Advantages
● Low
cost for control achieved
● High
torque at startup and low speeds
● Ruggedness
● Simplicity
of construction
● Can
operate in an open loop control system
● Low
maintenance
● Less
likely to stall or slip
● Will
work in any environment
● Can
be used in robotics in a wide scale.
● High
reliability
Disadvantages
● Require
a dedicated control circuit
● Use
more current than D.C. motors
● Torque
reduces at higher speeds
● Resonances
can occur if not properly controlled.
● Not easy to
operate at extremely high speeds.
PIR SENSOR
A passive infrared sensor (PIR
sensor) is an electronic sensor that measures infrared (IR) light radiating
from objects in its field of view. They are most often used in PIR-based motion
detectors.
PIR sensor allow us to sense the
motion, almost Always use to detect whether a human has moved in or out of the
sensors range.
It is commonly found in
appliances and gadgets Used in homes or business,
Sensitivity Range: up to 20 feet
(6 meters).
We, homo sapiens, radiate heat in
form of radiation at wavelength of 10-12 micrometer that can only detect by the
PIR sensor .
PIR sensors allow you to sense
motion, almost always used to detect whether a human has moved in or out of the
sensors range. They are small, inexpensive, low-power, easy to use and don't
wear out.
OPERATING
PRINCIPLES
All objects with a temperature
above absolute zero emit heat energy in the form of radiation. Usually this radiation
is invisible to the human eye because it radiates at infrared wavelengths, but
it can be detected by electronic devices designed for such a purpose.
The term passive in this instance refers to the fact that PIR
devices do not generate or radiate any energy for detection purposes. They work
entirely by detecting the energy given off by other objects.[1] PIR sensors
don't detect or measure "heat"; instead they detect the infrared
radiation emitted or reflected from an object.
CONSTRUCTION
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 materials which
generate energy when exposed to heat.Typically, the sensors are approximately
1/4 inch square (40 mm2), and take the form of a thin film.Materials commonly
used in PIR sensors include gallium nitride (GaN), caesium nitrate (CsNO3),
polyvinyl fluorides,derivatives of phenylpyridine , and cobalt phthalocyanine.
The sensor is often manufactured as part of an integrated circuit.
A PIR-based motion detector is
used to sense movement of people, animals, or other objects. They are commonly
used in burglar alarms and automatically-activated lighting systems. They are
commonly called simply "PIR", or sometimes "PID", for
"passive infrared detector".
Operation
An individual PIR sensor detects
changes in the amount of infrared radiation impinging upon it, which varies depending
on the temperature and surface characteristics of the objects in front of the
sensor. When an object,such as a human, passes in front of the background, such
as awall, the temperature at that point in the sensor's field of view will rise
from room temperature tobody temperature, and then back again. The sensor
converts the resulting change in the incoming infrared radiation into a change
in the output voltage, and this triggers the detection. Objects of similar
temperature but different surface characteristics may also have a different
infrared emission pattern, and thus moving them with respect to the background
may trigger the detector as well.
PIRs come in many configurations
for a wide variety of applications. The most common models have numerous Fresnel
lenses or mirror segments, an effective range of about ten meters (thirty
feet), and a field of view less than 180 degrees. Models with wider fields of
view, including 360 degrees, are available—typically designed to mount on a
ceiling. Some larger PIRs are made with single segment mirrors and can sense
changes in infrared energy over one hundred feet away from the PIR. There are
also PIRs designed with reversible orientation mirrors which allow either broad
coverage (110° wide) or very narrow "curtain" coverage, or with
individually selectable segments to "shape" the coverage.
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