In my article of February 27, 2014 about priority-controlled communication I already mentioned that visual signaling is important for Intercom and PA/GA systems so that the operators maintain the control over active functions and different system states at any time.
In this article, I will introduce you to 4 basic signaling types by using momentary rocker switches as example. They are used in weather-proof and explosion-proof outdoor intercom stations.
The following signaling types are covered in this article:
- Ready-to-listen signaling,
- Ready-to-talk signaling,
- Pre-busy signaling, and
- Priority override busy signaling.
Ready-to-listen Signaling
During an established two-way connection there is an indication at your intercom station that the other subscriber speaks to you and you listen to it. The LED at the key which has the other subscriber configured as target blinks with a frequency of 250:250. In other words, the LED goes on for 250 ms and off for 250 ms (250 ms on / 250 ms off). View the animated LED as an example on the right.
As this voice connection is a two-way connection you can directly answer the call by pressing the key with the blinking LED as soon as the ready-to-listen signaling goes off. At that moment, there will be another signaling type indicated – the ready-to-talk signaling.
Ready-to-talk Signaling
When you press the key down, the ready-to-talk signaling (LED with continuous light) indicates that a voice connection is established to the target and that you can speak into the microphone. View the picture on the right. It shows the continuous light at the momentary rocker switch.
Pre-busy Signaling
A special signaling type is pre-busy signaling. For pre-busy signaling, the LED at the operator’s intercom station indicates if the desired subscriber can be reached or not. Thus, he is informed in advance if the target is free and if the subscriber can accept his call. At intercom stations from INDUSTRONIC a busy line is indicated at the corresponding key with continuous light by default.
In contrast to ready-to-talk signaling which is also indicated with continuous light you do not press a key for pre-busy signaling. View the picture on the right.
With this signaling type you not only see if the target is busy but also that the existing connection cannot be interrupted. In the article about priority-controlled communication I mentioned that voice connections with higher priority can override the ones with lower priority. But how does the operator know when he can interrupt the existing connection? Here, the so-called priority override busy signaling gives the hint.
Priority Override Busy Signaling
Priority override busy signaling indicates that the desired subscriber is currently active in another connection, but that you can override it. So, if you see a LED at a key which blinks with a frequency of 900:100 (900 ms on / 100 ms off), you can override or interrupt the existing connection and speak to the desired target yourself. As soon as you press the key, ready-to-talk signaling is activated (as explained above).
Further Signaling Types
The signaling types described above by the example of outdoor intercom stations are only a small selection of INDUSTRONIC’s wide range of signaling types. Of course, even more complex signaling types can be created by using different colors or blinking frequencies to implement failure indication or warning and alarm scenarios, for example. In a follow-up article, I’ ll explain how this can be implemented and how flashing warning beacons or LED message boards can be used to visually attract attention.
