A scale that will not hold zero is the most common service call in weighing. The cause is usually not the cell, and a structured check finds it faster than swapping parts.
Six causes
Thermal drift from self-heating or sunlight; moisture in the cable or cell; mechanical settling of a new installation; a ground loop or electrical noise; barometric pressure on a sealed cell; and indicator electronics. Each has a distinct time signature: thermal drift follows the daily temperature curve, moisture follows humidity and rain, mechanical settling decays over days, electrical noise appears with other equipment, pressure tracks weather systems.
Isolating the cause
Disconnect the cell and measure bridge resistance and insulation resistance. Then load and unload three times to check return to zero. If the cell is stable on the bench but drifts in place, the problem is installation or wiring, not the cell.
Practical fix order
Check cable entry and junction box dryness, verify single-point shield grounding, re-torque mounting bolts, then re-zero. Only after those steps is replacing the cell justified. Keeping a log of zero against temperature and humidity turns guesswork into evidence.
Kevin Huang