VEGA VEGAMET 625 - Manual (Page 40)

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8 Application examples
VEGAMET 625 • Double channel HART
28970-EN-130701
to 5 %, this corresponds to 181 litres. The volume should be displayed
in litres.
Carry out the adjustment in the signal conditioning instrument as
described in chapter "Setup steps". No additional adjustment must
hence be carried out on the sensors. For the max. adjustment, fill the
vessel up to the requested max. level and accept the actually meas-
ured value. If this is not possible, the respective current value can be
entered alternatively. For the min. adjustment, empty the vessel up to
the min. level or enter the respective current value.
To display the percentage level correctly, select under "Measurement
loop - Linearization curve" the entry "Cylindrical tank".
To display the volume in litres, you have to enter "Volume" as unit in
litres under "Measurement loop - Scaling". The allocation is then car-
ried out, in this example 100 % ≙ 10000 litres and 0 % ≙ 0 litres.
Percent is selected as reference value for the relays. The mode of re-
lay 1 is set to overfill protection, relay 2 gets mode dry run protection.
To ensure that the pump switches off in case of failure, the reaction
in case of failure should be adjusted to switching status OFF. The
switching points are adjusted as follows:
•
Relay 1: Switch-off point 90 %, switch-on point 85 %
•
Relay 2: Switch-off point 5 %, switch-on point 10 %
Information:
The switch on and off point of the relays must not be adjusted to the
same switching point because this would cause a permanent switchin
on and off when this threshold is reached. To avoid this effect also
with fluctuating product surface, a difference (hysteresis) of 5 % is
useful between the switching points.
8.2 Weir control of a water power station
A water power turbine must be protected against impurities in flowing
water. These impurities get stuck on the weir like on a screen. The
must be removed cyclacylly so that the max. flow is ensured. If the
degree of impurity is too high, the water level in front of the system
raises because the total water volume can no longer flow through.
The difference between level in front of and after the weir is hence a
measure of the degree of impurity and can be used to control the weir
cleaner.
The water level in front of the weir (upstream water) and after the weir
(downstream water) is measured each with a VEGAWELL 72 HART.
VEGAMET 625 generates the difference (h3) out of these two levels
(measurement loop 3). If this difference is too high, a signal will be
outputted by one of the integrated relays triggering the weir cleaning.
Exemplary we assume a max. level of 2 m, the weir cleaning should
be started at a difference of 20 cm.
Adjustment
Linearization
Scaling
Relay
Functional principle
Example