Force measurement and load cells; the right tool for the job

With so many different load cells to choose from, how can you ensure you buy the right load cells for your requirements?

A detailed article in ‘Quality’ magazine cites how load cells are “Arguably the most important component in a force measurement or material testing system’s ability to provide accurate, precise and valid measurements.” It also gives some pointer as to other characteristics load cell users, and in particular materials testers, should consider before buying load cells.

Load cell capacity

It seems fairly obvious, but it’s important to buy a load cell with sufficient capacity for your requirements.

• Too low a capacity, and your load cell is in danger of being overloaded.
• Too high a capacity, and your load cell may be inaccurate when operating too close to its lowest specified load.

In general, load cells are less accurate when operating close to 10% of their rated capacity, but much less so within the top 10% of their capacity. At The Load Cell Shop, all our load cell types come in a range of capacities to suit a range of uses, If you’re not sure which capacity is best for your task, just call us and ask!

 

Zero balances, gravity and taring

Load cells are so sensitive that some can even be affected by gravity. The zero balance of any load cell is the signal produced when there is not load applied at all to the load cell. The easiest way to see the zero balance is to turn a load cell on its side. For very small or light load cells, the effect of earth’s gravity will show as a load reading if measured in their final working position. That’s why load cells should be tared (zeroed) before use. This taring accounts for the gravity and the weight of any mount or test rig fixings.

We manufacture our own load cells here in the UK, and every series we produce has a detailed and accurate data sheet available, containing important specification details including the zero balance. For an example for our Richmond Industries 100 series low profile load cells, click here

 

Resolution – beyond the load cell

It’s easy to assume in our modern age that the data a device records an the data we receive from it will be the same, unaffected by how it was transmitted from the load cell to the digital readout, screen, or software. Sadly, it’s the same as live reports from correspondents from the BBC – sometimes even the simplest of connections has a bad day! The load cell resolution is the change in load that the load cell can measure. And, as “Quality’ magazine say:

“Resolution is dependent on the stability of the electronics being used to measure the signal from the load cell to the ultimate digital readout instrument. Resolution is more dependent on the electronic signal received than by the load cell sensor’s signal output.”

So, always use the best quality cabling with your load cell, or opt for a wireless data transfer option that is less prone to external influences such as heat, damp or cold. Also, be aware of where your actual load cell will be positioned, and keep it free of dust, dirt, damp, and preferably out of direct sunlight. Our high quality load cells have an impressive thermal sensitivity of 0.005% of F.R.O/C or better. Our tech specs sheet also specify the recommended storage, operating and compensated temperatures for each type and size of load cell.

 

Load positioning and overloading

Load cells are sensitive items of equipment, so if you load them unevenly, they will not give an accurate reading, The same is true of overloading, when 9 times out of 10, load cell systems and testing jigs are overloaded due to human error. At The Load Cell Shop, our tech specs sheets give details of the safe overload limit, which for many give a:

• 150% Safe Overload
• 200% Ultimate Overload

 

Still not sure which load cells to choose?

Call us anytime during office hours, or send us an email with your requirements. We are genuinely always happy to help with advice and information. It’s better to check and get the right load cells first time than guess and then realise halfway through your project that you got the wrong ones!