Abstract:
A sensor includes a photosensitive resistor and a quartz glass located on the photosensitive resistor. The resistance of the photosensitive resistor variably changes with the received light rays. The quartz glass is used for filtering light incident onto the photosensitive resistor, and mainly allows UV light rays to travel therethrough.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a sensor, and more particularly, to a sensor having a UV-pervious quartz glass.  
         [0003]     2. Description of the Prior Art  
         [0004]     The Earth&#39;s ozone layer has been under attack by chlorofluorocarbons (CFCs) output from factories for a long time. This has led to the increase in ultraviolet (UV) radiation reaching the ground. UV light rays can cause dermopathy. If the strength of incident UV light rays can be detected immediately, human beings can directly protect themselves from harm. When UV radiation is considerable, people can stay inside and avoid going outside to protect themselves from the effects of UV radiation.  
         [0005]     Generally, UV light rays are of three types: UV-A having wavelengths from 320 nm to 400 nm, UV-B having wavelengths from 280 nm to 320 nm, and UV-C having wavelengths shorter than 280 nm. UV-C is the most dangerous of the three types. Fortunately, there is little UV-C radiation at ground level. However, due to the reduction of the ozone layer, UV-B radiation around the ground is dramatically increasing, rather than the less dangerous UV-A radiation. That is because the absorption efficiency of UV-B of the aerosphere is about 100 to 1000 times the absorption efficiency of UV-A. Therefore, the reduction of the ozone layer has resulted in great increase of UV-B at ground level.  
         [0006]     Please refer to  FIG. 1 , which is a graph of an erythema action spectrum. For human beings, the main wavelength range causing skin to turn red is between 280 nm and 298 nm UV-B, whose weighted coefficient is 1. When the wavelength is longer than 298 nm, the weighted coefficient drops quickly. The weighted coefficient drops to around one over ten thousand when the wavelength is about 400 nm.  
         [0007]     Therefore, we should detect the UV-B wavelength range from 280 nm to 298 nm to protect human health from UV radiation. However, conventional UV detectors, such as a photo multiplier tube, a silicon UV detector, and an AlGaN UV detector, are not suitable to be implemented for UV-B detection. The photo multiplier tube requires high voltage; its volume is large and it is not easy to operate. Also, the cost in making the photo multiplier tube is high. The silicon UV detector mainly detects visible light (wavelengths from 400 nm to 760 nm), and has an overall range of 350 nm to 950 nm. Therefore, the sensitivity of the silicon UV detector is not good enough to detect UV light rays. Although the AlGaN UV detector mainly detects wavelengths from 200 nm to 365 nm, it is susceptible to a lattice defect in manufacture. It is difficult to control this issue and the production yield is low.  
       SUMMARY OF INVENTION  
       [0008]     It is therefore a primary objective of the claimed invention to provide a sensor, which includes a UV-pervious quartz glass, to solve the above-mentioned problem.  
         [0009]     The claimed invention provides a sensor including a photosensitive resistor whose output value changes with received light rays, and a quartz glass located on the photosensitive resistor for filtering light incident onto the photosensitive resistor. The quartz glass mainly allows UV light rays to travel therethrough.  
         [0010]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]      FIG. 1  is a graph of an erythema action spectrum.  
         [0012]      FIG. 2  is a diagram of a sensor according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Please refer to  FIG. 2 , which is a diagram of a sensor  10  according to the present invention. The sensor  10  comprises a photosensitive resistor  20  and a UV-pervious quartz glass  30 . The photosensitive resistor  20  comprises two electrodes  22 , a zinc sulfide (ZnS) layer  24 , a ceramic substrate  26 , two lead terminals  28 , and a holder  21 . The ceramic substrate  26  is placed on the inner side of the holder  21 . The ZnS layer  24  is placed on the ceramic substrate  26  for receiving light rays. The two electrodes  22  are placed on the ZnS layer  24 . The two lead terminals  28  respectively pass through the electrodes  22 , the ZnS layer  24 , and the ceramic substrate  26  to act as two terminals of the photosensitive resistor  20 . The holder  21  is made of ceramic material or other materials.  
         [0014]     The ZnS layer  24  is photoconductive material. When light reaches the ZnS layer  24 , carriers are generated in the ZnS layer  24  to promote the electric conductivity of the ZnS layer  24 . Thus, the resistance between the two electrodes  22  changes with the light rays received by the ZnS layer  24 . Please note that in the prior art, the commonly used photoconductive material is cadmium sulfide (CdS), which mainly detects visible light having wavelengths over 540 nm, and thereby CdS is not suitable to detect UV light rays. The reason why the present invention utilizes the ZnS layer  24  is that the ZnS layer  24  mainly detects UV light rays having wavelengths shorter than 380 nm, which is more suitable to be implemented in the present invention.  
         [0015]     The quartz glass  30  is placed on the photosensitive resistor  20 , and mainly allows UV light rays to travel therethrough. One side of the quartz glass  30  includes a silver layer  32  whose purity is over 99%. Adjusting the thickness of the silver layer  32  can filter UV light rays of undesirable specific frequencies, such that the photosensitive resistor  20  only receives un-filtered UV light rays. For example, the thickness of the silver layer  32  can be adjusted to allow UV light rays having wavelengths from 280 nm to 380 nm to reach the ZnS layer  24  of the photosensitive resistor  20  for changing the resistance of the photosensitive resistor  20 . As long as the thickness of the silver layer  32  is proper, the wavelength range of UV light rays passing through the silver layer  32  can be controlled. In the present invention, the ZnS layer  24  can be replaced with other photoconductive materials capable of detecting UV light rays.  
         [0016]     As mentioned above, UV-B radiation does great harm to human beings. Therefore, the quartz glass  30  is made to allow UV-B to pass through, and to cooperate with the photosensitive resistor to efficiently detect UV-B rays. The present invention can be applied in products related to UV detection. When the strength of UV-B radiation on an ultraviolet index (UVI) exceeds the allowable range, the resistance of the sensor  10  of the present invention changes. The output value of the sensor  10 , the resistance, can be converted into current or voltage by using a simple circuit.  
         [0017]     Compared to the prior art, the present invention provides a sensor to detect a specific wavelength range. Compared to the photo multiplier tube, the silicon UV detector, and the AlGaN UV detector, the present invention is more suitable to be implemented in UV-B detection products, and is easily mass produced. However, the present invention is not intended to be limited to specific UV-B wavelength ranges. The thickness of the silver layer on the quartz glass can be adjusted depending on different requirement to filter different wavelength ranges of UV light rays.  
         [0018]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.