Temperature indicator for a glass ceramic cooking surface

A temperature indicator for a glass ceramic cooking surface, the temperature indicator having an indicating device, a heat-sensitive switching device including an auxiliary heating system, a temperature sensor and a switch operable by the temperature sensor for activating the indicating device, the switching device, temperature sensor and switch being disposed in a casing that is thermally coupled to said cooking surface, the temperature indicator comprising:

• two electrodes disposed in the casing, the auxiliary heating system being fixed therebetween by spring action, one of the electrodes forming a partition between the auxiliary heating system and the temperature sensor;
• the auxiliary heating system including a positive temperature co-efficient (PTC) resistor having a Curie temperature below the ambient temperature of the casing during continuous operation of the heating system and having a maximum rated operating temperature above the continuous operating ambient temperature;
• the switch for the indicating device being located away from the cooking surface for protection against thermal damage;
• and,
• the temperature sensor being thermally coupled so closely to the heating system of the glass ceramic cooking surface and to the glass ceramic cooking surface itself that the cooling time of the temperature sensor coincides with the cooling time of the glass ceramic cooking surface, notwithstanding variations in the cooling time of the glass ceramic cooking surface as normally occur.