Advice for recurring phantom alarms on door? (wired sensor already replaced)

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Old 01-24-19, 11:26 AM
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Advice for recurring phantom alarms on door? (wired sensor already replaced)

Dear Brain Trust,

Iíve had phantom alarms on my front door, which happen every few months in the middle of the night. Iíve had the sensor replaced by an alarm professional, but the problem kept reoccurring. Iíve now set up up a data logger on that particular zone to monitor the current and see if I can spot any significant current fluctuations that are coinciding with the phantom alarms. It hovers between 2.83mA and 2.94mA. About 90% of the wire from the panel to the sensor is exposed (itís in the unfinished part of the basement) and a visual inspection has not turned up anything unusual.

System: Ademco FA120C (wired)
Sensor: magnetic switch (located in door jamb, and magnet is on side of door)
User: I'm a basic DIY-er, so you'll need to keep explanations relatively idiot-proof for me!

Any advice? Let me know if any additional info would be helpful!

Thanks ahead of time!!
John
 
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Old 01-24-19, 03:34 PM
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Welcome to the forums.

magnetic switch (located in door jamb, and magnet is on side of door)
Did he replace the switch and magnet ?
Is this a 3/8" press fit switch ?
Wood door...... any metal involved ?

The 3/8" switches don't have much wiggle room. The magnet and switch must be very closely lined up.
I use 3/4" press fits as they allow for a greater margin in alignment error.
 
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Old 01-24-19, 07:10 PM
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Thanks for the response Pete!

The pro replaced both the switch and magnet. Looks like a 3/8" switch. And the door is indeed metal, with wood core.

I can see how the 3/8" switches require more precise alignment, but once it's properly aligned, should it not be good to go? My first switch was very sensitive and the alarm would trip if the door was opened even by 1/2". When the pro replaced the switch, he used a much stronger magnet (so he says), and I can now open the door approx. 4" before the alarm is tripped. Would that not mean that the current switch vs magnet position is very forgiving?
 
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Old 01-24-19, 07:33 PM
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That sounds like the magnet is in a good capture area. A 4" capture area sounds pretty large for a 3/8" switch. Magnetic switches are funny things. The reed switch can have field polarity to it. Meaning the magnet could have inches of capture but a problem when the magnet is directly in front of the switch.

I'd replace or have the switch replaced from one of a different lot.

I buy those in bags of 10. They come with attached wires or screw terminals. I have gotten several defective ones in one bag and other bags are ok. I've had them go intermittent in installations.
 
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Old 01-25-19, 05:46 AM
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I'll try replacing the switch again (I'll use a 3/4" one this time) and see if that solves the problem. I really appreciate your advice, Pete! Cheers
 
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Old 01-25-19, 05:46 PM
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Hi again Pete,
Just out of curiosity, if by chance replacing the switch doesn't resolve the issue, what might be your next suspect?
 
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Old 01-25-19, 05:53 PM
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Three things.....
1) the switch
2) the wire
3) alarm panel problem.

You could put a terminating resistor on the point and see if the zone stays normal.
Swap that zone for another for a few days. This could be a problem if that door is on a delayed zone.
 
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Old 01-26-19, 04:40 AM
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Awesome! Thank you, kind sir!
 
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Old 01-26-19, 01:48 PM
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I would never use a 3/8" press-fit contact in a steel door or frame. They put the magnet too close to ferrous material that "saps" the magnetic field. 3/4" contact for sure.

Have all the splices been remade? Was the new switch spliced directly to the cable, or to the leads from the old switch, leaving the original splices untouched. If there is an End-of-Line Resistor, has the splice to it been checked?

In the panel, tug gently on the wire to each zone terminal. Can you see copper wire going under the clamp for each terminal (I found wires stripped maybe 1/32" that had operated solid as a rock for years). I also found wires not stripped at all (amazing what can be forgotten).

There is no better splice that twisted and soldered, but today the time is rarely there to do it. I also found them easier to stuff back in the hole.
 
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Old 01-26-19, 03:43 PM
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Thanks ThisOldMan! Not sure how the pro connected the new switch, as those connections are tucked away out of sight right now. But when I replace the switch myself (I've already ordered a replacement 3/4 switch), I'll use the opportunity to verify/redo all the connections and splices too, since that still seems to be the most likely problem area. If I'm going to yank the old switch out, I may as well check everything in there! I had already checked the connection at the panel and it was fine. (although I don't think I had checked the resistor)

Thank you!
 
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