Redundant pressure monitoring for track-maintenance machine brakes

Redundant pressure monitoring keeps the pneumatic brakes of track-maintenance machines under control

On automated track-maintenance machines, a brake defect does not just stop one vehicle: it holds up the whole worksite and extends the track closure. Trafag describes how its NAR 8258 transmitters and Picostat 9R5 switches watch over the pneumatic brakes.

Monitoring the whole brake system, not single points

The application comes from a manufacturer of automated railway maintenance machines. Rather than reacting to a sudden brake failure on site, the builder opted for continuous, structured monitoring of the complete pneumatic brake system. The aim is simple: detect a loss of pressure before it turns into an unplanned stop that delays construction work.

The architecture is layered. Two mechanical pressure switches sit on the main air line of each machine. Every brake supply line is then monitored by two redundant pressure transmitters. On some brakes a third transmitter is added, specifically to confirm that pressure has been restored after an interruption of the air supply. The combination of electromechanical switches and electronic transmitters gives the control system both a simple threshold signal and a continuous pressure value.

A smaller transmitter without redesign

The transmitters previously used on the machines met the technical requirements, but they were large and comparatively expensive. Our supplier Trafag proposed its NAR 8258 railway pressure transmitter as a replacement. In this application it is used in a 0 to 10 bar range with an accuracy of ±0.3 %, and it is rated for -40 to +85 °C and compliant with the railway electronics standard EN 50155.

A decisive point for the machine builder was that the NAR 8258 uses the same pressure and electrical connections as the previous unit, so it could be fitted without changes to the design. At the same time, the housing is considerably smaller: according to Trafag, the transmitter measures about 18.8 mm in diameter and 59.6 mm in length.

“The railway pressure transmitter features a long-term stable thin-film-on-steel sensor cell.”

— Markus Degasperi, Managing Director, Trafag Austria

Brand-label parts against unauthorised replacement

Alongside the transmitters, Trafag supplies the Picostat 9R5 mechanical pressure switch for the main air line. Both devices are delivered in brand-label versions carrying the machine builder’s own marking. The intention is practical rather than cosmetic: it discourages the replacement of safety-relevant brake components with unapproved parts during maintenance in the field.

Key facts

• Transmitter: Trafag NAR 8258, 0 to 10 bar, ±0.3 % accuracy
• Temperature range: -40 to +85 °C; compliant with EN 50155
• Dimensions: approx. 18.8 mm diameter, 59.6 mm length
• Pressure switch: Trafag Picostat 9R5 on the main air line
• Two redundant transmitters per brake supply line, a third on selected brakes