Why is the Theben relay actuator pulse output not triggered by scene recall?

Consider the case where a bathroom fan is to be triggered as part of a scene and we would like it to turn off after a period of time.  The channel will be turned on like a standard switching channel using the scene group object, but because the pulse object has not been triggered the pulse will not time the channel off.  So in this case the fan will run on until switched off by another telegram.

To solve this you require an advanced pushbutton which has the ability to send multiple telegrams from a single button push. One example is the Theben TA 4 S KNX.  The following workaround is then possible.

Button Object 1 is used to trigger the bathroom light scene.  Note that the Scene Number (1-64) will be represented here in the form n-1 so "Scene 1” = Value 0, "Scene 25” = Value 24, and so on.

Button Object 2 is used to trigger the pulse function of the relay channel switching the fan on.  In this way the relay channel controlling the fan will time out as desired.

Two telegrams are sent consecutively to two group addresses with a single button push on Input 1 of the TA 4 S:

I1.1) the first telegram triggers the light scene

I1.2) the second telegram triggers the pulse function for the fan, independent of scene settings, therefore the the fan will turn off after the pulse time period.

One can also use the Scene Controller of the basalte Sentido and some other push button sensors to perform this type of workaround.