Carton, Paper & Board Robust, reliable precision
The stakes are high in the fast-paced world of papermaking, where machines often churn out a kilometre of tissue every minute. And a tear in the tissue can lead to costly disruptions, so reliable and precise web tension measurement is critical.
A
t the same time, a paper mill is a hostile environment for instrumentation and maintaining precise web tension measurement is
a challenge. This can make it diffi cult to achieve accurate measurements consistently over time, as well as resulting in a high maintenance burden. This article explores these issues in more detail and explains how ABB’s unique Pressductor technology is helping paper mills around the world to solve them.
THE PAPER MILL CHALLENGE Poorly controlled web tension impacts on product quality and machine effi ciency in paper production. Tension must be maintained within tight margins to protect the web – including during acceleration and deceleration when overloads are more likely. Poor control can lead to tearing of the web, or even a catastrophic ‘hay- out’, which results in hundreds of meters of tissue per minute cascading onto the factory fl oor. The tough industrial conditions commonly encountered in a paper mill are challenging for instrumentation. The typical atmosphere is hot, humid, and contaminated with particulates. Instruments are also subject to vibration and electrical interference, meaning that equipment that works fi ne in the lab can often struggle, with electronics and moving parts all potentially impacted by the hostile environment. In the case of the load cells used to measure web tension, problems often show up as drifting or unstable outputs. In fact, many customers say that mistrust of load cell data can be one of their biggest headaches when it comes to monitoring web tension.
It is therefore business-critical to choose robust, high-quality measurement systems that can meet these challenges.
Traditional tension measurement systems such as strain gauges or sensors based on linear variable diff erential transformer (LVDT) technology rely on physical movement – bending or stretching - to generate an electrical signal. However, this reliance on accurate, repeatable movement makes these systems vulnerable under the challenging operating conditions
14 June 2025
typically found in paper mills.
In contrast, ABB’s Pressductor systems rely on the magnetic properties of certain steels to produce a signal in response to the force applied – a phenomenon known as the magnetoelastic eff ect. All ABB Pressductor load cells are based on this principle, which is much more resistant to external interference than alternative technologies.
HOW DOES IT WORK?
Pressductor transducers feature two perpendicular windings of copper wire running through four holes of a steel membrane. An electric current generates a magnetic fi eld in one of the windings so that, when the transducer experiences a mechanical force, the magnetic properties of the magnetoelastic steel alters the magnetic fl ow 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 infl uence 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% of the cell capacity, depending on
the type of load cell, while the defl ection 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.
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 big advantage during 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 these extremes, the everyday vibrations and temperature variations associated with normal mill operations are no problem.
Pressductor gauges 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, as well as diminishing sensitivity and/or accuracy.
www.convertermag.com
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