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Tear-off detection in a paper machine: requirements, sensor types, installation practice
Which sensor reliably detects track breaks – and where can it be used?
Table of Contents
Track breaks are among the expensive malfunctions that can occur in a paper machine, but they are also part of the everyday life of papermakers.
Paper web break sensors detect and report a web break in fractions of a second, which automatically triggers the necessary protective functions – such as diverting the paper web into the pulper – and initiates necessary cleaning measures.
This page explains how paper web break sensors work, where they are used on the paper machine, what types of sensors are available, and what you should pay attention to when choosing one.
Note: The web break sensors described on sensorikaustria.com are specifically designed for monitoring the paper web in paper machines. They are not intended for other applications such as thread monitoring, belt conveyors, or wire break detection.
>>> SensoWeb “Guard” – the leading break-off sensors for drying groups and measurement on screens
What is a paper web tear sensor?
A paper web break sensor is a sensor that continuously monitors whether the paper web is present at a specific position in the machine.
If the track breaks, the sensor detects the missing track and immediately reports this to the machine control.
The control system can then react automatically, for example by:
- Activation of spray nozzles for cleaning the rollers
- Triggering an alarm for the operating personnel
- Adjustment of web tension or speed
- Documentation of the event for process analysis
Since a web break can spread very quickly within the machine (a break in the screening section often leads to subsequent breaks in the pressing or drying section), fast and reliable detection is crucial to limit consequential damage.
Why does the paper roll tear?
A tear sensor addresses the consequence, not the cause – however, to understand the application, it is still worthwhile to look at typical causes of tearing:
- Fluctuations in fiber quality or leaf formation
- Irregular moisture or dryness distribution across the width of the web
- Faulty path guidance or voltage spikes
- Deposits, holes or weak points in the leaf
- Malfunctions during roll changes or winding
Break-off sensors do not replace process optimization, but they significantly reduce the reaction time to a break and prevent a single crack from developing into a long machine downtime.
Consequences of railway line collapses that are not detected or are detected too late
If the paper web tears between the press section and the reel, high follow-up costs are likely:
- Production outage,
- extensive cleaning work, up to and including
- Damage to the drying sieve (as seen in the photo on the right), or
- even a roller.
Installation locations in the paper machine
Paper web tear sensors are used at several critical points along the machine, as tearing at different locations requires different protective measures:
- Press section
Detection of tears between the press nips to prevent damage to felts and roller coverings.
- Dry section
Monitoring along the drying cylinders, where a break can lead to windings around the cylinders – particularly fast detection is important here.
- Roll-up / Drum
Check the web shortly before winding to avoid faulty rolls and consequential damage to the winding unit.
Technologies and measurement principles used
Technology | Functionality | Benefits | Typical area of application |
Optical (light barrier/reflection) | Detects interruption of a light beam by the path | Non-contact, fast response time | Pressing section, drying section |
Ultrasonic | Measures distance/presence of the track using sound waves | Resistant to dust, steam, and moisture | Pressing section, drying section |
Camera-based | Image evaluation of the path edge or path completeness | Additional web path and edge control possible | Roll-up, quality control |
Measuring principle | Detects the presence of the paper web by | Benefits | Disadvantages |
Free movement | |||
Photocell | Interruption of the light beam from the transmitter | simple; cost-effective | Sensitive to high temperatures, steam, and contamination; potentially difficult to set up; no condition monitoring possible. |
Reflection- | wie oben | simple; cost-effective | Sensitive to high temperatures, steam, contamination, distortion (mirrors); potentially difficult to set up; no condition monitoring possible |
Reflex button | Evaluation of the received light intensity | simple; cost-effective; condition monitoring possible | sensitive to high temperatures, contamination |
Fiber optic reflex sensor | wie oben | Insensitive to high temperatures; flexible orientation; condition monitoring and clean-up function possible. | more expensive; more complex installation |
Background Drying Sieve | |||
Fiber optic reflex sensor | Evaluation of the received light intensity | like FO probes; known measuring principle | small signal difference between paper and drying screen |
color | Color difference compared to dry sieve | like FO buttons (if fiber optic); color difference visually perceptible. | sensitive to color change of paper or drying screen |
Material- | Material fingerprint | like FO switches (if fiber optic); robust against color change of paper or drying screen | Signal difference not visually perceptible; not widely used; more expensive |
Selection criteria for paper web tear sensors
The choice of the appropriate principle depends primarily on the environment at the installation site: temperature, steam and condensate, and the measurement background place different demands on the dry section than on dust and fiber mist in the sieving section.
When selecting a sensor for your paper machine, you should consider the following points:
- Site: Measurement inside or outside the drying group
- Measurement conditions: Monitoring of the paper web in the open train, against a background of screen or cylinder
- Environmental conditions: Temperature, steam, moisture, dust and fiber fly at the installation site
- Track width and installation position: Spot monitoring or control across the entire track width
- Ease of maintenance: Ongoing information about the status of the sensor system, accessibility for cleaning and adjustment
- Connection technology: Digital/analog signal transmission, integration into the existing machine control system (e.g. via relays or analog signal)
- Protection rating (IP class): Sufficient protection against moisture and contamination of the sensor head
- Reaction time: How quickly must the demolition be detected to avoid further damage?
Advantages for the production process
The use of reliable paper web break sensors directly impacts several key production indicators:
- Improved process data: Demolition events are documented and can be used for root cause analysis.
- Shorter downtime: Automated protection functions activate immediately after a demolition.
- Less severe long-term damage: Fast detection prevents windings on cylinders and rollers.
- Increase in productivity: a reliable and fast tear detection
Suitable solutions from Sensorik Austria
Sensorik Austria develops paper web break sensors specifically for use in paper machines – tailored to the respective measuring and environmental conditions in the press and drying section or before winding.