Temperature sensor and indicator

A temperature sensor comprising:

• a heat-sensitive element contained within a first chamber, the heat-sensitive element having a melting temperature corresponding to a predetermined temperature;
• a selectively permeable membrane defining a first edge portion of the first chamber and being in sealing engagement therewith, the selectively permeable membrane being impermeable to the heat-sensitive element to contain the heat-sensitive element within the first chamber when the heat-sensitive element is in a solid state and permeable to the heat-sensitive element when the heat-sensitive element is in a liquid state to allow the heat-sensitive element to exit the first chamber;
• and
• a biased member biased toward the first chamber to apply pressure on the heat-sensitive element, the biased member being initially prevented from entering the first chamber when the heat-sensitive element is in the solid state and movable toward the first chamber when the heat-sensitive element flows through the selectively permeable membrane.

A method of sensing an increase in temperature above a predetermined temperature threshold, the method comprising the steps of:

• providing a heat-sensitive element within a chamber, the heat-sensitive element being selected to have a melting temperature corresponding to the predetermined temperature threshold;
• biasing a biased member towards the chamber to apply pressure on the heat-sensitive element;
• allowing the temperature to rise above the predetermined temperature threshold to melt the heat-sensitive element;
• and
• allowing the heat-sensitive element to enter a selectively permeable material, the selectively permeable material being selected to be impermeable to the heat-sensitive element to contain the heat-sensitive element within the chamber when the heat-sensitive element is in the solid state and permeable to the heat-sensitive element when the heat-sensitive element is in the liquid state to allow the heat-sensitive element to exit the chamber so that the biased member can move toward the chamber to displace the heat-sensitive element.

A method of sensing an increase in temperature above a predetermined threshold, the method comprising the steps of:

• retaining a solid heat-sensitive element in an initial position within a chamber with a selectively permeable membrane, the selectively permeable membrane being impermeable to the heat-sensitive element when the heat-sensitive element is in a solid state but permeable to the heat-sensitive element when the heat-sensitive element is in a liquid state, and the heat-sensitive element being selected to have a melting temperature corresponding to the predetermined temperature threshold;
• biasing a biased member to apply pressure to the heat-sensitive element;
• allowing the temperature to rise above the predetermined threshold to melt the heat-sensitive element;
• allowing the heat-sensitive element to flow through the selectively permeable membrane and out of the chamber;
• and
• allowing the biased member to move towards the chamber as a result of the applied biasing force.