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2024-12-11
The integrating sphere is an important component of the colorimeter, which largely determines the service life, measurement accuracy and long-term repeatability of the colorimeter. However, the integrating sphere is a consumable part, and various problems may occur during use . So, does the integrating sphere of the colorimeter need to be replaced? How to maintain it? This article introduces this.
Colorimeter integrating sphere
The function of the integrating sphere of the colorimeter is to concentrate all visible light from the surface of the object being measured on a small sphere, and then transmit the light to the center of the integrating sphere through the slit. At this time, what you see through the slit is the light spot inside the integrating sphere. Since there are many particles inside the integrating sphere, the light of each wavelength can be separated.
The integrating sphere is a container that absorbs reflected light. When the reflected light passes through the integrating sphere, it is absorbed and transmitted to the optical components inside the instrument. These components convert the light signals into electrical signals and then output them to the display. By measuring the size of the electrical signal, we can get the color value.
The purpose of using an integrating sphere is to make the light entering it, after multiple reflections by the inner wall diffuse reflection layer, obtain uniform illumination on the entire inner wall surface, and this illumination is much greater than the illumination value of the incident light flux divided by the inner wall area of the sphere (which can improve the signal-to-noise ratio). In color measurement instruments, the integrating sphere has the following two functions:
1. Optical receiver
The light to be measured enters the integrating sphere through the small hole on the sphere, and one or more detectors are set on the inner wall. The photocurrent output by the photodetector is proportional to the illuminance of the inner wall of the integrating sphere, that is, proportional to the luminous flux entering the integrating sphere. In this way, the change in the luminous flux entering the integrating sphere can be known based on the change in the output photocurrent.
2. Evenly illuminated object surface
Several light bulbs (usually four or six) are placed symmetrically and evenly on the inner wall of the integrating sphere with the light exit hole. The light emitted by the light bulb is diffusely reflected by the inner wall many times to form a uniformly illuminated luminous spherical surface, which can be used as the object surface of the optical system under test with uniform brightness and large field of view (the entrance pupil of the optical system basically coincides with the light exit hole). This integrating sphere is used to measure the vignetting coefficient of the photographic objective lens and the uniformity of the image plane illumination.
In the configuration of the colorimeter, in addition to consumables such as cuvettes and sample cups, there are also some accessories inside the instrument that require regular maintenance to ensure the stability of the instrument and the accuracy of the measurement results. Integrating spheres are relatively common and easily damaged accessories.
The inside of the colorimeter integrating sphere is a highly diffuse reflective coating. Although it is better and more weather-resistant than most other brands in the industry, improper use or environmental reasons can also cause the inner wall of the integrating sphere to change color. The integrating sphere can gather the divergent light generated by the flash of the light source. If the integrating sphere is contaminated, it will absorb part of the light and turn the white light into colored light. When calibrating, the colored light at this time will be forced to match the whiteboard data input into the instrument. Therefore, a "whitening" effect will be produced. At the same time, when measuring the sample, the data will become whiter, which is manifested as a larger L*, and the b* of the yellow sample will become smaller.
When using the colorimeter daily, you should regularly use an ear cleaning bulb to blow clean the inner wall of the integrating sphere. The integrating sphere will gradually age and turn yellow in the air, so even if you are very careful when using the colorimeter, you still need to maintain it regularly or even replace it. It is generally recommended that the replacement cycle is 5-10 years. In addition, the following situations also require a new integrating sphere:
1. An unknown liquid drips into the integrating sphere, causing the inner wall of the integrating sphere to have a strange color;
2. When the inner wall of the integrating sphere is wiped with a solvent, the inner wall of the integrating sphere is damaged;
3. The instrument is stored in a retest environment, and the inner wall of the integrating sphere is corroded;
4. Obvious cracks and coating peeling occur inside the integrating sphere.
The maintenance of the colorimeter integrating sphere is the key to ensure measurement accuracy and extend service life. The maintenance of the colorimeter integrating sphere mainly includes the following points:
Maintenance: If you find that the colorimeter has a fault, such as the integrating sphere is dirty, the integrating sphere falls off, the bulb is not lit, the measurement results are inaccurate, etc., first check whether the power cord is plugged in tightly and whether the bulb is damaged. If replacing the bulb still cannot solve the problem, the integrating sphere, circuit board or other circuit components may be damaged, and you need to contact a professional maintenance personnel for repair.
Cleaning: Dust and dirt may be attached to the surface of the integrating sphere, so you need to wipe it gently with a soft cloth. Be careful not to use chemical solvents or water to clean it directly to avoid damaging the surface of the integrating sphere.
Maintenance: In order to keep the integrating sphere in good condition, it is recommended to perform maintenance regularly, including checking whether the line connection is good, cleaning the dust and dirt on the surface of the bulb and reflector, and checking whether the bracket and adjustment mechanism are flexible and reliable. If any problems are found, they should be dealt with in time.
Calibration: Calibration is an important step to ensure the accuracy of the integrating sphere measurement. Generally, a standard light source and a standard reflector are required for calibration. Before calibration, the sphere should be preheated and then operated according to the steps in the manual. The calibration cycle is generally determined by the frequency of use and environmental conditions, and it is recommended to be performed regularly.
In addition, in order to ensure safety and extend the service life of the integrating sphere, you should also pay attention to the following matters: Read the instructions carefully before use to understand the structure, principle and usage of the integrating sphere; Keep the integrating sphere stable during use to avoid collision and falling; After use, cut off the power supply and cover the integrating sphere with a soft cloth to prevent dust from entering; If the integrating sphere is found to have a fault or abnormality, stop using it immediately and contact professional maintenance personnel in time for inspection and repair.
