Can we install wireless alarm systems and expect the same reliability as we’ve got from wired systems? There are some nice RF alarm and automation solutions available, but many techs think wired is more reliable in the long term. What do you think?
A: All other things being equal, a wireless system can be as reliable as a hardwired solution with the latest generation including long range devices offering thousands of metres line of sight between sensor and controller. Having said that, some wireless systems can struggle with some types of building construction, especially if there’s a lot of steel-reinforced concrete between transmitters and the receiver – we’re talking about environmental Farraday shields. If you’re installing in timber and plaster houses and office spaces, there should be no problem, unless there are powerful RF frequencies about.
If a sensor is not working or is having intermittent trouble the installer’s first move should be to try to reposition the transmitters without moving them from their present location. It’s strange but true, that turning a device upside down or on its side will often sort out reception problems in short range wireless installations. The idea is to get the polar axis of the transmitter’s antenna nearly identical to the polar axis of the receiver. Getting polarization right means greater numbers of electromagnetic lines are getting from the transmitters to the antenna of the receiver – that means improved reception.
Sometimes repositioning is not enough. What can happen is that transmitter signals are messed up by conflicting RF signals or scattered by metal objects and the polar pattern of the signal shifts. Signal shift means that the receiver is grabbing a signal reflected from a surface in the system’s environment instead of the clean signal you’re trying to get through. If the polarization pattern is altered, the transmitter’s physical axis will look different – the transmitter won’t be recognized by the receiver.
Another problem is caused by nulls in the transmitter’s signal. These nulls are spots in the environment where the transmitter’s signal is at its weakest. The nulls are located at points where the signal crosses and re-crosses the x-axis of its waveform. Any sensor with dual antennas is pretty much assured of having one of its antennas located at a point on either side of an x-axis null. If your problem sensor has a single antenna, then you’re going to need to move it either towards or away from the receiver. What you’re doing is moving the antenna of the transmitter out of the signal’s null point, to a spot either higher or lower on the waveform.
The latest RF sensors are very good with long ranges and clever design and they should be a good options with the caveat that systems must be installed to suit an application. Regardless, there will be applications that get the better of wireless – reinforced concrete, Besser block stacks with steel poles hidden inside them, chicken wire behind plaster, certain kinds of metal foil insulation, metal walls in warehouses, etc.
Wireless is easy and it’s flexible and where it works, it’s brilliant. We’d use it with the caveat that batteries can be an issue. You want very, very long life from batteries. Users tend not to replace batteries, even if are capable of doing so. This means that if the battery life of a device – keypad, sensor, etc – is about 2 years, then past that time parts of the system will start to fold up. Wireless customers need to be managed to ensure that failure of batteries doesn’t mean the failure of the supplier/customer relationship. In a system with 20-30 devices, including user interfaces, all losing power around the same time, managing the process can be harder than it sounds – a blanket replacement of every battery in the system is best.
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