scope:

Introduction

SSI is an electronic microprocessor based replacement for the electromechanical technology used predominately in existing relay signalling schemes. Savings are achieved by the elimination of signalling relays except track circuit relays and relays required to interface with certain signalling equipment, e.g. point machines and ground frames, and by the replacement of lineside multicore cabling by serial Data Links. As a result, there is a reduction in the size of buildings, in the resources required for planning and installation and a reduced maintenance requirement.

SSI is intended to maintain the appearance and behaviour of current signalling schemes so far as the railway operating staff are concerned and it is therefore designed to interface with a conventional Signaller's Panel and lineside equipment. However, SSI is compatible with IECC, which includes automatic route setting and VDU based displays. This specification describes the connections from the SSI to the IECC network. Other aspects of IECC design are outside the scope of this document.

The components of a conventional SSI scheme are shown in Figure C1.

Located at the Control Centre are:-

The Signaller's Panel

• One or more CIs, the number depending on the size and complexity of the controlled area.

• One or more TTs, providing fault diagnostic, event logging and certain control facilities.

• The TD System if required.

At the trackside, the final connection to conventional signals, points and track sections is made through TFMs (SMs and PMs) which are linked to their parent CI by means of duplicated Data Links.

SSI has been designed to interface with all types of trackside signalling equipment although in some instances relays will be necessary (e.g. for point machines). The programs within the CI are sufficiently flexible to cope with the most obscure signalling function that may be required.