Magnetoelastic load cells still top the performance charts in paper mills

When it hit the market 70 years ago, Pressductor® technology from ABB offered a step change in the reliability of load cells for tough industrial environments. Today, these load cells can be found everywhere that companies are relying on tension measurement to optimize the production of strips and webs, including paper mills and steel production.

Solution | August, 2024

There have inevitably been some tweaks and updates in the meantime. For instance, developments in material, mechanical design and production techniques make it possible to design today’s Pressductor® cells with lower capacity ratings than earlier generations. Even so, the fundamental technology remains the same and continues to offer unrivalled performance in challenging applications.

The key difference with Pressductor® is the underlying transducer technology, which relies on the magnetic properties of certain steels to produce a signal in response to the force applied – also known as the magnetoelastic effect. All ABB Pressductor® load cells are based on this principle. In contrast, other systems rely on physical movement – bending or stretching the measurement elements - to generate an electrical signal. This includes sensors based on both linear variable differential transformer (LVDT) technology and strain gauges. This reliance of movement makes these systems more vulnerable under challenging operating conditions.

Pressductor® technology

Pressductor® transducers rely on two perpendicular windings of copper wire running through four holes of a steel membrane. An electric current generates a magnetic field in one of the windings so that, when the transducer experiences a mechanical force, the magnetic properties of the magnetoelastic steel alters the magnetic flow pattern and induces a corresponding AC voltage in the second coil.

The measurement signal is exceptionally strong, which means that magnetoelastic transducers are more resilient than alternative technologies to the influence of electrical interference – whether from induced currents in the signal cabling or other wireless devices.

This technology can also shrug off overloads of 300 to 1,000 percent of the cell capacity, depending on the type of load cell, while the deflection under typical industrial loads is between just 0.02 and 0.05mm. That’s between 10 and 100 times less than the displacement typically experienced with movement-based devices.

Withstands overloads and shocks

In other words, Pressductor® gauges can withstand the kind of overloads and shocks that would otherwise throw the calibration off or even destroy other instruments. That’s a critical advantage in an emergency stop, which can cause very high overloads as the rolls come to an abrupt halt, or when web material wraps around a roll after a break, for example.

Compared with that, the everyday vibrations and temperature variations associated with normal mill operations are no problem.

They are also less vulnerable to contamination and corrosion than other load cells. Of course, any installation can be compromised if moisture or fumes get inside the cables and electronics, but technologies that rely on movement within the transducer are more vulnerable in comparison. For example, contamination or corrosion can prevent the mechanical stops used as overload protection from working properly. If the stops engage too soon, it reduces the measurement range of the load cell in addition to diminishing sensitivity and/or accuracy.

Despite their robust reputation compared to alternative technologies, even Pressductor® installations are not entirely foolproof. Poor installation can impact the ability of even the toughest gauge to deliver long and reliable service, for example. It’s easy to underestimate the tendency of the roll structure to flex when subjected to tension in the web, while roll misalignment, improper bearing selection and a failure to take temperature-related expansion and contraction into account can all contribute to the creation of ‘irrelevant’ forces that can falsify measurement values.

However, it’s impossible to argue with the improvement that magnetoelastic gauges deliver in all-round performance. They are forgiving of excessive loads, electrical and temperature interference, contaminants and imperfections in specification and installation in a way that rival technologies simply can’t match.

To learn more about ABB’s Pressductor® transducers, including why they are the device of choice for many of the world’s leading names in the paper, metals and battery production industries, visit our web tension portal page.