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The New ETS4: Easy, Fast, Open

The New ETS4: Easy, Fast, Open

Singapore, Los Angeles, Johannesburg, London, Berlin, Moscow – building automation engineers from all over the world, use ETS as product and manufacturer independent programming tool in order to increase energy efficiency of buildings. This standardised tool is currently available in 15 languages, and supports KNX installations for all media: twisted pair, radio frequency, Ethernet/IP and power line.

To meet the latest technical and economic requirements and globalisation demands, KNX Association has now completely redesigned its Engineering Tool Software (ETS) including a set of many new functions. ETS4 makes it possible to implement KNX projects in a easy and fast way. Moreover, the use of the platform-independent universal standard XML makes it possible to access all KNX project related information in text form. The ETS4 is available from October 2010.

With the new ETS4, KNX Association has responded to new, tougher requirements in terms of handling, technical features, and economy – after all, the range of applications for which bus technology is used has recently tremendously increased. The average KNX installation has now also become quit larger. The functionality that non-residential buildings and intelligent residential buildings need to offer has also become more diverse.

KNX solutions need to handle current challenges like making buildings as energy-efficient as possible.

The demands from a technical and economic point of view for Electricians and system integrators designing, installing,
commissioning and supervising KNX systems, have increased.

Practical focus

It was essential that the new ETS4 would offer a clearly-structured, intuitive user interface meeting these increased demands. A new design for its user interface design was simply a top priority in its further development. A market leader from this sector was consulted in order to accomplish this requirement – which indicates the importance that KNX Association attaches to its device and manufacturer independent standard tool for home and building automation.

An international investigation was set up in order to optimise this new user interface, not only KNX professionals but also beginners with little or no KNX knowledge were consulted. System integrators with ETS3 expertise had the opportunity to try out the usefulness of the new features and at the same time the chance to give feedback based on their daily experience.

pic2

The tests with beginners were conducted to determine how intuitive the restructured work flows really are. In workshops held around the world, both professionals and beginners tested the tool on its daily usefulness in respect to maintaining projects quickly and offering highly demanding services.

The result of all of this research work is a stateof-the-art tool that meets the needs of a modern home and building control technology.

Highly visual interface

The tool’s new user interface is characterised by an up-todate, highly visual design. A new feature is for example an overview page, where users can view projects and access further information such as KNX news and the current ETS4 configuration. The project administration view, which shows project data and properties, is clearer than the ones from its predecessor.

The selective lists for opening databases, opening projects, importing data and viewing the most recently opened projects are together with the central toolbar, very useful features.

Initially ETS users – when working on projects – might miss the ‘old’ overview, because it’s no longer divided into three parts – topology view, group address view and building view. But professionals will quickly appreciate the simplified navigation and larger overviews of the “single window interface”. This is because of integrating various system views into one, crucial information is always visible and this without the need for additional menus.

In the topology overview for example, it only takes a mouse click via the line and device menu to quickly and easily reach communication objects, device details and comments. Important information can always be called via a sidebar. There is also a special Favourites window which can be personalised in order to quickly access customer-specific elements such as preconfigured devices or entire lines.

Intuitive

pic4Another advantage of the new ETS4 user interface is the “guided workflow” – a step by-step tutorial for creating bus configurations. Especially the topic-based Help features and the possibility to undo and repeat actions are very convenient.

System checks can be carried out at any time – this allows possible configuration errors to be detected quickly and in time. Drag & drop for e.g. assigning group addresses to communication objects, makes working with ETS4 yet even more intuitive. Thanks to the free-configurable views (dynamic folders), professionals can put together their own
interfaces in order to suit them to the way they work.

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An Example Of KNX Project Design

An Example Of KNX Project Design

It is basically possible to design a residential building according to criteria similar to those of a functional building and with that to plan the same functionality. The building installations usually seen up to now have for years been based on the distribution and switching of electrical energy. This method is long outdated. Private clients still tend to derive their requirements and expectations regarding electrical installations from their experiences with familiar installation technology.
But in terms of:

  • comfort
  • possibilities for flexible room usage
  • centralised and decentralised controls
  • security
  • the intelligent linking of systems across different building disciplines
  • communication possibilities
  • environmental considerations as well as
  • a reduction in the energy and operating costs,

modern installations have changed dramatically.

During a consultation, the private client is largely unaware of the range of possibilities and opportunities for future extension that are offered by an EIB installation. This information must be passed onto him as clearly as possible without overloading him with unnecessary details. He must be told that it is easily possible to expand or complete his EIB installation at a later date. Good and comprehensive consultation is the best foundation for follow-on contracts for the completion and extension of carefully planned EIB systems.

Incomplete or inadequate consultation can quickly turn an initially satisfied customer into a very unsatisfied customer, if he later learns that his investment in a bus installation cannot be fully exploited.  It must be made clear however, that the answers themselves do not define the installation. They only serve to analyse the customer’s requirements as a basis for determining the feasibility.

Some of the questions hint at technical solutions that will only be available on the market in the months or years to come. They do however play a role in the suggested solutions, as it is possible to take them into consideration for implementation at a later date (preparatory cabling). Completion of this questionnaire essentially represents the specifications. An offer can then be made on the basis of this document, using the “ZVEH calculation aid”. Project design begins once the contract is awarded.

KNX Project

Fig.1 - KNX Project

Writing the specifications based on a given example

The answers marked in the questionnaire yield the following basic requirements on the EIB project:

  • The private customer is building a one-family house with garden and garage on a remote site.
  • There are distinct demands on security.
  • Value is placed on ways to save energy and costs.
  • Particular demands have been made regarding comfort.
  • Some of the wishes cannot yet be technically realised, which means that a system planned with foresight is extremely important for follow-on contracts.
  • Subsequent extensions to the system and functionality must be taken into consideration.
  • A few of the possibilities mentioned in the questionnaire are viewed as critical; further information and more detailed explanations could extend the project and offer approaches to a service contract.

The system requirements essentially comprise the following:

Lighting
  • Within the house, switching points should be located near the doors as well as in the sleeping and seating areas.
  • Lighting control with movement detectors should also be planned for the garden and access paths.
  • Security lighting should be incorporated.
  • The simulation of an “occupied house” by adjustable sequences is required.
  • The lighting control should be integrated into the Home-Assistant.
Sockets
  • Switchable sockets should be provided for the exterior areas, kitchen, workroom and bedrooms.
  • Sockets must have child-protection.
  • For the simulation of an “occupied house”, switchable sockets should be planned for lights.
  • The switching status of the sockets should be represented in the HomeAssistant.
Room heating
  • Single room temperature control should be included, which in addition to manual intervention also allows monitoring and control via a HomeAssistant.
  • The radiators should be switched off when the windows are open.
  • Remote control and remote signalling should be possible for the heating system.
  • Reporting to a customer services department should be planned for a later date.
Heating system
  • The heating system should be adapted to the requirements in a way that saves energy and costs. It should also be possible to monitor it from a central position; i.e. it should be connected to the EIB and integrated into the HomeAssistant.
Hot water supply
  • The hot water supply should be investigated separately, as a combination of gas, electricity and perhaps at a later date solar energy must be taken into account.
Blinds and shutters
  • The blinds should be motorised and must react accordingly in adverse weather conditions.
  • In addition to manual operating possibilities located near to the windows, it should also be possible to control and monitor them from a central position.
  • In rooms subject to dazzling sunlight, it should also be possible to adjust the angle of the slats.
  • The open or closed status should be centrally displayed.
  • They should be incorporated into a security system.
Awnings
  • In addition to manual operating possibilities, awnings installed on the patio should be automatically retracted in strong wind or rain. It should also be possible to use them to influence the temperature of the shaded room.
  • They should also be used to simulate an “occupied house” and allow the possibility of control from a central position.
Window monitoring
  • The closed status of the windows should be monitored and displayed centrally.
  • Any tampering should be detected and incorporated into a security system.
  • Motor-driven operation should be included as a possibility for use at a later date.
Door and gate monitoring
  • The closed status of the house doors and garden gates is to be incorporated into a security system. Additional visual monitoring is also desired.
Monitoring the supply lines
  • For extra safety, the water and gas supplies should be monitored and integrated into a security system. As this is not yet on the market, a provisional installation must be planned.
Meter monitoring
  • As a prerequisite for measures to save energy and costs, the meter readings and running costs should be displayed. The installation should be designed for the future implementation of remote meter reading.
House appliances
  • Regarding new purchases, interest lies in the use of devices with a bus connection. It is therefore necessary to plan, at least provisionally, the corresponding number of communication sockets.
Garden system
  • In the garden and along the path to the house there should be lighting and movement detectors and these should be integrated into a general security system.
  • It should be possible to operate a sprinkler system depending on the dampness of the ground.
Security equipment
  • Measures should be included to increase security. This must include interior and exterior lighting, the windows, blinds and the entrance doors.
  • Monitoring at the HomeAssistant with remote signalling possibilities should be planned.
  • It should be possible to trigger emergency and help calls, quickly and easily.
Central operating and control unit
  • A device, which is capable of receiving television signals in addition to allowing the simple operation and control of the household installations, should be fitted in the kitchen (HomeAssistant).
Extras

There is also interest in the following extensions, planned for the future:

  • Cultivation of a winter garden with shadowing and utilisation of the heat energy that is produced in the transitional period.
  • Lighting in the living area.
  • Isolation of the bedrooms to avoid electromagnetic fields.
  • Connection to service stations for the various devices.
  • Construction of a garden pond with the ability to monitor the circulating pump and maintain a constant level.
  • Installation of a solar panel and integration into the existing hot water supply.

An example of designing a project

Although in comparison with a large functional building, we are dealing with a much clearer installation here, a  installation should be planned. This has as much to do with the variety of functions desired as well as with the high probability of later expansion. A separate line should be provided for each floor to ensure simple and clear structuring. Because this example deals with a new project, the project design is carried out with ETS 3. The result is an extensive set of detailed lists. For projects where there is a high probability of expansion or modification within subsequent years, other documents should be provided in addition to the lists.

Results of the project design stage form the foundation for all subsequent steps of the installation, commissioning and maintenance, and with that of course for all future expansion. Reference is made to the documents or wiring diagrams in accordance with the standards of the EN 61082 or DIN 40719 series, in particular to the bus devices and bus lines with physical and group addresses that are marked on the ground plan (see Fig. 1). The logic diagram indicates the bus devices and their physical addresses as well as allocation to the lines. If the complexity of the project demands, it may also be necessary to draw up a functional diagram. This saves a considerable amount of time during subsequent expansions or modifications.

If you also draw the parameter block for each of the bus devices, you are left with an excellent and very clear set of documents. The HomeAssistant necessary to implement this example system demands exact adherence to the rules of ETS 3 and to the design guidelines. Of particular importance is the entry of room structure, completion of the key fields and the addition of extra groups (so-called single actuator groups).

Adherence to these guidelines is important because the terms and names for the rooms and devices are derived from this data and appear in the operating menus of the HomeAssistant, allowing the end user to recognise his own individual system. The database created with ETS 3 is transferred into the HomeAssistant using the HomeAssistant Tool Software (HTS), which is included in the scope of supply.

SOURCE: Project Engineering for EIB Installations

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KNX Architecture

KNX Architecture

Building Control technology as provided by KNX is a specialized form of automated process control, dedicated to the needs of home and building applications. One premise for KNX is to furnish a radically decentralized, distributed approach; hence the term network.
The KNX Device Network results from the formal merger of the 3 leading systems for Home and Building Automation (EIB, EHS, BatiBus) into the specification of the new KNX Association. The common specification of the “KNX” system provides, besides powerful runtime characteristics, an enhanced “toolkit” of services and mechanisms for network management.

On the KNX Device Network, all the devices come to life to form distributed applications in the true sense of the word. Even on the level of the applications themselves, tight interaction is possible, wherever there is a need or benefit. All march to the beat of powerful Interworking models with standardized Datapoint Types and “Functional Block” objects, modelling logical device channels.

The mainstay of S-(“System”) Mode is the centralized free binding and parameterisation (typically with the PC-based ETS tool). It is joined by E (“Easy”)-mode device profiles, which can be configured according to a structured binding principle, through simple manipulations – without the need for a PC tool. These configuration modes share common run-time Interworking, allowing the creation of a comprehensive and multi-domain home and building communication system.
The available Twisted Pair and Powerline communication media are completed with Radio Frequency (868 MHz band).
KNX explicitly encompasses a methodology and PC tools for Project Engineering, i.e. for linking a series of individual devices into a functioning installation, and integrating different KNX media and configuration modes. This is embodied in the vendor-independent Engineering Tool Software (ETS) suites for Windows.

Elements of the KNX Architecture

KNX specifies many mechanisms and ingredients to bring the network into operation, while enabling manufacturers to choose the most adapted configuration for their market. Figure 1 below shows an overview of the KNX model, bringing the emphasis on the various open choices. Rather than a formal protocol description, the following details the components or bricks that may be chosen to implement in the devices and other components a full operational system.

The KNX Model

As essential ingredients of KNX, we find in a rather top-down view.

  • Interworking and (Distributed) Application Models for the various tasks of Home and Building Automation; this is after all the main purpose of the system.
  • Schemes for Configuration and Management, to properly manage all resources on the network, and to permit the logical linking or binding of parts of a distributed application, which run in different nodes. KNX structures these in a comprehensive set of Configuration Modes.
  • Communication System, with a set of physical communication media, a message protocol and corresponding models for the communication stack in each node; this Communication System has to support all network communication requirements for the Configuration and Management of an installation, as well as to host Distributed Applications on it. This is typified by the KNX Common Kernel.
  • Concrete Device Models, summarized in Profiles for the effective realization and combination of the elements above when developing actual products or devices, which will be mounted and linked in an installation.

Applications, Interworking and Binding

Central to KNX’ application concepts is the idea of Datapoints: they represent the process and control variables in the system, as explained in the section Application Models. These Datapoints may be inputs, outputs, parameters, diagnostic data,…The standardized containers for these Datapoints are Group Objects and Interface Object Properties.

The Communication System and Protocol are expected to offer a reduced instruction set to read and write (set and get) Datapoint values: any further application semantics is mapped to the data format and the bindings, making KNX primarily “data driven”.
In order to achieve Interworking, the Datapoints have to implement Standardized Datapoint Types, themselves grouped into Functional Blocks. These Functional Blocks and Datapoint Types are related to applications fields, but some of them are of general use and named functions of common interest (such as date and time).

Datapoints may be accessed through unicast or multicast mechanisms, which decouple communication and application aspects and permits a smooth integration between implementation alternatives. The Interworking section below zooms in on these aspects. To logically link (the Datapoints of) applications across the network, KNX has three underlying binding schemes: one for free, one for structured and one for tagged binding. How these may be combined with various addressing mechanisms is described below.

Basic Configuration Schemes

Roughly speaking, there are two levels at which an installation has to be configured. First of all, there is the level of the network topology and the individual nodes or devices.
In a way, this first level is a precondition or “bootstrap” phase, prior to the configuration of the Distributed Applications, i.e. binding and parameter setting.
Configuration may be achieved through a combination of local manipulations on the devices (e.g. pushing a button, setting a codewheel, or using a locally connected configuration tool), and active Network Management communication over the bus (peer-to-peer as well as more centralized master- slave schemes are defined).
As described in the corresponding section below, a KNX Configuration Mode:

  • picks out a certain scheme for configuration and binding
  • maps it to a particular choice of address scheme
  • completes all this with a choice of management procedures and matching resource realizations.

Some modes require more active management over the bus, whereas some others are mainly oriented towards local configuration.

Network Management and Resources

To accommodate all active configuration needs of the system, and maintain unity in diversity, KNX is equipped with a powerful toolkit for network management. One can put these instruments to good use throughout the lifecycle of an installation: for initial set-up, for integration of multi-mode installations, for subsequent diagnostics and maintenance, as well as for later extension and reconfiguration. Network Management in KNX specifies a set of mechanisms to discover, set or retrieve configuration data actively via the network. It proposes Procedures (i.e. message sequences) to access values of the different network resources within the devices, as well as identifiers and formats for these resources – all of this in order to enable a proper Interworking of all KNX network devices. These resources may be addresses, communication parameters, application parameters, or complex sets of data like binding tables or even the entire executable application program.

The network management basically makes use of the services offered by the application layer. Each device implementing a given configuration mode (see below) has to implement the services and resources specified in the relevant “profile” (set of specifications, see below).
For managing the devices, these services are used within procedures. The different configuration modes make use of an identified set of procedures, which are described in the “configuration management” part. As indicated above, and further demonstrated in the Configuration Modes section below, KNX supports a broad spectrum of solutions here, ranging from centralized and semi- centralised “master-slave” versions, over entirely peer-to-peer to strictly local configuration styles.

However, mechanisms and Resources are not enough. Solid Network Management has to abide by a set of consistency rules, global ones as well as within and among profiles, and general Good Citizenship. For example, some of these rules govern the selection of the (numerical value of) the address when binding Datapoints.

But now, we first turn our attention to how the Communication System’s messaging solutions for applications as well as management, beginning with the physical transmission media.

Communication: Physical Layers

The KNX system offers the choice for the manufacturers, depending on his market requirements and habits, to choose between several physical layers, or to combine them. With the availability of routers, and combined with the powerful Interworking, multi-media, and also multi-vendor configurations can be built.

The different media are :

  • TP 1 (basic medium inherited from EIB) providing a solution for twisted pair cabling, using a SELV network and supply system. Main characteristics are: data and power transmission with one pair (devices with limited power consumption may be fed by the bus), and asynchronous character oriented data transfer and half duplex bi-directional communication. TP 1 transmission rate is 9600 bit/s.
    TP1 implements a CSMA/CA collision avoidance. All topologies may be used and mixed ( line, star, tree, ….)
  • PL 110 (also inherited from EIB) enables communication over the mains supply network. Main characteristics are: spread frequency shift keying signalling, asynchronous transmission of data packets and half duplex bi-directional communication. PL 110 uses the central frequency 110 kHZ and has a data rate of 1200 bit/s.
    PL110 implements CSMA and is compliant to EN 50065-1 (in the frequency band without standard access medium protocol).
  • RF enables communication via radio signals in the 868,3 MHz band for Short Range Devices. Main characteristics are: Frequency Shift Keying, maximum duty cycle of 1%, 32 768 cps, Manchester data encoding.
  • Beyond these Device Network media, KNX has unified service- and integration solutions for IP-enabled (1) media like Ethernet (IEEE 802.2), Bluetooth, WiFi/Wireless LAN (IEEE 802.11), “FireWire” (IEEE 1394) etc., as explained in the KNXnet/IP section below.

Communication: Common Kernel and Message Protocol

The Communication System must tend to the needs of the Application Models, Configuration and Network Management. On top of the Physical Layers and their particular Data Link Layer, a Common Kernel model is shared by all the devices of the KNX Network; in order to answer all requirements, it includes a 7 Layers OSI model compliant communication system.

  • Data Link Layer General, above Data Link Layer per medium, provides the medium access control and the logical link control.
  • Network Layer provides a segment wise acknowledged telegram; it also controls the hop count of a frame. Network Layer is of interest mainly for nodes with routing functionality.
  • Transport Layer (TL) enables 4 types communication relationship between communication points: one-to-many connectionless (multicast), one-to-all connectionless (broadcast), one-to-one connectionless, one-to-one connection-oriented. For freely bound models (see below), TL also separates (“indirects”) the network multicast address from the internal representation.
  • Session and presentation Layers are empty.
  • Application Layer offers a large “toolkit” variety of application services to the application process. These services are different depending on the type of communication used at transport layer. Services related to point-to-point communication and broadcast mainly serve to the network management, whereas services related to multicast are intended for runtime operation.

Remember KNX does not fix the choice of microprocessor. Since in addition, KNX covers an extensive range of configuration and device models, the precise requirements governing a particular implementation are established in detailed Profiles, in line with the Configuration Modes. Within these boundaries, the KNX developer is encouraged to find the optimal solution to accommodate his implementation requirements! This is expounded in later sections.

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ABB i-bus KNX - Constant lighting control

ABB i-bus KNX - Constant lighting control

Lighting in modern buildings is more than a basic requirement – it can play an important role in the architectural design and the energy efficiency of the building, not to mention the health, safety and well being of the occupants.

With an impressive spectrum of products for the control, measurement, regulation and automation of lighting, ABB i-bus® EIB / KNX can perform challenging lighting tasks.

The following elaboration on the topic of constant lighting control should provide adequate background information to:
- better understand the method of operation of a constant lighting control
- ensure optimum placement of the light sensors required to detect the actual value
- recognise critical ambient conditions which interfere with the function of the constant lighting control
- evaluate the physical limitations to which a constant lighting control is subject.

For this purpose it is necessary to understand the most important terms used in the field of lighting technology.

How does constant lighting control function?

In constant lighting control a light sensor installed on the ceiling measures the luminance of the surfaces in its detection range, e.g. the floor or the desks.

How does constant lighting control function?

This measured value (actual value) is compared with the predefined setpoint value, and the control value is adjusted so that the divergence between the setpoint and actual values is minimal. If it is brighter outside, the share of artificial lighting is reduced. If it is darker outside, the share of artificial lighting is increased. The exact function of the light controller is described in detail in the manual of the Light Controller LR/Sx.16.1.
A Luxmeter placed underneath the light sensor, e.g. on a desk, is used for setting the setpoint. This Luxmeter detects the degree of illumination which illuminates the surfaces underneath the light sensor.

The objective of a constant lighting control is to retain the set degree of illumination when a setpoint is set. To perfectly implement this objective, the light sensor should be placed exactly on the spot where the Luxmeter was placed to adjust the setpoint value, in order to also determine the degree of illumination. As this is not possible for practical reasons, the light sensor is generally mounted on the ceiling.

This is a compromise. For the reference setting of the setpoint, a Luxmeter is used for measurement of the degree of illumination; however, the light controller primarily detects the luminance underneath the light sensor. In this way the light controller indirectly maintains a constant degree of illumination. If certain constraints are not observed with indirect measurement, it can mean that the constant lighting control will not function or not function as required.

This is not a specific phenomenon just affecting our constant lighting control, but rather is the case for all constant lighting controls.

What is the difference between degree of illumination and luminance?

In order to fully appreciate the problems relating to indirect measurement, it is necessary to examine the most important terms used in lighting technology. Only the basic terms are explained and we will forego a more exact and detailed explanation or mathematical derivation of more complex terms, e.g. luminous intensity = luminous flux/steradian.
A luminary, e.g. a fluorescent tube, converts electrical energy to light. The light rays emitted by a light source (luminous exitance) are referred to as a luminous flux. The unit is the Lumen [lm]. Luminaries convert the input energy to light at varying degrees of efficiency.

CategoryTypeOverall luminous
efficency (lm/w)
Overall luminous
efficency
.Incadescent lamp.5 W incandescent lamp.5.0.7%
.40 W incandescent lamp.12.1.7%
.100 W incandescent lamp.15.2.1%
.Glass halogen.16.2.3%
.Quartz halogen.24.3.5%
.High temperature incandescent lamp .35.5.1%
.Fluoroscent lamp.5 – 26 W energy saving light bulb.45 – 70.6.6 – 10.3%
.26 – 70 W energy saving light bulb.70 – 75.10.3 – 11.0%
.Fluorescent tube with inductive ballast.60 – 90.7%
.Fluorescent tube with electronic ballast.80 – 110.11 – 16%
.Light emitting diode.Most efficient white LEDs on the market.35 – 100.5 – 15%
.White LED (prototype, in development).up to 150.up to 22%
.Arc lamp.Xenon arc lamp.typ. 30 – 50;
.up to 150
.4.4 – 7.3%;
.up to 22%
.Mercury Xenon arc lamp.50 – 55.7.3 – 8.0%
.High pressure mercury vapour lamp.36 (50W HQL) –
.60 (400W HQL)
.up to 8.8%
.Gas discharge lamp.Metal halide lamp.93 (70W HCI) –
.104 (250W HCI)
.up to 15%
.High pressure sodium lamp.150.22 %
.Low pressure sodium lamp.200.29%
.1400 W sulphur lamp.95.14%
.Theoretical maximum .683.100 %

In addition to the luminous flux there is the item luminous intensity, also referred to as the lumi- nous flux density. The luminous intensity is measured in Candelas [cd]. The Candela is a mea- surement unit for luminous intensity emitted by a light source in a particular direction. An exact definition will lead to a complex mathematical analysis, e.g. the explanation of a steradiant.

Simplification: A luminous intensity of 1 cd corresponds to the measured degree of illumination of 1 lx at a distance of 1 m from the light source.

The luminous flux emitted by the light source illuminates the surfaces that it meets. The intensity with which the surfaces are illuminated is referred to as the degree of illumination. The degree of illumination depends on the magnitude of the luminous flux and the size of the surfaces.
It is defined as follows:

E = Φ/ A [lx=lm/m2]

E = degree of illumination
Φ = luminous flux in lm
A = illuminated surface

In accordance with the above table, a 100 W incandescent lamp with 15 lm/W generates a maximum luminous flux of 1500 lm. If the entire luminous flux of the incandescent lamp is not emitted in a spherical manner into the room, but rather concentrated and distributed evenly on a surface of 1 m2, then the value for the degree of illumination at every point on the surface would be 1500 lx.

The perceived brightness of an illuminated surface depends on the illuminated surface and the reflectance of the illuminated surfaces. The reflectance is the reflected share of the luminous flux from the illuminated surface. Typical values for the reflectance are:

  • 90% highly polished silver
  • 75% white paper
  • 65% highly polished aluminium
  • 20% – 30% wood
  • < 5% black satin

The perceived brightness of an illuminated surface or a self-illuminating surface, e.g. an LCD monitor, is designated as the luminance. The unit of luminance is cd/m2.

If white paper is subject to a degree of illumination of 500 lx, then the luminance is about 130 – 150 cd/m2. At the same degree of illumination, environmentally-friendly paper has a luminance of about 90 – 100 cd/m2.

On what does the luminance measured by the light sensor respectively the measured value of the light sensor depend?

The luminance “primarily” detected by the light sensor depends on different criteria. It depends on the degree of illumination which the surfaces in the detection range of the light sensor are illuminated. The higher the degree of illumination, the higher the luminance of the illuminated surfaces.
The same applies for the reflectance of the surfaces. The higher the reflectance, the higher the luminance of the surfaces and thus the measured value of the sensor. The measured value of the sensor is the actual value used for lighting control.

The installed height of the sensor also plays a role. If the light sensor was an ideal “luminance measurement device”, then the luminance which it measures would be indepen- dent of the installation height of the light sensor. As this is not the case, the measured value of the sensor decreases as the installation height increases.

SOURCE: ABB | Practical Knowledge: ABB i-bus® KNX Constant lighting control

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