Load cells, often called load cell transducers, are crucial components in most industrial weighing systems. The most basic definition of a load cell is that they measure weight – or, more accurately, directional force – usually via a combination of spring elements and strain gauges, converted into an electrical output.
Load cells are available in many different configurations and standards, depending on the intended application and environment. Some varieties rely on calibrated proving rings to measure load displacement, although these are somewhat less common than strain gauge types.
Among the various different types of load cells available, varying models and styles can be differentiated in two key ways:
- By the specific method they use to detect weight (compression load cells, tension load cells and other measurement types)
- By the type of output signal generated (hydraulic load cells, piezoelectric load cells and various other configurations)
It should be noted that, strictly speaking, a true load cell of any type will always be designed to work (and should therefore be aligned) in the direction of gravity. However, it’s very common to encounter the term ‘load cell’ being used in reference to a wide range of force-sensing device types, many of which are explicitly designed to measure forces applied from all directions.
These terms have largely become interchangeable in many workplace environments today, so it’s sensible to clarify exactly which type of device you’ll be using for your intended application when assessing load cell prices or planning to buy load cell parts.
Why do we use load cells?
Electronic load cells are now broadly accepted as the modern standard in most of today’s heavy industries, manufacturing plants, large-scale production floors and stringent quality control environments.
The fact that such a large proportion of all global sales still relies on precise weight measurement is one reason that load cells play such a vital role in modern commerce. In more directly industrial uses, load cells are extremely important in maintaining precise quality control systems for manufacturing consistency and safety processes. They’re also very widely used in all manner of medical and laboratory settings to achieve optimally accurate measurements for a wide range of scientific and research purposes.
Load cells are rapidly becoming far more common across a swathe of industries that are less intrinsically reliant on critically accurate weight measurements, too – for example, in general logistics and freight calculation. Load cell transducer technologies are inherently compatible with a wide array of other digital and computer-based communications technologies, which allows companies of all types to quickly access, monitor and respond to key diagnostics information in real time.
As this is so much more difficult to achieve using traditional mechanical platform weighing devices, load cell installation often proves to be a far more efficient and cost-effective choice for most companies in the long-run.
How do load cells work?
The spring elements attached to a strain gauge material (usually foil meshes or semiconductors) will most commonly be made from either steel or aluminium, giving them the property of being very strong but also very slightly elastic. They will therefore deform to some extent under sufficient pressure, be it downward force from above (compression) or a pulling force from below (tension), before returning to their original form and shape.
The strain gauges are able to measure the exact extent of this deformation in the spring elements to an extremely precise degree. In a typical load cell, it’s this micro deformation analysis that is then converted electronically into a highly accurate weight readout. Directional pressure thus creates an electrical signal in a load cell transducer, and the magnitude of this signal is directly proportional to the force being measured.
In operation, load cells are generally subject to a range of outside influences that must be carefully controlled, monitored and adjusted for. These include overall temperatures – which can affect the structure (and therefore the electrical resistance) of any material – as well as a broad array of other environmental challenges, including inclement weather, moisture and dust ingress, and changes in ambient conditions from one location to another.
Another factor to consider when purchasing these components is the type of load cell housing material they’re built from, with certain varieties being better suited to specific application environments. Common load cell housing materials include:
- Aluminum load cells
- Nickel plated load cells
- Polyethylene plated load cells
- Stainless steel load cells
Load Cells and Australian weighing equipment
The load cells are available in a variety of shapes, sizes, and functionalities and is now in high demand on the market. It might therefore be a mine location looking for the appropriate heap cell for your application. But first, I’ve discussed some of the modern discoveries that are most frequently made as well as their applications.
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How to test a load cell installation
Because load cells are such a crucial and integral component in most industrial, manufacturing, production and quality control-based weighing environments, it’s vital that they’re correctly installed and maintained. In most critical application scenarios, the key to achieving consistently reliable and accurate results from a high quality load cell in regular use is proper and regular calibration.
Like any tension or strain gauge that’s regularly placed under repeated high loads – particularly if they involve dynamic forces – load cells will eventually display signs of slight drift and misalignment as they age. Industrial best practice guides (including ISO9000 standards) generally indicate that calibration procedures should ideally be performed annually, but certainly every 18-24 months as an absolute minimum, in order to guarantee continued accuracy of measurement.
Typical calibration processes usually involve taking a wide range of both linear and repeated measurements on an incremental scale, working up or down (ideally both) from very low or very high loads in gradually stepped ratios towards the minimum/maximum rated load for the cell in question.
Measuring in five predefined steps, with each reading taken three times as you move up and down through the load scale, is widely seen as an appropriate standard for most load cell calibration testing routines. In many cases, load cell calibration will also have to be independently verified at the installation location in order to meet legal certifications regarding the sale of goods by weight.