Selecting the correct type and capacity of load cell
Load cells form the basis of over 99% of process weighing systems. Selecting the correct type and capacity is a critical issue that needs careful consideration from the outset. The key factors in the decision process must take into account:
- The overall capacity of the weighing system
- The dead weight of the weighing system itself when empty
- The working range of the weighing system
- Any overload requirements (e.g. wind forces, shock loading, vibration, seismic forces)
- Environmental factors (e.g. wash-down, chemicals, temperature changes)
- Accuracy requirements
- Legislative requirements (e.g. Legal for Trade, ATEX)
It should be remembered that in many applications, the actual live working range of the load cell (and hence the available electrical output) will be reduced depending on the dead weight of the vessel and any overload requirements. This can have an important affect on performance and further endorses the need to ensure load cells are of the highest quality.
Operationally weighing systems essentially fall into two main categories – compression and tension, depending on whether the vessel or similar ‘sits on’ or is ‘suspended from’ the load cells. These two fundamental modus operandi can then be sub-divided into the following main types of load cells:
- Single ended bending beam
- Shear beam (single and double ended)
- ‘S’ tension beams (bending and shear)
- Compression canister
- Ring torsion
- ATEX certified
Material of construction includes aluminium, plated tool steel, painted tool steel and stainless steel
Any final decision in the selection process will almost certainly involve a level of compromise to optimise performance versus system integrity and environmental compatibility.
In the majority of applications, mounting load cells without the use of proprietary mounting hardware can be difficult and very unsatisfactory. Well designed hardware not only plays an important role in terms of load introduction, vessel restraint, lift-off protection and overload protection, but also facilitates load cell fitting and removal.