Abstract: The electron beam is typically dynamically steered after its generation on the path to the target. The steering is performed by one or more source coils. These coils produce the magnetic field outside the vacuum vessel allowing air/water/oil cooling to remove undesired heat. The magnetic field is then picked up inside the vacuum vessel with pole pieces and guided towards the region where the magnetic field is needed to steer the electron beam.

Abstract: An X-ray source device includes an anode to generate X-rays; a drive to rotate the anode about an anode central axis, the drive including a stator and a first rotor, and the first rotor being rotationally fixed relative to the anode; and a cooling facility to cool at least one of the anode and the drive using a coolant. The drive includes a second rotor to circulate the coolant.

Abstract: The present disclosure provides systems and methods for create a scanning pencil beam of x-rays and the air cooling of the system. The system has an enclosure with an x-ray beam source disposed therein. An x-ray wheel having or holding an x-ray attenuating ring is disposed proximate to an end of the enclosure and is configured and disposed to rotate the x-ray attenuating ring and form a scanning pencil beam. The system has at least one air inlet and air outlet and at least one air moving device configured and disposed to move air through the air inlet and the air outlet and to air cool the x-ray system.

Abstract: A system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant.

Abstract: The invention proposes an insulator within an X-ray tube having a vacuum side and an ambient side and a feedthrough substantially coinciding with an axis of symmetry at the vacuum side and an axis of symmetry at the ambient side. The axis of symmetry at the vacuum side and the axis of symmetry at the ambient side have an angle of at least 5°, preferably 90°, with respect to each other. An X-ray source comprising such an insulator is presented as well and the present invention also extends to a medical imaging apparatus for generating X-ray images of a patient thereby using an X-ray source with such an insulator. In an embodiment, an X-ray source is provided wherein the insulator is plugged to an electrical connector at the ambient surface.

Abstract: A liquid metal or spiral groove bearing structure for an x-ray tube and associated process for manufacturing the bearing structure is provided in which journal bearing sleeve is formed with a number of structures thereon that function to dissipate heat transmitted to the sleeve during operation of the bearing assembly within the x-ray tube to minimize thermal deformation of the sleeve, thereby minimizing gap size alteration within the bearing assembly. The structures formed within the sleeve are slots disposed within the section of the sleeve in which the highest temperature gradients develop. The slots enable an increase in thermal conductance away from the sleeve while minimizing the stresses created from the deformation of the portion(s) of the sleeve between the slots.

Abstract: According to one embodiment, an X-ray tube comprises a cathode for emitting electrons, an anode having an anode target with which electrons emitted from the cathode collides to radiate X-rays, a glass container housing the cathode and the anode, an anode rod extending from the anode to an outside of the container, an annular metal member through which the anode rod is inserted, the annular metal member connecting the anode and the container to maintain an inside of the container in vacuum, and an electrically insulating molding resin member charged into a space formed between the anode rod and outer surfaces of the container and the metal member.

Abstract: In one example, a lift assembly may exert a force on a rotatable anode of an X-ray source. The lift assembly may include a lift shaft and a lift electromagnet. The lift shaft may be coupled to the anode and configured to rotate around an axis of rotation of the anode. The lift electromagnet may be configured to apply a magnetic force to the lift shaft in a radial direction. The lift electromagnet may include a curved surface that contours around at least a portion of the shaft wall. A radius of curvature of the curved surface of the lift electromagnet may be greater than a radius of curvature of the lift shaft, and the spacing between the curved surface of the lift electromagnet and the shaft wall may be non-uniform.

Abstract: A structure and method of operation of a journal bearing is disclosed that minimizes contact of the shaft with the sleeve during start up and slow down of rotation of the shaft relative to the sleeve, or vice versa. The bearing assembly includes a gravitational load reduction mechanism with magnets disposed on the sleeve and on the shaft in alignment with one another. The magnet(s) on the shaft interacts with the magnet(s) disposed on the sleeve to provide a force against the pressure of the shaft towards the sleeve generated by gravity on the rotating component. The magnets enable centering of the rotating component within the stationary component during low rotation and non-rotation. This prevents rubbing of the rotating journal bearing component surfaces, e.g., sleeve, against the stationary journal bearing component, e.g., shaft, during assembly, ramp-up, and coast-down when the journal bearing fluid provides minimal or no bearing centering capability.

Abstract: A ring seal is engaged with a liquid metal bearing assembly and operates to contain metal fluid lubricant leaking through the primary compression seals of a liquid metal bearing to prevent the fluid from entering the high voltage space within the x-ray tube and causing high voltage instability. The ring seal engages the existing configuration for the bearing assembly without deforming the bearing, including effects of thermal expansion and inertial body forces, thus maintaining the tight tolerances for the proper operation of the component parts of the bearing structure. The ring seal retains the leaking liquid metal within the ring seal regardless of the operating state and/or condition of the bearing assembly, such as during operating conditions. i.e., rotation of the bearing assembly or gantry, and non-operating conditions, e.g., shipping and stand-by, and regardless of the corresponding pressures and their locations exerted on the ring seal by the liquid metal.

Abstract: A thermionic emission device includes an indirectly heatable main emitter, which is constructed as a flat emitter with a main emission surface, and at least one connectible heat emitter with a heat emission surface. The heat emission surface is disposed at a predefinable distance from the main emission surface. The main emission surface can be asymmetrically heated by the heat emission surface. In the operating state, the main emitter is at a main potential and the heat emitter is at a heating potential which differs from the main potential. An x-ray tube with the thermionic emission device has a longer service life with a consistent image quality.

Abstract: An object of the present invention is to provide the X-ray tube which improves the workability of the baking for obtaining the ultra-high vacuum of the X-ray tube having a field emission type electron gun and have a stable performance. The X-ray tube comprises a field emission type electron gun chamber, an electron beam aperture, an X-ray target and a vacuum pump, in one body with a vacuum sealing structure (vacuum tube section). The vacuum tube section is attachable and detachable to the electromagnetic lens section in the X-ray tube, thereby it is possible to perform the baking by removing only the vacuum tube section. The fitting portions for positioning are provided at the vacuum tube section and the electromagnetic lens section, and therefore it is a constitution to easily perform an optical axis alignment at a mounting time after the baking.

Abstract: In one embodiment, an X-ray source target is provided that includes two or more layers of X-ray generating material at different depths within a source target for an electron beam. In one such embodiment the X-ray generating material in each layer does not extend fully across an underlying substrate surface.

Abstract: In an X-ray radiation source, a counter wall made of alkali-containing glass, out of walls of a housing of an X-ray tube, is arranged opposite to a high-voltage region VH of a power supply unit including a high-voltage generation module which generates a negative high voltage to be applied to a filament. This configuration prevents an electric field from being generated in the counter wall and thus suppresses precipitation of alkali ions from the glass. Therefore, it prevents change in potential relationship between electrodes at different potentials such as the filament, grid, and target and prevents occurrence of a trouble of failure in maintaining a desired X-ray amount, thus enabling stable operation to be maintained.

Abstract: An x-ray tube includes a frame forming a first portion of a vacuum enclosure, a rotating subsystem shaft positioned within the vacuum enclosure and having a first end and a second end, wherein the first end of the rotating subsystem shaft is attached to a first portion of the frame, a target positioned within the vacuum enclosure and attached to the rotating subsystem shaft between the first end and the second end, the target positioned to receive electrons from an electron source positioned within the vacuum enclosure, and a thermal compensator mechanically coupled to the second end of the rotating subsystem shaft and to a second portion of the frame, the thermal compensator forming a second portion of the vacuum enclosure.

Abstract: A high-temperature-resistant composite body is formed by joining over an area of a first, nonmetallic section via a bonding solder layer to a second, metallic section composed of Mo, an Mo-based alloy, W or a W-based alloy. A first arrangement composed of the first section, a first Zr solder and an intermediate layer is firstly soldered together in a first soldering step. A second arrangement of the resulting partial composite body, a second solder adjoining the intermediate layer and the second section is subsequently soldered together in a second soldering step. The intermediate layer at least 90 atom % of at least one of the elements Ta, Nb, W. The second solder is formed by precisely one material selected from Ti, Ti-based solder combination, V-based solder combination, Zr or Zr-based solder combination and it melts at a lower temperature than the first Zr solder in the second arrangement.

Abstract: A single-pole x-ray emitter includes an emitter housing, in which an x-ray tube with a vacuum housing and a drive motor are arranged. A cathode that generates an electron beam, and a rotating anode that is struck by the electron beam along a focal path are arranged in the vacuum housing. The vacuum housing includes a drive-side housing wall and an anode-side housing wall, and the rotating anode is held in a torsionally rigid manner on an anode tube that is rotatably mounted on a stationary part of a rotor shaft that is coupled to the drive motor. The stationary part of the rotor shaft is joined to the anode-side housing wall of the vacuum housing via a ring-shaped fixing. The anode tube incorporates a temperature compensation element. The focal path is arranged on a side of the rotating anode that faces away from the anode-side housing wall.

Abstract: According to one embodiment, an X-ray tube including an electron emission source which emits an electron, an anode target which comprises a target layer emitting an X-ray by the electron from the electron emission source, and a substrate supporting the target layer and composed from a carbide-strengthened molybdenum alloy, an evacuated outer surrounding envelope which contains the electron emission source and the anode target, a diffusion barrier layer which is integrally formed with the substrate by a powder metallurgy method on a part of a top surface of the substrate and is composed of a high-melting-point metal lacking of carbon-element content compared with carbon-element content in the substrate, and a thermal radiation film which is formed on at least a part of a top surface of the diffusion barrier layer and composed of metallic oxide.

Abstract: Finned anode. In one example embodiment, an anode suitable for use in an x-ray tube includes a hub, a front side, and a target surface disposed on the front side. The hub is configured to attach to a bearing assembly and the front side substantially faces the bearing assembly. The anode further includes a rear side substantially opposite the front side, as well as two or more annular anode fins extending from the rear side. The annular anode fins are positioned radially outward from the hub to an outer periphery of the rear side.

Abstract: A single-pole x-ray emitter includes an emitter housing, in which an x-ray tube with a vacuum housing and a drive motor are arranged. A cathode that generates an electron beam, and a rotating anode that is struck by the electron beam along a focal path are arranged in the vacuum housing. The vacuum housing includes a drive-side housing wall and an anode-side housing wall, and the rotating anode is held in a torsionally rigid manner on an anode tube that is rotatably mounted on a stationary part of a rotor shaft that is coupled to the drive motor. The stationary part of the rotor shaft is joined to the anode-side housing wall of the vacuum housing via a ring-shaped fixing. The anode tube incorporates a temperature compensation element. The focal path is arranged on a side of the rotating anode that faces away from the anode-side housing wall.

Abstract: Finned anode. In one example embodiment, an anode suitable for use in an x-ray tube includes a hub, a front side, and a target surface disposed on the front side. The hub is configured to attach to a bearing assembly and the front side substantially faces the bearing assembly. The anode further includes a rear side substantially opposite the front side, as well as two or more annular anode fins extending from the rear side. The annular anode fins are positioned radially outward from the hub to an outer periphery of the rear side.

Abstract: An x-ray tube includes a frame enclosing a high vacuum, a cathode positioned within the enclosure, and a target assembly. The target assembly includes a target cap, a focal track material positioned on the target cap to receive electrons from the cathode, and a foam material positioned within a cavity of the target cap and positioned proximate the focal track. The x-ray tube also includes a bearing assembly attached to the frame and configured to support the target assembly.

Abstract: This invention relates to high power X-ray sources, in particular to those equipped with a rotating X-ray anode capable of delivering a higher short time peak power than conventional rotating x-ray anodes. This invention can overcome the thermal limitation of peak power by allowing fast rotation of the anode and by introducing a lightweight material with high thermal conductivity in the region adjacent to the focal track material. The fast rotation can be provided by using sections of the rotating anode disk made of anisotropic high specific strength materials with high thermal stability that can be specifically adapted to the high stresses of anode operation. Uses include high speed image acquisition for X-ray imaging, for example, of moving objects in real-time such as in medical radiography.

Abstract: The present embodiments relate to active thermal control of X-ray tubes. In one embodiment, a system includes an X-ray tube having an electron beam target, a rotary bearing supporting the target in rotation, and a coolant flow passage, at least a portion of the coolant flow passage being disposed in the center of the rotary bearing, and the coolant flow passage is configured to receive a coolant. The system also includes a coolant circulating system coupled to the coolant flow passage and configured to circulate the coolant thorough the coolant flow passage, and a control circuit coupled to the coolant circulating system and the rotary bearing, the control circuit being configured to control heat flow between components of the X-ray tube by regulating extraction of heat from the X-ray tube via the coolant and by regulating a rotation rate of the rotary bearing.

Abstract: In one example, an x-ray tube comprises an evacuated enclosure and a cathode disposed within the evacuated enclosure. An anode is also disposed within the evacuated enclosure opposite the cathode so as to receive electrons emitted by the cathode. A rotor sleeve is coupled to the anode, the rotor sleeve being responsive to applied electromagnetic fields such that a rotational motion is imparted to the anode. A magnetic assist bearing assembly rotatably supports the anode.

Abstract: A distributed X-ray source (3) and an imaging system (1) comprising such an X-ray source (3) are proposed. The X-ray source (3) comprises an electron beam source arrangement (19) and an anode arrangement (17). The electron beam source arrangement (19) is adapted to emit electron beams (24) towards at least two locally distinct focal spots (27) on the anode arrangement (17). Therein, the X-ray source is adapted for displacing the anode arrangement (17) with respect to the electron beam source arrangement (19). While the provision of a plurality of focal spots allows acquisition of projection images under different projection angles thereby allowing reconstruction of three-dimensional X-ray images e.g. in tomosynthesis application, a displacement motion of the anode arrangement (17) with respect to the electron beam source arrangement (19) may allow for distributed heat flux to the anode arrangement thereby possibly reducing cooling requirements.

Abstract: An x-ray tube rotating anode. In one example embodiment, an x-ray tube rotating anode includes a hub configured to attach to a bearing assembly, rings positioned radially outward from the hub, bridges connecting the rings together, annular ring fins each attached to one of the rings, a focal track positioned radially outward from the annular ring fins, and annular focal track fins attached to the focal track.

Abstract: The x-ray target assemblies have an oxide dispersion strengthened (ODS) refractory metal alloy substrate that is bonded to a carbon-containing heat sink. The x-ray target assemblies have excellent bonding between the substrate and the heat sink. The improved bonding is achieved by placing an oxide-free barrier layer between the ODS metal substrate and the heat sink. The oxide-free barrier layer minimizes or eliminates chemical reactions that would otherwise be possible between the dispersed oxides and the carbon-based heat sink during the manufacturing process. Preventing these undesired reactions while manufacturing the x-ray target assembly yields a device with improved bonding between the heat sink and the substrate, compared to devices manufactured without the barrier layer.

Abstract: An x-ray tube includes a center shaft having an inner surface and an outer surface, the inner surface forming a portion of a cavity therein, a mount having an inner surface, the mount having an x-ray target attached thereto, and a liquid metal positioned between the outer surface of the center shaft and the inner surface of the mount. The x-ray tube further includes a flow diverter positioned in the cavity, the flow diverter having a wall with an inner surface, and a plurality of jets passing through the wall, wherein the plurality of jets are configured such that when a fluid is flowed into the flow diverter and passes along its inner surface, a portion of the fluid passes through the plurality of jets and is directed toward the inner surface of the center shaft.

Abstract: An x-ray tube includes a frame, an anode for generating x-rays disposed within the frame, a cathode disposed within the frame, where the cathode is configured to selectively emit an electron beam toward the anode, and at least one heating element disposed within the frame and configured to heat a portion of the anode.

Abstract: The present invention is related to high power X-ray sources, in particular to those ones that are equipped with rotating X-ray anodes capable of delivering a much higher short time peak power than conventional rotating X-ray anodes according to the prior art. The herewith proposed design principle thereby aims at overcoming thermal limitation of peak power by allowing extremely fast rotation of the anode and by introducing a lightweight material with high thermal conductivity (2) in the region adjacent to the focal track material (4). The extremely fast rotation is enabled by providing sections of the rotary anode disk made of anisotropic high specific strength materials with high thermal stability (1, 3, 6) which will be specifically adapted to the high stresses building up when the anode is operated, as for example fiber-reinforced ceramic materials.

Abstract: In one example, an x-ray tube comprises an evacuated enclosure and a cathode disposed within the evacuated enclosure. An anode is also disposed within the evacuated enclosure opposite the cathode so as to receive electrons emitted by the cathode. A rotor sleeve is coupled to the anode, the rotor sleeve being responsive to applied electromagnetic fields such that a rotational motion is imparted to the anode. A magnetic assist bearing assembly rotatably supports the anode.

Abstract: One example embodiment includes an anode. The anode comprises an anode hub, an annular target and a plurality of spokes. The spokes connect the anode hub to the annular target. The spokes are configured to substantially mechanically and/or thermally isolate the anode hub from the annular target.

Abstract: The x-ray target assemblies have an oxide dispersion strengthened (ODS) refractory metal alloy substrate that is bonded to a carbon-containing heat sink. The x-ray target assemblies have excellent bonding between the substrate and the heat sink. The improved bonding is achieved by placing an oxide-free barrier layer between the ODS metal substrate and the heat sink. The oxide-free barrier layer minimizes or eliminates chemical reactions that would otherwise be possible between the dispersed oxides and the carbon-based heat sink during the manufacturing process. Preventing these undesired reactions while manufacturing the x-ray target assembly yields a device with improved bonding between the heat sink and the substrate, compared to devices manufactured without the barrier layer.

Abstract: Methods and systems for providing thermal insulation in an X-ray tube are provided. The method includes configuring a metallic foam to resist the heat flow in an X-ray tube. The method further comprises configuring the metallic foam for positioning in the X-ray tube to resist heat flow to bearings in the X-ray tube.

Abstract: A method and apparatus for an x-ray apparatus. The x-ray apparatus comprises a vacuum tube. A cathode is located in the vacuum tube and capable of emitting electrons. A rotatable magnetic anode located in the vacuum tube, capable of being rotated by a motor located outside of the vacuum tube, and capable of generating an x-ray beam in response to receiving the electrons emitted by the cathode.

Abstract: Provided is a device for the emission of X-rays. The device includes a vacuum pump including a sealed peripheral casing containing a cathode which emits a flux of electrons, a rotary anode mounted at the end of the shaft of the vacuum pump, a collection device for collecting an emitted electron beam and at least one cooling element, disposed opposite one of the main radial faces of the rotary anode, which is fixed to one of the vacuum pump stator or to the sealed peripheral casing.

Abstract: A rotary anode x-ray radiator has an anode produced from a first material as well as a cathode. A structure for accommodation of at least one heat conductor element produced from a second material is provided on an external side of the anode facing away from the cathode, in an annular segment situated opposite the anode. The second material exhibits a higher heat conductivity than the first material. The heat conductor elements are accommodated in the structure to form expansion gaps.

Abstract: An x-ray tube has a cathode and an anode produced from a first material, the anode having a heat conductor element on the first side thereof facing away from the cathode. To improve the performance of the x-ray tube, the heat conductor element is composed of graphite doped with titanium having a heat conductivity of at least 500 W/mK.

Abstract: An anticathode is repeatedly moved along a rotating axis of the anticathode while the anticathode is rotated around the rotating axis. Then, energy beams are irradiated onto a surface portion of the anticathode which is located against a centrifugal force generated from the rotation of the anticathode to partially melt the surface portion through the heating said surface portion near the melting point of the anticathode or over the melting point of the anticathode, thereby generating an X-ray from the rotating anticathode.

Abstract: A coolant passage is formed inside the rotary shaft while an air passage is formed inside the casing. A mechanical seal is arranged between the coolant passage and the air passage. Leakage cooling water, which has leaked in the form of vapor from the mechanical seal, is relegated radially outwardly along with air by the action of a rotary vane, which is disposed in the air passage, and finally flows out of an air outlet. A coolant sensor may be provided to early detect the leakage water.

Abstract: A high-performance anode plate for a directly cooled rotary piston x-ray tube is formed of a high-temperature-resistant material such as tungsten, molybdenum or a combination of both materials. In the region of the focal spot path, the underside of the anode plate is shaped, and/or in this region a different highly heat-conductive material is inserted or applied, such that an improved heat dissipation and thus a lower temperature gradient results.

Abstract: The present invention relates to a device for generating X-rays having a source for emitting electrons, a carrier which is provided with a material which generates X-rays as a result of the incidence of electrons, and a bearing by means of which the carrier is journalled so as to be rotatable about an axis of rotation, the device further having a chamber that is bounded by a heat transferring surface of the carrier and by a heat transferring surface of the first bearing member, and that is at least partially filled with a heat transferring material, the material being urged, during operation, towards both heat transferring surfaces so that a relatively high rate of heat transfer is obtained between the heat transferring surfaces and the transferring material, which is not affected when the transferring surfaces thermally deform at relatively high temperatures because the transferring material will follow deformations of the heat tranferring surfaces such that the reduction of the overall rate of heat transfer

Abstract: An X-ray anode is produced by scoring at least a region of a surface of the anode, on which electrons are incident, with a number of defined microslits, thereby making the surface, or at least the region thereof, highly thermally stressable.

Abstract: A method for preventing overheating of an X-ray apparatus. The method includes controlling an X-ray tube and an X-ray detector which are opposed to each other with a subject between them so as to acquire projection data concerning the subject, estimating quantities of heat dissipated from the X-ray tube and a high-voltage generator that supplies power to the X-ray tube during the acquisition, and optimizing a control parameter, which is used to control the X-ray tube and the high-voltage generator, on the basis of estimates of the quantities of heat dissipated during the acquisition so as to prevent overheat of the X-ray tube and the high-voltage generator.

Abstract: In an X-ray tube having a metallic vacuum housing containing an anode and a cathode which emits an electron beam proceeding from said cathode to said anode, the metallic vacuum housing is improved by providing several notches into the surface of the metallic vacuum housing.

Abstract: The invention relates to a device (1) for generating X-rays (57). The device comprises a source (7) for emitting electrons (53) and a liquid metal for emitting X-rays as a result of the incidence of electrons. The device further comprises a displacing member (11) for displacing the liquid metal through an impingement position (55) where the electrons emitted by the source impinge upon the liquid metal. As a result of the flow of liquid metal through the impingement position the heat, which is generated in the impingement position as a result of the incidence of the electrons upon the liquid metal, is transported away from the impingement position. According to the invention, the displacing member (11) has a contact surface (61), which is in contact with the liquid metal in the impingement position (55), and a driving member (31) for moving the contact surface in a direction which, in the impingement position, is substantially parallel to the contact surface.

Abstract: An x-ray tube (10) includes an evacuated envelope (14), a cathode assembly (20) located in the evacuated envelope and a disk shaped anode assembly (18) located in the evacuated envelope in operative relationship with the cathode assembly for generating x-rays (40). The anode assembly includes an axis of rotation (26) and a target substrate (28) facing the cathode assembly. A heat pipe (33) is located within the anode assembly (18). The heat pipe is comprised of an evacuated shell (60) and is vacuum sealed at a first end (70) of the shell and at a second end (72). A material (80, 82) within the shell is a working fluid for the heat pipe at x-ray tube operating conditions. A porous wick (62) is located within the shell and the wick has a length extending from the first end (70) of the shell to the second end (72) of the shell. A shield (64) is attached to the wick to reduce working fluid loss out of the wick during x-ray tube operation.

Abstract: A method for assembling a rotating X-ray tube, the X-ray tube having a cathode for emitting electrons, and a rotor and a bearing assembly for facilitating rotation of an anode. The method includes using an interference fit assembly between the bearing assembly and the rotor to provide a joint having balance retention. The using interference fit assembly further includes selecting a rotor hub of the rotor having a coefficient of thermal expansion which results in a composite coefficient of thermal expansion for the rotor assembly which closely matches that of a shaft of the bearing assembly. An interference fit joint between a shaft extending from a bearing assembly and a rotor hub is also disclosed, wherein the joint is completed without using any mechanical fasteners or metallurgical bonding, yet can carry all of the operational loads placed on the joint.

Abstract: An X-ray system (10) includes an X-ray tube (16) that has a temperature sensor (22) coupled thereto. The temperature sensor (22) may be included in a heat exchanger (18). The temperature sensor (22) generates a temperature signal that is provided to a controller (12). The controller (12) generates a fan speed control signal that is used to control the speed of the fan (20) in response to the temperature signal.