Arrangement and a method for measuring level, interface level and density profile of a fluid in tanks or containers

A method for selectively performing one or more measurements of a level, an interface level, and a density profile of at least one fluid located in a container comprising:

• providing a nuclear radiation source and a nuclear radiation detector unit that covers a total height of the container, the nuclear radiation detector unit comprises a long vertical detector in the form of a scintillator rod that has a photo multiplier tube fixed to each end;
• inserting the nuclear radiation source into a first protective pipe;
• inserting the nuclear radiation detector unit into a second protective pipe;
• mounting vertically the first protection pipe and the second protection pipe onto the container at a suitable distance from each other;
• absorbing a radiation quant from the nuclear radiation source into the scintillator rod;
• transforming the absorbed radiation quant into an electric pulse that has an amplitude proportional to an intensity of the radiation quant at a respective position along the scintillator rod;
• measuring electronically the amplitude of two simultaneous electric pulses;
• and
• determining electronically the respective position along the scintillator rod of the absorbed radiation quant by a ratiometric calculation.