Users may find this situation: Color measurement instruments are also the same, prices vary widely, and the measured results are different. Therefore, when selecting a colorimeter, some "performance indicators" must be noted, so that you can purchase a best-cost-performing instrument.
1, this instrument is a "colorimeter" or "spectrophotometer color measurement instrument":
The accuracy of simple colorimeter is relatively low, and it must be noted that some can not even give the absolute value of the color's color coordinate space (L, a, b value), can only give between two samples (usually the standard (Delta-E) between the sample and the sample. This colorimeter cannot be purchased because there is no color absolute data, there is no way to exchange data with others, nor can you establish and manage your own color standard database. It is equivalent to 10% of the normal color and color difference instrument, and the price is low and it can not meet the test requirements. It can't be cheap and cheap, and purchases such instrument without any application value.
The spectrophotometer has high precision, and it is different from a simple colorimeter to measure color. The spectrophotometer can measure the "reflectivity curve" of each color point (10nm or 20nm wavelength interval), and the colorimeter cannot. Spectrophotometers can simulate a variety of light sources, and colorimeters typically have only one or up to two analog light sources.
2. “Spectrophotometric colorimeter†is divided into “0/45 degree†and “d/8 degree integrating sphere†two kinds of measurement - observation method: “0/45 degree†can only be used to measure the smooth surface, and Cannot be used for computer color matching. The "d/8-degree integrating sphere" can be used to measure various surfaces and can be used for computer color matching. Also, when choosing, consider whether or not to eliminate specular reflections, and measurement modes that include specular reflections. If both modes are available, it is useful when measuring smooth surfaces that have a noticeably reflective surface color.
3, the difference of various "d/8 degree integrating sphere" color measuring instrument:
Most companies use the "d/8 degree integrating sphere" colorimeter. However, it must be noted that there are still great differences between different brands and different models, leading to different measurement accuracy.
In addition to a microprocessor and its associated circuitry, a colorimeter has four main components: a light source, an integrating sphere, a grating (split monochromator), and a photodetector. This is also the main indicator to measure the merits of an instrument.
3.1 Is it the "double beam measuring principle" or "single beam measuring principle":
The dual beam instrument has two gratings and two detectors. The light source was flashed only once during the measurement and the sample and reference white were similarly measured. This overcomes the errors caused by system changes and the accuracy of the measured data is very high. Only the cost of the instrument is higher.
The single beam instrument has only one grating and one detector. Therefore, the light source flashes twice during measurement and the sample and reference white are measured separately. The system error (difference of light intensity distribution, light path change, temperature change, circuit drift, etc.) at the time of the two measurements is taken as the difference between the sample and the reference white, so the error is large, and the difference between the instruments is also large.
3.2 Light Sources: There is a problem that has been debated at present, and is described here in detail.
In a color measurement instrument, what light source is selected should first be considered for stability, light source orientation, lifetime, and the effectiveness of the resulting spectral curve. At present, two types of light sources, halogen quartz tungsten lamp and xenon lamp, are used.
Tungsten lamps are the most commonly used light sources for color measuring instruments (including various visible spectrum spectrophotometers). They are an incandescent light bulb filled with an inert gas or halogen (to prevent the oxidation and thermal evaporation of tungsten filaments). Tungsten is used as a filament material because tungsten is strong enough to withstand high temperatures. The spectrum curve of the tungsten lamp in the visible region was almost completely overlapped with that of the black body emitter. With the development of regulated power supply and pulsed power supply in recent years, tungsten lamps can provide a repetitive and stable, high color temperature beam, which can fully meet the needs of the appearance of color measurement on the light source.
The xenon lamp is another light source commonly used in color measurement instruments. It is a hermetically sealed glass tube fitted with a pair of electrodes. When a high voltage is applied to the electrode, the internal helium gas will be excited to generate an instantaneous arc, which is an inflatable discharge lamp. The advantage of a xenon lamp is that the spectrum is closer to sunlight than the incandescent lamp and the energy is higher. However, for most arc lamps it is difficult to obtain a stable light output, and for a precise and accurate color measurement, continuous ripple-free spectrum (a stable light output) is precisely the most important.
From the perspective of light detection, the intensity of an excessively strong light source will generally exceed the linear range of the detector. This is a common sense. In the light path design, the light intensity of the final arrival detection device must be weakened, which complicates the optical path design. In addition, as we all know, the vast majority of UV-Vis spectrophotometers currently use D2 lamps and tungsten lamps as light sources. In terms of measuring the surface color of objects, the visible light is seen by the human eye, and the energy consumption is small, and the circuit design is simple. The long, small system size, low cost, and easy maintenance and replacement of tungsten lamps are very suitable. In the 1960s and 1970s, all the polarimeters used sodium lamps as the light source because, according to the definition of optical rotation, the instrument needed energy to be concentrated at the light source of 589 nm. At that time, the sodium lamp was almost the only choice, but Like the xenon lamp, the sodium lamp is a vacuum discharge excitation device and it is difficult to ensure the service life and stability of the light intensity. The sodium lamp has become an expensive consumable of the polarimeter. Today, almost all polarimeters are used. Tungsten lamp + interference filter as a light source, the lamp life is almost infinite compared to the instrument, because the new low energy, pulsed quartz halogen tungsten lamp light source technology to solve this problem.