Berthold DUO XPERT LB 470RID, Operating Manual

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3 System Description LB 470RID Level
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56925-1BA2 Rev.02, 05/2021
3.2 Measuring Principle
Gamma radiation is used to penetrate a medium in a container. The attenuation
of the radiation is analyzed to measure the level in the container.
The evaluation DuoXpert LB 470RID (master EVU) is used for the evaluation, trans-
mission and visualization of measured values which it receives from the connected
detectors.
The EVU is an independent measurement channel. If several measurement chan-
nels are required, an independent EVU must be used for each channel.
For covering larger measuring ranges with level measurements, it is possible to
connect multiple detectors on a level measuring device LB 470. To do this, an addi-
tional slave module is required (optional) for each additional detector after the
first. A maximum of 16 slave modules can be connected per master EVU. A cascaded
measurement system with a maximum of 17 detectors can be set up in this way.
Tip
Further information on the functional principle of the detectors can be found
in the operating manual of the detector.
3.3 Radiation Interference
Radiometric continuous Level Measurements and Interference
Radiation
The highly sensitive large volume gamma-ray detectors used in continuous level
measurements are susceptible to the effects of strong radiation external to the
level measurement system. Problems can occur when very powerful radioactive
sources, (typically used in the testing of welds and other material properties in the
construction or refurbishment of pipes), are in use in the vicinity of the level meas-
urement system.
These strong and sporadic radiation fields are detected and counted by the level
system in addition to the valid counts resulting from the source used to determine
the level in the vessel. Without additional precautions, the evaluation unit would
add the unwanted counts to the wanted counts and provide an incorrectly low
reading for the level in the measured vessel. This type of process error can be ex-
pensive and even dangerous.
he standard LB 470 evaluation unit is configured to deal with the effects of spo-
radic unwanted radiation by recognizing a fast increase of input count rate due to
unwanted radiation and freezing the signal representing fluid level in the vessel at
the last correct value for the duration of the interference, then reverting to a nor-
mal measurement mode when the unwanted radiation stops. During this time, no
information about the actual fill level is available and the process has to be con-
trolled manually. This is satisfactory for situations where level changes are
relatively slow or interference takes place infrequently. However, in processes
where the level in the vessel fluctuates quickly and interfering radioactive sources
are in use at the site, automated safety features are required to avoid errors due
to interfering radiation.
Suppression of Unwanted Radiation Signals
A patented LB 440-RID 1 continuous level system is now available which almost com-
pletely eliminates the effects of interference radiation on the accuracy of level
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US patent 6,753,532 B2, EU patent pending