- This actual feed rate is compared with theoretical set point given to the
machine and corrective action is taken by PID control loop functions which
issues control command to variable frequency drive for increase / decrease of
belt speed. - To maintain consistency and better performance weigh feeder, constant belt
loading (material bed height on the belt) is maintained over the belt with
manual adjustment of feed gates. - Accuracy of the weigh feeder can be obtained approx. ±0.5% of the feed rate
if equipment is well maintained and calibrated. - There is totalizer function which accumulates instant feed rate of material and
gives total figures of flow material as on time. - Factors affecting the equipment performance:
o The weighing assembly should always be neat & clean and free from dust,
foreign particles,
o The belt should always be in centre of assembly. Drifting of the belt leads to
error in weighing results.
o The deposition of fine material on rollers of weighing assembly also lead to
error in weighing results,
o Any material stuck in Weighing idler gives erratic transfer of load on cells.
Although the system indicates feed rate but the operator cannot know
whether the reading is erratic or correct.
o Uneven bed height of material over belt affects performance of weigh feeder,
o Condition of belt also affects result of machine,
o The leakage in circuit diverter while drop test may lead to error in test results,
o If the drop test is taken for duration say 10 minute approx., minimum bin
capacity required, below the weigh feeders, is 25 T for lower feed rate
applications, however for higher feed rate applications like Raw mill, bin
capacity requirement shall be min. 50T, for collecting the material which
weight is to be cross checked at weigh bridge.
o Online verification of system accuracy is not possible unless significant
deviation is observed in the feed rate,
o The weigh feeders are suitable where controlled feed i.e. gravimetric
measurement is required like cement mills, raw mills, coal mills,
Important Note:
o The drop test without calibration bin is observed inaccurate. The continuous
running of the weigh feeder at fixed flow rate gives more accurate test
results.
o Without weigh bin, procedure of cross checking with weighbridge involves
shorter duration of drop test which does not reflect the accurate & reliable
results, as the material collected is only 10 to 15 % of total feed rate.