Calibration means comparing the cell output against a known force. Above a few tonnes, certified masses become impractical, so most industrial calibration is done by comparison in a force machine against a reference cell or proving ring.
Deadweight loading
Masses certified to OIML class M1 or better, applied vertically through a knife edge, give the lowest uncertainty because force is generated by mass times local gravity with no intermediate transfer. It is slow, limited to a few tonnes, and sensitive to air buoyancy and to any friction in the loading train. For small cells and for type approval work it remains the reference method.
Comparison in a machine
A force standard machine or a deadweight lever system applies load through a reference transducer calibrated to a higher class. Uncertainty depends on the reference, the machine alignment and the loading rate. The advantage is capacity and speed; the risk is that misalignment in the machine loads the cell with a bending moment and produces a calibration that does not transfer to the real installation.
Practical guidance
Calibrate in the orientation and with the mounting hardware used in service. A cell calibrated in compression between flat platens and then installed with a spherical seat will not repeat. For trade use, follow the national metrology requirement for the interval; for process weighing, an annual check with a known test weight plus a daily zero check catches most drift.
Kevin Huang