4.5.5 Timer period for pump enable and empty signal
The enable signal for the metering pump(s) (PUMP Enable) is only output if the level
switch is at the uppermost position, in other words if there is enough product in the lifting
vessel. If the level in the lifting vessel drops for longer than 5 seconds, due to air being
drawn out of the emptied container, the enable signal for the pump is interrupted.
The empty signal to the container is restored after an adjustable timer period, started by
the level switch in its lowest position. If this time expires without the level being reached
again, an empty signal is output for the active container and the compressed air supply is
interrupted. The switchover to the other container takes place automatically if the latter is
on standby
.
The time for empty signal can be adjusted using DIL switch on the control board in 2 steps
between 2 and 30 seconds
Ä
Chapter 4.5.4 ‘Adjusting elements’ on page 26. Suction
time of 10 seconds is pre-set ex-works. During commissioning, the time must be adjusted
to the then prevailing conditions (
Ä
Chapter 6 ‘Commissioning and operation’
on page 33).
In essence, the time is influenced by the length of the suction line(s), the suction power
obtainable at the injector, and the total capacity of the connected pumps. Long suction
times have the advantage that the containers are emptied to the best possible extent,
which is not possible with conventional suction lances. The time should therefore be set to
long enough to allow the upper level in the lifting vessel to be reached again during a
switch-over process, even with the pumps running.
Long suction times are not possible with large pump capacities, since the lifting vessel is
quickly emptied if there is a shortage of product in the container and the pump then starts
to draw in air. The enable signal (Pump Enable) is therefore generally interrupted after 5
seconds until the level in the lifting vessel is reached again.
NOTICE!
In the case of critical processes for which any interruption in metering is to be
preferably avoided, the suction time must be set as appropriately short. This
increases the residual quantity left in the container.
Functional description
27 Rev. 1-06.2018
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