The working principle
Radiometric level and density measurements are perfect for monitoring challenging processes with high temperature and high-pressure conditions. However, the performance of the measuring system i.e. the measurement sensitivity can be affected by changing ambient temperatures if no correction method is in place. The scintillation detectors used in state-of-the-art radiometric measurements are designed to detect gamma radiation which is emitted from an industrial source – usually Cs-137 or Co-60 isotopes. However, these detectors also pick up cosmic rays. The cosmic rays are much higher in energy which allows the radiometric detector to distinguish internally between gamma radiation coming from the measurement source (Co-60 or Cs-137) and the high-energy cosmic rays. By employing a reference channel measuring the cosmic radiation only, Berthold was able to introduce an innovative and unique stabilization technology that automatically and continuously corrects all external effects. Since the rate of cosmic radiation is known to be stable, any fluctuations detected in the reference channel will be related to a change of detector sensitivity caused by temperature effects. As a result the detector internal gain is automatically adjusted in such a way that the cosmic rate is kept within its target value and measurement sensitivity remains stable. Using this natural reference source and patented compensation method leads to higher reliability than any software correction method can achieve because it not only compensates for changing ambient temperatures but also the effect of detector degradation, caused by the aging of electrical components.
Field experience
The automatic detector stabilization method based on cosmic rays leads to outstanding long-term stability of radiometric level and density measurements. Where operators have previously observed temperature dependence of their measurement system, or have installed complicated methods to keep the detector temperature constant, the automatic stabilization has helped them overcome these problems. Ultimately, Berthold detectors have been able to increase reliability and drastically reduce operational costs in hundreds of applications ranging from coke drum levels to the measurement of molten glass. In safety-critical applications such as those of polypropylene loop reactors, the high stability and resulting reliability of the radiometric density measurement has helped operators push the process to the limits and thereby maximize production yield without compromising the operational safety of the process.
Conclusion
Due to cosmic radiation, Berthold was able to introduce a unique stabilization method that intrinsically compensates for all external effects – even without deeper knowledge of where the disturbing factor is coming from (temperature, aging, etc.). The result is a highly repeatable measurement which is used in thousands of applications worldwide and allows operators to run their processes a lot more safely and reliably. At the same time, the systems do not require recalibrations or readjustment of parameters throughout the operational life, which results in extremely low operational costs and high ease of handling.
Ultimately, the natural and ever-present reference measurement has resulted in the SIL2 and SIL3 certification of the Berthold detectors - for both point level applications (high level and low level alarm), continuous level, and density measurements.
SIL certified option
The SENSseries LB 480 offers detectors that are certified for use in SIL2 applications. SIL3 is achieved by adding an identical redundant SIL2 detector for homogenous redundancy. The certificate covers all measurement applications, from high level or low level alarms to continuous level and density measurements. Thus the safe measurement of critical processes is guaranteed.