Recently SEN posted a piece on capacitive field effect sensors for perimeter solutions, which operate on the basis of tuned circuits that create resonant frequencies broken by intruders to trigger alarm events. Is it true that filters are needed to ensure such solutions function reliably?

A: Yes – we pointed out in that article that when installing capacitive field effect sensors in external environments the system must include at least 3 band pass filters. You need a lower frequency filter to reject vibrations as a result of low-mass, slow moving items like paper, leaves or plastic being blown by the wind.

You should also have a high frequency filter to stave off the vibrations of wind in field wires, while the last filter will be a lightning protection surge arrester. Making sure these 3 filters are in place during installation will save time later on when techs are running around chasing the instigators of false alarms.

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