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SensoWeb 'Guard' - web break detectors
Fiber optic break detectors for every application, whether in front of free draft, drying screen and press – with contamination monitoring.
📋 The task
Web breaks are a common occurrence in paper production, but they can cause significant follow-up costs – their reliable detection is therefore essential for efficient operations. If the paper web breaks, defined protective and/or cleaning measures must be initiated immediately, such as diverting the web into the pulper. Errors or delays in detection can cause the paper web, which is still in production, to wrap itself around the hot dryer cylinders at high speed, leading to unplanned downtime and potentially serious damage to dryer screens or even rollers.
Practitioners who want to gain a fundamental understanding of demolition surveying will find a comprehensive guide here.
📋 Tear-off detection in a paper machine: Requirements, sensor types, installation practice
⚠️ The practical challenges
- High temperatures: Inside the enclosed hair dryer hood, ambient temperatures of well over 100 °C prevail continuously.
- Pollution: Flying fiber particles, high moisture, etc. can settle on the measuring head and impair the measurement.
- A wide variety of use cases: Depending on the location, measurements may need to be taken outdoors or with background noise – each with specific measurement requirements! Limited installation space or accessibility present further challenges.
❌ Why standard sensors fail
Conventional optical sensors with integrated electronics fail due to thermal overheating at approximately 60–65 °C, and reflectors within the drying unit become unusable due to warping or contamination. Standard sensors lack the necessary light intensity to cope with larger measuring distances or contamination, and they are also unable to handle the small signal difference when measuring against a changing screen background.
✅ The Sensorik Austria solution: SensoWeb “Guard”
Our tear sensors were developed specifically for the harsh environmental conditions in the paper machine and have been further optimized over many years:
Thanks to the fiber optic concept, the sensors can be placed in less exposed areas, the high-performance sensors offer high contamination reserves, the robust fiber optics minimize transmission losses and are also optimally protected against mechanical stresses!
This enables reliable tear-off detection in the long term, even under high temperatures, moisture, contamination , etc., in approximately 200 paper and cardboard machines worldwide!
Another highlight is our globally unique material-sensitive tear detectors, which enable reliable tear detection even against a screen background, regardless of paper color or screen age.
We offer specialized systems for every position – from the press section to the drying units and the winding unit, you'll find all solutions from a single source! On the following pages, familiarize yourself with the various models, each optimized for different applications over decades.
Tailor-made solutions for different positions
Paper web in the open draw or in front of the drying cylinder:
SensoWeb “Guard-HT”
(formerly SensoWeb "Standard" | "Slalom" | "Trian")
Technical data - Overview
SensoWeb Guard-mat/DF|PF | SensoWeb “Guard-HT” | SensoWeb | SensoWeb Guard-LT/(L|LS) | |
|---|---|---|---|---|
| Concept | Material differentiation | light/dark switch | Photocell | |
| Switching frequency | 19 Hz | 15 Hz | 100 Hz | |
| Operating Voltage | 24VDC / 230VAC | |||
| outputs | 2x changeover relays; 2x 4-20 mA | 2x changeover relay / 1x 4-20 mA (MID-..-2R1A) | 1x changeover relays | |
| Connection | jam | jam | jam | jam |
| Length fiber optic | to 15 m | to 25 m | on request | |
| Air purge | integrated | Boom Slalom (opt. Trian) | opt. | opt. |
| background suppression | Boom Trian | |||
| Independent of external light | ja | ja | ja | only Guard-LT/LS (MID-..-S) |
| working distance | 200 mm | 100-1000 mm | to 6 m | to 30m |
| Application | Drying screen: “mat-/DF” Press felt: “mat-/PF” | Free move, Free move with background (“HT/T”), Cylinder | Free train outside dry group | narrow gap, coater, press |
Your benefits at a glance
- Extremely robust systems, proven thousands of times over
- Highest performance with a long service life
- Excellent resistance to pollution
- High functional reliability
- No risk to functionality when changing the screen
- Without vulnerable reflectors
- Professional pollution control: binary, display, analog
- Long-term investment security through repair service
FAQ - SensoWeb "Guard" Breakaway Sensors
Can SensoWeb "Guard" tear-off sensors also be used with a screen background?
Yes, SensoWeb “Guard-mat” was specifically developed for detecting web breaks on a screen background. This SensoWeb “Guard-mat” detects web breaks through the material-specific signature (or fingerprint) of paper compared to the drying screen.
This means that SensoWeb “Guard-mat” is not affected by color changes in the paper or drying screen. Additionally, the sensors offer the possibility of monitoring the aging/contamination of the drying screen and detecting the need for replacement at an early stage.
Can SensoWeb "Guard" tear-off sensors also be used in the press sector?
Yes, in the press or film press sector, applications are very common! SensoWeb “Guard-HT/A” detectors with an air-washed sensor head are generally used here.
For positions where the powerful sensors would detect a disturbing background close behind the paper web, SensoWeb “Guard-HT/T” with physical background suppression is a good option.
For positions with particularly small available installation space, versions with a straight arm are available; alternatively, high-performance light barriers SensoWeb “Guard-LT” can also be used, for which even narrow gaps are sufficient.
Can SensoWeb "Guard" stall sensors be used on both the drive and driver sides?
Yes, the sensors from Sensorik Austria can be installed on both the drive side and the driver's side. However, on the driver's side, accessibility for cleaning is particularly important. Longer fiber optic cables are also usually required.
How many demolition sensors are needed per machine?
Since a tear at different points triggers different protective measures, sensors are typically placed at several locations along the machine – for example, in the press and dryer sections, as well as on the reel. The number of sensors also depends on the production speed and the width of the paper machine. As a rule of thumb for machines with high production speeds, for example, one sensor per dryer unit is used in the dryer section. On fast and wide machines, sensors are often used on both the drive and operator sides.
Can SensoWeb "Guard" breakaway sensors also be used in steam and high moisture?
Yes, thanks to fiber optics, our tear detectors measure close to the paper web and are only minimally affected due to the short measuring distance.
However, high moisture and steam also tend to increase "contamination" (the accumulation of dry to moist fiber material on the sensor head). Therefore, booms with air-washed sensor heads are typically used in these conditions. Additionally, the sensors offer extra signal outputs to monitor contamination levels in the control room.
Up to what lengths are fiber optic cables available?
Fiber optic cables (FOC) for SensoWeb “Guard-HT” are available in lengths up to 25m. FOCs for SensoWeb “Guard-mat” are available in lengths up to 15m.
What is the maximum permissible measurement distance?
For SensoWeb “Guard-HT” systems, the measuring distance is generally about 10-100cm; for SensoWeb “Guard-mat” it is about 10-20cm.
For sensors designed for installation outside of hot areas, SensoWeb “Guard-LT/R” offer sensing ranges of up to 5m and more, while SensoWeb “Guard-LT/L” light barriers offer a range of 30m.
Sensorikaustria.com – your partner for powerful sensor solutions
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