PETS-2 Crossing Telephone System
QUICKFIX INSTALLATION HANDBOOK
Page 33
of 40
Issue 2
13/12/99
33
Polarity is not important with this protocol. However, it is necessary to ensure that the
telephone is correctly wired and a ‘leakage current’ resistor has to be fitted to the
telephone.
5.8.2.2 Earth Recall
NOTE: The unit will require re-configuration to operate in this mode - seek instruction from
the System Design Authority.
This is a possible calling mode for a control telephone (in the level crossing equipment
room) connected to its own line card. Telephone line Leg a (+ve) is shorted to Earth
(telecommunications earth) to signal a call. This mode supports the monitoring of leakage
current, hence a resistor must be fitted across the line pair - normal inside the master LJU
of that telephone.
5.8.2.3 Master Line Jack socket for control telephone
Control telephones at the Signalbox and Level Crossing will normally be connected through
a standard master LJU. If ELR calling is required, then the polarity of wiring is important and
the socket should be polarity tested using a Linesman's Telephone.
If an ABSENT switch is installed in the Signalbox, it will be necessary to wire the Control
telephone line through a normally closed contact of the ABSENT switch, to ensure that the
telephone does not ring when the box is closed. Some arrangement with automatic
announcers will require the ABSENT switch to divert the line to the announcer unit.
5.8.3 Transmission Circuits
The Signalbox Unit and Level Crossing Unit have to be connected together via a
transmission medium. This medium may be physical (copper) or by means of a multiplexor (
D & I Mux, PCM link etc.). PETS2 may be configured for a 2 wire (one pair; bi-directional) or
a 4 wire (two pair; go & return, Tx/ Rx) circuit. If the facility is available, choose a 4 wire
interface since this will provide better transmission performance and will be easier to fault
find if there are transmission difficulties. Use a 2 wire interface on physical circuits where
pairs are in short supply. Seek expert advise for the modifications required to allow 2 wire
operation. This handbook assumes that the installation will use factory default configuration
of 4 wire operation. In this mode, the pair labelled T3 are the transmit circuit, i.e. audio is
transmitted out on T3. The circuit labelled T4 is the receive circuit. Transmit of the
Signalbox is connected to receive of the Level Crossing. Phasing of the pair is not
important, but it is good practise to maintain phasing. The transmission circuits should be
connected as follows:
Signalbox JB
Crossing JB
Cable Colour (mark up)
(T3-Tx) Block 3, pair 6a
(T4-Rx) Block 3, pair 4a
(T3-Tx) Block 3, pair 6b
(T4-Rx) Block 3, pair 4b
(T4-Rx) Block 3, pair 4a
(T3-Tx) Block 3, pair 6a
(T4-Rx) Block 3, pair 4b
(T3-Tx) Block 3, pair 6b
