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Passive Infrared Sensor
A passive infrared sensor (PIR sensor) can measures distance with infrared light
radiating from object. This electronic sensors are used generally motion detecting. They are
often referred to as PIR, "Passive Infrared", "Pyroelectric", or "IR motion" sensors. They are
small, inexpensive and low power, therefore it is used easily everywhere such as home or
business gadgets.
This detector can take the infrared light emission which cannot see the human eyes.
All of the materials have initial infrared lights and this sensors is effected changing
temperature from infrared lights. As an object, such as a human, passes in front of the
background, such as a screen, the temperature at that point will rise from room temperature
to body temperature, and then back again. This quick change triggers the detection, it
detects motion regardless of temperature.
Contrary to Active Infrared sensors, Passive Infrared sensors do not contain any
source of infrared radiation, they simply detect IR radiations.
Infrared radiation enters through the front of the
sensor, known as the 'sensor face'. At the core of a
PIR sensor is a solid state sensor or set of sensors,
made from pyroelectric materials—materials which
generate energy when exposed to heat.
The sensor is often manufactured as part of an
integrated circuit.
Gallium nitride (GaN), caesium nitrate (CsNO3) and
polyvinyl fluorides are commonly used in the PIR
sensors.
Primarily used for intrusion detection, passive infrared sensor as used as a special
purpose radiometer which detects the heat emitted by the body of an intruder. It offers high
probability of detection within a defined area even without responding to anything else. Its
presence is hard to detect which is not the case with active infrared sensors, ultrasonic
detectors and the like.
Passive Infra-Red Sensors were originally being used for military and scientific
applications. Nowadays they can be seen in a wide range of commercial products for
automatic light control, safety, cost-savings, etc. Almost any region where people
occasionally walk or move through and need not be continuously lit, could be benefitted
from the installation of a PIR sensor. Some examples are hallways, foyers, paths, driveways,
garden areas and car parkings.
Anemometer
An anemometer is a sensor which measures the wind speed. It is used to describe
any airspeed measurement instrument used in meteorology or aerodynamics in commonly
wheatear stations. In short, the sensor has four small hollow metal hemispheres set so that
they catch the wind and revolve about a vertical rod. An electrical device records the
revolutions of the cups and calculates the wind velocity. Also, sensor can calculate the wind
pressure.
There are 6 kinds of anemometer. First, cup anemometer which consists of four
hemisphere and a reference point which shown as upper figure. It is the simplest
anemometer, also when this hemispheres turns around the operation point, we can
calculate the winds speed. Second, Windmill anemometers which is the simple like first one
has a vertical direction. Its working principles the same as cups, and its figure shown as this:
Third, Hot-wire anemometers which has very small fine wire and
uses generally electrical circuits. This sensors have 2 heated wire with
voltage as shown left figure. After when the wind flows the between
wires they will be cooler and our wires resistors will change. We can
calculate the winds speed thanks to this changing.
Fourth, Laser Doppler anemometers use a beam of light from a laser that is divided into two
beams, with one propagated out of the anemometer.
Particulates flowing along with air molecules
near where the beam exits reflect, or
backscatter, the light back into a detector, where
it is measured relative to the original laser beam.
When the particles are in great motion, they
produce a Doppler shift for measuring wind
speed in the laser light, which is used to
calculate the speed of the particles, and
therefore the air around the anemometer.
Fifth, Sonic anemometers determines
instantaneous wind speed and direction
(turbulence) by measuring how much sound waves
traveling between a pair of transducers are sped
up or slowed down by the effect of the wind. Their
main disadvantage is the distortion of the flow
itself by the structure supporting the transducers,
which requires a correction based upon wind
tunnel measurements to minimize the effect.
The last one is Ping-pong ball anemometers which
name came from using this ball because of its very
light weight. Measuring the angle between the
string-ball apparatus and the vertical gives an
estimate of the wind speed.
Kinds of anemometers and its working principles are explained. People use the
suitable kinds of anemometer many different area. Most using area is meteorology.
Meteorologists use the bigger than bigger windmill anemometer for the calculation
winds speed, and the speed will use for weather estimation. Also anemometers use
in science of aerodynamics. All of the aircrafts must have an idea about the wind and
adjust own speed according to wind speed.
Electrical Measurement & Sensors
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