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ERICSSONREVIEW21989ERICON - Experience and Further DevelopmentCooling System BPA105 for Small Telephone ExchangesSupervision of Telephone Exchange BatteriesMD110/HT - a Hotel Communications System

ERICSSON REVIEWNumber 2. 1989 . Volume 66Responsible publisher GostaLindbergEditor GoranNorrmanEditorial staff MarttiSubscription PeterMayrViitaniemiSubscription one year $ 20Address S-126 25 Stockholm, SwedenPublished in Swedish, English, French and Spanish with four issues per yearCopyright Telefonaktiebolaget LM EricssonContents48 • ERICON - Experience and Further Development58 • Cooling System BPA 105 for Small Telephone Exchanges64 • Supervision of Telephone Exchange Batteries70 • MD 110/HT-a Hotel Communications SystemCoverThe picture shows the radar beacon ERICONinstalled on Trinda Brunskar at the entrance toGothenburg.The whole installation is fed by solar power

ERICON - Experience and FurtherDevelopmentBo MorwingIn 1980, Ericsson introduced a modern radar beacon, ERICON. It had beendeveloped in close collaboration with the National Administration of Shippingand Navigation, and in October 1981 the first series produced unit was put intooperation on Trubaduren, the lighthouse marking the entrance to Gothenburgharbour. ERICON was well received internationally and by now approximately600 units have been delivered to 30 countries. Today, at least one out of everytwo racons (RAdar beaCON) in service throughout the world is an ERICON.The author describes the operational experience gained and new applicationsmade feasible by ERICON, and also presents the second generation, ERICONMkll, which is characterized by very low power consumption.During the last few decades, radar hasbecome increasingly important to shipping.Today, it is an indispensable navigationalaid in many navigable channels,particularly in bad weather conditionswith reduced visibility. The importanceof radar to safe navigation is alsoemphasized by many international conventionsand regulations specifying requirementsfor radar equipment onships of different tonnage. The developmentof new types of indicators andmore advanced signal processing havemade the information provided by theradar more easily accessible to the operator,but in many situations it can still bedifficult to interpret the picture andidentify specific targets, fig. 2. A radarbeacon, a racon, is an active responsetransmitter which, when interrogated bya radar pulse, returns an extended, oftenencoded, pulse which can easily be distinguishedon the indicator, fig.3. Theresponse on the ship's indicator is alwaysshown behind the racon and radiallyoutwards from its position.radar equipmentnavigationradionavigationERICONWhen ERICON was developed at the endof the 1970s there were only about 400racons in operation throughout theworld. All these were technically imperfectin a way that limited their usability.The most common type, the slow sweepracon, offered low availability. The waitingtime between responses was longand the responses were displayed foronly a short time, which necessitatedincessant radar observation. The operationand technical background of oldertypes of racon have been described in aprevious issue of Ericsson Review. 1The rapid development of semiconductortechnology during the 1970s meantFig. 1The installation of ERICON on the Trubadurenlighthouse at the entrance to Gothenburg constituteda milestone in the use of racons

49BO MORWINGEricsson Radar Electronics ABFig. 2In many situations it may be difficult to distinguishand identify special targets on the radarindicator. The echo from a navigation buoy caneasily be confused with the echo from a smallshipthat new function principles could beapplied to ERICON. Most drawbacks ofthe older types of racon could thereforebe eliminated. ERICON could measureand respond to the frequency of the receivedradar pulse in a fraction of a microsecondand thus offered maximumavailability. A racon response could beprovided with each turn of the ship'santenna. This type of racon was giventhe designation Frequency Agile RaconIn addition to its ability to provide a directresponse at the individual frequencyof different radar equipments,ERICON offered functions for suppressionof side lobe interference, which canoccur when a ship passes close to aracon. ERICON was also the first raconthat could serve both 3cm and 10cmradar simultaneously. The latter type isbecoming increasingly common onlarge ships.Fig. 3If the buoy is equipped with a racon its positionand identity can be determined unambiguously.The encoded racon response is shown on theindicator as a line radiating outwards from theracon site. The position of the ship is in thecentre of the indicator displayExperienceInternationally, the reaction to ERICONwas very positive and in several countries- Sweden, Canada, Great Britainand Norway among others - the majorityof the slow sweep racons have beenreplaced by ERICON. The opinion ofusers has been positive throughout, andpilots and ships' officers in many regionshave expressed a desire for moreinstallations.The reliability has proved to be high.Analyses of failures as a function of theoperating time for a large number ofunits in Sweden and Canada have indicatedan MTBF (Mean Time BetweenFailures) of 15-25 years.Today, ERICON is installed in a widerange of environments, figs. 4 and5,from Spitzbergen in the north to Tierradel Fuego in the south. In some areas itforms the basis of the local navigationsystem. In the Gulf of Suez, 25 strategicallysited ERICONs provide easilyidentifiable position references for passingships, from Shaker Island in thesouth to the canal entrance in the north.Fig. 4A racon on the Argos Grund lighthouse in thesouthern part of the Baltic. The picture was takenduring a particularly bad winter. The ERICON andthe lighthouse light are powered by a windgenerator with battery reserves of 500 AhThe modular structure of ERICON hasproved advantageous from the point ofview of both production and maintenance,fig. 16. Clearly defined interfacesbetween the various subunits make itpossible to change a subunit without theothers being affected or needing adjust-

50Fig. 6ERICON is a cornerstone of the position findingsystem in a recently installed traffic separationscheme in the Gulf of SuezFig. 5ERICON on top of the Isla Perez lighthouse,Yucatan, Mexico. Hurricane Gilbert destroyed thelantern, but the racon continued workingment. Several lighthouse authoritieshave now trained staff to locate and replacefaulty subunits, and a racon canthus be quickly restored if a fault shouldoccur.New applicationsThe long waiting times between responsesfrom the slow sweep racon -often up to two minutes - make it unsuitablefor applications that requirequick updating of information. A shipmight already have passed a criticalpoint in a navigable channel by the timethe response arrives. Racons of theERICON type eliminate such disadvantagesand facilitate new applications.For example, a bridge that crosses anavigable channel can be marked. It isoften impossible to distinguish bridgesupports - and hence the navigablepassage under the bridge - on the radarindicator. A racon placed on or underneaththe bridge in the centre of the navigablechannel gives a clear indicationof the safe passage, figs. 7 and 8. Today,ERICON is installed on some fifteenbridges in Sweden and Norway.ERICON is also used to mark the centreof a turn with a constant radius. In thisapplication the variable radar range ringis used, set to the predetermined turnradius. When the racon signal is receivedabeam, and at the correct distance,the turn is initiated and then completedby maintaining the racon responseabeam until the new course hasbeen obtained, fig.9.An application that has met with muchinterest is the racon leading line, inwhich two racons are used to mark afixed course. The method is based onthe fact that the racon response on theindicator is always shown radially outwardsfrom the ship's position. It is illustratedin figs. 10a and b. When the raconresponses are aligned (10b) the ship ison the correct course. The accuracy ismainly dependent on the distance betweenthe racons. A larger distancegives better resolution and greater accuracy.The coding of the racon responsesis also important, and it hasproved advantageous to have an elementof the first racon response overlappingthe second.ERICON leading lines are now used onthe approaches to Helsinki and Stockholm,for example. Evaluations haveshown the accuracy to be in the order of±0.3 degrees.

Fig. 7, rightERICON installed underneath the span of thebridge between the mainland of Sweden and theisland of OlandFig. 8, far rightAs can be seen from the radar display, echoesfrom the bridge supports are hidden by the echofrom the bridge span. The racon response clearlyindicates the centre of the navigable channelunderneath the bridgeFig. 9The turn at Botto is a critical point in the passagein to Gothenburg. Over the years several shipshave run aground there. Today, an ERICONplaced on Trinda Brunskar identifies the centre ofa turn with a constant radius of 0.8 nautical milesFig. 10The figure illustrates how the responses from theleading line racons are shown on the ship's radarwhen the ship is out of alignment (10a, right) andproperly aligned (10b, far right)

52Fig. 11The racon response is completely masked byother echoes. Its code and the racon positioncannot be distinguishedITOFARClearly, modern racons of the ERICONtype were capable of solving most of theproblems associated with the oldertypes. However, one basic problem remained.Since ERICON responds at thefrequency at which the radar transmits,it follows that its signal is received togetherwith the reflections from the environmentnear the racon. If the reflections- e.g. from land, ice or heavy rain- are strong, the racon response can besubmerged in clutter and it might be difficulttodistinguish its code and startingpoint, fig. 11. Under such circumstancesit would be desirable to be able to offerthe radar operator a means of removingthe normal radar echoes so that theracon response and its position couldbe clearly identified.The International Association of LighthouseAuthorities,IALA, hasbeenstudyingvarious technical proposals for sucha facility. Ericsson has participated activelyin these studies. It was clear thatexisting radar equipment would have tobe modified if it were to be able to presentthe racon response without the normalechoes. One solution actually contemplatedwas to let the racon respondat another frequency and to tune theradar to the racon frequency when aclutter-free presentation was needed.This proposal would have required complicatedmodifications of existing radarequipment and did not gain anysupport.Another method, proposed by Ericsson,proved more feasible: to have the normalradar service and the racon servicework in time multiplex. The ability of theradar to measure the distance to a targetis based on measurement of the timefrom the transmission of a radar pulse tothe reception of an echo from the target.The velocity of propagation is knownand the distance can thus be calculated.When ERICON is hit by a radar pulse itrequires approximately 0.4 ^s before itcan start transmitting the response. Thismeans that the start of the racon responseis shown on the radar indicatorapproximately 60 m behind the actualposition. If the delay is increased, theracon appears to have been moved furtheraway and the racon signal will thenhave to compete with more distant, i.e.weaker, echoes. This fact is exploited inthe new system, designated ITOFAR (InterrogatedTime Offset Frequency AgileRacon).The ITOFAR system works as follows.When the radar operator wants a clutterfreeracon presentation he depresses aswitch that retunes the radar to a predetermined,accurately adjusted pulserepetition frequency, PRF. ERICON canbe equipped with an attachment thatidentifies this PRF, and which, for eachreceived pulse that meets the PRF criterion,will delay the racon response by375 us. The delay will ostensibly movethe racon 30 nautical milesfurtheraway,and the racon signal will compete withechoes from this distance. Echoes from30 nautical miles or more are rare and ifthey occur they will be very weak, whichmeans that the racon signal can be receivedwithout interference. When theradar is switched to the specific PRF adelay of 375us is introduced in its receivecircuits, which means that the delayin the racon is compensated so thatthe racon response will be presented atthe correct distance but without anyclutter, fig. 12.Fig. 12Intefering echoes disappear when the ITOFARservice is activated and the racon response isunambiguous. The faint echoes visible arecaused by indicator persistenceThe ITOFAR system can also provide anotherservice: removal of the racon responsefrom the indicator if it is distracting.This is done by not introducing thedelay in the radar receiver. In this casethe normal radar display is shown withoutany racon response, which has beenmoved 30 nautical miles away and thusfalls outside the range of the indicator.

53Fig. 13Radar equipment of different types and manufacturehas been adapted to the ITOFAR system bymeans of a simple attachmentFig. 14The diagram shows the annual materials cost as afunction of the power consumption for raconspowered by different types of battery. Labourcosts are not included and they can be very high,for example if replacement in a buoy requires theuse of a service vessel. A lithium battery hasconsiderably greater capacity than a manganeseoxide battery and, consequently, does not have tobe changed so often. In certain cases lithiumbatteries can therefore give lower overall operatingcostsWhile an ERICON with ITOFAR capabilityoffers these special services forappropriately configured radar equipmentit will continue to provide the normalracon service for all standard radarequipment.The ITOFAR services were introduced in1982 and the system has undergonepractical trials in several countries withsatisfactory results. In most cases thenecessary adaptation of the radar hasproved to be simple and the cost of themodifications has been low, fig. 13. Inthe Nordic countries some forty ITOFARracons were in permanent operation by1988 and several more are planned.ERICON Mk IIThe power consumption of the racon isan important factor. Buoys and manyisolated lighthouses are now poweredby rechargeable batteries with a limitedcapacity. Battery replacement is expensive,and thus the electrical equipmentshould have low power consumption,fig. 14. Solar panels are increasinglybeing used to power equipment with lowpower requirements, thus reducingmaintenance costs considerably. Theinstallation cost of a solar panel plant isgreatly dependent on the energy requirement.A large energy requirementnecessitates many panels, as well as alarge storage battery in order to ensurethe power supply during periods withlittle sunshine. Fig. 15 shows the estimatedinstallation cost, as a function ofthe mean power requirement, for a plantwith a power reserve of 50 days. All versionsof the first model of ERICON MK Irequire a primary input voltage of between9 and 35V. The mean power consumptionis dependent on the type ofERICON, its programming and the trafficintensity. It can vary between approximately2W for the simplest model and8W for the most elaborate. Regardlessof the type of energy source used, a substantialreduction in the power consumptionof ERICON would reduce installationand maintenance costs and,hence, increase the value of the productconsiderably.Further development of ERICON Mklwas initiated in 1986, with the aim ofreducing the power consumption to lessthan 1 W in normal operating conditions.The new racon was designatedERICON Mkll and the first units weredelivered to the Finnish and Swedishlighthouse authorities during the autumnof 1987.ConstructionThe structure of ERICON Mkll is identicalwith that of Mkl. Five different subunitscan be combined to form four versions,all of which can be supplementedby a separate ITOFAR unit, fig. 16.Fig. 15The installation cost of a solar panel plant isgreatly dependent on the power requirementUKT10 111 X-band racon with adaptivesensitivity regulationUKT10 112X- + S-band racon withadaptive sensitivity regulation

54Subunitscan be replaced or added, with-out any readjustments of other subunitsbeing necessary,The subunits are mounted in a magazineand connected through back plane wir-ing. Semi-rigid coaxial cables provideUKT 10 113 X-band racon with side lobesuppression unitUKT 10 114 X- + S-band racon with sidelobe suppression unitA basic version can quite easily be equippedwith additional facilities at any time.Fig. 16ERICONMkll UKT 10114, with X/S-band and SLSunits and ITOFAR attachment. The order of theunits in the magazine is, from the top,X-band cassetteS-band cassetteControl unitSide lobe suppression unitVoltage converterITOFAR unitFig. 17All programming of ERICON Mk II is done via thecontrol unit, using switches clearly marked withtheir functions. Programming is simple and requireslittle training

55Fig. 18In the SLS unit the X- and S-bands are dividedinto 2MHz frequency slots. The threshold level isset individually for each slot to a value 25dBbelow the strongest signal received in the slotconnections to the antenna system andbetween the microwave cassettes. Themagazine is mounted underneath a sturdyflange made of anodized aluminiumwith feed-through connectors for thepower supply cable and coaxial cablesto the antenna system. The magazine isprotected by a strong container made ofanodized aluminium screwed to theflange. The joint is sealed and the flangeis equipped with a dessication cartridgewith a colour indicator. The antennasare mounted on top of the flange andprotected by a radome made of structuredcellular plastic.FunctionThe basic functions are the same inERICON Mkl and II. The main differencesbetween the two models arethe drastically reduced power consumption,improved side lobe suppressionand increased programming facilitiesof MkII.When a radar pulse is received - via oneof the omnidirectional antennas - itsfrequency is measured and stored. Thestored value serves as a reference whenthe variable racon oscillator is adjustedto the frequency of the received radarpulse in a closed loop. In less than 0.5 nsafter the reception of the radar pulse theracon can respond with an extendedsignal. The response is divided into 16elements, which can be programmed individuallyto ON or OFF. Consequently,the response can be encoded as oneMORSE character or a large number ofcombinations of MORSE characters.Once a certain response code has beenprogrammed, the length of the responsecan be selected in 16 steps. The programmingis done in the racon controlunit, fig. 17.Side lobe suppressionThe basic version of ERICON Mkll usesadaptive sensitivity regulation to avoidtriggering by side lobes. When a shipcomes so close to the racon that there isa risk of triggering by side lobes the automaticsensitivity regulation function isput into operation. A voltage-controlledattenuator reduces the receiver sensitivityto a level approximately 25 dB belowthe strongest radar pulses received.The decrease in sensitivity means thatthe racon coverage is temporarily reducedwhen a ship passes close by.When the ship draws away, the sensitivityis restored to the nominal value,with a suitable time constant.If, for operative reasons, maximumracon coverage is required even duringthe time a ship passes close by, ERICONMkll can be equipped with a special unitfor side lobe suppression, SLS. Shipswithin the racon coverage range aregiven an identity based on the frequencyof the received radar pulses. The X- andS-bands are divided into approximately100 slots, each of about 2MHz. An individualthreshold level is set for each slot,25dB below the strongest signal receivedin the slot, fig. 18. The level ofeach new pulse received is measuredand compared with the threshold forthat frequency slot. Fast A/D convertersand memories are used to determine thefrequency and level, and the decisionwhether to respond or block the signal ismade in approximately 0.4[is. Thus thenew SLS unit in ERICON Mkll gives asingle pulse decision, unlike the SLSunit in Mk I which made a "present pulseto next pulse" decision; a fact which incertain circumstances could have anegative effect on the availability.Operating modesERICON Mkll can be programmed tomeet different operational requirements.The programmable operatingmodes are: active with side lobe suppression,active without side lobe suppression,and passive, i.e. not respond-Fig. 19The racon operating cycle of 30 (15) seconds canbe divided into intervals of different operatingmodes by means of programmingSLSNSLSSide lobe suppressionNo side lobe suppression

56Fig. 20The power consumption ot different racon versionsas a function of the number of radar sets inthe racon coverage area has been calculated in aMonte Carlo simulation. The distance betweenship and racon and such radar parameters astransmit power, PRF etc. have been chosen atrandom, within limits that can be expected in apractical case. The racon was programmed to beactive for 15 seconds and passive for 15 secondsduring each operating cycle of 30 secondsing, within an interval of 30 seconds. Theduration of the different modes can beselected in steps of three seconds,fig. 19. The cycle time can be changedfrom 30 seconds to 15; at the latter valuethe time increment for the differentmodes is reduced to 1.5 seconds. It isalso possible to program ERICON Mkllfor idle mode. In this case, if no radarpulse has been received during four cycles,the racon is made passive for fourcycles. Then it listens for signals duringone cycle. If no signal is received theracon is again passive for four cycles,etc. As soon as a radar pulse is detectedthe racon returns to its normal operatingmode. The idle mode means a considerablereduction of the energy consumption,particularly for racons installedin areas with little traffic.Energy consumptionAs has been stated already, the main aimin the development of ERICON Mk II wasa radical reduction of the energy consumption.The task was approached indifferent ways. Bipolar semiconductorswith high power requirements were replacedby low-power types, MOS. Achopper regulator replaced the previousseries regulator. This improvedthe efficiency of the converter, and itsno-load losses were greatly reduced.However, the greatest benefit was obtainedthrough betterexploitation of thefact that the racon "serves" a radar foronly a fraction of the total time. Thebeam width of a radar antenna is dependenton the antenna size and can varyfrom 0.8° for the largest to 3° for thesmallest. An X-band radar having an antennabeam width of 1.8° is served by theracon for 1.8/360, i.e. 0.5% of the time.Thus the racon need not operate for99.5% of the time. A ship's radar has anaverage pulse repetition frequency ofabout 1500pps and the antenna takes2.5 seconds to make one turn. In thisexample the racon will receive approximately18 pulsesduring one main beamillumination. If the racon did not respondto the first of the 18 pulses thisomission would not be detected on theradar. This fact is exploited by switchingoff the power supply to most circuits inthe racon between main beam illuminations.The first pulse in a main beamillumination receives no response but isused to switch on the power so that thesubsequent pulses will receive responses.When no pulses have been receivedfor three milliseconds the voltagesare again switched off.Thus ERICON Mk II operates in four differentmodes with greatly varying energyconsumption:Passive mode, power consumption

57ERICON Mkll-Technical dataX-band S-bandFrequencyrange GHz 9.32-9.50 2.92-3.10Frequencyaccuracy MHz 20Power supplyInput voltage VDC 9-35The power connection is equipped with internallightning protection and is filtered againstRF interferencePower consumptionDependent on type, programming and trafficintensity. In normal operating conditions

Cooling System BPA 105 for SmallTelephone ExchangesJohan KolteIt is becoming increasingly common for small units, for example subscriberswitches, to be removed from telephone exchanges and installed at somedistance from the parent exchange - in a building of their own or in a container.For this purpose, Ericsson has developed a cooling system. BPA 105. which is aversion of ERICOOL. Ericsson's system for cooling of telephony equipment.The author describes the properties, structure and function of the new system.telephone station equipmentcoolingSmall local exchanges are often placedat remote sites, which makes supervisionand inspection difficult. Coolingsystems for such equiment must thereforehave high reliability. They must neverallow the temperature to rise to a levelthat could interfere with the function ofthe telephony equipment.The cooling system must meet the followingrequirements:High reliabilityThe cooling system must include redundantunits so that individual faultscannot result in loss of system function.The components must meetstringent requirements since operatingconditions vary considerably andare often extremeCooling reserves during mains failuresRemote switches are often installed inplaces where mains failures must beexpected - some of long duration.The cooling must be maintained duringpower cuts, which means that thesystem must contain cooling reserves.Loss of cooling in an exchangewith high power density resultsin a very rapid increase in temperature,fig. 1 and box 1Minimum maintenanceThe cooling system in a remote exchangemust work satisfactorily with aFig.1The temperature in a telephone exchange risesvery quickly if the cooling system fails. A remotesubscriber switch, RSS, with a power density ofover 600 W/m 2 reaches a critical temperaturewithin an hour

59JOHAN KOLTEEricsson Components ABminimum of maintenance. Staff withoutany specialist knowledge shouldbe able to carry out what little maintenanceis necessary.In order to meet these requirementsEricsson has developed cooling systemBPA105, designed for small telephoneexchanges placed in buildings or containers.System functionEricsson has developed a unique constructionpractice for electronic systems.1 It is based on self-convection anduses a combination of series and parallelcooling. Much effort has gone intoreaching an optimum solution to theproblem of heat removal. The ERICOOLcooling system is designed for this constructionpractice, in which the generatedpower can amount to 1000W/m 2 .Practically all the power consumed bythe electronic equipment is convertedinto heat. This heat must be removed forthe temperature in the exchange to bekept within the specified limits. The systemconsists of the following main units:cooling coils, pump unit, water tank andBox1Calculation of rise in temperature in a telephoneexchange when the cooling system failsThe equation below can be used to study thefactors that affect the increase in temperatureduring a mains failure in an exchange that is notequipped with cooling reservestelephony equipment.The solution to the equation is, see fig. Athe logarithms and series development - becomesdTmc — = KA(T,-T) + PmcTtKAPT,mass (kg)specific heat (Ws/Kg°C)temperature (°C)time (s)heat transfer coefficient (W/m 2o °C)area (m 2 )power (W)ambient temperature (°C)The equation states that the increase in thermalenergy in the exchange is the sum of the inflowof power and the power dissipated from theTaking logarithmsThe equation shows that the reserve time isalmost independent of the value of K. Thismeans that initially the inflow or outflow of heatthrough walls and roof will not affect the rise oftemperature in the switchroom. On the otherhand the reserve time is directly proportional tomc, where the mass consists of the air andequipment in the switchroom. The result agreesvery well with practical full-scale measurements.2Fig. AThe increase in temperature as a function of timewhen the cooling equipment stops workingInitial temperatureAmbient temperatureCritical temperatureReserve time

Fig. 2Block diagram ot cooling system BPA105 withredundant unitsCUWTPUccISCooling unitWater tankPump unitCooling coilTemperatur sensorFig. 3The telephony equipment is cooled by means ofself-convection, i.e. air circulates from naturalcauses, without any fans. The cooling coils areplaced above the aisle between the equipmentrows. This gives efficient cooling and a quiet anddraught-free environmentcooling unit, fig. 2. The heat in theswitchroom is transferred to the water inthe cooling coils through self-convection,fig.3. The cooling coils areplaced above the aisles between therows of equipment.The ability of the cooling coils to assimilateheat is regulated by means of thewater temperature. Lower water temperaturegives higher cooling capacityand thus lower room temperature. Thecapacity of the cooling coils is also increasedwhen the air circulation is increased.This means that the racks withthe highest power dissipation have themost efficient cooling. The water thatcirculates in the system transports theheat from the switchroom to the watertank and from there to the cooling unit.In the cooling unit the water heat istransferred to the outdoor air. Pumps inthe pump and cooling units keep thewater circulating in the closed system.The system has built-in redundancy,with two or three cooling units and alsotwo pumps in the pump unit working inparallel. In case of a mains failure, onlythe pump unit remains working and thecooling ability of the system is maintainedthrough transport of heat fromthe switchroom to the cold water tank.System unitsCooling unitThe purpose of the cooling unit is to takeup heat from the water in the tank andtransfer it to the outdoor air. The maincomponents are a compressor, condenser,expansion valve and evaporator,fig.4 and box2. Heat is transferredfrom the water circuit to the refrigerantcircuit in the evaporator. The compressor,which is a motor in the refrigerantcircuit, transports the heatfrom the evaporatorto the condenser. Inthe latter, which is placed at an outerwall, the heat is transferred from the refrigerantto the outside air with the aid ofa fan. The refrigerant then circulatesback to the evaporator, where heat isagain absorbed from the water and theprocess is repeated. A thermostat in thewater tank controls the starting andstopping of the cooling units. The temperaturein the tank is kept at approx-Technical data for cooling unitBPB 105002Cooling capacity*)Water flowMains voltage, single-phnominallypermissible variationsfrequency rangePower consurr ption*)Current consumptionnormal*)maximumDimensionsheightwidthdepthWeight3.51.0ase220±1550-601.37.510495121066085kWm 3 /hV%HzkWAAmmmmmmkg*) Operation with condensation evaporation+40°C/+2°C1 W = 0.86kcal/h

Fig. 4Cooling unit BPB105002 is a compact unit whichis easily connected to the systemFig.BThe path ot the refrigerant in the cooling unit. Thered dashed line separates the different states ofaggregation of the refrigerant: liquid, vapour, anda mixture of liquid and vapourimately + 8 C C. If the water temperaturebecomes too low and if the refrigerantpressure is too high or too low the coolingunit is stopped and an alarm is sentto the supervision unit. After a mainsfailure the cooling units are restartedautomatically.Thecooling units have the following features:- they are easy to install and replace,thanks to their compact structure andplug-in connections for water andpower- they have a low noise level becausethe fan is speed controlled- the components have been chosen towithstand extreme operating conditions- the units can work in arctic as well astropical environments.Pump unitThe pump unit provides the coolingcoils with water at a temperature thatcorresponds to the cooling requirementsof the room. The main componentsare a mixing valve and two pumpsconnected in parallel. The valve regulatesthe temperature of the water to thecooling coils through the mixture ofcold water from the tank and warm returnwater from the coils. A temperaturesensor placed in the switchroom controlsthe mixing valve. In case of failureof a pump, an alarm is transmitted andthe other pump is automatically started.The pumps are powered by the exchangebattery via an inverter, and thecooling can thus be maintained during amains failure.Box 2CIRCULATION OF THE REFRIGERANT IN ACOOLING UNITA pressure-enthalpy diagram is often used todescribe the cooling process. If the main componentsof the cooling unit are incorporated inthe process diagram the result will be fig. B.At point A the condensed refrigerant is at temperaturet k (condensation temperature), pressurep k (condensation pressure) and enthalpyh 0 (heat content). When the liquid passesthrough the expansion valve (A to B) the pressureis reduced to p 0 (vapourization pressure)and the liquid starts to boil. No heat is added orremoved in the expansion, so the enthalpy isstill h 0 The refrigerant enters the evaporator as amixture of liquid and vapour and leaves it(pointC) as saturated vapour. Heat has beenassimilated from the water during the vapourization,so the enthalpy has changed to h,.During the passage through the compressorthe state changes from C to D. The pressurerises to the condensation pressure p k. The temperaturerises to t ov (which is higher than thecondensation temperature t k) because thevapour is greatly overheated. The activity of thecompressor adds more energy in the form ofheat, so the enthalpy changes to h 2. At the inputto the condenser (D) the refrigerant thus consistsof overheated vapour at pressure p k. In the condenser,heat is transferred to the environmentand the enthalpy returns to h 0, the value at thestarting point. A.

Fig. 5The supervision unit contains a panel for alarmindications trom system unitsThe pump unit has the following advantages:- the use of pumps instead of fansmeans that the transport of heat requiresvery little energy- the pump unit is designed with fullredundancy.Control unitThe starting order of the cooling unitsand the desired temperature in theswitchroom are programmed in the controlunit, which is placed on top of thepump unit. The cooling units are connectedin steps on a signal from a multistepthermostat placed in the watertank. The starting order is set with a sequentialswitch and is indicated byLEDs. The control unit has the followingadvantages:- the facility for selecting the startingorder of the cooling units makes iteasy to arrange approximately thesame operating time for all units- the minimum temperature of thewater to the cooling coils and theroom temperature is easily adjusted.Supervision unitThe supervision unit has the followingfunctions:- it supervises the cooling system continuouslyand also without interruptionssince it is powered by the exchangebattery- alarms from all units in the system arecollected, indicated and forwarded toa central operation and maintenanceunit- it monitors the temperature and humidityof the switchroom and initiatesalarms when necessary- the exchange can be shut down automaticallyif the room temperature becomestoo high - over 50°C - or theexchange battery voltage drops below38 V.Water tankThe water in the tank is kept at approximately+ 8°C, which makes it possibletocool the exchange even during a mainsfailure.Ventilation unitThe purpose of the ventilation unit is to- provide the switchroom with filteredfresh air- dehumidify the air to a specified value- generate overpressure in the switchroomto prevent untreated air, dust,sand etc. from penetrating.The ventilation unit consists of a fanwith a filter and a cold water element.Moisture in the incoming air is precipitatedon the element and thus the air isdehumidified. Water for the element istaken from the water tank.System featuresCooling system BPA105 has the followingfeatures:Flexible installation- the system can be installed in housesas well as containers- the system needs only a minimum offloor space- the system can be installed in switchroomswith low ceilings. It requires acouple of decimetres of free spaceabove the telephony equipment- indoor installation means that the systemis well protected against damageFig. 6A 20-foot RSS container for 2048 subscribers.Floor plan

Fig. 7Cooling system BPA105 installed in an RSScontainer. The cooling units and water tank canbe seen. In case of a mains failure the coolingunits will stop working, but the water tank isdimensioned so that the container can be adequatelycooled throughout the battery backuptime for the switching equipmentFig. 8The container seen from the telephony side. Thecooling coils are placed at the ceiling- the system can easily be adapted tospecified cooling requirements byequipping it with two or three coolingunits and up to four cooling coils.Easy installationAll units are tested before delivery fromfactory. Installation testing consistsmerely of pressure testing and a fewsimple function checks- all connections between system unitsare prefabricated, which means thatno soldering is needed and the installationtime is short- the system can be installed and put intooperation by personnel with limitedknowledge of cooling engineering.Small risk of condensation- the air humidity is supervised continuouslyand the air is dehumidified in theventilation unit, when necessary- the temperature of the water to thecooling coils is monitored so that itdoes not fall below the dew point- all parts of the system where the watertemperature is below the dew pointare well insulated.Good environment- the use of self-convention results in adraught-free, quiet and comfortablework environment in the switchroom- heat is assimilated at the place whereit is generated. There is no transportof large volumes of air through theswitchroom.Minimum maintenance- Unlike air-based cooling systemsthere is no need for regular filter replacementin order to maintain thecooling capacity. Filter maintenanceconsists only of checking the smallfilter in the ventilation unit.SummaryHigh power density means that heat hasto be absorbed where it is generated.Consequently, the cooling system has tobe integrated into the telephony equipmentto a greater extent than previously.The reliability of the telephony equipmentis thus greatly affected by the coolingsystem. Cooling system BPA105 canhandle the increase in power dissipationexpected in the future; it is reliable andmaintains its cooling ability in case of amains failure.References1. Hellstrom, B. and Ernmark, D.: CabinetConstruction Practice for ElectronicSystems. Ericsson Review 83 (1986):2pp. 42-48.2. Bovin, E.: Stenlose Varmebelastning1988 Report KTAS (Kjobenhavns TelefonAktieselskab).

Supervision of Telephone ExchangeBatteriesBertil LarssonIf the public AC mains supply to a telephone exchange should fail, the chance ofkeeping the exchange operating relies heavily on the state of its standby powersupply. In many exchanges, batteries are the only standby facility. Up to now.maintenance and supervision of batteries has been manual, which is timeconsumingand costly. Another disadvantage is that, for practical reasons, it isimpossible to check the batteries often enough to ensure their always having fullcapacity. Automatic supervision would be desirable, and it is now feasible, usingmodern microcomputer technology.The author describes the basic principles and eguipment for automatic batterysupervision and its advantages.telephone exchangescells (electric)power system computer controlFig 1Main computer, communications computers andlocal computers in ERICSSON ENERGYMASTERIt is important that the power supply to atelephone exchange be maintainedeven if the mains supply should fail: anexchange breakdown could have graveeconomic consequences. The conditionof the batteries is one of the factorsthat determine whether or not thenecessarily stringent demands for reliabilityof standby power equipmentcan be met.The battery is a vital part of a telephoneexchange. Regular supervision andchecking is essential in order to ensurethat the battery is in good condition andmaintains its capacity. Manual supervisionhas several disadvantages. Thecost of personnel and travel needed forscheduled maintenance of equipmentin remote exchanges can be considerable.The condition of the battery canalso deteriorate soon after a service visit,and the maintenance routines prescribedby the manufacturers are not alwaysfollowed. Together these factorscan lead to severe problems.One way of measuring the capacity of abattery is to initiate discharging manually.The process is time-consumingand also reduces the reliability of theexchange, since the battery is disconnectedduring the measurements. Automaticsupervision means that batteriescan be checked from a maintenancecentre, resulting in considerable savings.The reliability is increased -checks can be made daily, if necessary- and in addition all critical battery parametersare monitored, with alarm facilities.BatteriesThe batteries used in today's telephoneexchanges can be divided into two basicgroups:- ventilated batteries- valve-regulated batteries.The ventilated battery has been predominantas the standby power sourcein telephone exchanges. It requires regulartopping up with water and it givesoff hydrogen. It must be installed in aspecial, ventilated room. The frequencyof the topping up is dependent on howoften the battery is charged and on thevoltage level during trickle charging.The battery life, which is heavily dependenton the ambient temperature, is 10-15 years at room temperature. It is thenassumed that maintenance is carriedout correctly.

65BERTH LARSSONPower DivisionEricsson Components ABThe valve-regulated battery, which alsocontains lead electrodes, does not requiretopping up and does not give offgas. Hence, it can be placed in the sameroom as the electronic exchange it supplies.However, the valve-regulated batteryhas one weakness. The cells in a batterytend to take up different voltages duringtrickle charging. There is a risk of one ormore cells not having full capacity whenneeded. The voltage of each cell musttherefore be checked regularly; approximatelyevery three months. The batterylife - in this case, too, determined by theambient temperature - is 5-10 years atroom temperature.Experience has shown that both ventilatedand valve-regulated batteries haveto be supervised. This work has hithertobeen carried out manually, at intervalsof 2-4 months. 2Automatic batterysupervisionEricsson Components AB has developeda processor-based system forremote supervision of batteries. The system,BMP610, minimizes maintenancecosts and increases reliability.Two concepts that will be used here arecapacity and status. Capacity is thecharge, in Ah, held in the battery. It istheinitial value used in the calculation ofremaining storagetime. The nominal capacityis stamped on the battery. By statusis meant the ratio between the actualand the nominal capacity of the battery.Stat us is thus a measure of ageing and isused to determine whether a batteryneeds to be replaced.The system provides information aboutthe total battery voltage, all cell voltages,the temperature and level of theelectrolyte and the current to and fromthe battery.When an intentional discharge or amains failure occurs, the discharge processcan be monitored, the current batterycapacity determined and the remainingstorage time calculated.The checking of the electrolyte temperature,which is done in a pilot cell, is importantsince a rise in temperature from25 to 35°C would halve the battery life.Ericsson's battery supervision systemBMP610 can supervise all types of stationarylead storage battery. The systemforms part of a larger system, ERICS­SON ENERGYMASTER 3 , for supervisionof power and cooling equipment in exchanges.With ERICSSON ENERGY-MASTER one maintenance centre cansupervise all power supply equipment ina city or a telecommunications area.BMP610 monitors a number of batteryconditions and initiates alarms whennecessary. This provides informationfor decisions on measures to be taken.The monitoring function includes connections,cell voltage deviations, electrolytelevel, leakage, high temperature,low status and short storage time.ERICSSONENERGYMASTERERICSSON ENERGYMASTER can superviseup to 300 exchanges simultaneously,forexample within atelecommunicationsarea, fig.1 and Technicaldata. 3 In each exchange the followingtypes of equipment can be supervisedand controlled: 48V power, battery,standby diesel generator, coolingequipment, distribution panel and otherequipment belonging to the power supplysystem.Physically, the system is divided intothree levels. The top level consists of amain computer, MC. The middle levelcomprises a number of communicationscomputers, CC, controlled by theMC. The lowest level contains a numberof local computers, LC, under each CC.The local computers are in direct contactwith the supervised and controlledequipment, such as the batteries.The MC handles communication betweenERICSSON ENERGYMASTERand system users via local or central terminals,e.g. displays with keyboards. Itcontrols and manages the whole system,collects data from all CCs, processesand stores data which can thenbe printed out on command from a userterminal.

printed board assembliesforadaptationof signals to and from the supervisedbattery. The boards are connectedthrough a wiring unit. An LC can supervisea maximum of two batteries with 24cells each. A communications computercan handle several LCs.Fig 2Batteries with supervision equipment (top right)Each CC controls and supervises onefunction in the system, for examplepower supply equipment or coolingequipment. A CC collects data from andcontrols "its" local computers.Local computerAll local computers in ERICSSON EN-ERGYMASTER have the same basicstructure. Adaptation to different typesof supervised equipment is done withinterface boards.Interface boardsThe local computer cannot be connecteddirectly to the battery when theBattery supervision is handled by anumber of local computers, which arecontrolled either by a CC of their own orby the CC that supervises the rest of thepower supply equipment.Battery supervisionA battery supervision unit can bemounted on a wall or in a 19" rack, figs. 2and 3. It consists of an LC and one or twoTechnical data ofinterface boardsParameterBattery voltageCell voltageBattery currentElectrolyte temperatureElectrolyte levelLeakageNumber ofinputs2242222Measurementinaccuracy40 mV1mV0.3%0.5%AlarmAlarmFig 3Close-up of supervision equipment

67Fig 4Status list showing the condition of a supervisedbattery in detailFig 5Displayed alarm status of a battery. The textstates that battery no. 1 has too low electrolytelevelvoltage of a cell is to be measured. Thereason is that most cells do not haveearth potential, while the LC measuringcircuit does. The measurement procedureis as follows. A capacitor is connectedin parallel with the cell to be measuredand is thus charged until it attainsthe cell voltage value. The capacitor isthen disconnected from the battery andconnected to measurement circuits inthe LC. The relays needed for the switchingare placed on an interface board,together with the capacitor. One boardis sufficient for a battery with 24 cells.The cables that connect the battery tothe board are short-circuit protected toprevent sparking in case of a connectionfault. Electronic circuits that measurethe electrolyte temperature and initiatealarms in the event of leakage and lowelectrolyte level are mounted on the wiringunit board, together with a feedingfuse and a switch for selecting the relevantbattery type, see Technical data.PresentationAll measured values can be presentedon the main computer display, fig.4. Aprintout is obtained automatically foreach alarm, stating the cuase, e.g. leakage,the degree of urgency and in whichbattery and cell the fault has occurred,fig.5. It is also possible to call ERICS­SON ENERGYMASTER, e.g. from amanagement centre, and request thetransmission, via a modem, of the latestbattery data.The information about the degree ofurgency makes it clear whether actionmust be taken immediately or if it canwait, for example until the next scheduledservice visit.Ericsson Energymaster 1989-01-08 11:30:00Eskilstuna Alarms: 2 No observationsOgat Alarms: 1 No observationsPower supply Battery Battery no 1LISTING OF ALL ALARMSPagelA1 alarm Start time: 1989-01-06 08:39.00OgatRSS power supplyBatt 2*23 cellsSingle batteryLow electrolytelevel Battery no. 1OperationThe battery supervision unit automaticallycollects information about thetotal battery voltage, all cell voltages,the temperature, level and any leakageof the electrolyte, and the battery current.The information is normally collectedevery 15 minutes, but duringcharging and discharging the interval isreduced to one minute.The local computer is programmed withdata for many different types of battery.The type to be supervised is selected bymeans of a switch placed on the wiringunit board. The local computer scansthe switch and so obtains the basic dataneeded for prediction of the capacityand status of the battery in question.The connections to all cells are checkedby means of the cell voltages, which areadded up and, as a sum, compared withthe total battery voltage.Voltage measurementThe method has been described above.The result is used to predict the remainingcapacity and status of each cell.Current measurementThe battery current is measured in theform of the voltage drop across a shunt.When the supervision is started, theelectronic circuits are informed aboutthe shunt amperage by means of aswitch on the wiring unit. The local computerthen converts the voltage value tothe corresponding current value, whichis used inthecalculation of capacity andstatus. The current is measured with aninaccuracy of 0.3%. The current valuealso provides information about the batteryself-discharge, which provides ameasure of the age of the battery.Temperature measurementThe electrolyte temperature is measuredin one pilot cell per battery. Inventilated batteries the sensor is builtinto one of the valves that prevent anexplosion, and in valve-regulated batteriesit is mounted on the outside of acell. The signal from the sensor is converted- inthewiring unit board - intoavoltage, which the local computer thenconverts into a temperature value. Thetemperature is one of the parameters forthe prediction of capacity and status.

68Fig 7Displayed alarm status of a battery. The textstates that battery no. 1 is leakingFig 6The batteries in the Kelvin House exchange inLondonBattery predictionA mathematical model for the calculationof the remaining storage time andcapacity of batteries has been developedin collaboration with SvenskaTudor AB. The parameters for the algorithminclude the current, batteryvoltage, electrolyte temperature, dischargecurves and nominal capacity.During a battery discharge the remainingbattery capacity is predicted regularly,at optional intervals of three orten minutes. When the cell voltage hasdropped to a predetermined level thebattery status is calculated. It is given asa percentage of the nominal capacity.Capacity calculations performed duringa mains failure show how much timeremains until the battery is completelydischarged. In case of a mains failurethat affects several exchanges it is thuspossible to determine where mobilestandby diesel generators are most necessary.Insufficient or unreliable manual supervisionoften results in the battery beingreplaced too soon. The status valueshows the real capacity of the battery.The calculation provides an age valuewith an inaccuracy of 10%. It is estimatedthat the battery life will increase from9 to 12 years thanks to the possibility ofdetermining the battery status. This reducesreinvestment costs by 20%.AlarmsWith manual supervision, as a rule onlyundervoltage gives rise to an alarm. Introductionof automatic battery supervisionallows much more detailedmonitoring of the battery. The alarm supervisioncovers leakage, low electrolytelevel, cell voltage, faulty connections,temperature, too short standbytime and too low status.Leaking cells quickly lose their capacity.A leakage sensor is therefore placed inthe battery tray. It consists of two metallicconductors, and any electrolyte leakageestablishes electrical contact betweenthem. Sensors for electrolytelevel and temperature are placed together.A voltage deviation alarm is given if acell deviates by more than 20mV fromthe desired value.The alarm thresholds for the electrolytelevel, overvoltage and undervoltage areprogrammed into the main computer.Alarms are suppressed during chargingand discharging. Knowing the electrolytelevel and the voltage of individualcells greatly reduces the need for visitsto an exchange.An alarm indicating too low remainingcapacity during a discharge shows theoperating staff where the assistance of amobile diesel generator may be needed.A status alarm is initiated if the real capacityof the battery deviates by morethan 30% from the nominal value.The connection check does not onlypinpoint breaks but also voltage dropscaused by poor connection betweencells. If no action is taken, such deteriorationcan put the whole exchange atrisk during a mains failure.The alarm thresholds for temperature,voltage, capacity and status can be setby the operator.The data program is written in assemblerand is supervised by a watchdogtimer, which reacts on a programcrash. If the program is executed correctlya green LED on the front of thelocal computer board shines steadily. Ifthe program crashes, the LED starts toflash. At the same time a watchdog alarmis sent to the CC and the MC.

69Technical data ofERICSSON ENERGYMASTERMCSupply voltage48 V DCAlternatively110 V, 220 VAC16-bit microprocessorMain store2-4MbytePrograms loaded fromDisc2x700 kbyteAlternatively:Winchester disc20MbyteMagnetic tapeOperating systemERIOSProgramming languageERIPASCALAutomatic calling of remote modemsNumber of ports for serialcommunication 4-16Watchdog timerReal time clockAlarm given via potential-free relay outputsCCSupply voltage48 V DC8-bit microprocessorPorts for RS422. RS 232 and opto-insulated serial communicationAlternatively: a built-in modem for automatic answer.callingWatchdog timerReal time clockStorage capacity40-60kbyteLCSupply voltage48 V DCSingle-board computer with 8-bit microprocessorA port for differentiated and two-way serial communicationSited up to 1000 m from its CCI/O channels adapted to the power supply equipmentAnalog I/O channels for the range ± 10 Vvariable in steps of5 mVAlternatively:± 80 Vvariable in steps of40 mVInaccuracy of analog channels ± 0.03%Watchdog timerStorage capacity10 kbyteOperating experienceIf the batteries are not replaced in time, amains failure of some duration maycause a breakdown of the exchange.The reliability has been greatly increasedthrough the possibility ofchecking all batteries frequently.Battery supervision has been in operationat the Swedish TelecommunicationsAdministration's exchange at Kristianstadsince July 1986 Four batteriesare supervised. In Eskilstuna, the systemwas taken into service in November,1987. It supervises 41 batteries In theBritish Telecom exchange in KelvinHouse, London, eight batteries are supervised,fig. 6. The system was put inoperation in March, 1987.Experience has shown that the numberof manual battery supervisory visits canbe reduced by 75%. They are replacedby central supervision through ERICS­SON ENERGYMASTER. The remaining25% are carried out as before. One majorfactor in the reduction is that informationabout the electrolyte level isavailable centrally.During a severe thunderstorm in theKristianstad region, the course of eventswhen equipment broke down could bestudied with ERICSSON ENERGYMAS­TER, which survived intact.The reliability of the battery supervisionsystem has proved to be high. No faultshave been reported in the 41 systemsthat have been in operation for threeyears. Of the 150 local computers alreadyinstalled only one has had anyfaults.SummaryThe application of computer aids for themaintenance and supervision of telecommunicationsequipment results inlarge savings and increased reliability.This goes particularly for batteries,whose manual maintenance is timeconsumingand hence costly. In reality itoften happens - for example ongrounds of economy - that prescribedmaintenance routines are not followed,which reduces reliability. Under unfortunatecircumstances this could resultin the breakdown of an exchange.System BMP610 reduces costs and improvesthe accuracy of the supervisionof batteries. This increases reliability,and maintenance actions can be limitedto those occasions on which they arereally necessary.References1. Lindman, P. and Wolpert, T.: The Reliabilityof Power and Cooling Equipment.Ericsson Review 63 (1986)3pp. 94-103.2. Bjork, D.: Operation and Maintenanceof Power Supply Equipment. EricssonReview 64 (1987):1, pp. 9-15.3. Eriksson, M. and Samsioe, P.: SupervisionSystem for Energy Equipment.Ericsson Review 64 (1987):1, pp. 2-8.4. Svensk, R.: Datorstyrd overvakning avkraft och klimat. TELE (1989)1pp. 71-73.

MD110/HT - a Hotel CommunicationsSystemKjell HassaEricsson Business Communications AB has developed a moderncommunications system for hotels by supplementing its PBX MD110 with thespecial functions required by the hotel sector. Naturally, great consideration waspaid to the requirements of the customers, i.e. hotels, when designing thesystem.The author describes the system structure and the functions specific to thisversion of MD110.mation and wants simple operationand facilities for call transfer- the office staff needs access to completeoffice functions- the booking staff requires a PBX withhigh traffic handling capacity and facilitiesfor distributing incoming callsto several extensions.Staff turnover is high in hotels and itmust therefore be easy for new employeesto learn to handle the system.private telephone exchangeshotel industryreservation computer systemFigiThe reception desk in the Marriott Hotel, HamburgFor many years, Ericsson BusinessCommunications AB has supplied PBXsto hotels. It has therefore been naturalfor Ericsson to adapt its modern PBXsystem MD110 to the special requirementsof the hotel sector. The hotelcommunications system is designatedMD110/HT and designed to meet thehigh functional requirements of firstclassand business hotels. These representthat part of the hotel sector which isexpanding most rapidly.A hotel PBX must meet many differentfunctional demands:- guests want telephones that are easyto handle, with self-instructions andfacilities for single-digit calls- the service staff requires much infor-The hotel sectorThe travel and hotel sectors are amongthe most rapidly expanding in the world.At present there is no downward trend intheflowsof travellers, fig. 2; instead theyare expected to increase in future. Thisprovides the basis for an increase in thenumber of hotel beds, and communicationsrequirements will thus also grow.The standard offered differs greatly indifferent types of hotel. The most commontypes are:- business hotels- tourist hotels- conference hotels- airport hotels- motels.Business hotels charge normal pricesduring the week when the hotel is occupiedby businesstravellers, butattracttourists during weekends by means oflower prices.The hotels with the largest revenue andwhich need most communicationsfunctionsare first-class and business hotels.Businessmen need to be able to communicatein an efficient and convenientway. They also demand more serviceand facilities than other guests.The product marketed by a hotel differsfrom those on a shop shelf. The differencecan be put in a few words: "Aroom that is vacant today can never besold tomorrow; the income is lost forever."Business hotels of the future willprovide services and facilities of higherquality. In certain hotel rooms a fullrange of office services will be madeavailable, which will affect both the furnishingand equipment.

71Kjell HassaEricsson Business Communications ABFig 2The growth in travel throughout the world createsthe prerequisites for growth in the hotel market.Consequently, the communications needs ofhotels are also growingPBXThe success of a hotel is measured in itsdegree of occupancy. The hotel usesservice as a competitive means to increaseoccupancy. A guest who receivesgood service, and thus considers thehotel good, will probably return thereduring the next visit to the city. The telephonesystem plays an important role inthis context since it is frequently usedfor the contacts between the hotel andits guests. The first contact between aguest and the hotel is often via the telephone,and already at that stage thehotel can show some of its qualities; notablyits ability to provide service.Hotel computersDemands for greater profitability, growingpersonnel costs and more stringentaccounting requirements have createda need for interconnection of the varioussystems used in hotels. For example,it must be possible to interconnectthe PBX and the hotel computer in orderto achieve the best possible handling ofcertain matters.A hotel computer may be a minicomputeror a PC LAN (Local Area Network).Special software provides the requiredfunctions. The front desk system handlesall functions concerning the guest,such as room reservation, checking inand out, billing. The back office systemhandles the internal hotel accounting:ledgers, wages, personnel, and statistics.The front desk system is often connectedto other systems in the hotel, e.g.the PBX and the restaurant system. Allcosts incurred by a guest can thus becollected centrally, and the front desksystem can print out a full bill when theguest checks out.MD110/HT - systemstructureThe structure of MD1107HT is the sameas that of MD110. The same modularhardware is used in both types. Themain blocks in the system are line interfacemodules, LIM, and group switch,GS, fig. 3. If the PBX consists of two LIMsthey can be interconnected via PCMlinks. If more LIMs are neded they mustbe interconnected via a group switch,GS. The flexible MD110 architecturemakes it possible to equip MD110/HTwith remote LIM units, connected to thePBX via PCM links.Fig 3The structure of MD110LIMGSLine Interface moduleGroup switch

72Fig 4The structure of MD 110/HTIOUSIUICUTLU23I/O unitSerial interface unitInformation computer unitE&M Tie lineMD110/HT, fig. 4, consists of a PBX(MD110), a communications unit, awake-up call unit with equipment formessage waiting indication, and guestname displays. The communicationsunit manages the databases for chargingof telephone calls, wake-up calls andguest information. It also handles thecommunication with the hotel computer,controls the functions in MD110anddrives guest name displays. The wakeupcall unit handles message waiting indications,generates wake-up calls,gives wake-up messages to guests andinitiates an alarm if a guest does notanswer such a call.Facilities and servicesIn addition to the specific hotel services,MD110/HT also provides all standardservices included in MD110. The servicesare available to the administrativestaff at the hotel but can also, to a limitedextent, be made available to guests. Theservices include:- automatic recall on busy, no answeror on busy trunk routethree-party and multi-party conferenceabbreviated numbersinquirycall transfertrunk traffic controlinternal calls set up by operatordirect call diversiondirect inward dialling.Connection to the hotel computerMD110/HT has been designed with aview to having it connected to the hotelcomputer. Such a connection wouldmean a great saving in manual work andalso reduce the risk of mistakes.MD110/HT continuously provides informationabout:- call charging- room statusMD110/HT receives information about:- checking in- checking out- name of and language used by theguest- message waiting indications- wake-up call requests.

73Fig 6Using the guest room telephone a maid reports toMD1107HT that the room has been cleaned.MD1107HT automatically forwards the informationto the hotel computer, which immediately makesthe room available for checking inWith MD110/HT some of the routinesnow performed manually can be automatized,which is particularly advantageousif the hotel is not equipped witha computer. Checking in and checkingout is then done via the communicationsunit, fig. 5, which is also used to recordmessages, report room status, billguests for their telephone calls, arrangewake-up calls, etc. However, the bill forthe room and other costs must be preparedmanually.Call chargingMD110/HT handles all outgoing calls,whether from guest rooms or the administration.The calls are priced and thedata stored in the system. Informationabout each guest room call is also sentto the hotel computer, which puts itdown to the bill.The price of calls can be calculatedusing two different methods based on:- call metering pulses from a public exchange- the number dialled, date, time of dayand call duration.MD110/HT permits different tariffs forguests and administration. The PTT tariffis used for the administration, whereasguests are charged in accordancewith a higher tariff.Call data can be stored in the systemeither individually per extension orjointly per department All guest roomsbelong to one department, whereas theadministration can be divided into differentdepartments depending on costcentreThe system can generate a number ofdifferent statistics reports; individuallyper extension or jointly for a group ofextensions.Room status informationWhen a maid has finished with a roomshe reports via the telephone that theroom is clean, fig. 6. MD110/HT automaticallyforwards the information to thecomputer, which immediately makesthe room available for checking in. Thereport codes consist of two digits whichare programmed into the system in accordancewith the practice of the hotel.A maximum of 99 different codes can beused.Checking inWhen a new guest has checked in, thehotel computer sends informationabout the guest - room number, name,language and day of departure - toMD110/HT. The system then automaticallyopens the telephone for outgoingcalls and stores the received informa-Fig5Checking-in menu in MD110/HT

74Fig 7Messages for the guests are recorded in the hotelcomputerFig 8A hotel reception with service quarter telephonesand guest name displaystion in a database. Any remaining informationabout the previous guest is erased.Checking outThe hotel computer informs MD110/HTwhen a guest checks out. MD110/HTthen changes the telephone status sothat only calls within the hotel can bemade.Message waitingMessages to guests who are not availableare stored in the hotel computer,which informs MD1107HT, fig. 7. The latteractivates the message waiting lampon the telephone. When the guest seesthe flasing light he calls the reception ora special answering position for information.If the guest uses an analog telephonehe must dial the number, but witha digital telephone it suffices to press abutton in order to reach the answeringposition. When the message has beenacknowledged in the hotel computer, anacknowledgement signal is sent toMD110/HT, which turns off the lamp.Wake-up callGuests can order wake-up calls from theroom telephone, via the operator orfrom a designated service point, e.g. thereception. Such calls can also be orderedfrom the hotel computer, whichthen transfers the relevant informationto MD110/HT. When the guest answersthe wake-up call, an announcement machinedelivers a recorded wake-up message.The machine can deliver messagesin four languages. MD110/HT selectsthe language on the basis of theinformation obtained from the hotelcomputer when the guest checked in.The system stores information about allevents related to the wake-up service:ordered wake-up calls, which are storedin chronological order, number of callsanswered, cancelled calls, etc. If a guestdoes not answer a wake-up call, the systemrepeats the call a few minutes laterIf no answer is obtained despite repeatedcall attempts, the system sends analarm so that the hotel staff can takeaction.Service quarterNormally every hotel has several departmentsthat provide services for theguests, such as the reception, fig.8,laundry, bar and restaurant. Most servicequarters are allocated single-digittelephone numbers for easy access byguests. The number of service telephonesneeded at each point can varyconsiderably. MD110/HT therefore permitsindividual selection of the numberof telephones for each service quarter.The service quarters can also be assignedto different groups in MD110/HT inorder to meet different types of requirement:- service quarters that handle one servicefor the whole hotel, with one ormore telephones- floor service quarters whose destinationsare determined by the floor fromwhich a call is made- common service quarters, which answercalls diverted from other servicequarters.Calls to service quarters are queued. If aqueue is full, the call is automaticallydiverted to another service quarter. Diversionis also applied if a service quarteris free but the call is not answeredwithin a certain time. During periods oflow traffic, e.g. at night, some servicequarters can be closed and calls divertedto those manned at night. Thus thelevel of service can be maintained with aminimum of staff.

75Fig 9A service quarter telephone with a display thatshows the name of the calling guestDisplay showing the guest's nameTelephones at service quarters and operators'sets can be equipped with anattachment, fig.9, which shows thename of the caller before the call is answered.The hotel can thus provide personalservice and make all guests feelthat they are cared for. The display canshow the guest's name and title, whatlanguage he speaks, day of departure,VIP status, etc.For calls from administrative sets thedisplay only shows the name and indicatesthat the call comes from an administrativeextension.When a call has been diverted, the displayshows - before the call is answered- the service quarter originally called.When the call is answered, the displayshows the guest information. Thus, thestaff can answer with the name of thecorrect service point also during periodsof low traffic.PagingPaging systems can be connected toMD110/HT. Calls are automatically divertedto the paging system when noanswer is obtained at the regular extension.The paged person can take the callat any telephoneDo-not-disturb functionGuests who do not want to be disturbedby telephone calls can easily initiate thedo-not-disturb function in the PBX. Allcalls to the extension concerned arethen rerouted to the operator, who canput through those calls the guest wants.Guests who do not want to initiate thefunction themselves can receive assistancefrom the operator or the reception.The function can also be initiatedby the hotel computer.The individual function described aboveis supplemented by a common do-notdisturbfunction. It is initiated and cancelledautomatically at predeterminedtimes and provides do-not-disturb servicefor all guests in the hotel. This functionis mainly used at night to avoid unwantedcalls.Repetition of external callsMD110/HT provides facilities for repetitionof the latest external call dialled.Thus, a guest need not dial the wholenumber in order to renew an attempt toreach a subscriber; a simple code is sufficient.Any stored number is erasedwhen the guest checks out in order tosafeguard personal integrity.Telephone setsBoth analog and digital telephones canbe connected to MD110/HT, thus meetingdifferent requirements within thehotel. Digital sets, fig. 10, have programmablefunction buttons and can be allocatedadditional numbers. It is thus possibleto set up manager-and-secretarystations and multi-line systems for thebooking staff.Fig 10The digital telephone family DIALOG 2500DIALOG 2501 (bottom right). Basic set with fiveprogrammable function buttons and volume controlDIALOG 2531 (bottom left). The set has 12 programmablefunction buttons, monitor loudspeakerand volume controlDIALOG 2561 (top left). The set has an alphanumericaldisplay, 12 programmable function buttons,loudspeaker and volume controlDIALOG 2562 (top right). The set has an alphanumericaldisplay, 39 programmable function buttons,loudspeaker and volume control

76Fig 12Guests can be ottered data communications facilitiesvia MD110/HTThe guest room telephone is an analogset, fig. 11, with a message waiting lamp.Guest rooms can be equipped with digitaltelephones, but analog sets are preferablesince more than one telephoneis often required and parallel connectionis simpler for the analog type.Data communicationMD110/HT allows data communicationbetween digital extensions and subscribersin the public network, fig. 12.Fig 11The analog telephone set DBC 2103 is intendedfor guest rooms. The set is always equipped witha lamp which indicates waiting messages. Thisset shows the single digit numbers to differentservice quarters and the hotel logoSummaryThe system can easily be expandedthanks to hardware and software modularity,together with the distributed architecture.MD110/HT can meet future demands.Since MD110 constitutes thebasis for MD110/HT it follows that allrationalization and improvements inMD110 will also benefit the hotel system.In addition, there is continual developmentand improvement of the specialservices and functions in MD110/HT.References1. Hedman, J.-0.: MD 110. a PBX for theISDN Era. Ericsson Review 64(1987):B, pp. 61-65.2. Barnicoat, G., Boman, L. and Ulander,O.: Data Communications in MD110.Ericsson Review 59 (1982):2, pp.67-75.3. Morlinger, Ft.: MD 110 - a Digital SPCPABX. Ericsson Review 59 (1982):1,pp.2-13.4. Ericsson, B.-l. and Forsell, S.-A.:MD 110/20 - the Greatest Little Systemin the World. Ericsson Review 65(1988):4, pp. 130-136.

ERICSSONISSN 0014-0171 Telefonaktiebolaget LM Ericsson 89516 Liungfbretagen. Orebro 1989