CANopen pressure transmitters monitor freight wagon brakes

Miniature CANopen pressure transmitters monitor freight wagon brakes for condition-based maintenance

Digitalising a freight train means fitting sensors to wagons that run for years outdoors, without on-board power infrastructure. Trafag describes how its CMP 8271 CANopen miniature pressure transmitters measure brake pressures on each wagon of a connected freight train.

Brake pressure as the key health indicator

The application is a digital monitoring platform for freight rail developed by a provider of rail telematics systems. Each wagon is equipped with an onboard unit carrying a set of sensors and a low-power wireless link; it is powered autonomously by an axle-mounted generator. By connecting the individual wagons, the system turns a conventional freight consist into what the industry calls a smart train.

Pressure is the central measurement. Up to nine transmitters per wagon record the brake pipe pressure, the brake cylinder pressures and the pressures at the control valve. Together these values show whether the brake is applying and releasing correctly. That makes it possible to automate parts of the brake inspection, detect brake faults at an early stage, move towards condition-based maintenance and reduce unplanned stops in service.

Mounted outside, exposed for years

The transmitters are mounted externally on the wagon, where they are exposed to wind, weather, vibration and debris thrown up from the track for many years of operation. According to the system developer, the robustness requirements for the sensors are just as demanding as those for measurement accuracy. Freight wagons also cross mountain routes, so the readings must stay accurate despite large changes in altitude and temperature.

Our supplier Trafag uses its CMP 8271 for this task. The miniature transmitter is based on a thin-film-on-steel sensor, is rated for media and ambient temperatures from -40 to +125 °C and communicates via CANopen (DS301/DS404), which simplifies integration into the onboard unit. Markus Degasperi, Managing Director of Trafag Austria, says the CMP 8271 “is designed for demanding applications in harsh environments.”

From retrofit to new wagons

According to Trafag, rolling-stock manufacturers have started integrating the monitoring system into new freight wagons, while some operators are retrofitting their existing fleets. For instrumentation engineers the case is a good illustration of how a standard industrial pressure transmitter with a fieldbus interface can serve as a building block in rail IIoT, provided the mechanical and environmental ratings match the exposed mounting position.