4 factors that can impact EnOcean wireless sensor signals
Smart-sensor systems are the future of building management. They allow you to know exactly what’s going on inside your building – from how rooms and resources are being used, to how equipment is functioning, or what the conditions are – and automate controls based on real-time conditions.
Before you can install your system, however, you’ll need to spend a little time working out the optimum locations for your sensors and receivers. And that means understanding a few basics about how wireless signals work, as well as considering the conditions that can reduce or interfere with the signal.
Radio signals are electromagnetic waves that have a limited range. The further the signal travels, the weaker it becomes – just like ripples on water. When there are no obstacles in the signal’s path, we refer to it as a direct line-of-sight path. The waves travel in a straight line from the sensor to the receiver.
There’s a few things to bear in mind when you plan how many sensors and receivers you need and where to position them:
1. The materials your building is made from
Of course, the path between sensor and receiver won’t always be clear. You might have an awkwardly shaped room or corridor, or objects or machinery that get in the way.
That’s not necessarily a problem. Radio waves can travel through some materials easier than others. They can penetrate most walls, but will lose more or less signal strength depending what the wall is made from.
Not surprisingly, dense materials like metal and concrete are the worst, since they reflect the waves rather than letting them through. It’s for this reason that fire-safety walls, lift shafts and stairwells are all obstacles you’ll need to work around when planning your system. Metal partition walls, insulated hollow walls and inserted ceilings with metal or carbon-fibre panels can all decrease signal strength.
|Wood, plaster, uncoated glass||0 – 10%|
|Brick, plasterboard||5 – 35%|
|Metal, concrete, mirrors||10 – 90%|
2. The shape of the room or area
While radio waves travel in a straight line, it’s not quite as simple as looking at the obstructions that fall directly in the path between sensor and receiver. If you could see the signal’s range it would be shaped like an ellipsoid – a bit like a rugby ball – with the sensor at one end and the receiver at the other. If you want to use the technical term, this is called the Fresnel zone. It means that narrow corridors and low ceilings can both limit the sensor’s range.
3. The angle at which the signal hits the wall
You need to think about angles too. Ideally, the angle the signal penetrates a wall should be as direct, or as close to perpendicular, as possible. As you can see from the diagram, the more of an angle the signal hits the wall at the further it has to travel, so you’re effectively making the wall thicker. If you come across this problem, you can either move the sensor or receiver or use a repeater to create a better angle.
4. The position of the receiver
Radio waves can be affected by interference or reflections if they travel along a wall, so we always recommend you position the sensor and receiver on opposite or adjacent walls. Ideally, the receiver should be close to the centre of the room, and at least 10cm away from the corner of the wall or concrete ceiling.
While working out the optimum positioning for sensors and receivers may seem complicated, consider these principles alongside a floorplan of your space and you should find it relatively easy to map out. If not, the beauty of a wireless system is that sensors can easily be moved or added if the signals aren’t strong enough in one position.
Free resource: Download our step-by-step guide to planning your smart-sensor system using EnOcean wireless standards.