How does a radioactive level gauge work
A radioactive level gauge is a level sensor located in a beam that has a radioactive source as a transmitter and is coupled to a detector at the opposite point of the tank. To determine the level of material, the detector looks for a “dispersion pattern” that is compatible with the organic matter in the tank. In the process industry, precision systems are essential for measuring surface and surface switches and make an important contribution to the safety and high quality of manufacturing and logistics processes.
Applications are mostly made in liquids and solids contained in process tanks, storage tanks or silos. However, there are requirements that surface measurement is not possible or achievable with conventional measuring technology due to severe boundary conditions. Or only possible with very high installation and maintenance costs. This applies, for example, to environments with high pressure or high temperatures, or to aggressive or abrasive devices.
Radioactivity can be classified into approximately three types, each of which is emitted by radioactive isotope decay:
- Alpha radiation: Radiation of particles in the form of helium nuclei (alpha particles)
- Beta radiation: Radiation of elemental particles in the form of electrons and / or positrons (beta particles)
- Gamma radiation: High-energy electromagnetic waves similar to radio and light waves
By measuring the radiometer level and density, only gamma rays are used. Alpha and beta rays are not strong enough to penetrate solids, but high energy and high-frequency wavelengths of gamma rays radiate through matter in the path of the beam.
As the gamma ray passes through the material, the amount of absorption is proportional to the thickness of the layer, the density of the material, the cross section of the material absorbed, and the wave energy. Therefore, absorption and energy are the main factors affecting the required source size and quality of radiometric measurements.
Typical industrial isotopes used in radiometric applications are cesium-137 (Cs-137) and cobalt 60 (Co-60). The two isotopes differ in their physical properties, so that cesium has a longer half-life but less gamma-ray energy. Cobalt 60 has a shorter half-life with higher energy.
The half-life is the time it takes for the source of decay to reach half of the activity created by the original isotope. The half-life of Cs-137 is 30.17 years and Co-60 is 5.2 years. The Cs-137 is typically used in industrial applications because it requires less maintenance (ie, resource replacement) and its performance or power is sufficient for most applications. In certain cases, Co-60 may be required for irradiation through concentrates or high-density liquids.
The measurement formula determines the source by considering everything in the beam path (vessel wall, insulation, heating coils and obstruction) and the distance from the source to the detector. The calculation uses the following equation:
P = F a · F s · F i
P = the required source activity in mCi
K = the isotope coefficient (K = 3.55 for Cs-137 and 13.2 for Co-60)
Fa = r۲, where r refers to the distance from the source to the detector
Fs = absorption, depending on the density of the material and the thickness of the material in the beam path
Fi = the sensitivity of the detector
Beam-based surface sensor
This technology is not generally used in the gasoline storage industry, as the measurement accuracy can be compared to that of servo floating measuring devices or radar systems at a lower financial cost for initial purchase, installation, periodic inspection and without Acquired perceived risks associated with radioactivity.
Resources on the site More attention to these systems is that because of the radioactive sources, the licenses used are often required. This is a preferred measurement system for highly corrosive materials because it does not expose the measuring system directly to existing materials.
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