theben KNX RF Flash-Mounting Wireless Actuators Instruction Manual
- June 5, 2024
- theben
Table of Contents
KNX RF
System Manual
2021-02-08 Version 1.0
KNX RF system description
The KNX RF system ( Radio Frequency) is a manufacturer-independent KNX
radio standard operating in the 868 MHz frequency range. The transmittable
data rate is 16 KBit/s. The packet size is in the range of 8 bytes – to 23
bytes. The latency times are low enough not to be noticed by humans, even when
using relatively time-critical sensors such as buttons.
The maximum range in buildings is approx. 30 m. KNX RF devices can be used to
extend existing KNX installations without a bus line. A wide range of flush-
mounted devices such as switching, dimming, blind, or heating actuators is
available for this purpose. There is also an RF button interface for the
integration of buttons or temperature sensors.
In addition, each Theben RF actuator also has 2 binary inputs for connecting
switches, buttons, temperature sensors or signal contacts. This range will be
further extended, while all Theben KNX RF components support secure
communication on RF as well as on TP (media coupler) according to the KNX Data
Secure standard. The media coupler is used to connect or extend wire-bound
systems with the RF devices. KNX RF is a bidirectional radio system, so the
devices can receive as well as send information. As with TP devices (
**** Twisted Pair), the start-up is also carried out by the ETS.
Technical features
The KNX RF radio standard uses a frequency from the SRD frequency band (Short
Range Device), which also has a relatively small range due to its particularly
low output power. It, therefore, has high electromagnetic compatibility and
does not interfere with other systems. It is a license-free frequency range
for low power and can therefore generally be used in all states that recognize
European Union standards and directives. However, the 868 MHz frequency range
used is not reserved exclusively for KNX RF but is also used by various other
devices/systems, e.g. gate drives, radio alarm systems, and various other
building automation systems.
KNX RF has a transmission power of 0.5-25 mW, and the medium frequency is
fixed at 868.3 MHz. Each transmitter has the LBT function ( ****Listen Before
Talk). This means that each transmitter, before sending anything, first
listens to see if the radio channel is free. In addition, each transmitter
waits for a random, ever-changing time before actually transmitting. This
avoids radio collisions as far as possible.
Also, in the following constellation, it could lead to devices A and C
transmitting at the same time, as they are not in the reception range to one
another. This causes a radio collision at device B and the telegrams might not
be processed.
Radio characteristics
Attenuation of radio waves
| Material | Attenuation | Examples |
|---|---|---|
| Wood | low | Furniture, ceilings, partition walls |
| Plaster | low | Partition walls without metal mesh |
| Glass | low | Window panes |
| Water | average | Humans, wet materials, aquarium |
| Bricks | average | Walls, ceilings |
| Concrete | high | solid walls, steel-reinforced concrete walls |
| Coated glass | high | Glasses coated with metal |
| Plaster | high | Partition walls with metal mesh |
| Metal | very high | Reinforced concrete structures, fire doors, lift shaft |
The attenuation also depends on the thickness of the material
During radio transmission, the following negative effects occur:
- Attenuation/absorption: Signal is swallowed
- Reflection: Signal is reflected
- Refraction: Signal is deflected into another direction
- Scattering: Signal multiplication
Wall or ceiling thickness is effective for the attenuation
Selecting the installation location for RF devices
Example of the good central placement of the TP-RF media coupler
Example of poor non-central placement of the TP-RF media coupler
Example with activated repeater function with a Theben KNX-RF actuator
Repeater function
It is possible to use each Theben RF device additionally as a repeater, to
amplify the RF signal in the system. This repeater function can be activated
in the ETS in the properties of the device under Settings.
However, it is not advisable to activate the function on each or many devices
in the system. The picture above shows which device is suitable to be
configured as a repeater in the system. It is therefore imperative to know the
spatial arrangement of the devices and to use the “Retransmitter” function in
a targeted manner. The media coupler can also be configured as a
retransmitter. This can be useful if the media coupler is placed centrally and
RF devices need to receive telegrams from other devices placed on the opposite
side of the media coupler.
Other negative influences on reception
Reflections can be interference factors for radio transmission. They occur
when radio signals hit obstacles and are reflected from there into a different
direction. In the worst case, however, the waves received directly and via the
reflection overlap unfavorably at the target location, resulting in a signal
that receivers can no longer reliably evaluate.
The positive and negative superposition of radio waves directed in the same
direction is also called interference. This can distort or even completely
erase the signal.
Also, avoid spreading along a long wall, e.g. in a long corridor. The devices
that need to communicate with each other should already be taken into account
during the planning stage.
Radio shadow e.g. due to metal parts
Installation location
The following aspects must be considered when planning KNX RF installations with regard to the installation locations:
- For fixed installations, align all RF devices in the same way ****identical polarisation of the antenna
- Observe structural conditions with regard to shading, reflections, attenuation, absorption, refraction, and scattering
- Keep as wide a distance as possible from larger metal surfaces, e.g. doors, frames, distribution cabinets, aluminum roller shutters …
- Penetrate Walls and ceilings over the shortest possible distance (beeline)
- Keep as much distance as possible from the following devices: Electronic transformers, electronic ballasts, microwaves, motors, cordless telephones, WLAN devices …
- If possible, do not install RF devices close to the ground
- Do not install RF devices in metal enclosures, e.g. control cabinets
Range
Under favorable conditions, the range inside buildings can be up to 30 m. In unfavorable cases, however, it can be only a few meters. In the open field, ranges of up to 100 m are possible. When planning, consider the radio range critically, in order to ensure functional reliability.
KNX RF topology
The KNX RF media coupler is the interface between wired and radio-based (RF) communication. The media coupler works like a conventional range/line coupler and also has filter settings. The corresponding filter tables are loaded by the ETS when programming the application. In this way, the media coupler forwards only the required telegrams between TP-RF and vice versa. This is also important with regard to the telegram traffic on the RF side. It is important to keep this as low as possible in order to minimize problems caused by telegram collisions.
Differences between TP and RF
When communicating via TP, CSMA/CA ( Carrier Sense Multiple Access/Collision Avoidance) prevents several devices from sending simultaneously before each individual participant has access to the bus. Thus, this procedure checks the bus at any time to see if it is occupied. Data will only be sent when it is free. In addition, with TP, the telegrams of each participant addressed are acknowledged with Ack, Nack, or Busy. This means that after sending a telegram, each device receives feedback as to whether at least 1 device has received and understood the telegram. If the sent telegram is not acknowledged with Ack, it can be repeated up to 3 times by the transmitter. For KNX RF communication according to RF1.R standard, there is only the LBT method ( Listen Before Talk). This means that each transmitter, before sending anything, first listens to see if the radio channel is free. In addition, each transmitter then waits for a random, ever- changing time before actually transmitting. This avoids radio collisions as far as possible. An acknowledgment of the telegrams and a repetition in case of an unacknowledged telegram do not exist in the RF1.R standard. Thus, a telegram that has not arrived, due to whatever circumstances, will not be repeated. However, the media coupler acknowledges on the TP side, like any other TP device, its telegrams are received and forwarded to the RF side.
Domain address
Since radio signals can also cross the room, flat, or even property
boundaries, each RF line receives its own domain address from the ETS. Should
the area line be configured as an RF media type, all sub-lines also receive
the same domain address as the area line.
KNX RF devices can only communicate with each other if they have the same
domain address. The domain address assigned by the ETS can also be changed
manually in the ETS if another KNX installation were to accidentally use the
same one. The domain address is automatically programmed into the KNX RF
devices together with the physical address.
A physical interference of different KNX RF systems or KNX RF lines that are
spatially within the radio range cannot be completely excluded by the LBT
method ( ****Listen Before Talk). Different RF telegrams sent almost
simultaneously can overlap each other and can therefore no longer be
evaluated. However, due to the unique domain address contained in each
radiotelegram, no external interference can occur. Example of a domain
address: 00FA:8CD128CA
Media coupler in the line
Media coupler as a line coupler
- Further lines can be set up with TP line couplers or RF media couplers
- Each line may only contain 1 media coupler (unless the media coupler is configured as a repeater)
Media coupler in the area
Media coupler as area coupler
- If the media coupler is to work as an area coupler, a backbone with media type TP is absolutely necessary
- Each area may only contain 1 media coupler (unless the media coupler is configured as a repeater)
General recommendations
- Place the media coupler as centrally as possible in the reception area of all RF participants
- In smaller RF installations, RF devices as repeaters are preferable to several media couplers. Repeaters should be located in the reception area each other. The repeater mode should only be activated for needed devices in order to keep the number of repeated RF telegrams as low as possible
- Multiple media couplers or RF lines should only be used if the radio ranges are congruent with each other or strictly separated. If the different RF lines are only in intersections with each other in the reception area, communication problems due to overlapping telegrams may occur.
- Due to the nature of the protocol (LBT and lack of acknowledgment of receipt), we recommend using KNX RF as a supplement to TP systems for setting up the room, island, and extension solutions. The practical maximum size depends on the building condition, the placement of the devices as well as the telegram volume.
- Since the media coupler has the filter characteristics of a line coupler, the media coupler must usually also be reprogrammed after changes to other RF devices.
Secure devices in new installation
KNX RF devices that have already been safely started up in a project cannot simply be used in a new project. Since the FDSK is replaced by a tool key during programming, it is necessary to reset the devices. A master reset restores the device to its original FDSK. The device can then be transferred to a new project.
Master reset via ETS
Via a right-click on the device in the ETS, the device can be unloaded. Selection: “Unload physical address and application”
Master reset at the device
On Theben RF actuators and sensors:
De-energise the device. – Press and hold the Phys. address button on the
device. – While the button is held, switch on the power again. After approx. 2
s the button can be released. The physical LED goes out.
On Theben TP-RF media coupler:
De-energise the device. – Press and hold the Phys. address button on the
device. – While the button is held, switch on the power again. Only release
the button when the reception LED starts to light up.
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