Tension load cells are not new, however traditionally they have either been heavy steam-gauge style machines or complex combinations of electrical components that seem more at home in a science lab than out on a roping job.

## Rock Exotica enForcer Load Cell

Weight: 400g plus optional iOS iPhone/iPad for Bluetooth remote display.

Sample rate: selectable at 2 or 500 samples per second

Full scale range: 20kN

MBS: 36kN

Accuracy: better than +/- 0.4kN (+/- 2% of range)

The Rock Exotica enForcer retails for under \$US1,000.  It is self-contained in a small unit and is excellent for use in the field and monitoring real loads in rope based systems.  The Bluetooth functionality is useful but limited by a range of 10m or less.  I have certainly found that the accuracy is “better than +/-2%” but users must keep this value in mind.  This +/-2% corresponds to +/-40kg (or +/- 88lbs) so it is not really appropriate for “experiments” measuring hand-held tensions.  Stick with minimum tensions of 1kN for robust results.

Users need to be aware of the testing capacity of this device.  The technical notice for the enForcer states: “The Enforcer will measure up to 20kN. If you exceed 20kN it will permanently say “Overloaded” on the display. You can still use it for testing, but not for life safety. You should establish your own Working Load Limit depending on use. For example a 6:1 safety factor from the 36kN breaking strength would be a WLL of 6kN.”

## Summary

Tension Load Cells come in many shapes and sizes and it has not been easy to understand their specifications and how these potentially limit practical use.  Hopefully, I have made this a little clearer.  In short, the Rock Exoctica enForcer has revolutionised the accessibility of these devices, however we still need to be attentive in the way it is used.

Richard Delaney, RopeLab, 2017