ECT week 2 - The passive infrared sensor
(Leer en español)
For this entry, I will write a bit of theory on how the trail camera works.
First, the parts of the camera:
The camera is integrated into a sturdy case that will resist low/high temperatures, rain and other rough weather. The lenses are at the top, surrounded by the infrared flash (to take pictures in low light conditions). It has a microphone to record audio with the videos, a light sensor and an LCD that is exposed when the cover is open.
But what I wanted to talk about is the motion sensor to activate the camera. In this case, is a PIR or passive infrared sensor. As all object with temperatures above zero emits heat radiation, the PIR can detect changes in the amount of infrared radiation that is receiving. Trail camera’s PIR sensors usually detect 3°C or above changes in temperature within their field of vision. A good PIR will increase its sensitivity by dividing their field of view into three or more zones and detecting changes for any of these zones.
Many false triggers are caused by the sensor detecting heat radiation that is not due to an animal: sun on the lens, objects warmed by the sun moving (like the bird feeders in my garden). It could happen as well than the animal is detected by the PIR but most of the animal (like the squirrel) is out of frame or moved too fast out of it.
The time between the PIR detecting movement and the picture was taken it’s called trigger speed. It’s usually expressed with decimal seconds and most cameras will have something in the proximity of 0.2 to 0.5 seconds. The lower the number, the better.