Siemens ET 790 Series Información técnica descargar pdf (Pagina 250)

Application Examples

System overview

18/2

Siemens ET G1 · 10/2008

■

Overview

General information

Ever increasing demands made on the flexibility and convenience

of electrical installations, combined with the demand to minimize

energy requirements, have led to the development of building

management systems. The bus technology used in these systems

is based on manufacture-independent and internationally

standardized technology: KNX. More than 100 manufacturers

support this standard and have joined forces to form the

KNX Association.

The member companies ensure the availability of bus-compatible

products. This has made it possible for devices from various

manufacturers to be used in a single KNX system.

Demand for more convenience and the fact that more and more

is technically possible means that an increasing amount of time

and effort is being devoted to electrical installations. While

conventional electrical installation technology has reached the

limits of its capabilities, GAMMA

instabus

, the intelligent building

management systems from Siemens based on KNX has made it

possible to satisfy these comprehensive demands with solutions

that are both easy to manage and affordable.

System arguments

In conventional electrical installations, each function needs its

own cable and each control system a separate network.

By contrast, GAMMA

instabus

allows all operational functions

and processes to be controlled, monitored and signaled over a

single common cable. This means that the energy feeder can be

routed directly to consumers without any detours.

Not only does this reduce the amount of cables required, it also

has other huge advantages: electrical installations in buildings

are far simpler to install and it is also easy to add any subse-

quent extensions and make modifications. If the purpose or

configuration of a building is changed, the GAMMA

instabus

system is easy to adapt by simply reassigning the various bus

devices (changing their parameters), without the need to lay any

new cables. These parameters can be reassigned using a PC

connected to GAMMA

instabus

and the configuration and

commissioning software ETS (

ngineering

ool

oftware).

With the right interfaces, GAMMA instabus can also be connected

to the control centers of other building management and automation

systems (e.g. SICLIMAT X) or to a public telephone network (e.g.

ISDN) or using a LAN/Internet connection. It is therefore just as

cost-effective to use the GAMMA

instabus

in the family home as

in hotels, schools, banks, office buildings or complex non-

residential buildings.

Transmission technology

GAMMA instabus based on KNX is a distributed, event-controlled

bus system with serial data transmission for the controlling,

monitoring and signaling of operational functions.

All the connected bus devices can exchange data over a common

transmission path, the bus. Data is transmitted in serial mode

and in compliance with precisely defined rules (the bus protocol).

The data to be transmitted is packed into a telegram and sent

over the bus from a sensor (the command output) to one or more

actuators (the command receiver).

Each recipient acknowledges receipt of the telegram when the

transmission is successful. If no acknowledgement is issued,

transmission is repeated up to three times. If the telegram is still

not acknowledged, the send operation is aborted and the error

noted in the memory of the transmitter.

Transmission of data using KNX is not electrically isolated as the

power supply for the bus devices (24 V DC) is transmitted at the

same time. The telegrams are modulated on this direct voltage,

whereby a logic zero is transmitted as a pulse. The omission of

a pulse is interpreted as a logic one.

The individual data of the telegrams are transmitted in asynchronous

mode. However, transmission is synchronized by start and stop

bits.

Access to the bus as the shared physical medium of

communication for asynchronous transmission must be

controlled unambiguously. In the case of KNX, the CSMA/CA

procedure is used for this purpose. The CSMA/CA procedure

guarantees collision-free access to the bus without any

reduction of bus data throughput.

All stations listen in but only those actuators actually addressed

respond. If a station wants to transmit, it first has to listen in and

wait until no other station is transmitting (

arrier

ense). When

the bus is unoccupied, any station can begin a transmission

operation (

ultiple

ccess).

If two stations begin to transmit simultaneously, the higher-priority

instantly asserts itself on the bus (

ollision

voidance), while the

other station pulls back and restarts the transmission operation

some time later.

If the two stations have an identical level of priority, the one with

the smaller physical address asserts itself.

Addressing

Every letter needs an address in order for it to be correctly

delivered by the postal service. The addressing of bus devices

is similar, but the form used for postal purposes is unsuitable in

this case.

During configuration with the ETS, each bus device is assigned

its own physical address with which it can be uniquely identified;

just like a postal address is a unique ID for the recipient of a

letter. However, the physical address has to be expressed in the

language of the bus and is based on the topological structure of

the KNX system.

Physical addressing is used by the ETS only for commissioning

the individual bus devices or for servicing and diagnostics

activities. In this case the addressing is performed along the

same lines as for the postal delivery service.

By contrast, the KNX system uses a different address for

telegram traffic: the logical or so-called group address. This

address is not based on the bus topology but on the operational

functions (applications) of the building.

I2_05799c

Controlling, monitoring, signaling

Bus line

230/400 V

Sensors

(control

stations)

Actuators

(receivers)

ET_G1_2009_en.book Seite 2 Freitag, 28. November 2008 9:50 09

1 2 ... 245 246 247 248 249 250 251 252 253 254 255 ... 291 292

Comentarios a estos manuales

Sin comentarios

Siemens ET 790 Series Información técnica Pagina 250

Comentarios a estos manuales

Relacionado con productos y manuales para Placas Siemens ET 790 Series