Berthold DUO XPERT LB 470RID, Руководство по эксплуатации

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LB 470RID Level 3 System Description
56925-1BA2 Rev.02, 05/2021
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3.3.6 Restrictions and Limits of Interference Radiation Sup-
pression
To be able to use the total functionality of the LB 470RID and to avoid incorrect
settings, understanding of the restrictions and limits of the interference radiation
suppression system is required.
Radioactive sources
Because interference radiation and measuring radiation are distinguished by rec-
ognizing the different energies of the employed isotopes, the difference in these
energies must be sufficiently large for the suppression system to operate properly.
This means that an isotope with high-energy gamma radiation must be used for
the measuring source.
Therefore, continuous level measurements using the LB 470RID are only effective
if the measurement isotope is Co-60. The radiation energy of Cs-137 sources and
typical interference radiation are too close together to be distinguished by the
measurement system. Existing level measurements with Cs-137 sources must be
converted to Co-60 to be able to work with the interference radiation suppression
of the LB 470RID.
Interference Radiation Sources
Interference radiation cannot be suppressed reliably if isotopes with high radiation
energy are used in the welding checks. In such cases the Measuring and the Sec-
ondary Channel are both influenced by the interference radiation. Then
interference radiation is recognized merely as a sudden increase in pulse rate and
the level signal is frozen for the duration of the interference.
However, high energy isotopes (e.g., Co-60) are used extremely rarely in weld
checking and material testing. The vast majority of testing applications use Ir-192
and Se-75, which are recognized reliably by the LB 470RID system as an interference
radiation and are suppressed.
Strong Interference Radiation
If weld checking using extremely strong interference radiation sources (activity of
40 Ci and more) takes place in less than approx. 50-100 m from the measuring ar-
rangement, the pulse rate in the Secondary Channel can also be influenced and
lead to errors in the continuous level measurement. If an inadmissibly high increase
in pulse rate occurs in the Secondary Channel, the measuring signal is frozen and
an error message is given.
Automatic CD Minimization
Accurate balancing of the measuring channel to the second channel takes place in
those parts of the measuring range in which the filling level is located. The other
parts of the measuring range are also corrected according to this adjustment.
If reliable interference radiation suppression is required in all parts of the measur-
ing ranges, it must be ensured that the entire measuring range is passed from time
to time.