Re: RF Immunity in Smoke Detectors

[Eyeball Kid <jimbo1@xxxxxxx>]

Just a follow up for anyone who was curious.  I visited the premises and
found the customer was able to trip the zone the smoke detector was on
when tranmistting on either 3.8 MHz or 21 MHz (running about 700 watts).
  Interestingly when he did this the siren on the system sounded but not
the piezo on the smoke detector (leading me to believe he is not
tripping the detector just the zone)

I pulled the detector off the mount and found the customer had installed
a snap on ferrite around the wires.  Went to the panel and found he had
also put a ferrite around the telephone line (about the only wiring that
was accessible without opening the panel).  I moved that ferrite on to
the pair running into the zone being tripped and we ran a test.

No more problems at 21 MHz but he was still able to trip it at 3.8MHz.
So I took my mother's approach to cooking ("If a little makes it good -
a lot will make it better") and installed a 2nd ferrite that I had
happened to bring along.  Voila - no more problem - I told him to spend
the weekend trying to make it trip and went home.  Almost a week later
and I haven't heard from him.

So the lesson learned is - RFI Problems are easily solved with Ferrites!


The ferrites he had are from DX Engineering
(http://www.dxengineering.com/TechArticles.asp?ID={54C2338D-3ED0-48C3-946F-F343A5C7555D}

\\\Eyeball Kid wrote:
> I have a customer who is an amateur radio operator and is complaining
> that whenever he is transmitting he trips the smoke detector we
> installed (System Sensor 2012HA).  He is asking for a smoke that is
> better designed for RF Immunity.
>
> Almost all the motions I have seen have some spec listing RFI  (typicall
> 30v/m 10-1000Mhz)  but I have not found any such spec on any of the
> smokes I have looked at.  (System Sensor, GE-Interlogix, DSC)
>
> Anyone have any suggestions for a smoke detector in a RF rich environment?
>
> Anyone done an install at a radio station (the transmitter not the
> studio) and what did you use?
>