How do Wolf water detectors work?
As soon as water is detected in the fibre enclosure, the optical sensor expands and causes a bend in the monitoring fibre. This measurable increase of attenuation is quickly located.
Preventative solution for water leakage in telecommunication splice closures
- The water detector (optical sensor E9/125 ITU-T G.652) detects and pinpoints the source of water or chemicals leaks in closed cable joint boxes or water collecting tanks.
- An optical fibre is selected and inserted into optical sensor E9/125 for monitoring purposes. This may be done subsequent to the initial installation without any interruption of on-going processes.
- The optical sensor works on the basis that single mode optical fibres acc. to ITU-T G.652 are bending-sensitive.
- As soon as the target medium is detected, the optical sensor causes bending in the monitoring fibre, with a measurable increase of attenuation.
- This enables early detection of any increase of attenuation (e.g. alert given by the activated sensor) or other optical events.
- If the sensor has been activated, the cause of the problem can be dealt with and attenuation returns to normal.
- Networks with optical fibres acc. to ITU-T G.657 can be monitored after splicing a fibre loop with fibres acc. to ITU-T G.652 (length > 0,3 m)
How the optical fibre sensor works
The materials used in the sensor react to the target media to be detected. When the materials in the sensor (the measuring-signal trigger) come into contact with the target medium, their shape or properties change. For example, they may:
- The water detector works on the basis that single-mode fibres are bend-sensitive
- The water detector causes defined bending in the optical fibre selected for monitoring, resulting in a measurable increase of attenuation on water contact.
- With regular measurement checks, comparing control traces with reference measurements, attenuation increases can be quickly detected.
OTDR trace showing increase of attenuation caused by activation of the optical water sensor.
The attenuation change caused by the water detector is dependent on the fibre type (bend-sensitive, bend-insensitive), fibre colour etc. The water detector type is selected according to the optical fibre specification.
In operation, the water detector fulfils the requirements laid down in DIN EN 60793-2-50 and IEC 86A/1343/CD:2010, and does not disturb any on-going processes.
Detecting increases of attenuation
The OTDR uses "backscatter" technology to provide information about the properties of the optical fibre connection. In other words:
- The laser transmitter of the OTDR sends out a light pulse to the optical fibre route.
- All the optical events along the route (splices, bends, plug connections etc) and the fibresthemselves scatter part of the light pulse back to the OTDR.
- The OTDR receiver measures the backscattered pulse power.
- The route and the optical events on it (plug connectors, splices, bends, fibre ends) are shown onthe OTDR display as a trace.
The diagram above shows a sensor inserted into the route without splicing. The activated sensor appears on the trace as a non-reflecting event ("big fusion splice").
Reasons for using water detectors in monitored optical fibre networks with RTU alarms
Distribution of faults causing network failure
According to a publication of the International Telecommunication Union ITU; Genf, 1998, the annual distribution of faults for LAN: 0.93 faults per 100 cable-km. For WLAN, 1.22 faults per 100 cable-km.
Fault source distribution
Fault statistics for structural damage, Fibre Optics CT GmbH
31% of all network failure is caused by unnoticed water entry in optical cable junction boxes
Causes of water leakage in splice closures for optical communication systems, DIN EN 50411-2-3: 2012
RTU- network monitoring with alarm (SMS, e-mail etc.) enables early detection of network failures.
- Cable production
- Cable sheath faults (length change)
- Structural damage
- Excavation work
- Temperature extremes
- Faults at cable junction box
- Cable entry seal
- Cable installation fault (length change)
- Tensile strain on the cable
- Assembly fault
- Plants and roots
- Water damage
- Untight sealing elements
- Joints ( ceiling, wall, floor)
- Air conditioning
- Burst pipes
Consequences of water leaking into splice closures
Contact with water mixtures affects the fusion splice protection (crimp or shrink-type splice protection), as they cause the metal or plastic to disintegrate.
Consequences of unnoticed water leakage in telecommunication splice closures
Alkali or basic water leaking in unnoticed over a longer period leads to fibre breakage and network failure. This may be because of product-specific properties of the cable parameters, e.g. the materials used for cabling the optical fibres (fibre dyes, filling compounds, core materials), or because of installation factors, e.g. cleaning and marking agents or fusion splice connectors used for cable and splice closure components.
If soil has pH values of 2-3, e.g. brown soil or forest floor, or if the soil is saline (near roads or motorways etc.) then fibre breakage may occur within a year after water entry, unless the fault is dealt with in time.
The route should be checked regularly (at least once a month) by carrying out a measurement for each fibre type, to detect any discrepancies in relation to the reference measurements taken initially at the acceptance of the route. In this way, attenuation increase (e.g. caused by an activated detector) or other incidents can be discovered in good time. If a water detector has been activated, the fault can be corrected and the attenuation increase remedied.
This ensures that network failure can be avoided.
Advantages gained by using water detectors
- Reliable detection of leakage
- Economical monitoring
- Simple, quick installation or retrofitting at any time
- Detection of leaks over distances of more than 80 km at short or big leak intervals
- No disturbance of on-going processes: the water detector in operation fulfils the requirements laid down by DIN EN 60793-2-50 and IEC 86A/1343/CD:2010
- No activation at a relative humidity of less than 70% 0 cm
- Savings on repair costs caused by fibre breakage (EUR values for reference):
- Avoiding fibre breakage reduces the amount that needs to be spent on repairs:
- Cutting and stripping the cable 55 € per joint-box
- Fusion splice 6 € per fibre
- Acceptance measurement 12 € per fibre
Documentation and references