PETS : MMI Products : Telecoms : STS Signals

PETS

The PETS system allows road users to warn the Railway signaller in case of hazards on the crossing. An automatic monitoring facility checks the operational status of the crossing barrier equipment, telephone handsets and the transmission path.

The STS Signals PETS Interface allows up to four telephones at a railway level crossing to be linked directly to a CONCEPT 32 or CONCEPT 16 telephone concentrator system, via an existing PETS trackside unit manufactured by Whiteley Electronics Ltd.

How does it work?

When a crossing telephone is taken off-hook and the call button pressed, a call signal is automatically sent to the signal control centre, and a locally generated ring tone is heard in the callers’ telephone earpiece.

The presence of an urgent call is displayed on the Signaller’s keypanel, together with a distinctive two-tone audible alarm that can only be silenced by answering the call. Automatic Half Barrier Level Crossing equipped with a Public Emergency Telephone System (PETS) The speech path is opened when the call is answered at the keypanel.

If one crossing telephone is not replaced correctly ‘On-hook’, or is vandalised, the other telephones will remain operational, ensuring maximum safety for crossing users.

While no calls are in progress, the PETS interface polls the remote PETS unit using DTMF tone signalling to check system status and to identify cable faults. Status responses are given automatically.

System Configuration

The PETS Interface comprises one or more PETS Line card, and a PETS Alarm card and Alarm Display. In additon to the speech facility, the PETS interface raises alert signals to the Signaller in the event of certain fault conditions.

The PETS Line card occupies one card position in a standard CONCEPT 32 equipment shelf or CONCEPT 16 enclosure, and enables all calls from the level crossing to be answered using the Concentrator keypanel handset.

The connection to the remote PETS trackside unit is via a 2-wire (volt free) interface, and carries both speech and DTMF signalling using a Magneto (LB) interface.

Two call handling modes are available:
• ‘Solo’ mode – the four external telephones are assigned to individual push-button indicators on the Signaller’s keypanel.
• ‘All-Call’ mode – the four external telephones are presented on a single push-button indicator on the Signaller’s keypanel

Note that four push-button indicators are allocated to each PETS Line card regardless of which handling mode is being used.

All status changes detected by the PETS trackside unit are passed to the Concentrator and are displayed as individual LED’s on the front edge of the PETS Line card.

Alarm data may be relayed to any external location via an RS485 data interface.

PETS Alarm card and Alarm Display.

The PETS Alarm card is mounted within the Signaller’s keypanel and alarm information is presented on the keypanel as a group of four indicators –

A PETS Alarm Accept push-button is provided on the Signaller’s keypanel and is used to acknowledge alarms from the PETS trackside unit. The pushbutton is dual purpose since its integral lamp provides visual indication of the system power-on condition, and also provides a lamp test and audible alert test function if held for more than 2 seconds.

The PETS alarm display unit may be integrated within a free standing keyboard or console mounted keypanel. A stand-alone unit is also available for retrofit applications ensuring minimum disruption to the Concentrator system.

Red = Crossing PSU fault
        “Remote Power Fail”
Amber = One phone off-hook
        “Single Off-hook”
Red = >Two phones off-hook
        “Multiple off-hook”
Red = Crossing system failure

System Alarm Signals

The following condition signals are raised on the PETS Line card:
Line card ‘Run’ indicator – 400mS on/off flashing
Incoming call in progress / Outgoing call in progress / Speech path connected
DTMF Transmit / DTMF Receive / DTMF Receive checksum error
No reply from PETS unit
Power to remote display OK

In addition, the following alarms are generated by the PETS unit:
Remote equipment fail
Vandal Alarm / Multiple off-hook alarm
Barrier 1 / Barrier 2 / Barrier 3 / Barrier 4 Status

PETS Alarm Display
The PETS system includes dedicated alarm signals which are transmitted through an RS485 or RS 232 interface to an Alarm Display on the Signaller’s keypanel. The RS485 serial interface can connect a single PETS Alarm card to up to eight PETS Line cards.

A PETS Alarm display is provided for each level crossing - each display consists of four indicators; one amber and three red.

A detailed indication of the nature of the alarm is available by referring to the specific LED indicator on the edge of the PETS Line card.

PETS System Operation

A call from the level crossing is initiated by lifting a handset, and if necessary pressing the call button as indicated on the unit.

The call is presented to the Signaller as a distinctive flashing lamp with an audio alert at the Signaller’s keypanel. A speech path is established once the Signaller selects the flashing keyswitch: the call is cleared by repeat selection of the keyswitch.

When an alarm condition occurs, the appropriate indicator (amber or red) illuminates and an audible alarm sounds. Momentarily pressing the “AHB Alarm Accept” pushbutton silences the audible alarm. Any new alarm condition occurring will re-trigger the audible alarm.

If a crossing telephone is not replaced within 30 seconds of the call being cleared, the AMBER “Single Off-Hook” alarm is activated.

If further telephones are also left off-hook, the Multiple Off-Hook alarm is activated. In the event of local power failure at the crossing, the RED “Remote Power Fail” alarm is activated.

In the event of physical damage to any of the crossing telephones, or a failure in the comms link from the crossing to the Control Centre, or other system failures the RED “Call Tech” alarm is raised. This alarm may also be configured to indicate failure of the crossing barriers.

Protocols and Data Interfaces

The PETS trackside unit protocol conforms to the format specified by BR document ‘Public Emergency Telephone Systems – Installation and Maintenance Manual’. The alarm data interface is RS485 (bus) for PETS Line card Variant /01 or RS232 (point-to-point) for the variant /02. Power supplies: The PETS Alarm card is powered from a single +5V supply derived from a +12V d.c input via an on-board regulator, drawing 30 to 50mA.