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The train now standing...

05 September 2013

While the big railway construction projects hit the headlines, communications is undergoing a quiet revolution. Andy Pye looks at some of the latest developments and applications.

Railway construction projects are big business these days. Whether or not HS2 gets underway, there are many national and international examples of big railway development projects. But behind the scenes it is the automation and communications systems which are underpinning the railways of the future.

On the face of it, train communications systems have advanced little in the time since the first modern rail systems were established 200 years ago. Many rail networks still use basic "Mark I eyeball” visual signalling systems that would not be unfamiliar to a 19th century operator. However, new wireless data technologies now make it possible to create train communications systems that are as advanced as the electric, Maglev, and Hydrail locomotives that are powering the train systems.

To meet modern needs, train communications systems must improve in three key areas: bandwidth, response time, and reliability. Telephony, data, and passenger infotainment systems are all bandwidth-hungry applications that tax the limits of existing networks. Train operators now use telephony and data systems for real-time surveillance and modern passenger infotainment systems. With enough bandwidth it becomes possible to consolidate voice, video, and other operational data on one train control network, dramatically simplifying operations and maintenance.

As Communications-Based Train Control (CBTC) takes over from human operators, fast response time becomes central. The old-fashioned method of train control relied on human operators who were given directions through some combination of radio, visual signals, and track circuits. This method had a slow response time, and for safety reasons tracks were divided into long sections with only one train allowed on a section at a time.

A CBTC system with a long response time is cumbersome to use and provides little improvement, while with real-time response time, CBTC can safely and efficiently maximise the number of trains on the track at once.

Wireless Networks communications must be sufficiently resilient to overcome weather, shock, vibration, and electromagnetic interference. The EN50155 and EN50121-1/2 standards are useful benchmarks for confirming that the communications devices are sufficiently robust for on-board and trackside applications.

Wireless technology frees operators from the limitations and complications of cabling, which is arduous in a train system which has many moving parts. Of all currently available wireless technologies, WLAN stands out as having the best balance of capabilities and cost.

Wireless technology frees operators from the limitations and complications of cabling

With WLAN, not only are the installation costs low, but there is also no need to pay a satellite or cellular provider for data service. Optimised roaming technology has made WLAN mobile enough to support train to ground communications, even at relatively high cruising speeds.

Trackside networks consist of numerous wayside cabinets that share data up and down a length of track. These networks contribute to the operation of track elements such as axle counters, track switches, cameras, and railroad crossings. In addition, the trackside network provides the access points for a train-to-ground communications network.

Existing trackside networks often rely on cables between wayside cabinets to deliver communications. This fragile cable can become a weak link in the trackside infrastructure, as th valuable metal can be targeted by vandalism or damaged by the weather.

Revolutionary, next-generation railway applications such as rich passenger infotainment systems and Automatic Train Operations (ATO), simply would not be possible with conventional train-to-ground communications systems and the sheer magnitude of throughput required is far beyond the capabilities of radio, which is able to transmit only a trickle of data. This level of demand even strains the capacity of modern satellite and cellular data technology such as GSM and HSDPA. The IEEE 802.11 WLAN standard can transfer up to 300Mbits of data to comfortably enable all the applications envisioned today, with plenty of throughput left over for applications of the future.

Antennas provide cost-effective coverage: there may be additional complications when the track goes through sharp twists and turns, but simply increasing the AP density will ensure continued wireless coverage.

There is far more interference above ground, especially in busy urban areas. Still, rugged outdoor wireless APs with fast roaming and dual RF redundancy are well-suited for meeting this scenario, especially when deployed with high AP density. Waveguides or leaky coaxial cables (LCX) provide an even more secure link between client and access point, albeit at increased cost. A track lined with waveguides or LCX cables offers wireless clients very stable, interference-proof access.

On-board energy measurement

Energy consumption is becoming increasingly important in many sectors, and the rail industry (although it produces lower emissions per passenger mile than other forms of transport) is no exception. By monitoring the energy used by individual trains, and billing its cost, train operating companies can be incentivised to optimise energy use.

The system must record both energy consumption and position, to allow operators to understand the causes of higher consumption and to enable billing from different network operators. This is a particular challenge in Europe, where international rail travel is common. The need for monitoring systems to support multiple rail networks and train operators demands standardisation. The provisional EN50463 standard has been developed to meet every possible need related to traction energy measurement. LEM’s new suite of components meets the demands of the new provisional EN50463 standard.

For fossil fuel-powered engines, measuring fuel consumption is relatively straightforward, but on electrified lines, accurate traction energy measurement systems that allocate both the cost and the carbon impact of each train journey to each operator are required. In the future it is possible that drivers will be presented with a recommended speed that can be used to optimise energy consumption, which could result in savings of more than 10-20%.

The core of the system is the Energy Measurement Function (EMF) specified in part 2 of the standard, which measures the current and voltage and calculates the energy consumed. The EMF consists of three parts:

  • The voltage measurement function (VMF)
  • The current measurement function (CMF)
  • The energy calculation function (ECF)

The huge power requirement to drive modern trains – in excess of more than 6.4MW in the case of standard multi-system freight locomotives – means that the EMS must cope with very high voltages and currents. Any EMS must also have a VMF that can deal with the different voltages used in electrified railways (AC supplies of 25kV at 50Hz and 15kV at 16.7Hz or DC supplies at 750, 1500 or 3000V).

The huge power requirement to drive modern trains means that the EMS must cope with very high voltages and currents

With such high supply voltages, a key challenge for the VMF is ensuring sufficient isolation. LEM’s DV family, which is designed specifically for traction applications, enables measurement of these high voltages with low offsets, high accuracy (class 0,5R and class 0,75R) and excellent linearity. The transducers also exhibit good common mode behaviour – measuring the actual voltage difference between the two conductors and ignoring any common voltage offset to ground.

Developing a CMF is very challenging, as measuring the high currents at class 0.5R accuracy is difficult to achieve. The most common current transducer technology – the Hall Effect – cannot achieve the accuracy required. A simple alternative solution might be the use of a shunt, where the voltage dropped across a small resistance is measured, allowing the current to be calculated with Ohm’s law. This approach, however, is inherently inefficient and the power wasted in the shunt causes heat dissipation problems.

Using closed-loop fluxgate technology – an approach that ensures excellent accuracy, very good linearity and eliminates insertion losses – LEM has developed a transducer for the CMF that meets the requirements of class 0.5R accuracy. The ITC4000 transducer measures up to 4kARMS and meets the requirements of prEN 50463 class 0.5R accuracy.

The ECF is a complex function. In a rail environment, the voltage and current will vary continuously, and in the case of AC supplies, the voltage and current are unlikely to be exactly in phase. The LEM EM4T II (Energy Meter for Traction II) takes readings from the CMF and VMF, as well as interfacing to a GPS unit to allow the load profile to be tagged with location data. The GPS interface also provides a highly accurate clock signal for time stamping the load information.

Mobile flat camera

The latest addition to Samsung Techwin’s WiseNetIII 2MP Full HD (1080P) network range is a vandal-resistant camera which has been designed to meet the challenging conditions on-board trains, buses and other modes of public transport.

The SNV-6012M mobile flat camera, which complies with the EN50155 standard, is able to operate reliably when subject to the rigorous conditions and extreme vibrations which can occur on-board and it also meets the EN50121 standard which covers electromagnetic emissions in railway environments. The SNV-6012M is IP66 rated and is equipped with a rugged M12 connector that is able to withstand vibration and harsh weather environments.

Utilising bandwidth friendly H.264 compression with the option to also use MJPEG compression, the SNV-6012M can capture high quality colour images when the lighting level is as low as 0.03 lux and has an ultra-fast frame rate. A Defog feature can be used to help improve the clarity of images captured in poor weather conditions.

The SNV-6012M is also ONVIF compliant to work with all types of recording and viewing systems.

Digital video recording

For rail operators such as Northern Rail who do not wish to incur the cost of changing to a Video over IP system, Samsung Techwin’s 960H digital video recording system offers an instant upgrade in the resolution of the live or recorded video that can be displayed on a high definition monitor from images captured by analogue cameras.

The SRD-1673D is able to record 650TVL in real-time across all 16 channels and with HDMI available as a main monitor video output, images in a 16 way-split screen can each be displayed at considerably clearer 480 x 270 resolution compared to what is possible with an SD video output. It also features enhanced network bandwidth of up to 32Mbp, which is four times faster than can normally be expected from industry standard DVRs. This ensures that there is no ‘jitter’ or distortion in the display of video transmitted over a network.

Roger Houldsworth, CCTV Technical Manager for Northern Rail, has recently overseen the installation by an in-house engineer of two 16-channel Samsung Techwin SRD-1673D DVRs at Horwich Station, Lancashire. "We wanted to see if we could improve the playback image quality of video captured by all the cameras installed at the station, and to do so at a higher frame whilst maintaining the ability to store the recorded video for up to 31 days,” said Roger. "The SRD-1673Ds, which have 4TB of on-board storage capacity, have allowed us to achieve these objectives.”

SRD-1673Ds are being installed at four other Northern Rail stations, with plans for a much larger number of stations to be upgraded in the future.

Key Points

  • To meet modern needs, train communications systems must improve in three key areas: bandwidth, response time, and reliability
  • By monitoring the energy used by individual trains, and billing its cost, train operating companies can be incentivised to optimise energy use
  • Samsung Tecwin's SRD-1673D digital video recorders are being installed at Northern Rail stations