The thought ran through Frank Haran’s mind more than once. “We’re breaking a whole lot of rules.” Haran, a sensor physicist with Honeywell’s Process Solutions business, wanted to use optical fiber sensor technology in one of industry’s most demanding environments: papermaking.
But OFS Specialty Photonics Division provided a solution that met the most demanding requirements.
“You’re not supposed to use optical fiber in high temperatures and high humidity. You’re not meant to drag an optical fiber over pulleys for millions and millions of cycles. You’re also not meant to use a fiber optic cable to drive a sensor head back and forth,” recalls Haran.
With the help of OFS Specialty Photonics Division, Honeywell has developed ExPress Moisture, a compact, robust, high-speed system to remotely measure moisture throughout the papermaking machine.
Simply put, the papermaking process starts with a slurry composed of wood fiber and water and other additives, such as dyes. This slurry passes through a series of presses and dryers that gradually remove the water and ensure that the resulting paper meets exacting specifications for thickness and other properties.
According to Ross MacHattie, a Honeywell product manager, “Our quality control systems measure different characteristics of paper, such as moisture content, so they can be controlled during the manufacturing process. 
We design and manufacture sensors and the equipment that is used to position those sensors over the sheet of paper. Some sensors are in fixed positions while others are mounted so that they move across the sheet and provide measurements at specific intervals, such as one centimeter, across a 10 meter wide sheet.”
Honeywell’s ExPress Moisture cross-directional sensors are guided by carbon fiber rails and are actually moved across the width of the paper by a reinforced fiber optic cable. The sensor measures moisture by selective infrared absorption and transmits this data to a computer system that calculates control information and directs the paper machine to make minute adjustments to keep the paper consistently within specifications. By maintaining uniform moisture distribution and removing water at optimal rates along the length of the machine, paper can be produced more uniformly and efficiently.
In a typical papermaking machine, the area where the process of removing water from the slurry begins – the so-called “wet end” – is characterized by a very harsh environment. “With temperatures in excess of 70° C and nearly 100 percent humidity, we couldn’t use traditional light sources, active optics, electronics, or complex mechanical systems,” says Haran.
The objective was to place only the passive sensor components in the machinery environment. To do this, Haran and the Honeywell development team wanted to use fiber optics to deliver light to the sensor and to return the data to the computer. “Some fiber manufacturers told us this wouldn’t work, and one that did think it could was unwilling to produce the fiber in the quantities we needed,” recalls Haran.
Honeywell turned to OFS Specialty Photonics Division. "We said 'here's what we need, can you make it for us?' That’s when I thought about breaking all the rules about using optical fiber in this environment,” Haran recalls.
ExPress Moisture uses a hard clad silica (HCS®) fiber. This type of fiber resists heat and humidity and is extremely durable, withstanding tight bend radii and repeated mechanical cycling over extended periods of time. In HCS fiber, the hard polymer that surrounds the core not only acts as a cladding to guide light, but it also acts as a strength enhancer. This polymeric material forms "bridge bonds" that heal (passivate) small flaws on the surface of the silica. Fiber strength is greatly enhanced, static fatigue significantly retarded, and tighter bend radii are possible. HCS fiber can withstand less than an inch bend for 20 years.
According to MacHattie, “OFS was very responsive to our technical concerns. Their team got fully involved, and we talked at the same level. Their technical people came up with very good ideas. They were willing to take on our problems and concerns – and very willing to help out.”
In order to physically push and pull the sensor along its tracks, the optical fiber was reinforced using a proprietary fiber sheathing. OFS was helpful in resolving questions about connectorization of the fiber and the reinforcing material. They also worked with Honeywell on solutions to ensure that water would not get in through the connection.
Honeywell has put the OFS solution to the test. “We’ve run over 10 million cycles at 70° C and 100% humidity. There has never been a breakage of fiber,” noted Haran.
Thanks to an innovative optical fiber solution from OFS, Honeywell’s customers can take advantage of a scanning system that is faster, more accurate, and more durable than conventional scanners. It’s a turnkey automation system that helps them produce a very good roll of paper,” says MacHattie.
