comprising a housing, a lens dividing said housing into first and second chambers, said housing being such that when the housing is immersed in a fluid, said second chamber is filled with the fluid, light transmitting means for radiating light into said first chamber to illuminate an end of said lens, light conducting means orientated relative to said lens so as to receive light reflected and refracted by said lens and electrical means responsive to light received by said light conducting means to provide at least one signal to a display means.

2. A device as claimed in claim 1, wherein said light conducting means comprises light pipe means mounted in at least one block.

3. A device as claimed in claim 2, comprising a first block adjacent the lens and a second block adjacent an end of the housing for the second chamber.

4. A device as claimed in any preceding claim, wherein the portion of the lens exposed to the first chamber is shaped so as to focus light from said light transmitting means.

5. A device as claimed in claim 4, wherein said portion of the lens is aspherical.

6. A device as claimed in claim 4 or 5, wherein the light is focused on the face of the lens exposed to the second chamber.

7. A device as claimed in any of claims 4 to 6, wherein reflected light is focussed at an end of the lens opposite said shaped portion.

8. A device as claimed in any preceding claim, wherein said first chamber is a sealed chamber containing air.

9. A device for determining fluid density

substantially as herein described with reference to the accompanying drawing.

10. A fuel tank containing a device as claimed in any preceeding claim, wherein said display means indicates fluid density and fluid contamination.