Q. How does radiation-based measurement work?

A. From a big-picture perspective, understanding nuclear measurement isn’t as difficult as you might think. Gamma radiation is sensed by a detector and the signal is converted into a level, density, or weight measurement. That’s it.

Gamma energy is emitted from a small ceramic pellet of radioactive material in a double-encapsulated, stainless steel cylinder.  The manufacturer loads the capsule into a source holder, which is mounted on the outside of the process vessel. The source holder's job is to direct gamma energy solely through the vessel and to the detector. The gamma energy field is minimized in all other directions.

Process material in the vessel will either absorb or scatter the gamma energy, a mechanism called attenuation. Gamma energy attenuation is proportional to process level and density. The greater the attenuation, the greater the level and density.

A radiation detector is mounted on the opposite side of the vessel on the outside and registers counts per second based on the strength of the gamma energy field. The electronics inside the detector use the field strength to infer a process reading. Process value is inversely proportional to the number of counts. High attenuation leads to fewer counts, and fewer counts indicate a greater level or density inside the vessel.       

Measurements made using radiation-based technology can be summed up in the following equation:

High gamma attenuation = low counts = high process condition.

See? Nothing to it.