The Beta Dust Monitor F-904-20 consists of a sampling-system and a measurement device.
The sampling-system, with or without the dilution system, consists of a sampler probe (chap-ter 10.14. ) and sampler line. The sampling system is heated to avoid drops in dew point. The method behind heating the sampling system is the principle of low voltage re-sistance heating. The sampling system presents an ohmic resistance. A low voltage trans-former carries current through the sampler hose and facilitates the warming. There is anoth-er method that heats the sampling hose through an encased heating tube. It is then possible to establish the pipe temperature either with a pre-configured installable regulator or a self-regulated heating system equipped with a pre-set temperature.
The measurement principle of the dust emissions meter F-904-20 is based on the absorption of Beta radiation (electrons) emitted from a radioactive source through the mass that is sam-pled from the exhaust stream. Dependent on their energy, the electrons are absorbed by each material (solid materials, liquids, gas). The absorption constant (effectively and absorp-tion) based on the energy (in MeV) of the emitted electrons as well as on the chemical com-position of the absorbing materials. In simplified terms, the lower the energy of the electrons, the less substance dependence of the absorption.
A C-14 emitter is installed in the Verewa F-904-20. The use of these isotopes presents some advantages over other isotopes used for analysis. A half-life of 5,730 years, the little energy of the electrons from only 0,156 MeV and the decay in a non-radioactive element. With the use of a C-14 source, the beta absorption measurement of the dust content nearly independent from the chemical composition of the dust particles.
Further details on the theory of C-14 radiation and the beta absorption are available in the theory fundamentals.
In contrast with the optical dust meters (especially scattered light photo meters), the meas-urement with the F-904-20 is independent from particle size, cooler and specific weight. The Verewa F-904-20 is specifically designed for use with wet scrubbers and is not affected by the presence of water drops or water vapour in the gas. Because of the difference in the size of grain, a place-specific calibration, such as with photometers is not necessary. The F-904-20 will be fully calibrated before delivery. It can also be installed on changing locations.