Nuclear Level Measurement

Introduction

Continuous nuclear level measurement is typically used where most other technologies are unsuccessful. Different radioactive isotopes are used, based on the penetrating power needed to pass through the tank. Radiation from the source is detected on the other side of the tank. Its strength indicates the level of the fluid.

Theory

Nuclear continuous level measurement works by directing a narrow fan of radiation through the vessel to a detector. As the process level rises, it shields the detector from the from the radiation. The more radiation the detector sees, the lower the process level . The less radiation detected, the higher the process level

 

 

Source Radioisotopes used for Level Measurement Emit Gamma Radiation that Penetrates the Vessel Wall and process media
A Target Detector on the Opposite side Measures the Radiation Field Strength and Infers a Level in the Vessel, a transmitter is mounted on the opposite side of the tank or pipe which converts the radiation received into an electric signal
•The Radiometric or Nucleonic Principle is Based on the Fact that Gamma Radiation is Attenuated when it Penetrates a Material 
•Cesium 13(Half Life 30 Years) and Cobalt 60 (Half Life 5.26 Years) are the Most Commonly Used Industrial isotope.

 

 

Advantages

Sometimes works, when no other method is available
External mounting often possible
Easy zero check
Motor-driven models available for high-accuracy applications

Disadvantages 

Costly to install

Requires licensing by regulatory agency

Dangerous to handle unless precautions are followed

Original calibration and checkout often difficult and costly

Errors caused by density variations in measured materials

Lack of application data

Difficult to obtain linear readout over wide ranges

Problems presented by materials that coat walls
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