GB2198533A

GB2198533A - Liquid level monitor

Info

Publication number: GB2198533A
Application number: GB08628735A
Authority: GB
Inventors: Roy Williams
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1986-12-02
Filing date: 1986-12-02
Publication date: 1988-06-15
Also published as: GB8628735D0

Abstract

A liquid level monitor includes a probed which has a flexible membrane 8 secured over its lower end. The membrane 8 contains an oil or spirit 12 and the specific gravities of membrane 8 and the oil 12 are such that when the level of a liquid 13 to be monitored rises the membrane 8 floats on the liquid 13 to bring the oil 12 into contact with the probe to cause a switching action. The switching action is either optical, electrical e.g. capacitative or conductive, or electromechanical e.g. a float switch. The monitor is used to sense oil levels in engines and gear boxes. It avoids false readings due to the oil getting dirty and e.g. leaving a film on a probe. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO LIQUID LEVEL MONITORS This invention relates to a liquid level monitor including a probe member for sensing the level of a first liquid in a container.

The monitor is primarily designed to use a probe member which operates on an optical system using fibre optic conductors. However the probe member may equally effectively operate on an electrical or elect;o-mechanical system using electrical switches or switching actions.

The invention is particularly useful for installations where it is necessary to know whether a liquid is above or below a predetermined level. It is often not necessary to know the exact quantity of liquid in a container but only to be able to know merely that there is sufficient liquid there for a job to be performed. A typical example of a monitoring situation of this kind is in an engine or a gearbox where it is essential that a minimum level of oil in the engine or gearbox should be maintained and if the oil falls below a minimum level then action must be taken in order that damage to the'engine or the gearbox does not occur. The invention can also be used in the reverse context in as much as if a liquid rises above a predetermined level then an indication can be given.

One of the problems which arises with this type of monitor is that the liquid being monitored may progressively get more and more dirty and change some of its chemical characteristics. This may mean that whenever the liquid contacts the surface of the probe the liquid is likely to leave a film on the probe which, particularly with an optical type of probe member, may cause the member to give a false reading. It is an object of the present Invention to provide a liquid level monitor in which the probe member of the monitor is isolated from direct contact with the liquid being monitored and is able to give a consistent accurate reading of when a level is reached by the liquid.

According to the present invention a level monitor includes a probe member for sensing the level of a first liquid in a container, a flexible membrane sheathing the probe and isolating it from contact with the first liquid, a second liquid contained within the sheath in a first position out of contact with the probe member, the combined specific gravity of the membrane and the second liquid being less than the specific gravity of the first liquid so that the membrane and the second liquid will float on the first liquid and rise or fall with its level, within the limits of the probe member, to bring the second liquid to a second position in contact with the probe member.

The probe member may be optically operated having a fibre optic connection to it and with a prismatic sensor element.

Alternatively the probe member may be electrically operated either by direct contact or indirectly for example in a capacative manner or an electrically conductive manner.

The second liquid preferably has a refractive index which is substantially different to that of the optical sensor element when such an element is used. If an electrical element is used then the liquid has to be chosen for its dielectric properties or its electrically conductive properties.

The flexible membrane is preferably secured to the monitor by a releasable connector means. This flexible membrane may have a rigid tubular part extending over the end of the monitor and this rigid part may be provided either by a separate support or by thickening part of the membrane.

The flexible membrane may be constructed of sufficient length to enable it to be attached to the monitor when the monitor is in a horizontal, or near horizontal, mounted position so that the membrane can curve into a vertical position.

The second liquid may be a light oil or, if the monitor is operating at low temperatures, a suitable spirit which does not volatilise easily.

In order that the invention may be readily understood one example of a liquid level monitor in accordance with the invention and operating in first a vertical mode and secondly, a horizontal mode will now be described with reference to the accompanying drawings.

In the drawings figure 1 shows in schematic form the active end of a liquid level monitor mounted for vertical operation.

Figure 2 shows the same monitor when operating with a liquid level which has risen to the level of the monitor. Figure 3 shows the same monitor mounted for horizontal use in its normal position and figure 4 shows the monitor with a raised liquid level.

It is assumed in this example that the liquid level monitor is to monitor the level of oil in a gearbox and the monitor is of the optical type where light is sent along fibre optic paths to determine the level of the oil. In figure 1 the probe head is shown generally at 1 and this is mounted as one of a plurality of probe heads in the casing in a gearbox (not shown). The probe head has two fibre optic conductors 2, 3 connected to it and these terminate in a transparent block of plastics material 4 which has its end 5 formed in a prismatic shape. The ends of the fibre optic conductors 2, 3 are led away from the gearbox to a remote positioned control panel where light is fed into the end of conductor 2 and is received back through the end of conductor 3 into a lens.A typical arrangement is shown in our co-pending patent application no. 8505311 (publication no. 2171796).

In figure 1 the arrows indicate the light into conductor 2 and out of conductor 3 in the normal operating position. Dotted path 6 shows the light being reflected internally in the prism 5 and as the light travels down fibre optic conductor 2 impinges on the wall of the prism and is reflected through the 90" to the opposite wall of the prism where it is reflected again through 900 up to conductor 3.

A groove 7 is cut in the block 4 and fitted into this is a flexible membrane indicated generally at 8. This membrane is constructed of a lightweight highly flexible rubber or plastics material which is inert to oil or the particular liquid whose level is being monitored. The membrane 8 comprises two parts. The first is a rigid collar 9 which surrounds the lower end of the block 4 and extends past the bottom of the prismatic section 5. This collar 9 has a lower flexible portion 10 which hangs below the block 4.

The collar 9 and the flexible portion 10 can all be made of the same material but the important point is that the collar 9 is relatively rigid and portion 10 is flexible. The collar 9 in this example is formed with an internally extending rim 11 which fits into the groove 7. The collar and the rim are slightly flexible so that the collar is held in close proximity with the block 4 but is releasable therefrom by virtue of the rim being able to sprung out of the groove 7.

A quantity of a light oil 12, in this example a calibration oil, is inserted in the flexible membrane 8 and, as shown in figure 1, sits at the bottom of the flexible portion 10. This oil 12 is chosen so that it does not react with the material of the flexible membrane 8 nor does it react with the material of the block 4 or have any propensity to adhere to the block 4.

It is important that the specific gravity of the flexible portion 10 and the oil 12 is less than that of the oil 13 (figure 2r whose level is to be monitored which is contained in the gearbox.

This means that as the level of the oil 13 rises and contacts the flexible membrane 8 the membrane together with the oil 12 will effectively float on the surface of the oil 13.

Referring now also to figure 2 this figure shows the position when the level of the oil 13 has risen to the level of the probe of the monitor. As the level rises the flexible portion 10 of membrane 8 floats on the surface and the oil 12 is lifted nearer to the prism 5. When it reaches the prism and in fact touches the area of the prism under the fibre optic conductor 2 there is a change in the refraction which occurs in the prism and the light path 6 is no longer refracted internally by the prism but passes through the prism. This effectively causes an optical switching action and no light now is transferred up the fibre optic conductor 3. This switching is then able to be noted at the remote monitoring station.

Due to the flexible nature of the portion 10 it will deform round the bottom of the block 4 as indicated in figure 2. If the level continues to rise the membrane will merely flatten itself against the sides of the collar 9 and will not be damaged. All the time that the oil 12 is contact with the prism 5 no light will be conducted up the conductor 3. As the oil level falls the flexible portion of the membrane 8 will revert to its position as shown in figure 1 and the oil 12 will settle at the bottom of the flexible portion 10. As soon as the oil 12 comes off the prism 5 the prism will again internally reflect light in conductor 2 up to conductor 3 to give an indication the oil level has fallen.

The continuing rise and fall of the oil 13 will operate the switch without any damage to the switch even if the oil 13 becomes heavily contaminated. There is no risk of this contamination reaching the prism 5 since the flexible membrane 8 will ensure that it is isolated from the prism and the oil 12 will remain clean and not allow any false readings to be given.

It will thus be seen that the liquid level monitor provides an effective switch which is particularly useful in hazardous areas where the electrical currents are likely to cause problems. There is no risk of the switch being affected in its operation by contamination of the liquid which is being monitored and is able to give a safe and reliable indication of the changes in the liquid level as it rises and falls below the present level determined by the position of the probe head 1.

Referring now to figures 3 and 4 this shows essentially the same probe head 1 as shown in figures 1 and 2 mounted horizontally.

From figure 3 it will be seen that the flexible portion 10 in this mounting hangs vertically into the position where the oil 12 is maintained at the bottom of the drooped position assumed by the portion 10. It may be necessary in certain applications to modify the collar 9 so that the collar is not symetrical and the uppermost part of it extends further beyond the end of the prism 5 than the lower part.

The operation of the probe in the horizontal mounting is essentially the same as in the vertical mounting and, as shown in figure 4, when the level of the oil 13 rises the flexible portion 10 is floated up on the level of the liquid causing the oil 12 to surround the end of the prism 5 and to switch the light in conductor 2 so that no indication light is given along conductor 3.

It will be appreciated that the probe can be mounted not only in the vertical and horizontal positions as shown but in any suitable position in between.

Although an oil has been referred to as being contained within the membrane the oil 12 may in suitable applications be replaced for example by some other liquid medium of a suitable refractive index such as a spirit. However account has to be taken of the temperatures at which the probe is expected to operate since too high a temperature may cause the spirit to volatilise and to build up a pressure within the membrane 8. The collar itself may not necessarily be made of the same material as the flexible portion 10 but may be a rigid collar to which the flexible portion 10 is attached. It may also be necessary to have a separate fixing means such as a band (not shown) to replace or supplement the rim 11.

It will be appreciated that although an optical system has been described there are other forms of probe which would equally well operate using the principle of the present invention. For example, if an electrical system is used which relies on the capacitive effect between two electrodes the oil 12 can be chosen to have a suitable dielectric constant which when pushed up between the electrodes alters the capacitance of the probe to perform an electrical switching action. Alternatively the oil may be sufficient electrically conductive as to form an electrical path between two electrical conductors which would replace conductors 2, 3. This would give an normal switching action. If oil was not used a known switching technique is to use mercury to perform a switching action although this could only be used with oil 13 of a very high specific gravity.

Alternatively, the probe may be of a electro-mechanical nature which has an actuating element which is caused to float up by the oil 12 to cause a physical electrical connection between two conductors carrying electrical current.

Claims

CLAIMS:

1. A liquid level monitor including a probe member for sensing tha level of the first liquid in a container, a flexible membrane sheathing the probe and isolating it from contact with the first liquid, a second liquid contained within the sheath in a first position out of contact with the probe member, the combined specific gravities of the membrane and the second liquid being less than the specific gravity of the first liquid so that the membrane and the second liquid will float on the first liquid and rise and fall with its level within the limits of the probe member to bring the second liquid to a second position in contact with the probe member.

2. A liquid level monitor as claimed in claim 1 in which the probe member is an optical probe having an optically operated sensor element.

3. A liquid level monitor as claimed in claim 2 wherein the sensor element is of a prismatic form.

4. A liquid level monitor as claimed in claim 3 wherein the second liquid has a refractive index such as to switch the optical sensor element when in contact therewith.

5. A liquid level monitor as claimed in any preceding claim in which the flexible membrane is secured to the monitor by releasable connector means.

6. A liquid level monitor as claimed inany preceding claim wherein the flexible member has a rigid part extending over the end of the probe member.

7. A liquid level monitor as claimed in claim 5 wherein the releasable connector means is separate from the probe member.

8. A liquid level monitor as claimed in any preceding claim in which the flexible membrane has a rigid support part encompassing the active end of the probe member.

9. A liquid level monitor as claimed in claim 8 wherein the support of a tubular form.

10. A liquid level monitor as claimed in any preceding claim in which the flexible membrane is of a substantial length in order to enable it to be mounted at an angle between the horizontal and vertical positions and to allow the second liquid to be held out of contact with the probe member in its non operating position.

11. A liquid level monitor as claimed in any preceding claim in which the second liquid is an oil or a spirit.

12. A liquid level monitor substantially as hereinbefore described with reference to figures 1 and 2 or figures 3 and 4 of the accompanying drawings.