VEGA VEGAMET 391 With SIL qualification - Manual (Page 39)

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9 Application examples
VEGAMET 391 • With SIL qualification
38704-EN-130228
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 "Dry run protection". The
switching points are set as follows:
•
Switch-on point (switching point Hi) 40 % ≙ 10.4 mA
•
Switch-off point (switching point Lo) 5 % ≙ 4.8 mA
In this example, the vessel can be emptied until the relay switches off
when 5 % are reached and the emptying pump thus switches off. If
the level rises again to over 40 %, the relay is switched on and empty-
ing begins again.
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.
9.3 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:
•
Pump control 1: The upper switching point determines the switch-
off point for the relay, whereas the lower switching point deter-
mines the switch-on point
•
Pump control 2: The upper switching point determines the switch-
on point for the relay, whereas the lower switching point deter-
mines the switch-off point
Scaling
Relay
Functional principle