Competition among telecommunications services means that high demands are placed on the quality, reliability and availability of transmission paths. All around the clock fibre-optic lines are used for the transfer of large quantities of data, thus creating the expectation of practically 100% availability, especially where individual optical fibres are rented out to customers.
A study commissioned by Hewlett-Packard and carried out by Techconsult has revealed that critical infrastructures tend to break down about four times a year in medium-sized companies in Germany, leading to a total or partial paralysis of operations .
Fibre-optic alarm systems for infrastructures (EMA & GMA)
Network failure may be caused either deliberately through unauthorised entry in telecom infrastructures by vandals, for example, or through heat/fire. Another frequently-occurring cause is water entry in cable manholes affecting both connecting joints and transmission components. Remote monitoring of the network with utilisation of Wolf GmbH fibre-optic alarm systems for infrastructures (EMA & GMA), ensures that most network failure can be prevented.
1. Cable manhole from Mönninghoff
2. Sensors from Wolf GmbH
2-1 EMA sensors
For monitoring manhole access covers
2-2 GMA sensors (with dead-zone TO Box)
For monitoring water levels
3 Corrugated tubing, slit,
from Fränkische Industrial Pipes:
To protect the sensor cable and fix
it in place in the manhole
Why does water entry occur in connecting joints, in fibre-optic
communication systems that are in conformity with DIN EN 50411-2-3:2012?
Permanently assigned active sources of heat
Permanently assigned application of cold
O-rings, washers, shaped rubber inserts
Mastic, tapes, pastes
unsuitable construction, e.g.
Joints have not been tested under working conditions or have not been tested at all
The standard DIN EN 50411-2-3:2012 has not
been updated in conformity with current
technology for the new generations of…
DIN IEC 60794-5-10
Version 2008 Part 5-10
Single mode fibres, categories
B1.1, B1.3, B2, B4, B5 and B6t.
The technical requirements for protective boxes and joint boxes
are ontained in DIN EN 61753-1 and DIN EN 50411-2-3. 2012.
In practice, many installed protective boxes and joint boxes do not fulfil the requirements
of DIN EN 61753-1, which explains why joint faults constitute 31% of all network failure.
According to Table A.12 in the standard – wall connecting-boxes, protective boxes, ODF modules and
joint sleeves - Category C controlled environment, the following compliance tests are applicable for joints:
Optical fibres installed in cable manholes or underground are sensitive to immersion in water. Contact with
water affects the fusion splice protection (whether crimp or shrink), causing the metal and plastic matrices to disintegrate.
Alkaline water entry that goes unnoticed for a certain time leads to fibre breakage and network failure. This is due to product-specific properties of, for example, materials used when the glass fibres are cabled (fibre dyes, filling compounds, core materials), or to the cable-processing parameters, or to items such as cleaning and marking agents or fusion splice connectors used in the cable assembly process.
Depending on the pH value of the water mixture, the onset of fibre breakage - with consequent danger of network failure
- can occur within a year (e.g. at pH2-3, as in brown earth, forest floor or the saline earth associated with roads and motorways).
If fibre breakage occurs, the whole cable must be cut and re-spliced, leading
to temporary power cuts, high repair costs and possibly liability costs.
The operating principle of the fibre-optic remote alarm system (EMA & GMA)
Unauthorised entry, heat/fire or water can be promptly detected with the fibre-optic remote alarm system (EMA & GMA) plus network monitoring.
The detection units in the hazard and intrusion alarms are fibre-optic sensors that operate on the
basis of the bending sensitivity of single mode fibres in accordance with ITU-T G.652.D.
EMA sensors: For monitoring the opening of (manhole) covers, break-in and people climbing or reaching inside:
The respective signal generator is triggered if the access covers are opened, or if people climb or reach inside.
GMA sensors: Hazard detection e.g. fill-level indication, detection of water mixtures, accumu-lation of heat or fire:
Each signal generator is triggered on contact with the medium it is designed to detect.
Information from the activated signal generator is transmitted mechanically to the sensor via the differ-ential-pressure signal transmitter.
The monitoring single-mode optical fibre is bent in a defined way within the sensor itself, thus causing a measurable attenuation change.
The signal generator (3) is external to the sensor, being located at the place to be monitored (access cover, door etc.). It is connected to the sensor via a
mechanical transmission line (2). In the sensor itself (1), the monitoring single-mode optical fibre in the distribution-module (4) is bent in a defined way