Deltron Equipment & Systems Pvt. Ltd.
Automatic Block Signalling using MSDAC , UFSBI & Non-Vital Mux
Introduction to Automatic Block Signalling in Indian Railways
In the rapidly modernising landscape of Indian Railways, Automatic Block Signalling (ABS) stands out as a cornerstone of operational advancement. It has emerged as a pivotal development that addresses the dual imperatives of safety and capacity enhancement. ABS replaces conventional manual block working systems with an intelligent, fail-safe automation model, enabling continuous, real-time management of train movements. The system divides the railway track into multiple defined sections, or ‘auto-blocks’, each controlled by automatically governed signals that respond to train occupancy without manual intervention. The result is a substantial increase in line capacity by 50 to 100%, allowing substantially more trains to be pushed successively into a section with minimal headway, while upholding uncompromised safety standards.
The core components of this system include the Universal Fail-Safe Block Interface (UFSBI) and the Multi-Section Digital Axle Counter (MSDAC), which together deliver a highly reliable, Safety Integrity Level 4 (SIL-4) compliant signalling solution. These components operate cohesively over dual redundant optical fibre communication (OFC) channels, forming a digital signalling backbone that is robust, modular, and designed for resilience.
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UFSBI: The Vital Communication Nerve Centre
The UFSBI lies at the heart of the ABS architecture, performing a role far beyond that of a conventional communication interface. It functions as a Fail-Safe 16 Input and 16 Output multiplexer, specifically engineered for the secure exchange of Vital Inter-Cabin Control (ICC) information. This includes the transmission of essential control signals between adjacent Auto Signalling Huts and terminal stations, enabling the real-time coordination necessary for automatic signal aspect control and block occupancy verification.
Deployed in a dual-redundant configuration, each UFSBI operates over dual dark OFC paths, offering both hardware and media-level redundancy. This ensures high availability and fault tolerance under all operational conditions. By maintaining constant vital information exchange between distributed Auto Signalling huts, the UFSBI is effectively entrusted with the responsibility of signalling Inter Cabin Control (ICC) states across the entire block section. It facilitates the safe operation of signals by exchanging occupancy status, interlocking conditions, and vital commands with precision and reliability. In this regard, the UFSBI acts as the digital backbone of the ABS system, maintaining system coherence through deterministic data exchange.
Alongside the vital I/O multiplexer, a Non-Vital Multiplexer is also employed to handle and disseminate operational information not critical to safety but crucial to monitoring. This includes automatic signal aspect status, track section occupancy, MSDAC health (main and redundant), level crossing (LC) gate inputs, and fire alarm conditions. These inputs are relayed to Visual Display Units (VDUs) located at both terminal stations of the section, offering operators complete situational awareness. The logical separation between vital and non-vital channels exemplifies the thoughtful design of the system, balancing safety, monitoring, and maintainability.
MSDAC: Precision Detection with Redundant Design
Complementing the UFSBI, the Multi-Section Digital Axle Counter (MSDAC) is responsible for precise detection of train presence and clearance within defined block sections. These systems monitor the passage of trains by counting axles as they cross designated Detection Points (DPs), and this information feeds directly into the control logic governed by the UFSBI. Depending on the operational requirement and OEM specification, MSDAC systems may be deployed in either 2-out-of-2 hot standby or 2-out-of-3 fail-safe configurations, both offering high reliability and fault tolerance.The architecture ensures that detection is accurate and resilient. The main and standby detection points are typically installed on opposing rails in close parallel, ensuring that the detection time difference is negligible, thus avoiding unnecessary auto-resets. In the event that either the main or standby track section fails to clear, the system’s automatic reset feature—based on internal timer circuits or reset modules—will restore normal operation. Where both systems fail, a preparatory manual reset procedure is invoked, requiring coordinated action between the dispatching and receiving stations through a common reset box and co-operative button mechanism.MSDACs, while crucial to the detection layer of ABS, work in direct symphony with UFSBIs to translate occupancy information into real-time signal aspect changes. This allows signals to automatically revert from 'clear' to 'danger' when a block becomes occupied, and vice versa once the block is vacated, thereby enabling the safe and efficient progression of multiple trains in a single block section.
Integrated SIL-4 Safety and Operational Gains
The integration of UFSBI and MSDAC systems, connected via dual dark OFC routes, forms the bedrock of a SIL-4 compliant, high-availability automatic signalling solution for Indian Railways. Each component of the system is rigorously validated and deployed under the technical directives of RDSO and zonal railway circulars. By maintaining both physical and logical redundancy across all communication and detection systems, the infrastructure guarantees continued service even under adverse conditions or partial system failure.
This design enables proactive fault management through real-time diagnostics and exception reporting via data loggers, ensuring that maintenance interventions can be made well before total system failure occurs. Moreover, the substantial increase in line capacity—achieved by reducing train headway within a block section—makes ABS particularly effective in high-density and suburban corridors where throughput is critical.
In essence, ABS is not just a signalling upgrade—it is a paradigm shift in how railway operations are conceived and controlled. By combining fail-safe vital signalling with operational intelligence and automation, Indian Railways is setting a new benchmark in railway safety, capacity, and reliability, positioning itself among the most forward-looking rail networks globally.
Integrated SIL-4 Safety and Operational Gains
The integration of UFSBI and MSDAC systems, connected via dual dark OFC routes, forms the bedrock of a SIL-4 compliant, high-availability automatic signalling solution for Indian Railways. Each component of the system is rigorously validated and deployed under the technical directives of RDSO and zonal railway circulars. By maintaining both physical and logical redundancy across all communication and detection systems, the infrastructure guarantees continued service even under adverse conditions or partial system failure.
This design enables proactive fault management through real-time diagnostics and exception reporting via data loggers, ensuring that maintenance interventions can be made well before total system failure occurs. Moreover, the substantial increase in line capacity—achieved by reducing train headway within a block section—makes ABS particularly effective in high-density and suburban corridors where throughput is critical.
In essence, ABS is not just a signalling upgrade—it is a paradigm shift in how railway operations are conceived and controlled. By combining fail-safe vital signalling with operational intelligence and automation, Indian Railways is setting a new benchmark in railway safety, capacity, and reliability, positioning itself among the most forward-looking rail networks globally.
Zonal Railway Approved Schematics & Guidelines for Auto Signalling using UFSBI & Non-Vital Mux with MSDAC, Part 1
Zonal Railway Approved Schematics & Guidelines for Auto Signalling using UFSBI & Non-Vital Mux with MSDAC, Part 2
Zonal Railway Approved Schematics & Guidelines for Auto Signalling using UFSBI & Non-Vital Mux with MSDAC, Part 3