Functional safety in paper industry

The production unit called Paper Machine 1 consists of a wet section, a press section and a drying section, as well as quality control and reeling. The various sections extend for several metres. The kraftliner material is transported in a complex system over several floors. Wire cloths help the water to run off before the paper is pressed.

FSI 800 series fulfils the Machinery directive

”A stable and safe drive system is the heart of a paper machine”, says system engineer Björn Lidström, responsible for the mill’s drive systems, and explains that the mill operates around the clock with a six-shift schedule. This means that the Machinery directive for functional safety must be observed, as there are parts of the machinery where people need to have access even when it is in operation. Here, Leine Linde’s incremental SIL2/PLdcertified FSI 862 encoder model is used.

The encoder lives up to the demands for accuracy and reliability of the application. It does not only provide speed feedback from its position on the motor shaft to the frequency controller in the drive system, it also plays an important part in the functional safety system.

Each green dot is an encoder that is installed on a motor, and motor speed can be monitored in real-time. All is working in compliance with the Machinery directive for functional safety.

Thanks to their high-current HTL signals, the FSI 800 series encoders can use cables up to a length of 300 meters and more. Therefore, there is no problem to run the cables the whole way to the control cabinets, which are gathered in a separate room, where they cannot be affected by the paper machine’s often high temperatures and humidity. ABB’s frequency converters and their safety modules are installed in the cabinets, easily recognisable by their yellow colour.

The FSI 800 encoder monitors its own square wave signals internally. If a fault is detected, the encoder signals will immediately enter safe state, or indicate faults via the status output. This makes the installation safe.

The drive system is visualized on screens in the control room. Every green dot is an encoder, situated on a motor, where rotation speed can be monitored in real time. In some moments, the paper needs stretching, whereas in other moments it should be slightly released. This means that motors have to work with different loads and speeds, but in a system with an even flow. Reliable encoder performance encoders is crucial for production uptime, in the process where the rotating press cylinders are 7.10 meters long, and the speed of the paper in the can exceed 1000 metres per minute.