What is overload protection on a load cell?

Overload protection, in a general sense, refers to how a system or device is protected from damage that can result from an input that exceeds a designed limit. For example, overload protection in an electrical application might involve using a fuse or circuit breaker to protect the system from a current overload.

Overload protection on a load cell refers specifically to the means used to prevent the cell’s diaphragm from deflecting beyond its designed elastic limit. Without overload protection, a load cell’s diaphragm experiences irreversible damage under too much applied input.

To achieve overload protection in a load cell, a mechanical stop is inserted to prevent the diaphragm from deflecting beyond its elastic limit. The mechanical stop bottoms out when excessive load is applied.

Load cells that do not have mechanical overload protection enjoy an overload capacity by default typically 50%. This means that a 100 lbf load cell, without mechanical overload protection, can sustain a 150 lbf load without incurring damage.

Notice that when a load cell’s maximum designed input limit is exceeded, the load cell’s output does not increase further (the output becomes asymtopic).

Mechanical overload protection lends itself more easily to compression load cells than to tension load cells. Because of the internal mechanical design of tension load cells, it is difficult to insert a mechanical stop that provides sufficient overload protection.

Note: Honeywell sensors operate in an elastic range of .002 - .003 inch. Because of the typical design of most load cells, Honeywell can fit overload stops on most compression load cells, but on only a few tension load cells. There are also some load cells that, because of their unique shape, are unable to have overload stops in either compression or tension. At Honeywell, every load cell has a slightly different deflection. Because tolerances on a load cell’s internal dimensions are not tight enough to permit a generic overload protection stop, any protection stop that is inserted must be custom made, custom fitted and then custom tested. This process increases the cost significantly.