The function of the colorimeter detector is to convert light of different intensities into electrical signals proportional to it, and then send the power to the star measuring instrument for processing. There are three types of photocells, photocells and photomultipliers. Among them, the most common is photocell, and the best performance is photomultiplier tube, colorimeter electrical measuring instrument (indication part) generally adopts ammeter for analog indication, or through a series of processing such as A/D conversion and finally displays in digital form. Although the colorimeter has many advantages, it is inevitable that various failures will occur after a long time of use.
Spectral bandwidth variation
The first thing to do is to determine if the slit width is set too wide. Most instruments now have adjustable slit widths. In the case of confirming that the slit width is appropriate, observe whether the brightness of the light source is normal and whether there is flickering, so as to determine whether the power supply voltage part of the instrument is normal. When the light source is normal, the main unit can be disassembled to observe whether the optical system is out of balance, such as the position of the light source, the displacement or looseness of the reflection, the displacement of the photoelectric receiver, and the reflectivity of the reflection surface is reduced due to dust accumulation. Finally, the sensitivity of the detector is decreased, the performance of the photocell is unstable, and the noise ratio of the amplified electric pedal is reduced.
Worse wavelength accuracy and repeatability
In the first wash, the influence caused by the temperature change of the working environment should be excluded, and the influence on the temperature of the prism colorimeter is particularly obvious. After exclusion, white cardboard can be placed in the position of the cuvette to observe whether there is a yellow spot on the white cardboard at a wavelength of 580 m. Disassemble the instrument and observe whether the dispersive element (prism or grating) in the optical path is displaced. When adjusting the wavelength, observe whether the shaft of the prism table or grating table is loose or blocked, whether the wavelength cam or sine mechanism is worn, and the reflectivity of the mirror surface. Reduced due to dust accumulation, etc.
Deterioration of transmittance accuracy and repeatability
The deterioration of transmittance accuracy and repeatability is the main manifestation of the deterioration of the optical characteristics of the instrument, which is often caused by the deterioration of the working stability of the electronic system. Due to the unstable power supply of the light source, the luminous characteristics of the light source will change. It can be judged by observing the brightness of the light source lamp and monitoring the electric power of the light source. The fluctuation of the working voltage of the photodetector part will cause the electrical signal generated under the same light intensity to change. , which can be judged by monitoring the voltage of the photoelectric detector> the drift of the amplifier operating point or the phantom drop of the letter-grass ratio, which will eventually lead to the deterioration of the accuracy and repeatability of the shooting ratio. In terms of the use of the portable colorimeter, if the measurement is not carried out in strict accordance with the operating procedures, the working parameters of the instrument (such as slit width, response speed, sweeping speed and other parameters) are not properly selected, the colorimetric melon slot is not positioned correctly, and the placement position and angle are improper. It will also lead to an error in the transmittance ratio.
The Baseline bending
After it is found that the instrument is 100% bent, you should first check whether the light source part is displaced, loose, or tilted. If there is no fault in the light source part, white cardboard can be used to check the light spot before entering the missing slit. If there is defocus, deviation, cutting, asymmetry, etc., the working position of the reflector in the condensing system should be checked and adjusted. If the beams are misaligned, non-overlapping, and uneven in brightness, it is necessary to carefully check whether the mirrors or dispersive elements are displaced or loose, and adjust them item by item.
The Transmission ratio cannot be adjusted by 100 %
After it is found that the instrument is 100% bent, you should first check whether the light source part is displaced, loose, or tilted. If there is no fault in the light source part, white cardboard can be used to check the light spot before entering the missing slit. If there is defocus, deviation, cutting, asymmetry, etc., the working position of the reflector in the condensing system should be checked and adjusted. If the beams are misaligned, non-overlapping, and uneven in brightness, it is necessary to carefully check whether the mirrors or dispersive elements are displaced or loose, and adjust them item by item.