GB2415784A - Apparatus for determining if an environment temperature exceeds a threshold - Google Patents

Abstract

The apparatus, e.g for use in a refrigerator or freezer compartment, comprises a vessel 2 containing a medium 1 having a melting point at the threshold temperature, i.e. a critical temperature in respect of food preservation, and a weight 3 which lies on the medium surface when the medium is solid but which sinks when the medium melts. At least a part of the vessel and the medium may be transparent to visible light.

Description

Annaratus and Method for Indicatina the exceeding of a Temperature

Threshold The invention is concerned with indicating whether the temperature of a given environment has exceeded a chosen threshold (critical temperature) and has utility in any situation where products or samples must be maintained below a given temperature for example food storage or storage of clinical samples.

During deep freeze storage of meat for human consumption, the product must typically be maintained at a temperature below -1 8 C. See for example European Community Directives 89/108 and 98/108). If the temperature of the freezer interior exceeds this value during, for example, a power cut, then the safety of the product for consumption can no longer be guaranteed. If the duration of the power cut is sufficiently short, the freezer interior may not exceed this critical threshold but the likelihood of the critical temperature being exceeded is clearly increased if the freezing compartment is opened during the power cut and warmer air is allowed to enter.

An ordinary thermometer may be used to determine the temperature of a environment at.

the time of inspection but, in the case of a freezing compartment, this necessitates opening of the compartment. There exists a need for a means of allowing a freezer compartment to remain closed during a power cut and determining thereafter whether a. ...

critical temperature has been exceeded. The current invention provides this means and,...

generally provides a simple, reliable and robust means of determining whether the; temperature of a given environment has exceeded a chosen temperature. ' ' The design of a system for indicating whether a temperature threshold has been exceeded is not in itself a novel concept but previous solutions have, in relation to the current invention, been complicated and consequently more difficult (and expensive) to implement.

For example, US Patent 4,999,615 describes an apparatus comprising a sealed container in which is located a medium having a melting point at the critical temperature and a first movable part. Outside the container is located a second moving part and each moving part switches between a number of positions by virtue of a variety of different forces they exert on each other as the medium switches between liquid and solid phases.

According to the present invention, apparatus for determining whether the temperature of an environment has exceeded a critical temperature comprises a medium having a melting point substantially at the critical temperature and a weight formed in material of greater density than the medium.

The medium and weight may be conveniently located in a sealed container wherein at least part of the container comprises material that is transparent to visible light. The medium itself may also be transparent to visible light although this may not be necessary if the configuration of the assembly is such that the weight is always immediately adjacent the transparent part of the container.

According to a second aspect of the invention a method of determining whether the temperature of an environment has exceeded a critical temperature comprises the steps of, freezing a medium having a melting point substantially at the critical temperature; ., , : ...e supporting a weight having a density greater than the medium on or in the frozen medium;'' : placing the weight and frozen medium assembly in the environment and.',: subsequently inspecting the weight and medium assembly to determine whether the weight has sunk through the medium.

The medium used in respect of either aspect of the invention could be, for example, a brine or other solution where the concentration is selected to provide the required melting point. A mixture of polypropylene glycol and water is particularly suitable as its freezing point can be controlled by the relative quantities of the two components and it safer to use in food environments than (say) the polyethylene glycol used in conventional antifreeze.

Where the melting point of such a medium is said to be substantially at the critical temperature, this is intended to mean that the melting point is sufficiently close to the critical temperature for operation of the invention. How accurately the melting point of the medium reflects the critical temperature will depend on the accuracy required by a particular application of the invention.

The invention will now be described, by non-limiting example, with reference to the following figures in which: figure 1 illustrates apparatus of the invention in its simplest form and figure 2 illustrates a convenient implementation of the invention Referring to figure 1a, in a simple form, the invention comprises a medium 1 having a melting point that is substantially at the critical temperature located in a convenient vessel 2, and a weight 3 formed in material of greater density than medium 1. At least part of vessel 2 and the medium itself are transparent in order to facilitate visual inspection.

During operation medium 1 is frozen before weight 3 is located on top and the assembly is placed in the environment to be monitored. In the event that the temperature of the *, environment exceeds the critical temperature, medium 1 melts allowing weight 3 to sinl<.

within the medium 1 (figure 1 b) providing a visual indication that the critical temperature has been exceeded even if the temperature of the environment has subsequently fallen...

back below the critical temperature. (The weight may not have sunk all the way to the. . ' bottom of the vessel: the fact that it has moved at all would indicate a temperature rise to around the critical temperature). '' Referring to figure 2, the medium 1 may, for convenience be located in a sealed vessel 2 formed (at least in part) of transparent material. The weight 3 is also located within the vessel and is visible from the exterior of the vessel 2.

During operation, the assembly may be placed in the environment to be monitored so that the medium 1 freezes with weight 3 at the bottom of the assembly adjacent face 4 (figure 2a).

After the medium 1 has frozen, the assembly is inverted (and restored to the environment) so that weight 3 and face 4 are at the top of the assembly (figure 2b).

Should subsequent inspection reveal that weight 3 has fallen through medium 3 then this is taken as an indication that the temperature of the environment has exceeded the critical temperature even if it has subsequently fallen back below it. :'

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Claims (3)

1. Claims 1. Apparatus for determining whether the temperature of an

   environment has exceeded a critical temperature comprising a medium having a melting point substantially at the critical temperature and a weight formed in material of greater density than the medium.
2. 2. Apparatus according to claim 1 wherein the medium and weight are located in a sealed container and at least part of the container comprises material that is transparent to visible light.
3. 3. A method of determining whether the temperature of an environment has exceeded a critical temperature comprising the steps of, freezing a medium having a melting point substantially at the critical temperature; supporting a weight having a density greater than the medium on or in the frozen medium, placing the weight and frozen medium assembly in the environment and en..

   subsequently inspecting the weight and medium assembly to determine whether the weight has sunk through the medium.