GB2215463A

GB2215463A - Magnetic liquid level indicator

Info

Publication number: GB2215463A
Application number: GB8721939A
Authority: GB
Inventors: Roger Sidney Mole; Ath Henry Thomas De; Lesley George Presley
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-09-18
Filing date: 1987-09-18
Publication date: 1989-09-20
Also published as: GB8721939D0

Abstract

An indicator 1 for giving a visual indication of the level of a liquid contained in a non-magnetic tube 2 comprises a float 5 containing a magnetic dipole and a plurality of elongate magnetic indicator elements 4 with distinguishable opposing faces disposed vertically in a display housing 3 affixed to the tube. The elements 4 contain mounting wires 8a, 8b which enter seats or holes provided in the sides of the display housing 3 and are pivotable about their longitudinal axes. A miniature permanent bar magnet 7 is integrally moulded into the body of each element. Under the influence of the float magnet dipole, the elements 4 rapidly rotate to provide the liquid level indication but otherwise they remain disposed in a vertical attitude from which they are not readily disturbed. <IMAGE>

Description

1(ETIC LIQUID lEE INDICATZ 1. Field of the Invention This invention relates to magnetic liquid level indicators for giving a visual indication of the level of liquid contained in tanks, vessels and the like, operating by means of a float containing a permanent magnet dipole, which is able to cause a plurality of magnetic dipole indicator elements disposed one above the other and having faces of two different colours, to rotate such that they indicate the position of the float.

2. Prior Art Magnetic liquid level indicators are known in the art, having magnetic indicator elements which are mounted in a display housing disposed on the face of a vertical, non-magnetic tube in which the float is contained. The indicator elements are rotatable about an axis perpendicular to that of their magnetisation and have two different coloured faces, one of which is visible at any one time through a part of the display housing made of transparent material. The vertical, non-magnetic tube containing the float is connected to the vessel containing the liquid, the level of which is to be indicated.

As the liquid in the vessel flows into or out of the vertical tube, it causes the float to rise or fall past the indicator elements contained in the display housing. As the float contains a permanent magnet dipole it causes the indicator elements, which are also magnetised, to rotate in turn such that those disposed below the liquid level present one colour to the viewer (for example red) and those above, another (for example white).

With such devices, there is the advantage that there is no contact or mechanical connection between the float and the indicator elements or the display housing in which they are mounted. Therefore such devices can be used with dangerous, poisonous, inflammable, explosive or chemically aggressive liquids without fear either that the user will come into contact with them or that there will be a leakage of such liquids to atmosphere, for example as a result of the accidental breakage of a glass tube which might instead be used for the direct visual sighting of the liguid level. Such devices also have the advantage that they may be used to indicate the interface between two immiscible liguids which have identical optical characteristics but different specific gravities.

In the prior art, there has until now been the problem of providing an indicator element which combines stable magnetic characteristics together with the ability to withstand elevated operating temperatures, for exarrple over about 100 degrees Celsius. Conventional indicator elements made, for example, from pressed steeL have the ability to withstand such temperatures but they can only be provided with a weak magnetic field which is unevenly distributed over their face and edge surfaces. This causes them to be relatively unstable to external influences such as shock, vibration and extraneous magnetic fields.It is also known that such indicator elements may suffer such large diminutions in their magnetic field strength at elevated working temperatures increases as to allow the possibility that they will not rotate correctly under the influence of the float magnet.

Previous attempts to overcome such problems by bonding bar magnets to the surfaces of the indicator elements have met with only limited success, proving cumbersome in construction and expensive in manufacture.

Alternative forms of indicator elements have been previously disclosed (see for example EP 0 063 020 Al) but sate of these not only have the disadvantage of being constructed from materials which are relatively un-resistant to elevated working temperatures, thereby necessitating the use of cumbersome and expensive heat insulation materials between the vertical tube containing the float and the display housing at working temperatures over about 100 degrees Celsius, but also have the disadvantage that the magnetic material which they contain rmst be only partially magnetised to a relatively low magnetisation level (for example 25% of maximum possible magnetisation) so as to maintain the correct balance between the magnetic field strengths of the indicator elements and the magnetic dipole contained in the float. It is known that such so-called unsaturated magnets are less magnetically stable than magnets which are magnetically saturated i.e.

magnetised to 100 & of the maximum possible magnetisation level.

There is a further problem which can affect indicators in which the magnetic characteristics of the indicator elements differ from those of the float magnet dipole as a result of the use of different types of magnetic material in the construction of these ccmponents. If there is sufficient difference between the rates at which the magnetic field strengths of the magnetic materials used in the said components diminish as the working temperature increases, this may lead to a failure of the float magnet to bring about the desired rotation in the indicator elements above certain operating temperatures.

In conventional magnetic liquid level indicators and some embodiments of the present invention, the float magnet normally takes the form of a single bar magnet which is magnetised with a centrally located pole and poles of opposite polarity at each end. A central iron ring is provided encompassing the body of the magnet to concentrate the field of the central pole into a desired narrow area and it is intended only for the magnetic field of this central pole to cause the magnetic indicator elements to rotate. The disadvantage of such an arrangement is that it provides only a relatively weak magnetic field to operate the indicator elements and these therefore have also to be provided with only a relatively low magnetic strength in order to maintain the correct balance between the magnetic strengths of the float magnet dipole and the indicator elements.The lower the magnetic strength of the indicator elements, the weaker are the attractive forces between adjacent indicator elements and the more prone the elements become to the effects of shock, vibration and extraneous magnetic fields.

3. Sarrnarr of the Invention We provide a magnetic liquid level indicator comprising a vertical non-magnetic tube connected to the vessel containing the liquid the level of which is to be indicated, a float containing a magnetic dipole which is freely slidable within the vertical tube and an indicator housing containing a plurality of elongate magnetic indicator elements rtcunted on the face of the vertical tube.

In a preferred magnetic liquid level indicator in accordance with the invention, the magnetic materials employed in the float magnet dipole and the magnetic indicator elements are of identical material while in an especially preferred device, such materials are also fully magnetically saturated.

The magnetic dipole contained in the float can take the form of a conventional single bar magnet magnetised with poles of like polarity at each end and a pole of opposite polarity encataessed by a field concentrator ring located centrally between them. Hbwever, such an arrangement provides only a relatively weak magnetic field to act upon the indicator elements and in a preferred indicator in accordance with the invention, a float magnet dipole is constructed fram two identical cylindrical bar magnets which are affixed with like poles facing each other at the central points on either side of a plain, unaragnetised disc of magnetisable material, for example mild steel.

In such an arrangement, however, the magnetic attraction of the cylindrical bar magnets to the disc cannot solely be relied 42on to maintain the attachment of the magnets to the disc and a means of positive attachment must be employed. Within the scope of the present invention, this can be achieved in a variety of ways, and when the bar magnets are fully magnetised, such an arrangement provides a significantly greater magnetic field strength to operate the indicator elements than does a conventional, fully magnetised single bar magnet of the same overall dimensions. This in turn also allows the indicator elements to be provided with a correspondingly greater magnetic field strength.The disc is of a diameter slightly less than the internal diameter of the float such that the magnet dipole system so constructed is fully contained within the walls of the body of the float.

The float which is conveniently in the form of a hollow cylinder with closed ends, can be constructed from a variety of non-magnetic materials, for example from metals such as Stainless Steel, Titanium or Aluminium or from plastics such as PVC or PVDP. The volume and weight of the float are adjusted in order to place the disc at the same level as the surface of the liquid when the float is buoyed thereon.

In a magnetic liquid level indicator in accordance with the invention, the magnetic indicator elements are mounted one above the other in the display housing and are rotatable about their respective longitudinal axes under the action of the float magnet dipole as it rises and falls according to the liguid level in the vertical tube. The longitudinal axes of the indicator elements are perpendicular to their axes of magnetisation and according to a mathod later described, the elements may be constructed from a lightweight material and provided with a significantly stronger and more stable magnetic field capared to conventional magnetic indicator elements of, for example, pressed steel.Adjacent indicator elements which are not under the influence of the magnet system in the float have magnetic poles of opposite polarity adjacent to their respective edges, namely the lowentcst edge of the upper element and the uçeermDst edge of the lower element.

Therefore they experience a strongly attractive magnetic force and remain constrained by the force in a vertical position. It is arranged for elements which are magnetically locked in such a way to each reveal a face of like colour, for example red for those below the level of the liquid and white for those above.

Under the influence of the float magnet dipole, the attractive force between adjacent indicator elements is overcome and the elements provide a positive and rapid rotation as a result of their strong magnetic field and low rotational inertia. In sate devices falling within the scope of the present invention a tendency may arise for the poles at the ends of the bar magnets opposite to those in contact with the disc to rotate the indicator elements in the opposite sense to that which is desired. In such cases it is simple to provide stops to prevent the elements from so rotating.

In a liquid level indicator in accordance with the invention, the elongate magnetic elements are arranged generally in a vertical plane when not acted upon by the float magnet, such vertical disposition arising from the strong attractive forces generated by small bar magnets which are integrally moulded into the body of each element on an axis which is perpendicular to the axis of pivotal support. Such elements can be produced by a nrethod described later in more detail using plastics carrier materials which form the bodies of the elements. This elegant and sire method of manufacture provides indicator elements which are thin-bodied and light in weight.Also, according to the teaching of the invention, by carefully selecting the magnetic materials employed in the bar magnets and the grades of plastics carrier materials employed in the construction of the element bodies, it is possible to produce indicator elements which are capable of operating at working temperatures of 200 degrees Celsius or more. Preferred magnetic materials are those which suffer only relatively small diminutions in their magnetic field strength at increased operating temperatures and which fully recover their original strength on cooling.

The small bar magnets used in the indicator elements are selected such that their magnetic strength is sufficiently great to achieve the aforementioned vertical locking but not so great as to prevent the magnetic strength of the magnet dipole contained in the float fram overcoming the aforementioned attractive forces between adjacent elements in order to achieve the desired rotation. This can be quite easily achieved for a preferred indicator in accordance with the invention once the correct relative sizes of the magnets employed in the float magnet dipole and the indicator elements have been determined due to the fact that in such a device, all of the magnets are always provided with 100% magnetic saturation and their magnetic characteristics are therefore readily reproducible.

4. Brief Dsscription of the Drawings Figure 1 shows a side elevation of a magnetic liquid level indicator in accordance with the invention including a float containing a magnetic dipole. Part of the Figure is cut away.

Figure 2 shows a front elevation of the indicator with part cut away.

Figure 3 shows an enlarged front elevation of one form of a magnetic indicator element in the indicator of Figure 1 with part cut away to show its enclosed miniature permanent bar magnet and mounting pins.

Figure 4 shows a cross section along a line A-A in Figure 3.

Figure 5 shows a cross section along a line B-B in Figure 3.

Figure 6 shows an alternative fran of magnetic indicator element to that shown in Figure 3.

Figure 7 shows a cross section along a line X-X in Figure 6.

Figure 8 shows a cross section along a line Y-Y in Figure 6.

5. DescriPtion of the Preferred Ehbodiments considering the content of the Figures in detail, Figures 1 and 2 show a magnetic liquid level indicator generally indicated as 1, wherein an indicator housing 3 is vertically disposed upon the face of a nonmagnetic tube 2. The tube 2 is connected by tubes 6a and 6b to the vessel containing the liquid the level of which is to be indicated. The e tube 2 contains a float 5 constructed of nonemagnetic material capable of sliding freely up and dbwn within the tube 2 as the liquid level in the tube rises and falls.

The e float 5 contains a permanent magnet dipole as shown in Figure 9, for example two cylindrical bar magnets 15a and 15b with their like poles affixed to a mild steel or magnetic iron disc 16 disposed such that the longitudinal axes of the bar magnets correspond with the longitudinal axis of the float and the disc lies on an axis which is perpendicular thereto at a position in the float corresponding to the level at which the float is buoyed by the liquid.

The indicator housing 3 contains a plurality of magnetic indicator elements 4 which are suspended one above the other on horizontal wire pins 8 which are shown in more detail in Figures 3, 4, 5, 6, 7 and 8. The wire pins are inserted into a plurality of suitably sized seats or holes which are provided one above the other, equally spaced in opposite sides of the indicator housing 3. These serve to support the wire pins 8 and allow them to act as pivots for the indicator elements 4. The surfaces of each indicator element are provided with a different colour (for example one surface red and the other white) as indicated by the shading in Figure 2 and each indicator element is coloured in a like way save for those in the area 10 which are optionally coloured in the opposite sense to the other indicator elements.

As the liquid level in the tube 2 rises or falls, the float 5 moves up and down past the indicator elements 4 and the magnet dipole in the float causes them to rotate through 180 degrees in the conventional way. As shown in Figure 1, at a given position, all indicator elements including element 4c below the liquid level present a face of one colour to the viewer while all those above including element 4a the other colour. Element 4b presents itself edgeewise to the viewer and the result is to provide a clearly observable indication of the liquid level, as shown in Figure 2.

It is possible to extend the indicator elements into a section 10 which is beyond the lowest level to which the float would normally fall when buoyed by the liquid in the tube 2. The elements in this section are only caused to rotate by the float magnet dipole when the float sinks as a result of becaning damaged and as the colouring of the elements is reversed in this section, this therefore gives a ready indication that damage to the float has occurred.

Figures 3, 4 and 5 show one form of indicator element 4 which is generally plate-like but with two perpendicular cylindrical portions ila and llb moulded into its body containing the miniature permanent bar magnet 7 and the wire mounting pins 8a and 8b. The body of the element is provided with a cuts 9 allowing it to only rotate through 180 degrees under the action of the float magnet dipole.

The body of the indicator element 4 is manufactured from a suitable msuldable plastic material and the indicator element including the miniature permanent bar magnet and mounting pins is constructed as a one-piece unit by a special technique of moulding whereby the miniature bar magnet and the mounting pins are provided with suitable tettporary supports within the rnculd of the indicator element while the plastic material from which the element is manufactured is injected and compressed. This technique is referred to as Insert Moulding. The said plastic material is carefully selected to provide the required high level of temperature resistance and materials especially suitable for this purpose have been found to include certain grades of Polycarbonate and Nylon.

The indicator element shown in figures 3, 4 and 5 may require suitable spacing washers to be placed on the mounting pins 8a and 8b on either side of the body of the element to prevent excessive lateral movement and facilitate aligrment of each element's miniature bar magnet. Figures 6, 7 and 8 show a preferred form of indicator element in which such spacing washers may be anitted as a result of the provision of rounded body extensions 12a and 12b.

The float is constructed of a non-magnetic material, for example Stainless Steel, Titanium, Aluminium or a suitable plastic material. A magnetic dipole consisting of a permanent bar magnet with a central pole surrounded by a concentrating ring and with complementary opposite poles on each end is mounted in the float with its magnetic axis corresponding to the longitudinal axis of the float. A preferred indicator in accordance with the invention contains a dipole constructed fmn two identical permanent bar magnets with like poles affixed to the centre points on either side of an untagnetised mild steel or magnetic iron disc. This provides a much stronger magnetic field than the previously described method of construction. An especially preferred device in accordance with the invention includes a float containing bar magnets constructed of the same material as that used in the indicator element bar magnets.

The magnetic field strengths of the float magnet dipole and the indicator element bar magnets have to be carefully balanced to ensure that the attractive forces operating between adjacent indicator elements are overcome by the magnetic field of the float magnet dipole. This is easier for elements manufactured according to the invention than for conventional indicator elements once the relative sizes of the magnets employed in the float magnet dipole and the indicator elements have been determined since by employing magnetically saturated magnets in each, their magnetic field strengths are highly stable and their magnetic characteristics are readily reproducible.

Claims

1. A magnetic liquid level indicator comprising a vertical non-magnetic tube containing the liquid the level of which is to be indicated, a float containing a magnetic dipole which is freely slidable within the vertical tube and an indicator housing mounted on the face of the tube containing a plurality of elongate magnetic indicator elements disposed one above the other and pivotable about their respective longitudinal axes under the influence of the float magnet dipole so as to provide said indication of liquid level, characterised in that a miniature permanent bar magnet is integrally moulded into the body of each indicator element on an axis which is perpendicular to its axis of pivotal support.

2. A magnetic liquid level indicator according to Claim 1 wherein the magnetic materials employed in the float magnet dipole and the elongate indicator elements are of identical material.

3. A magnetic liquid level indicator according to Claim 1, or 2 wherein the magnetic materials employed in the elongate indicator elements are magnetically saturated.

4. A magnetic liquid level indicator according to Claim 1, 2 or 3 wherein the magnetic indicator elements are each formed in one piece by moulding a plastic carrier material around a miniature bar magnet and the indicator element mounting wires, oposite ends of the mounting wires being rotatable within seats or holes in supports located in each side of the indicator housing.

5. A magnetic liquid level indicator according to Claim 4 wherein the magnetic indicator elements are each formed by Insert moulding.

6. A magnetic liquid level indicator according to any one of the preceding claims wherein the float contains a magnetic dipole characterised in that two identical cylidrical bar magnets are affixed with like poles facing each other at central points on either side of a plain, unmagnetised disc of magnetisable material, the float being adapted to float in a vertical sense with the axes of the bar magnets corresponding to the longitudinal axis of the float.