BERTHOLD TECHNOLOGIES LB 3602, Руководство по эксплуатации

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LB 379
6
1 Overview
The radiometric density measuring system offers the possibility to measure the density of
liquids, suspensions, slurries and bulk goods. The measurement can be carried out directly
in a product line. The measurement is independent of variations in pressure or viscosity,
and on the flow rate of the product.
1.1 The Principle of Measurement
The density measurement utilizes as a measuring effect the attenuation of gamma radia-
tion passing through the product being measured. The residual radiation picked up by the
detector (scintillator) is a measure of the density of the product being measured.
The attenuation of radiation takes place in accordance to the following law:
Figure 1: Principle of measurement
I = radiation picked up by the detector
Io = unattenuated radiation
µ = mass attenuation coefficient (absorption coefficient in cm 2 /g
 = density of absorbing material in g/cm
3
d = thickness of absorbing material in cm
The intensity of the radiation arriving at the detector is also dependent on the distance
between source and detector. As in the case of light, the function involved is a square
function, i.e. doubling the distance reduces the radiation intensity to ¼ if all other condi-
tions remain unchanged.
In the measuring paths LB 379 and LB LB3602/3603, source, measurement pipe and de-
tector are combined into one unit. This ensures a fixed geometry and a constant distance.
Under these conditions, the radiation arriving at the detector is only dependent on the
density of the material to be measured.
An activation of the product being measured, or of the pipe used for the measurement by
the gamma radiation is completely excluded.
With the isotopes
241
Am and
244
Cm the absorption is dependent, in addition to the density,
on the atomic number of the absorber. It increases with increasing atomic number (see
Figure 2), so that with the substances occurring in practice we can almost always assume
that a higher atomic number can also be equated with a higher absorption coefficient. Due
to this relationship, very high measurement accuracies can be achieved for products con-
taining substances with a high atomic number (e.g. hydrochloric acid, milk of lime, sulfuric
acid, etc.), with the measuring paths LB 379 and LB 3602/3603, which are equipped with
one of these isotopes.
d
o
e I I
* *
*
 
 
d
Io
I
Radiation
source
Detector