Abstract:
The invention provides a radiation sensor including a housing, an attenuator with at least one cavity for attenuating optical radiation, and a detector, as well as an optical attenuator including an attenuator body, an entrance with one multi-stage input opening or plural input openings, and means for transferring radiation inside of the attenuator body and then to a detector. The invention further provides methods for using the radiation sensor or the optical attenuator.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the benefit of U.S. Provisional Patent Applications Ser. No. 60/399,436 filed on Jul. 31, 2002, the entire disclosures of which are incorporated herein by reference. 

   TECHNICAL FIELD 
   The invention relates generally to radiation sensors and, more particularly, to a UV radiometer that includes a collection unit with an attenuator having an entrance with one multi-stage input opening or plural input openings, or with at least one cavity for attenuating optical radiation, a detector and electronics to measure UV dose and UV irradiance applied to products and materials in a UV curing system or in other UV exposure systems. 
   BACKGROUND OF INVENTION AND DESCRIPTION OF PRIOR ART 
   In measuring of UV or other light irradiance and cumulative dose inside of UV chambers as well as in UV curing systems or in any UV emitting environment as from an output of UV light guides, the performance and efficiency of, e.g., a UV curing system, can be distorted due to contamination and degradation of UV lamps. 
   In the prior art, several UV radiometers have been developed for portable and stationary devices. U.S. Pat. No. 5,514,871 and U.S. Pat. No. 6,278,120 describes radiation sensors for measuring levels of ultraviolet intensity. They were developed for measuring high intensity radiation and have similar design for optical attenuation, which result in a large overall size because several optical elements are needed to be placed in a linear fashion, i.e., with a detector immediately following an attenuation device and directed toward a radiation source. U.S. Pat. No. 5,382,799 describes a radiation sensor for measuring levels of ultraviolet intensity which has a smaller size of the attenuator but the attenuation device requires several distinct parts, such as a diffuser window, one or more Teflon® diffusers, an aperture plate separated from the Teflon® diffuser by an O-ring, a cut glass filter, a spacer, etc., which result in challenges for reproducibility of the desired attenuation. U.S. Pat. No. 5,497,004 describes a radiation sensor with an attenuator made of a quartz glass. This sensor requires one or several discrete steps of attenuation conducted via complex elements, such as a dispersive element comprises a quartz glass having interior boundary surfaces, and an optical filter for visible light, to achieve appropriate attenuation. 
   There are several variants of optical attenuators described in the U.S. Pat. No. 6,167,185, U.S. Pat. No. 6,351,329, U.S. Pat. No. 6,292,616, U.S. Pat. No. 6,404,970, which share the same deficiencies as described previously. 
   There is a need for a compact radiation sensor with high radiation tolerance and less frequent calibration to maintain and monitor the level of UV irradiation and dose received from the light emitting device and level of exposure to the materials inside an exposure unit. 
   SUMMARY OF INVENTION 
   It is an object of the present invention to improve optical sensor designs for measuring UV radiation, especially with in a UV curing system. 
   It is another object of the present invention to improve the performance of radiation sensors using an attenuator with a high level of attenuation, which protects the UV detector from degradation after exposure of the radiation sensor to high doses of UV radiation. 
   It is a further object of the present invention to provide a way for ease of calibration of the sensor during manufacturing and subsequent calibration efforts. 
   It is also an object of the present invention to improve radiation sensor tolerance and extend a time period between calibration using information about temperature and total accumulated dose during the sensor operation. 
   Other objects and advantages of the present invention may be seen from the following detailed description 
   In accordance with the present invention, the radiation sensor has multiple attenuators to receive a high level of attenuation, a small sized detector unit and allows for ease of adjustment for the sensitivity of different detectors. Preferably, the radiation sensor has a multi-cavity attenuator, which has inside means for adjusting and filtering radiation. The radiation sensor has a micro controller, which allows for correcting an output signal if it is affected by detector aging, optical part solarization or temperature. 
   The radiation sensor, according to the present invention, includes one or more simple and efficient filters made of plastic plates for correction of the spectral sensitivity of different photodiodes used therein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings in which like reference numerals designate like elements and wherein: 
       FIG. 1  shows the front view of one embodiment of an assembled radiation sensor with a multi-cavity attenuator according to the present invention. 
       FIG. 2A  shows the back view with a closed lid of the embodiment of a radiation sensor depicted in  FIG. 1 . 
       FIG. 2B  shows the back view of one embodiment of an open lid of the embodiment of a radiation sensor depicted in  FIG. 1 . 
       FIG. 2C  shows the back view of another embodiment of an open lid of the embodiment of a radiation sensor depicted in  FIG. 1  reconfigured to work with a surface mount photodiode. 
       FIG. 3  snows a schematic diagram of one embodiment of a radiation sensor according to the present invention. 
       FIG. 4  shows a multi-cavity attenuator with a detector according to the present invention. 
       FIG. 5A  shows an adjustable multi-cavity attenuator with a detector according to the present invention. 
       FIG. 5B  shows a multi-cavity attenuator with an improved cosine response according to the present invention. 
       FIG. 5C  shows a multi-cavity attenuator with more than one secondary cavity according to the present invention 
       FIG. 6  shows an embodiment of a UV sensor for sensing radiation density (irradiance) from different light guides according to the present invention. 
       FIG. 7A  shows another embodiment of a UV sensor for sensing radiation density (irradiance) from different light guides according to the present invention. 
       FIG. 7B  shows a UV sensor according to the present invention with an inserted 3 mm light guide. 
       FIG. 7C  shows a UV sensor according to the present invention with an inserted 5 mm light guide. 
       FIG. 7D  shows a UV sensor according to the present invention with an inserted 8 mm light guide. 
       FIG. 8  shows an operation sequence of a radiation detector according to the present invention. 
       FIG. 9A  shows a perspective view of the adjustable insert depicted in  FIG. 5A ; and  FIG. 9B  shows a perspective view of the insert depicted in  FIG. 5B . 
       FIG. 10  shows a spatial response of the multi-cavity attenuators depicted in  FIG. 5A  and  FIG. 5B . 
       FIG. 11  shows a spectral correction of G5842 photodiode using a 1.6 mm polyester plate. 
       FIG. 12  shows a spectral correction of G6262 photodiode using a 3 mm polycarbonate plate. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A radiation sensor according to the present invention is an optical electronic device for measuring UV irradiance from high intensity UV sources. One of the embodiments of the radiation sensor optimized for using in UV curing chambers comprises a housing, a housing lid, an attenuator, a detector, a preamplifier, an amplifier, a controller with an analog to digital converter, one or several push buttons, memory, a display, batteries and a power supply. The front view of the radiation sensor is shown in  FIG. 1 . A housing  1  has a display  2  and a Power button  3  and a Mode button  4 . The back view of the radiation sensor is shown in  FIG. 2A . The housing  1  has dimensions of 100 mm×100 mm×12 mm and is closed with a lid  56 . There is a thermo isolative material under the lid that protects any electronics inside from excessive heat during operation. The lid  56  is secured with screws  57  and has a window  5 . The view of the radiation sensor without lid is shown in  FIG. 2B . The housing  1  holds a printed circuit board  34 A and batteries  18 . The printed circuit board  34 A has an opening in the center with an adjustable insert  32 . The opposite side of the adjustable insert  32  is fixed inside of an attenuator  6 . The attenuator  6  is shown with a thin line as it is located under the printed circuit board  34 A and secured with screws  30 A through holes in the printed circuit board  34 A. A photodiode  34  is inserted in the attenuator  6  through another opening on the printed circuit board  34 A. The printed circuit board  34 A has a reserved place for soldering a surface mount photodiode  34 B. As the embodiment shown in  FIG. 2C , the printed circuit board  34 A has only the photodiode  34 B installed thereon. To work with the photodiode  34 B the same attenuator  6  is rotated around the insert  32  and secured with screws  30 A in a second position as shown in  FIG. 2C . For some embodiments, both photodiodes  34 ,  34 B are installed and the attenuator is modified to have one first cavity and two secondary cavities associated with both photodiode  34 ,  34 B. The photodiode  34  or the surface mounted photodiode  34 B can be a silicon carbide UV A, UV B, or UV C photodiode, a GaAsP UV photodiode, an AlGaN UV photodiode, and a GaN UV photodiode. 
   The radiation sensor, according to the present invention, can work with one or several photodiodes having a traditional package or surface mount package. The embodiment with several photodiodes allows receiving information about irradiance in several spectral ranges. 
   The schematic diagram of the radiation sensor according to the present invention is shown in  FIG. 3 . The radiation sensor has an attenuator  6 , a detector  7 (e.g., a photodiode), a preamplifier  8 , a scaling amplifier  9 , a controller  10  with an analog to digital converter  11  and an internal temperature sensor  12 , a Power pushbutton  3 , a Mode pushbutton  4 , a memory  13 , a RS-232 means  14 , a RS-232 connector  15 , an external temperature sensor  16 , a digital display  2 , batteries  18 , a power supply  19 , a real time clock  58 , etc. There is a connector  59  reserved for connecting an outside temperature sensor  59 A to be placed outside of the radiation sensor to measure an actual temperature inside of a UV chamber. 
   The design of a multi-cavity attenuator, according to the present invention, is shown in  FIG. 4 . The lid  120  has an entrance aperture  121  (diameter of 3 mm) with a window  122 . The printed circuit board  126 A has a hole under the window  122  to let light enter inside of the first cavity  124  (a cylindrical hole with a 5 mm diameter and a 7.5 mm depth) of an attenuator body  123  made of fluoropolymer or metal (such as aluminum or stainless steel) to scatter and redirect the light inside the first cavity  124 . The window  122  comprises a sapphire plate which has extremely high resistance to scratching. For some embodiments the window  122  is made as a positive lens to correct a spatial response of a radiation sensor. The attenuator body  123  is attached to the printed circuit board  126 A with screws  123 A and has a second cavity  125  (a cylindrical hole with a 8.5 diameter and a 7.5 mm depth), which directs scattered and attenuated light to a photodiode  126 . The internal surface of the first and second cavities comprises a machined surface of fluoropolymer or metal without any reflective or absorptive coatings. In case of a metal attenuator body, the machined surface is preferably polished to provide multiple reflection with low attenuation after each reflection. The radiation entered into the first cavity  124  is reflected, scattered and redirected therein, and only portion of it (less than 1%) enters into the second cavity  125 . There is a hole  123 C (diameter of 2 mm) in the wall  123 B (of 2 mm thick) between the first cavity  124  and the second cavity  125 . The radiation entered into the second cavity  125  is reflected, scattered and redirected therein such that it is again attenuated in more than  200  times. The size of the hole  123 C is chosen to obtain an appropriate total attenuation of attenuator because the amount of radiation that pass from the first cavity into the second cavity is approximately proportional to the surface area of the hole  123 C. Such a multi-cavity design provides of attenuator with a high level of attenuation and a small size so as to reduce the size of a radiation sensor comprising the attenuator. 
   The invention provides a compact, stable, resistant to high level of irradiance sensor which can be easily expanded to have many UV ranges. For example, one central cavity with input window can be surrounded with several (2, 3, 4, 5, 6 . . . ) cavities having photodetectors with different UV ranges. 
   Prior art radiation detectors do not use cavity to attenuate radiation. Usually, the walls of the prior art cavity walls do not reflect light, such as being made black or having a size and orientation that the radiation follows from an inlet to a filter or a diffuser and to output as a collimated beam. On the other hand, the invention is designed with cavity walls of a high reflection rate such that the radiation hits walls many times. 
   An adjustable attenuator with a detector is shown in  FIG. 5A . The lid  127  has an entrance aperture  128  (diameter of 3 mm) with a window  129 . The printed circuit board  134 A has a hole under the window  129  to let light enter inside of the first cavity  131  of an attenuator body  130 . The attenuator body  130  is attached to the printed circuit board  134 A with screws  130 A and has a second cavity  133 , which directs scattered and attenuated light to the photodiode  134 . An optical filter  135 A is placed in front the photodiode  134 . There is a hole  130 C in the wall  130 B between the first cavity  131  and the second cavity  133 . The first cavity  131  (a cylindrical hole with a 5 mm diameter and a 7.5 mm depth) has an adjustable insert  132  made as a brass tube polished inside and having an outside diameter 5 mm, an inner diameter 4 mm, and a 7.5 mm length. The adjustable insert  132  can be moved to change the open area of the hole  130 C to obtain an appropriate total attenuation of attenuator.  FIG. 9A  shows a perspective view of the adjustable insert  132 . The adjustable insert  132  has two notches  132 A on its upper end to rotate the insert with a screwdriver for an adjustment. On its lower end, it has a cut segment  1   32 B. By orientating the adjustable insert  132  differently relative to the hole  130 C, different amount of radiation will pass from the first cavity  124  into the second cavity  125 . In this embodiment, the interior surface of the insert  132  works as reflective surface of the first cavity  124 . After adjustment, the insert  132  is secured with a screw  132 A. The multi-cavity attenuator with such an adjustable insert operates in a much broader range of UV irradiance (e.g., from 100 W/cm2 to 0.5 W/cm2) and measures more accurately. For example, radiation sensors with maximum range 10 W/cm2 and 1 W/cm2 need different attenuation to bring an output signal from the photodiode into the optimal range in which the photodiode works lineally and without saturation. 
   The effects of a radiance incidence angle on a detector output is very important for many applications where light sources are different for calibration and for real measurements. An ideal irradiance detector has an angular response, which can be described as a cosine function of the angle of incidence. The proximity of the measured angular response to the theoretical cosine function shows the quality of a detector. The example of a theoretical cosine response in Polar and Cartesian Coordinates are shown in the International Light Measurement Handbook published by International Light, Inc. (Newburyport, Mass.) A multi-cavity attenuator with an improved cosine response is shown in  FIG. 5B . The lid  160  has a window  161 . A fluoropolymer tape  162  (e.g., a white PTFE tape according to Mil.Spec.T-27730A, minimum of 99% Polytetrafluoroethylene, made by McMaster-Carr, Chicago, Ill.) is secured a sapphire plate  166  to the window  161  with a washer  163 . The sapphire plate  166  has a first portion with a diameter approximately equal to a diameter of a hole of the lid  161  and a second portion with a diameter smaller than the diameter of the hole of the lid  161 . The printed circuit board  165  has a hole under the window  161  to let light enter inside of the first cavity  167  (a cylinder with a 5 mm diameter and a 7.5 mm deep) of an attenuator body  164  made of a fluoropolymer. The fluoropolymer has no absorption in visible and UV range and it is temperature resistant. It has white color and provides good diffuse reflection. The attenuator body  164  is attached to the printed circuit board  165  with screws  164 A and has a second cavity  168  (a cylinder of a 8.5 mm diameter and a 7.5 mm deep) which directs scattered and attenuated light to the photodiode  173 . The UV radiation from the first cavity  167  penetrates to the second cavity  168  through the semi transparable wall  164 B of 0.2–5 mm thick between them. The first cavity  167  has an insert  171  made as a brass tube polished inside. The insert  171  has an outside diameter 5 mm, an inner diameter 4 mm, and a 5 mm length. The insert is secured with a screw  172 .  FIG. 9B  shows a perspective view of the insert  171 . The length of the insert  171  and the thickness of the wall  1   64 B between the cavities are chosen to obtain an appropriate total attenuation of attenuator. The attenuator body  164  is wrapped with a layer of another fluoropolimer tape  169  and then with a layer of aluminum foil  170 . The fluoropolimer tape  19  and the aluminum foil  170  increase uniformity of a UV light field inside the first cavity and the second cavity to protect the fluoropolimer body from contamination and mechanical stress. The multi-cavity attenuator with a fluoropolimer tape directly under the window has a spatial response close to cosine as shown in  FIG. 10 . 
   Another embodiment of a multi-cavity attenuator with more than one secondary cavity is shown in  FIG. 5C . The lid  180  has a window  181 . A fluoropolymer tape  182  is secured near the window  181  with a washer  183 . The printed circuit board  185  has a hole under the window  181  to let light enter inside of the first cavity  187  (a cylinder with a 5 mm diameter and a 7.5 mm deep) of an attenuator body  184  made of a fluoropolymer. The attenuator body  184  is attached to the printed circuit board  185  with screws  184 A and has two secondary cavities  188 ,  189  (cylindrical holes of a 5 mm diameter and a 7.5 mm deep) which directs scattered and attenuated light to photodiodes  190  and  191  having different spectral ranges of sensitivity. The UV radiation from the first cavity  187  penetrates to both of the secondary cavities  188 ,  189  through the semi transparable wall  184 B and  184 C of 0.2–5 mm thick between them. The attenuator body  184  is wrapped with a layer of another fluoropolimer tape  192  and then with a layer of aluminum foil  193 . The photodiodes  190 ,  191  connected to an electrical schematic and work simultaneously to provide data about the irradiance in two different spectral ranges. In other embodiments, a multi-cavity attenuator has several secondary cavities therein, e.g. four secondary cavities connected to the front, back, right and left sides of the first cavity, each of which is associated with one respective photodiode, one respective optical filter or plastic correction filter. A radiation sensor with such embodiments measures irradiance in all spectral ranges important for specific application. In other embodiments, more than four small diameter secondary cavities are associated with the first cavity. 
   One embodiment of a UV sensor with an attenuator for measuring of the irradiance from UV light guides is shown in  FIG. 6 . An attenuator body  236  is made of metal and covered with a layer of a fluoropolimer tape  236 A and an aluminum foil  236 B. The attenuator body  236  has a main cavity  237 , several channels for inserting light guides with different diameters. Each channel has a beginning bigger diameter(e.g.,  238 A,  239 A,  240 A ) equal to the outer diameter of a corresponding light guide, for example 10 mm, 7 mm and 5 mm, to accommodate light guides with optical diameters of 8 mm, 5 mm and 3 mm respectively. Another section of each channel has a diameter slightly smaller (e.g.,  238 B,  239 B,  240 B) than outer diameter of the light guide, for example 9 mm, 6 mm and 4 mm, so as not to restrict radiation from the light guides of 8 mm, 5 mm and 3 mm. The channel parts  238 B,  239 B,  240 B are made with a polished surface and serve as a first cavity of a multi-cavity attenuator. The radiation enters the channel parts  238 B,  239 B,  240 B from the light guide. For example, an 8 mm light guide  254  is shown. The radiation gets first attenuation after reflection and scattering inside of the channel and through the end of the channel then enters into the main cavity  237 . Walls of the main cavity  237  reflects and scatters the radiation and deliver it to the UV photodiode  243  placed in a mortise of the attenuator body  236 . For some embodiments without enough attenuation, there is a scattering device  241  (with a 12 mm diameter) made of (1) an opal glass or a fluoropolimer film and (2) a UV long pass filter, which corrects a spectral range of UV photodiode  243  to have a specified spectral sensitivity. 
   An embodiment of a UV sensor with a multi-cavity attenuator for measuring of the irradiance from different UV light guides is shown in  FIG. 7 . An attenuator body  244  is made of metal and has a variable diameter channel  244 A having a 5 mm length of a 5 mm diameter, a 7.5 mm length of a 7 mm diameter, and a 7.5 mm length of a 10 mm diameter and a main cavity  244 B (a cylinder with a 4 mm length and a 15 mm diameter). A photodiode cover  245  has an opal glass insert  246  and a printed circuit board  249  with a photodiode  248 . The photodiode cover  245  and the printed circuit board  249  are attached to the attenuator body  244  with screws  250  and  251 . The variable diameter channel  244 A provides stable fixation for accommodating light guides with different diameters.  FIG. 7B  shows the UV radiation sensor with a 3 mm light guide  252  inserted in the channel of the attenuator body  244 .  FIG. 7C  shows the UV radiation sensor with a 5 mm light guide  252  inserted in the channel of the attenuator body  244 .  FIG. 7D  shows the UV radiation sensor with a 8 mm light guide  252  inserted in the channel of the attenuator body  244 . The attenuator body  244  has a polished internal surface in the main cavity  244 B and on the first two smaller diameter portions of the variable diameter channel  244 A. As shown in  FIG. 7B , for the 3 mm light guide, only one section of the main cavity serves as an attenuator. For the 5 mm light guide, two sections of the main cavity serve as an attenuator, and for the 8 mm light guide, three sections of the main cavity serve as an attenuator The depth of each step in the variable diameter channel is chosen to provide an appropriate attenuation for each diameter of a corresponding light guide. Such a UV radiation sensor with a variable diameter light guide channel and with several stages of attenuation as a single or multi-cavity attenuator, opal glass, a fluoropolimer film provides portable and efficient sensor for main industrial devices with UV light guides. 
   The attenuator design according to the invention also works for visible light or other wave length. The ones for UV A, UV B, UV C, visible, or their combination are used as examples. The dimensions for visible light or other wave length can be two times less or three times more. 
   An operation sequence of a radiation detector according to the present invention is shown in  FIG. 8 . At the beginning the radiation detector is in a Sleeping mode  101 . After the POWER button  3  (see  FIG. 3 ) is pressed a Setting mode  102  is activated and the controller  10  checks a voltage of batteries  18  and retrieves data of the last run of the measurements from the memory  13 . If the battery voltage is lower than a limit, a warning LOW BATTERY will be shown at the display  2 . After the Setting mode  102  is done, the display  2  works in Mode “1” in which the results of the last measurement from the memory  13  are shown on the display  2 . In  FIG. 1 , the first line of the display shows the total dose in Joules per Centimeter Square (e.g., 3.82 J/cm 2 ) and the second line shows the maximum irradiance during last run in Watts per Centimeter Square (e.g., 0.630 W/cm 2 ). After pressing the MODE button  4  the display  2  is switched from the Mode “1” into the Mode “2”. In the Mode “2,” the display  2  shows the maximum irradiance during the last run in Watts per Centimeter Square and time in seconds for the time when this maximum irradiance was detected. Pressing the MODE button  4  again, the display  2  is switched from the Mode “2” into the Mode “3”. In the Mode “3,” the display  2  shows the maximum temperature during the last run in degrees of Celsius and time in seconds for the time when this maximum temperature was detected. Pressing the MODE button  4  again returns the display  2  into the Mode “1”. If digits and units of measurement on the display  2  during the Modes “1”, “2” and “3” are not blinking, the data on the display are taken from the memory  13 . During the Modes “1”, “2” and “3,” the analog to digital converter (A/D converter)  11  in the controller  10  (see  FIG. 3 ) periodically measures outputs of the scaling amplifier  9  to check for the presence of UV radiation. 
   If the level of UV irradiance I C  exceeds a threshold I TR  (I C &gt;I TR ), the controller  10  automatically starts the Mode “4”. In this mode, the controller  10  constantly measures the outputs of the scaling amplifier  9  with the amplified output (×10). If the amplified output comes close to saturation, the controller  10  uses non-amplified output (×1). Using of two outputs increases the dynamic range of the radiation detector and allows measuring irradiance from 20 W/cm 2  to 0.001 W/cm 2 . The controller  10  continuously integrates irradiance data to find a cumulative dose from the beginning of the current run and shows results of current measurement on the display  2 . The first line of the display shows the dose in Joules per Centimeter Square and the second line shows the current irradiance during last run in Watts per Centimeter Square. Digits and units of measurement on the display during the modes “4” are blinking, that serves an indication that data on the display are results of running measurements. The controller  10  operates with the real time clock  58  and continuously saves in the memory  13  all data about the dose, the maximum irradiance together with time stamped data about momentarily levels of irradiance and temperature from temperature sensors. 
   In the Mode “4,” if the POWER button  3  or the MODE button  4  is pressed, the controller  10  stops running measurements, saves new data in the memory  13 , renew data about total cumulative dose measured since the last calibration, and activates the Mode “5” in which the results of the new measurement are shown on the display  2 . The first line of the display shows the total dose in Joules per Centimeter Square and the second line shows the maximum irradiance during new run in Watts per Centimeter Square. After pressing the MODE button  4 , the display  2  is switched from the Mode “5” into the Mode “6”. In the Mode “5,” the display  2  shows the maximum irradiance during new run in Watts per Centimeter Square and time in seconds for the time when this maximum irradiance was detected. By pressing the MODE button  4  again, the display  2  is switched from the Mode “6” into the Mode “7”. In the Mode “7,” the display  2  shows the maximum temperature during a new run in degrees of Celsius and time in seconds for the time when this maximum temperature was detected. By pressing the MODE button  4  again, the display  2  is returned into the Mode “5”. In the Modes “5”, “6” and “7,” digits on display are not blinking and units of measurement are blinking, that serves an indication that data on the display are results of the new run. To start manually a new run of measurements during any mode of operation the MODE button  4  should be pressed and hold. To turn off the radiation sensor during any mode of operation, the POWER button  3  should be pressed and hold. 
   The detector can be adjusted and calibrated such that a certain irradiance signal should give a predetermined current. The detector is adjusted and calibrated by using regulate means to transfer maximum radiation, putting a light guide with a standard known irradiance (which is measured with an independent calibrated sensor), reading an output of the radiation detector, and using the regulate means to transfer radiation to have a predetermined output signal. Accordingly, the detector is calibrated and ready for measurement. It has a specified sensitivity and an output current under the maximum irradiance which will not exceed allowed a current limit. 
   The radiation sensor according the present invention has a RS-232 means  14  comprising a RS-232 line driver and a RS-232 connector  15 . Any calibration information can be verified and corrected directly from a computer through a RS-232 port. After the radiation sensor finishes a current measurement, the RS-232 port is used to download an irradiance and temperature profile from the memory  13 . 
   The controller  10  also measures temperature signals from an internal temperature sensor  12 , an external temperature sensor  16 , and an outside temperature sensor  59 A that can be connected to the connector  59 . The internal temperature sensor  12  is a part of the controller  10  and monitors the controller temperature. The external temperature sensor  16  monitors the temperature in the radiation sensor housing near the UV detector. Those two sensors are used to start a sound signal if either temperature comes close to the safe limit and to turn off the power supply  19  if either temperature exceeds the set level to protect electronics. The controller  10  uses data from the external temperature sensor  16  to apply correction factors to the current readings of the A/D converter so as to compensate for a zero shift and a variation of sensitivity of the detector  7 , the preamplifier  8  and the scaling amplifier  9 . Compensation coefficients are stored in the memory  13  for continuously correcting the irradiance measurements during operation. 
   In some embodiments, the radiation sensor has an optical filter  135 A inside of the attenuator  130  (see  FIG. 5A ) to correct a spectral sensitivity of the photodiode  134 . For example a cheap GaAsP UV photodiode Model No. G5842 made by Hamamatsu Photonics K.K. (Shizuoka Pref., 430-8587, Japan) has a spectral response range from 260 nm to 400 nm and cannot be used as sensor for the UV A range without spectral correction with a long pass filter. A glass or interference optical filter can be used but they are expensive and usually have big dimensions. According to the present invention, a small polyester plate with thickness of 1 m to 4 mm can be used together with the GaAsP G5842 photodiode to detect light of 320 nm to 400 nm that corresponds to the UV A range.  FIG. 11  shows a spectral correction of a G5842 photodiode using a 1.6 mm polyester plate. A detector sensitivity for each specific wavelength is defined as a ratio of the detector output signal (e.g. output current for photodiodes) to irradiance level at the detector input, assuming that only narrow band radiation of this specific wavelength is present. Relative sensitivity for each wavelength is defined as a ratio of the detector sensitivity for this wavelength to the maximum detector sensitivity. The curve “a” shows the relative sensitivity of the G5842 photodiode without correction. The curve “b” shows the relative sensitivity of the photodiode with an additional 1.6 mm polyester plate for correction. The polyester plate absorbs radiation with a wavelength shorter than 320 nm forming consequently a sensitivity that corresponds to the UV A range (320–400 nm). Under the UV radiation, the polyester plate gradually changes transmission. The lifetime of the detector with the polyester long pass filter can be extended with a correction coefficient applied to the results of current measurements. The radiation sensor, after each run, renews data about the total cumulative dose measured after last calibration and the controller  10  applies a correction factor to compensate for variation in the detector sensitivity. Same correction methods are used if the detector changes its sensitivity after exposure to the UV radiation. 
   In some embodiments, the radiation sensor uses a cheap GaAsP photodiode G6262 by Hamamatsu with a spectral response range from 300 nm to 580 nm. The spectral response of the photodiode can be corrected with a long pass filter to make a detector for a visible light.  FIG. 12  shows a spectral correction of a G6262 photodiode using a 3 mm polycarbonate plate. The curve “a” shows the relative sensitivity of the G6262 photodiode without correction. The curve “b” shows the relative sensitivity of the photodiode with an additional 3 mm polycarbonate plate for correction. The polycarbonate plate absorbs radiation with wavelength shorter than 320 nm forming consequently a sensitivity that corresponds to the visible light range (400–580 nm). A glass or interference optical filter can be used, but they are expensive and usually have big dimensions. According to the present invention, a small polycarbonate plate with thickness of 1 m to 4 mm can be used together with the GaAsP G6262 photodiode to detect light of 400 nm to 580 nm. 
   Both embodiments in  FIGS. 11–12  described above use a cheap photodiode together with a small cheap plastic plate inside of the second cavity of the multi-cavity attenuator to form the spectral curve “b”. This solution provide a cheap, compact and reliable alternative to an expensive silicon carbide photodiode (SiC) which has an internal interference optical filter for UV A and to a bulky silicon (Si) photodiode with a glass or external interference optical filter. The outside temperature sensor  59 A is optionally connected to the connector  59 . The outside temperature sensor  59 A may be a microchip digital temperature sensor, e.g., Model No. LM 74 made by National Semiconductor (Santa Clara, Calif.) The temperature sensor  59 A is located on the small printed circuit board and protected from direct UV light with an aluminum foil. The aluminum foil serves as substrate for materials used in UV curing procedure, such as paint, glue or compound. The radiation sensor with the outside temperature sensor  59 A provides information of a real temperature profile that is very important for optimization of the technological procedure since the efficiency of the UV activation can be different for different temperatures and real temperature varies for different optical properties of the materials used. The outside temperature sensor  59 A may be made as a disposable unit to be replaced with a new sensor after each run or can be made as printed circuit board with the sensor having a disposable aluminum cover. 
   The radiation sensor according to the present invention is especially efficient for measuring high levels of UV irradiance in UV A, UV B and UV C ranges. It operates up to 20 W/cm 2  in UV A and UV B ranges and to 2 W/cm 2  in UV C and visible ranges. Such levels of irradiance are present in some UV curing equipment and at the output of some UV illuminating systems with UV light guides. The embodiment in  FIG. 6  is optimized for using with UV light guides having different diameters. One of light guides is inserted in a channel that corresponds its diameter. Light from the UV light guide enters the main cavity  237  through the cylindrical channels  238 B,  239 B or  240 B. Each of the cylindrical channels  238 A,  239 A or  240 A has a different depth of an enlarged diameter so as to stop the end of the light guide at the different distance from the channel end. After initial scattering and reflection in a cavity between a light guide end and an end of the cylindrical channel, the radiation enters main cavity  237 . After the scattering and reflection in main cavity  237 , the radiation is additionally attenuated with the scattering device  241  and passes through the UV long pass filter  242  to the detector  243 . The lengths and positions of the channels  238 B,  239 B,  240 B are chosen to obtain on the photodiode  243  an irradiance level corresponding to the irradiance level at the outputs of the respective light guide. For example, if the light guides deliver light beams to an identical UV power but with different cross sections, the irradiance is inversely proportional to the surface of the cross section. Therefore, the channel for the light guide with a bigger diameter is made longer and placed at the bigger distance from the photo detector  243 . 
   A more compact embodiment for a UV sensor with a light guide holder is shown in  FIG. 7A , which works in a similar way. The attenuator body  244  has a main cavity  244 A and a cylindrical channel with sections of different diameters  244 B.  FIG. 7B  shows a UV sensor with inserted 3 mm light guide.  FIG. 7C  shows a UV sensor with inserted 5 mm light guide.  FIG. 7D  shows a UV sensor with inserted 8 mm light guide. Light from the UV light guide enters the cylindrical channel. After initial scattering and reflection in the channel, the radiation enters the main cavity  244 A. After the scattering and reflection in main cavity  244 A, the radiation is additionally attenuated with the opal glass  246  and passes through a fluoropolimer film  247  to the photodiode  248 . The length of the parts with different diameters are chosen to obtain on the photodiode  248  an irradiance level that corresponds to the irradiance level at the outputs of the light guides. 
   The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification by taking UV as an example. However, the invention, which is intended to be protected, is not limited to the particular light or embodiments disclosed. The embodiments described herein are illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.