Radiometric Level Measurement

Radiometric Level Measurement

Radiometric level measurement uses gamma radiation attenuation to determine level, point level, interface, and density - often from outside the vessel. It is a specialized solution reserved for the most difficult services, where other technologies cannot perform due to extreme process conditions or mechanical constraints. The method is intrinsically non-contact with respect to the process media.

The measuring principle places a shielded radioactive source on one side of the vessel and a detector on the other. Gamma radiation passing through the vessel and process is attenuated based on material presence and density; as level changes, the detector signal changes accordingly. The system typically consists of the source, a source container (shield/collimator), and a receiver/transmitter that converts detector output into usable signals.

Radiometric measurement is beneficial for “last-resort” applications: thick-walled vessels, high pressures and temperatures, aggressive media, internal obstructions, severe build-up, and heavily agitated or foaming services. Because components mount externally, process penetrations can be minimized and measurement can remain stable even when internals would destroy contact sensors. Properly designed shielding and beam geometry improve measurement reliability while controlling radiation exposure.

Typical applications include coke drums, autoclaves, crystallizers, separators with interface tracking, and solids or slurry vessels where abrasion and build-up are extreme. It is also used when vessel geometry is complex (coils, trays, agitators) or when process conditions exceed the limits of radar/ultrasonic/pressure methods. Density measurement with radiometric techniques can additionally support concentration or interface determination in challenging slurries and suspensions.

Implementation requires rigorous attention to regulatory compliance, licensing, radiation safety procedures, and mechanical mounting design. Source activity and detector selection must match the vessel diameter, wall thickness, and desired accuracy. Commissioning typically involves careful calibration and documentation, and long-term support should include periodic verification aligned with site safety programs and measurement criticality.

Forberg Smith, an exclusive authorized representative of sales and service for Endress+Hauser.