Load cells - How they work

Strain gauge bonded to load cell

Load cells - Introduction

Load cells technology started back in 1937 when the first straingauges were developed. By bonding a resistive wire (straingauge) to an element (transducer) a load cell is produced. When a load is applied to the element, the straingauge will change electrical resistance proportionally to the load cell, giving a useable electrical signal that can be measured.

Load cells - Material

The quality of load cells is in large part dependent on the material used, which needs to be Pillar load cell
stable and hysteresis free. Usually aluminium alloy or high tensile stainless steel is
selected, although other metals can be used.

Load cells - Accuracy

This is designed as a percentage of rated load. For example a 50 tonne rated load cell giving a 0.5 tonne error at any given load can be said to have an accuracy of 1% of rated load. This
is not to be confused with actual accuracy. For example the same load cell measuring 25 tonne but reading 24.5 tonne will have the same error, but a true accuracy of 2% of that load.

The calibration certificate shows the output in a controlled environment. In practice when in Load Shackle
the final installation it may be subject to wild temperature fluctuations or mechanical factors,
such as friction and hysteresis that could affect performance. However, all Strainstall load cells are designed to keep these effects to a minimum.

Many different types of load cells have been developed and include:

Common Types of Load cell

Strainstall compression load cells include the Type 2800 low profile load cells. Ratings
of these go from 200kg to 1000 tonne, and they are particularly good for offset loads or
where there are height restrictions. Also available are our pillar load cells with capacities from
5 tonne to 1000 tonne. These types are generally more economical at ratings above 100 load pins
tonne.

For tension weighing we can offer load shackles. These are very versatile in situations
where high accuracy is not important. Rating is from 3 tonne to 1000 tonne. Where better
measurement is required tension load links can be used. These are normally supplied in aluminium alloy, however stainless options are available. They have the disadvantage of needing load shackles at each end which can create a weight problem.

Load pins are the most versatile of all. Easy to retrofit or fit into new equipment, load pins
come in all sizes and ratings. All are made to suit each individual application.

Strainstall also supply a variety of other less common load cells and specials to customer requirements.