Abstract:
A turbo-molecular pump has components including a stator column, a rotary shaft, and a blade connected to the rotary shaft for rotation therewith. A radiation temperature measuring apparatus has a radiation thermometer for measuring a temperature of a preselected one of the components of the turbo-molecular pump disposed within a view angle range of the radiation thermometer and in accordance with heat energy radiated from the preselected component. A hood is connected to the radiation thermometer so as to not interfere with the view angle range of the radiation thermometer and is configured to block heat energy radiated from components of the turbo-molecular pump disposed outside of the view angle range of the radiation thermometer.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a turbo-molecular pump equipped with a radiation temperature measuring apparatus capable of measuring the temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object and improved in terms of accuracy in temperature measurement. 
   2. Description of the Related Art 
   With the recent development of electronics, there is a rapid increase in the demand for semiconductor devices such as memories and integrated circuits. 
   Such semiconductor devices are manufactured, for example, by doping a semiconductor substrate of very high purity with impurities to impart electrical properties thereto or by forming minute circuits on a semiconductor substrate through etching. 
   Furthermore, such manufacturing operation has to be conducted in a high-vacuum chamber in order to avoid the influence of dust, etc. in the air. To evacuate the chamber, a vacuum pump is generally used. In particular, as the vacuum pump, a turbo-molecular pump, which involves little residual gas and is easy to maintain, is widely used. 
   Further, a semiconductor manufacturing process involves a number of steps in which various process gases act on a semiconductor substrate, and the turbo-molecular pump is used not only to evacuate the chamber but also to discharge these process gases from the chamber.  FIG. 6  is a longitudinal sectional view of the turbo-molecular pump. 
   In  FIG. 6 , a turbo-molecular pump  100  has at the upper end of an outer cylinder  127  an intake port  101 . Inside the outer cylinder  127 , there is provided a rotor  103  in the periphery of which a plurality of rotary blades  102   a ,  102   b ,  102   c , . . . constituting turbine blades for sucking and discharging gas are formed radially in a number of stages. 
   Mounted at the center of the rotor  103  is a rotor shaft  113 , which is supported so as to levitate and be positionally controlled by, for example, a so-called 5-axis control magnetic bearing. 
   An upper radial electromagnet  104  is composed of four electromagnets arranged in pairs in the X- and Y-axis directions. An upper radial sensor  107  composed of four electromagnets is provided in close vicinity to and in correspondence with the upper radial electromagnet  104 . The upper radial sensor  107  detects radial displacement of the rotor  103  and sends the detection result to a control device (not shown). 
   Based on the displacement signal detected by the upper radial sensor  107 , the control device controls the excitation of the upper radial electromagnet  104  through a compensation circuit with a PID adjusting function to adjust the upper radial position of the rotor shaft  113 . 
   The rotor shaft  113  is formed of a material with high magnetic permeability (e.g., iron) or the like, and is attracted by the magnetic force of the upper radial electromagnet  104 . Such adjustment is performed independently in the X- and Y-axis directions. 
   Further, a lower radial electromagnet  105  and a lower radial sensor  108  are arranged in the same manner as the upper radial electromagnet  104  and the upper radial sensor  107 , adjusting the lower radial position of the rotor shaft  113  in the same manner as the upper radial position thereof. 
   Further, there are arranged axial electromagnets  106 A and  106 B, with a metal disc  111  provided on the lower portion of the rotor shaft  113  being therebetween. The metal disc  111  is formed of a material with high magnetic permeability such as iron. To detect axial displacement of the rotor shaft  113 , there is provided an axial sensor  109 , whose axial displacement signal is transmitted to the control device. 
   Furthermore, based on this axial displacement signal, the axial electromagnets  106 A and  106 B are excitation-controlled through the compensation circuit with PID adjusting function of the control device. The axial electromagnet  106 A magnetically attracts the metal disc  111  upwardly, and the axial electromagnet  106 B attracts the metal disc  111  downwardly. 
   In this way, the control device properly adjusts the magnetic force applied to the metal disc  111  by the axial electromagnets  106 A and  106 B to cause the rotor shaft  113  to magnetically levitate in the axial direction and to support it in a non-contact fashion. 
   A motor  121  is equipped with a plurality of magnetic poles circumferentially arranged so as to surround the rotor shaft  113 . Each magnetic pole is controlled by the control device so as to rotate the rotor shaft  113  through an electromagnetic force acting between it and the rotor shaft  113 . 
   Further, an RPM sensor  110  is mounted to the lower end of the rotor shaft  113 . The control device detects the RPM of the rotor shaft  113  from a detection signal of the RPM sensor  110 . 
   Further, in the vicinity, for example, of the lower radial sensor  108 , there is mounted a phase sensor (not shown), which detects the rotation phase of the rotor shaft  113 . By using the detection signals of the phase sensor and the RPM sensor  110 , the control device detects the position of each magnetic pole. 
   A plurality of stationary blades  123   a ,  123   b ,  123   c , . . . are arranged with slight gaps between the rotary blades  102   a ,  102   b ,  102   c , . . . . The rotary blades  102   a ,  102   b ,  102   c , . . . downwardly transfer the molecules of exhaust gas through collision. For this purpose, they are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft  113 . 
   Similarly, the stationary blades  123  are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft  113 , and are arranged alternately with the rotary blades  102  so as to extend toward the inner periphery of the outer cylinder  127 . 
   Furthermore, each stationary blade  123  is supported, with its one end being inserted between a plurality of stationary blade spacers  125   a ,  125   b ,  125   c , . . . stacked together. 
   The stationary blade spacers  125  are ring-like members formed, for example, of a metal, such as aluminum, iron, stainless steel, or copper, or an alloy containing some of these metals as the components. 
   In the outer periphery of the stationary blade spacers  125 , there is secured in position the outer cylinder  127  with a slight gap therebetween. At the bottom of the outer cylinder  127 , there is arranged a base portion  129 , and a threaded spacer  131  is arranged between the lower portion of the stationary blade spacers  125  and the base portion  129 . Additionally, formed in the lower portion of the threaded spacer  131  in the base portion  129  is an exhaust port  133 , which communicates with the exterior. 
   The threaded spacer  131  is a cylindrical member formed of a metal, such as aluminum, copper, stainless steel, or iron, or an alloy containing some of these metals as the components, and has in its inner peripheral surface a plurality of spiral thread grooves  131   a.    
   The spiral thread grooves  131   a  are oriented such that when the molecules of exhaust gas move in the rotating direction of the rotor  103 , these molecules are transferred to the exhaust port  133 . 
   At the lowermost portion of the rotary blades  102   a ,  102   b ,  102   c , . . . of the rotor  103 , a rotary blade  102   d  extends vertically downwards. The outer peripheral surface of this rotary blade  102   d  is cylindrical and protrudes toward the inner peripheral surface of the threaded spacer  131  so as to be in close vicinity to the inner peripheral surface of the threaded spacer  131  with a predetermined gap therebetween. 
   The base portion  129  is a disc-like member forming the base portion of the turbo-molecular pump  100 , and is generally formed of a metal such as iron, aluminum, or stainless steel. 
   The base portion  129  physically supports the turbo-molecular pump  100 , and also serves as a heat conduction path, so that it is desirable for the base portion  129  to be formed of a metal, such as iron, aluminum, or copper, which has rigidity and high heat conductivity. 
   In this construction, when the rotary blades  102  are driven by the motor  121  to rotate with the rotor shaft  113 , exhaust gas from a chamber is taken in through the intake port  101  by the action of the rotary blades  102  and the stationary blades  123 . 
   The exhaust gas taken in through the intake port  101  flows between the rotary blades  102  and the stationary blades  123  and is transferred to the base portion  129 . At this time, the temperature of the rotary blades  102  rises due to the frictional heat generated when the exhaust gas comes into contact with the rotary blades  102  and the conduction of the heat generated in the motor  121 , and the heat thus generated is transmitted to the stationary blades  123  side through radiation or conduction by the molecules of the exhaust gas. 
   The stationary blade spacers  125  are joined together in the outer periphery thereof, and transmit to the exterior the heat received by the stationary blades  123  from the rotary blades  102 , the frictional heat generated when the exhaust gas comes into contact with the stationary blades  123 , etc. 
   The exhaust gas transferred to the base portion  129  is sent to the exhaust port  133  while being guided by the thread grooves  131   a  of the threaded spacer  131 . 
   While in the above-described example the threaded spacer  131  is arranged in the outer periphery of the rotary blade  102   d , and the thread grooves  131   a  are formed in the inner peripheral surface of the threaded spacer  131 , it is also possible, in some cases, to form the thread grooves in the outer peripheral surface of the rotary blade  102   d  and to arrange in its periphery a spacer having a cylindrical inner surface. 
   Further, in order that the gas taken in through the intake port  101  may not enter the electrical component section constituted of the motor  121 , the lower radial electromagnet  105 , the lower radial sensor  108 , the upper radial electromagnet  104 , the upper radial sensor  107 , etc., the electrical component section is covered with a stator column  122 , and the interior of the electrical component section is maintained at a predetermined pressure by a purge gas. 
   For this purpose, piping (not shown) is arranged in the base portion  129 , and the purge gas is introduced through this piping. The purge gas introduced is sent to the exhaust port  133  by way of the gap between a protective bearing  120  and the rotor shaft  113 , the gap between the rotor and stator of the motor  121 , and the gap between the stator column  122  and the rotary blades  102 . 
   In some cases, to increase reactivity, the process gas is introduced into the chamber while at high temperature. And, when cooled to a certain temperature while being discharged, the process gas may solidify and deposit a product in the exhaust system. 
   Furthermore, in some cases, such process gas attains low temperature in the turbo-molecular pump  100  to solidify, adhering to the inner surfaces of the turbo-molecular pump  100  to be deposited thereon. 
   As can be seen from a vapor pressure curve, when, for example, SiCl 4  is used as the process gas in an Al etching apparatus, a solid product (e.g., AlCl 3 ) is deposited to adhere to the inner surfaces of the turbo-molecular pump  100  under low vacuum (760 [torr] to 10 −2  [torr]) and at low temperature (approximately 20 [C]). 
   When a deposit substance from the process gas is deposited on the inner surfaces of the turbo-molecular pump  100 , this substance narrows the pump flow passage, resulting in a deterioration in the performance of the turbo-molecular pump  100 . 
   The solidification and adhesion of such product is likely to occur in the portion near the exhaust port, which is at low temperature, and, in particular, near the rotary blades  102  and the threaded spacer  131 . This has conventionally been coped with by winding a heater, a water-cooling tube, etc. (not shown) around the base portion  129 , etc., and embedding a temperature sensor (e.g., thermistor) (not shown) in, for example, the base portion  129 , maintaining the base portion  129  at a fixed temperature based on a signal from this temperature sensor through heating by the heater or cooling by the water-cooling tube (which is hereinafter referred to as TMS (temperature management system)). 
   Prior to normal operation of the turbo-molecular pump  100 , the turbo-molecular pump  100 , the semiconductor manufacturing apparatus, and the piping connecting them are heated at temperature over fixed one for a fixed period of time for degassing (hereinafter referred to as baking). Then, they are restored to room temperature, whereby it is possible to increase the degree of vacuum of the interior of the intake port of the turbo-molecular pump  100  and the interior of the chamber (which leads to an improvement in so-called ultimate pressure). 
   When the temperature of the rotary blades  102  of the turbo-molecular pump  100  exceeds the long-term permissible heat-resistant temperature (which is 150 [C] when the rotary blades are formed of an aluminum alloy), the turbo-molecular pump is affected by heat, and mainly the rotary blades  102  undergo a deterioration in strength, suffering breakage in the worst case. 
   The higher the set temperature of the TMS, the less likely the deposition of the product. Thus, it is desirable for the set temperature to be as high as possible. However, raising this set temperature results in a rise of the temperature of the portion around the rotary blades  102 , which hinders heat dissipation of the rotary blades  102 . As a result, the temperature of the rotary blades  102  rises, so that there is a fear of the service life of the rotary blades  102  being shortened and their suffering breakage or the like. 
   Similarly, the higher the baking temperature, the more improvement in ultimate pressure. Thus, it is desirable for the baking temperature to be as high as possible. However, when the baking temperature is too high, the temperature of the rotary blades  102  rises, so that there is a fear of the service life of the rotary blades  102  being shortened due to the heat. 
   Thus, it is desirable to monitor the temperature of the rotary blades  102 . Conventionally, as shown, for example, in  FIG. 6 , a radiation thermometer  141  is embedded in the base portion  129 , and directed to the bottom surface of the rotary blade  102   d . However, the monitoring of the temperature of the rotary blade  102   d  involves the following inconvenience. 
   The portion of the base portion  129  in which the radiation thermometer  141  is embedded is susceptible to product deposition, which means the accuracy in temperature measurement is likely to be affected by the product. 
   Further, the radiation thermometer  141  is designed such that the closer to 1 the emissivity of the measurement object, the more accurate the measurement. 
   However, the material of the rotary blades  102  generally includes an aluminum alloy with nickel plating, etc. so that the emissivity of the blade surfaces is as low as 0.1 or less, resulting in a rather poor measurement accuracy. 
   Further, with respect to the measurement object, there exists a view angle (angle α in  FIG. 7 ) for the radiation thermometer  141  within which measurement is possible. And, when, as shown in  FIG. 7 , the surface constituting the measurement object is the bottom surface of the rotary blade  102   d , it is subject to the influence of backlight, and radiation heat from a non-measurement object outside the measurement region indicated by the view angle α, such as the base portion  129 , enters the radiation thermometer  141  directly or after being reflected, resulting in a rather poor measurement accuracy. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above-mentioned problem in the prior art. It is an object of the present invention to provide a turbo-molecular pump equipped with a radiation temperature measuring apparatus capable of measuring the temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object and improved in terms of accuracy in temperature measurement. 
   Therefore, according to a structure of the present invention, a radiation temperature measuring apparatus for a turbo-molecular pump includes: 
   a radiation thermometer for measuring a temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object; and 
   a hood arranged so as not to interfere with a view angle range of the radiation thermometer and adapted to block radiation heat from a non-measurement object outside the view angle range. 
   In the present invention, the hood is arranged so as to surround the view angle range of the radiation thermometer, whereby radiation heat from a non-measurement object is blocked by the hood and does not easily enter the interior of the hood, thereby making it possible to improve the accuracy in temperature measurement. 
   Further, the inner surface of the hood may be coated with a coating material having an emissivity higher than that of an aluminum alloy or nickel. 
   Due to this arrangement, radiation heat entering the hood is easily absorbed, and radiation heat from a non-measurement object is reflected to prevent it from entering the radiation thermometer, making it possible to improve the accuracy in the measurement of the temperature of the measurement object. 
   Further, according to the present invention, there is provided a radiation temperature measuring apparatus for a turbo-molecular pump including: 
   a radiation thermometer for measuring a temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object; and 
   a groove in a semispherical configuration or with a semicircular section or a section with a corner of R 1  or more formed in a measurement object so as to include a view diameter which is a range enclosed through crossing of a view angle range of the radiation thermometer and the measurement object. 
   Without such groove, the radiation heat from a non-measurement object is reflected by the surface constituting the measurement object and is likely to enter the radiation thermometer, thereby deteriorating the accuracy in temperature measurement. However, due to the provision of a groove which is semispherical or whose section is semicircular or whose corner is R 1  or more in the surface constituting the measurement object, if radiation heat from a non-measurement object enters the measurement object to be reflected by the surface constituting the measurement object, it does not easily enter the radiation thermometer, thereby making it possible to improve the accuracy in temperature measurement. 
   Further, the surface of the groove may be coated with a coating material having an emissivity higher than that of an aluminum alloy or nickel. 
   Due to this arrangement, the emissivity of the measurement object becomes higher compared with that when there is no coating applied thereto. 
   Further, according to the present invention, there is provided a radiation temperature measuring apparatus for a turbo-molecular pump including: 
   a radiation thermometer for measuring a temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object; 
   a hood arranged so as not to interfere with a view angle range of the radiation thermometer and adapted to block radiation heat radiated from a non-measurement object outside the view angle range; and 
   a groove in a semispherical configuration or with a semicircular section or a section with a corner of R 1  or more formed in a measurement object so as to include a range enclosed through crossing of an imaginary line defined by imaginarily extending a leading edge of the hood and the measurement object. 
   The edge line of the opening of the groove is situated outside the range surrounded by the imaginary line defined by the view angle of the radiation thermometer and the groove crossing the same, so that it is possible to prevent more effectively the radiation heat from a non-measurement object from being reflected by the surface constituting the measurement object and entering the sensor portion of the radiation thermometer. 
   Preferably, the radiation thermometer of the radiation temperature measuring apparatus is mounted on a stator column of the turbo-molecular pump. That is, direct passage of the process gas is not allowed in the gap between the stator column and the rotary blades, so that as compared with the case where the radiation thermometer is embedded in the base portion, adhesion of the product is less likely to occur. Thus, it is possible to prevent the product from being deposited in the groove to change the emissivity of the measurement object and to prevent the product from being deposited in the optical system of the radiation thermometer to change the measurement accuracy. 
   Further, it is also desirable to mount the radiation thermometer to a spacer. In this case, as compared with the case where the radiation thermometer is embedded in the base portion, the pressure is lower although passage of the process gas is allowed, with the temperature being high, so that adhesion of the product is less likely to occur. Thus, it is possible to prevent the product from being deposited in the groove to change the emissivity of the measurement object and to prevent the product from being deposited in the optical system of the radiation thermometer to change the measurement accuracy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a schematic diagram showing a first embodiment of the present invention; 
       FIG. 2  is an enlarged view of a radiation thermometer and a groove; 
       FIG. 3  is an enlarged view of a groove with a corner of R 1  or more; 
       FIG. 4  is a diagram showing how, when there is no groove, radiation heat from a surface in the non-measurement range is reflected and enters the radiation thermometer; 
       FIG. 5  is a schematic diagram showing a second embodiment of the present invention; 
       FIG. 6  is a longitudinal sectional view of a turbo-molecular pump; and 
       FIG. 7  is a diagram showing how radiation heat from a surface in a non-measurement range is reflected and enters the radiation thermometer. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A first embodiment of the present invention will now be described.  FIG. 1  is a schematic diagram showing the first embodiment of the present invention. In the drawing, the components which are the same as those of  FIG. 6  are indicated with the same reference numerals, and a description of such components will be omitted. 
   In  FIG. 1 , in the inner side surface of the rotary blade  102   d , a groove  1  with a semicircular section is formed circumferentially and horizontally as seen in the drawing. The semicircular opening is directed toward the stator column  122 . A radiation thermometer  141  is embedded in the stator column  122  such that its sensor portion is opposed to the groove  1 . The radiation thermometer  141  is arranged near the motor  121 . 
     FIG. 2  is an enlarged view of the radiation thermometer  141  and the groove  1 . In  FIG. 2 , a conical hood  3  diverging toward the groove  1  is mounted to the radiation thermometer  141  so as to surround the view angle a of the radiation thermometer  141 . 
   The opening area of the groove  1  is larger than the area of the region of the inner peripheral surface of the rotary blade  102   d  surrounded by an imaginary line as defined by this inner peripheral surface and the imaginary extension of the diverging leading edge of the hood  3  crossing each other. That is, the edge line of the opening of the groove  1  is situated outside the imaginary circle as defined by the imaginary extension and the inner peripheral surface crossing each other. 
   Furthermore, the inner peripheral surface of the groove  1  and the inner side surface of the hood  3  are coated, as indicated at reference numeral  5 , with a coating material having an emissivity higher than that of an aluminum alloy or nickel. 
   In this construction, the hood  3  is arranged so as to surround the view angle α of the radiation thermometer  141 , so that radiation from the non-measurement range is blocked by the hood  3  and does not easily enter the interior of the hood  3 . Further, since the edge line of the opening of the groove  1  is situated outside the above-mentioned imaginary crossing circle, radiation heat from a surface in the non-measurement range is reflected by the surface of the rotary blade  102   d , and does not enter the sensor portion of the radiation thermometer  141 . 
   Further, the groove  1  and the radiation thermometer  141  are arranged in the region between the stator, column  122  and the rotary blade  102   d , where the purge gas, which is a pure gas, passes. And, as compared with the portion of the base portion  129  in which the radiation thermometer  141  is embedded as shown in  FIG. 6 , this region between the stator column  122  and the rotary blade  102   d  provides an environment relatively free from product deposition since the process gas does not pass therethrough directly. Thus, it is possible to prevent product deposition in the groove  1  leading to a change in the emissivity of the measurement object and to prevent product deposition in the optical system of the thermometer leading to a change in the measurement accuracy. 
   Further, due to the coating  5  of the inner peripheral surface of the groove  1  with a coating material having an emissivity higher than that of an aluminum alloy or nickel, the emissivity of the measurement object is higher than when there is no coating  5 , whereby it is possible to improve the accuracy in the measurement of the temperature of the object. 
   Further, by providing the coating  5  also on the inner side surface of the hood  3 , radiation heat entering the hood is easily absorbed, and radiation heat from a non-measurement object is reflected to prevent it from entering the radiation thermometer  141 , making it possible to improve the accuracy in the measurement of the temperature of the object. 
   When there is radiation heat from a surface in the non-measurement range, due to the semicircular section of the groove  1 , any radiation heat from a non-measurement object reflected by the surface constituting the measurement object does not easily enter the radiation thermometer, thus making it possible to improve the accuracy in temperature measurement. Of course, the groove  1  is not restricted to the peripheral one; it may also consist of a semispherical dent (in which case the section of the groove  1  is the same as that shown in FIG.  2 ). Further, the section of the groove  1  is not restricted to the semicircular one; as shown in  FIG. 3 , it may also be a rectangular one with a corner of R 1  or more. 
   Further, due to the provision of the hood  3 , it is possible to reduce the probability of radiation heat from a non-measurement object entering the sensor portion of the radiation thermometer  141  as compared with the case in which there is no hood  3 . Thus, it is possible to improve the accuracy in temperature measurement. 
   In the case where only the hood  3  is provided and no groove  1  is formed, radiation heat from a non-measurement object, as shown in  FIG. 4 , gets around the hood  3  and is reflected by the surface constituting the measurement object to enter the radiation thermometer  141 , resulting in a deterioration in the accuracy in temperature measurement. 
   The arrangement position for the groove  1  and the radiation thermometer  141  is not restricted to the region between the stator column  122  and the rotary blade  102   d  near the motor  121 ; it may also be position A or B encircled in FIG.  1 . 
   In the case of position A, the groove  1  and the radiation thermometer  141  are arranged between the stator column  122  and the rotary blade  102   d  near the upper radial electromagnet  104 . In this case, they are arranged, as in the above-described case, in the region between the stator column  122  and the rotary blade  102   d , where the purge gas, which is a pure gas, passes, and the region is less subject to product deposition, making it possible to further improve the accuracy in temperature measurement. 
   In the case of position B, the groove  1  and the radiation thermometer  141  are arranged in the region between the rotary blade  102   d  and the threaded spacer  131 . The radiation thermometer  141  is embedded in the body portion of the threaded spacer  131 , and the hood  3  can be arranged by utilizing the space of the thread grooves  131   a  of the threaded spacer  131 . 
   The groove  1  is circumferentially formed in the outer periphery of the rotary blade  102   d . In this case also, as compared with the case where the radiation thermometer  141  is embedded in the base portion  129  as shown in  FIG. 6 , although passage of the process gas is allowed, this region is at lower pressure and at higher temperature, so that it provides an environment less subject to product deposition. Thus, it is possible to prevent product deposition in the groove  1  leading to a change in the emissivity of the measurement object and to prevent product deposition in the optical system of the radiation thermometer leading to a change in the measurement accuracy. 
   Next, a second embodiment of the present invention will be described.  FIG. 5  is a schematic diagram showing the second embodiment of the present invention. The components which are the same as those of  FIG. 2  are indicated with the same reference numerals, and a description of such components will be omitted. 
   In  FIG. 5 , there is provided a cylindrical hood  7 , which is mounted to the outer peripheral wall portion of the cylinder of the radiation thermometer  141 . The hood  7  has at its bottom an opening  7   a , which is directed to the groove  1 . The hood  7  is arranged so as not to intersect the view angle α of the radiation thermometer  141  and as to protrude by a predetermined length from the leading edge of the radiation thermometer  141 . 
   This helps to obtain the same effect as that of the first embodiment of the present invention. 
   As described above, in accordance with the present invention, a hood is arranged so as to surround the view angle range of the radiation thermometer, whereby radiation heat from a non-measurement object is blocked by the hood and does not easily enter the interior of the hood, thereby making it possible to improve the accuracy in temperature measurement.