Z-Wave Groups, Scenes & Associations

Z-WAVE TECHNOLOGY - GROUPS, SCENES AND ASSOCIATIONS

With Z-Wave, you can not only operate individual actions with appliances such as lights, heating and window blinds, but also create “Scenes” like “Leave for Work”, and select what you want to happen in your home, when you leave for the day.

Also you can create “Events” which react when something happens – so for example, when a motion detector is tripped, a light can come on for 5 minutes.

And if that wasn’t enough, there is a “Timer” setting where you can set the lights or the thermostat to go on or off at a certain time.

If you’re at work, it’s good to be reassured that lights are going off when they should for example. The VERA Gateway is great for this, as VERA can reassure you with an optional text message alert to tell you everything is ok! Through the FREE optimised iPhone application, VERA offers additional support to help you manage all your Z-Wave devices.

VERA is focussed on simplicity. It does “complicated” things but in a really simplistic way. It’s centred on usability and practicality, making managing your home energy consumption a joy rather than a chore. Literally, just plug in the VERA Gateway and setup is quick and automatic. It even doubles up as a pre-configured Wi-Fi access point, Firewall, gateway and router, giving you a secure wireless home network.

Z-Wave technology is really effective when setting up a home security management system. You can control your alarms remotely using Z-Waves, as well as set your doors, windows and motion sensors to high alert. With the aid of Z-Waves, the components can be managed by a central home hub - Gateway VERA, so if a detector senses an intruder, then a signal to VERA will set off lights, alarms and even a text message to alert you at work.

The use of more complex usage patterns are best managed using Association, Groups and Scenes.

Associations

In a typical Z-Wave network, the controller communicates with slaves in two typical ways. They send out commands to change the status of slaves, e.g. switch them on or off – and they receive status information from sensors, e.g.movement info from a motion detector (only from routing slaves).

Meaningful function in a network may include dependencies and interaction between two slaves as well.

Example: One Z-Wave device is a motion detector, a second device shall be a power switch controlled by a remote control. It’s the desire that the switch shall switch on, if a motion is detected.

One setup would be that the motion detector sends a signal to the controller and as a second step the controller sends the switch command to the power switch. However this means that:

The controller is added as additional source of failure;
The communication takes much longer then necessary;
The controller needs to be in the listening mode, which means it needs to be a static controller;

An association allows that the motion detector sends its signal directly to the power switch without involving the controller. This allows using sensor even in a network without a static controller. This saves time, reduces the complexity of the communication and the amount of airtime, which directly translate into allocation of the wireless communication channel and the electromagnetic emission.

To be able to use an association,the sending node (in the example the motion detector) must have the knowledge of a valid route to the destination (in the example the power switch). Therefore only a routing slave or a controller can use associations. A normal slave does not have any information about routes and only send signals as answer to received commands.

In order to set an association the sender needs to learn about the node id (s) of the receiving node (s).

There are two different ways to accomplish an association scenario:

Direct Association:

The source node of the association will be turned into an “association set mode” waiting to receive a node information frame from the device to associate. The receiving node needs to send out a node information usually accomplished by just pressing a button. The node information frame received contains the Node ID of the association partner and allows the source node to set the association.

Because the node information frame is always send out as a broadcast to all nodes “in range” direct association only works if both sender and receiver as “in range” which means they have a direct not routed wireless connection established.

Assigned Association

Assigned associations allow connecting two Z-Wave devices, which are not in range. To do this the help of a third node –a controller with knowledge of the complete network and its routes is needed.

The connecting controller needs to be turned into a association mode by either pressing dedicated buttons or selecting a function on a PC software controlling a USB connected Z-Wave transceiver.

The controller now expects (1) a node information frame from the desired source and in a second step (2) a node information frame from the desired target node. Again the Node Information frame can only be received by nodes in range, hence the controller need to be brought in direct wireless range of the two nodes, but not at the same time.

First the controller is near the source node receiving its Node information frame and in the second step it needs to be places near the target node to receive its node information frame as well.

In a last step the controller will communicate with the source node and set the association by informing this node about the association target and the route to reach this target. The user accomplishes this without further interaction. Since the controller knows the route to the target node its not required to bring the controller back in range to the target to perform the final configuration.

A node needs to announce its capability to accept an assigned association configuration in his node information frame.

It‘s possible to have multiple target nodes assigned to one single source node. All these target nodes will receive the same command at the moment when the event takes place triggering the event, which was configured by association.

It is possible that there are multiple different events, which may cause to send commands to different nodes. The number of target node that can be associated to this given node for the given event are called association groups.

The number of different association groups (i.e. different event which can cause to send out a command to associated nodes) and the maximal number of nodes, which can be associated to a given group, are a performance indicator for Z-Wave devices.

An example of a Z-Wave device with association is a wall switch with two switching paddles.

For this particular product there should be at least two association groups, one for the left and one of the right paddle. A lot of vendors of wall switches offer even more groups, which get activated when doing a double press or press both paddles at the same time.

The number of receiving nodes per groups is typically limited to five devices. This limitation is caused by the limited memory space of the device, hence it’s possible that certain device without memory constrains offer many more possible target nodes.

If nodes are assigned to one of the association groups of a device this device will send a signal to all the target devices every time this groups gets activated – typically by pressing a button, a combination of buttons or when a sensor value reached a certain level.

To make sure a maximum number of different target devices can be controlled, most devices with association functions will use the BASIC command class to control target devices. However there are devices on the market offering to configure which command class to be used to control target devices. With this feature it‘s possible to execute very special functions on the target device.

The inclusion function of a device includes the device into a network and makes sure that the device is able to communicate with other devices in the network. The association function describes a specific action between a specific sending and a specific receiving node. The action is triggered by a certain condition at the sending node (e.g. button pressed) and will cause a certain action at the receiving node.

Associations are also used to assign certain remote control buttons to certain devices in a Z-Wave network.

Groups

It is possible and usual to connect multiple devices from one single button on a remote control. These controllers, joins certain devices into a group and control them, as if they are one device. This means that all devices are switched simultaneously when the button is pressed. Since all devices in a group receive the very same switching commands, it’s useful to only group similar devices into one group. If different devices are mixed, the result can be surprising and confusing.

Similar to associations, most remote controls only use the BASIC command class to control groups. This allows to mix different devices but only to a certain extent. Mixing a dimmer and a switch will result in the dimmer acting as a switch.

Most remote controls describe the switching of groups but don’t refer to the switching of a single device. In order to switch a single device its possible to just place this single device into a group and switch the group. It‘s also possible to assign one device into different groups.

Scenes

The definition and the usage of scenes is a very powerful tool to control Z-Wave networks. Like a group, a scene groups together multiple Z-Wave devices. While groups tread all devices similarly, scenes cause a controller to send different commands to different devices. This results in endless possibilities such as: “turn switch off and open the window B” or “dim all lamps to 50 % and turn on the TV”.

Scenes are very flexible and much more powerful than groups, but take a lot of memory to store the different commands. Hence in a remote control the number of scenes is typically much smaller than the number of groups. Static controllers such as IP gateway or PC software typically allow an almost unlimited amount of scenes.

Comparison of groups, scenes and associations

Groups, Scenes and Associations are different ways to realise functions and interactions within the z-wave network.

	Used in	Function
Associations	Slaves	Sends control signals to one of more target devices (Slaves or controller)
Groups	Slaves and controllers	Grouping of multiple devices receiving the same control message - typically via association (from Slaves or controllers)
Scenes	To controllers	Activation of a scenes leads to switching different devices using different control messages

Usage of IP-Gateways

IP gateways allow a very user-friendly configuration and usage of a Z-Wave network. Different functions and sensor values can be access using a convenient web interface or even a mobile phone like the iPhone.

The user friendly and usually self-explaining web interface allows performing all relevant functions of a Z-Wave network in a convenient way.

These gateways offer user interfaces for user management and special interfaces for mobile access.

In order to increase usability, devices can be assigned to different rooms or zones of the home. Some gateways offer an upload opportunity for floor plans.

The central function of an IP gateway is the definition and activation of scenes. Scenes define a certain switching state for different devices; e.g. switch is switched off, window is closed, dimmer is at 50 %, window blind is 90 % open. Scenes can be defined for the whole home or for different parts of the home, such as different rooms.

Defined Scenes can be activated depending on certain conditions, e.g.:

A certain sensor values (Activate open window scene with open windows, and heat turned down when CO2 sensor reached 100 ppm);

A certain button is pressed (Turn off al electrical devices and turn down all light when the “all off” button near the front door is pressed);

A certain time is reached (Turn down all window blinds 30 minutes after sun set);

A Boolean logic determines the event (Turn on all outside lights when time is between 18.00 and 0600 AND all off button is pressed);

It’s typically possible to run multiple scenes in parallel. In this case the user need to make sure no contradicting commands and settings are defined.

Besides switching devices the activation of a scene may trigger more functions such as sending of an email or an SMS or calling a predefined phone number.

During configuration and usage of an IP gateway there are three challenges worth to be discussed:

Reporting of status changes of devices cause by local usage rather than initiated via the wireless network;
Associations configured directly on the devices rather than set by the user GUI of the IP Gateway;
Scene activation using Z-Wave remote controls or other wall controllers.

Display of Switching Status Information

Users want to see the status of their electrical devices on their mobile phone or PC screen. The gateway is able to poll the states of each devices but the poll interval is way too long to ensure a real-time update of the status. In case the status is changed from the gateway using a phone or the PC interface, the gateway is initiating the status change and is able to request the new status right after executing the switching command.

However, certain devices offer to switch the state locally by pressing a button (e.g. a wall plug switch of a simple wall switch). In this case the gateway does not get any update information from this particular switch.

Activating a scene from a wall controller or a remote control is a desirable function of a Z-Wave network. In order to activate the scene, the IP gateway must receive information, if and which button of a remote control or a wall controller is pressed.

So whether it’s by Groups, Associations, Scenes or all three, you can personalise your Z-Wave wireless system to the way you want it.