Evolution of Moisture Measurement: From static electricity to high-speed electronic scanning and papermaking optimization

Moisture levels have always been central to paper production, but new global environmental legislation around energy use is creating an urgent need for even tighter measurement and control in what can be highly energy intensive processes.


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Steeped in over 4,000 years of tradition, the pulp and paper industry has, at times, been slow to deploy new technologies. Mills are often operating an installed base of old machinery, which, to a certain degree, is understandable when one considers the capital outlay for new equipment in plants of this scale.

It's not that there is no investment, it’s just that traditionally it has been deployed for short term, immediate requirements, as opposed to long-term, optimization programs.

However, with recent environmental legislation demanding even more stringent targets, compounded by global competition and supply issues, the industry must look even harder for ways to become more efficient and deploy higher repeatable quality levels to reduce its environmental impact.  

Article by Michael O’Hora, B.Sc. Ph.D., R&D Principal Engineer, ABB, originally published in Pulp, Paper & Logistics

Measurement is at the heart of this opportunity. Without fast and accurate measurements, controlling and optimizing a process is futile. Modern, unblinking, and high-speed measurements are opening up a new world of control and optimization to modern papermakers. 

Historical perspective

The industry has come a long way in terms of technology. One hundred years ago, there were very few tools for paper-quality evaluation. Instead, companies relied upon the innate skills of the line operators who checked paper uniformity by sight, reel hardness with a stick and water content using the effect of static electricity on their arm hair.

Less ambiguous measurement techniques for moisture emerged in 1927 when Louis Thompson of General Electric was granted US patent 1,645,077. He had noticed that the insulating properties of paper are reduced at higher moisture levels. His idea used an electrode with high voltage on one side of the sheet and a grounded roll on the other. In operation, the voltage was increased until an arc formed through the paper between the electrode and the roll, with the voltage level when the circuit completes correlating with the paper’s moisture level.

This level of technology could best be described as “better than nothing”. It was a good indicator of moisture but provided very little in terms of trending, cross sheet profiles or control capability.

Moisture content was a particularly key metric then and remains just as important today, due to its ability to impact quality, throughput and most notably in today’s economy, drying efficiency. As a result, the development of more accurate and efficient ways to both measure and control its levels has attracted a commensurate level of attention.


The atomic age

As paper machines widened, production tolerances increased, paper thickness decreased and throughput ramped up, the marketplace and scale of production demanded more efficiency. Newer, faster online technologies that could deliver greater accuracy were required. Initially this was achieved by measuring the reel hardness or using the paper’s caliper. Further developments including electrical arcing, which was complemented by non-contact capacitance-based devices used to measure paper weight. This was then taken one step further with systems based on radioactive attenuation. One company that commercialized this technology was Industrial Nucleonics, founded in 1950, and a forerunner to ABB in the paper industry.

Eventually, technology more akin to what we see today was developed. Using non-contact sensors, which deploy visible light, microwaves, ionizing radiation, and infrared, coupled with online scanners that could scan the full width of the web, mills could get about 60 measurements per second. It is these technologies that underpinned the modern renaissance in measurement capabilities and accuracy.

So why was this development such a game changer at the time?  In operation, the organic materials within paper webs exhibit strong infrared absorption. As a result, the moisture concentration can be estimated by measuring the differences in absorption.

Signal processing used in this older generation of infrared moisture sensors exploits what is known as amplitude modulation, which is used to suppress any background phenomena that can influence the measurements. It was a major stepping stone to keeping moisture at desired levels.

Plus, the eventual emergence of digital control technologies enabled the first big leap in moisture controls. The decades that followed focused on the development of Machine Direction (MD) and Cross-Machine Direction (CD) Controls with a continuous stream of enhancements that could react to the always improving measurements, enabling faster start-ups, reduced variability, and faster grade changes.

Modern, continuous, and high-speed measurements are opening up a new world of control and optimization to modern papermakers.

Blink and you'll miss it

So, what became of the above described modulating approach? Because it is akin to a blinking eye, the system only catches measurements when the eye is open. This leads to disadvantages that are incompatible with many of today’s modern, high-speed production processes. The measurement speed is limited by the frequency of the signal and the capabilities of the electronics used to reassemble the signal. The level of optical power launched into the sheet is also lower, reducing the effectiveness of the signal.

Non-modulating technology enables ABB's HPIR sensors to behave like an all-seeing eye

What was needed was a way to keep the eye open all the time, to capture as much information as possible and avoid the blind spots while “blinking”. This solution arrived in 2010 with the introduction of non-modulating technology – touted as the biggest breakthrough in moisture measurement in 30 years!

It’s fair to say that it arrived just in time; with paper-making machines growing to immense proportions. With this new non-modulating technology, such as that exclusively deployed in ABB’s proprietary High-Performance Infrared (HPIR) sensor portfolio, it can continuously measure and simultaneously compensate for background radiation. Indeed, it has set new standards in precision; the newest HPIR reflection moisture sensor calculates measurements 5,000 times per second, some 83 times more data points than 50 years ago.


The benefits of an all-seeing eye

The greater amount of data from HPIR sensors equates to greater control, and even small percentage gains or savings can have a huge impact on the bottom line. When you consider the drying stage of paper production, a mere one percent change in moisture can equate to energy savings as much as $400,000 per annum!

With this elevated level of data, paper producers can be far more confident that their moisture measurements are universally reflective of nominal values. They can also shift their moisture targets closer to acceptable quality limits. This not only reduces fiber costs, but also saves significant amounts of energy – supporting sustainability objectives – while remaining within strict quality specifications.

This innovation is delivering new-found levels of measurement capabilities, giving mill owners and operators the ability to control and optimize like never before. It is also the enabling technology for the next generation of optimization approaches which will elevate control to an even higher level.


A one percent change in moisture can equate to energy savings as much as $400,000 per annum!

Innovation is key

Beyond the basics of moisture control, the unblinking eye of moisture measurement is enabling a global paradigm shift as companies increasingly adopt Industry 4.0 working practices and the Industrial Internet of Things (IIoT) to serve up all-important operational data.

Modern information-based systems thrive on sharing and analyzing data, so quality levels can be constantly gauged and compared historically against other variations in shift patterns, operator capabilities, seasonal temperature ranges and raw materials, to name a few. This explosion in capability and controllability has led to the creation of ever faster and more efficient production and optimization solutions, namely the ability to correlate the final measurement to process conditions farther up the machine, control more variables and attribute disturbances to their true root cause. The pulp and paper industry has tremendous opportunities to exploit these new technologies and legislation may prove to be the driving force, including issues such as traceability across the entire value chain, from tree planting to eventual recycling.


ABB’s 140 years’ experience in this highly demanding industry has resulted in multiple evolutions in quality control for pulp and paper makers, who have gone from looking at arm hair to digital moisture measurements. Further progress has been encouraged by the evident benefits that the evolution of measurement brings.

Simply adding the newest moisture sensor, for example, can provide a clearer picture of operations, to both tighten controls and address contemporary sustainability targets. With other technologies already in development, alongside improvements in existing infrared and microwave solutions, moisture measurement is certain to evolve even further.

This innovation is delivering new-found levels of measurement capabilities, giving mill owners and operators the ability to control and optimize like never before. 

Contact us to learn more.





Did you know ABB has the fastest paper machine moisture sensor in the world?

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