Summer Heat, Camera Placement & PIR Sensors

Summer heat. It is something we are used to here in the south, Georgia specifically. In testing cameras, lots of them, we noticed that the range of the PIR sensing is reduced, sometimes drastically in high summer heat.

As July and August approach it can become very hot here and the day temperatures can reach or equal the body temperature of many of the target animals. The PIR sensor, a chip located on the main board of the camera and located behind a fresnel lens, converts changes in heat to voltages, monitored by the firmware and chipset on the camera board.

Heat is actually light in the infrared spectrum and the fresnel lens focuses that light onto the PIR sensor. Some fresnel lenses are very narrow angled, like on your Cuddeback cameras while most of the industry has adopted a wider angle fresnel.

The PIR sensor in combination with the camera firmware is designed to accept the gradual warming from the sun without triggering the cam in most cases. Suppose we place a camera looking down a trail at a foliage background in a fairly warm time of the year. Now let’s put an animal on a direct approach to the camera. The camera perceives a slow progression of heat build up at a distance compared to the background and will typically not trigger until that heat source is very close.

Think of the approaching animal as producing a gradual heat change. Now suppose an animal passes the camera from behind or from the side at a close distance to the camera.  In a relatively short period of time, the animal displaces a large portion of the sensing zone relative to that foliage background.  This will be perceived by the camera as a motion event much more readily.

We actually tested this theory using a camera stand that allowed us to mount two scoutguard SG550 cameras back to back and place this mount along a trail.  Keep in mind each camera looked down a trail.  We analyzed weeks of photos and found that the cameras triggered faster (actually earlier) when the animals walked past a camera from behind than when they approached the camera from a distance.

Now, how do we make a correction to our typical mounting setup  to improve our success on the approaching animals?  We can aim our camera and still look down the trail this time of year but not straight down the trail. Moving a distance off the trail and looking down the trail at an angle should do the trick. An approaching animal will trigger the camera when it is closer to the camera and thus create a larger % change in relation to the background foliage.  Remember that, in general, the reason for looking up and down the trail is to compensate for a slower trigger time.  Modern cameras have faster and faster trigger times thus the sharper the angle to the trail can be.


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