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SEQUENCE OF
CONTROL
When the PLC
controller is switched on, it starts to scan for convey stations that
are in need of material, as indicated by the conveyors’ flap switch
(level switch).
When the first
station is found, its’ convey valve is opened and material is
transferred for a preset time.
This time can be
adjusted to suit the conveyor size or distance etc.
While this station
is loading, the controller searches sequentially for the next conveyor
that requires material.
When one is found,
the controller stops scanning and waits until the present convey is one
second away from completion.
It then opens the
convey valve on this next station, before closing the convey valve of
the first unit after its preset transfer time is completed.
On a common
material system this ensures that the product is kept moving and does
not lay in the pipe.
The controller now
searches for the next conveyor requiring material.
These searches
always take place sequentially so that no station is overlooked.
After a station has
finished loading, the controller monitors the flap switch of that
conveyor.
If the switch does
not remain made for at least 1 second, (indicating that little or no
material has been conveyed), the controller senses this and after three
consecutive occurrences it activates a no load alarm.
This alarm
automatically resets itself when the situation is corrected.
When the controller
cannot find any station on the system in need of material, the vacuum
breaker valve on the vacuum pump is operated and the central filter is
purged.
The vacuum pump
continues to run for approximately 30 seconds while the controller
re-checks the material level conditions, if there is still no demand
during this time then the pump will shut down.
On systems using
rotary vane pumps the pump shutdown feature is not used and the pump
runs continuously.
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Jenco -
Plastics
Jenco - Food
Jenco -
Pharmaceutical
Jenco -
Chemical
Controls up to 30 Convey Stations and 6 Vacuum Pumps
