Method and devices for measurements involving fluids

Abstract

This invention relates to a method for measuring the fluid level of a fluid. The method comprises providing a surface in contact with the fluid, the surface being associated with a measurement line marking at least a first point and a second point; and viewing the surface to visually determine the fluid level of the fluid based on the position of a fluid interface relative to the first point and the second point. The measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line. The first direction is normal to a plane parallel to the fluid interface and the reference line is defined by the intersection between the plane parallel to the fluid interface and the surface. The present invention also relates to a method of manufacturing apparatuses for carrying out this method and the apparatuses themselves.

Description

[0001] METHOD AND DEVICES FOR MEASUREMENTS INVOLVING FLUIDS

[0002] Field of the invention

[0003] The present invention relates to methods for measuring fluid levels, particularly fluid volumes, and devices for measuring fluid levels.

[0004] Background to the invention

[0005] Precise measurement of fluid levels relative to a surface the fluid is in contact with is important for several applications. For example, experimental laboratory work regularly requires the precise and accurate volume measurement of chemical reagents. Typically, a graduated container is used to make these measurements. One example of a such a graduated container is a measuring cylinder. These are typically manufactured of transparent glass or plastic. They have graduation lines marked along the longitudinal axis of the cylinder which represent the volume of a fluid inside the cylinder based on the position of the fluid level along the longitudinal axis of the container. It will be understood that measuring devices such as measuring cylinders may also be used to determine the volume of an object by using the displaced volume of fluid, obtained by measuring the fluid level before and after an object is added to the container. Another example of a measurement device used in laboratories (as well as other environments) is a measuring syringe. Syringes typically comprise a plunger which is moveable within a (normally cylindrical) barrel, such that liquid enters or exits the barrel through an opening. The barrel has graduation marks along its longitudinal axis which correspond to the volume of the liquid contained in the barrel.

[0006] Similar measurement procedures are used in other technical applications. For example, ships have load lines on their hulls (also known as draft marks). Load lines indicate the immersion depth of the vessel and can be used to calculate the weight of the cargo onboard the vessel. As another example, hydrometers are used to measure the relative density of liquids and typically include a graduated scale along their longitudinal axis.

[0007] However, these known measuring devices can be difficult to use for obtaining precise measurements. Accordingly, there is a need for improved measuring devices and methods for easily obtaining precise fluid level measurements. It is in this context that the present invention has been devised.

[0008] Summary of the invention

[0009] In accordance with an aspect of the present invention, there is provided a method for measuring the fluid level of a fluid comprising: providing a surface in contact with the fluid, the surface being associated with a measurement line marking at least a first point and a second point; and viewing the surface to visually determine the fluid level of the fluid based on the position of a fluid interface relative to the first point and the second point; wherein the measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the fluid interface; wherein the reference line is defined by the intersection between the plane parallel to the fluid interface and the surface; wherein the first point and the second point are offset from one another along the first direction; wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the fluid interface.

[0010] By measuring the fluid level of a fluid using a measurement line defined hereinbefore, it is possible to obtain particularly precise fluid measurements. Conventional measuring devices (e.g., conventional measuring cylinders) have graduation marks defined along a measurement line normal to a plane parallel to the fluid interface (i.e. typically vertically). The present inventor has realised that the same range of fluid levels can be expanded over a measurement line having a longer length compared to the measurement line of a conventional measuring container (assuming that the containers being compared have the same shape and size) by orienting the measurement line at an angle away from the vertical. This allows for a greater number of measurement indicia to be provided on the line for a given vertical distance of the line, without having the indicia spaced so closely as to make it difficult or even impossible to read the measurement accurately, compared to a vertically-oriented measurement line. Thereby, it is possible to distinguish more reliably between similar fluid levels.

[0011] It will be understood that measuring the fluid level of a fluid typically means that a fluid level is determined based on a position of a fluid level relative to points along a measurement line, each point indicative of a pre-determined fluid level. The surface typically extends over the fluid interface. The fluid level is typically between the first point and the second point in the first direction.

[0012] The reference line may be defined by the intersection between the plane of the fluid interface (e.g., the plane intersecting with the peak or trough of the meniscus of the fluid interface and parallel to the fluid interface) and the surface. The measurement line may be provided on the surface in contact with the fluid. A body may define the surface, the body having the measurement line and the measurement line being visible through the surface. The measurement line may be etched or printed, for example the measurement line may be printed or etched on the surface. The measurement line may be provided on a different surface (such as a film) which is then attached to the surface. Thus, the measurement line is associated with the surface whether it is provided directly on the surface, on a further surface of the body defining the surface in contact with the fluid, or on a different body attached or otherwise provided with the surface. Importantly, the measurement line is visible along with the intersection between the fluid interface and the surface in contact with the fluid.

[0013] The measurement line may comprise a continuous line extending between at least the first and second point. In other words, the measurement line may extend continuously between the first point and the second point.

[0014] The first point and / or the second point may be a point along the measurement line. In other words, the first point and / or the second point may each be spaced from an end of the measurement line. In other embodiments, the first point and / or the second point may each be an end of the measurement line. For example, the first point may be one end of a line defining the measurement line and the second point may be the other end of the line defining the measurement line. In some embodiments, the first point and / or the second point may be associated with a marker (e.g., a marker to visually indicate a fluid level). Each marker may be a numerical label, for example.

[0015] The fluid interface is the interface between the fluid and a further substance. The further substance may have a different density than the fluid. The further substance may be a lower density substance (compared to the fluid), such as air. In embodiments where the fluid interface is defined by a fluid meniscus, visually determining the fluid level of the fluid involves determining the fluid level of the fluid based on the position of the peak or trough of the meniscus. I n these embodiments, a line normal to the plane parallel to the fluid interface is a line normal to a plane tangential to the peak or trough of the meniscus. The fluid interface may be defined (at least in part) by the interface between the fluid and a float. The fluid is typically a lowermost substance in a container defined by the surface. Thus, measuring the fluid level of a fluid relative to a base of the container provides a volume of the fluid within the container. The fluid interface may be the interface between the fluid and a surface of a plunger (for example, in embodiments where the surface associated with the measurement line is part of a syringe).

[0016] The fluid interface may be positioned between the first point and the second point - i.e. , the fluid interface may appear to intersect the measurement line between the first point and the second point. Thus, the relative distance between the intersection of the fluid interface and the first point, and between the intersection of the fluid interface and the second point can be used to allow a fluid level, between the fluid level associated with the first point and the fluid level associated with the second point, to be determined particularly precisely.

[0017] The first point and the second point are offset from one another as defined hereinbefore. Typically, the first reference line is not marked on the surface (i.e., it is a notional line), defined to aid with description of the inventive subject-matter included herein. Typically, the first direction is aligned with the direction of gravity (i.e. vertical) and the plane parallel to the interface is transverse to the first direction (i.e. horizontal). The gradient of the measurement line is defined using the relative separation between the first point and the second point along the first reference line and the first direction. The first direction together with the reference line effectively provide a co-ordinate system which can be used to define the gradient of a measurement line associated with the surface in contact with the fluid, independent of the surface topography. Effectively, the co-ordinate system allows the measurement line to be mapped to a manifold which is associated with the surface.

[0018] It may be that the surface defines at least part of a burette.

[0019] Conventional burettes typically comprise a long and narrow container, which extends along a longitudinal axis. Typically, in use, the longitudinal axis is aligned with the vertical direction. For example, a 50ml burette will typically be around 80 cm in length and have an inner diameter of around 14 mm. Conventional burettes have graduation marks defined along a measurement line normal to a plane parallel to the fluid interface (i.e. the measurement line is defined along the longitudinal axis). These dimensions are chosen to provide the necessary measurement precision. However, the length of these conventional burettes can make measurement procedures challenging because it is difficult for users to view the device at the appropriate height. The present inventor has realised that by providing a burette having a measurement line having a gradient as defined herein, that the required measurement precision can be provided over the same volume range but using a reduced container length (compared to a conventional burette with the same volume capacity).

[0020] The method may further comprise viewing the surface from a viewing position facing the surface. Typically, the surface is viewed from a viewing position facing the surface at a position on the surface between (and including) the first point, the second point and any point therebetween along the measurement line. The surface can be viewed from a side-on direction (as opposed to from above), making it easier to see the relative point of intersection of the fluid interface between the first point and the second point, for determining the fluid level.

[0021] The method may further comprise viewing the surface along a line of sight coincident with a viewing plane. The viewing plane may be transverse to the plane parallel to the fluid interface. Additionally or alternatively, the viewing plane may be coincident with the normal to the surface at the point where the plane parallel to the fluid interface intersects the surface, at the first intersection point, the second intersection point, or any point therebetween along the reference line. It will be understood that any point therebetween along the reference line will typically be taken to mean any point corresponding to a point along the measurement line. Thus, by viewing the surface from a direction aligned, at least partially, with a normal of the surface, a more accurate fluid level measurement can be obtained. The line of sight may be coincident with the plane defined by the fluid interface. It may be that the viewing plane may be coincident with the normal to the surface at a point where the plane parallel to the fluid interface intersects the measurement line.

[0022] It will be understood that a line of sight is the imaginary line between the objective lens of the viewing device (e.g., the objective lens of an observer’s eye) and the object being viewed (e.g., the point along the measurement line where the measurement line appears to intersect the interface). An accurate reading can be obtained by measuring the fluid level by viewing the surface along a line of sight which is coincident with a viewing plane perpendicular to the interface and coincident with the normal to the surface at the point where the measurement line intersects the fluid interface. This means that, for accurate measurements, each point along the measurement line requires a different line of sight. Thus, to accurately measure the fluid level, it may be that the method comprising viewing the surface along at least two different lines of sight, one each for any of the points along the measurement line against which the fluid level is to be assessed. For some applications, each preferred line of sight is coincident with the plane defined by the fluid interface (i.e., the plane coplanar with the fluid interface), because this viewing direction provides the most accurate reading.

[0023] The method may comprise rotating the surface relative to the direction from which the surface is to be viewed so that the surface can be viewed along the line of sight coincident with the viewing plane. Thus, by rotating the surface, it may be that multiple different lines of sight relative to the surface can be achieved without the observer / viewing device having to move.

[0024] In some embodiments, the line of sight intersects a point along the measurement line between the first point and second point.

[0025] In some embodiments, the method comprises viewing the surface along a first line of sight coincident with a first viewing plane and passing through the first point and viewing the surface along a second line of sight coincident with a second viewing plane and passing through the second point, wherein the first viewing plane is transverse to the plane parallel to the fluid interface and coincident with the normal to the surface at the first point, wherein the second viewing plane is transverse to the plane parallel to the fluid interface and coincident with the normal to the surface at the second point. In some embodiments, the first line of sight and / or the second line of sight is parallel to the plane defined by the fluid interface.

[0026] In some embodiments, the first point is associated with a first predetermined fluid level and the second point is associated with a second predetermined fluid level. These predetermined fluid levels may correspond to predetermined fluid volumes. Thus, the method can be used for determining a volume of fluid in a container, the surface being an inner surface of a wall of the container.

[0027] The method may comprise determining the fluid level of the fluid based on the position of a fluid interface relative to the first point and the second point, wherein the first point is a first predetermined fluid level and the second point is a second predetermined fluid level. In other words, the method uses points that correspond to a particular fluid level. The fluid level corresponding to each of the first point and the second point may have been determined using a calibration procedure. In some embodiments, the first predetermined fluid level corresponds to a first predetermined fluid volume and the second predetermined fluid level corresponds to a second predetermined fluid volume. Thus, a particularly precise measurement of fluid level or fluid volume can be obtained. In some embodiments, the first point is a predetermined maximum fluid level and the second point is a predetermined minimum fluid level. In some embodiments, the first point is a predetermined maximum fluid volume and the second point is a predetermined minimum fluid volume.

[0028] The first predetermined fluid level may be greater than the second predetermined fluid level, and the method may further comprise: determining whether the fluid level is within a range of less than the first predetermined fluid level and greater than the second predetermined fluid level based on the position of the fluid interface relative to the first point and second point. The method may further comprise, based on said determination, adjusting the fluid level so that it is within this range.

[0029] Thus, it is possible to more precisely determine whether a fluid level falls within a predetermined range, compared with previous fluid level viewing-based measurement techniques.

[0030] The method may comprise providing an additional surface that is moveably (e.g. rotatably) mounted relative to the surface in contact with the fluid, wherein the additional surface has the measurement line provided therewith. The method may comprise moving (e.g. rotating) the additional surface to align the measurement line with a viewing direction of an observer or viewing device. Thus, the surface in contact with the fluid need not itself be repositioned, but instead an additional surface can be moved (e.g. rotated) without disturbing the fluid in contact with the surface. In this way, measurements can be taken without causing excessive movement of the fluid even where the position of the measurement line needs to be altered without altering the position of the observer / viewing device.

[0031] In accordance with another aspect of the present invention, there is provided a method of manufacturing a device for carrying out the above-mentioned methods comprising: providing the surface associated with the measurement line; marking at least the first point and the second point along the measurement line.

[0032] The first point and the second point may be marked on the surface, or on the additional surface.

[0033] The method may comprise marking at least the first point and the second point along the measurement line based on a calibration procedure. The calibration procedure may comprise determining the position along the measurement line that the first point should be marked to correspond to a first predetermined fluid level and the position along the measurement line that the second point should be marked to correspond to a second predetermined fluid level. The first point may be indicative of the first predetermined fluid level, and the second point may be indicative of the second predetermined fluid level.

[0034] According to another aspect of the invention there is provided a measuring device for measuring the fluid level of a fluid using any of the methods described herein. The measuring device comprises a main body defining a surface having a first measurement line, wherein either: the main body is partially immersible in the fluid such that the measurement line intersects the fluid level; or the main body comprises a container for accommodating the fluid.

[0035] In some embodiments, the measuring device for measuring the fluid level of a fluid may be a measuring device for measuring the volume of the fluid. In particular, it will be understood that any references to measuring the fluid level of a fluid can be replaced with measuring the fluid volume of a fluid. Likewise, any references to fluid levels may be replaced with references to fluid volumes. For example, references to a first fluid level, a second fluid level, a further fluid level, a maximum fluid level, a minimum fluid level may be replaced with reference to a first fluid volume, a second fluid volume, a further fluid volume, a maximum fluid volume and a minimum fluid volume, respectively.

[0036] In embodiments where the main body comprises a container, the container may have a base (e.g., a flat base) for supporting the container on another surface (e.g. a ground surface, or a table-top). The container may have a longitudinal axis perpendicular to a plane of the base. It will be understood that in any of the description herein directions are described with reference to a plane parallel to the fluid interface, this may instead be defined with reference to a plane parallel to the plane of the base.

[0037] In addition, it will be understood (whether or not the main body comprises a container) that in any of the description herein directions are described with reference to a plane parallel to the fluid interface, this may instead be defined with reference to a plane parallel to horizontal direction.

[0038] In some embodiments where the main body comprises a container, the container comprises an opening for receiving the fluid. In some embodiments, the measurement line is angled relative to a plane parallel to the opening and the longitudinal axis. That is, the first point and the second point are separated from one another at least along a direction perpendicular to the plane parallel to the opening. In some embodiments, the opening is parallel to the base. Alternatively, in some embodiments, the container will be configured to be held (e.g., clamped) in use rather than supported on a base.

[0039] It may be that the measuring device comprises (e.g., is) a burette.

[0040] According to another aspect of the invention there is provided a measuring device for measuring a fluid level, the measuring device comprising: a main body comprising a container for accommodating a fluid; the container comprising a surface associated with a first measurement line marking at least a first point and a second point; wherein, in use, the fluid level is determinable based on the position of a fluid interface relative to the first point and the second point, wherein the first measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the fluid interface; wherein the reference line is defined by the intersection between the plane parallel to the fluid interface and the surface; wherein the first point and the second point are offset from one another along the first direction; wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the fluid interface.

[0041] By measuring a fluid level using a measurement line having a gradient as defined hereinbefore it is possible to obtain particularly precise measurements. More specifically, this method makes it possible to distinguish reliably between similar fluid levels (e.g., similar fluid volumes).

[0042] In some embodiments where fluid volume is measured, the volume which can be measured using the measuring device may be a volume of fluid accommodated within the container. The volume may be a volume of an object immersed in fluid accommodated within the container.

[0043] In some embodiments, the ratio of the distance between the first point and the second point along the first direction to the distance between the first intersection point and the second intersection point along the reference line is less than 1 . The magnitude of the ratio may be less than 1. More generally, the measurement line has a gradient which is at least distinct from a vertical line (i.e., a line aligned with the first direction).

[0044] By providing a measurement line having gradient defined in this way it is possible to provide particularly precise measurements. The ratio may be less than 0.9. The ratio may be less than 0.8. The ratio may be less than 0.7. The ratio may be less than 0.6. The ratio may be less than The ratio may be less than 0.5. The ratio may be less 3 than 0.4. The ratio may be less than 0.3. The ratio may be less than 0.2. The ratio may be less than 0.17. The ratio may be greater than 0.05. The ratio may be greater than 0.1. The ratio may be greater than 0.17.

[0045] It may be that the measurement line comprises a first portion which shares the same gradient as a second portion of the same measurement line. It may be that the measurement line has the same gradient over its full length. In some embodiments, the first point is associated with a first indicator positioned along the first measurement line to visually indicate a first fluid level and the second point is associated with a second indicator positioned along the first measurement line to visually indicate a second fluid level.

[0046] The first indicator may comprise a visible label of the numerical value corresponding to the first fluid level. The second indicator may comprise a visible label of the numerical value corresponding to the second fluid level.

[0047] For example, the first indicator and second indicator may comprise volume measures (e.g., “100 ml”, “200 ml”, ...etc.).

[0048] Labelling the first and second points with corresponding numerical values makes it straightforward for the user to quickly determine fluid levels using the device.

[0049] In some embodiments, the first point is visible along a first line of sight coincident with a first viewing plane and the second point is visible along a second line of sight coincident with a second viewing plane, wherein the first viewing plane is transverse to the plane parallel to the fluid interface and coincident with the normal to the surface at the first point, wherein the second viewing plane is transverse to the plane parallel to the fluid interface and coincident with the normal to the surface at the second point, and wherein the first viewing plane is non-coplanar with the second viewing plane.

[0050] An accurate reading can be obtained by measuring the fluid level by viewing the surface along a line of sight which is coincident with a viewing plane perpendicular to the interface and coincident with the normal to the surface at the point where the line of sight intersects the surface. That is, the first point and second point are at least visible along their respective lines of sight where the fluid level at these points can be read accurately.

[0051] The first measurement line may have a further point positioned along the measurement line, wherein the further point is associated with a further indicator to visually indicate a third fluid level (e.g., a third volume). The further indicator may comprise a visible label of the numerical value corresponding to the third fluid level.

[0052] The further point may be between the first point and the second point. There may be a single further point. Alternatively, the further point may be one of a plurality of further points positioned along the measurement line, each associated with a respective further indicator to visually indicate a fluid level. For example, each of the further indicators may comprise a further line (which is short in length relative to the measurement line) extending from the measurement line. In some embodiments, each of the further indicators indicate a fluid volume. The further indicators may be spaced along the first measurement line such that the volumes associated with adjacent indicators differ by 1 ml or less (e.g., 0.5 ml). In conventional measurement containers, graduation lines extend from the vertical measurement line. These are parallel to the fluid interface. By providing a first measurement line with a gradient defined herein, more further lines can be provided along the measurement line (compared to the number of graduation lines provided along a vertical measurement line). These further lines may be parallel to the first direction (i.e., vertical). In embodiments where the ratio of the distance between the first point and the second point along the first direction to the distance between the first intersection point and the second intersection point along the reference line is 1 or less, a greater number of vertical further lines can be provided compared to the number of horizontal graduation lines practically possible (i.e., whilst still being readable) along a vertical line.

[0053] In some embodiments, there may be multiple indicators corresponding to a single fluid level. For example, the first measurement line may be associated with a first set of indicators positioned above the measurement line, and a second set of indicators positioned below the measurement line. The first set of indicators may mark fluid levels in terms of different measurement units compared to the second set of indicators. For example, the first set of indicators may indicate fluid levels using a metric scale and the second set of indicators may indicate fluid levels using an imperial scale.

[0054] In some embodiments the first measurement line is one of a plurality of measurement lines, each of the plurality of measurement lines having a respective first point and second point, and wherein each measurement line of the plurality of measurement lines between its respective first point and second point has a gradient defined with respect to the first direction and the reference line.

[0055] In some embodiments, any indicators along one of the plurality of measurement lines other than the first measurement line may comprise labels marking fluid level measurements in terms of different measurement units compared to indicators along the first measurement line. For example, a metric scale may be marked along the first measurement line, and an imperial scale may be marked along another one of the plurality of measurement lines.

[0056] In some embodiments, the plurality of measurement lines includes an orientation line separate from the first measurement line. That is, the plurality of measurement lines includes an orientation line in addition to the first measurement line. In some embodiments, the first point of the orientation line lies on the same plane parallel to the fluid interface as the first point of the measurement line and indicates the first fluid level, and the second point of the orientation line lies on the same plane parallel to the fluid interface as the second point of the measurement line and indicates the second fluid level. In some embodiments, the first point of the orientation line may be associated with a first orientation indicator positioned along the orientation line to visually indicate the first fluid level and the second point of the orientation line may be associated with a second orientation indicator positioned along the orientation line to visually indicate the second fluid level.

[0057] In some embodiments, the gradient of the orientation line between the first point of the orientation line and the second point of the orientation line, defined with respect to the first direction and the reference line, is the same as the gradient of the measurement line between the first point and the second point of the measurement line.

[0058] By providing a container comprising an orientation line it is possible for the user to quickly check whether the device is orientated correctly, thereby facilitating improved measurement accuracy. In particular, the user can compare the fluid level readings obtained using both measurement lines. If the respective readings are different then this provides an indication that the orientation of measurement device is incorrect. For example, a discrepancy between the fluid level indications could mean that the device is not positioned on a level surface, or that the user is holding the measurement device at an angle.

[0059] The orientation line between the first point and the second point may have a gradient defined with respect to the first direction and the reference line. The first point and the second point of the orientation line may be offset from one another along the first direction. A first orientation intersection point and a second orientation intersection point may be offset from one another along the reference line. The first orientation intersection point may be the point closest to the first point of the orientation line where a first orientation intersection plane intersects the reference line, and the second orientation intersection point may be the point closest to the second point of the orientation line where a second orientation intersection plane intersects the reference line. The first orientation intersection plane passes through the first point of the orientation line and is normal to a first orientation tangent to the surface at the first point of the orientation line. The second orientation intersection plane passes through the second point of the orientation line and is normal to a second orientation tangent to the surface at the second point of the orientation line. The first and second orientation tangents may be parallel to the plane parallel to the fluid interface.

[0060] In some embodiments, the orientation line is effectively a displaced version of the measurement line. That is, for each point along the measurement line there is a corresponding point along the orientation line. Likewise for each indicator along the measurement line there is a corresponding indicator along orientation line (where the corresponding indicators indicate the same fluid level).

[0061] In some embodiments, the plurality of measurement lines includes an alignment line separate from the first measurement line. That is the plurality of measurement lines includes an alignment line in addition to the first measurement line. In some embodiments, the main body comprises an alignment surface, the alignment line being associated with the alignment surface. The first point of the alignment line may lie on the same plane parallel to the interface as the first point of the measurement line and indicate the first fluid level, and the second point of the alignment line may lie on the same plane parallel to the interface as the second point of the measurement line and indicate the second fluid level. In some embodiments, at least the region of the main body adjacent to the first measurement line is transparent. A first alignment component of a surface normal of the alignment surface at the first point of the alignment line, directed inwardly within the main body, the first alignment component being parallel to the fluid interface, may have a first fluid interface parallel component in the opposite direction to a first measurement component of a surface normal of the surface at the first point of the measurement line, directed inwardly within the main body, the first measurement component parallel to the fluid interface. A second alignment component of a surface normal of the alignment surface at the second point of the alignment line, directed inwardly within the main body, the second alignment component parallel to the fluid interface, may have a second fluid interface parallel component in the opposite direction to a second measurement component of a surface normal of the surface at the second point of the measurement line, directed inwardly within the main body, the second measurement component parallel to the fluid interface.

[0062] In some embodiments, the first fluid interface parallel component may be greater than a first fluid interface perpendicular component of the first alignment component, wherein the first fluid interface perpendicular component is parallel to the fluid interface and perpendicular to the first fluid interface parallel component. In some embodiments, the second fluid interface parallel component may be greater than a second fluid interface perpendicular component of the second alignment component, wherein the second fluid interface perpendicular component is parallel to the fluid interface and perpendicular to the second fluid interface parallel component. That is, the surfaces associated with the measurement line and alignment line predominately face one another.

[0063] In some embodiments, the first fluid interface parallel component may directly face the first measurement component and the second fluid interface parallel component may directly face the second measurement component. That is, the first point on the alignment line is directly opposite the first point on the measurement line, and the second point on the alignment line is directly opposite the second point on the measurement line.

[0064] In some embodiments, the first fluid interface parallel component is the only non-zero component of the first alignment component and the second fluid interface parallel component is the only non-zero component of the second alignment component.

[0065] In some embodiments, the surface normal of the alignment surface at the first point of the alignment line is collinear to the surface normal of the surface at the first point of the measurement line, and the surface normal of the alignment surface at the second point of the alignment line is collinear to the surface normal of the surface at the second point of the measurement line.

[0066] In some embodiments the alignment surface is associated with a second surface of the container. Alternatively, in some embodiments the measurement line is associated with a first part of the surface and the alignment line is associated with a second part of the surface. That is, the alignment surface is part of the same surface associated with the first measurement line. This may be the case in embodiments where the surface extends around the perimeter of the container (e.g., cylindrical containers).

[0067] By providing a container comprising an alignment line it is possible for the user to quickly check whether they are reading the device along an appropriate viewing direction, thereby facilitating fast and accurate measurement.

[0068] The alignment line between the first point of the alignment line and the second point of the alignment line may have a gradient defined with respect to the first direction and the reference line. The first point and the second point of the alignment line may be offset from one another along the first direction. A first alignment intersection point and a second alignment intersection point may be offset from one another along the reference line. The first alignment intersection point may be the point closest to the first point of the alignment line where a first alignment intersection plane intersects the reference line, and the second alignment intersection point may be the point closest to the second point of the alignment line where a second alignment intersection plane intersects the reference line. The first alignment intersection plane passes through the first point of the alignment line and is normal to a first alignment tangent to the alignment surface at the first point of the alignment line. The second alignment intersection plane passes through the second point of the alignment line and is normal to a second alignment tangent to the surface at the second point of the alignment line. The first and second alignment tangents may be parallel to the plane parallel to the fluid interface.

[0069] In some embodiments, the alignment line and measurement line appear to form a cross.

[0070] In some embodiments, the alignment line is effectively a displaced version of the first measurement line. That is, for each point along the measurement line there is a corresponding point along the alignment line. Likewise for each indicator along the measurement line there is a corresponding indicator along the alignment line (where the corresponding indicators indicate the same fluid level).

[0071] In some embodiments, the ratio of the distance between the first point and the second point of the first measurement line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 1 , and / or the ratio of the distance between the first point and the second point of the alignment line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 1.

[0072] This steeper gradient (a ratio greater than 1) of the first measurement line and / or alignment line is beneficial because the alignment procedure can be performed more easily. That is, the steeper gradient makes the measurement line and alignment line easier for the user to read and compare.

[0073] In some embodiments, the first point along the alignment line is associated with a first alignment indicator positioned along the alignment line to visually indicate the first fluid level and the second point along the alignment line is associated with a second indicator positioned along the alignment line to visually indicate the second fluid level.

[0074] It may be that the alignment line is one of a plurality of alignment lines. It may be that each of the plurality of alignment lines is associated with the alignment surface. It may be that each of the plurality of alignment lines is associated with another (e.g., a corresponding) measurement line. For example, it may be that a first alignment line is associated with the first measurement line, a second alignment line is associated with a second measurement line...., and an nth alignment line is associated with an nth measurement line. That is, it may be that there are multiple pairs of measurement lines (e.g., first, second,... nth measurement lines) and alignment lines (e.g., first, second,... nth alignment lines).

[0075] It may be that the first measurement line covers the same range of fluid levels as the first alignment line. It may be that the second measurement line covers the same range of fluid levels as the second alignment line. It may be that each of the first to nth measurement lines covers the same range of fluid levels as each of the respective first to nth alignment lines.

[0076] It may be that the first measurement line covers a different range of fluid levels compared to the second measurement line. It may be that the first alignment line covers a different range of fluid levels compared to the second alignment line. It may be that each of the first to nth measurement lines covers different ranges of fluid levels from one another. It may be that each of the first to nth alignment lines covers different ranges of fluid levels from one another. It may be that different ranges overlap.

[0077] It may be that a first point of each alignment line lies on the same plane parallel to the interface as a first point of the corresponding measurement line and indicates a first respective fluid level, and a second point of each alignment line lies on the same plane parallel to the interface as a second point of the corresponding measurement line and indicates a second respective fluid level.

[0078] It may be that at least the region of the main body adjacent to each measurement line is transparent.

[0079] It may be that a first respective alignment component of a respective surface normal of the alignment surface at the first point of each respective alignment line, directed inwardly within the main body, the first respective alignment component being parallel to the fluid interface, has a first respective fluid interface parallel component in the opposite direction to a first respective measurement component of a respective surface normal of the surface at the first point of the corresponding measurement line, directed inwardly within the main body, the first respective measurement component parallel to the fluid interface.

[0080] It may be that a second respective alignment component of a respective surface normal of the alignment surface at the second point of each respective alignment line, directed inwardly within the main body, the second respective alignment component parallel to the fluid interface, has a second respective fluid interface parallel component in the opposite direction to a second respective measurement component of a respective surface normal of the surface at the second point of the corresponding measurement line, directed inwardly within the main body, the second respective measurement component parallel to the fluid interface.

[0081] It may be that each first respective fluid interface parallel component directly faces each first respective measurement component and each second respective fluid interface parallel component directly faces each second respective measurement component. It may be that each first respective fluid interface parallel component is the only nonzero component of each first respective alignment component and each second respective fluid interface parallel component is the only non-zero component of each second respective alignment component.

[0082] It may be that the ratio of the distance between the first point and the second point of each measurement line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 1. It may be that the ratio of the distance between the first point and the second point of each alignment line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 1.

[0083] It may be that the first point along each alignment line is associated with a first respective alignment indicator positioned along the respective alignment line to visually indicate the first respective fluid level and the second point along each alignment line is associated with a second respective alignment indicator positioned along the respective alignment line to visually indicate the second respective fluid level.

[0084] Advantageously, by providing pairs of alignment lines and corresponding measurement lines, it is possible for the user to easily ensure that they are viewing the surface at the correct viewing angle for determining the fluid level over a wider range of fluid levels. Accordingly, parallax error is avoided for measurements over a wider volume range (compare to just providing a single alignment line and corresponding measurement line).

[0085] It may be that each measurement line is separate from each other measurement line. It may be that each alignment line is separate from each other alignment line.

[0086] The inventor has released that it is easier to mark surfaces with multiple pairs of (separate) measurement lines and corresponding alignment lines which correspond to different volume ranges, compared to a continuous line which extends around a container. Accordingly, devices having multiple pairs of (separate) measurement lines and corresponding alignment lines are more straightforward to manufacture. It may be that each measurement line (including each alignment line) comprises one or more indicators, each indicating a particular fluid level (e.g., a fluid volume). Each indicator may comprise a further line (which is short in length relative to the respective measurement line) extending from the measurement line. These further lines may be parallel to the first direction (i.e., vertical). One or more of the indicators (e.g., each indicator) may comprise a numerical label - e.g., a visible label of the numerical value corresponding to fluid level. For example, the first indicator and second indicator may comprise volume measures (e.g., “100 ml”, “200 ml”, ... etc.). At least part of one or more of the indicators (e.g., each of the indicators) may be positioned below the respective measurement line.

[0087] It may be that the size of at least part of one or more of the indicators is selected based on the refractive properties (e.g., the refractive index) of the fluid to be measured, the refractive properties of a material of the container (e.g., the surface associated with the one or more measurement lines), and / or the refractive properties of the surrounding medium (e.g., the air outside the container). It may be that the size of at least part of one or more of the indicators is selected based on the shape of the surface associated with at least one of the measurement lines. Typically, the surface defines at least part of a container for accommodating the fluid. It may be that the size of at least part of one or more of the indicators is selected based on the shape of the container.

[0088] Refraction causes the apparent depth and size of indicators associated with an alignment line and viewed through the fluid to be changed (compared to the real size of these indicators). These changes depend on at least the shape of the container and refractive index of the fluid (and the other mediums through which light forming an image of the indicator travels). Typically, the user is looking through the first surface associated with the measurement line towards the alignment line (through the fluid). For example, when the container is shaped like a measuring cylinder the indicators associated with the alignment line(s) appear magnified when observed through fluid within the container. By adjusting the real size of indicators based on the expected magnification, the inventor has realised that the readability of the indicators on the alignment line is much improved - thereby making it easier to make more accurate measurements that avoid the parallax error.

[0089] It may be that at least part of one or more indicators (e.g., numerical labels) associated with at least one alignment line may be smaller than at least part of one or more indicators of the corresponding measurement line. Each of the indicators associated with the alignment lines may be smaller than each of the indicators of the corresponding measurement lines. It may be that the (real) size of the indicators is chosen so that any indicators associated with an alignment line appear to be approximately the same size as any of the indicators associated with the corresponding measurement lines when viewed through the surface associated with the corresponding measurement line and through the fluid.

[0090] It may be that the indicators are marked so that any text and / or numbering is readable in the conventional way (i.e., from left to right) by a user looking through the surface associated with the measurement line towards the corresponding alignment line (through the fluid) - e.g., along a line of sight parallel to the fluid interface from a point along the first measurement line to a point along the first alignment line. That is the any indicators on the alignment line may appear as if flipped from left to right when viewed by a user facing the surface associated with the alignment line (i.e., not through the fluid).

[0091] For example, the order of individual letters of a word may be reversed or digits of a number may be reversed when viewed by a user facing the surface (i.e., not through the fluid) associated with the alignment line. Likewise, the individual characters (e.g., digits and / or letters) will appear flipped about an axis aligned along the height of the characters (i.e., an axis perpendicular to the reading direction) when viewed by a user facing the surface associated with the alignment line. Advantageously, this makes it easier to read indicators on the measurement line and corresponding alignment line at the same time.

[0092] In some embodiments, the plurality of measurement lines includes an additional measurement line, separate from the first measurement line, which covers a different range of fluid levels relative to the first measurement line, and optionally wherein the additional measurement line is spaced (i.e., shifted) along the first direction relative to the first measurement line.

[0093] In some embodiments, the lowest fluid level indicated by the first measurement line is different from the lowest fluid level indicated by the additional measurement line and / or the highest fluid level indicated by the first measurement line is different from the highest fluid level indicated by the additional measurement line. In some embodiments, the additional measurement line covers a fluid level range that overlaps the fluid level range covered by the first measurement line by at least 80%, such as by at least 90%. In other embodiments, the additional measurement line covers a fluid level range that overlaps the fluid level range covered by the first measurement line by less than at least 60%, such as by less than at least 50%, or less than at least 40%.

[0094] By providing a measuring device comprising a plurality of measurement lines spaced along a direction perpendicular to the fluid interface it is possible to measure fluid levels precisely over a wide range, even for relatively tall containers, whilst maintaining relatively shallow gradients for the measurement lines. In some embodiments where the measuring device is for measuring fluid volumes, the volume range may be between 0 ml and the total volume that can be accommodated by the container.

[0095] In some embodiments, it may be that each measurement line of the plurality of measurement lines between its respective first point and second point has a gradient defined with respect to the first direction and the reference line, wherein each respective first point and respective second point are offset from one another along the first direction, wherein, for each measurement line, a respective first intersection point and a respective second intersection point are offset from one another along the reference line; wherein, for each measurement line, the respective first intersection point is the point closest to the respective first point where a respective first intersection plane intersects the reference line, and the respective second intersection point is the point closest to the respective second point where a respective second intersection plane intersects the reference line; and wherein, for each measurement line, the respective first intersection plane passes through the respective first point and is normal to a respective first tangent to the surface at the respective first point, the respective second intersection plane passes through the respective second point and is normal to a respective second tangent to the surface at the respective second point, wherein the respective first and second tangents are parallel to the plane parallel to the fluid interface. At least a portion of one of the plurality of measurement lines may have the same gradient as at least a portion of another one of the plurality of measurement lines.

[0096] In some embodiments, any measurement lines of the measurement device that each intersect a plane parallel to the fluid interface have the same gradient at their respective points of intersection.

[0097] In some embodiments, any of the shifted measurement lines and the first measurement line of the measurement device that each intersect a plane parallel to the fluid interface have the same gradient at their respective points of intersection.

[0098] It will be understood that the term “any measurement lines” includes both the situation where each of a plurality of measurement lines, as well as measurement devices having only a single measurement line.

[0099] It may be that any of the measurement lines comprise a respective first portion which shares the same gradient as a respective second portion of the same measurement line. It may be that any of the measurement lines have the same gradient over their full respective lengths.

[0100] In some embodiments involving a plurality of measurement lines, any of the measurement lines of the measuring device share the same gradient over at least a portion of their respective lengths. It may be that any of the measurement lines of the measuring device share the same gradient over their full lengths.

[0101] In some embodiments involving a plurality of measurement lines, any of any of the shifted measurement lines and the first measurement line of the measuring device share the same gradient over at least a portion of their respective lengths, and optionally over their full lengths.

[0102] In some embodiments involving a single measurement line, the measurement line extends around the main body at least once, about an axis of the main body parallel to the first direction. In some embodiments where the main body comprises a container, it will be understood that the measurement line may extend around the container at least once, about an axis of the container parallel to the first direction.

[0103] By providing a container comprising a measurement line that extends around the container at least once it is possible to measure fluid levels (e.g. fluid volumes) precisely over a wide range. The volume range may be between 0 ml and the total volume that can be accommodated by the container. The measurement line may make at least one revolution of the container. The measurement line may extend around the container multiple times. The measurement line may extend around the container fewer than 20 times. The measurement line may extend around the container more than twice. For example, if the container is cylindrical in shape, the measurement line may be a spiral.

[0104] According to some embodiments, the first point is associated with a maximum fluid level indicator to visually indicate a maximum fluid level and the second point is associated with a minimum fluid level indicator to visually indicate a minimum fluid level.

[0105] By providing a measuring device having these minimum and maximum fluid indicators it is possible to precisely determine whether a fluid level falls within a predetermined range. For example, it is possible to precisely determine whether a volume of fluid falls within a predetermined range.

[0106] In some embodiments the maximum fluid level corresponds to the volume when the container is completely filled and / or the minimum fluid level corresponds to the volume when the container is completely empty - i.e., 0 ml. In some embodiments, the minimum fluid level corresponds to a volume when the container is not completely empty and / or the maximum fluid level corresponds to a volume where the container is less than completely filled. Nevertheless, typically the maximum fluid level corresponds to a fluid level greater than the fluid level corresponding to the minimum fluid level.

[0107] In some embodiments, there are no further fluid level indicators other than the maximum fluid level indicator and minimum fluid level indicator. The measurement device may further comprise an additional surface that is moveably attached to the surface in contact with the fluid, wherein the additional surface has the measurement line provided thereon.

[0108] By providing the measurement line on an additional surface that is moveably attached to the surface in contact with the fluid it is easier for the user to view the measuring device along an appropriate viewing direction, thereby facilitating convenient and accurate measurements. For example, a user that is positioned so that they cannot view the device along an appropriate line of sight (e.g., a line of sight coincident with a viewing plane, wherein the viewing plane is perpendicular to the fluid interface and coincident with the normal to the surface at the relevant point along the measurement line) the user can move the additional surface rather than change their own position or re-position the device as a whole. In some embodiments, the additional surface may be rotatably mounted relative to the surface in contact with the fluid. The additional surface may be part of a sleeve arranged to rotate around the container accommodating the fluid. For example, the additional surface and the sleeve may each have a circular cross section, wherein in use, the additional surface is concentric with the sleeve. In some embodiments, the additional surface and the sleeve may be cylindrical. In some embodiments, the additional surface may be slidable relative to the surface in contact with the fluid.

[0109] In some embodiments, the main body is attachable, or integral with a water-going vessel. The fluid level is associated with the volume of water displaced by the vessel and may be used to determine the draft of the vessel. In use, readings may be taken using the measurement device before and after loading or unloading of the vessel.

[0110] According to another aspect of the invention, there is provided a vessel comprising a measurement device for measuring the fluid level of a fluid, the measurement device comprising: a main body defining a surface having a measurement line, the main body being partially immersible in the fluid, wherein the measurement line is angled relative to the horizontal and the vertical direction, such that the measurement line intersects the fluid level of the fluid.

[0111] It will be understood that the fluid may be a body of fluid (e.g., a lake, sea or ocean). In some embodiments involving a vessel comprising a measurement device, the measuring device may be for determining the draft of a vessel for travelling in a body of water, wherein the main body is attachable, or integral with the vessel.

[0112] In some embodiments, the vessel may comprise a plurality of measurement devices, each comprising a main body attachable, or integral with the vessel. For example, a first measurement device may be provided towards the front of the vessel and a second measurement device may be provided towards the rear of the vessel. Comparing the water level measured using the measurement line of the first measurement device to the water level measured using the measurement line of the second measurement device provides an indication of how evenly the vessel has been loaded. In some embodiments, one or multiple measurement devices may be provided on each side of the vessel.

[0113] It will be understood more generally that any measuring device described herein and having main body partially immersible in fluid, that the main body may comprise a plurality of measurement lines arranged at different positions around the body. Thereby, it is possible to compare fluid levels at different positions of the main body.

[0114] It will be understood that any of the features or steps described in relation to one or more of the aspects of any method or device described hereinbefore is applicable to and should be considered disclosed in relation to any other one or more of the aspects of any method or device described hereinbefore unless inherently incompatible therewith.

[0115] Description of the Drawings

[0116] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0117] Figures 1-3 are schematic representations of a measurement device for measuring a fluid volume, according to an embodiment of the invention;

[0118] Figure 4 is a schematic representation of a measurement device for measuring a fluid volume, according to another embodiment of the invention;

[0119] Figure 5 is a schematic representation of a cross section of a measurement device for measuring a fluid volume, according to an embodiment of the invention; Figure 6 is a schematic representation of a cross section of a measurement device for measuring a fluid volume, according to another embodiment of the invention;

[0120] Figure 7 is a schematic representation of a measurement device for measuring a volume, according to another embodiment of the invention;

[0121] Figure 8 is a schematic representation of a measurement device for measuring a fluid volume, according to another embodiment of the invention;

[0122] Figure 9 is a schematic representation of a portion of a measurement device for measuring a fluid volume, according to another embodiment of the invention;

[0123] Figure 10 is a schematic representation of a portion of a measurement device for measuring a fluid volume, according to another embodiment of the invention;

[0124] Figure 11 is a schematic representation of the measurement device shown in Figure 10, viewed from above;

[0125] Figure 12 is a schematic representation of a measurement device for measuring a fluid volume, according to an embodiment of the invention;

[0126] Figure 13 is a flow chart, illustrating a method of manufacturing a measurement device according to an embodiment of the invention;

[0127] Figure 14 is a flow chart, illustrating a method of measuring a fluid level according to an embodiment of the invention; and

[0128] Figure 15 is a schematic representation of a portion of a measurement device for measuring a fluid volume, according to another embodiment of the invention.

[0129] Detailed Description of an Example Embodiment

[0130] Figures 1-3 are schematic representations of a measuring device 100 for measuring a volume. The measuring device includes a container 105 having a surface 103. The measurement device also includes a measurement line 120 marking at least a first point 130 and a second point 140. In use, the container 105 accommodates a fluid 107. The fluid 107 within the container 105 defines a fluid interface 110. The volume to be measured is determinable based on the position of the fluid interface 110 relative to the first point 130 and the second point 140.

[0131] Figures 1-3 show an embodiment of the measuring device where the container is cylindrical in shape. The measurement line 120 is provided on the surface 103 of the container 105. The first point 130 corresponds to one end of the measurement line 120 and the second point 140 corresponds to the other end of the measurement line 120. Figure 2 shows a first direction 150 and a reference line 160. The first direction 150 is normal to a plane parallel to the fluid interface 110. The reference line 160 is defined by the intersection between a plane parallel to the fluid interface 110 and the surface 103. The measurement line 120 between the first point 130 and the second point 140 has a gradient defined with respect to the first direction 150 and the reference line 160.

[0132] As shown in Figure 3, the first point 130 and second point 140 are offset along the first direction 150. That is, the first point 130 and second point 140 are separated along the first direction 150 by a first distance 155. A first intersection point 161 and a second intersection point 163 are offset from one another along the reference line 160. That is, the first point 130 and second point 140 are separated along the reference line 160 by a second distance 165. In Figure 3, only a portion of the reference line 160 is shown. The first intersection point 161 is defined by the closest point to the first point 130 where a plane which passes through the first point 130, and is normal to a tangent to the surface 103 at the first point 130, intersects the reference line 160. The second intersection point 163 is defined by the closest point to the second point 140 where a plane which passes through the second point 140, and is normal to a tangent to the surface 103 at the second point 140, intersects the reference line 160.

[0133] In use, the position of the fluid interface 110 relative to the first point 130 and the second point 140 can be used to determine the volume of the fluid. The volume range represented by the measurement line 120 between the first point 130 and the second point 140 is effectively expanded over a longer distance compared to the same range if a conventional measuring cylinder was used, with the measurement line running vertically up the container (parallel to the first direction 150) thereby more precise volume measurements can be obtained.

[0134] Figures 4 is a schematic representation of a measuring device 200 for measuring a volume according to another embodiment. The measuring device includes a container 205 having a surface 203. The measurement device also includes a measurement line 220 marking at least a first point 230 and a second point 240. In use, the container 205 accommodates a fluid 207. The fluid 207 within the container 205 defines a fluid interface 210.

[0135] The difference between the embodiment shown in Figure 1 and Figure 2 is that the first point 230 and the second point 240 of the measurement line 220 are associated with a marker for visually indicating a first and second volume, respectively. Each marker is short line. In addition, the measurement line 220 has a further marker 250 positioned along the measurement line 220 between first point 230 and the second point 240 for visually indicating a third volume. Figure 4 shows an example where the fluid interface 210 appears to intersect the measurement line 220 at the further marker 250. That is, the volume of the fluid 207 accommodated within the container 205 corresponds to the volume indicated by the further marker 250, in this example.

[0136] Figures 5 is a schematic representation of a cross section of a measuring device 300 for measuring a volume according to another embodiment. The measuring device includes a container 305 having a surface 303. In use, the surface 303 is in contact with a fluid. The cross section has been taken at the level of the first point 330. As shown in Figure 5, the first point 330 should be viewed along a line of sight 370 coincident with a viewing plane which is transverse to a plane parallel to the fluid interface and is coincident with the normal to the surface at the first point 330 for an accurate reading. Preferably, the line of sight 370 should be coincident with the normal to the surface at the first point 330.

[0137] Figure 6 is a schematic representation of a cross section of a measuring device 400 for measuring a volume according to another embodiment. The measuring device includes a cylindrical container 405 having a surface 403. The cross section has been taken at the level of the first point 430. The measuring device 400 also includes a cylindrical additional surface 480 having the measurement line. In use, the additional surface 480 is rotatable relative to the surface 403 in contact with the fluid.

[0138] Figure 7 shows an embodiment of the measuring device 500 having a container 505 with a measurement line 520 on its inner surface 503. The measurement line 502 marks a first point 530 and a second point 540. In use, the container 505 accommodates a fluid 507 having a fluid interface 510. The measuring device 500 can be used to measure the volume of an object based on the position of the fluid interface 510 along the measurement line 520 before and after the object is submerged in the fluid 507.

[0139] Figure 8 is a schematic representation of a measuring device 600 for measuring a volume according to another embodiment. The measuring device includes a container 605 having a surface 603. The measurement device also includes a measurement line 620 extending around the container 605. The measurement line 620 extends around the container 605 in a helical shape. A plurality of points are marked around the measurement line 620. In use, the container 605 accommodates a fluid 607. The fluid 607 within the container 605 defines a fluid interface 610. The volume of the fluid 607 within the container can be determined based on the position of the interface 610 relative to the plurality of points along the measurement line 620.

[0140] Figure 9 is a schematic representation of a portion of a measuring device for measuring a volume. The measuring device includes a container 705 having a surface 703. The measurement device also includes a plurality of measurement lines 721 , 722. Each of the plurality of measurement lines 721 , 722 mark a plurality of points along their respective lengths. A subset of the plurality of points are associated with numerical labels to visually indicate the volumes associated with those points. Each measurement line 721 , 722 has the same gradient defined with respect to the first direction and the reference line.

[0141] Figure 9 shows a schematic representation of when the fluid interface 710 may form a meniscus. An additional line 712 may be visible due to surface tension. However, the skilled person will understand that it is typically the position of the trough of the lower line 711 (rather than the upper line 712) relative to the closest measurement line that should be considered for providing accurate volume measurements.

[0142] Figure 10 is a schematic representation of a portion of a measuring device for measuring a volume of a fluid 807. The measuring device includes a cylindrical container 805 having a surface 803. The measurement device also includes a measurement line 820 marking a first point 830, a second point 840 and multiple further markers between the first point 830 and second point 840. The container 805 is made of a material that is transparent such that an alignment line 860 can be observed through the surface 803. The alignment line 860 is provided on the same surface 803 as the measurement line, and is diametrically opposed to the measurement line. The alignment line marks a first point 831 and a second point 841 . In use, when viewed at the correct viewing position, the alignment line and the measurement line both seem to intersect the fluid interface 810 at the same point. In this embodiment, the alignment line 860 together with the measurement line 810 appear as a cross. It will be understood that the meniscus can causes a region of the alignment line to be obscured - leading to an obscured region 812. This means that the point of intersection itself may not be visible. Nonetheless, the user can interpolate where this intersection must be using points of the alignment line 860 and measurement line 820 that are visible. Accordingly, the user can easily ensure that they are viewing the container 805 at the correct viewing angle for determining the fluid volume, thereby avoiding parallax error.

[0143] Figure 11 shows the same embodiment of the invention as Figure 10 from above, where like numerals refer to like features. Figure 11 also schematically shows a first fluid interface parallel component 833, a second fluid interface parallel component 843, a first measurement component 832 and a second measurement component 842. In this embodiment, the alignment line is arranged relative to the measurement line such that the first fluid interface parallel component 833 is directly opposite the first measurement component 832, and second fluid interface parallel component 843 is directly opposite the second measurement component 842.

[0144] Figure 12 is a schematic representation of a measuring device 900 for determining a displaced volume of fluid. The measuring device 900 includes a main body 905 defining a surface 903. The measurement device also includes a measurement line 920 marking at least a first point 930 and a second point 940. In use, the main body 905 is partially immersible in a body of fluid 907 and the fluid level 910 intersects the measurement line 920. The measurement line 920 has a gradient defined relative to the vertical direction 950 and the horizontal direction 960. The position of the fluid level 910 relative to the first point 930 and second point 940 can be used to determine a displaced fluid volume.

[0145] Figure 13 is a flow chart, illustrating a method of manufacturing a device 1000 for measuring a fluid level according to an embodiment of the invention. The method 1000 involves a step of providing a surface associated with a measurement line 1100 and marking at least a first point and a second point along the measurement line 1200. In some embodiments, the respective positions that the first point and second point are marked along the measurement line is based on a calibration procedure. The method of manufacture 1000 is typically for manufacturing one of the devices described herein.

[0146] Figure 14 is a flow chart, illustrating a method 2000 of measuring a fluid level according to an embodiment of the invention. The method 2000 involves a step of providing a surface in contact with the fluid 2100. Said surface is associated with a measurement line marking at least a first point and a second point. The method 2000 also involves the step of viewing the surface to visually determine the fluid level of the fluid based on the position of a fluid interface relative to the first point and the second point 2200. Optionally, the method 2000 may involve measuring a fluid volume. Alternatively, the method 2000 may involve measuring a displaced volume. The method 2000 is typically for measuring fluid levels using one of the devices described herein.

[0147] Figure 15 is a schematic representation of a portion of a measuring device for measuring a volume of a fluid 1807. The measuring device includes a cylindrical container 1805 having a surface 1803. The measurement device includes a first measurement line 1821 and a corresponding first alignment line 1861. The measurement device also includes a second measurement line 1822 and a corresponding second alignment line 1862. That is, the device comprises two pairs of measurement and corresponding alignment lines. The container 1805 is made of a material that is transparent such that the alignment lines 1861, 1862 can be observed through the surface 1803. In use, when viewed at the correct viewing position, an alignment line and the corresponding measurement line both seem to intersect the fluid interface 1810 at the same point. Parallax error is avoided by viewing the device along the unique line of sight along which the first measurement line and corresponding alignment line seem to intersect the fluid interface 1810 at the same point. By providing multiple measurement lines and alignment lines this advantage can be achieved over a wider range of fluid levels.

[0148] The device comprises multiple indicators corresponding to specific volume levels (e.g., 100 ml, 125 ml and 150 ml). A subset 1881 - 1886 of these indicators comprise numerical labels corresponding to the volume of the fluid within the container when the fluid interface intersects the measurement line at that point. The numerical label of indicator 881 appears smaller than the other indicators 1882-1886. This is because the size of the label has been selected based on the magnifying effects of the fluid and curved container shape. However, in the embodiment shown the fluid level is below this indicator and therefore the fluid is not causing this indicator to appear larger. Below the fluid interface, indicators associated with the alignment lines appear to be around the same size as the indicators associated with the measurement line because they have been printed in a reduced size (compared to the indicators on the measurement lines 1821 , 1822). In this embodiment, only the size of the numerical label of the indicators associated with the alignment lines is selected based on the expected magnifying effects - the further lines providing additional volume indications each have the same size. The indicators (e.g., indicator 1881) associated with the alignment lines are printed on the container so that they are readable from left to right (in the conventional way) when viewed through the fluid through the surface associated with the measurement lines 1821 , 1822. In this schematic representation the indicators corresponding to 125 ml on the alignment lines 1861 , 1862 and measurement lines 1821 , 1822 appear to overlap. It is noted that this would not occur in a real embodiment of the device when the device is viewed along a preferred line of sight which is coincident with a viewing plane perpendicular to the fluid interface 1810 and coincident with the normal to the surface 1803 at the point where the first measurement line 1821 intersects the fluid interface 1810.

[0149] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0150] It will be understood that when any directions / orientations are defined relative to a plane parallel to the interface these directions / orientations could be defined relative to the base, i.e., the wording of a “plane parallel to the fluid interface” could be used interchangeably with the wording of a “plane parallel to the base”. Similarly, it will be understood that when any directions / orientations are defined relative to a direction normal to the fluid interface these directions / orientations could be defined relative to the longitudinal axis, i.e., the wording of a “line parallel to the longitudinal axis” could be used interchangeably with the wording of a “line parallel to a direction normal to the fluid interface”.

[0151] Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1. A method for measuring the fluid level of a fluid comprising: providing a surface in contact with the fluid, the surface being associated with a measurement line marking at least a first point and a second point; and viewing the surface to visually determine the fluid level of the fluid based on the position of a fluid interface relative to the first point and the second point; wherein the measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the fluid interface; wherein the reference line is defined by the intersection between the plane parallel to the fluid interface and the surface; wherein the first point and the second point are offset from one another along the first direction; wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the fluid interface.

2. The method according to claim 1 , further comprising viewing the surface from a viewing position facing the surface.

3. The method according to claim 1 or claim 2, the method further comprising viewing the surface along a line of sight coincident with a viewing plane, wherein the viewing plane is transverse to the plane parallel to the fluid interface and coincident with the normal to the surface at the point where the plane parallel to the fluid interface intersects the surface at the first intersection point, the second intersection point, or any point therebetween along the reference line,and optionally wherein the line of sight is coincident with the plane defined by the fluid interface.

4. The method according to any preceding claim, wherein the first point is associated with a first predetermined fluid level and the second point is associated with a second predetermined fluid level.

5. The method according to claim 4, wherein the first predetermined fluid level is greater than the second predetermined fluid level, wherein the method further comprises: determining whether the fluid level is within a range of less than the first predetermined fluid level and greater than the second predetermined fluid level based on the position of the fluid interface relative to the first point and second point; and, optionally, based on said determination, adjusting the fluid level so that it is within this range.

6. A method of manufacturing a device for carrying out the method according to claim 4 or claim 5 comprising: providing the surface associated with the measurement line; marking at least the first point and the second point along the measurement line.

7. A measuring device for measuring the fluid level of a fluid using any of the methods of claims 1-5, the measuring device comprising a main body defining a surface having a first measurement line, wherein either: the main body is partially immersible in the fluid such that the first measurement line intersects the fluid level; or the main body comprises a container for accommodating the fluid.

8. A measuring device for measuring a fluid level, the measuring device comprising: a main body comprising a container for accommodating a fluid; the container comprising a surface associated with a first measurement line marking at least a first point and a second point; wherein, in use, the fluid level is determinable based on the position of a fluid interface relative to the first point and the second point,wherein the first measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the fluid interface; wherein the reference line is defined by the intersection between the plane parallel to the fluid interface and the surface; wherein the first point and the second point are offset from one another along the first direction; wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the fluid interface.

9. The measuring device according to claim 7 or 8, wherein the ratio of the distance between the first point and the second point along the first direction to the distance between the first intersection point and the second intersection point along the reference line is less than 1.

10. The measuring device according to any of claims 7-9, wherein the first point is associated with a first indicator positioned along the first measurement line to visually indicate a first fluid level and the second point is associated with a second indicator positioned along the first measurement line to visually indicate a second fluid level.

11. The measuring device according to claim 10, wherein the first indicator comprises a visible label of the numerical value corresponding to the first fluid level and / or the second indicator comprises a visible label of the numerical value corresponding to the second fluid level.

12. The measuring device according to any of claims 7-11, wherein the first point is visible along a first line of sight coincident with a first viewing plane and the second point is visible along a second line of sight coincident with a second viewing plane, wherein the first viewing plane is perpendicular to the plane parallel to the fluid interface and coincident with the normal to the surface at the first point, wherein the second viewing plane is perpendicular to the plane parallel to the fluid interface and coincident with the normal to the surface at the second point, and wherein the first viewing plane is non-coplanar with the second viewing plane.

13. The measuring device according to any of claims 7-12, the first measurement line having a further point positioned along the measurement line, wherein the further point is associated with a further indicator to visually indicate a third fluid level, and optionally wherein the further indicator comprises a visible label of the numerical value corresponding to the third fluid level.

14. The measuring device according to any of claims 7-13, wherein the first measurement line is one of a plurality of measurement lines, each of the plurality of measurement lines having a respective first point and second point, and wherein each measurement line of the plurality of measurement lines between its respective first point and second point has a gradient defined with respect to the first direction and the reference line.

15. The measuring device according to claim 14, wherein the plurality of measurement lines includes an orientation line separate from the first measurement line, wherein the first point of the orientation line lies on the same plane parallel to the fluid interface as the first point of the measurement line and indicates the first fluid level, and the second point of the orientation line lies on the same plane parallel to the fluid interface as the second point of the measurement line and indicates the second fluid level, and optionally wherein the first point of the orientation line is associated with a first orientation indicator positioned along the orientation line to visually indicate the first fluid level andthe second point of the orientation line is associated with a second orientation indicator positioned along the orientation line to visually indicate the second fluid level.

16. The measuring device according to claim 14 or 15, wherein the plurality of measurement lines includes an alignment line separate from the first measurement line, wherein the main body comprises an alignment surface, the alignment line being associated with the alignment surface, wherein the first point of the alignment line lies on the same plane parallel to the interface as the first point of the measurement line and indicates the first fluid level, and the second point of the alignment line lies on the same plane parallel to the interface as the second point of the measurement line and indicates the second fluid level, wherein at least the region of the main body adjacent to the first measurement line is transparent, wherein a first alignment component of a surface normal of the alignment surface at the first point of the alignment line, directed inwardly within the main body, the first alignment component being parallel to the fluid interface, has a first fluid interface parallel component in the opposite direction to a first measurement component of a surface normal of the surface at the first point of the measurement line, directed inwardly within the main body, the first measurement component parallel to the fluid interface, and wherein a second alignment component of a surface normal of the alignment surface at the second point of the alignment line, directed inwardly within the main body, the second alignment component parallel to the fluid interface, has a second fluid interface parallel component in the opposite direction to a second measurement component of a surface normal of the surface at the second point of the measurement line, directed inwardly within the main body, the second measurement component parallel to the fluid interface, and optionally wherein the first fluid interface parallel component directly faces the first measurement component and the second fluid interface parallel component directly faces the second measurement component, and further optionally wherein the first fluid interface parallel component is the only non-zero component of the first alignment component and the second fluid interface parallel component is the only non-zero component of second alignment component.

17. The measuring device according to claim 16, wherein the ratio of the distance between the first point and the second point of the first measurement line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 1 , and / or the ratio of the distance between the first point and the second point of the alignment line along the first direction to the distance between the first intersection point and the second intersection point along the reference line is greater than 118. The measuring device according to claim 16 or 17 wherein the first point along the alignment line is associated with a first alignment indicator positioned along the alignment line to visually indicate the first fluid level and the second point along the alignment line is associated with a second indicator positioned along the alignment line to visually indicate the second fluid level.

19. The measuring device according to any of claims 14-18, wherein the plurality of measurement lines includes an additional measurement line, separate from the first measurement line, which covers a different range of fluid levels relative to the first measurement line, and optionally wherein the additional measurement line is spaced along the first direction relative to the first measurement line.

20. The measuring device according to claim 19, wherein at least a portion of one of the plurality of measurement lines has the same gradient as at least a portion of another of the plurality of measurement lines.

21. The measuring device according to any of claims 14-20, wherein any measurement lines of the measuring device that intersect the same plane parallel to the fluid interface have the same gradient at their respective points of intersection.

22. The measuring device according to any of claims 19, 20, or 21 when dependent on claim 19 or claim 20, wherein any of the measurement lines of the measuring device share the same gradient over at least a portion of their respective lengths, and optionally over their full lengths.

23. The measuring device according to any of claims 7-22, wherein the first measurement line extends around the main body at least once, about an axis of the main body parallel to the first direction.

24. The measuring device according to any of claims 7-22, wherein the first point is associated with a maximum fluid level indicator to visually indicate a fluid level and the second point is associated with a minimum fluid level indicator to visually indicate a minimum fluid level, and optionally wherein there are no further fluid level indicators other than the maximum fluid level indicator and minimum fluid level indicator.

25. A measuring device according to any of claims 7-24, further comprising an additional surface that is moveably attached to the surface in contact with the fluid, wherein the additional surface has the measurement line provided thereon.

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