GB2152669A - A liquid level indicator - Google Patents

Abstract

A water level indicator consists of a substantially flat front part (1) made of a transparent plastics material and attached to a channel- shaped, open-ended, opaque rear part (2) of semi-circular cross- section. An elongated prism (5) is attached to, or integrally formed with, the inner surface of the front part (1), and a gap between the prism (5) and concave surface of rear part (2) forms a vertical bore, into which water is introduced via aperture (9). The rear part may be coloured. Below the water level in the bore, the relative refractive indices of water and the prism material make visible the opaque rear part (2) through part (1). Above the water level, the relative refractive indices of air and the prism material cause total internal reflection within the prism (5), so that rear part (2) is not visible. <IMAGE>

Description

SPECIFICATION A liquid level indicator This invention relates to liquid level indicators and in particular, though not exclusively, to water level indicators for use in such applications as water jugs, steam irons, etc.

It is known to provide water jugs, which are made from an opaque plastics material, with a water level indicator to provide a visible indication of the level of water within the jug.

In one example of a known water jug incorporating a water level indicator, the indicator consists of a transparent plastics tube mounted, in a substantially upright manner, in an external groove formed in a side wall of the water jug, so that the open lower end of the tube communicates with the interior of the jug, thereby allowing water to rise up the tube as the jug is filled. To ensure that the water level within the tube is easily visible, a floating element, such as a coloured ball member, which floats on the water in the tube, is usually provided.

However, such indicators containing moveable elements of this kind may be prone to malfunction, and obviously cannot function at all if the moveable element is removed or becomes jammed.

It is therefore an object of the present invention to provide an improved liquid level indicator to those known hitherto.

According to the invention there is provided a liquid level indicator comprising a substantially upright hollow member, which communicates with liquid in a container, the liquid assuming, within said member, a level commensurate with the level of liquid in the container itself, said member consisting of a front part and a rear part, at least a substantial portion of the surface of said rear part being opaque and said front part being substantially transparent, said front part being provided with prismatic means for rendering said rear part substantially invisible, when viewed through said front part, above said level, and substantially visible below said level.

The prismatic means preferably consists of an elongated prism provided along the length of the front part of the tubular member, the prism being angled so as to produce total internal reflection when there is no liquid therebehind within the tubular member, so that the opaque rear part is not visible, and to deviate the optical path when liquid is present therebehind, so that the opaque rear part becomes visible.

It can therefore be envisaged that, if the rear part is suitably coloured, the level to which the colouring is visible within the tubular member, when viewed facing the front part, indicates the liquid level therewithin, the total internal reflection produced above this level causing only a silvery-white colouring to be visible thereat.

The invention will now be further described by way of example only with reference to the accompanying drawings, wherein: Figure 1 shows a front view of one embodiment of the present invention, Figure 2 shows a sectional view along line A-A in Fig. 1, Figure 3 shows a sectional view along line B-B in Fig. 1, Figure 4 shows a sectional view along line X-X, Figures 5 and 6 show schematically two optical paths, through the embodiment, without and with liquid respectively, and Figure 7 shows one application of the embodiment shown in Figs. 1 to 4.

Referring to Figs. 1 to 4, a water level indicator consists of a substantially flat, front part 1, made from a transparent plastics material and attached to a channel-shaped, openended, opaque rear part 2 of semi-circular cross-section, so as to face the concave surface of the part 2. The width of the front part 1 is greater than the diameter of rear part 2, so as to form oppositely-extending flanges, 3 and 4.

An elongated prism 5 is attached to (or formed integrally with) the inner surface of the front part 1. The gap between apex 7 of the prism 5 and the surface of the rear part 2 forms a bore 6. Lower end 8 of the bore 6 is disposed substantially orthogonal to bore 6 and ends in a circular aperture 9 forming part of a short tube which communicates with the liquid.

The material from which the indicator is constructed is preferably a relatively strong, heat resistant, transparent thermoplastics material, which can easily be moulded into complex forms. Two examples of a suitable material of this type are Nylon 1 2 (Grilamid TR 55) and a polycarbonate material.

In use, water introduced into the aperture 9 rises up the graduated bore 6. Figs. 5 and 6 show, schematically, optical paths through the indicator, when viewed facing the front part 1, as shown in Fig. 1, when only air is present in bore 6 and when water is present therewithin, respectively.

In Fig. 5, wherein air only is present in bore 6, the relative refractive indices of the material of the prism 3 and of the air cause total internal reflection of optical path 10 at faces 11 and 1 2 of the prism 3. Only a silverywhite colour is therefore visible from within the prism 3 and the opaque rear part 2, the concave surface of which is preferably brightly coloured, cannot be seen.

However, when water is present in bore 6, as shown in Fig. 6, the relative refractive indices of the water and of the prism material causes optical path 1 3 to be deviated and refracted at faces 11 and 1 2 of the prism 3, thereby enabling the opaque rear part 2 to be clearly seen. When viewing along optical path 13, that is, incident on the front part 1, a full view of the coloured rear part 2 is visible, and this remains visible, although to a lesser extent, from any angle up to a maximum oblique optical path 14.

In order for the level indicator to function effectively, apex angle B of the prism 5 should satisfy the following two conditions: 1. iCw > i1 pica 2. iz > ica where: ii = angle of incidence at face 11, 'angle of incidence at face 12, icw = critical angle for total internal a reflection from prism to water, ica = critical angle from prism to air.

To satisfy these two conditions, it has been found that, at least for the above-mentioned two preferred materials, the apex angle 8 should preferably fail within the range from 86 to 102" However, maximisation of viewing angle 3, when viewed along the oblique optical path 14, shown in Fig. 6, also needs to be taken into consideration, and to this end it has been found that an apex angle of approximately 98"-100" results in a maximum oblique viewing angle of approximately 274-29=, for the above-mentioned materials.

The present level indicator may be formed by injection moulding/extruding the elongated prism 5 and the front part 1 respectively, and then ultrasonically welding these two parts together. Alternatively a complete construction consisting of the prism 5 and an integrally formed front part 1 may be formed by injection moulding which, although involving only one single manufacturing operation, may require considerable tooling skill to prevent warping of the construction, and to ease this difficulty, a draft angle B of approximately 0.5 may be incorporated.

In accordance with the present invention, it can therefore be envisaged that the level to which water has risen up the bore 6 can readily be seen, as the coloured rear part 2 is visible below the water level and is invisible, due to total internal reflection, above the water level.

Fig. 7 shows one application of the water level indicator, in accordance with the present invention. The indicator 1 5 is mounted in a groove formed in a side wall of a water jug 16, so that the aperture 9 in Fig. 4 extends into the interior of the jug 16, thereby causing water to rise up the indicator 15, as it is poured into the jug 1 6. Water level 1 7 within the indicator 1 5 is clearly visible, because the coloured rear part will be visible in the region 18, below the level 17, and invisible in region 19, above level 17.

The indicator 1 5 may be provided with calibration markings 20, so that the level 1 7 within the indicator 1 5 is indicative of the amount of water within the jug 1 6.

Alternatively, the rear part may be provided with regions of different respective colours, each region along its length representing, for example, maximum and minimum levels to which the jug 16 should be filled The level indicator, in accordance with the invention, utilises no moving parts and thus may be employed In many other applications.

wherein a liquid level is required to be monitored, such as steam irons, etc. Moreover, it may be utilised in applications Incorporating alternative liquids to water, as long as the coloured rear part is still visible therethrough.

Claims (10)

1. A liquid level indicator comprising a substantially upright, hollow member. which communicates with liquid in a container. the liquid assuming. within said member, a level commensurate with the level of liquid In the container itself, said member consisting of a front part and a rear part, at least a substantial portion of the surface of said rear part being opaque and said front part being substantially transparent, said front part being provided with prismatic means for rendering said rear part substantially invisible, when viewed through said front part, above said level and substantially visible below said level.

2. A liquid level indicator as claimed in Claim 1 wherein said prismatic means are arranged so as to provide total internal reflection above said level of liquid.

3. A liquid level indicator as claimed in Claim 1 or 2 wherein said front part comprises a substantially flat member.

4. A liquid level indicator as claimed in any one of Claims 1 to 3 wherein said rear part comprises an open-ended, channelshaped member provided with respective substantially concave and convex surfaces.

5. A liquid level indicator as claimed in Claim 4 wherein said front part is attached to said rear part so that a surface of said front part faces said concave surface of said rear part, so as to form said hollow member.

6. A liquid level indicator as claimed in Claim 4 or 5 wherein said concave surface of said rear part is coloured.

7. A liquid level indicator as claimed in Claims 5 or 6 wherein said prismatic means comprises an elongated prism attached to said surface of said front part facing said concave surface.

8. A liquid level indicator as claimed in any preceding claim and including an aperture provided at a lower end of said rear part for introduction of liquid into said hollow member.

9. A liquid level indicator substantially as herein described with reference to the accompanying drawings.

10. A water jug incorporating, in a side wall thereof, a liquid level indicator as claimed in any preceding claim, so that, when water is introduced into said jug, an amount of said water is caused to rise up said indicator.