KB Sheet Break Detector

RGB-based color break detector

With the increased speed of modern paper machines, open draws are more often replaced by closed draws - the web of the paper works on the top of yarn or felt. These fabrics come in different colors, the contaminants in the paper change the color of the fabric surface, and the optical reflection characteristics of the fabrics change over time. This is a major challenge for conventional optical bandwidth detectors that use a single wavelength for detection. They require regular maintenance and often retuning when there is a new felt or the color of the paper is changed.

Each breakage lost in a 1600 m / s machine generates a tremendous amount of breakage to be cleaned out from inside the machine which causes considerable loss of production.

The line break detection signal is normally connected for PLC / process control, machine monitoring and quality reporting. A missing page break or incorrect page break triggers incorrect information and causes additional problems. Modern paper machines require fast and reliable information about the break of the web.

A new fiber optic web break detector uses an RGB (Red-Green-Blue) light source for detection to overcome the aforementioned reliability problems. The detector sends a red, green and blue light at the measurement point.

The detector is designed to handle all break detection applications. The fiber optic cable isolates the light source and electronics from the measurement environment, expanding applications to the high temperature sections of the machines, as well as to highly humid conditions. The unique air purge arrangement keeps the optical fiber of the sensor clean in dusty and humid locations, eliminating maintenance. The small size of the sensor head allows installations in very tight locations within the machines.

CONVENTIONAL ROLLER BREAK DETECTORS

Traditionally, photographic cells have been used to detect web breaks. They work satisfactorily in applications where eye contact from one side of a machine to the other can be arranged and where the ambient air is clean. Photographic cells require continuous attention, cleaning and maintenance.
IR-based optical fiber break detectors have been used in difficult applications and in cases where the web is supported by fabrics. The disadvantage is that they cannot separate between web and red thread or felt.

NEW PROJECT FUNCTIONS

Kajaani Process Measurements Ltd. has developed a new web break detector for demanding applications. The new KB KB detector has an RGB light source for color measurement. The best of the colors R (red), G (green), B (blue) or a combination of them can be selected for break detection for each application. Break detection is reliable, even with different fabric colors. The user can monitor color readings and trends and then choose the optimal trigger levels to break.

Figure 1: KB band break detector in the dryer. The felt color (red in this case) does not affect reliability.
The KB Detector is inside a stainless steel rod and has no active electronics inside the probe. The internal air purge keeps the window openings clean. No regular cleaning is necessary. In case of a problem, the KB Detector provides a maintenance alarm.
KB web break detector uses proven high temperature resistant optical fiber that also makes it usable in hot environments, such as dryer sections of a machine. The air purge arrangement expands applications to very humid, hot and dirty places.

Figure 2: KB Detector System
The optical signals are passed through the fiber optic cable to the local control box where the electronic signal receivers are located. The local display allows access to the rupture detection signals, calibrations and configuration parameters.

MAINTENANCE TOOLS
StoraEnso, Oulu Mill has more than 10 web break detectors on the PM6, originally delivered with the machine over 10 years ago. Regular adjustments were required to keep the rupture detectors working reliably. In some applications, the fabric edge has been painted black to improve break detection performance. Many of the original detectors have been replaced by the KPM KB detector.
In PM6, the KB band break detector is configured to use the blue color for measurement, which gives the most reliable break detection between the white web and the red fabric behind it. The difference in signal between the paper and a break is very clear.

Figure 3: Local control box
The KB break detection system self-diagnosis is continuously monitoring for crude break detection signals and a maintenance send alarm to the user if the signals have been reduced to the maintenance alarm limit. If the detector is in maintenance alarm mode, it will not be possible to give an interrupt alarm to avoid false breakage alarms. These pleasant features give operations and maintenance technicians time to do maintenance work without worrying about false alarms.

APPLICATIONS:
The most common application is free design where there is only paper and air behind.
The most demanding applications are where there is a need to detect the paper web in the felt. Traditional IR web break detectors work for only a few applications due to limited detection performance. The RGB based KB web detector can detect different colors and then separate wire / felt reflection easily from the web paper signals.

Figure 4: Maintenance and alarm signal

ABSTRACT
Modern RGB-based KB break detectors are used in many paper and board machines to detect web breaks.
The main features and benefits of modern break detectors
RGB color detection with LED light source
Detects against "air", felt and roll
Detects color changes in the web, felt or roll
Easy and quick start-up and maintenance
Reliable sensitive head for harsh conditions
Fast web break signal processing
Applicable for hot applications (up to 180 oC)
Modular and small construction
Self-cleaning sensor head
Safe operation on the remote display
Low-cost installation
Analog output signals for DCS
Optional computer software
Reliable break detection is the key aid for paper mill operators in optimizing machine production and uptime, obtaining accurate and reliable break information for paper machine control and monitoring.