General Information
There is hardly a physical phenomenon applied in analysis technology as widely as the interaction of electromagnetic radiation with matter. The advantages of applying this phenomenon are manifested in continuous, non-contact and non-destructive measurements in product analysis and quality control.
Definitions
- Spectrum: Show Spectrum: Close
Electromagnetic radiation is in general a mixture of many small packets of energy. Each packet, also called photon, possesses a certain amount of energy. Each photon behaves like a wave with a definite frequency and wavelength. If the radiation is visible light, the wavelength corresponds to a colour: the wavelengths of 444, 555, and 666 nanometers are blue, green, and red light, respectively. White light contains all colours.
A spectrum is a kind of representation that shows how much of each wavelength is present in a given field of electromagnetic radation. The solar spectrum is an important example. It contains large amounts of visible light with an emission maximum around 500 nanometers. However, it also contains considerable amounts of ultraviolet and infrared radiation.
- Wavelength: Show Wavelength: Close
Electromagnetic radiation is created by the propagation of two coupled oscillating fields, an electric and a magnetic field. The wavelength of a packet of radiation is the distance between two maxima (or minima) of that oscillation. It can be converted into frequency or energy of the radiation. It is usually measured in meters or a derived unit such as nanometers. Visible light was wavelengths between 400 and 700 nanometers.
- Absorption: Show Absorption: Close
When light (electromagnetic radation) encounters matter, some fraction of that light can be absorbed by the matter. Each kind of matter (atoms, molecules, crystals, plasmas...) absorb a certain set of wavelengths depending on, for instance, the distribution of electrons or the mobility of particles in the material. When a known spectrum of radiation is sent into a sample, then the spectrum that is detected behind the sample contains information about the composition about the sample. With good calibration, it is possible to obtain very precise quantitative results.
- Transmission: Show Transmission: Close
Transmission is the process to make light (electromagnetic radiation) pass through a sample. Commonly, the original spectrum of radiation is compared to the transmitted spectrum in order to identify absorption at certain wavelengths. That absorption pattern contains information about the composition of the sample. Additional reflection or scattering processes need to be considered and can be taken into account by adequate spectral calibration. If the sample is so dense that it is opaque, transmission measurements are not possible. Reflection measurements are an alternative for such cases.
- Reflection: Show Reflection: Close
Reflection occurs when light (electromagnetic radiation) hits a sample and is directed back instead of entering the sample. Reflection can be diffuse (evenly distributed in all directions, think of sand) or specular (angle of reflection equals angle of incidence). Most common, however, are intermediate forms - think of the vague reflection of the sun on an otherwise matte surface). Reflection depends on wavelength, and in general certain wavelengths (not necessarily visible) are still capable of penetrating the probe and are subject to absorption. Therefore, reflection measurements can also be used to investigate the composition of a sample.
Many properties of absorbing components can be detected by selecting different spectral ranges and suitable wavelengths.
Our analysis systems can be used for many applications. They can be adapted to various environmental conditions. The optics are based on tempax, quarz glass, or sapphire, which makes them robust and low on maintenance. Measurements in reactors can be performed with the help of optical fibres.
Measurement principles
Transmission (types TMK-550 or 480-CT)
Transmission measurements are the method of choice to probe liquids and gases. The beam of light passes through a flow cell of defined thickness that is filled with the liquid or gas sample. The transmitted light contains the spectral information about the sample composition. In addition, the sample temperature (and in the case of gases, also the gas pressure) can be detected and used for mathematical compensation of the measured data.
Advantage: Exactly defined conditions; high energy efficiency.
Diffuse Reflection (types RMK-10 or RMK-24)
This method is commonly used to probe powder samples or other solids, such as paper, sheet metal, granulates, or gels. Near-infrared (NIR) radiation penetrates into the sample and is refracted and reflected by its atoms and molecules. The reflected light contains the spectral information about the sample composition.
Advantage: Chemical and physical information without sample preparation.
Transflection (type RMK-9T)
Our special foil measurement system combines transmission and reflection to measure PVB moisture: NIR radiation penetrates the foil, is reflected by a mirror and penetrates the foil again.
Advantage: Increased sensitivity due to the doubled optical path.
