Bruder - Movement Sensors- Group E

Movement sensors, or motion detectors as they are usually referred to as, are used mostly indoors to control electric lighting. Motion detection can be defined as “the process of detecting a change in position of an object relative to its surroundings or the change in the surroundings relative to an object. Motion detection can be achieved by both mechanical and electronic methods. When motion detection is accomplished by natural organisms, it is called motion perception.”[3] Movement sensors have many different uses however. They can be used for burglar detection, automatic doors, automatic sinks and paper towel dispensers and soap dispensers, anything that you could think of really. What I’m trying to get at is that they are very multi-useful. Most of the motion detectors that we see in everyday life are passive systems that detect infrared energy.

“These sensors are therefore known as PIR (passive infrared) detectors or pyroelectric sensors. In order to make a sensor that can detect a human being, you need to make the sensor sensitive to the temperature of a human body. Humans, having a skin temperature of about 93 degrees F, radiate infrared energy with a wavelength between 9 and 10 micrometers. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers.”[1] The sensors do not just pick up of the heat given off, what they are really looking for is a dramatic change in the infrared light the sensor is changing.

Some of the other types of movement sensors include ultrasonic, microwave, and tomographic motion detector. An ultrasonic sensor works by sending “…out pulses of ultrasonic waves (acoustic sound waves above the frequency that a human can hear) and measures the reflection off a moving object. Motion causes the frequency of the reflected wave to change (Doppler effect).”[2] A microwave sensor works by sending “…out electromagnetic pulses and measures the changes in frequency (Doppler) due to reflection off a moving object.”[2] Finally a tomographic motion detector works by sensing “…disturbances to radio waves as they pass from node to node of a mesh network. They have the ability to detect over complete areas because they can sense through walls and obstructions.”[2] All of these different types of motion detection sensors all have advantages and disadvantages. That being said, their uses are possible for just about anything your mind can imagine.

Comments:

Michael: I had no idea the importance of pressure sensors. I never realized how common they actually are either. I really liked how you included many different uses for a pressure system; it really puts the importance into perspective. Really well written post, two thumbs up!

Audrey: I think it’s awesome that different types of temperature sensors had different limitations, so each sensor has a different uses. I was surprised to find out that the majority of the sensors that require contact to the heat source could contaminate the readings. Do you think there is one sensor that is the best for universal use? Very informative post!

References:

[1] "How do motion sensing lights and burglar alarms work?"  01 April 2000.  HowStuffWorks.com. <http://home.howstuffworks.com/home-improvement/household-safety/security/question238.htm>  17 February 2014.

[2] "Motion Detector." Wikipedia. Wikimedia Foundation, 02 Nov. 2014. Web. 17 Feb. 2014.

[3] "Motion Detection." Wikipedia. Wikimedia Foundation, 02 Oct. 2014. Web. 17 Feb. 2014.