VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 43)

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8 Application examples
VEGAMET 391 • 4 … 20 mA/HART
36032-EN-130701
of the menu item "Acknowledge failure". If the fault message is reset
via the menu and the pump still signals failure, a fault message is
triggered after the enquiry period. The enquiry period is started as
described above when the relay is switched on.
Switch on reaction of the pump control 2
When the signal conditioning instrument is switched on, the relays are
at first in a switched-off status. Depending on the input signal and the
switched-on period of the individual relays, the following relay switch-
ing conditions can occur after the start procedure:
•
Input signal is higher than the upper switching point -> Relay with
the shortest switch on period is switched on
•
Input signal is between lower and upper switching point -> Relay
remains switched off
•
Input signal is smaller than the lower switching point -> Relay
remains switched off
8.3 Pump control 3/4 (sequentially controlled)
Pump control 3/4 is used to control several pumps with the same
function alternately and in a fixed sequence. In case of an increased
requirement, all pumps can run at the same time depending on the
entered switching points. With this measure, a steady utilization of the
pumps is reached and the reliability increased.
All relays with activated pump control are not assigned to a certain
switching point but are switched on and off alternately. When a switch-
on point is reached, the signal conditioning instrument selects the
relay that is next in the sequence. When a switch-off point is reached,
the relays are switched off in the sequence they were switched on.
Via the digital inputs, possible fault signals of the pumps can also be
evaluated. You can find the description in the application example
"Pump control 1/2" under "Pump monitoring".
With this pump control, there are two different versions:
•
Pump control 3: 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 4: The upper switching point determines the switch-
on point for the relay, whereas the lower switching point deter-
mines the switch-off point
The sequence cannot be changed, the relay with the lowest index is
switched on first, then the relay with the next higher index. After the
relay with the highest index, the relay with the lowest index follows,
for example Rel. 1 -> Rel. 2 -> Rel. 3 -> Rel. 4 -> Rel. 1 -> Rel. 2 … The
sequence applies only to those relays assigned to the pump control.
In a waste water disposal system, a sump should be pumped empty
when a certain level is reached. Three pumps are available for this. At
60 % level, pump 1 should run until the level has fallen below 10 %.
If the 60 % point is exceeded again, the same task is transferred to
pump 2. In the third cycle, pump 3 is activated; after that, pump 1
Functional principle
Example