NR SSI8003-102D ISSUE 1 PDF

Introduction

General

A basic arrangement for the signalling functions for a Level Crossing on a bi-directional track with one signal is shown on drawing X03200 of the "AHBC Typical Circuits" Issue 2.0 and also in the layout shown in Chapter B, Section 1.1.

The Over-run Treadle, BC Q, is positioned less than 10 seconds running time, but more than 25 metres, from the Crossing. In this situation the dual, directionally sensitive, Treadles would not have returned to their normal state before the Over-run Track Circuit is no longer occupied by the train. In effect the Interlocking would receive the report of the Track Circuit clear 10 seconds after the last wheel had operated the Treadle; this could be some seconds after the train was no longer occupying the Track Circuit and would be detrimental to the correct operation of the Crossing. In this situation, therefore, the state of the Track Circuit and the state of the Treadles must be returned separately to the Interlocking.

TFM Requirements – Protecting Signal TFM

The Protecting Signal TFM should be allocated an address three or four lower than the address of the associated Crossing Input TFM.

For the Protecting Signal the only outputs and inputs required are those necessary for the control and indication of that signal.

However, one additional input is required for the Over-run Treadle. The identities and data for the Over-run Treadle, however, are specified in Chapter B Sections 2.3 and 3.2.4 respectively.

The Overrun Track Circuit is already allocated to the Crossing Input TFM for the track, as specified in Section 1.2.2 in Chapter B.