VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 40)

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8 Application examples
VEGAMET 391 • 4 … 20 mA/HART
36032-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 Pump control 1/2 (running time controlled)
Pump control 1/2 is used to control several pumps with the same
function dependent on the previous running time. Always the pump
with the shortest running time is switched on and the pump with
the longest running time switched off. With increased requirement,
all pumps can also run at the same time dependent on the entered
switching points. With this measure, a steady utilization of the pumps
is achieved and the reliability increased.
All relays with activated pump control are not assigned to a certain
switching point but are switched on or off depending on the accu-
mulated operating time. The signal conditioning instrument selects
the relay with the shortest operating time when the switch-on point
is reached and the relay with the longest operating time when the
switch-off point is reached.
Probable failures of the pumps can be processed in addition via the
digital inputs.
With this pump control, there are two different versions:
Adjustment
Linearization
Scaling
Relay
Functional principle