VEGA MINITRAC 31 4 … 20 mA_HART - four-wire With SIL qualification - Manual (Page 9)

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3 Product description
MINITRAC 31 • 4 … 20 mA/HART - four-wire
43389-EN-131119
on the density of the measured media. The measuring principle has
proven to be very reliable in conjunction with extreme process condi-
tions because it measures contactlessly from outside through the ves-
sel wall. The measuring system ensures maximum safety, reliability
and plant availability independent of the medium and its properties.
3.3 System limitations
There are several measuring principle-specific factors which can influ-
ence the measuring result. Keep these factors in mind in order to fully
utilize the capabilities of the instrument with respect to measurement
certainty and reproducibility.
The implemented radioactive isotope and its activity must be selected
according to the properties of the vessel and the medium. The neces-
sary radioactive activity must be calculated on the basis of the plant
data.
To this end, make use of our planning service for an optimum layout of
the measurement and selection of the isotope. This applies particu-
larly to SIL applications.
Due to the physical properties of the radioactive radiation, the pulse
rate is subject to slight fluctuations. Set a suitable damping level to get
a stable measured value.
The relation between level and the pulse rate measured by the sensor
is not linear.
Set up a linearization table to get a linear level signal. For precise
mesurement results, make sure when setting up the linearization
table that the actual filling height of the measuring points is entered as
exactly as possible.
External radiation sources can influence the measured value (e.g.
welding joint tests). In safety-relevant applications, the safety function
must be treated as unreliable as long as the external radiation occurs.
If necessary, you must take measures to maintain the safety function.
Make sure during the planning that for the planned application, a
possibly large different of the pulse rate with empty and full vessel is
reaced. This applies mainly for products with low density or in vessels
with extremely small diameter.
3.4 Packaging, transport and storage
Your instrument was protected by packaging during transport. Its
capacity to handle normal loads during transport is assured by a test
based on ISO 4180.
The packaging of standard instruments consists of environment-
friendly, recyclable cardboard. For special versions, PE foam or PE
foil is also used. Dispose of the packaging material via specialised
recycling companies.
Activity of the source
Non-linearity of the pro-
cess value
External radiation
Span
Packaging