Sensors used within the rail industry need to be capable of withstanding harsh environments, with extremes of shock and vibration, yet ensure high levels of reliability. Jesse Bonfeld at Sherborne Sensors examines some of the applications served by inertial sensors within this industry
Sensors have been in use in the rail industry almost since its inception. Initially, lanterns were used as signalling devices to communicate between the engineer and the conductor; rudimentary gauges monitored the operation of the engine; and mechanical level indicators were used to monitor water levels in the tenders.
Today, however, there are a multitude of sensors used to not only monitor conditions, but also to enable and enhance the performance, safety, economy and efficiency of modern passenger and freight operations.
As with many industrial applications, sensors used in the rail industry must be able to perform in very harsh and aggressive environments, having to withstand extremes in temperature, vibration, shock and electrical noise. In addition, many are tasked with performing critical functions – meaning very high levels of reliability, repeatability, robustness and accuracy are essential.
Furthermore, being a highly regulated industry responsible for the safety of lives and property, railway owners, operators, equipment managers and their vendors need to implement proven technologies and solutions that are capable in such environments.
Within the rail industry, there are three common applications for inertial sensors: passenger car acceleration modulation; alignment functions in rail line repairs; and rail line condition compliance and monitoring.
Many of the electrified and mechanical rail systems in operation today are highly automated – to maximise operational elements, improve the service experience and minimise cost.
Train, subway or airport rail systems feature rapid acceleration on departure, and deceleration on arrival. This, however is quite complex, having to replicate the acceleration condition with variations in track inclination, highly variable weight loads due to changes in onboard passenger volumes, and track conditions including ice, rain and snow.
Optimising the g forces during these events is accomplished using a sophisticated accelerometer, which provides a feedback signal to the train’s main control system. This means passengers can at least know what to expect regardless of the high level of variability that exists where these vehicles operate.
Most of the repair work performed on rail lines is accomplished using highly automated machinery capable of removing damaged sections and completely rebuilding them in a single integrated procedure. However, strict rules exist through regulatory agencies as to the configuration of the rails to the surface where they are mounted, and to each other. Very slight errors in positioning can lead to repairs that are out of specification, and ultimately present a significant safety hazard and liability.
To ensure proper orientation and alignment, most repair systems are equipped with both single and dual axis inclinometers which help to ensure that track conditions are optimised and in compliance once repairs are complete.
Rail line condition inspection
Although some situations exist where the need for rail repair work is obvious, many other conditions worthy of repair are more subtle – such as where there is ground subsidence due to track bed undermining, or the warping of tracks due to excessive wear which can put sections of rail out of compliance with their rated load and speed schedules.
In the United States, there are four categories for rail systems that define how fast a train can run, and how much weight the rails can carry. If a section of track falls out of compliance, operators are compelled to reduce loads and speed, which can add significantly to their costs. As a result, the decision to take a rail section out of service is not taken lightly.
The industry has addressed these issues by developing equipment to proactively inspect their rail systems and ensure compliance. This equipment includes wheeled vehicles that ride the system while collecting and logging critical data such as rail gauge, incline and offset. Incline and offset data is captured using highly sophisticated dual axis inclinometers, whose performance is optimised to allow these vehicles to travel at very high speeds, while still being able to pinpoint compliance problems to within just a few inches.
Over the years, sensors have played a key role in improving rail travel reliability, affordability and safety. Nevertheless, rail owners and operators continue to look to the sensor industry for novel solutions as new challenges arise with every advance in rail system and equipment designs.
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