At some point, all concrete batch plants will begin to give cement away as the scale lever system wears down.  Mobile batch plants that are relocated more frequently can show even greater abuse to the plant scale system.  Some concrete batch plant manufactures are replacing the scale lever system with compression load cells.  Compression load cells fix the weigh batcher to the batch plant frame and eliminate any excessive scale movement.  Eliminating scale movement can also reduce your batch time by 25%.  Compression load cells cost about $1,200 each and are typically grouped in 3 or 4 per set.  Calibration is accomplished with test weights as typical scales require.  For even greater accuracy, you can incorporate a summing box ($700) that allows the spanning of each load cell to the overall scale display.

Before you invest in a set of compression load cells, I would suggest the following steps to confirm your scale accuracy.
1.  Inspect the scale system, including levers, load cells, bearing points and hoppers. Correct any  damaged parts or altered factory adjusted settings.
2.  Confirm the plant foundation is level and not settling.
3.  Perform a scale build-up with certified test weights.  Each build up increment should be no more than 20% of full scale capacity. At each scale build up point, add a test weight equivalent to 1 grad to a scale corner.  Record the added weight before checking the 1 grad weight at the next corner.  Any required adjustments can be completed with a summing box.
4. Confirm the Automatic Batch Controller is not capturing a lighter weight then the actual batch weight. Settle time of 3-4 seconds is common for most plants.
5.  Make sure the Bag House cartridge or bags are clean.  Plugged bags will pressureize the silo pushing cement past a 3 psi butterfly valve seal.  Also confirm the “cleaning sequence” time is adequate for the amount of cement being offloaded.
6.  Last but not least, confirm the bulk truck driver is offloading the complete load of cement.