New communication system keeps Denver’s
commuter trains rolling
By Levi Gustin
The Regional Transportation District (RTD) of Denver maintains and operates a fleet of light rail vehicles (LRV) for public transportation in the Denver metropolitan area. The existing LRV train cars operated as intended, but did not provide ample feedback to the operators during operation nor to mechanics about causes of failure. RTD approached National Instruments (NI) and CSIA-certified member Optimation about incorporating a data logging, communication, and display system into the trains.
System designed for quick response
An RTD supervisor described the project requirements, including incorporation of global positioning system (GPS) satellite data, TTL/RS232 (transistor-transistor logic/serial communication protocol) communications with existing control equipment, and a graphical user interface (GUI) for the light rail vehicle operator. The GUI screens were designed so that an operator can quickly determine the source of problems and correct them, if possible. If problems are beyond the abilities of the operator, maintenance can be summoned without delay.
Optimation system developers created a data-logging system for individual cars using National Instruments’ LabVIEW software. The individual systems read and record digital and analog signals that are unique to each end of the car. This data is then transferred via Ethernet Modbus communication between the two integrated processor and I/O units in the car and logged locally to one of the touchscreen computers in the car.
In addition to the acquisition of data, the individual systems can receive a GPS signal to set and synchronize system clocks throughout the train. Data acquired on two different pieces of hardware at opposite ends of the car is synchronized for analysis by the GPS time stamps. The system also writes this GPS time to the train car’s internal computer system through serial communication. This information helps the RTD personnel correlate a generic error signal in the train’s existing computer with a more detailed, signal-by-signal record of events logged in the hardware.
Caboose-to-cab communication proved challenging
The most challenging portion of the system was communicating data through the entire length of the train. Car-to-car communication is accomplished through serial Modbus via the couplers that join two individual train cars together. In order for a piece of data to make it from the very back car of a train up to the front cab where the operator display resides, it had to alternate between Ethernet communication internal to the cars and serial communication between the ends of two adjoining cars. An additional communication challenge was that RTD’s LRVs can be driven or coupled from either end in either direction. This means that the software had to be flexible in order to propagate data in the correct direction (Modbus slave versus Modbus master).
Troubleshooting time reduced, efficiency improved
When the complete set of data is delivered to the lead cab of the train, it is displayed on a touch panel computer. In the event of equipment failure, this GUI allows the driver to quickly determine what is keeping the train from moving. Before the Optimation solution was incorporated into the train, the driver had only a single warning light that illuminated when the train could not move, and the driver would have to search the whole train for the cause. The new system drastically reduces troubleshooting time by telling the driver the specific car and signal that is malfunctioning.
The implementation has greatly benefitted RTD’s mechanical operations by providing more information related to mechanical failures through the data logs. RTD has also noted a gain in efficiency and decrease in downtime by providing train-wide signals to the driver.