VEGA VEGAMET 391 With SIL qualification - Manual (Page 37)

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9 Application examples
VEGAMET 391 • With SIL qualification
38704-EN-130228
the guided microwave. Filling is carried out by a pump controlled via
a PLC. Relay 3 of VEGAMET is connected to prevent overfilling. The
max. filling should be at 90 % level, which corresponds to 9538 litres
in a standard vessel (according to sounding chart). The filling quantity
should be displayed in litres.
Carry out the adjustment as described in the respective operating
instructions of the sensor. After that, further adjustment must not be
carried out on the signal conditioning instrument.
To have the percentage volume displayed correctly, a lineariza-
tion must be carried out. As described in the respective operating
instructions of the sensor, select the linearization curve "Cylindrical
tank". After that, a linearization must not be carried out on the signal
conditioning instrument.
To display the volume in litres, you have to enter in the signal con-
ditioning instrument under "Measurement loop - Scaling" as unit
"Volume" in litres. Then the allocation is carried out, in this example
100 % ≙ 10000 litres and 0 % ≙ 0 litres.
The mode of relay 3 must be set to mode "Overfill protection". The
switching points are set as follows:
•
Switch-off point (switching point Hi) 90 % ≙ 18.4 mA
•
Switch-on point (switching point Lo) 60 % ≙ 13.6 mA
In this example, the vessel can be filled until the relay switches off
when 90% are reached and thus the filling pump switches off. If the
level falls below 60%, the relay is switched on again and thus enabled
for the filling process.
Information:
The switch-on and switch-off points of the relays must not be set to
the same switching point because this would cause a continuous
switching on and switching off when this threshold is reached. Hence,
this setting is not accepted and a corresponding error message is
outputted. To avoid this effect also with a fluctuating product surface,
setting a difference (hysteresis) of 5 % between the switching points
is a good idea.
9.2 Dry run protection according to SIL2
The described setup of sensor and VEGAMET is specified as dry run
protection according to SIL2. Filling and emptying are realized via a
separate control (e.g. PLC).
The level is detected via a sensor and transfered by means of the
4 … 20 mA signal to the signal conditioning instrument. To prevent
dry run, the SIL relay integrated in the signal conditioning instrument
switches off the emptying pump when the level falls below the adjust-
able switching threshold.
Due to the geometrical form of the spherical tank, the vessel volume
does not increase linearly with the level. This can be compensated for
by selecting the linearization curve integrated in the sensor. It speci-
Adjustment
Linearisation
Scaling
Relay
Functional principle