The Digital Counter: EN 50617-2 Axle Counter Standards

Introduction to EN 50617-2

In modern railway signalling, the traditional “Track Circuit” (which relies on electrical contact between wheel and rail) is rapidly being replaced by the Axle Counter. This system works by counting how many axles enter a block section and ensuring the exact same number leave it. If the count is net zero, the track is clear.

EN 50617-2, titled “Railway applications – Technical parameters of train detection systems for the interoperability of the trans-European railway system – Part 2: Axle counters,” is the interface standard that ensures a Spanish train can be correctly detected by a German axle counter. It defines the “magnetic geometry” that every train must respect to trigger the sensors reliably.

Snippet Definition: What is EN 50617-2?

EN 50617-2 is a European standard specifying the technical interface parameters between the rolling stock and the trackside axle counting system. It defines the minimum requirements for wheel geometry (dimensions, material), the mandatory “metal-free space” around the wheels to prevent false counts from magnetic brakes, and the electromagnetic immunity limits required for the system to function safely under TSI CCS regulations.

The Detection Principle

Axle counters typically use two inductive coils mounted on the rail web.

• Transmitter (Tx): Generates an alternating magnetic field.
• Receiver (Rx): Detects the field.
• Interaction: When a wheel passes, the ferromagnetic steel of the wheel flange distorts or shields the magnetic field coupling between the coils. The system detects this change as an “axle pulse.”

Interface Requirements for Rolling Stock

For the system to work, the train must look like a train. EN 50617-2 imposes strict constraints on vehicle design:

1. Wheel Geometry

The sensor is looking for a specific shape passing close to the rail head.

• Minimum Wheel Diameter: Typically defined (e.g., 330 mm) to ensuring the sensor “sees” enough metal mass.
• Flange Dimensions: The height and thickness of the flange are critical because they are the primary elements interacting with the magnetic field.

2. The “Metal-Free Space”

This is the most critical concept for vehicle engineers. Equipment hanging low on the bogie—such as Magnetic Track Brakes, sanding pipes, or eddy current brakes—can be mistaken for a wheel, causing a “Ghost Train” detection or a miscount.

EN 50617-2 defines a specific volume (box) around the wheel and along the track where no ferromagnetic material other than the wheel itself is allowed.

Comparison: EN 50617-2 vs. EN 50617-1

These two parts cover the opposing technologies for train detection.

Operational Challenges

Reset Procedures: Unlike track circuits, which automatically clear when a train leaves, an axle counter can get “confused” if a power failure occurs or if a maintenance trolley is lifted off the track mid-section (Count In = 1, Count Out = 0). EN 50617-2 supports the technical basis for reliable counting to minimize the need for manual resets, which are a major safety risk.