Erroneous Alarms

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Old 09-14-16, 11:08 AM
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Erroneous Alarms

I've got a PC1555 with an LCD5501 keypad. In the last couple of days about 15 minutes after I arm the system the alarm goes off. The display says zone 2 which is the door to the garage. A call to the central office is generated and I have to deal with the usual follow up.

But the sensor to that door seems fine. When the door is opened the display says OPEN and when closed the display is ready to be armed. The problem only occurs some time (5-15 minutes) after the system is armed. It acts like someone opened the door. I get the delay warning from the keypad and then a short time later the alarm siren sounds. But obviously that door was never opened.

I can't trust the system so I'm not arming it.

Any ideas on where to look?
 
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Old 09-14-16, 11:16 AM
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I can't answer why but you can still set the alarm - just bypass zone #2.
 
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Old 09-14-16, 11:50 AM
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What kind of sensor is on that door ?
Surface magnet, press fit magnet, roller ball, plunger ?

It is very possible that the switch is at the very end of it's "capture" range. Anything could cause a trigger. You need to see how much the door opens before it goes into fault.

Depending on the type of switch.... replace it.
 
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Old 09-14-16, 03:38 PM
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sttgiu

marksr - I am aware & know how to bypass the zone. But it has to be bypassed every time the alarm is armed. This doesn't work well for people that have access to the house like maids or cat sitters (or my wife for that matter).

PJmax - the sensor is magnetic. It was installed when the house was built. The sensor is in the door jamb and the magnet is in the edge of the door. I did check the sensor's range by opening, closing,pushing, wiggling, etc the door when the system is not armed. The keypad only said 'open' when it was truly opened and the 'open' went away before the door fully latched. And 'open' would not appear no matter what I did to the door when the latch was engaged.

Anyone ever hear of a magnetic sensor failing by indicating momentary opens let's say of milliseconds duration? I don't know what the algorithm is for when the alarm actually declares a zone failure. I do know that it seems to take on the order of 1 second for the 'OPEN' to appear on the display after I open the door.

I would assume that there is a reasonable amount of filtering done on the zone signals to prevent false alarms. (It could be done in either hardware or software or both.)

This all makes me believe that the magnetic sensor is not having millisecond failures. After all, it's a electromechanical device.

So for now, I'm leaning toward it not being the sensor. Sounds like the processor board acting up to me.
 
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Old 09-14-16, 03:43 PM
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Anyone ever hear of a magnetic sensor failing by indicating momentary opens let's say of milliseconds duration?
Yes.... absolutely. That's why I said change the switch.

Whenever I get an intermittent problem I try to address all the angles.

It only takes a split second for the alarm to sense a fault. It may take a second or two to show up on the screen.

If you think it's a board problem...... temporarily remove the zone wiring and replace with an EOL resistor.
 
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Old 09-14-16, 03:57 PM
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Hardwired System? Can you check the wire running to the door sensor? I had a problem with a zone...service tech checked everything and said the only thing left was to check the wiring which ran up a wall. Long story short we pulled the wire and found that the wire was chewed.....probably by a mouse.
 
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Old 09-14-16, 05:54 PM
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sttgiu

OK, thanks everyone. I'm going to run some tests.

I'll let you know what I find.
 
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Old 09-14-16, 06:36 PM
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Or try switching two zones and see if the problem follows the door....
 
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Old 09-22-16, 09:41 AM
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Repaired

I think I got it fixed.

First I shorted out the troublesome zone at the PC1555 PCB and ran the system for several days awaiting the arrival of a new magnetic switch. The system behaved normally and could be armed with no false alarms. (This test eliminated the PC1555 as a culprit.)

As I was removing the old magnetic switch from the door jamb it came loose from the wiring in the wall. I was extremely careful pulling it out applying very little pressure because I didn't want this to happen. The original connection by the installer was simply twisting a stranded wire from the sensor around a solid wire from the in-wall wiring and then a little piece of black electricians tape. IMHO the least reliable connection one can make. Was this the source of the erroneous alarms? Unless I get more false alarms, I'm going with this as the cause.

I was still able to fish the in-wall wiring out through the sensor hole and install the new sensor. (Installer left basically no slack.) Just to slam dunk it, I soldered the new connections and installed heat shrink tubing. Then pushed the new sensor back into the original hole. Heck, I even replaced the magnet in the door since the new sensor came with one.

Thanks to everyone who responded.
 

Last edited by sttgiu; 09-22-16 at 09:41 AM. Reason: sttgiu
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Old 09-22-16, 10:08 AM
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It sounds like you definitely found the culprit (a bad connection due to the unprofessional non-bonded connection) and seem to have solved it well!

Keep us posted if it happens to false again.
 
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