A load cell is a small sealed cavity with a thin element. When atmospheric pressure changes, the pressure difference across the element changes, and the element deflects slightly, producing an output shift. For most industrial cells the effect is small but not zero.
Magnitude
A typical weather swing is about 3 kPa, roughly 3% of an atmosphere. On a cell with a large internal volume and thin diaphragm the resulting zero shift can reach a few hundredths of a percent of rated output, which matters for high resolution weighing such as laboratory balances but is negligible for a 10 t hopper.
Vented versus sealed
Vented cells equalise pressure through a breather and are immune to the effect, but they need a desiccant to keep moisture out. Sealed cells are preferred in washdown areas; the pressure effect is accepted as part of the error budget.
Practical consequence
If a high resolution scale drifts slowly over days with no load change, and the drift correlates with weather, pressure is a candidate alongside temperature. A simple check is to log zero against local barometric pressure for a week before replacing anything.
Kevin Huang