Optics: measuring and testing – Photometers – Photoelectric
Reexamination Certificate
1999-12-17
2002-08-27
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Photometers
Photoelectric
Reexamination Certificate
active
06441896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and apparatus for measuring spatial uniformity of a radiation beam from a pulsed or continuous radiation source and, more particularly, for simultaneously measuring the intensity of the radiation from the radiation source at a number of locations in a cross sectional area of the radiation beam to provide spatial uniformity data in less time and with improved temporal accuracy to characterize and facilitate alignment, adjustment, and calibration of the radiation source.
2. Description of the Related Art
Radiation sources are well-known and have a wide range of uses, ranging from standard light sources to x-ray machines to solar simulators. Typically, it is desirable that such radiation sources produce radiation beams having known or adjustable intensities, spectrums, and crosssectional shapes and sizes to suit a particular use. For example, radiation sources are useful for producing radiation beams that are used for testing or causing a predictable reaction with numerous materials and systems that react to a given type of radiation in a known and desired manner. For example, solar or photovoltaic cells are designed and constructed to receive solar radiation and convert it into electrical energy. It is important that the solar simulator radiation source provide a radiation beam having identical, or only slightly varying, intensity at any point in the cross section of the beam, i.e., spatial uniformity, so as to obtain acceptable test results and equal reaction rates across the tested material.
In particular, solar simulator-type radiation sources have .become increasingly important and are used to produce radiation beams with characteristics, such as intensity and spectrum, that simulate radiation that would be received from the sun at various geographic, atmospheric, or orbiting locations. In this way, solar simulators can be used to imitate actual field conditions, which is useful for testing photovoltaic conversion efficiencies of solar cells/arrays, resistances to solar radiation of various materials including sun screen compounds, numerous biological and. medical interactions with solar radiation, and other material or system properties. As, discussed above, for these tests to be accurate, i.e., give similar results at any point on the surface area being tested, it is necessary that the solar simulator produce a radiation beam with acceptable spatial uniformity. Certain American Society for Testing and Materials (ASTM) specifications dictate that the spatial uniformity for solar simulators be very high with a variance from a median intensity value of less than 10 percent for Class C, less than 5 percent for Class B, and even more restrictive, less than 2 percent for Class A. Without such high spatial uniformity, the test results can include errors that can go undetected thereby resulting in the test subject being rejected or even redesigned based on inaccurate test data. Therefore, an important and necessary step in using a radiation source, such as a solar simulator, is the alignment, adjustment, and calibration of the source to establish spatial uniformity, and, of course, it is desirable that this step be accomplished accurately and inexpensively.
A currently accepted method of checking spatial uniformity on a test surface, such as a photovoltaic array, involves placing a single radiation or photo detector at a first location on the test surface and measuring the intensity of a radiation beam produced by a radiation source. The detector is then moved to a number of other locations on the test surface, and the intensities of additional radiation beams from the radiation source are measured. A median intensity is calculated, and variance from this median intensity is determined at each measuring location on the test surface. If the results of the measured intensities and calculated variances indicate an unacceptable intensity variance in the radiation beam, the radiation source is adjusted in an attempt to better align the source to achieve an acceptable spatial uniformity. Each of these steps is then repeated until an acceptable spatial uniformity is achieved. As can be understood, this can be a tedious and time consuming process, especially with larger test surfaces, such as typical solar cell array modules, that require numerous measurements to provide an accurate representation of intensities across the entire surface area.
This procedure is used for aligning both continuous and pulse radiation sources with the assumption that temporal variation of the radiation beams produced by the source is negligible or in other words, that each beam produced is identical. In the case of a pulse source, each pulse is assumed to be equivalent in intensity and the intensity of the radiation beam is typically calculated by integrating or summing the intensity values over the entire length of the pulse, i.e., without making discrete measurements during transmission of the pulse beam. Additionally, the cost and difficulty of aligning/calibrating a radiation source are often further increased because making adjustments to the radiation source may be a complicated process itself that requires an operator to make simultaneous adjustments of several interrelated components to try to properly align the source.
For examples of various single-detector, radiation measuring devices, see U.S. Pat. No. 5,3274210 issued to Okui et al., U.S. Pat. No. 5,548,398 issued to Gaboury, and U.S. Pat. No. 4,218,139 issued to Sheffield.
Some efforts have been made to develop devices that can automate the movement or scanning of the single radiation detector across the radiation beam and that, at least potentially, can reduce error caused by the human placement and movement of the single radiation detector. For example, U.S. Pat. No. 3,867,036 issued to Detwiler et al. discloses a limit display circuit that includes a device for sequentially sampling or measuring intensities of a radiation beam by using a control motor to move a single photocell sensor across a radiation beam. However, use of this device for aligning and adjusting a radiation source is limited by the size, shape, and movement capabilities of the control motor, which itself has to be carefully calibrated and designed to control accuracy and can cause errors by introducing moving components into the testing device. As illustrated, the device is likely only useful for relatively small beams having linear cross-sectional shapes.
Consequently, there remains a need for devices and methods that will reduce the time that is required to measure the spatial uniformity of a radiation beam produced by a radiation source, such as a solar simulator, to facilitate quick, accurate, and inexpensive adjustment, alignment, and/or calibration of the radiation source.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a method and apparatus for use in characterizing, aligning, adjusting, and/or calibrating a radiation source with improved accuracy and speed.
It is a related object of the present invention to provide a more effective method and apparatus for measuring the spatial uniformity of the intensity of a beam(s) from a radiation source(s).
It is a specific object of the present invention to provide a method and apparatus for use in aligning, adjusting, and/or calibrating pulse and continuous radiation sources that minimizes possible testing errors due to temporal variances of the radiation produced by the source.
It is another specific object of the present invention to provide a method and apparatus for determining spatial uniformity of a pulsed radiation source based on a single pulse.
It is another specific object of the present invention to provide a method and apparatus for determining spatial uniformity of a radiation source that does not require movement of a radiation detector(s).
Additional objects, advantages, and novel features of the invention are set forth in part in the description that follow
Font Frank G.
Midwest Research Institute
Stafira Michael P.
White Paul J.
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