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In Line Ash Monitoring

MEASURING PRINCIPLE

Electro-magnetic waves, like X-rays or gamma-rays are absorbed into material in different ways, therefore it depends on the energy of the radiation and the material  itself as to  which way it is absorbed. High energy waves and low atomic numbers are absorbed according to the density (or bulk density) of the material. Of course the absorption also depends on the thickness of the absorbing layer. That means the absorption is dependent on the weight of the material the radiation has passed through (the weight increases if the way becomes longer or if the density becomes higher). Density and thickness can be measured by means of radiations: if one is constant the other can be calculated. Lower energy radiation and higher atomic numbers are absorbed in the same way, but additional, according to the atomic weight.The higher the atomic weight the lower the energy and higher the absorption.

For analysis purposes a weak energy is needed to determine the atomic composition. But weight will influence the absorption. So a higher energy radiation must also be applied to get a signal which is influenced by weight only and not by the atomic composition. Both signals can be used mathematically to determine the composition.

THE TECHNIC

 To measure radiation it must first be absorbed. Absorption is higher the more dense the absorbing material is. Gas filled ionisation chambers or Geiger tubes are available but the most sensitive is a crystal of NaJ with a density of 3.7 g/cm3. This crystal produces small light flashes when exposed to radiation which must be detected by a light amplifier called photo- the belt. The measuring paths should have a minimum distance of 1 m to each other. A firm mechnical frame is needed to prevent changes of the distance between source and detector; it must be absolutely constant to avoid measuring errors for 30 days.

In the service menu the software is able to change the wiring terminals so that a relay or an analogue output can be switched from one terminal to another. Therefore the evakuation unit is not only a display of ash but fits into the process and can help to control it.

 

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