Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Reexamination Certificate
2003-04-16
2004-06-22
Verbitsky, Gail (Department: 2859)
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
C374S141000, C374S163000, C374S208000, C219S497000, C219S452130
Reexamination Certificate
active
06752531
ABSTRACT:
The present invention relates to a temperature sensor for use in a cooking appliance of the kind in which an electric heater incorporating at least one heating element is located behind a glass-ceramic sheet.
A temperature sensor is required in such heaters, which sensor is set to respond when the glass-ceramic reaches a predetermined temperature to de-energise the heater and prevent damage to the glass-ceramic which would otherwise occur if such predetermined temperature was to be exceeded for an extended period of time.
The most commonly used form of temperature sensor, generally referred to as a temperature limiter, comprises a rod assembled inside a tube, the rod having a significantly different coefficient of thermal expansion from the tube. The rod and tube are secured together at one end thereof and connected to a switch assembly at the other end. The device is arranged on the heater such that the rod and tube assembly is located between the heating element or elements in the heater and the glass-ceramic sheet. When the heater is operated, differential expansion occurs between the rod and tube and the device is tuned such that at a predetermined temperature the switch assembly is operated to de-energise the heater.
It is known to alter the sensitivity of the device to thermal radiation by forming the tube of a radiation reflecting or absorbing material, or by providing a reflecting coating on the surface of the tube. The arrangements of the prior art result in substantially uniform directional sensitivity to thermal radiation around the circumference of the tube.
Instead of the rod-in-tube differential expansion type of temperature limiter, temperature sensors have also been proposed in which a device having an electrical parameter which changes as a function of temperature is provided in the heater or in contact with the glass-ceramic sheet. The parameter is monitored such that, when a value thereof is obtained corresponding to a predetermined temperature of the glass-ceramic, the heater is arranged to be de-energised.
Such a temperature sensor when connected to suitable electronic control circuitry is capable of providing adaptive control of a heater with which the sensor is used and is advantageous over the rod-in-tube differential expansion type of device which is set to switch at a predetermined temperature selected under worst case abuse conditions of the heater.
The temperature sensor may comprise a device, for example, the electrical resistance of which changes with temperature, such as a platinum resistance temperature detector or a thermistor. Alternatively, the sensor may comprise a thermoelectric device, such as a thermocouple, providing a voltage output as a function of temperature.
It is therefore an object of the present invention to provide a temperature sensor of the type comprising a device having an electrical parameter which changes as a function of temperature and which exhibits preferential directional sensitivity to thermal radiation.
According to the present invention there is provided a temperature sensor for use in a cooking appliance of the kind in which an electric heater incorporating at least one heating element is located behind a cooking plate, the temperature sensor being for location between the at least one heating element and the cooking plate, the sensor comprising a sensing element having an electrical parameter which changes as a function of temperature and a housing for the sensing element, the housing having a first surface region thereof with high thermal radiation absorption relative to a second surface region thereof, the sensor being for location with the first surface region of the housing facing substantially towards the cooking plate and the second surface region facing substantially towards the at least one heating element.
The cooking plate may comprise a glass-ceramic sheet.
The housing may comprise a single component or a plurality of components and may be of generally tubular form, such as of substantially circular, rectangular or elliptical cross-section.
In one embodiment, the housing is provided with at least one surface layer to form the first and second surface regions.
When a first or second surface layer is provided to form the first or the second surface region, material comprising the housing may be selected and/or adapted to form a corresponding second or first surface region.
The first surface region of the housing may comprise, or be coated with, a material which has a higher thermal radiation emissivity, or a lower thermal radiation reflectivity, than a material which comprises, or with which is coated, the second surface region of the housing.
The housing may comprise a heat-resistant metal or alloy, such as a stainless steel, a first part of whose surface forms the first surface region, a second part of whose surface having thereon a coating of a material having higher thermal radiation reflectivity than the first surface region and constituting the second surface region. The material having the higher thermal radiation reflectivity may be selected from silver, gold and reflecting oxide material such as aluminium oxide.
Alternatively, the housing may comprise a heat-resistant metal or alloy, such as a stainless steel, a first part of whose surface forms the second surface region, a second part of whose surface having thereon a coating of a material having higher emissivity than the second surface region and constituting the first surface region. The material having the higher emissivity may comprise a heat-resistant black paint.
As a further alternative, the housing may comprise a ceramic material, a first part of whose surface forms the first or second surface region, a second part of whose surface having thereon a coating of a material having higher or lower reflectivity or emissivity than the ceramic material and constituting the corresponding second or first surface region.
The housing may comprise two parts, each such as of semi-cylindrical form, joined together and having different thermal radiation absorption properties, such that one part has higher or lower thermal radiation emissivity or reflectivity than the other, the two parts providing the first and second surface regions.
The sensing element in the housing may comprise a resistance temperature detector, such as a platinum resistance temperature detector, the electrical resistance of which changes as a function of temperature.
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Ceramaspeed Limited
Dorman Ira S.
Verbitsky Gail
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