Page
32 of 40
Issue 2
13/12/99
PETS-2 Crossing Telephone System
QUICKFIX INSTALLATION HANDBOOK
32
The ‘D’ connector is a solder bucket type. A small soldering iron is required to make these
connections. The pin number are moulded into the plastic adjacent to each pin - look close
as the number are very small.
5.8.2 Local telephone wiring (Level Crossing)
Local telephones are the crossing telephones (similar to signal Post telephones) or the
Equipment Room Control Telephone. Two different types of interface may be used, a brief
explanation of each is given in the following sections 5.8.2.1 & 5.8.2.2
Local telephone wiring connections are made onto QDF Block 2, pairs 7 to 10. When Earth
Recall operation is used, an earth is available on both legs of pair 6 of the QDF Block 2.
Please refer to Figure 7 for the layout of the QDF Blocks.
Earth Recall (ELR) is signalled by connecting ETH to Leg a (+ve) of the telephone line pair.
However, ELR will not be used normally and the units are factory configured for Loop
Disconnect calling. Loop Disconnect calling is preferrable as this method will operate over a
single pair ( ETH is not required by the telephone).
NOTE: Signal Post telephones designed for use at level crossings will normally incorporate
a ‘bell’ capacitor, and normal installation practise will allow the circuit to be wired directly to
the telephone. If ‘domestic’ type telephones are used in the equipment room, then a BT
Master LJU is to be used to interface the telephone with the PETS2 line circuit.
IMPORTANT NOTE: If overhead circuits are to be used, or if circuits operate parallel to
electrified lines, then protection magazines should be added to the QDF line circuits. In
cases of high risk of lightning or induced transient, then a separate transient suppresser/
lightning arrestor should be connected to the circuit, with its own safety earth.
5.8.2.1 Loop Disconnect Calling
NOTE: The line circuits are configured to this mode at factory.
This is the normal interface to be used on Crossing Telephones. This interface has the
advantage of being 2 wire (one pair). The ‘protocol’ is probably unique to PETS and has
three phases:
1. Quiescent Phase (telephone handset on hook) - a current of approx. 5mA flows in the
pair, and through a loop in the telephone handset
2. Off Hook Phase - current increase to >15mA
3. Calling Phase - current reduces from >15mA to zero for a defined period.
If the current remains at zero for more than 30 seconds, an alarm is logged; indicating the
possibility of an open circuit pair or vandalised handset.
