By Dave Wilson, Academic Marketing Director, National Instruments
About 1.7 billion people ride the London Underground every year. The Victoria Line alone operates 33 trains per hour and carries 213 million passengers per year. An 8-year, £1 billion investment program upgraded and replaced the Victoria Line’s rolling stock and signaling and control systems. The upgraded system uses 385 JTCs (jointless track circuits) to detect train position and maintain safe train separation while delivering train headways (the tme or distance between trains) capable of meeting the line’s extremely demanding timetable. JTCs are now the sole means of train detection on the Victoria Line and play a critical role in the safe and reliable operation of the railway. However, no provision was made for track condition monitoring during the design and installation of the new track. That’s a problem. London Underground track signal failures cost the operation £1.7 billion annually.
Modern railway track is often continuously welded; joints are welded during track installation. Jointless track offers many benefits but really complicates railway signaling because there are no natural breaks in the rail to form block sections. Instead, different audio frequencies are injected into each block section as markers. Tuned circuits are connected across the rails at section boundaries to confine one block’s signals to one track section.
The London Underground’s Victoria Line employs variable-length, frequency-driven, tuned electrical JTCs. The circuits energize and de-energize as trains pass over each section. Each JTC includes an electrical receiver unit matched to the frequency of the track circuit. The receiver processes the incoming signal and provides a sample signal that can be used to check the health of the track circuit.
After the track upgrade, the original method for establishing the track’s health was to check each track circuit manually with a digital multimeter—a test procedure that somehow seems out of step with a passenger load of nearly a quarter billion passengers per year. Clearly, test automation was needed to detect and predict track failures and to inform a pre-emptive maintenance plan. London Underground engineers selected National Instruments’ (NI) FPGA-based CompactRIO reconfigurable embedded control and acquisition system to automate JTC testing and to monitor 385 deep Tube assets in real time on an operating railway.
Here’s a block diagram of the system:
The test system’s design distributes data acquired by the CompactRIO units across 14 sites using a new high-bandwidth fiber-optic network specifically installed for track testing and monitoring. A central condition-monitoring server processes live 10 Hz data streams from every CompactRIO unit, totaling more than 7,000 data samples per second. The system compares each received frame of data to a predefined standard frequency and voltage so the server can evaluate the health of each connected track circuit in real time. The central server can then push asset condition alerts to an HMI (human-machine interface), smartphone, or tablet where an operator can intuitively navigate the displayed information.
Each deployed unit pairs an NI cRIO-9025 Real-time Controller with an 8-slot NI cRIO-9118 chassis, which integrates a Xilinx Virtex-5 FPGA that provides computational acceleration for the controller’s microprocessor—the FPGAs provide the real-time response needed by time-critical loops—and gives the chassis its I/O flexibility. The CompactRIO chassis accepts as many as eight NI 9220 analog input modules to provide a maximum of 128 physical inputs per CompactRIO system. This hardware is programmed using NI’s LabVIEW graphical system design software and LabVIEW FPGA Module.
The London Underground engineering team selected NI Alliance Partner Simplicity AI to develop the CompactRIO FPGA and real-time software because of the company’s high level of FPGA and real-time experience. Simplicity AI met the challenge of calculating frequency and RMS voltage simultaneously on all 128 channels by developing a serial process architecture that uses the FPGA’s high clock rate and performance to process data for each channel sequentially.
The project was delivered on schedule and under budget and now provides a reliable, automated remote condition-monitoring system that empowers maintainers to proactively respond to failures before they occur—just as designed.
Note: Sam Etchell, Dale Phillips, and Barry Ward, London Underground Limited submitted this project to the NI Engineering Impact Awards 2014 competition. It was a finalist in the Transportation category. It also won the Xilinx Award in the competition.