Networked PA System

Ajay Kumar, IRSSE, Chief Communication Engineer, SER

Abstract

PA systems are being used at almost all the Railwaystation in India. Although the world is becoming in-creasingly networked with each passing day, the PAsystem at stations remains an isolated one. This ar-ticle describes a digital PA system that was tried inEastern Railway in Sealdah division.

1 Introduction

The need for safety and control at stations is be-coming ever more crucial with an increasingly greaternumber of people using railways as their main methodof transport. The information is to be given to peo-ple for train availability and any emergency arising inform of voice alarm in rail industries. The railwayswhich are a major player in the transport of manshall utilise IP legacy solutions to latest generationof digital networked audio distribution products.

2 Requirement Analysis

A Public Address system to be chosen will have to bedesigned specifically for rail application. These mustbe IP65 rated and shall have vandal resistant sta-tion announcement points. It shall also feature hand-held microphone with wireless connectivity. The needof announcement from central location to remote lo-cation cannot be denied. It should be possible tomake announcement from central location like divi-sional headquarter to remote station including Flagand Halt station where station masters are not avail-able.

The centralized announcement system is providedto make announcement remotely from central controlto different halt and flag stations through Manualmode or through Auto announcement by announce-ment server taking data from train tracking server.Announcement to remote station can be done fromCentral location to remote station one station beforetrain arrival to a particular station. The announce-ment to be done for all the UP as well as for DNtrains. As announcement has to be done in differentstations over a line there should be Number of trainsto be defined in the design itself to have better re-

liability. The response time between announcementand actual announcement at the station should notbe more than 1sec. It should be possible to make an-nouncement at local level. The priority for announce-ment at local level should be more than the announce-ment from central control. The central announce-ment should be stored and after local announcement,the central announcement should take place.

The Networked digital Public address system andvoice evacuation system should meet following mini-mum criteria at the platform:

• Room acoustic speech transmission index -IRASTI > 0.5

• Total sound pressure level - Total SPL > 85 dB

• The sound pressure level should be such that aminimum 10 dB above the ambient noise levelsare achieved.

The high quality fast-acting IP Based Public addressand vice alarm system should complying with BS5839 part 8 and EN60849.

3 IP Based Digital PA System

The IP Digital PA system provides digital audio sig-nal processing and transmission of audio signals viaIP network. The audio transmission in the systemis in digital form except for the 100V line from thepower amplifiers to the loudspeakers. The block sys-tematic of the equipment at the Central office andthe equipment at the different station is given in theblock diagram in Figure 1.

In the Figure 1, Central control equipment asshown in the block systematic has all the componentsrequired for networked digital public address systemat central location connected with IP enabled equip-ments.

Shown in the figure 2 is the Halt and Flag stationequipment block systematic, along with all compo-nents required for networked digital public addresssystem at Halt and Flag station in remote.

Figure 3 shows the man machine interface for thedigital PA system showing connection of differentequipment as well.

Figure 4 shows the Digital PA system with bank ofPower amplifier controllers and communication unit.

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Figure 1: IP PA System Block Diagram

Figure 2: Arrangement at Halt Station

Figure 5 shows the IP routers used to establish IPcommunication among the stations.

Figure 6 shows the Power amplifier bank used forthe purpose.

Figure 3: Network PA System MMI

Figure 4: Power Amplifier Controllers

Figure 5: IP Routers

4 Function & Facilities

4.1 Station Facilities

The following Equipment is to be provided at eachstation

• PA system cabinet.

• Digital system matrix/network controller.

• IP Interface.

• Digital Call station.

• Speakers for platforms.

• Logging and configuration PC.

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Figure 6: Bank of Power Amplifier

• Universal Interface for Analog Inputs.

• Noise sensing microphones.

• Digital Audio Storage.

4.2 Station Function

The following are the functions at station.

• The station supervisor can make an announce-ment to any zone or any combination of zone bydigital announcement call station.

• The announcement made by the supervisor willbe at the highest priority over the announcementdone by the central control announcer. Aftergetting finish of the announcement by the sta-tion supervisor the central announcement shouldbe broadcast. The central office announcementshould wait in queue till the finish of the localannouncement.

• It should be possible to do pre recorded an-nouncement.

• It should be possible to play Background music.

• Pre recorded emergency announcement.

• The pre recorded announcement can initiated bythe fire alarm system.

• The central control announcer should able to an-nounce to any combination of zone in any num-ber of station in the system.

• The pre-recorded announcement can be acti-vated from The pre-defined keys of the digitalcall station, to be played at specific times.

• The failure of the PA equipment will be notifiedto the call station at station and the fault willalso be presented at the configuration / diagnos-tic and logging PC located in the central office.

4.3 Central Control Office

At the central control office the Digital PA systemconsists of the following equipment:

• PA system cabinet.

• Digital Call station.

• Logging and configuration PC in hot standbymode.

• Announcement server in hot standby mode.

• Universal Interface for Analog inputs.

• Digital AUdio Storage.

• PA MMI, PA GUI AND PA DVA in hot standbymode.

• IP Interface.

• IP Digital Public address System.

• Interface between train tracking server and An-nouncement server.

The following functionalities are expected.

• Full net availability (copper wired and fibre opticcabled).

• Capability to extract information from traintracking server working on SIMRAN and makingannouncement one station before.

• Different simultaneous announcements in realtime within the networked units.

• Announcements to be done simultaneously.

• Permanently operating automatic volume con-trol.

• Digital storage of voice announcements.

• Time scheduled announcements.

• Line monitoring.

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• Self Monitoring system in real time even for ofthe different equipment installed at other sta-tions.

• Announcement in three languages viz. English,Hindi and local language.

• Digital call stations should be having Brail in-scription so, a blind person can also able to an-nounce.

• The IP digital public address system for OCChas to be in 100% hot standby configuration.

• The priority of announcement will be the an-nouncement from station to be given first pri-ority, till such time the central announcement towait at station equipment or at OCC equipment.

• Visulaized Public address man machine Interface(PAMMI). It should be PA Graphical user inter-face and PA DIGITAL Voice announcer.

5 Technical Specification

5.1 Equipment Rack

The equipment rack at OCC and equipment rack ateach station has to be a 42U standard rack with Fantrey having four no. fans on each rack. The serverand different equipment should have 1U gap. Theblank space has to be filled up with blank.

5.2 IP Digital network Controller

The network controller can be industrial grade serveror it can be standard IP Digital audio network con-troller/Router and switching system. The functionof this controller is to process audio signal and rout-ing, interfacing with power amplifiers and switchingof the loudspeaker lines. The audio channels con-nected to the inputs of the inputs of digital poweramplifier. The routing and switching of audio signalto any combination or all associated freely selectableloudspeaker lines. Permanently supervision of con-nected power amplifier with pilot signal. At failureof a digital power amplifier, a standby power amplifierautomatically and immediately replaces the affectedpower amplifier. Permanent, non-audible supervisionof the loudspeaker lines (ground leakage, short andopen circuit), also during power saving mode, irre-spective of activation of messages. Reaction less dis-connection of the impaired loudspeaker line i.e. otherlines connected to the same power amplifier outputare not concerned.

It should do permanent supervision of the digitalcall station or universal input modules. All errors aredetected within seconds, displayed and logged (Logview), Filters, e.g. parametric equalizer, high andlow pass filter, delays etc. The system should able togive status of other station equipment status instan-taneous without any delay.

At OCC IP Digital network controller required tobe installed in a hot standby mode. At stations thenetwork controller to be installed stand alone mode.Each of the network controller should have Inter-nal flash memory up to 176 sec for audio recording.Should have different chimes and alarm signals com-plying to DIN VDE 33404.The network controllershould have permanently operating automatic vol-ume control (AVC).It should have capability to un-limited networked to realise arbitrary complex con-figuration.

It should comply with IEC EN 60849/VDE 0828.

5.3 Digital Power Amplifier

The Digital power amplifier should be as per designand should be remotely configured and alarm can beextended from station to OCC. The offered amplifiershould be of 2X500 watt or 4X125 watt configuration.The digital amplifier should be possible to functionon standby battery or on UPS supply. The technicaldetail of amplifier offered should be deposited alongwith tender document. The amplifier should meetevacuation standards IEC EN60849 and BS 7443.

5.4 Universal Interface Module

Interface module for interfacing analogue inputs, ana-logue outputs, and control terminals.

5.5 System Communication Unit

The function of system communication unit is thedigital audio storage in a digital public address sys-tem. It provides recording and play back of severalaudio signals at the same time. This unit is requiredto be connected over Ethernet to a network. The con-nection is permanently supervised. The audio stor-age of alarm messages that are availability criticalin cases of emergency is compliant to EN60849 Stan-dard and therefore takes place in a flash memory .Thestorage capacity should be of minimum 40 minutes.Other massages should be stored in the hard disc ofthe system. The unit can be used as logging record-ing of the announcements. These can be out-playedannouncements now also automatically buffered and

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within a time limit with release of the desired targetautomatically.

5.6 Digital call station /Digital Keymodule

Digital call station should comply to IEC 60849/VDE0828/BS7443 .The call station at OCC should haveat least 12 free configurable buttons and can be ex-tended with digital key module, so the total capacityof free configurable buttons should be 24.

5.7 Public Announcement MMI

This should be supplied to support software appli-cation which complements the evacuation and soundsystem as per IEC EN60849 and BS 7443.The systemshould function like PA SERVER, PA GUI (GRAPH-ICAL USER INTERFACE) and PA Digital voice an-nouncer. It should have fully digital call station andwideband speaker for monitoring pre listening andintercom operation for networked IP Digital publicaddress system. The call station can be connectedto networked public address system with the help ofCAT cable or through fibre optic cable. The fibre op-tic interface module and associated other equipmentrequire to be clearly indicated. The optional trans-parent key covers to prevent accidental use of Keys(i.e. alarm Key). System status can be seen on thescreen.

5.8 Train Tracking Server

Can be based on SIMRAN software or based onGoogle map duly mapped for the route and matrixto be loaded for the announcement.

6 Conclusion

This type of IP digital public address system is be-coming need of the day on Indian Railways as to an-nounce and give public awareness information from acentral location.

The information / views expressed in this pa-per is of the authors and are based on theirexperience. Comments / observations may besent to the author at ajaycse1962@gmail.com

Ajay Kumar belongs toIRSSE 1986 Batch and haveworked in various capac-ities in Indian Railways.He has implemented mod-ern Signalling and telecom-munication projects. Hehas also worked with WSATKINS in Sharjah for Sig-nalling projects of Net-workrail, UK. He has under-gone management training inICLIF Malaysia, INSEAD Singapore and variousmanagement institutes of India. He is also an em-panelled member for selection of officers in DamoderValley Corporation. He is currently working as ChiefCommunication Engineer in South East Railway.

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