Engineering Application Sheet E017 - Lifting With Loadcells - Safety

Loadcells are not load rated in the same way as lifting equipment. As measuring devices it is necessary for higher stress levels to be present within a loadcell compared to a lifting eye or hook for example. However by correctly specifying a loadcell load rating it is possible to maintain a consistent safety margin or safety factor within a lifting system i.e. by applying a safety factor to a loadcells rated load you can determine the working load limit (WLL).

Novatech loadcells do have ultimate overload limits which are usually a factor of 2 times the rated load, however, this factor is designed for loadcells in perfect loading conditions so it is, in our opinion, prudent to consider the RATED LOAD (RL) not the ultimate overload limit as the key to ensuring that the correct safety factor is employed. So ignore the data-sheet overload values and only use the rated load for the loadcell.

Example:

The application requires a machine with an estimated weight of 1 tonne to be lifted.

Appropriate standard safety rules require a safety factor (SF) of 4.

Therefore select a loadcell with a rated load of 4 tonnes.

Normally for lifting applications other than aircraft or spacecraft the degradation of measurement accuracy is negligible. However, if you are lifting with a requirement for normal loadcell force measurement precision we can improve the accuracy by calibrating the loadcell to the estimated range. In the previous example we could calibrate the 4 tonne rated load loadcell to 1 tonne.

Obviously different generic types of loadcells possess different structural capabilities and our recommendation of a safety factor of 4 is open to detailed interpretation for specific applications. Please contact our engineering department to discuss any deviations from this practice. It is the client's responsibility to ensure a good safe lift using our equipment.

Precautions:

1. Apply a safety factor (÷3 or 4) to the loadcell rated load to obtain a working load limit (WLL).
   WLL = RL ÷ SF
2. Never ‘snatch’ load the loadcell.
3. Ensure that the weight of all lifting tackle is taken into account when estimating the load.
4. Only apply loads in the intended load sense of the loadcell i.e. normally axial.
5. Ensure your lifting tackle fitments are rated in accordance the load and safety factor applied.
6. Never exceed the rated load of the loadcell. Always apply your lifting system safety factor to the loadcell rated load to determine the WLL for your lifting system.
7. It is a false economy to underrate the loadcell; Nova tech's hire price is the same for all load ranges.
8. If in doubt about your lifting system's working load limits please seek assistance before using it to lift a load.
9. Ensure all fittings are secured and locked in place before use.
10. Never allow the load to exert a torque through the loadcell. If it must rotate provide a swivel joint within the lifting system.

Essential References:

HSE Standard EP2005 vol2, ref EP2005-0264-ST Lifting and Hoisting.

LOLA Lifting Operations and Lifting Equipment Regulations 1998.

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