Abstract: A CVD processing reactor employs a pyrometer to control temperature ramping. The pyrometer is calibrated between wafer processing by using a thermocouple that senses temperature during a steady state portion of a processing operation.

Abstract: A system for controlling process temperatures for semi-conductor wafers comprises a heater to heat the wafer, an element to generate a plurality of ultrasonic vibrations in the wafer, a Sagnac interferometer adapted to sense the ultrasonic vibrations and generate a wafer temperature signal responsive thereto, a system to calculate the wafer temperature on the basis of the generated wafer temperature signal, and a control element the wafer heater on the basis of the calculated wafer temperature.

Abstract: An automatic, dynamic window anti freezing system for the windshield and the rear window of a motor vehicles parked in cold weather, connected to a battery, comprises a temperature range control-switch unit, an optic frost-monitor, and a sweeping time (frequency)- control to drive a wiper system to work for preventing frost accumulating on the window glass. The temperature unit sets up a certain working range to turn on the system, covering the real freezing stage of the windows. The sweeping time control sets up predetermined sweeping timely manner for the wipers to sweep. The monitor emits light signals to monitor the frost accumulating on the window glass, and actuates the sweeping control to drive wipers to sweep it off when detecting it. The energy consumption is generally exceptional low due to that working is effectively controlled and easily done. Thus a related window is substantially able to avoid freezing on.

Abstract: Apparatus and methods of thermally processing a substrate inside a processing chamber including a radiation source for heating the substrate are described. In one aspect, a detection system is configured to receive radiation from the substrate and to produce first and second detection system signals respectively representative of different first and second spectral portions of the received radiation. A processor is coupled to the detection system and configured to compute a measure of substrate temperature based upon the second detection system signal and to compute an indication of the relative accuracy of the computed measure of substrate temperature based upon the first detection system signal.

Abstract: A method of exhausting vapors emanating from a surface. The method includes enclosing the surface and dividing the enclosed area into a stagnant region adjacent the surface and an interior region in communication with the stagnant region. The method also includes applying a suction to the interior region and admitting air into the interior region.

Abstract: An apparatus for processing a semiconductor substrate mounted in a thermal processing chamber includes a heating system for heating the substrate, which includes lamps facing a front side of the substrate and a power supply system providing power to at least one of the lamps with a DC power component and an AC power component at a selected frequency. The AC power component is a selected fraction of the DC power component. The apparatus also has a sensor facing a back side of the substrate for providing a detected signal indicative of measured radiation from the back side of the substrate. A lock-in system provides a lock-in signal indicative of a magnitude of an AC component of the detected signal at the selected frequency in response to the detected signal and a reference signal at the selected frequency.

Abstract: A process and cooking area for in-service measurement of temperature in at least one cooking zone of the cooking area with a glass ceramic plate is based on an empirically derived correlation between transmission of light through the glass ceramic plate in a wavelength range of a temperature that is typical of the respective glass ceramic material. The process includes irradiation of the glass ceramic plate in the cooking zone from the inside toward the outside with light in the wavelength range of 700-1500 nm, with the light being reflected at the outer surface of the glass ceramic plate and passing through the glass ceramic plate a second time. Detection of reflected light with a photocell, generates a photocurrent that corresponds to the transmission of the glass ceramic plate in the cooking zone. The temperature of the cooking zone is derived from the derived correlation between the transmission of light of the specified wavelength and the temperature of the glass ceramic plate.

Abstract: A monitoring and control system for monitoring the boil states of the contents of a cooking utensil located on a cooking surface of a cooktop, indicating the state to a user, and controlling the energy applied to the cooking surface, which may be a glass ceramic. The system includes at least one controllable heat source located below the lower surface of the cooktop so as to heat the cooktop and cooking utensil, at least one sensor located in proximity to the cooktop, which senses the temperature of at least one of the cooktop and the cooking utensil, at least one power indicative signal, and a signal processing device receiving a temperature signal from the sensor, and the power indicative signal. The signal issued by the sensor is representative of the temperature of either the cooktop, or the cooking utensil.

Abstract: An exhaust particle and particulate containment system for a coffee roaster comprises a filter chamber for exhaust coffee roasting by-products including chaff and smoke particulates and oils is comprised of a screen for separating chaff from the exhaust coffee roasting by-product effluent and a filter for containing chaff and removing smoke particulates and oils when the screen is in a closed position.

Abstract: A vehicle (10) includes a windshield presenting an inner surface (14) including a test section (16) therein. A cooling device (24) is attached to the inner surface (14) for cooling the section (16) to a temperature a few degrees below the temperature of the inner surface (14) adjacent the test section (16). A sensor (26) is disposed adjacent the inner surface (14) for sensing condensation on the test section (16) and for providing a heating signal to a defogging control (28) in response to condensation on the test section (16) for initiating the heating of the surface surrounding the test section (16) by the vehicle heater (18) to prevent condensation from forming on the surface surrounding the test section (16).

Abstract: An electric toaster comprises an infrared detector (6) directed toward a heating device for the toaster, and a control device for the supply of electricity to the heating elements which is subordinated to a device (10) for measuring the radiation received by the detector, and which comprises a device (12) for processing the signal emitted by the detector. A comparator (13) compares a signal (S) leaving the processing device (12) with a signal (N) emitted by an adjustment device (14) of the degree of toasting. The measuring device (10) comprises, between the processing device (12) and the comparator device (13), a device (16) for diverting the signal (S) whose control is directed by a timer (18) of short duration which re-establishes at the end of that short duration the passage of the signal (S) toward the comparator (13).

Abstract: An apparatus for heating, according to a predetermined heating profile, a surface carrying a film. The invention includes a source of radiant energy. The source of radiant energy has several peak wavelengths, with each peak wavelength having a unique absorption profile related to the thickness of the film. The source of radiant energy is positioned to direct radiant energy toward the surface. Means are included for holding the source of radiant energy in a manner such that the combination of peak wavelengths produce the desired predetermined heating profile.

Abstract: Safety device composed of a radiation emitter, a radiation receiver disposed for receiving radiation which is produced by the emitter and which traverses a radiation path between the emitter and the detector, the detector producing an output signal representative of the quantity of radiation received by the detector, and an electronic circuit coupled to the detector for analyzing the output signal produced by the detector and identifying a reduction in the magnitude of the output signal as a result of an obstruction in the radiation path, wherein the emitter and the detector are mounted on a cooking appliance in a manner which allows extraneous radiation in the vicinity of the cooking appliance to traverse the radiation path.

Abstract: Lengths of coiled tubing have sensor carrier elements mounted therebetween such that a plurality of sensor carrier elements are positioned along a length of coiled tubing. Each sensor carrier element carriers a sensor implemented with one or more intrinsic fiber optic sensor elements positioned therein for measuring one or more parameters in an environment. The intrinsic fiber optic sensor elements are multiplexed on one or more optical fibers along the length of the coiled tubing thereby forming a length of coiled tubing having a plurality of spaced apart sensors. The optical fiber or fibers positioned along the length of the coiled tubing are positioned in a fiber carrier which protects the fiber or fibers from the harsh environment. The fiber carrier may be interconnected to each of the sensors to isolate the fibers from the harsh environment.

Abstract: A method and apparatus for measuring radiation doses based upon thermoluminescence which occurs when a thermoluminescence element is heated by a heat source after having been exposed to radiation. A heat energy sensor is provided for the heat source for detecting the heat energy output from the heat source toward the element. Based on the detected heat energy, the temperature of the element is calculated. The calculated temperature is used to determined if remedial action is necessary. For instance, the calculated temperature may be compared with a predetermined optimum heating temperature. If the calculated temperature deviates from the predetermined optimum heating temperature, responsive action is taken. An increase rate of the calculated temperature may also be calculated. The calculated increase rate would be compared with a predetermined heating rate.

Abstract: An apparatus and method for controlling the temperature profile of the surface of a medium such as a solid or a liquid. The surface is imaged onto an array of detectors which generate an electronic output indicative of the temperature profile of the surface. A heating beam provided by a laser is scanned across the surface, providing radiation which heats the surface locally in a pattern based upon the detected temperature profile and the desired temperature profile.

Abstract: A container sensing system for controlling the heating in a microwave oven of a container carrying control information which may be read by an optical reading device. The optical reading device includes a light transmitter and a light receiver for sensing a reflectance of a sensor. The sensor includes a first and second region. The first region is provided for establishing a start and non-start condition while the second region is provided for reading temperature information. To avoid the surface reflected portion of incident light to gain an accurate reading, the axes of transmission and reception are offset in the same angular direction to a perpendicular of a sensor surface wherein the transmitter directs an inclined reading light beam onto a region of the sensor and the receiver receives the scattered light therefrom depending on the reflection properties of the sensor region.

Abstract: A method for controlling a heating procedure in an oven by using an optically readable information carrier with or on the heating object. The oven may be provided with an optical reading device for touchless reading of the information carrier before and/or during the heating. By providing the information carrier with one or more fields that exhibit color shift at temperatures at will, a feed-back control of the procedure is made possible with simple technical solutions. The special feature of the method is the use of an additional information field for control of the start of the oven.

Abstract: A method and apparatus for characterizing and controlling the heat treatment of a metal alloy employing non-contact sensors selectively positioned to minimize the effects of background temperature contributions. The sensors monitor the temperature of the part being treated at a location that is remote from the surface that is being irradiated directly. In preferred embodiments, the surface where the temperature measurements are taken are located within a black body source. The collected temperature information is used to control the heat treatment of the metal alloy.

Abstract: A method and apparatus for efficiently heating for instance a semiconductor wafer or reticle substrate in either vacuum or air, by exposing the wafer or reticle to radiation whose spectrum is such that it includes only wavelengths which have been determined to be efficiently absorbed by the material of the wafer or reticle. This advantageously allows more rapid and uniform heating than is allowed by prior art broadband radiation, convection heating, or conduction. The wavelength and bandwidth of the radiation are selected to be those wavelengths efficiently absorbed by the wafer or reticle, depending on its particular material and thickness. Typical applications are to a wafer or reticle located in a vacuum where convection or conduction heating are inconvenient or absent.

Abstract: Apparatus for detecting a characteristic of a product undergoing heating senses a parameter of reflected light from the product and determines a point at which the sensed parameter reaches a certain level to detect the characteristic.

Abstract: The apparatus and method measures the shrinkage of rocket motor propellant hat is caused during curing and may control this shrinkage by thermally expanding it to prevent creation of voids and cracks. The apparatus heats the propellant compound during curing. A laser emits radiation onto the compound and a detector receives reflected radiation from the compound and provides signals representative of the size of the volume of the compound. An interconnected indicator provides readouts representative of the size. A temperature controller coupled to a processor and a heater controls the heating of the compound to regulate its thermal expansion and consequent volume. The method calls for heating the compound during curing and radiating it with a laser. Reflected radiation is detected to provide signals representative of the volume. Readouts of the signals represent the relative size of the compound.

Abstract: The present invention is generally directed to a system and process for accurately determining the temperature of an object, such as a semiconductive wafer, by sampling from the object radiation being emitted at a particular wavelength. In particular, a reflective device is placed adjacent to the radiating object. The reflective device includes areas of high reflectivity and areas of low reflectivity. The radiation being emitted by the object is sampled within both locations generating two different sets of radiation measurements. The measurements are then analyzed and a correction factor is computed based on the optical characteristics of the reflective device and the optical characteristics of the wafer. The correction factor is then used to more accurately determine the temperature of the wafer. Through this method, the emissivity of the wafer has only a minor influence on the calculated temperature.

Abstract: The invention calls for a discrete material (1) such as a gas, a liquid or a living being, to be exposed to electromagnetic radiation from a large-area irradiator (2) causing the molecules to resonate at their natural frequency and hence to become warmer. In order to lower the temperature of the material (1), the radiant energy emitted by its is extracted via a receive antenna (5), resulting in a loss in energy and hence cooling of the material. Working in an enclosed fluid-filled space, the fluid can also be included, by suitable choice of radiation spectrum, in the resonance interaction producing the warming or cooling effect.

Abstract: A power control device for a pressing iron includes a position sensor that has a casing, an optical coupler and a shielding plate. The optical coupler is mounted in a lower part of the casing, and has a photoemitter and a photoreceiver that faces the photoemitter and that forms a clearance therewith. The shielding plate is received in the casing, and has an upper plate portion pivoted to an upper part of the casing, and a lower plate portion that extends into the clearance of the optical coupler. The lower plate portion is formed with a notch to permit light transmission between the photoemitter and the photoreceiver when the pressing iron is in an ironing position. The shielding plate pivots by virtue of gravity such that the notch is moved out of alignment with the photoemitter and the photoreceiver, and such that the lower plate portion blocks the light transmission between the photoemitter and the photoreceiver when the pressing iron is in a resting position.

Abstract: A method for Rapid Thermal Processing (RTP) is presented, wherein the broadband reflectivity of an object is measured, and the results of the measurement used by the RTP system to adjust the RTP system parameters used in processing the object.

Abstract: A nondestructive product level calibration method which is based on reflectance of intensity of UV and visible light that is measured from the top surface of a semiconductor wafer in a RTP closed loop process control environment in which the temperature of the wafer is regulated as a function of reflectivity of radiation at a preselected wavelength from the top surface of the wafer. In the method, sheet resistance of the wafer is measured as a function of the intensity of the UV and IR light directed at the wafer over a predetermined temperature and time range. Then, the reflectance intensity off wafer is measured to develop a model of the top surface. The reflectance model will indicate a wavelength where the reflectance is the greatest. Next, the wafer is subjected to UV radiation at the most sensitive wavelength and the reflectance is plotted against intensity of heat treatment.

Abstract: Electrothermal conversion elements, apparatus and methods for use in comparing, calibrating and measuring electrical signals utilizing a thin film heater on a thin, low mass, low thermal conductivity substrate and low mass thermoresistive or PN junction thermal radiation sensors. The element emits IR radiation in response to electrical input. The radiation is collected and converted to an electrical signal proportional to the RMS value of the input signal. Isothermal operation enhances both IR and electrical operation.

Abstract: In a light beam heating apparatus generating a light beam for heating a work, optical energy of the light beam is deteriorated as the lamp is used. The optical energy is controlled by detecting an optical intensity of the light emitted by the lamp. If the optical intensity is decided not to be increased to a desired value due to an increase in arc light source or the like, an exchange of the lamp is cautioned. Thus, a timing of the exchange of the lamp can be decided before the temperature of a work becomes lower than the desired value.

Abstract: An infrared sensor is particularly well suited for the detection of heat sources, specifically from fires. It comprises an infrared detector receiving infrared radiation from a focused refractive optical unit. An optical chopper and electronic amplifier enable the sensor to operate without drift and with immunity to temperature changes in the sensor itself. The infrared radiation from the optical unit is appropriately filtered so as to optimize reception in a frequency band between 2.6 and 2.8 microns. In this band, there exists negligible energy from the sun due to absorption by gas molecules in the earth's atmosphere. Consequently, the sensor can be used in full sunlight without becoming saturated by the large magnitude infrared radiation of the sun. The sensor contains circuitry providing an audible output signal whose pitch is proportional to the intensity of the infrared radiation received from nearby heat sources. The device does not require any visual attention from a firefighter.

Abstract: A power control device is to be used with a pressing iron which includes a soleplate, a housing mounted on the soleplate and provided with a handle, a heating device disposed in the housing and operable so as to heat the soleplate, and a power supplying unit for supplying electric power to the heating device. The power control device includes a switch circuit adapted to connect electrically the heating device and the power supplying unit, an optical sensor unit adapted to be mounted on the handle of the housing, the optical sensor unit generating a first control signal when the handle is released and a second control signal when the handle is gripped, and a timer circuit connected electrically to the switch circuit and the optical sensor unit.

Abstract: The control arrangement for cooking devices with an embedded control for regulating cooking process whose various parameters can be set by actuating elements at the cooking device is characterized by an external programming unit comprising a hand programming device for setting and storing, independently from the embedded control of the respective cooking devices, different cooking programs, diagnostic programs and user functions which can be called, checked and changed optionally and for transmitting such programs to every embedded control of every optional cooking device.

Abstract: In a toaster, a system is constructed to vary the duration of the toasting cycle. An RC network provides an oscillating signal to a counter, which upon the required number of oscillations being counted, triggers a transistor switch. The switch energizes the main solenoid switch which in turn deactivates the heating elements of the toaster. The RC network of the system comprises a variable resistor which may be manually operated, a heat sensitive resistor, and a light sensitive resistor.

Abstract: A safety apparatus for shutting off a unit having a manually operated power interruption switch or fuel supply valve upon detecting a predetermined condition where the condition is detected remotely from the location of the switch or valve. The sensor for detecting the predetermined condition communicates with a receiver that contacts an actuator for opening the interrupt switch or closing the fuel supply valve without an interconnecting electrical wire.

Abstract: An automatic burner assembly is disclosed, which assembly is adapted to be automatically and selectively actuatable upon the placement of a given vessel thereon or in close proximity thereto, this assembly comprising a heating element operably coupled to a sensor assembly, where this assembly is capable of detecting the presence of a given vessel on or proximate to the heating element.

Abstract: The radiation generated by at least one radiation source is controlled so as to generate a constant radiation intensity, thereby to cause the object to be heated, and the radiation intensity from the object at a first wavelength is sensed until it is equal to the present radiation intensity generated by the at least one radiation source, whereby the temperature of the object has a predetermined value. From that time on, the development of the actual temperature of the object is controlled accurately according to a predetermined program merely by sensing the radiation intensity from the object at a second wavelength larger than the first wavelength, and using the measuring signal representative of the sensed radiation intensity to continuously control the radiation intensity generated by the at least one radiation source.

Abstract: A nondestructive product level calibration method which is based on reflectance of intensity of UV and visible light that is measured from the top surface of a semiconductor wafer in a RTP closed loop process control environment in which the temperature of the wafer is regulated as a function of reflectivity of radiation at a preselected wavelength from the top surface of the wafer. In the method, sheet resistance of the wafer is measured as a function of the intensity of the UV and IR light directed at the wafer over a predetermined temperature and time range. Then, the reflectance intensity off wafer is measured to develop a model of the top surface. The reflectance model will indicate a wavelength where the reflectance is the greatest. Next, the wafer is subjected to UV radiation at the most sensitive wavelength and the reflectance is plotted against intensity of heat treatment.

Abstract: Temperature control apparatus for controlling the temperature of an electrically heated moveable object such as an electrically heated rotatable drum. A temperature control mechanism, rotatably mounted in conjunction with the cylindrical drum and electrically coupled to the electrical heater, controls the temperature by controlling the flow of electricity to the electrical heater in response to control signals. A temperature sensor mechanism, rotatably mounted in conjunction with the cylindrical drum and electrically coupled to the temperature sensor, senses the temperature of the surface of the cylindrical drum and produces temperature signals indicative thereof. A microprocessor, non-rotatably mounted with respect to the cylindrical drum, controls the temperature of the electrically heated drum by generating the control signals in response to the temperature signals.

Abstract: The present invention is an apparatus for controlling a water delivery system utilizing an instant flow tankless water heater. It includes a programmable microprocessor with support circuitry to achieve control of the outlet temperature of a varying flow rate and varying inlet temperature stream. The system senses a water outlet temperature and controls AC power through an on/off mechanism to regulate power to heating elements embedded in the water stream. The capabilities of the heating elements are improved through the application of using a microprocessor to perform a proportional (P), integrating (I) and derivative (D) calculation. The calculations are used to determine the operating characteristics of the heating system and to control the heating system.

Abstract: A transition sensor is responsive to transition of a positive temperature coefficient resistive element from a nominal low resistance state to a protective high resistance state. A positive temperature coefficient (PTC) element is placed in a power distribution circuit between a power source and a load. Excessive load current in the event of a high current fault heats the PTC element to a threshold temperature at which the PTC element transitions into a protective state of high resistance, limiting current flow to the load. The LED of an optoisolator is coupled in parallel with the PTC element, preferably with a resistor in series with the LED. Under nominal current conditions the voltage across the LED is less than its forward bias voltage. During a high current fault, the LED becomes forward biased and switches on the optoisolator phototransistor to operate an alerting device such as an audible alarm and/or a light.

Abstract: An automatic switching apparatus for a hand held electrically operated appliance, such as a pressing iron. The automatic switching apparatus is provided within a circuit board located within the housing of the iron. The automatic switching apparatus includes a first timing circuit and a photosensitive switch which function in conjunction with one another such that when the user breaks contact with the photosensitive switch located on the handle portion of the iron, the first timing circuit is enabled to de-energize the heating element of the iron after contact has been broken with the photo-sensitive switch for a predetermined period of time. A second timing circuit is provided to disable the first timing circuit for a second predetermined period of time when the iron is initially plugged into the wall outlet so as to permit the heating element to reach a temperature level suitable for ironing without necessitating the user to contact the photosensitive switch when the heating element is initially energized.

Abstract: A pyrometer for measuring thermal radiation and emissivity for both diffusely and specularly reflecting surfaces of an object which includes, a thermal radiation detector and an optical system connected to the detector for concentrating thermal radiation originating from an object surface area on the detector, an emissivity meter connected to the optical system, the meter further comprising a radiation source supplying measuring radiation and a measuring radiation detector, an optical integrator adjacent to the object surface area arranged in the radiation path of the measuring radiation between the radiation source and the measuring radiation detector, wherein the radiation source extends through an aperture of the optical integrator and diffusely irradiates the object surface, and a shield connected to the optical integrator for preventing measuring radiation from irradiating the object surface area directly, is described.

Abstract: An improved heater and control apparatus (10) suitable for maintaining a proper temperature in a liquid environment such as an aquarium (12) is provided. The apparatus (10) includes a heater element (26) housed within a protective casing (28) to reduce the likelihood of heater element (26) breakage. A number of openings (30) are provided in casing (28) to permit direct contact between the heater element (26) and water in the aquarium (12). The control assembly (16) includes a novel active light display (99). Additional novel features and corresponding advantages of the apparatus (10) are disclosed.

Abstract: An electric circuit is disclosed which includes a heater element for generating heat, a power switch for controlling the current to the heater element, a night light for providing illumination, and a night light switch for controlling the current through the night light. The night light is operable separately and independently of the heater element. In one embodiment for use in a humidifier the electric circuit further includes a thermo fuse, a thermo disc and a refill light. In another embodiment for use in a heater the circuit further includes a fan, a power light and a second heater element for generating heat.

Abstract: Electrothermal conversion elements, apparatus and methods for use in comparing, calibrating and measuring electrical signals. The element emits IR radiation in response to electrical input. The radiation is collected and converted to an electrical signal proportional to the RMS value of the input signal. Isothermal operation enhances both IR and electrical operation.

Abstract: A cooking apparatus for heating food to be served and capable of being operated with utmost simplicity without using and choosing various cooking-mode selection keys so as to achieve superb ease-of-operation. The cooking apparatus includes a cooking chamber for placing and storing food to be heated by the apparatus and a detector for detecting a state of a door attached to the cooking chamber, the door being freely openable and closable against an opening portion of the cooking chamber. An optical sensor, having a plurality of light emitting portions is disposed in a side of the cooking chamber and a plurality of light receiving portions are disposed counter to the light emitting portions. A drive unit is provided for driving the optical sensor and a judgement unit verifies and determines a cooking mode suitable for the food placed in the cooking chamber responsive to a signal from the optical sensor, where the drive unit is activated when the detector detects that the door is closed.

Abstract: A microwave oven has a photosensor to detect an objected in a cooking compartment. The photosensor, including a light emitter and a light receiver, detects whether a turntable is absent or present in the cooking compartment. The light emitter projects a plurality of pulses of light in sequence. A controller counts the number of pulses of light detected by the light receiver and controls the oven based on the number of pulses of light detected as compared to the number of pulses of light emitted.

Abstract: A coffee roaster which roasts coffee beans in an oven chamber employing both radiant and convection heating techniques while the beans are continually intermixed in a fluidized bed rotating in the horizontal plane. Roaster control means are provided to terminate the roasting process by quenching the beans and oven chamber while maintaining the beans in a fluidized bed to avoid scorching or further roasting by the residual heat of the coffee bean mass. The oven chamber includes an upper transparent section through which the roasting charge of beans may be viewed and thereby allow manual control of the process in response to visual observation.

Abstract: A visual indication is provided in a heater of an electric cooking appliance which incorporates a user-operable multi-position switch for switching the heater from one power output to another. The heater incorporates at least one heating element which is capable of emitting a significant amount of visible radiation, the at least one heating element being de-energized and subsequently re-energized as the heater is switched from one power output to another. Such a heater is of particular value where the heating element is capable of emitting fewer distinct levels of visible radiation than the number of distinct heat settings of the heater selectable from the multi-position switch. The heating element may be de-energized and subsequently re-energized only between adjacent heat settings in which there is no substantial change in the level of visible radiation.

Abstract: In a food service system, prepared meals including chilled foods are assembled in individual meal trays (10) and held in the trays for a period prior to regeneration to prepare the food for heating. A control system of a rethermalizing trolley (12), which accommodates a large number of trays, can discern for itself which dishes (30) in the trays need heating and which are to remain cool. Dishes for hot and cold foods have white and black markings respectively, which results in reflected infra-red signals from sensors (42, 44) of the control system to be of discernably different strengths, so identifying the hot food dishes. Dish temperature is continually monitored by the control system by means of thermal contact with thermistors (46), which enables the system to oversee food temperatures both prior to and during regeneration.