Loss
In Weight Feeders
Constant Rate Feeding
Principle and Operation
The Rospen loss-in-weight feed system has been designed to weigh
and control the output of variable products continuously to weight
accuracies of ±0.25% to ±1%.
The general principle of operation is as follows:
- The loss-in-weight hopper is rapidly filled via an automatic
filling valve. At a hopper-full weight, pre-set within the PLC,
the filling
- The metering feeder starts (or is already running from the last
cycle) and feeds product into the process; thus the weight in
its product hopper gradually falls.
- The falling weight is measured every few milli-seconds and this
information is averaged and stored by the PLC or as a
falling weight per unit time (Kg/Sec). This weight per unit time
is compared to a weight per unit time already pre-set by the operator
via the HIM and stored in memory.
- Any difference in the characteristic slope of the falling weight
per unit time and the slope of the pre-set weight against time,
is fed to a process controller and used to speed up or slow down
the product feeder in order to make the two slopes identical.
- At a pre-set hopper low weight, the metering feeder is locked
onto it’s last average speed and the filling valve opened
again, so rapidly filling the hopper.
- When the hopper is again filled, the metering feeder will be
brought back onto automatic control at the original correct speed
that was memorised by the PLC during the previous cycle.
- Thus the cycle will repeat, with the PLC going through a continuous
learning curve which will get more accurate with each cycle.
- The cycle time will be approx 10:1 running to filling e.g. 10
mins run to 1 min fill, or 5 mins to 30 seconds fill.
|
|
