PIR False Pickup

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  #1  
Old 03-30-03, 02:44 PM
Willem
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PIR False Pickup

I have had an alarm in operation for four years. Over the last three weeks one of my PIR motion dectors has gone off for no appanant reason. It was always around the same time in the morning. I cleaned the face and made sure nothing was in front blowing. I have no pets. The alarm company just came out and could not find anything wrong. Their most recent visit they changed the delay befor3e the contacts were sealed in.

Just wondering if anyone had any experiece wity these issues. The first false alarm the police were automatically called.

Gene
 
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Old 03-30-03, 04:14 PM
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Check to make sure that the wires in terminals are screwed down tight. Often the screw compresses the copper wire, and it gets just enough movement room that when the building moves slightly, a vibration from traffic, etc. will break the circuit just enough for a a false alarm.

Another source of false alarms are heat/air vents. If the system is set to kick on with a substantially low/high setback, the difference between ambient temp and the vent air can do the deed.

Finally, the device can simply wear out, remember, those contacts cycle everytime someone passes by. You can't beat the third law of thermodynamics....
 
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Old 03-31-03, 11:48 AM
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If you're having falses at the same time every day, then my guess is the motion is ok, but you have a constant somewhere that trips it - like the vents. Another possibility is heat caused by sunlight. Check the windows around the motion to see if that could be a possibility. If you think you may have found the cause of the falses, try masking off that area of the lens. Make sure you use vinyl tape (electrical tape) or something as heavy or heavier, otherwise it will still "see" that area.

Worse comes to worse, try some trial and error, place a piece of tape over one side of the motion and see if you get falses, if so, try the other side, etc.

Good luck!
 
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Old 04-05-03, 07:08 AM
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And make sure while you are testing, that your monitoring company has that zone in test or no action. In other words, tell them not to call anyone on that particular zone for a month, or whatever. That way you don't annoy the police while you troubleshoot.
 
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Old 04-05-03, 03:07 PM
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Another source of false alarms from PIR devices that I only recently became really aware of is laser printers and fax machines that use a laser print engine. The page apparently comes out of the printer at 100 degrees F+. If a PIR happens to be aimed at the location of the unit, an after hours incoming fax or remote printing request can trigger a false alarm.

It's one of those things that the recent proliferation of laser faxes threw an unexpected curve at things...
 
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Old 04-05-03, 03:41 PM
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Hmm, never would have thought of that. But it definitely brings up a good point - Look for anything that can cause any kind of heat suddenly. You just never know, every house is different.
 
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