Abstract:
There is described an optical radiation sensor device for detecting radiation in a radiation field. The device comprises a sensor element capable of detecting and responding to incident radiation from the radiation field and a radiation window interposed between the sensor element and the radiation field. The radiation window comprises a non-circular (preferably square) shaped radiation transparent opening. The optical radiation sensor device can be used in a so-called dynamic manner while mitigating or obviating the detection errors resulting from the use of a circular-shaped attenuating aperture and/or angular (even minor) misalignment of the sensor device with respect to the array of radiation sources when multiple such circular-shaped attenuating apertures are used.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application claims the benefit under 35 U.S.C. §119(e) of provisional patent application Ser. No. 60/525,839, filed Dec. 1, 2003, the contents of which are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Generally, the present invention relates to an optical radiation sensor system. 
   2. Description of the Prior Art 
   Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems. 
   It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of microwatt seconds per square centimetre). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UV Max™ and Trojan UV Swift™, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the trade-names UV3000™ and UV4000™, employ the same principle to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of a treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:
         U.S. Pat. No. 4,482,809,   U.S. Pat. No. 4,872,980,   U.S. Pat. No. 5,006,244,   U.S. Pat. No. 5,418,370,   U.S. Pat. No. 5,471,063,   U.S. Pat. No. 5,504,335,   U.S. Pat. No. 5,539,210, and   U.S. Pat. No. 5,590,390 (Re.36,896).       

   In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water under treatment. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection or treatment process. The information so-obtained may be used to control lamp output to a desired level and/or determined when it would be desirable to clean the exterior of the protective sleeves typically used to contain the radiation lamp(s). 
   It is known in the art to monitor the ultraviolet radiation level by deploying one or more sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These sensor devices may be photodiodes, photoresistors or other devices that respond to the impingement of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (e.g., in volts or amperes) on output leads. 
   Conventional optical radiation sensors, by design or orientation, normally sense the output of only one lamp, typically one lamp which is adjacent to the sensor. If it is desirable to sense the radiation output of a number of lamps, it is possible to use an optical radiation sensor for each lamp. A problem with this approach is that the use of multiple sensors introduces uncertainties since there can be no assurance that the sensors are identical in their response. Specifically, vagaries in sensor materials can lead to vagaries in the signals which are sent by the sensors leading to a potential for false information being conveyed to the user of the system. 
   U.S. Pat. No. 6,512,234 [Sasges et al. (Sasges)] teaches an optical radiation sensor system which allows determination of lamp output information for a single lamp in an array of lamps. An advantage of the Sasges system is that a single sensor device can be moved with respect to the radiation field to allow determination of the dose delivered to the fluid (i.e., in place of the multiple sensors conventionally required as discussed above). More specifically, the optical radiation sensor taught by Sasges allows for on-line determination of ultraviolet (UV) transmittance of the fluid being treated in a UV radiation lamp array. 
   While optical radiation sensor taught by Sasges is a significant advance in the art, there is room for improvement. Specifically, the field of view of conventional sensor devices (e.g., photodiodes, photoresistors, etc.) is relatively large thereby making it possible for the sensor device to detect in a simultaneous manner the output of more than one lamp. This can be problematic if the object is to determine lamp output information for a single radiation source (e.g., elongate lamp) in an array of radiation sources (e.g., elongate lamps). 
   One solution to this problem is to restrict the field of view of the sensor device so that the sensor device can “see” only one lamp at any particular point in time. Restricting the field of view of the sensor device to one particular lamp can be accomplished by interposing an appropriately sized circular-shaped aperture between the sensor device and the array of radiation sources (e.g., elongate lamps). As will be described in more detail below, interposition of a circular-shaped attenuating aperture between a sensor device and an array of radiation sources (e.g., elongate lamps) can create a further problem. Specifically, as the particular radiation source (e.g., elongate lamp) and circular-shaped attenuating aperture are moved with respect to one another (typically, the latter will be moved with respect to the former), the area of the lamp “seen” by the sensor device changes. This change in area results in unwanted changes to the radiation intensity detected by the sensor device. 
   Further, restriction of the field of view of the sensor device so that the sensor device can only “see” one particular radiation source (e.g., elongate lamp) may be accomplished by interposing multiple decreasingly-sized, circular-shaped attenuating apertures between the sensor device and the array of radiation sources (e.g., elongate lamps). The use of such multiple apertures in this manner can result in the intensity of the radiation detected by the sensor device varying sharply as a function of the angular position of the sensor. In the result, any angular (even minor) misalignment of the sensor device with respect to the array of radiation sources will result in an unwanted significant change in detected intensity. 
   These problems can cause significant errors in detection of radiation intensity from the array of lamps, thereby undermining the reliability of the radiation sensor system. 
   Accordingly, it would be desirable to have a radiation sensor system which could be used in a dynamic application such as the Sasges sensor system referred to above while obviating or mitigating the detection errors referred to above resulting from the use of a circular-shaped attenuating aperture and/or angular (even minor) misalignment of the sensor device with respect to the array of radiation sources when multiple such circular-shaped attenuating apertures are utilized. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a novel optical radiation sensor device which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art. 
   Accordingly, in one of its aspects, the present invention provides an optical radiation sensor device for detecting radiation in a radiation field, the device comprising a sensor element capable of detecting and responding to incident radiation from the radiation field and a radiation window interposed between the sensor element and the radiation field, the radiation window comprising a non-circular shaped radiation transparent opening. 
   In one of its aspects, the present invention provides an optical radiation sensor device for detecting radiation in a radiation field comprising an elongate radiation source having a longitudinal axis, the device comprising a sensor element capable of detecting and responding to incident radiation from the radiation field and a radiation window interposed between the sensor element and the radiation field, the radiation window comprising a radiation transparent opening having a shape such that, upon relative movement (e.g., rotational or non-rotational) between the radiation source and the radiation transparent opening in a direction substantially transverse to the longitudinal axis from a first position to a second position, a first area of the lamp as a function of a second area of the window is substantially unchanged in the first position and the second position. 
   Thus, the present inventors have discovered a novel optical radiation sensor device which can be used in a so-called dynamic manner such as in the Sasges sensor system described above while mitigating or obviating the detection errors referred to above resulting from the use of a circular-shaped attenuating aperture and/or angular (even minor) misalignment of the sensor device with respect to the array of radiation sources when multiple such circular-shaped attenuating apertures are used. Specifically, in the present radiation, a radiation window is interposed between the sensor element and the radiation field. The radiation window is of a design such that the area of the radiation source (e.g., elongate lamp) “seen” by the radiation sensor device remains substantially unchanged as the radiation window is swept (e.g., rotationally or non-rotationally) by the radiation source (e.g., elongate lamp) in a dynamic sensor system such as the one taught by Sasges referred to above. In one preferred embodiment, the radiation window comprises a non-circular (e.g., square, rectangular, etc.) shaped radiation transparent opening. 
   The use of a radiation window in the present optical radiation device results in detection of a substantially constant signal by the sensor device while the entire width of the radiation source (e.g., elongate lamp) is within the field of view of the sensor. A further advantage of the present optical radiation sensor is that any variation of the signal due to a change in angle between the sensor device and the radiation source (e.g., elongate lamp) will be in the form of the so-called “cosine response” (discussed below) for which compensation can be readily implemented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will be described with reference to the accompanying drawings, wherein like reference numerals denote like parts, and in which: 
       FIGS. 1   a  and  1   b  illustrate a schematic view of a prior art optical radiation sensor device; 
       FIG. 2  illustrates the response of an optical radiation sensor device such as the one in  FIG. 1  to ultraviolet radiation of constant intensity as a function of sensor angle to the radiation source; 
       FIG. 3  illustrates the field of view of a sensor with attenuation apertures of different shape (circular and square); 
       FIG. 4  illustrates a schematic view of a sensor with attenuating apertures relative to a radiation source; 
       FIGS. 5   a ,  5   b  and  5   c  illustrate a schematic exterior view of a sensor device in accordance with the present invention; and 
       FIGS. 6-7  illustrate the response of an optical radiation sensor device such as the one in  FIGS. 5   a ,  5   b , and  5   c  to ultraviolet radiation of constant intensity as a function of sensor angle to the radiation source. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Prior to describing the preferred embodiments of the present invention, a brief description will be presented concerning the prior art approach referred to above. 
   Thus, with reference to  FIGS. 1   a  and  1   b , there is illustrated an optical radiation sensor device  100  comprising a radiation sensor element  10  disposed at a proximal end thereof and a first radiation transparent window  15  disposed at a distal end thereof. Interposed between radiation transparent window  15  and sensing element  10  is an attenuating disk  20  provided with an aperture  25 . Of note, window  15  and aperture  25  are both circular in shape with the former having a larger diameter than the latter. 
   In this embodiment, window  15  serves as a so-called second aperture and aperture  25  serves as a so-called first aperture. The specific diameters and relative displacement of these two apertures in sensor device  100  is such that there is achieved a field of view of ±10.5° relative to the concentric axis through the first aperture and the second aperture. This facilitates keeping one radiation source in view when the radiation source is located along the concentric axis. 
   When the first aperture is chosen to have the diameter of 0.075 in. and the second aperture is chosen to have a diameter of 0.125 in. The spacing between the sensing element and the first aperture was 0.110 in. whereas the spacing between the first aperture and the second aperture was 0.232 in. This yields a field of view of 10.5°. The angular response data of the sensor device is shown in  FIG. 2 . Thus, as the radiation source comes into the field of view of the sensor, the normalized intensity rises to the maximum value near 0° then decreases as the radiation source leaves the field of view. The angular reach with a so-called “cosine response” is relatively narrow—i.e., ±1°. Unfortunately, this means that the detected intensity of ultraviolet radiation will quickly decrease if the alignment of the sensor device is outside the limits of ±1°. 
   As stated above, the present optical radiation sensor device mitigates or obviates the problems associated with using circular-shaped attenuating apertures in the design of the sensor device. This is achieved by using, for example, a non-circular (e.g., square, rectangular, etc.) shaped radiation transparent opening or aperture. In other words, the radiation window is of a design such that the area of the radiation source (e.g., elongate lamp) “seen” by the radiation sensor device remains substantially unchanged as the radiation window is swept by the radiation source (e.g., elongate lamp) in a dynamic sensor system. 
   This can be seen with reference to  FIG. 3 . Specifically, when a circular-shaped attenuating aperture is used in the sensor device, the area of the lamp in the field of view (i.e., within the area of the circular aperture) of the sensor is constantly changing from when the lamp first enters the field of view to when the lamp leaves the field of view—i.e., regardless of whether the lamp is wholly or partially within the field of view of the sensor device. In contrast, when a square aperture is used, once the lamp is wholly within the field of view (i.e., within the area of the square aperture), the area of the lamp in the field of view is unchanged until the lamp starts to leave the field of view. 
   The intensity of radiation sensed will be in proportion to the area of the lamp in the field of view of the sensor. In the result, the intensity of the radiation when a circular-shaped attenuating aperture is used will be constantly changing whereas that seen for the square-shaped attenuating aperture (a preferred embodiment of the present invention) will result in a substantially constant intensity reading once both sides of the lamp are within the field of view. 
   With the square-shaped attenuating aperture preferred embodiment of the present optical radiation sensor device, the change of intensity will occur (typically a reduction) when the sensing device is tilted away from the radiation source and varies as the cosine of the angle of the sensor relative to the lamp by prescribed angle (θ) as shown in  FIG. 4 . 
   Thus, a particularly preferred form of the present optical radiation sensor device is to utilize square-shaped or rectangular-shaped attenuating apertures (other shapes are also possible) in place of the conventional circular-shaped attenuating apertures used in the prior art approach discussed above with reference to  FIGS. 1-2 . Of course, those of skill in the art, will recognize that the particular shape of the attenuating aperture is not restricted provided that when the lamp is fully contained in the field of view, the surface area of the lamp in the field of view is substantially unchanged for at least two location points at which the radiation intensity may be determined. 
   In a preferred example, the sensor device of  FIG. 1  was modified to use a square-shaped attenuating aperture such that the first aperture was a 0.075 in.×0.075 in. square and the second aperture was a 0.125 in.×0.125 in. square. The relative spacing between the first aperture, the second aperture and the sensing element was not changed from that of  FIGS. 1   a  and  1   b  discussed above. This also yields a field of view of 10.5°. A schematic view of such a sensor device is shown in  FIGS. 5   a ,  5   b  and  5   c . In  FIGS. 5   a ,  5   b  and  5   c , the same reference numerals in  FIGS. 1   a  and  1   b  are used to denote like elements in  FIGS. 5   a ,  5   b  and  5   c . The principal difference in  FIGS. 5 ,  5   b  and  5   c  is that the first aperture and second aperture are both square-shaped. 
   With reference to  FIG. 6 , there is shown the angular response data using the optical radiation sensor device illustrated in  FIG. 5 . For this optical radiation sensor device, the angular range with a cosine response is ±2.5°—i.e., a significant increase over the angular range seen using the optical radiation sensor device of  FIG. 1  notwithstanding the fact that the field of view in both devices is the same. Visually, it can be seen that the angular response data for the optical radiation sensor device of  FIG. 5  has a somewhat “flatter top” ( FIG. 6 ) as compared to the data shown in  FIG. 2  obtained using the conventional optical radiation sensor device of  FIG. 1 . As a result, there is a 5° range over which the detection error of measured intensity is low—for example, as a result of misalignment of the sensor device. Also, since the signal drops to &lt;5% of the peak value at relatively wide angles, the use of such a non-circular (e.g., square) aperture suppresses stray reflections within the body of the sensor device. 
   Thus, an advantage of the present optical radiation sensor device is the ability to maintain the intensity of radiation in the form of a cosine response while the radiation source is entirely contained within the field of view of the sensor. Thus, the dimensions of the attenuating aperture (or apertures if multiple such apertures are used) can be changed to change the angular field of view of the sensor device. 
   For example, the dimensions of the first aperture and the second aperture discussed above in accordance with  FIGS. 5   a ,  5   b  and  5   c  can be changed to 0.090 in.×0.090 in. and 0.150 in.×0.150 in., respectively, to provide a field of view of ±13°. This would have the effect of widening the “flat top region” of the angular response data—this is confirmed by reviewing the data shown in  FIG. 7 . The resulting optical radiation sensor device can “see” a wider field of view and the region with the cosine response has now been increased to ±4°. 
   It should be noted that the sensing element used in the present optical radiation sensor device can be a semi-conductor sensing element suitable for detecting, for example, ultraviolet radiation from lamps producing such radiation. For example, the sensing element can be made of silicon carbide or silicon sensing elements conventionally used in optical radiation sensor devices. The optical radiation sensor device can also be equipped with one or more filters to limit the wavelength response of the sensors. See, for example, U.S. patent application Ser. No. 60/506,144 filed Sep. 29, 2003. 
   The present optical radiation sensor device may be used for on-line determination of ultraviolet transmittance of a fluid being treated in an ultraviolet lamp area. The details of conducting the on-line transmittance analysis may be found in Sasges referred to above. 
   While this invention has been described with reference to illustrative embodiments and examples, the description is not intended to be construed in a limiting sense. Thus, various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments. 
   All publications, patents and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.