CA1190762A - Fibre optic level gauge and valve head provided with a fibre optic level gauge, for pressure vessels - Google Patents
Fibre optic level gauge and valve head provided with a fibre optic level gauge, for pressure vesselsInfo
- Publication number
- CA1190762A CA1190762A CA000417142A CA417142A CA1190762A CA 1190762 A CA1190762 A CA 1190762A CA 000417142 A CA000417142 A CA 000417142A CA 417142 A CA417142 A CA 417142A CA 1190762 A CA1190762 A CA 1190762A
- Authority
- CA
- Canada
- Prior art keywords
- optical fibre
- fibre
- level gauge
- fibre optic
- inlet
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000835 fiber Substances 0.000 title claims abstract description 49
- 239000013307 optical fiber Substances 0.000 claims abstract description 64
- 230000003287 optical effect Effects 0.000 claims abstract description 40
- 239000007788 liquid Substances 0.000 claims abstract description 27
- 239000003566 sealing material Substances 0.000 claims abstract description 7
- 238000004891 communication Methods 0.000 claims abstract description 6
- 230000006854 communication Effects 0.000 claims abstract description 6
- 239000012530 fluid Substances 0.000 claims description 13
- 229920002379 silicone rubber Polymers 0.000 claims description 2
- 239000004945 silicone rubber Substances 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 21
- 230000005540 biological transmission Effects 0.000 description 7
- 238000000034 method Methods 0.000 description 4
- 239000011521 glass Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- NCGICGYLBXGBGN-UHFFFAOYSA-N 3-morpholin-4-yl-1-oxa-3-azonia-2-azanidacyclopent-3-en-5-imine;hydrochloride Chemical compound Cl.[N-]1OC(=N)C=[N+]1N1CCOCC1 NCGICGYLBXGBGN-UHFFFAOYSA-N 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000001902 propagating effect Effects 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 238000005452 bending Methods 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-M methacrylate group Chemical group C(C(=C)C)(=O)[O-] CERQOIWHTDAKMF-UHFFFAOYSA-M 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/284—Electromagnetic waves
- G01F23/292—Light, e.g. infrared or ultraviolet
- G01F23/2921—Light, e.g. infrared or ultraviolet for discrete levels
- G01F23/2922—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms
- G01F23/2925—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms using electrical detecting means
- G01F23/2927—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms using electrical detecting means for several discrete levels, e.g. with more than one light-conducting sensing element
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
A B S T R A C T
FIBRE OPTIC LEVEL GAUGE AND VALVE HEAD
PROVIDED WITH A FIBRE OPTIC LEVEL GAUGE, FOR PRESSURE VESSELS
Fibre optic level gauge for controlling the liquid level in a pressure vessel for liquefied gas, comprising at least one inlet optical fibre (12) and at least one outlet optical fibre (13) for providing optical communi-cation between the exterior and the interior of said pressure vessel, the inlet optical fibre (12) having one end adapted to be optically connected to an external light source, and the outlet optical fibre (13) having one end adapted to be optically connected to an external light detector, the inlet optical fibre (12) and the outlet optical fibre (13) having the other ends located within the vessel in spaced positions so that light emitted from one of these other ends is receivable by the other of these ends, wherein the inlet optical fibre (12) and the outlet optical fibre (13) enter the vessel through a housing (8), the interior of the housing (8) being filled up with a mass of a sealing material (17).
FIBRE OPTIC LEVEL GAUGE AND VALVE HEAD
PROVIDED WITH A FIBRE OPTIC LEVEL GAUGE, FOR PRESSURE VESSELS
Fibre optic level gauge for controlling the liquid level in a pressure vessel for liquefied gas, comprising at least one inlet optical fibre (12) and at least one outlet optical fibre (13) for providing optical communi-cation between the exterior and the interior of said pressure vessel, the inlet optical fibre (12) having one end adapted to be optically connected to an external light source, and the outlet optical fibre (13) having one end adapted to be optically connected to an external light detector, the inlet optical fibre (12) and the outlet optical fibre (13) having the other ends located within the vessel in spaced positions so that light emitted from one of these other ends is receivable by the other of these ends, wherein the inlet optical fibre (12) and the outlet optical fibre (13) enter the vessel through a housing (8), the interior of the housing (8) being filled up with a mass of a sealing material (17).
Description
7~2 FIBRE OPTIC LEVEL GAUGE AND VALVE HEAD
PROVIDE~ WITH A FIBRE OPTIC LEVEL GAUGE, FOR PRESSURE VESSELS
The invention relates to a fibre optic level gauge for use in pressure vessels for liquefied gases, such as LPG, and a valve head for press~lre vessels provided with such a fibre optic level gauge.
The most convenient ~method for storing gas in a liquefied state is pressurizing the gas. For s~oring gas under pressure, pressure vessels must be applied which are able to withstand the vapour pressure of the stored gas at the r~1mllm occurring external temperature and which must comply with relevant governmental regulations in the field of safety. There are, for example, regulations stating that pressure vessels should be designed to withstand prede-termined min~ working pressures. There are further regulations stating that the vessels filling capacity should lS be such ~hat the vessels will become not more than 97%
liquid full due to expansion of the liquefied gas with a rise of temperature to the highest operational temperature.
Therefore each vessel for pressurized fluids has a prede-termined m~;mllm fill level, depending on the type of fluid and the area for which the vessel is intended.
From the above it will be clear that during filling of pressure vessels the filling level has to be controlled to avoid overfilling.
A number of methods are kno~n to prevent overfill of ~S vessels. A traditional method for detecting overfill consists herein that 2 vent tube having an open end and a valved end has its open end inside a vessel to be filled9 at the ~ mllm permitted filling level. The valved end is arranged outside the vessel under the control of the filling `~' D71~i2 operator. During filling the vent is held in an open position so that there is a discharge of gas through the vent until the liquid level reaches the open end of the vent tube, whence liquid appears at the vent. A diszdYantage of this type of overfill control system is that the escape of gas may easily create a hazardous risk for the filling operator, due to easy inflammability of the gas. ~ further disadvantage of this known control system consists herein that it cannot be readily automated, and therefore requires fully concentrated attention of the filling operator.
Other known level control systems such as gauge glasses and float level indicators provide a continuous level indication but are not explicit to detect overfill. Gauge glasses further involve considerable mechanical design problems in their protection against mechanical damage, and inherent in float level indicators are the problems of float stickin~.
More recently, with the advanced development of so-called optical fibres, the use of such optical fibres as level detectors has become known. The basic principle of optical fibres as level detectors consists herein that light is beamed through an optical fibre probe and the light returning after transmission is detected by a photo-electric detector. A known example of fibre optic level control apparatus consists of one or more inlet optical fibres cooperating with one or more outlet optical fibres. One end of the inlet optical fibre(s) is connected to a light source, and one end of the outlet optical fibre(s) is connected to a photo-electric detector. The other ends of the inlet and outlet optical fibre(s) are spaced apart from each other in a vessel to be filled in such a manner that the liquid in the vessel will cause light emitted from the inlet optical fibre to be directed through the outlet optical fibre. The sensitivity of the photo-electric deteceor can be adjusted so that it will be energized by the light transmitted at the predetermined liquid level in the vessel.
Optical fibre level control apparatuses have a number of advantages over the above-mentioned more traditional sensing methods, such as the absence of moving parts and requires therefore little, if any, maintenance. The detector and the light source used with such apparatuses may be installed away from the vessel at a safe distance therefrom.
Th known fibre optic level control apparatuses have a main disadvantage in that they are not suitable for use in pressure vessels, such as vessels for LPG, wherein the gas should ~ot be exposed to the atmosphere.
The object of the invention is to provide a fibre optic ]S level gauge for controlling the fluid level in a pressure vessel.
The fibre optic level gauge for controlling the liquid level in a pressure vessel for liquefied gas thereto comprises according to the invention at least one inlet optical fibre and at least one outlet optical fibre, for providing optical communication between the exterior and the interior of said pressure vessel, said inlet optical fibre having one end adapted to be optically connected to an external light source, and the outlet optical fibre having one end adapted to be optically connected to an ex~ernal light dPtector, said inlet optical fibre and said outlet optical fibre having the other ends located within the vessel in spaced positions so that light emitted from one of these other ends is receivable by the other of these ends, wherein the inlet optical fibre and the outlet optical fibre enter the vessel through a housing, the interior of ~he housing being filled up with a mass of a sealing material.
The housin~ may be adapted to be mounted on a pressure vessel either directly or via the valve head of a ~ ~ ~US~
pressure vessel. The sealing between the optical fibres and the housing prevents the escape of liquid or vapour from a pressure vessel via the fibre optic level gauge.
The invention further provides a valve head for pressure vessels for liquefied gas having a body provided with an internal passage adapted to form a fluid communi-cation between the interior of a pressure vessel and the exterior, wherein the valve head is provided with a fibre optic level gauge according to the invention as described ] o above .
The invention will now be described by way of example in more detail with reference to the accompanying drawings, wherein Figure 1 shows a longitudinal cross section of a pressure vessel provided with a fibre optic level gauge according to the invention;
Figure 2 shows detail II of Figure 1 on an enlarged scale;
Figure 3 shows a longitudinal cross section of a valve head for pressure vessels, provided with a fibre optic level gauge according to the invention; and Figure 4 shows schematically the light propagation and transmission at the end of an inlet optical fibre, shown in the preceding Figures.
It should be noted that identical elements shown in the Figures have been indica~ed with the same reference numeral.
Figure 1 shows a pressure vessel 1 for liquefied gas, such as LPG, provided with a schematically shown valve head
PROVIDE~ WITH A FIBRE OPTIC LEVEL GAUGE, FOR PRESSURE VESSELS
The invention relates to a fibre optic level gauge for use in pressure vessels for liquefied gases, such as LPG, and a valve head for press~lre vessels provided with such a fibre optic level gauge.
The most convenient ~method for storing gas in a liquefied state is pressurizing the gas. For s~oring gas under pressure, pressure vessels must be applied which are able to withstand the vapour pressure of the stored gas at the r~1mllm occurring external temperature and which must comply with relevant governmental regulations in the field of safety. There are, for example, regulations stating that pressure vessels should be designed to withstand prede-termined min~ working pressures. There are further regulations stating that the vessels filling capacity should lS be such ~hat the vessels will become not more than 97%
liquid full due to expansion of the liquefied gas with a rise of temperature to the highest operational temperature.
Therefore each vessel for pressurized fluids has a prede-termined m~;mllm fill level, depending on the type of fluid and the area for which the vessel is intended.
From the above it will be clear that during filling of pressure vessels the filling level has to be controlled to avoid overfilling.
A number of methods are kno~n to prevent overfill of ~S vessels. A traditional method for detecting overfill consists herein that 2 vent tube having an open end and a valved end has its open end inside a vessel to be filled9 at the ~ mllm permitted filling level. The valved end is arranged outside the vessel under the control of the filling `~' D71~i2 operator. During filling the vent is held in an open position so that there is a discharge of gas through the vent until the liquid level reaches the open end of the vent tube, whence liquid appears at the vent. A diszdYantage of this type of overfill control system is that the escape of gas may easily create a hazardous risk for the filling operator, due to easy inflammability of the gas. ~ further disadvantage of this known control system consists herein that it cannot be readily automated, and therefore requires fully concentrated attention of the filling operator.
Other known level control systems such as gauge glasses and float level indicators provide a continuous level indication but are not explicit to detect overfill. Gauge glasses further involve considerable mechanical design problems in their protection against mechanical damage, and inherent in float level indicators are the problems of float stickin~.
More recently, with the advanced development of so-called optical fibres, the use of such optical fibres as level detectors has become known. The basic principle of optical fibres as level detectors consists herein that light is beamed through an optical fibre probe and the light returning after transmission is detected by a photo-electric detector. A known example of fibre optic level control apparatus consists of one or more inlet optical fibres cooperating with one or more outlet optical fibres. One end of the inlet optical fibre(s) is connected to a light source, and one end of the outlet optical fibre(s) is connected to a photo-electric detector. The other ends of the inlet and outlet optical fibre(s) are spaced apart from each other in a vessel to be filled in such a manner that the liquid in the vessel will cause light emitted from the inlet optical fibre to be directed through the outlet optical fibre. The sensitivity of the photo-electric deteceor can be adjusted so that it will be energized by the light transmitted at the predetermined liquid level in the vessel.
Optical fibre level control apparatuses have a number of advantages over the above-mentioned more traditional sensing methods, such as the absence of moving parts and requires therefore little, if any, maintenance. The detector and the light source used with such apparatuses may be installed away from the vessel at a safe distance therefrom.
Th known fibre optic level control apparatuses have a main disadvantage in that they are not suitable for use in pressure vessels, such as vessels for LPG, wherein the gas should ~ot be exposed to the atmosphere.
The object of the invention is to provide a fibre optic ]S level gauge for controlling the fluid level in a pressure vessel.
The fibre optic level gauge for controlling the liquid level in a pressure vessel for liquefied gas thereto comprises according to the invention at least one inlet optical fibre and at least one outlet optical fibre, for providing optical communication between the exterior and the interior of said pressure vessel, said inlet optical fibre having one end adapted to be optically connected to an external light source, and the outlet optical fibre having one end adapted to be optically connected to an ex~ernal light dPtector, said inlet optical fibre and said outlet optical fibre having the other ends located within the vessel in spaced positions so that light emitted from one of these other ends is receivable by the other of these ends, wherein the inlet optical fibre and the outlet optical fibre enter the vessel through a housing, the interior of ~he housing being filled up with a mass of a sealing material.
The housin~ may be adapted to be mounted on a pressure vessel either directly or via the valve head of a ~ ~ ~US~
pressure vessel. The sealing between the optical fibres and the housing prevents the escape of liquid or vapour from a pressure vessel via the fibre optic level gauge.
The invention further provides a valve head for pressure vessels for liquefied gas having a body provided with an internal passage adapted to form a fluid communi-cation between the interior of a pressure vessel and the exterior, wherein the valve head is provided with a fibre optic level gauge according to the invention as described ] o above .
The invention will now be described by way of example in more detail with reference to the accompanying drawings, wherein Figure 1 shows a longitudinal cross section of a pressure vessel provided with a fibre optic level gauge according to the invention;
Figure 2 shows detail II of Figure 1 on an enlarged scale;
Figure 3 shows a longitudinal cross section of a valve head for pressure vessels, provided with a fibre optic level gauge according to the invention; and Figure 4 shows schematically the light propagation and transmission at the end of an inlet optical fibre, shown in the preceding Figures.
It should be noted that identical elements shown in the Figures have been indica~ed with the same reference numeral.
Figure 1 shows a pressure vessel 1 for liquefied gas, such as LPG, provided with a schematically shown valve head
2 for fi~ling the vessel 1. For determining the liquid level in the vessel, the vessel 1 is provided with a fibre optic level gauge~ genPrally indicated with reference numeral 3 mounted in an opening in the wall of the vessel 1, at a substantial distance from the valve head 2. The fibre optic level gauge 3 is connected to a light source 4 and a light detector 5, such as a photo-electric cell, by means of a plurality of connecting optical fibres 6 and 7 respectiv ly.
The fibre optic level gauge will now be discussed ln more detail with reference to Figure 2.
The fibre optic level gauge 3 comprises a housing 8 provided w$tb a flange 9, bolted to a flange construction lO, welded in an opening in wall 11 of th~ vessel l. A
plurality of inlet optical fibres 12 and outlet optical fibres 13 having inclined lower parts pass through openings ]0 in the bottom part of the housing 8 alld are partly arranged in the vessel l. The optical fibres 12 and 13, having their lower ends arranged opposite to each other, are connected to a fr~me struceure formed by blades 14 and 159 said blades being secured to the bottom part of the housing 8.
The lower ends of the optical fibres 12 and 13 may be cemented in holes in the blad~s 14 and 15 respectively. The blades 14 and 15 are spaced apart from each other to form a gap 16 between the inlet optical fibres 12 and the outlet optical fibres 13. The optical fibres 12 and 13 may be made of any material suitable for transmitting light. A suitable material is for example glass. Another suitable material is plastic, offering the advantage of having a tight bending radius and being relatively cheap. The optical fibres 12 and 13 may for example consist of a polymethyl methacrylate core sheathed with a transparent polymer. The diameter of the optical fibres 12 and 13 may be relatively small, for example, in the order of magnitude of 0.7 mm.
The interior of the housing 8 is filled with a sealing material 17, such as cured silicone rubber, held under pressure by a pressure cover 18 mechanically tightened onto the housing 8~ by means of a flange construction. The op~ical fibres 12 and 13 pass through holes in the pressure cover 18. For joining the connecting fibres 6 and 7 to the f`~7~
optical fibres 12 and 13, respectively, a connector 19 is aounted on th~ pressure cover 18, in such a manner that ends of the fibres 6 and 7 arranged in holes ln the connector 1~, mate the upper ends of the optical fibres 12 and 13~ re-spectively.
The operation of the fibre optic level gauge as shown in the Figures 1 and 2 will now be described, with further reference to Figure 4, showing the light paths in the lower part of an inlet optical fibre 12. When the vessel 1 has ~o l be filled with liquefied fluid under pressure, a fluid transfer line is connected with the valve head 2, whereas the fibre optic level gauge 3 is connected to the light source 4 and the light detector 5, by mounting connector 19 provided with the connecting fibres 6 and 7 onto the pressure cover 18. It should be noted that the fibre optic level gauge 3 is so arranged with respect to the vessel 1 that the lower ends of the optical fibres 12 and 13 are arranged substantially at the desired fluid level in the vessel. The operation of the fibre optic level gauge relies on the optical principles of total internal reflection.
Snel's law n1 sin~1 = n2 sin~ 2 describes the relationship between the angles of incidence ~1 and refraction ~2 for a ray propagating in a medium of refractive index n1, incident on a medium of refractive index n2. Using this equation it is evident that for n1 > n2 there is a limiting angle of incidence ~1~ give~ by the e~uation ~1 = sin 1 n2 nl beyond which total internal reflection occurs. Let us assume that the fibre used is provided with a core 20 with a refrac~ive index of 1.49 and a sheath 21 superposed on said core, with a refractive index of 1.39. Then the critical angle for rays propagating within the core of the fibre is 69. Hence, the rays incident on the interface formed by the end 22 Df the optical fibre 12 lie within a propagation cone 23 having a half angle of 21 . Independent of this there is a transmission cone 24 within the fibre 12 which describes the acceptance cone of rays which if incident on ~he inter-face formed by the end of the fibre would refract into themedium present in the gap 16. The half angle of this trans-mission cone 24 is given by the formula sin 1 ~nmedium nfibre and is for example 42 for gaseous butane and 63 for liquid ]O bu~ane.
The light transmitted from the fibre 12 into the medium in the gap 16 is determined by the intersection area of the propagation cone 23 and the transmission cone 24 and is therefore dependent on the angle of the fibre lower end 22 with the vertical cross section of the fibre. Since the transmission cone for liquid is substantiaIly wider than the transmission cone for gas it will be clear that substantial-ly more light from the optical fibre 12 is refracted into liquid than into gas. The light that is transmitted from the ~0 fibre 12 propagates across the gap 16, whereafter the major part of the light enters an output optical fibre 13 arranged in the extension of said inlet optical fibre 12.
When the ~essel 1 i9 filled with press~lrized liquefied gas the medium in the gap 16 is in first instance formed by gas, un~il the liquid reaches the r~irlm level and the gap 16 between the inlet optical fibres 12 and the outlet optical fibres 13 is thereby filled with pressurized liquid.
As long as the gap is filled with gas a minor amount of light emitted from the light source 4 is transmitted from the inlet optical fibres 12 and enters the outle~ optical fibres 13. When however the gap 16 i~ filled with liquid subs~antially more light will be transmitted via the gap 16 and will be detected by the light detector 5. The light '7~
detector 5 may be coupled to a not shown trigger mechanism giving a trigger signal as soon as the liquid in the vessel has reached its ~;r~lm level and the light detector 5 detects a substantial amount of light. The li~ht detector 5 may also be electrically connected to the valve head 2~ so that the filling valve i9 automatically shut off as soon as the amount of light detected by the light detector S exceeds a predetermined value or is considerably increasedO
Reference is now made to Figure 3 showing a valve head provided with a fibre optic level gauge according to the invention.
The valve head, generally indicated by reference numeral 30, comprises a filling valve 31 mounted in an opening of an adapter 32, being at one end provided with screw thread for connection into a flange 33 of a not further shown pressure vessel for liquefied gas.
The filling valve 31 is provided with a cond~it 34 forming a fluid ~ommunication between a connecting head 35 of the ~illing valve 31 and an internal passage 36 in the adapter 32. A handwheel 37 is provided for displacing a val~e body 38 to open or close the fluid communication between the connecting head 35 and the internal passage 36.
An inlet optical fibre 12 and an outlet optical fibre 13 pass through the internal passage 36 in the adapter. The upper part of said optical fibres is arranged in the housing 8 provided with the pressure cover 1~3, said housing 8 being mounted on the adapter 32 for example by means of welding.
The lower ends of the optical fibres 12 and 13 are fixedly mounted in openings of blades 39 and 40, respectively, arranged apart from each other to form a gap 41. The blades 39 and 40 are secured to the adapter 32 via an intermediate part 42 provided with openings 43 in the wall thereof forming a fluid communica~ion between the internal passage 36 and ~he interior of the prPssure vessel on which the L f O ~
valve head 30 is arranged. When the vessel is to be filled with pressuriæed liquefied fluid a transfer conduit is arranged on the connecting head 35 and the filling valve 31 is opened so ~hat fluid flows via the connecting head 35, conduit 34, and internal passage 36 into the vessel.
Connector l9 is positioned on the pressure cover 18 so that the connecting fibres 6 and 7 ma~e the inlet optical fibre 12 and the outlet fibre 13, respectively. The lower ends of the optical fibres are arranged at the ~xlml~m liquid level ]U in the vesse3. Via connecting fibre 6 and inlet optical fibre 12 light i8 transmitted to the interior of the vessel during the filling operation.
When the liquid in the vessel has reached the lower end of the optical fibres 12 and 13, the light transmitted via the liquid through the outlet optical fibre 13 and the connecting fibre 7 is detected by a not shown photo-electric cell which may be electrically connected to the valve head 30, so that the valve is automatically shu~ off when the liquid level has reached the lower ends of the optical fibres 12 and 13~
To prevent excessive interference of the liquid with the optical fibres 12 and 13 due to splashing or excessive turbulence during the filling operation not shown guide plates may be arranged in front of the ~ap 41 or the blades 39 and 40 may be enclosed by an open-ended sleeve.
Although in the Figures only one or two inlet optical fibre(s) co-operate with one or two outlet optical fibre(s?
it is to be understood that any other number of inlet and outlet optical fibres may be applied.
When a pressure vessel is intended to be used for storage of different types of liquid~ the optic fibr~ level gauge is preEerably provided with a number of inlet and outlet op~ical fibres equal to the number of types of ~L~s~7~
liquid, each re~uiring a specific m~Yiml7~ fill level in the vessel .
Although in the embodiments shown in the Figures the optical fibres are so arranged that their lower parts are inclined with respect to the horizon~al, and their lower ends make an angle with their vertical cross sections, other positlons of the optical fibres may be applied. A different arrangement may for example be obtained by positioning ~he optical fibres at an angle with respect to each other. The an~le of inclination and the hori70ntal distance between the lower ends of the fibres should be chosen such that light from an inlet optical fibre will be transmitted via the liquid/gas interface in a vessel to an outlet optical fibre when the liquid has reached its ~i level. In this arrangement the lower ends of the optical fibres preferably are perpendicular to the longitudinal axes of the fibres.
A further alternative arrangement of the fibre optic level gauge may be obtained by connecting the lower ends of the inlet and outlet optical fibres tD a light transmitting body provided with at least two non-parallel surface portions in the path of light emit~ed via the inlet optical fibre. The outlet optical fibre is so arranged relative to ~he inlet optical fibre that light from the inlet optical fibre after internal reflection from said non-parallel surface portions of the light transmitting body is trans-mitted to the outlet optical flbre. When said non-parallel surface portions are surrounded by gas the major part of the light emitted by the inlet optical fibre is reflected to the outlet optical fibre. When howe~er liquid surrounds said non-parallel surface portions, essentially no light is reflected to the outlet optical fibre.
The fibre optic level gauge will now be discussed ln more detail with reference to Figure 2.
The fibre optic level gauge 3 comprises a housing 8 provided w$tb a flange 9, bolted to a flange construction lO, welded in an opening in wall 11 of th~ vessel l. A
plurality of inlet optical fibres 12 and outlet optical fibres 13 having inclined lower parts pass through openings ]0 in the bottom part of the housing 8 alld are partly arranged in the vessel l. The optical fibres 12 and 13, having their lower ends arranged opposite to each other, are connected to a fr~me struceure formed by blades 14 and 159 said blades being secured to the bottom part of the housing 8.
The lower ends of the optical fibres 12 and 13 may be cemented in holes in the blad~s 14 and 15 respectively. The blades 14 and 15 are spaced apart from each other to form a gap 16 between the inlet optical fibres 12 and the outlet optical fibres 13. The optical fibres 12 and 13 may be made of any material suitable for transmitting light. A suitable material is for example glass. Another suitable material is plastic, offering the advantage of having a tight bending radius and being relatively cheap. The optical fibres 12 and 13 may for example consist of a polymethyl methacrylate core sheathed with a transparent polymer. The diameter of the optical fibres 12 and 13 may be relatively small, for example, in the order of magnitude of 0.7 mm.
The interior of the housing 8 is filled with a sealing material 17, such as cured silicone rubber, held under pressure by a pressure cover 18 mechanically tightened onto the housing 8~ by means of a flange construction. The op~ical fibres 12 and 13 pass through holes in the pressure cover 18. For joining the connecting fibres 6 and 7 to the f`~7~
optical fibres 12 and 13, respectively, a connector 19 is aounted on th~ pressure cover 18, in such a manner that ends of the fibres 6 and 7 arranged in holes ln the connector 1~, mate the upper ends of the optical fibres 12 and 13~ re-spectively.
The operation of the fibre optic level gauge as shown in the Figures 1 and 2 will now be described, with further reference to Figure 4, showing the light paths in the lower part of an inlet optical fibre 12. When the vessel 1 has ~o l be filled with liquefied fluid under pressure, a fluid transfer line is connected with the valve head 2, whereas the fibre optic level gauge 3 is connected to the light source 4 and the light detector 5, by mounting connector 19 provided with the connecting fibres 6 and 7 onto the pressure cover 18. It should be noted that the fibre optic level gauge 3 is so arranged with respect to the vessel 1 that the lower ends of the optical fibres 12 and 13 are arranged substantially at the desired fluid level in the vessel. The operation of the fibre optic level gauge relies on the optical principles of total internal reflection.
Snel's law n1 sin~1 = n2 sin~ 2 describes the relationship between the angles of incidence ~1 and refraction ~2 for a ray propagating in a medium of refractive index n1, incident on a medium of refractive index n2. Using this equation it is evident that for n1 > n2 there is a limiting angle of incidence ~1~ give~ by the e~uation ~1 = sin 1 n2 nl beyond which total internal reflection occurs. Let us assume that the fibre used is provided with a core 20 with a refrac~ive index of 1.49 and a sheath 21 superposed on said core, with a refractive index of 1.39. Then the critical angle for rays propagating within the core of the fibre is 69. Hence, the rays incident on the interface formed by the end 22 Df the optical fibre 12 lie within a propagation cone 23 having a half angle of 21 . Independent of this there is a transmission cone 24 within the fibre 12 which describes the acceptance cone of rays which if incident on ~he inter-face formed by the end of the fibre would refract into themedium present in the gap 16. The half angle of this trans-mission cone 24 is given by the formula sin 1 ~nmedium nfibre and is for example 42 for gaseous butane and 63 for liquid ]O bu~ane.
The light transmitted from the fibre 12 into the medium in the gap 16 is determined by the intersection area of the propagation cone 23 and the transmission cone 24 and is therefore dependent on the angle of the fibre lower end 22 with the vertical cross section of the fibre. Since the transmission cone for liquid is substantiaIly wider than the transmission cone for gas it will be clear that substantial-ly more light from the optical fibre 12 is refracted into liquid than into gas. The light that is transmitted from the ~0 fibre 12 propagates across the gap 16, whereafter the major part of the light enters an output optical fibre 13 arranged in the extension of said inlet optical fibre 12.
When the ~essel 1 i9 filled with press~lrized liquefied gas the medium in the gap 16 is in first instance formed by gas, un~il the liquid reaches the r~irlm level and the gap 16 between the inlet optical fibres 12 and the outlet optical fibres 13 is thereby filled with pressurized liquid.
As long as the gap is filled with gas a minor amount of light emitted from the light source 4 is transmitted from the inlet optical fibres 12 and enters the outle~ optical fibres 13. When however the gap 16 i~ filled with liquid subs~antially more light will be transmitted via the gap 16 and will be detected by the light detector 5. The light '7~
detector 5 may be coupled to a not shown trigger mechanism giving a trigger signal as soon as the liquid in the vessel has reached its ~;r~lm level and the light detector 5 detects a substantial amount of light. The li~ht detector 5 may also be electrically connected to the valve head 2~ so that the filling valve i9 automatically shut off as soon as the amount of light detected by the light detector S exceeds a predetermined value or is considerably increasedO
Reference is now made to Figure 3 showing a valve head provided with a fibre optic level gauge according to the invention.
The valve head, generally indicated by reference numeral 30, comprises a filling valve 31 mounted in an opening of an adapter 32, being at one end provided with screw thread for connection into a flange 33 of a not further shown pressure vessel for liquefied gas.
The filling valve 31 is provided with a cond~it 34 forming a fluid ~ommunication between a connecting head 35 of the ~illing valve 31 and an internal passage 36 in the adapter 32. A handwheel 37 is provided for displacing a val~e body 38 to open or close the fluid communication between the connecting head 35 and the internal passage 36.
An inlet optical fibre 12 and an outlet optical fibre 13 pass through the internal passage 36 in the adapter. The upper part of said optical fibres is arranged in the housing 8 provided with the pressure cover 1~3, said housing 8 being mounted on the adapter 32 for example by means of welding.
The lower ends of the optical fibres 12 and 13 are fixedly mounted in openings of blades 39 and 40, respectively, arranged apart from each other to form a gap 41. The blades 39 and 40 are secured to the adapter 32 via an intermediate part 42 provided with openings 43 in the wall thereof forming a fluid communica~ion between the internal passage 36 and ~he interior of the prPssure vessel on which the L f O ~
valve head 30 is arranged. When the vessel is to be filled with pressuriæed liquefied fluid a transfer conduit is arranged on the connecting head 35 and the filling valve 31 is opened so ~hat fluid flows via the connecting head 35, conduit 34, and internal passage 36 into the vessel.
Connector l9 is positioned on the pressure cover 18 so that the connecting fibres 6 and 7 ma~e the inlet optical fibre 12 and the outlet fibre 13, respectively. The lower ends of the optical fibres are arranged at the ~xlml~m liquid level ]U in the vesse3. Via connecting fibre 6 and inlet optical fibre 12 light i8 transmitted to the interior of the vessel during the filling operation.
When the liquid in the vessel has reached the lower end of the optical fibres 12 and 13, the light transmitted via the liquid through the outlet optical fibre 13 and the connecting fibre 7 is detected by a not shown photo-electric cell which may be electrically connected to the valve head 30, so that the valve is automatically shu~ off when the liquid level has reached the lower ends of the optical fibres 12 and 13~
To prevent excessive interference of the liquid with the optical fibres 12 and 13 due to splashing or excessive turbulence during the filling operation not shown guide plates may be arranged in front of the ~ap 41 or the blades 39 and 40 may be enclosed by an open-ended sleeve.
Although in the Figures only one or two inlet optical fibre(s) co-operate with one or two outlet optical fibre(s?
it is to be understood that any other number of inlet and outlet optical fibres may be applied.
When a pressure vessel is intended to be used for storage of different types of liquid~ the optic fibr~ level gauge is preEerably provided with a number of inlet and outlet op~ical fibres equal to the number of types of ~L~s~7~
liquid, each re~uiring a specific m~Yiml7~ fill level in the vessel .
Although in the embodiments shown in the Figures the optical fibres are so arranged that their lower parts are inclined with respect to the horizon~al, and their lower ends make an angle with their vertical cross sections, other positlons of the optical fibres may be applied. A different arrangement may for example be obtained by positioning ~he optical fibres at an angle with respect to each other. The an~le of inclination and the hori70ntal distance between the lower ends of the fibres should be chosen such that light from an inlet optical fibre will be transmitted via the liquid/gas interface in a vessel to an outlet optical fibre when the liquid has reached its ~i level. In this arrangement the lower ends of the optical fibres preferably are perpendicular to the longitudinal axes of the fibres.
A further alternative arrangement of the fibre optic level gauge may be obtained by connecting the lower ends of the inlet and outlet optical fibres tD a light transmitting body provided with at least two non-parallel surface portions in the path of light emit~ed via the inlet optical fibre. The outlet optical fibre is so arranged relative to ~he inlet optical fibre that light from the inlet optical fibre after internal reflection from said non-parallel surface portions of the light transmitting body is trans-mitted to the outlet optical flbre. When said non-parallel surface portions are surrounded by gas the major part of the light emitted by the inlet optical fibre is reflected to the outlet optical fibre. When howe~er liquid surrounds said non-parallel surface portions, essentially no light is reflected to the outlet optical fibre.
Claims (11)
1. Fibre optic level gauge for controlling the liquid level in a pressure vessel for liquefied gas, comprising at least one inlet optical fibre and at least one outlet optical fibre for providing optical communication between the exterior and the interior of said pressure vessel, the inlet optical fibre having one end adapted to be optically connected to an external light source, and the outlet optical fibre having one end adapted to be optically connected to an external light detector, the inlet optical fibre and the outlet optical fibre having the other ends located within the vessel in spaced positions so that light emitted from one of these other ends is receivable by the other of these ends, wherein the inlet optical fibre and the outlet optical fibre enter the vessel through a housing, the interior of the housing being filled up with a mass of a sealing material.
2. Fibre optic level gauge as claimed in claim 1, wherein the mass of the sealing material is held in a pressurized condition.
3. Fibre optic level gauge as claimed in claim 2, wherein the mass of the sealing material is held in a pressurized condition by a pressure cover covering an opening in the housing.
4. Fibre optic level gauge as claimed in claim 3, wherein the inlet optical fibre and the outlet optical fibre pass through openings in the pressure cover.
5. Fibre optic level gauge as claimed in claim 1, wherein the sealing material is formed from silicone rubber.
6. Fibre optic level gauge as claimed in claim 1, wherein the other ends of the inlet optical fibre and the outlet optical fibre are held in a sub-stantially fixed position relative to each other by means of a frame structure connected to the housing.
7. Fibre optic level gauge as claimed in claim 6, wherein the frame structure consists of blade-shaped elements, each holding an optical fibre in a substantially fixed position.
8. Fibre optic level gauge as claimed in claim 1, wherein at least the other ends of the inlet optical fibre and the outlet optical fibre is surrounded by a sleeve.
9. Fibre optic level gauge as claimed in claim 8, wherein the sleeve is connected to the housing.
10. Fibre optic level gauge as claimed in claim 1, wherein the other ends of the inlet optical fibre and the outlet optical fibre are connected to a light transmitting body provided with at least two non-parallel surface portions so arranged that light emitted from the inlet optical fibre can be transmitted via the light transmitting body to the outlet optical fibre.
11. Valve head for pressure vessels, having a body provided with an internal passage adapted to form a fluid communication between the exterior and the interior of a pressurized vessel wherein the valve head is provided with a fibre optic level gauge as claimed in claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08139074A GB2112929B (en) | 1981-12-30 | 1981-12-30 | Fibre optic level gauge and valve head for pressurized vessels |
| GB8139074 | 1981-12-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1190762A true CA1190762A (en) | 1985-07-23 |
Family
ID=10526882
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417142A Expired CA1190762A (en) | 1981-12-30 | 1982-12-07 | Fibre optic level gauge and valve head provided with a fibre optic level gauge, for pressure vessels |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1190762A (en) |
| GB (1) | GB2112929B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4870292A (en) * | 1988-03-15 | 1989-09-26 | Focal Marine Limited | Fibre optic sensor for liquid level and other parameters |
| US4942306A (en) * | 1988-12-30 | 1990-07-17 | Focal Technologies Incorporated | Fibre optic sensor for the continuous measurement liquids level and other parameters |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3409003A1 (en) * | 1983-06-16 | 1984-12-20 | Shipley Co., Inc., Newton, Mass. | MEASURING PROBE FOR MEASURING THE METALION CONCENTRATION |
| GB2176290A (en) * | 1985-05-03 | 1986-12-17 | Grampian Regional Council | Apparatus for monitoring fluid level |
| US4782226A (en) * | 1987-07-06 | 1988-11-01 | Semi-Gas Systems, Inc. | Optoelectronic chemical reaction detector |
| FR2623624B1 (en) * | 1987-11-19 | 1990-08-10 | Telemecanique Electrique | METHOD AND DEVICE FOR DETERMINING THE FLOW CHARACTERISTICS OF A MATERIAL WITHIN A MOLD, DURING A MOLDING PROCESS |
| GB2550149A (en) * | 2016-05-10 | 2017-11-15 | Linde Ag | A cylinder for pressurised liquefied gas and a method of calculating the liquid level |
-
1981
- 1981-12-30 GB GB08139074A patent/GB2112929B/en not_active Expired
-
1982
- 1982-12-07 CA CA000417142A patent/CA1190762A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4870292A (en) * | 1988-03-15 | 1989-09-26 | Focal Marine Limited | Fibre optic sensor for liquid level and other parameters |
| US4942306A (en) * | 1988-12-30 | 1990-07-17 | Focal Technologies Incorporated | Fibre optic sensor for the continuous measurement liquids level and other parameters |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2112929B (en) | 1985-08-29 |
| GB2112929A (en) | 1983-07-27 |
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