PIR Sensor Field of View and Sensitivity

[joelq 0]

Hi all -

 

I have Sercomm OC821 outdoor IP cameras that were included with my home security bundle. Their motion sensitivity is driving me crazy, giving several false alarms every hour. My post isn't so much to figure out why these cameras are so sensitive, but more to understand how PIR cameras in general work, and in turn help me experiment on ways to reduce the false alarms. For example, I have one camera looking down on a driveway, and still gets many false alarms even when there's clearly no activity on the driveway.

 

I understand at a high-level how PIR sensors work (this site was awesome: http://www.ladyada.net/learn/sensors/pir.html), but one thing I can't get an answer to is what the PIR sensor's field of view is, and whether or not it matches (I doubt it does) the field of view of the camera itself - which I think might be part of the problem, as there might be things outside the field of view of the camera that could still be setting off the PIR sensor.

 

Does anyone know roughly what the field of view is for PIR sensors? The lens on the camera supposedly has a 66 degree view angle, which is pretty narrow. I'm just trying to figure out if the PIR sensor needs its view angle cut to match the view angle of the camera.

 

Thanks for any info!

[GrouchoBoucho 0]

Hi all -

 

I have Sercomm OC821 outdoor IP cameras that were included with my home security bundle. Their motion sensitivity is driving me crazy, giving several false alarms every hour. My post isn't so much to figure out why these cameras are so sensitive, but more to understand how PIR cameras in general work, and in turn help me experiment on ways to reduce the false alarms. For example, I have one camera looking down on a driveway, and still gets many false alarms even when there's clearly no activity on the driveway.

are you sure it's the pir triggering the alerts and no video motion detection?

 

I understand at a high-level how PIR sensors work (this site was awesome: http://www.ladyada.net/learn/sensors/pir.html), but one thing I can't get an answer to is what the PIR sensor's field of view is, and whether or not it matches (I doubt it does) the field of view of the camera itself - which I think might be part of the problem, as there might be things outside the field of view of the camera that could still be setting off the PIR sensor.

since alerts are so frequent, have you tried simply watching the area out the window, to see if there's something happening that's setting off the pir?

 

Does anyone know roughly what the field of view is for PIR sensors? The lens on the camera supposedly has a 66 degree view angle, which is pretty narrow. I'm just trying to figure out if the PIR sensor needs its view angle cut to match the view angle of the camera.

there is no "universal" fov for pir sensors; pirs have "lenses" as well, to control the fov. that's what that little white plastic bit is over the sensor.

[joelq 0]

Thanks for the quick reply, Groucho!

 

Good question - I don't know for sure that it's the PIR or video motion detection that's tripping, but review after-the-fact of the video capture after the motion was detected doesn't show any motion - at least to my eye, which leads me to believe it's the PIR that is tripping. Below is the view from the camera. It's a pretty tight view and I would think it would be obvious is there is any visual motion.

 

 

Do cameras like this typically have the PIR sensors active during the daytime as well? I ask because I seem to have more false alarms during the daytime, and if the PIR sensors are typically disabled during the daytime, then that would point to some funkiness in the video motion detection.

[buellwinkle 0]

Maybe the view is so tight that the subject has already left the field of view? Is there an option to capture pre-trigger frames? I use built in PIR motion detectors on Mobotix, AVTech and Axis and they all work very well as one would expect.

[Kawboy12R 0]

Is the light level changing from clouds passing? That'll trip video motion detectors. Also, it helps to view a zoomed in image (thumbnail no good) to see if the cam is doing any picture adjusting of its own. Auto iris, compression (look for blocks of pixels changing a bit), or whatever other reason. Also, look to see if there's any way to show a motion detection video overlay to visually display a flashing block, red square, or whatever on the screen for areas that are moving enough to be triggering a motion event. Also, is there some way to distinguish between video motion and PIR events in your recordings? That'll narrow it down. If it's definitely PIR, then you might be picking up passing cars, pedestrians, or whatever.