Loss In Weight Feeder – How To Deal With Issues
Some types of loss in weight feeders are affected by external influences which affect the weighing mechanism. Even if these disturbances produce only a minimal instantaneous weight change, the effect on the feed rate can be huge.
Symptoms of mechanical problems
You can recognise mechanical issues that lead to a reduced loss in weight feeder performance by several symptoms.
- The feeder calibration isn’t repeatable
- When the discharge device isn’t working the controller feed-rate display shows a feed-rate or unstable weight readings
- While the discharge device is working the controller feed-rate display fluctuates unpredictability and out of the allowable range
- Sample checks – in which the weight of material samples taken from the discharge device’s outlet over a 1 to 5 min. period compared with the controllers’ set point – indicates the federate is out of the allowable range
- Lab tests of the final product show material inconsistencies
How to run Screw Feeder Trials
With screw feeders exhibiting these symptoms, it is a good idea t find out if the feeder has been correctly installed and is operating without mechanical problems, that is assuming all the feeder’s electronics are accurate and set up correctly.
There are three main areas to consider – weight stability, repeatability and linearity tests. In general, refer to the feeder manufacturer’s performance specifications to for guidelines to interpreting the results.
Weight Stability Test
When the screw feeder’s discharge device is stopped, does the controller display’s weight reading fluctuate dramatically? If these fluctuations are large, the feeder installation may have one or more mechanical problems.
First, check that all the equipment near the feeder is operating, then record the highest and lowest weight readings on display. The weight reading fluctuations minus the feeder’s specified stability should reveal the amount of variation introduced by the surrounding equipment. By turning off each surrounding piece of equipment one at a time and watching the weight reading for fluctuations, you can determine if one piece of material near the feeder is causing the most problem.
It is of course, vital to have repeatability in measurements, so this test involves adding known weights, typically one-tenth of the feeder’s maximum weight.
When the hopper is empty, the initial weight reading should be zero. Then the test weights are added, and the new weight recorded until all ten have been added. Then the procedure is reversed, and the descending weights recorded. When plotted on a graph, the increasing and decreasing weights chart should match. If they don’t, there is a problem with repeatability.
For solutions for your meter feeders give Trantec a call on 01282 777566.
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