The operation of nearly all level measurement devices depends upon the material’s propensity to either reflect or absorb radiations. Various types of radiation based level gauges are available which consist of
Another significant type is optical electromagnetic radiation which is mainly employed for point-switch applications.
“In radiation-based measurement, a low level source is safely embedded into a shielded source holder with an aperture that emits focused gamma rays. Process medium or level changes progressively shield the electromagnetic energy emitted from the source and received by the detector. This measured radiation intensity is directly proportional to the continuous level, point level, density or mass flow rate.”1
Major elements employed for the source of radiation in these devices are
- Caesium-137 or
- Cobalt-60 isotope
Major advantages associated with the use of radiation based level gauges include:
- They consist of no moving parts, hence free from wear and maintenance.
- Radiation based level measurement is basically external to the process since these are non contact type of level sensors which do not require making physical contact with the liquid substance under level measurement.
- They can be easily applied in severe process conditions where other level measurement devices fail, for example areas involving high temperatures, intense pressures and complex installation conditions.
- They are quite adaptable and reliable in difficult level measurement areas.
- Unlike other level sensors, the working of radiation based level gauges doesn’t depend upon environmental conditions such as pressure, temperature, viscosity etc. It is also free of all the chemical characteristics of the process fluid.
- Radiation based level measurement technique doesn’t cause any affect on the process liquid under detection. It just keeps maintaining its original state.
“Because they can in effect “see” through solid tank walls, nuclear radiation gages are perhaps the ultimate in non-contact sensing. Because they require a gamma radiation source and are relatively expensive, however, nuclear gages are often considered the level gage of last resort.”
Following are the major application areas of Radiation based level measurement techniques
- These gauges are mainly used for continuous level measurement applications.
- They can be applied for density and concentration measurement too.
- They are also capable to detect level between interfaces.
- At times, they can be employed for point level measurement.
- They are extremely useful for mass flow measurement of massive solids over conveyor belts or in screw conveyors.
- They are brought into use for flow-rate detection of fluids also.