GB2119511A

GB2119511A - Sensor for signalling that a preselected temperature has been exceeded

Info

Publication number: GB2119511A
Application number: GB08212284A
Authority: GB
Inventors: Luigi Bolla
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-04-28
Filing date: 1982-04-28
Publication date: 1983-11-16

Abstract

A temperature sensor to detect if a certain limiting temperature has been exceeded, such as limiting temperature in the storage of deep frozen foodstuffs, comprises a casing (11) having transparent walls and containing a rupturable closed vessel (12) filled with a liquid (13) which is expanded upon solidification and so breaks the vessel. If subsequently the limiting temperature is exceeded the solidified liquid (13) becomes fluid again and warns the user that the preselected limiting temperature has been exceeded. <IMAGE>

Description

SPECIFICATION Sensor for signalling that a preselected temperature has been exceeded An object of the present invention is to provide a sensing device for signalling that a well determined temperature has been exceeded, said device being simple and convenient in use. More particularly, it is known that in the field of deep frozen foodstuffs it is necessary to arrive at the use of the products through an uninterrupted refrigeration chain in which, by way of suggestion temperatures are adopted of at least 250C during shipping, -350C during extended storage and -200C in the retailers' premises. From deep freezing to consumption, the product must be stored at a temperature which must never exceed a preselected limiting value, for example -1 80C.

A disruption of the refrigeration chain at any instant of time prior to using the product irremediably jeopardizes the organoleptic integrity and the hygienic conditions of the product, so that the latter is to be discarded.

The principal object of the present invention is to provide a means which is substantially simple and which gives a response capable of being immediately understood for signalling the possibility that a deep frozen foodstuff may have undergone a disruption of the refrigeration chain.

In order that the object mentioned above may be achieved, the present invention provides a sensor, more particularly one which is adapted to be packaged with a product for which it is desired to signal that a preselected temperature has been exceeded, said sensor being characterized in that it comprises a transparent wrapper in the interior of which a rupturable container is held, which is filled with a liquid the volume of which is expanded upon solidification, and the solidification temperature of which substantially corresponds to said preselected temperature.

In order that the features and the advantages of the invention may be better understood, an exemplary embodiment thereof will now be described without limitation, reference being had to the FIGURES of the accompanying drawings.

FIGURE 1 diagrammatically shows in lengthwise cross-sectional view a sensor according to the invention.

FIGURE 2 is a cross-sectional view taken along the line ll-Il of FIGURE 1, and FIGURES 3 and 4 are views of the device of FIG. 2 in a few stages of its use, and FIGURE 5 diagrammatically shows a crosssectional view of the device according to the invention.

According to the embodiment shown in FIGURES 1 and 2, a device according to the invention, which is particularly adapted to be packaged together with a deep frozen product, comprises a casing 11 having a substantially boxlike shape, made of an undeformable and transparent plastics material. Within said casing a cylindrical seat 1 6 is defined, in which there is, stably positioned, an ampoule 12, also cylindrical, made of thin glass.

The ampoule 12 is filled with a liquid 13, for example a mixture of water and a glycol, the volume of which is expanded upon solidification, and the temperature of solidification of which, to be preselected with great accuracy, corresponds to the preselected limiting temperature, for example -1 80C, above which the disruption of the refrigeration chain for the product concerned is defined.

The device shown in FIGURES 1 and 2 is packaged, upon deep freezing, together with the deep frozen foodstuff for which it is desired to make conspicuous any disruption of the refrigeration chain. At the temperature of deepfreezing, generally comprised between -300C and --400C, the liquid 13 contained in the ampoule 12 solidifies and, due to its increase in volume, causes the thin ampoule to break.

As shown in FIGURE 3, under these conditions, the frozen liquid has taken the cylindrical shape of the ampoule in which it was initially contained and remains stably positioned in the seat 16.

If the foodstuff to which the device according to the invention has been applied comes to the user after having been subjected to a correct refrigeration chain, that is it has constantly been held at a temperature below-180C, the device is in the conditions of FIGURE 3, that is, the initially liquid mixture retains its solid cylindrical shape.

If, conversely, in any instant of time prior to use there has been a disruption of the refrigeration chain, that is the deep frozen product has undergone a temperature rise above -1 80C, the mixture 13 has been brought back to its liquid state, as shown in FIGURE 4. Even if, after that instant, the temperature of the deep frozen product has been restored below the limiting temperature, the liquid 13, even though it is frozen again, cannot resume, obviously, its position and its cylindrical shape shown in FIGURE 3 any more.

Any user is thus warned that the refrigeration chain for the foodstuff concerned has been interrupted.

According to the present invention, the same functionality of the device shown in the previous example can be obtained by adopting, as shown in FIGURE 5, an ampoule 14 in which a thin diaphragm 1 5 is formed, which is rupturable and defines a couple of chambers, in either of which the liquid 13 having a low melting point is contained.

Inasmuch as the rupturable diaphragm 15 is substantially thinner than the sidewalls of the ampoule 14, the solidification of the liquid 1 3 breaks the diaphragm.

The operation and the readout of the response given by the sensor of FIGURE 5 are substantially akin to those which have already been described for the sensor of FIGURES from 1 to 4.

The sensor according to the invention permits to achieve the object aforementioned, that is to give a response capable of being understood at a glance and by a means which is essentially simple and easy to use.

This device, which is especially useful for being adopted in the field of deep frozen products, is anyhow capable of being employed for the most differentiated applications in which it is required to detect that a certain critical temperature has been exceeded.

For example, it appears of interest and with a wide field of application the use of a sensor according to the invention in a freezer such as that of a conventional household refrigerator, in which deep frozen foodstuffs are to be stored prior to be consumed.

Placing a single sensor in the freezer is enough to establish if the temperature has risen above a preselected critical value, in correspondence of which it can be affirmed that a disruption of the refrigeration chain has taken place within the freezer concerned.

By knowing from time to time the critical temperature it is sufficient to select the low melting liquid in such a way that its melting point is calibrated in correspondence with the critical value of the temperature which is desired to be detected as soon as it is exceeded.

It is appropriate to note that, in the practical application of the invention, it is provided not to fill the container completely with liquid, but to maintain therein a certain volume of air, in order to provide an air blanket which may allow a uniform crystallization from the container walls to the core and permits to control the volume increase in the liquid-solid transition until said transition is completed; this has the purpose of preventing the rupturable container from breaking before the complete solidification of the liquid. The volume of the air maintained in the interior of the liquid-filled container must therefore be carefully measured by carrying out preliminary tests.

A number of changes may be introduced in the device as substantially described above, without departing from the scope of the invention. For example, a plastics material sheath can be provided to surround the ampoule and the shape itself of the container and the outer wrapper can be varied as desired relative to what has been shown in the examples.

Claims

1. A sensor adapted to signal that a certain critical temperature has been exceeded, characterized in that it comprises a transparent casing (11) within which a rupturable container (12) is held which is filled with a liquid (13) the volume of which is expanded upon solidification, and the solidification temperature of which substantially corresponds to said preselected critical temperature.

2. A sensor according to Claim 1, characterized in that said container from said liquid is defined by the wails of said casing and by a rupturable diaphragm (15) positioned internally of said casing.

3. A sensor substantially as hereinbefore described and illustrated in the accompanying drawings.