e012042.PDF

GENERAL INTEREST

Home Bus Systems

By H.-J. Peifer, G. Krause and J. Rütten

Aachen Polytechnic, Germany

The future of automatic control of home and office environments is with

Building Management Systems. The dream is of greater comfort, func-

tionality and security with more efficient use of energy and optimised

building running costs. These systems however have found a slow uptake

and difficult Marketing.

The idea of intelligent buildings conveys

images of some future utopian dream where

the environment inside the home is controlled

for maximum comfort and convenience. Cam-

eras outside watch for any unauthorised move-

ments and silently convey your alarm status to

some distant security monitor. At the office

each area senses occupancy and reduces the

heating and lighting to empty rooms. Alto-

gether the promise is of more comfort, better

functionality, ﬂexibility, security and energy

saving. This is precisely the aim of current

Building Management Systems (BMS).

For most complex control situations it is

usual to employ a bus system so that control

and data can be transferred using relatively

few interconnecting wires. In the beginning

of bus based Building Management Systems,

industry standard field buses were used.

These were later phased out as improved

dedicated BMS buses were developed.

We already see buses used to link several

intelligent sub-systems together with one

main management controlling unit. The cen-

tral management unit analyses conditions

within the building gathering data from

peripheral sensors and sending control com-

mands to individual equipment. This is an

example of a centralised energy management

system. One such open communication sys-

tem built on this principle is the BACnet

(Building Automation and Control Networks).

The network protocols are designed for use at

the management and automation level of the

network and provide a comprehensive set of

objects for organising the data in building con-

trollers and a set of communication services to

convey data between devices. The protocol

has also been extended to include trend logs.

facility engineering

reductions in

investment and

operating costs

000144 - 18

This standard should not be seen as

competing with current systems but

as a kind of common denominator

while it can be interfaced with all the

other existing standards.

One level deeper at the ﬁeld level

where terminal units, controllers and

sensors connect to the bus, there is

another entirely different set of

industry standards.

The proprietary systems include

the Local Control Network (LCN)

and Peha House Control (PHC). The

LCN uses an additional line in the

mains socket to pass control and

data information around the build-

ing. Installation of this system is

really only feasible if it is installed in

a new building where the mains

cabling has yet to be installed. Seg-

ments of the network can be linked

to an Arcnet backbone allowing a

bus capacity of 2.5 Mbit/s. This sys-

tem is therefore suitable for large

commercial installations. In contrast,

PHC is designed more for residential

and home environments while it has

a limited number of connections and

the equipment available is more

Current Systems

In the building control technology

there are some propriety systems

(with only one supplier) and also

systems supported by many compa-

nies that conform to generally

agreed standards.

Elektor Electronics

2/2001

GENERAL INTEREST

suited to these applications. Both of

these systems have, so far, not

gained wide acceptance.

Globally accepted standards

include the systems X10, CEBus,

LON, EHS, BatiBus and EIB. X10 and

CEBus have been developed specif-

ically for the U.S. market and adap-

tation of these standards for Europe

is unlikely.

Likewise from the USA the com-

pany Echelon developed the Local

Operating Network (LON). This sys-

tem was originally conceived as a

general control standard for auto-

mated tasks. It is well suited to

building management applications.

Worldwide it is estimated that over

10 million LON based units are cur-

rently in use.

The European standards are cur-

rently undergoing a convergence pro-

cedure whereby three of the main

European standards the EIBA, Bati-

bus Club International (BCI) and the

European Home Systems Association

have pooled their experience and

resources to form the Konnex Associ-

ation. This association is now

responsible for deﬁning the transfer

protocols for these three systems.

Currently there are over 10 million

EIB compatible units in use. Globally,

this puts its market share as roughly

equal to the LON based systems.

Bosch-Siemens Appliances have

introduced household equipment

that feature an EIB approved bus

interface for their Home Electronic

System (HES). Using a software

package called Home Assistant, it is

possible for the user to control these

appliances and receive status infor-

mation either using a PC or via a

touchscreen.

Based on the technical capabili-

ties and the open architecture of

both LON and the EIB (Konnex) sys-

tems, they are likely to remain the

main players in the ﬁeld of building

management systems.

LonMark Organisation took respon-

sibility for the LON standard. Unlike

the EIB, the LON Certiﬁcation proce-

dure is not obligatory, consequently

some LON equipment on the market

from diverse manufacturers are not

fully compatible in every aspect.

EIB and LON broadly offer similar

functions but have strengths in dif-

ferent areas of application. Many

companies support the two stan-

dards. Producers of electrical installa-

tion technologies who supply a wide

range of sensors and actuators sup-

ply EIB systems. LON based systems

are supplied by companies with a

background in control technology,

lighting control etc. It could be said

that the EIB standard has grown up

from the installation side of the indus-

try gradually building more complex

control functions whereas the LON

system has come from the other

direction. There is little information

available to compare the relative per-

formance of the two systems in dif-

ferent control environments, what is

probably more important is the cost

and availability of the system.

The most important and most

widely deployed communication

medium for both systems is the

twisted pair cable.

The EIB system allows a maxi-

mum distance between users in the

same segment of 700 m. The bus

topology allows users to be con-

nected in a line, star or tree conﬁgu-

ration provided that no loops are

formed in the signal routing.

The data rate of 9.6 kbit/s gives a

bit length of 104 µs which is much

longer than any signal propagation

delay down the bus, so data is sent

directly onto the bus without the

need for terminating resistors at the

ends of bus branches.

A network interface unit connects

the user to the bus and an internal

inductor matches the signal to the

bus impedance. Figure 2 shows how

the data appears on the bus. The

bus voltage is normally at 24 V.

When a ‘0’ is sent, the bus voltage is

pulled low to 10 V for a period of

35 µs. To send a ‘1’, the bus voltage

remains high at 24 V.

The bus protocol used is Carrier

Sense Multiple Access with Collision

Avoidance (CSMA/CA). This method

allows each bus user to only send

data onto the bus when they know it

000144 - 11

Figure 1. EIB Topology.

104 µ s

2V/

Div

50 µ s/

Div

0011

000144 - 12

Figure 2. EIB Twisted Pair Signal.

will be free, thereby avoiding collisions

between users which would otherwise occur

if two or more send data simultaneously.

The most widely used LON network con-

ﬁguration uses the medium of a twisted-pair

cable in a free topology. This allows loops to

be made in the signal routing. The maximum

distance between users in a segment

depends on the cable type employed and can

be up to 500 m. Using a data rate of 78 kbit/s

means that the signal bit duration of 12.8 µs

is in the order of the propagation delay down

the bus. LON uses special signal coding to

overcome this potential problem. Signal

encoding employs the DC-free Differential

Manchester coding ( Figure 4 ). A logic ‘1’ is

represented by only one edge change within

a bit period whereas a logic ‘0’ has two edge

changes, the additional change occurs in the

middle of the bit period. This gives a line fre-

quency of 39 kHz if a series of logic ones is

sent, and 78 kHz for a series of zeroes. Equip-

ment connected to a LON network can be

powered from the net but this is not obliga-

tory although it removes the necessity for a

mains unit and is the preferred option. The

Link Power net unit provides bus termination.

EIB and LON

The EIB standard was originally con-

ceived jointly by a group of compa-

nies headed by Siemens. In 1990, the

European Installation Bus Associa-

tion (EIBA) was formed and took

over responsibility for the speciﬁca-

tion and certification of EIB compli-

ant appliances. Similarly in 1993 the

2/2001

Elektor Electronics

GENERAL INTEREST

The EIB have speciﬁed frequency

modulation as the modulation

method (Binary Frequency Shift Key-

ing) while LON (at least in Europe)

uses phase modulation (Binary Phase

Shift Keying). The frequencies used

by the EIB are in the B-Band (95 kHz

- 125 kHz) or for LON and EHS in the

C-Band (125 kHz - 140 kHz). This

description applies to only one of the

methods of data transfer allowed for

EIB and LON equipment. Other

options are available

offer expertise and advice to the

installation industry. A further hur-

dle to overcome if this bus technol-

ogy is to become acceptable is the

natural scepticism of architects,

builders and administrators. Not

least we also have to convince the

user that these systems offer real

advantages. Part of the problem here

is the user-unfriendliness of past

systems. It is important for a user to

be able to exercise some control over

the equipment rather than being a

helpless bystander when the equip-

ment refuses to work properly. Even

when the equipment is working per-

fectly, it is useful to have some

method of user input.

A more important aspect of user

acceptance may be the system cost.

There is a division here between

commercial buildings and residential

buildings. Most new houses are pur-

chased on a mortgage and the loan

institutions are not convinced of the

necessity of the additional outlay for

a building management system, the

cost of which is not likely to be

recouped at the time when the

house is later sold. By contrast, com-

mercial buildings are likely to see the

installation of a building manage-

ment system as an investment that

will repay itself in reduced running

costs and maintenance over the

building’s lifetime.

000144 - 13

Figure 3. LON Free Topology.

12,8

How near are we to the

Intelligent House?

There are many reasons why the

intelligent building has not gained

widespread acceptance. If you read

the sales leaflets of the equipment

manufacturers it is clear that all you

need to satisfy your need for com-

fort, security flexibility and energy

efficiency is the latest building con-

trol system. But when you get down

to the nuts and bolts you will most

probably find that the functionality

that is important to your application

is not available or at least not with-

out a greater investment in more

equipment. In the early 90’s the

technique for building bus based

equipment was to copy the func-

tionality of the existing installation

units and simply add a bus interface.

More recently, the principle of shared

functionality has been introduced

into the design. This refinement

process is by no means complete,

experimenting with existing systems

always creates new ideas and pos-

sibilities that inﬂuence the next gen-

eration of equipment.

The principle of an open system

ensures that each manufacturer can

compete in the market place with

similar products but offering improved

features. The effect of this competition

is to increase the sophistication of

equipment. The same process also

applies to the LON equipment.

From the point of view of the

installation engineer with the ever-

growing numbers of equipment from

diverse manufacturers, the situation

must be somewhat daunting. A one-

week introductory course in Build-

ings System Management is surely

not sufficient. There may be a role

here for an independent advisory

organisation to be set up that will

1,5V/

Div

5,5 µ s/

Div

000144 - 14

Figure 4. LON Twisted Pair Signal.

The bus protocol used here is Carrier Sense

Multiple Access with Collision Detection or

CSMA/CD. This method allows any user to

send data at any time. Collisions only occur

when two or more users send packets of data

at the same time. When a collision is

detected, each user backs off for a random

time interval before re-sending the data pack-

ets. Special algorithms are employed to

reduce the likelihood of collisions thereby

ensuring a good bus bandwidth even at

times of high traffic density.

A further medium for sending data is over

the mains wiring in a building. This solution is

particularly attractive when considering the

installation of networks into existing build-

ings (retro-ﬁtting). Here the cost of the addi-

tional cabling can be prohibitive so this

method incurs no additional cabling costs.

The disadvantage is the relatively poor band-

width available. The EIB speciﬁes a data rate

of only 1.2 kbit/s while LON offers 4.8 kbit/s.

This may be sufficient for simple control

applications but when you consider the band-

width necessary for internet, speech and

video information, it is far too limiting to con-

sider. The actual mains signalling bands are

defined by CENELEC, the electrical stan-

dards agency of the European Union.

Current developments

The development causing the great-

est excitement for LON and EIB

standards is the coupling of the bus

with the Internet. LON compliant

equipment is already in existence,

allowing remote monitoring and con-

trol using a normal web browser.

The system also allows for remote

maintenance and system reconﬁgu-

ration via an Internet connection.

For the EIB this development is

not so far advanced and the Internet

connectivity using the software tools

ANubis (Advanced Network Tech-

nology for Unified Building Integra-

tion Services) is partly deﬁned while

some equipment is already available.

iETS is the internet version of the

EIB software tools that provide rou-

tines to allow remote monitoring and

remote equipment re-programming

over the Internet. Software drivers

are available to assist developers

Elektor Electronics

2/2001

GENERAL INTEREST

who intend to program their own

applications. Falcon drivers are avail-

able for EIB environments and there

are many development kits available

in the market place for LON applica-

tions. With intra and Internet con-

nections there is no reason why the

status and control of several build-

ings cannot be managed remotely.

The Konnex Association that we

mentioned earlier is not just a single

organisation that looks after the

three bus systems, it also specifies

the technical development of the

systems. Three modes of program-

ming and operation of Konnex sys-

tems are planned. The so-called sys-

tem mode is the same as the previ-

ous EIB programming procedure

using the EIB programming tools

(ETS). This mode offers the greatest

ﬂexibility and power but is relatively

complex, so requires a certain

amount of investment in personnel

training. Easy mode requires no

start-up tools but offers fewer fea-

tures than the system mode. It is

intended that the installation engi-

neer will use this level. The simplest

mode is the auto conﬁguration mode

and is designed for the end user of

the equipment. The use of this mode

is very easy (plug and play philoso-

phy) but offers limited flexibility for

the equipment setup. It remains to

be seen if these features will make a

big impact in the industry.

The technology you choose is depen-

dent on the complexity and require-

ments of each particular installation.

A good knowledge of all currently

available systems is also necessary.

Uppermost in the building planner’s

mind will surely be the cost of such a

system compared with a conven-

tional electrical installation. Here is

a bit of a chicken and egg situation in

that high initial costs mean that sys-

tems are not widely used. Once they

are widely deployed, sales revenues

should ensure that increased devel-

opment leads to cheaper and more

convenient systems. One method to

encourage greater acceptance may

be to rent or lease out complex instal-

lations similar to those we see today

for car leasing or the rental of expen-

sive office equipment. Alternatively,

the industry could go down the path

taken by the mobile phone operators,

here the high cost of producing the

phone is partly paid for by the con-

tract that you sign-up for when you

purchase the phone. This allows the

shop price of the phone to be kept

low and is partly the reason for its

phenomenal success.

More recently we see the emer-

gence of Bluetooth technology which

threatens to replace the wired bus

with a radio network. It remains to

be seen what impact this will have

on the market. What is more certain

is that the intelligent building is here

to stay and we can look forward to

seeing more sophisticated systems

accepted as part of everyday life.

(000144-1)

000144 - 15

Figure 5. Frequency modulation (EIB).

000144 - 16

Figure 6. Phase modulation (LON).

The future looks bright

The intelligent house is already here.

Some Web Links

Author contact:

peifer@fh-aachen.de

For more information:

http://www.eiba.org

http://www.lonmark.org

http://www.echelon.com

http://www.batibus.com

http://www.ehsa.com

http://www.lcn.de

http://www.peha.de

http://www.bacnet.org

http://www.ukosa.org/

Figure 7. A LON Internet connection.

2/2001

Elektor Electronics

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