Mine Communications in the 21 st Century

Transcription

1 Mine Communications systems for non ferrous metal mines, have come a long way over the last 10 years, while similar systems for coal mines have remained dormant, mainly due to the difficulty in obtaining IS approvals in Australia. Today non ferrous metal mines have multiple choices when it comes to communications systems, i.e. VHF, UHF, 800/900Mhz and even 2.4Ghz based leaky feeder systems, as well as fibre optic systems. The main difference being, leaky feeder systems are wireless based and therefore provide MOBILITY, where fibre is fixed, immobile. These systems come at a cost and mine management must decide on the level of cost they are prepared to go to. To date the most proven and reliable form of underground wireless communications has been leaky feeder based systems. Other forms of underground communications in many cases appeared to be cheaper, because they utilised existing services such as power cables, water pipes, or used cheap materials such as the old fashioned TV ribbon cable etc. But while they worked to a certain degree, they were ineffectual, were limited to voice communications and did not utilise off-the-shelf products. Radios had to be built (albeit in limited quantities) especially for the system, therefore expensive and generally weighed more than a couple of house bricks. In recent years VHF based leaky feeder systems have taken precedent, mainly due to their lower start up cost. The better quality versions provided Voice, Data and Video communications using a relatively low-cost leaky feeder cable developed especially for mining in the UK 25 years ago. The use of higher frequencies in mining circles has been limited, for one reason, cost. Higher frequencies required the use of more expensive, larger diameter, lower signal loss, and ultimately more fragile forms of leaky feeder cable, which could be best described as corrugated copper tube, with a row of holes punched along its length to let the signal leak in/out. It had to be suspended 100mm below its own dedicated catenary cable, requiring additional (and expensive) mounting hardware. Whereas the low-cost mine VHF leaky feeder cable, is more flexible, radiates 360 degrees and can be strapped directly on to existing pipes, cables, rock bolts, cable tray etc. A leaky feeder cable, just like a power cable, is subject to losses, as the signal passes along the cable, signal is lost due to attenuation. The level of signal loss is dependant on the quality, construction, diameter of the cable and the frequencies being used. For instance based on a 16mm diameter cable, the 80Mhz would be around 2dB per 100 meter 160Mhz - 4dB 450Mhz as much as - 6dB or higher. If you used a 30mm dia. cable and the losses would be approx 50% less at the same frequencies. Today you can buy a low-cost, flexible leaky feeder cable for use with their UHF system, at around the same cost as the VHF cable used in mines. The mounting hardware is also cheaper, and the amplifiers are smaller and cheaper, thereby reducing the overall cost of a mine based UHF system making them more affordable. Therefore UHF systems are only marginally more expensive than a comparable sized VHF system. The small difference in cost is off-set when you consider the advantages such as greater off-air coverage from the cable, up to 5 times more bandwidth (equals higher data speeds and/or more channels), but the main bonus is - a wider selection of off-the-shelf products such as wireless modems etc. Of course if you have a bigger budget and want more bandwidth, you can go up to 800/900Mhz and add in a couple of GSM or CDMA channels, or even up to the next level 2.4Ghz and get both high speed data and real time video. When it comes to budget-v-technology you can break up the mines into 3 different categories - Budget Conscious - 60% of mines work to a very tight budget, they tend to have the same needs as other mines, but they are forced to buy a Kmart product rather than a Myer product or nothing at all. Their need for technology is limited and more focused on meeting government safety requirements, so they will opt for a bare bones voice communications. Having installed the system and experienced the benefits, they want more. If they can enhance the existing systems capabilities without breaking the bank, they will spend the money to add i.e. data transmission - a low cost telemetry system for control & monitoring, or Personnel & vehicle tracking system.

2 The problem is they tend to buy for today and don t worry about what they will need in 6 or 12 months time, so the system they purchased cannot be enhanced without major surgery, leaving them frustrated. Technology Focused 30% of mines focus on the use of technology, go lighter on manpower, they turn to automation and/or semi-automation to reduce the cost of production and provide their workforce with the tools they need to get the job done. They will be very selective and buy more up market products (a Myer or David Jones product) to achieve their aim to control production costs AND run at a profit. Their need for technology will be mainly focused on Data communications for control and monitoring pumps, fans, air quality ~ Personnel & Vehicle tracking system ~ Vehicle management system ~ remote control of vehicles, Voice communications for improved mine safety, to exercise control over their work force i.e. best utilisation of maintenance staff to reduce equipment down time, redirection of work teams. Video could also be considered to monitor conveyor cross over s, explosive magazines, sub-stations, lone workers etc. They definitely buy for tomorrow, they will have a five year plan, they will have a small team of engineers who will be focused on knowing exactly what they will need and when they will need it. Technology Reliant 10% of mines will be totally reliant on technology, striving for full automation where possible. They are willing to pay more for products and will even pay to have products tailored to suit their individual needs. They will have a large team of dedicated engineers to plan expansion projects well in advance and will have one or more teams of consultants monitoring current trends in technology for them. They will want to test and trial products to determine which is the best and the most reliable for their operation. Their need for technology will be the same as a technology reliant mine above PLUS wireless automation of all possible mobile plant and equipment. The leaky feeder system will operate in tandem with a high speed fibre optic network, fibre optic networks can move more data and video at much higher speeds than leaky feeder, therefore they make ideal partners in a mine wide communications network. They definitely buy for tomorrow, have a five year plan, PLUS they will more likely collaborate with manufacturers to jointly develop new products or to improve existing products that will benefit their mine and the industry in general. Current technology. Leaky Feeder wireless based systems In this day and age a national Telco regard their wired telephone & data network infrastructure as a valuable asset, the more products and services that they can sell, lease, hire, to hang off it, the more valuable it becomes. Mines should think the same way, about their leaky feeder backbone. Many mines spend a lot of money installing the leaky feeder infrastructure simply to provide a single service - voice communications. A data-ready 2005 model leaky feeder system can provide added value by carrying services such as Telemetry, SCADA, Wireless Automation of Ore Trains, Mine Hoist systems (Cages and Skips), Conveyor Belt systems, Gas monitoring, Stench Gas activation, Personnel Tracking, Remote Access to the underground Stores PC, PLUS added value to Voice services such as Radio-to-Telephone calls, Fax services, Alpha-Numeric Pocket Pagers and many, many more services. One Australian mine now has in excess of 260 kilometers of leaky feeder cable installed, the initial installation was 42 kilometers. It costs peanuts to add-on additional services, AFTER the backbone is installed. Why keep paying for additional cables to be installed, when that single 16mm leaky feeder cable has the capacity to carry all of the above services. Some of the above services are now available for in-line operation, simply cut the cable and install the device (just like an amplifier) it s powered by the leaky feeder cable so no additional power source is required. Video can also be added to the same leaky feeder system to provide one way video from underground to the surface. Install fixed video cameras or in-line cameras to monitor conveyor belts, sub stations, explosive storage areas. OR if you don t need video, hook up the local AM or FM radio station(s), or a CD player instead and transmit stereo music, talk-back shows, sports programs etc it will relieve boredom & help to overcome fatigue with staff carrying out repetitive tasks, such as ore truck drivers & loaders, just install a normal FM car radio to pick up the programs.

3 VHF based Leaky Feeder Systems General The VHF leaky feeder has been the entry level mine-wide system for many years and will be for many more years to come, simply because of its price. Many mines with a voice, data & video capable leaky feeder system are underutilizing it, in most cases because the owners are not aware of the full capability of the system. Some mines have opted for a Voice only leaky feeder system because it was the lowest cost start up solution. Other mines have opted for a Voice, Data & Video capable leaky feeder systems because they provide more functionality, suffer least from random noise ( noise-floor - generated within the mine from plant and electrical services) but the devices cost a little more than voice only devices. Frequency band - 148Mhz to 175Mhz (15Mhz to 20Mhz separation between TX & RX). Bandwidth Voice/Data from 1 to 5Mhz TX/RX, Video 100Mhz Amplifier spacing - 350m or 500 meters (dependant of amplifier gain/brand) Voltage Down line powered from a battery backed 12, 24 or 48 volts DC supply. Off-Air Coverage - Varies from 10 meters to 60 plus meters depending on whether tunnel walls are bare rock or shotcreted & the brand used. UHF 400 to 500Mhz based Leaky Feeder Systems - General - UHF leaky feeder systems were considerably more expensive until recently, mainly due to the high cost of low loss leaky feeder cable. Some current UHF leaky feeder systems use a new improved version of the lowcost VHF leaky feeder mine cable, which is 100% to 300% cheaper, more flexible and easier to handle. The main differences between a VHF leaky feeder system and a UHF leaky feeder system besides the amplifiers, is that UHF leaky feeder cables MUST be suspended below the backs by 100mm, to propagate/radiate efficiently. UHF frequencies offer greater off-air coverage over VHF systems and up to 10Mhz bandwidth allowing for more voice and data channels. UHF systems currently offer 25Mhz separation (wide bandwidth versions) OR 10Mhz separation (narrow bandwidth versions) between Transmit and Receive frequencies. The later is rapidly gaining popularity in Europe, as it allows mines to use existing surface UHF radios underground as well without having to carry 2 separate radios. UHF systems are compatible with Analogue Conventional radios, Analogue Trunking systems, however Digital Trunking systems can operate only over the narrow bandwidth version. UHF frequencies are generally well above the mine noise floor and are not prone to interference like some older VHF designs. Other positive factors are There are more off-the-shelf UHF products available, compared to VHF products, due to its higher popularity world wide. Improved Redundancy, UHF systems can offer a looped leaky feeder backbone so that if the cable is damaged, the amplifiers on the down-side automatically reverse direction and maintain communications on both sides of the cable break. Frequency band - 400Mhz to 500Mhz (10Mhz & 25Mhz separation between TX & RX). Amplifier spacing - 350m to 800 meters (dependant on type of cable used) Bandwidth 10Mhz TX/RX Wide band 1.5Mhz TX/RX Narrow band UHF 800/900Mhz based Leaky Feeder systems - General - UHF 800/900Mhz leaky feeder systems are considerably more expensive, due to the high cost of very low loss leaky feeder cable used. The leaky feeder cable MUST be suspended below the backs by 100mm, to propagate/radiate efficiently. 800/900Mhz frequencies currently offer 30 & 50Mhz separation between Transmit and Receive frequencies and are compatible with Analogue Conventional radios, Analogue Trunking systems and Digital Trunking systems. 800/900Mhz frequencies are well above the mine noise floor.

4 Due to the high cost per kilometer their use is mainly restricted to the working face (except in smaller high grade mines) providing high speed data for automation of mobile plant and equipment. A large mine will still employ a VHF system or a UHF system for mine wide voice communications due to their lower cost per kilometer. Other positive factors are There are even more off-the-shelf products available, compared to 400/500Mhz products, especially in the area of high speed data radio modems 800/900Mhz systems allow the use of GSM mobile phone channels underground Frequency band - 800Mhz to 900Mhz Amplifier spacing - 500m to 800 meters (dependant on type of cable used) Bandwidth 15Mhz & 30Mhz TX/RX UHF 2.4Ghz based Leaky Feeder systems - General 2.4Ghz leaky feeder systems are more expensive again, due to leaky feeder cable costs. However this cost can be limited by using a combination of fibre optics and leaky feeder cable. The use of RF to Fibre interfaces means that leaky feeder cables can be tapped-off a fibre backbone, as and where needed along the route. Again the leaky feeder cable MUST be suspended below the backs by 150mm, to propagate/radiate efficiently. 2.4Ghz frequencies can provide everything from Voice over IP, WiFi, Digital Video, very high speed data. 2.4Ghz frequencies are also well above the mine noise floor. Again due to the high cost per kilometer their use is mainly restricted to the working face (except in smaller high grade mines) providing high speed data for automation of mobile plant and equipment. A large mine will still employ a VHF system or a UHF system for mine wide voice communications due to their lower cost per kilometer. Other positive factors are 2.4Ghz is a growth market with more and more off-the-shelf products becoming available on a daily basis, we have not even begun to see the full potential of this frequency band. Some 2.4Ghz amplifiers incorporate an 800/900Mhz amplifier to enable the use of GSM mobile phone channels underground Frequency band 2.4Ghz (2,400Mhz.) Amplifier spacing - 300m to 500 meters (dependant on type of cable used) Bandwidth 50Mhz TX/RX MUST DO There are some points that MUST be taken into consideration if the system is to work reliably and be available when it is most needed, in an emergency - produce a scope of works that defines your requirements Today, 1 year, 2, 3, 4 and 5 years do not be satisfied with yes our system does that function, ask where you can go and see a system working in the field with those features operational the leaky feeder system MUST be designed around the mine tunnel network it is to be installed in amplifiers MUST have ALC (Automatic Level Control) plan for the installation of the system, (most mines install the hardware themselves and simply get the supplier to commission it) Head End location, power requirements, PABX connections, fibre connections, concrete foundations if required etc.

5 have 2 or 3 sparkies trained up for maintenance of the system and to oversee system expansions. (every time one leaves, organise training for the replacements) you MUST maintain the system and you MUST carry out preventive maintenance if it is to provide reliable service you MUST place the amplifiers at the manufacturers recommended spacing, no more and no less - some newer amplifiers on the market will adjust their output levels automatically (do not exceed the maximum distance), to match the spacing/ distance to the next amplifier. you MUST provide for redundancy, one example is to centrally locate the Head End underground and to use as many of the 4 leaky feeder output ports as possible, so that if one cable is damaged, something less than 25% of the system is out of action thereby limiting the impact on day to day operations