NR SSI8500D ISSUE 16 PDF

Introduction

For an SSI scheme, signalling plans and Control Tables shall be produced and approval obtained as normal practice. Minor Control Table differences required for SSI are explained in Section 2. It is then necessary to produce a Location Plan showing the boundaries between each location and where necessary, between each CI. At the same time, a set of TFM Schedules, described in Sections 3 and 4 and showing the allocation of signalling functions to PMs and SMs shall be completed. The Schedules are then entered into the scheme database held in the SSI DWS (see SSI8300 - "SSI Design Workstation Users' Guide").

Following finalisation of the Control Tables and allocation of the TFMs and Interlocking boundaries the geographic data shall then be produced as described in SSI8003 "SSI Data Preparation" and entered into and compiled on the DWS. The data procedures in "SSI Data Procedures" (SSI8505) shall be followed, and documentation produced and issued in accordance with Chapter J of this document.

The capacity of each CI is limited and, for most schemes, the limiting factor will be the number of TFMs each CI is allowed to address. TFMs shall therefore be allocated carefully. Not all outputs and inputs to TFMs will be used but additional outputs and inputs shall not be left unallocated for future use, such outputs and inputs are likely to be in the wrong place and will be too limited in quantity for any practical future expansion. It is more advantageous to retain spare TFM addresses within each Interlocking which may then be allocated to any site at a future date, the quantity to remain unallocated is discussed in Section 6 of this specification. Signalling functions should be allocated to TFMs which can then be grouped into location areas to maximise the number of TFMs connected to each pair of DLMs. Some interchange of feed and relay ends of track circuits may also need to be considered to obtain the best arrangement of TFMs. However, other factors may be more important in determining the design of track sections and siting of locations.

Where information on a TFM input is required in more than one CI, then it shall be input via one TFM to one of the CIs and then passed onto the other CI(s) via the IDL.

Where automatic and semi-automatic signals are controlled from an SSI, they shall be treated in the same way as controlled signals for Module allocation. They will act in the same manner as if they were controlled by relays.

Where controls are provided via SSI for automatic level crossings and other items where strike in points are time dependent then two seconds shall be allowed for system reaction time.

Where One Train Working using track section/treadle sequential operations is required, consideration shall be given to the effects of power failure on its operation. To provide full battery/UPS back up requires the logic to be carried out in relays at the trackside, rather than using SSI data, as the latter method cannot achieve the required reliability. Further details are given in SSI8003-80.

The remainder of this Chapter describes the constraints in the allocation of TFMs and the division of the scheme into separate CIs. Figure D1 summarises the output, return current path and input data requirements of the TFMs for various signalling functions and Figure D4 shows typical circuits.