A load cell measures strain in its sensing element, and any force that strains that element produces output, whatever direction it came from. Side load and bending moment are therefore not just mechanical risks; they are measurement errors.
How the error appears
A side load typically produces a zero shift that changes with the direction of the force, so the reading drifts as a vessel expands or a platform is pushed. Bending moment produces a change in sensitivity, so the span error grows with load and looks like nonlinearity.
Hardware that helps
Spherical seats, rocker pins and self-aligning mounts let the cell tilt slightly so the load stays axial. Load buttons with a spherical radius transmit force through a point, eliminating moment transfer. For platform scales, check that the cells sit on flat, level surfaces and that the deck is restrained horizontally by separate stays.
Diagnosis
Load the system, then push horizontally on the vessel with a few kilograms of force and watch the reading. Any change beyond the resolution indicates that side load reaches the cell. Fix the restraint before recalibrating, because calibration will only hide the error at one load.
Kevin Huang