8
A
pplication examples
8
.
1
L
evel measurement in a cylindrical tank with
over
fi
ll protection
/
dry run protection
T
he level is detected via a sensors and transmitted to the signal
conditioning instrument by means of a
4
…
20
m
A
signal
.
H
ere
,
an
adjustment is carried out converting the input value delivered by the
sensor into a percentage value
.
D
ue to the geometrical form of the cylindrical tank
,
the vessel volume
does not increase linear with the level
.
T
his can be compensated by
selecting the linearization curve integrated in the instrument
.
T
his
curve states the relation between percentage level and vessel volume
.
I
f the level should be displayed in litres
,
also a scaling must be carried
out
.
F
or this purpose
,
the linearized percentage value is converted into
a volume
,
for example with the unit litres
.
T
he
fi
lling and emptying is controlled vial relay
1
and
2
integrated in
the signal conditioning instrument
.
D
uring
fi
lling
,
relay mode
"
O
ver
fi
ll
protection
"
is adjusted
.
T
he relay is hence switched o
ff
(
safe
currentless condition
)
when the max
.
level is exceeded
,
when falling
below the min
.
level it is switched on again
(
switch on point
<
switch o
ff
point
).
D
uring emptying
,
mode
"
D
ry run protection
"
is used
.
T
his relay
is hence switched o
ff
when falling below the min
.
level
(
safe
currentless condition
),
when falling below the min
.
level it is switched
on again
(
switch on point
>
switch o
ff
point
).
Rel. 1
Rel. 2
Rel. 1: 90%
Rel. 2: 5%
100%
0%
F
ig
.
11
:
E
xample for a level measurement
,
cylindrical tank
A
cylindrical tank has a capacity of
10000
litres
.
T
he measurement is
carried out with a level sensor operating according to the principle of
the guided microwave
.
T
he
fi
lling by a tank car is controll via relay
1
and a valve
(
over
fi
ll protection
).
T
he discharge is carried out via a
pump and is controlled by relay
2
(
dry run protection
).
T
he max
.
F
unctional principle
E
xample
42
VEGAMET
625
•
D
ouble channel
HART
signal conditioning instrument
8
A
pplication examples
28970
-
EN
-
110801
