UIC 541-6: Electropneumatic Brake (ep) & Passenger Alarm Signal (PAS) Specifications

UIC 541-6 Chapter 5 provides the technical specifications for the Electropneumatic (ep) Brake and the Passenger Alarm Signal (PAS) on vehicles used in international hauled consists (RIC coaches). While the pneumatic brake provides the muscle, this standard defines the electrical “nervous system” ensuring that a German locomotive can interpret the emergency alarm pulled in an attached Italian coach.

This leaflet specifies the voltage tolerances, signal loop continuity, and the precise pin assignments required to ensure the safety loop remains closed across the entire trainset.

1. Passenger Alarm Signal (PAS) Architecture

In modern operations, the “Emergency Brake” handle is no longer a simple mechanical valve opening the brake pipe. It is an electrical switch integrated into a safety loop. UIC 541-6 mandates:

• Loop Integrity: The alarm signal relies on a “Closed Circuit” principle. If the wire breaks or a plug disconnects, the system interprets it as an alarm (Fail-Safe).
• Transmission: When a handle is pulled, the signal is transmitted via the UIC cable (Pins 9 and 10 usually) to the locomotive, triggering an acoustic/visual alert in the cab.
• Acknowledgement: The system must allow the driver to acknowledge the alarm, activating the Override mode (see UIC 541-5) to bridge out the brake application.

2. Electropneumatic (ep) Brake Control Logic

To achieve simultaneous braking, the ep-brake uses solenoid valves powered by the train line. UIC 541-6 defines the electrical states required for different braking commands.

3. Test Specifications for Interoperability

Before a train departs, the integrity of the electric brake control must be verified. UIC 541-6 outlines the static test procedure:

• Continuity Check: Verifying the electrical resistance of the PAS loop from the locomotive to the tail lamp of the last wagon.
• Voltage Drop: Ensuring that the voltage at the last vehicle (even on a 15-coach train) is sufficient to trigger the ep-valves (>70% of nominal voltage).

4. Priority of Systems

The standard establishes that while the ep-brake is the primary operational mode for comfort and speed, the Pneumatic Brake remains the ultimate master. If the electrical signal contradicts the pneumatic pressure (e.g., ep says “Release” but Brake Pipe is empty), the safety-critical pneumatic state (Emergency Brake) always takes precedence.