Fibre optic connectivity for hostile mining environments

| Global Environmental Processes

Expanded Beam Cable Assembly
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The Expanded Beam Cable connector from Harting provides robust fibre optic connectivity without sensitivity to dirt in difficult and hazardous environments.

Digitisation is just as much finding its way into tunnel excavation projects and mining as it is into industrial automation or the consumer segment. But in contrast to the latter, the requirements are many times more challenging underground and in other rough environments.

The large distances and great bandwidths required at the same time make fibre optic cables an indispensable conduction medium. But as optical interfaces are known to be highly sensitive to soiling, an answer had to be found for mining and tunnel excavation operations. At Harting, the answer for high data rates under extreme conditions goes by the name of Expanded Beam Cable Assembly. It ensures that HD-TV at machines and plants or also the localisation of personnel for emergencies down to the furthest corners of a pit are no longer a problem. Fibre optic cables safely packaged in a plug-in connector that neither dust, water or severe operations are able to harm. For a safe data connection right through to every machine.

An oil lamp, hammer and pick, sometimes also a canary bird. These are the utensils a German miner refers to as “Gezähe” (toolset) and that were needed for underground mining 200 years ago. Little remains of these times looking at the machines, conveyor systems and sophisticated technology behind tunnelling or resource extraction in today’s pits and mining operations. Digitisation is also making inroads here, improving efficiency and safety by ever more transparency in real time.

Drill jumbos, wheel loaders, shearers and explosive transporters/water wagons are only some of the equipment of large mining operations where better monitoring would be desirable in the future. Besides economic interests such as measuring production volumes in real time or the quantity of explosive used, safety also needs to be improved. The live localisation of people and machines available with modern monitoring systems enables them to be found and saved more quickly in emergencies. But how will all this data find its long way to the surface? Taking the Gotthard Tunnel as an example, a good 25 kilometres needed to be bridged towards the end of the construction phase, per side. Ethernet transmission using copper cables is therefore excluded, while fibre optic cables and/or their interfaces are unsuitable for this kind of terrain. They may bridge long distances with a large bandwidth but are too sensitive…. Until now, that is.

Robust connectivity

Optical plug-in connectors based on ceramic ferrules such as ST, SC, LC and E2000 connect glass fibres by the physical contact between the polished surfaces of their ends. This type of plug-in connector is already widespread in LANs, WLANs and computer centres. They are particularly popular for these applications because the dry, clean and climate-controlled conditions provide a safe environment for optic cabling. For outdoor applications, these IP20 plug-in connectors need to be configured with various housings, however, to reach a protection level of up to IP65 / IP67. This is the only way to render them usable for outdoor applications. At least as long as they are plugged in.

Once the interface is opened, contamination becomes unavoidable in the extremely rough conditions underground. This is because damage to these ferrules cannot be prevented in areas where optical connections are frequently installed and dismantled, or where plants and their components are frequently relocated. Whether they are protected with an additional IP65/67 housing or not makes little difference in this regard. Opening an optical connection is always critical. Minimal quantities of dust, moisture or other contaminations are quickly deposited on the ferrules and prevent successful transmission.

Despite the difficult environmental conditions and problems in mining, there is a growing demand and need for data communication and a connection to the company network. The long transmission distances and attendant high data volumes meanwhile make optical fibres the only viable solution. But this can only be achieved with a novel and robust plug-in connector that is immune to dirt and water and easy to clean.

Possible mining tasks include remote control of machines from a control centre, HD video surveillance for machines and plant, network connection to the company network for retrieving data, capacity and output, integration of WLAN routers in the systems for telephony, localisation of vehicles, objects and people and sending of assignments to work machines or transport vehicles.

An important reason for this is that the personnel in mining or tunnel excavation neither have the time nor the material required for cleaning standard fibre optic plug-in connectors properly and compliantly. Machine outages and losses in the mining output create enormous costs for companies in these sectors, which makes their avoidance mandatory.

Harting Expanded Beam Cable

Harting’s Expanded Beam cable design is the answer for using glass fibre underground and in rough industrial sectors. This product was developed to guarantee a reliable optical connection even in the hardest, roughest and dirtiest situations of any application. And it also enables the cables to be regularly installed and dismantled without difficulties in these rough environments. Optical lines can even be extended by simply connecting another cable without needing to pay attention to the laying direction. And there is also no need for additional adaptors thanks to the hermaphrodite connector face, to highlight just two of this technology’s many advantages. Harting’s product is thus usable in areas exposed to extreme external conditions. Mining and tunnel boring machines are just two of the many possible applications.

Direct comparison

The glass fibre of ferrule-based plug is glued into the ferrule of a standard fibre optic plug-in connector. What is important for the fibre ends is that they need to be smoothed and polished, enabling the plug-in connectors to bring them into contact, so that light from the one fibre is coupled into the other. The light-transmitting areas of the fibres have a diameter of 0.009 mm to 0.065 mm, depending on their type. A consequence being that the tiniest contamination in precisely this minimal area will already let the attenuation of the optical signal grow very quickly, severing the connection.

As can be seen from the name, Harting’s Expanded Beam Connector expands the light beam’s diameter by a factor of 40 by means of a lens. This expanded light beam can thus be coupled into the opposite plug and collimated (directed in a straight line) back to the fibre diameter by the lens of the second plug. This process is referred to as collimation in optics and thereby enables the light beams to be absorbed by the fibre again. The resulting benefit is clearly evident:

With the beam diameter travelling between the plugs expanded by a factor of 40, dust particles measuring 0.020 mm will no longer be able to interfere. With an IP20 solution, dust contamination of this scale would cause the connection to be lost. The Expanded Beam plug-in connector has protection class IP68 and is additionally also much easier to clean. Even if it is delivered as standard with a cap for protecting the lenses and threads in an unplugged condition, dust and water will not present any problem without this protection either. Simply rinse off the contact areas, wipe them crudely with a cloth or on your clothing and then connect them. That’s all. A simple but brilliant product for gigabit ethernet right into the furthest corners of tunnels, mines or other major industrial facilities. Digitisation and I4.0 can thus ensure better process monitoring and greater safety in mining.

The following industrial areas also fall into the sector for optically reliable connections:

* Oil and gas extraction
* Mining, opencast and/or underground mining
* Tunnel excavation
* Concerts and television events (mobile use outdoors)
* Industrial outdoor facilities (non-stationary)
* Harbour logistics (container terminal, crane technologies and transport vehicles)
* Sewer monitoring

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