Device for indicating level of liquid contents on a container

Claim 1

A device (1) for providing a visual indication of the level of a liquid contained in a container haying walls (11) with good heat conducting properties, the device comprising temperature-sensing strip means (2-10) for making good thermal contact with the external surface of the container walls and including at least one thermochromatic liquid crystal composition for exhibiting colour play over a broad temperature range, characterised in that the temperature-sensing strip means comprises a number of temperature-sensing strips (3-7) which exhibit colour play over a plurality of narrow, spaced apart temperature ranges selected so that on placing the strips in thermal contact with walls of a container containing liquid so that the strips bridge across the level of the free surface of the contained liquid, at least one of the strips (3-7) will exhibit colour play, to provide a visual indication of the level of the contained liquid, when detecting a temperature gradient established on the external surface of the walls (11) of the container adjacent said level of the contained liquid as a result, at least in part, of vaporisation of the liquid occasioned by withdrawing some of the contents from the container.

Claim 2

A device (1) for providing a visual indication of the level of a liquid contained in a container haying walls (11) with good heat conducting properties, the device comprising temperature-sensing strip means (2-10) for making good thermal contact with the external surface of the container walls and including at least one thermochromatic liquid crystal composition for exhibiting colour play over a broad temperature range, characterised in that the temperature-sensing strip means comprises a number of temperature-sensing strips (3-7) which exhibit colour play over a plurality of narrow, spaced apart temperature ranges selected so that on placing the strips in thermal contact with walls of a container containing liquid so that the strips bridge across the level of the free surface of the contained liquid, at least one of the strips (3-7) will exhibit colour play, to provide a visual indication of the level of the contained liquid, when detecting a temperature gradient established on the external surface of the walls (11) of the container adjacent said level of the contained liquid as a result, at least in part, of vaporisation of the liquid occasioned by withdrawing some of the contents from the container.

Claim 6

A device according to any of claims 2 to 4, characterised in that at least some of the temperature-sensing strips exhibit colour play over more thah one temperature range.

Claim 7

A device according to any of the preceding claims, characterised in that the thermochromic liquid crystal composition of each temperature-sensing strip is applied to a substrate in one or more layers as a liquid crystal ink or inks.

Claim 9

A device according to any of the preceding claims, characterised by magnetic means for enabling the device to be removably fixed to a container wall made of magnetic material.

Claim 12

A device according to any of the preceding claims, characterised in that the said maximum expected naturally occurring variation in temperature is less than 3.5°C.

Claim 13

A device according to any of the preceding claims, characterised in that the difference between the maximum and minimum temperature of each colour play temperature range is from 0.25 - 2.5°C.

Claim 14

A device according to any of the preceding claims, characterised in that the temperature difference between the median temperature of any two adjacent temperature ranges is from 0.5 - 4.0°C.