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In-depth interpretation of the test misunderstanding of white light leakage in non-destructive testing black light lamps

2022-02-19

      

When I recently traveled to visit users, I found the distressing problems encountered by users, especially the problems encountered by railway users who used the Beijing Normal University ST-80C white light meter to measure the white light leakage in the lamp and found that it exceeded the standard. In this regard, I did a comparative experiment with the Beijing Normal University ST-80C white light meter and the American Spectroline XRP-3000 black and white light meter, and then consulted the technicians of Beijing Normal University and consulted the aviation industry "2297" about leaking white light test. It took some specs to find the answer. Below, please set up two questions first, and then throw a few bricks to attract jade for your reference.


1. What is the function of nondestructive testing black light?


Black light is used in surface inspection (including magnetic particle inspection and penetrant inspection), which emits ultraviolet rays to make the magnetic suspension or penetrant on the surface of the workpiece fluoresce, and can directly display defects in the dark.


2. What is white light leakage in black light lamps? What is visible light? What is ambient light?


   When designing a fluorescent magnetic particle inspection darkroom or a fluorescent penetration inspection darkroom, it is required that the white light in the black light should not exceed 20Lux, which refers to the white light leakage content in the black light.


   Ambient light refers to the light intensity of the environment in which it is located.


   Visible light is a superposition of leaky white light and ambient light.

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Figure 1: Correlation diagram of spectral regions and energy transitions

3. How to correctly measure and correctly select the black light leakage white light meter?

3.1. Experimental tools: Shanghai Lifeng FiNDT-6000 hand-held illuminance adjustable LED cold light source black light, Beijing Normal University ST-80C white light meter and American Spectroline XRP-3000 black and white light meter.


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Figure 2: FiNDT-6000 Black Light 

3.2. Comparative experiment:

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It can be seen from the figure that the domestic white light probe glows under the illumination of the black light lamp, which leads to an increase in the leakage of white light in the black light lamp, while the white light probe of the American XRP-3000 black and white illuminometer does not have the phenomenon of probe reflection.

According to the cases encountered, there are two reasons for the leakage of white light from black light lamps exceeding the standard:

1. The probe of the white light meter produces reflection under the LED black light, which will stimulate the increase of white light leakage in the black light;

2. The probe of the white light meter has been polluted by fluorescent substances, which will lead to an increase of white light leakage in the black light under the irradiation of the black light.


In a word, when users measure the white light leaking in the black light, it is recommended to use a photosensitive probe that can filter out the violet light or a white light meter with a white light probe and a color filter.


Author: Li Yanli, a designer and R&D worker of Shanghai Lifeng Testing LED black light