Abstract: A temperature measuring device includes an ultrasonic sensor attached to a rear surface side of the structural body having the multilayer structure, an acquisition unit configured to, through the ultrasonic sensor, acquire a signal of a reflected wave of an ultrasonic wave incident at the internal side of the structural body, an extraction unit configured to extract, from the signal of the reflected wave, a domain including a reflected wave reflected on a surface on the internal side of the structural body, and an identification unit configured to, based on a signal of the reflected wave in the extracted domain, identify the temperature of the surface on the internal side of the structural body.

Abstract: A measurement mechanism having a body and a vacuum chamber that is located on the body and in which a measurement process is performed is disclosed. A first sample and a second sample between which a heat transfer occurs are placed in the vacuum chamber and contact each other. A piston that provides the first sample and the second sample to continuously contact each other and a cooler that is located below the first sample and the second sample is also disclosed.

Abstract: This temperature monitoring device (100) can be placed in a furnace together with a composite material. The temperature monitoring device (100) includes: a pair of internal components (10) that each have a temperature detection surface (11) and are layered such that the temperature detection surfaces (11, 11) face each other; a temperature detection unit (30) disposed so as to be sandwiched between the temperature detection surfaces (11, 11); at least a pair of external components (20) that are respectively disposed on reverse sides from the temperature detection surfaces (11); and an adjustment part (50) capable of adjusting the sizes of the thickness-direction gaps between the internal components (10) and external components (20).

Abstract: A measuring arrangement for a thermal analysis of a sample, having a crucible for storing a sample in the crucible, as well as a sensor for measuring a sample temperature of the sample when the crucible is arranged on the sensor. To reduce the risk of damages to or even the destruction of used components as a result of chemical or physical reactions, it is provided according to the invention that the measuring arrangement further has a washer arrangement, which is inserted between the crucible and the sensor and which has a first layer, which contacts the crucible, of a first material and a second layer, which contacts the sensor, of a second material, which differs from the first material. The invention further includes a method for the thermal analysis of a sample, which is performed by using such a measuring arrangement.

Abstract: We disclose herein a flow and thermal conductivity sensor comprising a semiconductor substrate comprising an etched portion, a dielectric region located on the semiconductor substrate, wherein the dielectric region comprises at least one dielectric membrane located over the etched portion of the semiconductor substrate and a heating element located within the dielectric membrane. The dielectric membrane comprises one or more discontinuities located between the heating element and an edge of the dielectric membrane.

Abstract: Disclosed are systems and methods for providing an adiabatic power compensation differential scanning calorimeter to minimize a temperature difference between a sample and a reference. For instance, methods can include providing ramp-up heating power to heat a sample container and a reference container based on a preprogrammed temperature ramp rate; minimizing a temperature difference among the sample container, the reference container, and at least one furnace; providing compensating heat to the sample container and the reference container when a self-heating activity of the sample material is detected; providing container-only compensating heat to the sample container to block heat transfer from the sample material to the sample container once the self-heating activity of the sample material is detected; and providing compensating heat to the reference container to facilitate container-only compensating heat calculation and control.

Abstract: A core body thermometer includes a substrate, a heat receiving terminal with which heat from a subject is received and which divides the heat into first heat flow and second heat flow and causes the first heat flow and the second heat flow to flow out, a first heat flow measurement system that measures the first heat flow using a first input-side temperature sensor and a first output-side temperature sensor, a second heat flow measurement system that measures the second heat flow using a second input-side temperature sensor and a second output-side temperature sensor, a first thermal resistance body provided between the heat receiving terminal and the first input-side temperature sensor, and a second thermal resistance body provided between the heat receiving terminal and the second input-side temperature sensor.

Abstract: Apparatuses and methods for measuring and characterizing ultrasound using thermoacoustic sensors are provided. Thermoacoustic sensors can include heat flux sensors for detecting a temperature difference (between the front and back of the heat flux sensor) and an absorber layer attached to the heat flux sensor for absorbing ultrasound, converting it to heat, and also acting as an acoustic impedance matching layer. An heat sink can also be used. In some embodiments, thermoacoustic sensors can be arranged into an acoustic integrating sphere and face inward to form a cavity. The sphere can have an opening to the cavity, wherein ultrasound emitted through the opening can cause a temperature difference that can be detected by the thermoacoustic sensors. These apparatuses and others can provide for methods of measuring ultrasound power and/or methods of determining an ultrasound profile as the angular distribution of emitted ultrasound power generated by an ultrasound transducer.

Abstract: An oven is provided. The oven includes a housing comprising a baking surface and an enclosure. The baking surface extends within the housing and includes side apertures with a first plurality of in-shot burners that extend through each aperture, wherein during operation heated combustion gas from the burners is directed toward the roof of the enclosure during operation. The oven additionally includes a box disposed below the baking surface with an interior that is in thermal communication with the baking surface, wherein the box supports a burner that is oriented such that heated combustion gas from the burners flows through the box and a portion of the heat from combustion is transferred through the baking surface.

Abstract: A heat flux sensor to be attached to a hole portion defined in a surface of an object includes a body portion having an outer circumferential face, and an exterior end face that is flush with the surface of the object. The body portion includes a plurality of bored holes extending from an outer face other than the exterior end face of the body portion, with respective tips of the bored holes being arranged on the same normal line of the exterior end face. The heat flux sensor further includes a plurality of heat sensors having wiring lines leading to the outer face of the body portion through the bored holes, and a filling material that fills the bored holes to seal the heat sensors.

Abstract: A temperature sensor array includes several temperature sensors at different positions for installation within an instrumentation tube of a nuclear reactor. The temperature sensors measure temperature at multiple axial positions of the nuclear reactor, and plant operators are able to access and interpret this measurement data. Temperatures associated with vessel coolant boiling or loss and/or fuel damage can be detected by the temperature sensors to permit more direct determinations of core fluid levels. Multiple temperature sensor arrays permit vessel fluid levels and conditions to be measured at multiple core locations.

Abstract: A process condition measuring device (PCMD) may include first and second substrate components. One or more temperature sensors are embedded within each substrate component. The first and second substrate components are sandwiched together such that each temperature sensor in the second substrate component is aligned in tandem with a corresponding temperature sensor located in the first substrate component. Alternatively first and second temperature sensors may be positioned in parallel in the same substrate. Temperature differences may be measured between pairs of corresponding temperature sensors when the PCMD is subjected to process conditions in a workpiece processing tool. Process conditions in the tool may be calculated from the temperature differences.

Abstract: The present invention concerns a method for measuring the thickness of any deposit of material on the inner wall of a structure conducting a fluid stream of hydrocarbons, the method comprising the steps of: applying a first heat pulse or continuous heating to at least one first section of the structure removing deposits on the inner wall of the first section of the structure; applying a second heat pulse to both the first section of the structure and at least one second section of the structure, the first and second sections being spaced apart, which heat pulse does not loosen any deposit of material in the second section; measuring the temperature of the wall of the structure or the fluid during the second heat pulse at both the first and second sections; and determining the thickness of any deposit of material on the inner wall of the structure at the second section based on the measured temperatures. The present invention also relates to a corresponding device and arrangement.

Abstract: Method and equipment for measuring the heat flow (J) through a construction (K) having a thickness (D), where a temperature difference (?T) is formed transversely through the thickness of the construction. According to the invention, at least two temperature sensors (G1, G2) are placed against a first surface (S1) and at least one first temperature sensor (G1) is insulated thermally from the second temperature sensor (G2), so that the temperature (T1?) sensed by the thermally insulated sensor (G1) is affected by the heat flow through the construction (K) more than the temperature (T1?) detected by the second temperature sensor.

Abstract: A system and method are disclosed for controlling a drywell including a receiver having upper and lower ends with the lower end being more insulated than the upper end having a temperature sensor in thermal contact therewith. Upper and lower heating elements are in thermal contact with the upper and lower ends, respectively. A controller includes an integrated circuit having a temperature sensor. A reading from the integrated circuit is used to control power to the upper heating element and reduce a temperature gradient between the upper and lower ends of the receiver.

Abstract: Techniques for determining one or more heat transfer characteristic values of a structure, such as an electronic device, are disclosed. A heat flux vector magnitude and a temperature gradient vector magnitude for a portion of the structure are determined, and a product of the heat flux vector magnitude with the temperature gradient vector magnitude is obtained. More particularly, the dot product of the heat flux vector magnitude with the temperature gradient vector magnitude may be obtained to provide a bottleneck heat transfer characteristic value. Alternately or additionally, a cross product (or related operation) of the heat flux vector magnitude with the temperature gradient vector magnitude is obtained to produce a shortcut heat transfer characteristic value.

Abstract: A differential scanning calorimeter (1) includes: a sample container (2) for receiving a measurement sample; a reference substance container (3) for receiving a reference substance; a heat sink (10); a thermal resistance (5), which is connected between the sample container and the heat sink, and between the reference substance container and the heat sink to form heat flow paths therebetween; a sample-side thermocouple (7), which is thermally connected to the thermal resistance at a portion in the vicinity of the sample container with its hot-junction (7c) being insulated; and a reference substance-side thermocouple (8), which is thermally connected to the thermal resistance at a portion in the vicinity of the reference substance container with its hot junction (8c) being insulated, in which the sample-side thermocouple and the reference substance-side thermocouple output a heat flow difference signal indicating a temperature difference between the measurement sample and the reference substance.

Abstract: In a method for the automatic inspection of a welding seam using heat flow thermography, a feature vector is established which represents a time course of a detected heat flow. The feature vector is used to determine, from a series of thermal images, a first characteristic thermal image, which corresponds to a minimum heat flow through an object to be examined, and a second characteristic thermal image, which corresponds to a maximum heat flow through the object, wherein a heat flow directly from an excitation source has already dissipated. A suitable thermal image is used from the series of thermal images to detect and evaluate the welding seam in relation to defects of various defect types, for each defect type, the characteristic thermal images being used as references to determine the respective suitable thermal image.

Abstract: A method and apparatus for estimating the temperature sensed upon contact with a surface. The method includes contactless heating of the surface, contactless measurement of a time change in temperature of the surface, and estimation of the temperature sensed upon contact with the surface on the basis of this time change in temperature.

Abstract: A heat flux measurement apparatus 100 includes a first measurement unit 110, a second measurement unit 120, and heat flux calculation units 130, 140. The first measurement unit 110 measures a temperature difference between a first measurement location and a second measurement location that is lower in temperature than the first measurement location, using a thermocouple 112. The second measurement unit 120 measures a temperature difference between a third measurement location that can be assumed to be isothermal with the first measurement location and a fourth measurement location that can be assumed to be isothermal with the second measurement location, using a thermocouple 122 different in time constant from the thermocouple 112.

Abstract: Methods and apparatus for measuring heat flux in a material are disclosed. A disclosed example method involves emitting an acoustic signal into the material and determining a first propagation time associated with the propagation of the acoustic signal through the material. A first heat flux value indicative of a first heat flux of the material is then determined based on the first propagation time.

Abstract: In a method for automated, contactless and non-destructive testing of a material joint (4), a dynamic threshold value is varied between a minimum threshold value and a maximum threshold value, with regions of a heat flow dynamics through the material joint (4) being determined which represent values of the heat flow dynamics exceeding the dynamic threshold value. The regions of the heat flow dynamics are examined with respect to an abrupt change in perimeter. An Abrupt change in perimeter occurs if a boundary (7) between a molten zone (5) and a non-molten but still adhering zone (6) of the material joint (4) is being crossed.

Abstract: Methods and apparatus for measuring substrate uniformity is provided. The invention includes placing a substrate in a thermal processing chamber, rotating the substrate while the substrate is heated, measuring a temperature of the substrate at a plurality of radial locations as the substrate rotates, correlating each temperature measurement with a location on the substrate, and generating a temperature contour map for the substrate based on the correlated temperature measurements. Numerous other aspects are provided.

Abstract: Provided is a micro heat flux sensor array having reduced heat resistance. A micro heat flux sensor array may include a substrate, a plurality of first sensors formed on a first side of the substrate, and a plurality of second sensors formed on a second side of the substrate. Each of the plurality of first and second sensors may include a first wiring pattern layer of a first conductive material, a second wiring pattern layer of a second conductive material contacting the first wiring pattern layer, and an insulating layer in contact with the first and second wiring patterns.

Abstract: A device, such as a heat meter for measurements of hot tap water energy usage, separated from building heating energy usage, in a district heating substation. The device is connected only to sensors attached to the supply pipe and return pipe of the district heating substation. A device, such as a heat meter, has a detector to detect a deviation in the total power (P) usage in the district heating substation which deviation depends on the use of warm tap water.

Abstract: Methods and apparatus for measuring heat flux in a material are disclosed. A disclosed example method involves emitting an acoustic signal into the material and determining a first propagation time associated with the propagation of the acoustic signal through the material. A first heat flux value indicative of a first heat flux of the material is then determined based on the first propagation time.

Abstract: Provided is a micro heat flux sensor array having reduced heat resistance. A micro heat flux sensor array may include a substrate, a plurality of first sensors formed on a first side of the substrate, and a plurality of second sensors formed on a second side of the substrate. Each of the plurality of first and second sensors may include a first wiring pattern layer of a first conductive material, a second wiring pattern layer of a second conductive material contacting the first wiring pattern layer, and an insulating layer in contact with the first and second wiring patterns.

Abstract: A heat flux measurement device includes at least two thermocouples disposed within a front portion of the device at different axial distances from a front wall of the device. A correlation between the measured heat fluxes from the device over a period of time is used to estimate a fouling thickness on a wall, for example, a water wall of a radiant syngas cooler (RSC).

Abstract: There is provided a differential scanning calorimeter in which a base line stability and a responsiveness are improved. There is made a constitution in which the stability is ensured by making a neck-like part in a heat passage from a heat reservoir 1 to a sensor plate 4 and, at the same time, a two-dimension heat flow passage to a sample holder 5a is ensured.

Abstract: A modulated differential scanning calorimeter that accounts for heat flow due to evaporative solvent loss. The calorimeter modulates the temperature applied to a sample and a reference to determine the amount of heat flow that is due to evaporation. By calculating the amount of heat flow due to evaporation, the user can determine how much of the heat flow of any given well is due to the process of interest as opposed to evaporation.

Abstract: First and second thermal sensors measure the respective temperatures of portions of a surface of a structure such as an aircraft component. An alert signal is emitted if the temperatures of the surface portions are substantially different. An energy source causes heat flow within the structure. Subsurface irregularities such as disbanded areas between composite layers and foreign materials obstruct heat flow within the structure and cause proximate surface portions to exhibit different temperatures. A non-alert signal may be emitted if the temperatures of proximate surface portions are essentially the same.

Abstract: The invention provides a universal rate-based transducer for advancing diagnostic and predictive analyses of low frequency physical phenomena, such as associated with heat and mass transfer, solid and fluid mechanics, pressure and seismic analysis. In many applications, such as in the fire metrology, aerospace, security and defense sectors, rate information is crucial for reaching fast and reliable diagnosis and prediction. In one preferred embodiment, the invention comprises a universal voltage rate sensor interface that accurately recovers the instantaneous heating/cooling rate, dT/dt. Upon appropriate calibration, this sensor interface allows real-time extraction of rates associated with many physical quantities of interest (e.g., temperature, heat flux, concentration, strain, stress, pressure, intensity, etc.).

Abstract: Techniques for precision testing of thermal interface materials are described. An apparatus may include multiple anvils each having multiple sensors disposed along its axis. A thermal interface material may be disposed between the anvils. A control module may be communicatively coupled to said sensors and arranged to receive temperature readings from the multiple sensors to form a temperature gradient, determine a surface temperature for each anvil based on the temperature gradient, determine a heat flux through the thermal interface material based on the surface temperature, and determine a resistance value for the thermal interface material based on the heat flux. Other embodiments are described and claimed.

Abstract: A mechanism and method for directly observing data from which the thermal emissivity or absorptivity of a surface can be calculated. The invention teaches the use of a substantially planar heat-flux or heat-flow sensor employing a thermopile, to measure the rate of heat dissipation from a radiating surface thermally attached to one side of the heat-flux sensor where the radiating surface is exposed to a first temperature and where the second side of the heat flux sensor is in thermal contact with a heat source at a second higher temperature.

Abstract: The novel method and device provide for process control—closed-loop control or open-loop control—for a thermal system with an obstruction-curved and/or thick-walled component through which a medium flows. The wall temperatures of the component are detected, the heat flux density of the heat flux from the medium into the wall of the component is determined, the respective heat transmission coefficient is determined, using the wall temperatures. The heat flux density, and the heat transmission coefficient thus determined are used to influence the medium properties, with the heat stresses in the component being taken into account.

Abstract: A deep-area temperature calculating device 441 calculates the temperature Tcore of a deep area on the basis of a first body-surface temperature and second body-surface temperature from body-surface sensors 31A and 31B, and on the basis of a first intermediate temperature and second intermediate temperature from intermediate sensors 32A and 32B. Since the temperature Tcore of the deep area is determined from two body-surface temperatures and two intermediate temperatures, the temperature Tcore of the deep area can be calculated regardless of the heat resistance of the thermometer without making any assumptions regarding the heat resistance of the area that extends from the deep area of the human body to the body surface. Thereby, the temperature Tcore of the deep area can be calculated and the body temperature can be measured with high precision regardless of differences in the body type or contact with clothing or bedding.

Abstract: An automated test method characterizes the performance of commercially available thermal interface materials (TIM) for electronic cooling. Such automated internal test vehicle provides an independent study of various TIM's. A spectrum of materials are preferably tested using automated methods so the results are reported in a consistent way. Such reports simplify the comparison and selection of appropriate TIM material for various end-user applications. Such automated test method is observed to be faster and easier to use. It requires minimal operator intervention during the test.

Abstract: An electronic clinical thermometer has a probe including a variable-temperature heater and one or more temperature sensors and may also include a heat flux sensor. Physical variables such as temperature, time rate of change in temperature and/or heat flow rate are directly measured at positions on the surface of a patient while being heated by the heater through a thermally insulating member. Such measured values are used to solve a heat transfer equation rewritten as lower-order equations. Measurements may be controlled to be taken at a desired timing such as at specified intervals. The probe for contacting the patient's body may be planar or in an elongated bar-shape.

Abstract: A device for thermal sensing is based on only one thermopile. The junctions of the thermopile are coupled thermally to a first region which includes a first substance while the hot junctions of the thermopile are coupled thermally to a second region which includes a second substance. The first and second regions are separated and thermally isolated from each other. The device can further include a membrane to thermally and electrically isolate the thermopile and to mechanically support the thermopile.

Abstract: A furnace temperature detector includes a spike thermocouple attached to a heating chamber; an overheat thermocouple attached to the heating chamber; an inner thermocouple installed inside a reaction tube; a temperature controller connected to the spike thermocouple and the inner thermocouple; an overheat controller connected the overheat thermocouple; and a control switch for directing the output line of the overheat thermocouple. When the furnace overheats, the overheat thermocouple detects the overheating and generates and outputs an electric signal corresponding to the overheating to the overheat controller; the overheat controller generates and outputs an overheat control signal.

Abstract: A heat-flux gage, a manufacturing method and a manufacturing device thereof which are improved from circular foil heat-flux gage disposed in ASTM E511 comprise: a cylindrical body having a receiving space therein, and a foil mounting hole on one end thereof; a foil including a heat absorption surface, an inner surface facing the heat absorption surface, and a radiant side surface connecting the heat absorption surface and the inner surface, wherein the inner surface faces toward the receiving space and the radiant side surface is contacted to a side surface of the foil mounting hole; a foil lead wire connected on a center of the inner surface of the foil; a body lead wire connected to an opposite end of the foil mounting hole on the cylindrical body; and a filler filled in the inner receiving space, to prevent the foil lead wire from being damaged by fixing the foil lead wire.

Abstract: A device for measuring the temperature within a body from a body surface at a different temperature, comprising: a heat shield for application to the body surface, comprising an outer heat-conducting portion (52), and an inner heat-insulating portion (50); a heater or cooler (41) to heat or cool the outer portion (52) of said heat shield to the temperature of the body surface; a first temperature sensor (37) positioned on a surface of the inner heat-insulating portion (50) of the heat shield which is applied to the body surface; a second temperature sensor (38) positioned to measure the temperature of the outer portion (52) of the heat shield; a heater or cooler control circuit to heat or cool the outer portion (52) of the heat shield towards the temperature measured by the first the first temperature sensor (37); and a second control circuit to forecast the first temperature sensor (37) equilibrium temperature.

Abstract: According to one embodiment of the invention, a method includes providing a conduit having a fluid flowing therethrough, disposing a plurality of temperature measurement devices inside a wall of the conduit, positioning at least some of the temperature measurement devices proximate an inside surface of the wall of the conduit, positioning at least some of the temperature measurement devices at different radial positions at the same circumferential location within the wall, measuring a plurality of temperatures of the wall with respective ones of the temperature measurement devices to obtain a three-dimensional temperature topology of the wall, determining the temperature dependent thermal conductivity of the conduit, and determining a multi-dimensional thermal characteristic of the inside surface of the wall of the conduit based on extrapolation of the three-dimensional temperature topology and the temperature dependent thermal conductivities.

Abstract: A sensor designed for measurement of conducted heat flux passing through a solid object consists of a thin film thermopile deposited on a planar substrate whose thermal properties match those of the solid object. The thermopile is protected by a thin rectangular plate made of the same material as the substrate. The sensor is imbedded in the solid object and measures the vector of heat flux along the thermopile axis with minimal distortion of the heat flow pattern. Applications include measurement of heat flux in casting molds, boiler tubes, well surveying instruments and laser weapons testing.

Abstract: The present invention discloses a method and apparatus (5) for condition diagnosing of an inductive power device (1), such as a transformer or reactor, having power windings (2) immersed in a fluid (3) being cooled by cooling devices (4). The diagnosing method basically compares and evaluates expected heat flows into and out from the inductive power device (1) system together with an actual and a previous heat content of such a system. From the heat flows the heat balance in the system may be obtained and is used for diagnosing the operation conditions of the inductive power device (1). The results from the condition diagnosing may be used as indicators (70) that can alarm operators, may be sent as a data signal (80) to remote and/or portable display means (85), such as a computer, or may be used as input data to control or simulation systems.

Abstract: When a micro-heater heats fluid using an external driving current, an upstream thermopile 8 detects the temperature of the fluid before it is heated to produce a first temperature detected signal and a downstream thermopile 9 detects the temperature of the fluid before it is heated to produce a second temperature detected signal. The flow rate is computed based on the difference signal between both detected signals. A right thermopile 11 and a left thermopile 13, which are arranged in a direction orthogonal to the flow direction of the fluid, detect the temperature of the fluid to produce a right temperature detected signal and a left temperature detected signal. The property of the fluid is computed on these right and left temperature detected signals. The flow rate is corrected on the basis of the property thus computed. The flow rate of an object fluid for measurement can be accurately measured by a flow sensor whose output characteristic varies when the kind or composition of the fluid changes.

Abstract: A multipoint temperature sensor for measuring fluid temperature in a duct includes multiple thermistors of equal resistance, spaced apart in a circuit. Each thermistor has a positive lead and a negative lead for connecting electrically with the circuit. Wires connect the thermistors such that half of the thermistors are placed in parallel with the other half of the thermistors. The total number of thermistors in the circuit is a perfect square. Shrinkwrap fits over the thermistors and the leads. Tabs disposed on bridging clips bend around the shrinkwrap and the wires on either side of each thermistor such that the tabs do not overlap the leads. All the wires between adjacent thermistors are contained in a single, plenum rated sheathing.

Abstract: A device for thermal sensing is disclosed based on only one thermopile. The cold junctions of said thermopile are coupled thermally to a first channel comprising a first substance while the hot junctions of said thermopile are coupled thermally to a second channel comprising a second substance, said first and said second channel are separated and thermally isolated one from another. Said device can further comprise a membrane to thermally and electrically isolate said thermopile and to mechanically support said thermopile. Particularly a liquid rubber, i.e. ELASTOSIL LR3003/10A, B can be used as a membrane material. Further disclosed is a method for fabricating such a device using micromachining techniques.

Abstract: An improved and accurate enthalpy tunnel is presented, designed to condition and control airflow patterns within the main tunnel and air sampling subsystem so as to present a homogenous volume immediately upon introduction into the enthalpy tunnel. The air volume velocity is slowed and the air volume is completely mixed in a settling chamber which also serves to maintain the static discharge pressure on the unit under test. The rectangular design in use in the industry is replaced with circular geometry, using a cylindrical tunnel shape as opposed to a rectangular shape. The circular geometry creates a flat, uniform velocity profile. This tunnel improves the design of current art enthalpy tunnels by using a single nozzle instead of a bank of nozzles, presenting to the sampling mechanism a smooth, stable and uniform flow profile. The sampling method used in the prior art is replaced with a sampling tunnel that also conditions its air flow profile, leading to consistent sampling.

Abstract: A heat flux measuring device for transporting through a heated chamber, the device having an array of sensors, each sensor comprising first and second surfaces bounding a region, a thermally insulating layer substantially occupying said region, and means for providing a signal which is a measure of the temperature difference across the layer. The said first surface of each sensor is in thermal contact with a heat sink and the said second surface of each sensor is exposed.