PIR sensor false triggers - how to stop? (trailcam)

[TheNiceGuy]

I have a Stealthcam G42 I bought primarily for surveillance. It's not bad, but I am unsure exactly how to avoid most false triggers. Ideally it triggers when a heat source enters the field. However, it seemed to get triggered repeatedly by small pieces of tape blowing in the wind. How can they be generating a triggerable heatsource when sometimes even an animal passing in front doesn't?

 

[William Gaatjes]

If i recall correctly from some measurements i did once.
Most heat activated sensor are PIR sensors. Passive Infrared Sensors where two sense elements are connected in opposite orientation. For example an LHI778 or LHI954.
The effect is that when a heat source passes by, one sense element gives of a positive voltage and the other a negative voltage. This looks like an ac signal with a positive bump and a negative bump.
This is then converted by an electronic circuit in the activation of for example a relay to turn on a light. Or to turn on a camera.
Most PIR sensors use a fresnel lens. If i remember correctly, (It has been a few years) This lens has the effect on the sensor that when you pass by, there is not just one pulse generated when you pass by, but several pulses that can be used to increase the reliability of the trigger by making the circuit more critical about the amount of pulses seen. The fresnel lens divides the view area into sections. And when a heat source passes from one section to another, a pulse is generated. You can test this with any PIR sensor. If you walk at the PIR sensor at a straight line inside a section where the PIR sensor cannot detect you, you can walk towards it and touch it without setting it off. That is why proper security system should always use two PIR sensors at perpendicular angles.
Also, the PIR sensor becomes a lot more sensitive because of the fresnel lens.

Perhaps your camera does not use a fresnel lens (If my upper explanation is correct ) or the trigger circuit is way to sensitive. Are the pieces of tape heated by the sun and in close proximity of the PIR sensor ?

 

[TheNiceGuy]

Here's the cam. I'm really not sure what exact hardware is used in it.
http://www.amazon.com/Stealth-Cam-No-Glo-Camera-STC-G42NG/dp/B00HMN7H04
The tape was far enough that I can't imagin heat being an Issue. It's possible with the 1+ second trigger speed that birds or bugs flew through. Just trying to rule out things I can.
I'm impressed generally speaking for the cost. It seems to be getting the basic job done.

 

[John Connor]

The middle part is the IR detector and has an IR filter, no Fresnel lens. That must be the reason.

 

[William Gaatjes]

Could it be that the IR leds are emitting ?
I doubt that that is the case, because it would be a drain on the battery and stand by time. But maybe those IR leds are active and the light reflected of the tape and triggered the sensor ? I wondered about it. IR leds emit at near Infrared. Between 700 and 900nm. But i have no idea at what wavelength a PIR sensor is sensitive. I did a little googling and found far infrared at around 10um wavelength. So, an array of infrared leds should not set off the PIR sensor. My above assumption cannot be true. I have no idea why your camera trigger sensor is so sensitive.

 

[TheNiceGuy]

So only heat emitted should trigger it, correct?
I've tested a bit more, and this may have been triggered from cars, birds, or bugs. The trigger speed is over a second, so an object can come, trigger, and go. The tape trigger may have actualy been a parking lot entrance 100' behind dead center. Iiuc, Large objects can trigger it from far away.