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functor
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11 Jan 2015
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functor

from London

functor was last seen:
11 Jan 2015
    1. bernardgreen
      bernardgreen
      It would be easier to move this conversation to e-mail it that is OK with you.

      syemon.es@btinternet.com

      False alarms, both accidental and intentional are a serious problem with any alarm system.

      When jamming is detected a covert or silent alarm should be raised as jamming can be a precursor to criminal entry to the protected area.
    2. bernardgreen
      bernardgreen
      Hi

      Yale state the sensors go to sleep for a minute after decting motion. The 250 millisconds was measured using a spectrum analyser on a Yale sensor's transmissions.. ( not by me ).

      Using a baby monitor receiver ( 433.92 MHz ) it was clear the Yale sensors sent a very short pip of RF when they detected movement.

      The jamming detection is problematic as Yale reccomend disabling the jamming detection if there are too many false alarms.

      When a PIR sensor can see a door fitted with a magnetic contact it has happened that the signals from the two sensors collide and neither are recognised by the panel or siren.

      Regards

      Bernard
    3. bernardgreen
      bernardgreen
      Hi

      The Yale system sends less than 250 milliseconds of triggers and then goes to sleep until about a minute of no motion activity has occured when it wakes up.

      So 500 milliseconds of interference will knock out the alarm from a sensor.

      As the system is one way the sensor cannot be told that the system is armed or not armed so it would be transmitting triggers when ever some one was moving in the room. Continuous triggers while motion is detected would reduce battery life. This would almost certainly be in violation of the 10% rule for licence exempt systems.

      Best regards

      Bernard
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