Siemens ET 790 Series Información técnica descargar pdf (Pagina 251)

Application Examples

System overview

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Siemens ET G1 · 10/2008

Unlike the postal service, which delivers a letter to the recipient's

address, the configured group address is written into each

telegram sent by the transmitter. Every bus device listens to this

telegram, reads the group address contained in it, and checks

whether the telegram is addressed to it or not.

The group address to which a bus device should respond is

assigned during configuration of the KNX system using ETS.

Unlike the postal delivery service, several group addresses can

be assigned to one bus device.

When a bus device is listening to a telegram on the bus, it will

always receive the telegram if it responds to the group address

entered in the telegram. If not, it will discard the telegram as not

being intended for it.

Topology

Up to 64 bus-compatible devices (stations) can be connected to

and operated on the smallest unit of the KNX system, i.e. on a

single line. Using line couplers connected to the so-called main

line it is possible to bundle up to 15 lines in an area.

Fifteen areas can be joined together by means of backbone

couplers, which are connected to the so-called backbone lines,

in order to form a larger unit.

Interfaces (gateways) to third-party systems (SICLIMAT X, LAN,

etc.), or additional KNX systems are connected to the backbone

line.

Although more than 14,000 devices can be interconnected in a

single unit, the clear-cut logic of the system is preserved.

Telegrams only ever overstep the interfaces to other lines and

function areas if they are needed in those areas. This minimizes

the telegram load on the main line. Line/backbone couplers

carry out the necessary filter function.

The physical address is based on this topological structure:

every device can be uniquely identified through the specification

of its area, line and device number. For assignment of the

devices to the operational functions the group addresses are

divided into main groups and su/jointfilesconvert/296211/bgroups.

During configuration it is possible to divide the group addresses

for different management functions into as many as 14 main

groups, e.g. for

• Lighting control

• Shutter/blind control

• Room control for heating, ventilation, air conditioning.

Each main group can include as many as 2048 su/jointfilesconvert/296211/bgroups, to

suit the user's requirements. This means that each device is able

to communicate with every other one.

Technology

Each line requires its own power supply unit for the devices and

is therefore self-sufficient.

The Siemens power supply unit supplies the individual devices

on the line with SELV (safety extra-low voltage) of 24 V DC and,

depending on the version, can be loaded with 160 mA, 320 mA

or 640 mA. It features both voltage and current limiting and is

therefore short-circuit resistant. Short system interruptions are

jumpered with a buffer period of 200 ms.

The bus load depends on the type of devices connected. The

devices are ready for operation at a minimum of 21 V DC and

typically draw 150 mW from the bus. If there is a concentration

of a large number of bus devices in a single location, the power

supply unit must be located in the near vicinity.

A maximum of two power supply units are permissible in one

line. A minimum distance of 200 m of cable length must be

observed between the two power supply units.

The length of a cable plus all junctions must not exceed 1000 m.

The distance between a power supply unit and a device must

not exceed 350 m. In order to guarantee no telegram collisions,

the distance between two devices should be limited to a

maximum 700 m.

The bus cable can be laid parallel to the mains cable. It can

be looped and branched. A cable terminating resistor is not

required. The devices are connected to the bus by means of

either pressure contact or bus terminals. Connection by means

of pressure contact is effected by snap-fitting the devices

(designed for installation in distribution boards) on to the

standard mounting rail (EN 50022-35 mm × 7.5 mm) with

integrated data rail. Transition from the data rail to the bus cable

is effected by a connector. The bus cable is connected to

surface-mounting, flush-mounting, wall-mounting, ceiling-

mounting and built-in devices by plugging on the bus terminal.

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14 15

64 6464

64 64

64 64 64

I2_05798d

Line coupler

Line

LC LC

LC LC LC

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