Radiometric measurement, also known as nuclear or gamma based measurement, is an extremely reliable and safe, non invasive solution that is ideally suited for; level limit detection, continuous level, density and interface layer measurement.
Due to its non-contact detection principles, it is ideally suited for applications with extreme process conditions involving abrasive, corrosive or toxic mediums, high temperatures or pressures.
The principle of radiometric measurement employs a radioactive source which emits gamma radiation that passes through the walls of the pipe or vessel containing the medium being monitored.
A detector is mounted on the opposite side of the container which senses the radiation that is not absorbed by the medium and is directly related to the parameter being measured.
Applying the basic principles of radiometric measurement and using just a few components, several types of measurement are possible including level limit detection, continuous level measurement, interface layer measurement, density or concentration measurement and temperature compensated density or concentration measurement.
Specialised software is used to simplify the selection of source intensity and material ensuring effective measurement while keeping the level of radiation used to an absolute minimum to optimise operator safety. Critical system safety parameters and installation criterion are automatically calculated and graphically represented.
The radioactive source is enclosed in a lead lined steel source container that is designed to direct the radiation emission only in one direction screening it off in all other directions.
During commissioning, a background calibration eliminates the effects of constant ambient radiation. However all radiometric measurement systems become unreliable when subjected to fluctuating ambient radiation caused by gammagraphy (non-destructive material testing), a dense population of radiometric measurement points or process radioactive slurries such as uranium.
Because of its variable nature, it is impossible to compensate for fluctuating ambient radiation.
However, this problem can be solved by a gamma modulator that contains a slotted shaft that rotates and alternatively screens off the gamma beam or allows it to pass.
Using a frequency filter, the system’s detector is able to separate the useful signal from the interference radiation allowing accurate measurement and improved system reliability in spite of fluctuating ambient radiation.
Simon Rigling of Endress+Hauser Australia is Product Manager – Gamma. For more information visit www.gamma.endress.com or call 1300 363 707