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Active motion Sensor vs Passive motion Sensor-Difference between Active motion Sensor and Passive motion Sensor

This page compares Active motion Sensor vs Passive motion Sensor and mentions difference between Active motion sensor and Passive motion sensor types. Advantages and disadvantages are also mentioned in order to choose the right motion sensor. We will take examples of microwave motion sensor and PIR motion sensor. PIR stands for Passive Infrared.

Definition of motion sensor:
As we know motion is a change in the position of object or person with respect to time and its initial reference location. The motion can be specified in terms of displacement, velocity, direction, acceleration and time. The device which senses motion is known as motion sensor. Following are the types of motion sensor.
• PIR sensor
• Ultrasonic sensor
• Microwave sensor
• Tomographic sensor
• Combination of any of the above sensors in a single device

Active Motion Sensor | Microwave Motion Sensor

Microwave Motion Sensor

Following are the features of the active motion sensor (of microwave type):
• The figure-1 depicts microwave motion sensor. As shown it emits frequency in the microwave region and will analyze the returned/reflected microwave frequency for determining motion.
• Detects change in frequency or change in amplitude to determine the motion of the object/person. Often amplifier and DSP algorithms are used to determine the motion accurately in noisy environment.
• Senses based on speed and size of the object
• coverage distance of microwave sensor depends on speed of the object, size of the object and height of the pole/place where it is mounted. Usually it will be 1.5 to 2 times of height of the object for slow/fast moving (at 40 Kmph) objects.

Advantages and Disadvantages of Microwave motion sensor

Following are the advantages of microwave motion sensor:
• Used in harse environment where heat cycles are irregular
• It has lifespan of about 100,000 Hours

Following are the disadvantages of microwave motion sensor:
• Microwave radiation is hazardous for health and hence low power microwave sensors are preferred.
• Microwave frequency do not penetrate metal objects.
• Prone to false alarms due to blowing of objects due to wind and also emission from fluorescent lights.
• They operate at irregular intervals and hence intruders sometimes are left unnoticed.

Passive Motion Sensor | PIR motion Sensor

PIR motion sensor

Following are the features of the passive motion sensor (of PIR type):
• PIR stands for Passive infrared motion sensor
• PIR sensor houses pyro-electric sensor as shown in the figure-2. It generates energy when exposed to heat. Human or animal body radiates energy in the form of infrared radiation. Hence when human/animal come in the range of PIR motion sensor, it receives thermal energy and hence motion is detected by the sensor.
• Detects increase in received thermal energy to determine the motion of the object/person
• Senses based on heat and light

Advantages and Disadvantages of PIR motion sensor

Following are the advantages of PIR motion sensor:
• Detects motion reliably in indoors as well as in day or dark

Following are the disadvantages of PIR motion sensor:
• It does not operate greater than 35 degree C
• It works effectively in LOS (Line of Sight) and will have problems in the corner regions.
• It is insensitive to very slow motion of the object
• In outside environment, during day and night, PIR motion sensor triggers alarms.

To reduce likelihood of false alarms microwave motion sensors are combined with passive infrared sensors. This type of sensors are known as dual motion sensors. This sensors leverage benefits of both microwave as well as PIR sensor types.

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