UNIT III Motion, Proximity, Ranging, Force, Magnetic and Heading
UNIT III Motion, Proximity, Ranging, Force, Magnetic and Heading
UNIT III Motion, Proximity, Ranging, Force, Magnetic and Heading
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Part I
Motion Sensors,
Proximity Sensors
&
Ranging Sensors
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Sensor
• A sensor is a device which receives and responds to
a signal.
• A sensor (also called detector) is a converter that
measures a physical quantity and converts into a
signal which can be read by an observer or by an
(today mostly) electronic instrument.
• The sensors are used to measure and/or detect a
huge variety of conditions including: temperature,
pressure, level, humidity, speed, motion, distance,
light or the presence/absence of an object and
many other types.
3
Motion Sensors
• The term 'Motion sensors' can be used to refer to any kind of
sensing system which is used to detect motion; motion of any
object or motion of human beings.
• Motion sensor is also called as motion detector.
• Motion sensors are commonly used in security systems as triggers
for automatic lights or remote alarms and similar applications.
• Active motion sensors emit a signal typically a burst of (light,
microwaves or sound) waves which is reflected by the
surroundings.
• The reflected signal is received by the sensor and takes necessary
action. When something moves within the area of an active
motion sensor, the change in signal that is reflected to the sensor
activates the system.
• The active sensor is one of the most common and reliable sensors
used in a security system
4
Motion Sensors
• Passive motion sensors are a type of motion sensor
that do not emit a signal but instead detect infrared
radiation around the sensor.
• Motion sensing is used in a number of applications
Automated lighting system
Security systems
Smart floodlights
Burglar alarm
Radar guns
• Advantages of motion sensor
Saves time
Security
Easy to install
Saves energy
Powerful transmission 5
Motion Detection
• Motion detection is 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 can be detected by:
Infrared (Passive and active sensors)
Optics (video and camera systems)
Radio Frequency Energy (radar, microwave motion
detection)
Sound (microphones and acoustic sensors)
Vibration (seismic sensors)
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Types of Motion Sensing
⇒Local Motion Sensing
⇒Ultrasonic Motion Sensing
⇒Microwave Motion Sensing
Local Motion Sensing
• Infrared light is a spectrum of non-visible – for humans at
least - light that is emitted by objects when they produce
heat.
• Infrared motion sensor systems are one of the cheapest
and most reliable systems available.
• An infrared motion detector uses infrared sensing to
detect motion in a given area.
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Local Motion Sensing
8
Ultrasonic Motion Sensing
• Ultrasonic motion detectors use sound waves to detect
motion. If movement is detected, the sound wave pattern
is disrupted and alarm is signaled.
• It senses motion by analyzing sound waves in its
environment.
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Resistive Sensors
13
Capacitive Sensors
• The capacitive sensor is the capacitor with variable capacitance.
• Comprises of two parallel metal plates that are separated by the
material such as air, which is called as the dielectric material.
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Potentiometer
A potentiometer consist of a resistance element with a sliding
contact which can be moved along the length of the element.
Such element can be used for linear or rotary displacements, the
displacement being converted into a potential difference
The motion of the wiper may be
1. Linear
2. Rotational
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Potentiometer
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Potentiometer
Construction
• Resistance wire is wound on a non-metal
• The physical quantity under measurement is
connected to the shaft of the wiper in contact with
the resistance wire
Working Principle
• Input physical variable is applied to shaft
• Shaft moves the wiper left and right according to
increase or decrease in input variable
• This causes displacement (position change) of the
wiper on resistive wire
• In turn it causes change in resistance R₂
• Hence, output voltage changes
• Vo is proportional to physical quantity.
• Vo ~ R₂ ~ xi ~ physical quantity under measurement
• It may be force / pressure / Level / Temperature 18
Potentiometer
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Potentiometer
Advantages
1. They are inexpensive
2. Simple to operate
3. Useful for measurement of large amplitudes of
displacement
4. High efficiency
5. Large outputs
Disadvantages
1. Large force is required to move the sliding contacts
2. Noise generation due to sliding contact wear out
20
Resolver
• A resolver is an electromagnetic transducer that can be
used in a wide variety of position and velocity feedback
applications.
• It is a variable transformer with a rotary electromagnetic
coupling between the primary and secondary winding.
• Two windings are provided at right angle to one another
for both stator and rotor.
• All resolvers produce signals proportional to the sine and
cosine of their rotor angle.
• Since every angle has a unique combination of sine and
cosine values, a resolver provides absolute position
information within one revolution (360°) of its rotor
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Resolver
22
Resolver
• The resolver consist of stator and rotor.
• Stator is the stationary part and rotor is revolving part. A shaft is
attached to the rotor.
• The rotor carries the primary winding. The stator carry the two
secondary winding displaced angularly offset with respect to one
another by 90°.
• These secondary windings are designated as the sine winding and
the cosine winding.
• The basic function of a resolver is to resolve a vector into its sine
and cosine components.
• An AC voltage is applied to the reference winding in the rotor.
• This inductively couples to the sine and cosine windings, and hence
generating an output voltage with a magnitude that varies as the
sine or cosine, respectively, of the angular position of the input
shaft relative to some zero point.
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Resolver
Applications
Servo motor feedback
Speed and position feedback in steel and paper mills
Oil and gas production
Aircraft flight surface actuators
Communication position systems
Control systems in land based military vehicles
Advantages
High reliability
High accuracy
Infinite Resolution
Operating angle of 360 degree & capable of continuous rotation.
No wear and tear except slip rings.
High operational speed.
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Synchro
• The synchro is a motor-like, electromechanical device with an
analogue output.
• Apart from having three stator windings instead of two, it is similar
in appearance and operation to the resolver and has the same
range of physical dimensions.
• Used for measurement of angular positions, axis measurement in
machine tools
• The primary winding of the transformer, fixed to the rotor, is
excited by an alternating current, which by electromagnetic
induction, causes voltages to appear between the Y-connected
secondary windings fixed at 120 degrees to each other on the
stator.
• The voltages are measured and used to determine the angle of the
rotor relative to the stator
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Synchro
Working principle of Synchro :
• When the rotor is excited by ac voltage, the rotor current flows,
and a magnetic field is produced.
• The rotor magnetic field induces an emf in the stator coils by
transformer action.
• The effective voltage induced in any stator coil depends upon the
angular position of the coil’s axis with respect to the rotor axis
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Microsyn
• This is a variable-reluctance transducer used to detect
small motions, giving output signals as low as 0.01° of
changes in angles.
• The coils are connected in such a way that at the null
position of the rotary element, the voltages in coils 1 and
3 are balanced by voltages induced in coils 2 and 4.
• The motion of the rotor in the clockwise direction
increases the reluctance of coils 1 and 3 while decreasing
the reluctance of coils 2 and 4, thus giving a net output
voltage vo.
• The movement in the counterclockwise direction causes
a similar effect in coils 2 and 4 with a 180° phase shift.
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Microsyn
• A direction sensitive output can be obtained by using phase-
sensitive demodulators The sensitivity of the device can be made
as high as 5 V per degree of rotation. The nonlinearity may vary
from 0.5% to 1.0% full scale.
• The key benefits of these transducers are that the rotor does not
have windings and slip-rings and the magnetic reaction torque is
also negligible.
• Used in applications involving gyroscopes
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Encoder
• Encoders are used to translate rotary or linear motion
into a digital signal.
• Encoders use common encoder technologies such as
optical, magnetic, inductive and capacitive.
• Based on the motion encoders can be rotary and linear.
• Encoders may produce either incremental or absolute
signals.
• An absolute encoder generates a unique code for each
position of the object.
• The code contains information about the exact position
of the object at any given time.
• An absolute encoder does not need a reference point or a
reset signal to .determine the position
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Encoder
• Incremental Encoders generates a series of pulses as the
object moves.
• The number and frequency of the pulses indicate the amount
and speed of the movement.
• However, an incremental encoder does not keep track of the
absolute position of the object.
• It needs a reference point or a reset signal to determine the
initial position
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Optical Encoder
• Optical Encoders consist of a rotating and a stationary
part.
• The rotor is usually a metal, glass, or a plastic disc
mounted on the encoder shaft.
• The disc has some kind of optical pattern, which is
electronically decoded to generate position information.
• The rotor disc in absolute optical encoder uses opaque
and transparent segments.
• The stator has corresponding pairs of LEDs and
phototransistors arranged so that the LED light shines
through the transparent sections of the rotor disc and
received by photo-transistors on the other side.
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Optical Encoder
• After the electronic signals are amplified and converted, are
then available for the evaluation of the position.
• An optical encoder is precise and accurate but may be
sensitive to dust, dirt, and moisture
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Magnetic Encoder
• The magnetic encoder detects rotational position
information as changes of the magnetic field, converts
them into digital signals.
• The simplest magnetic encoder consists of a permanent
magnet and a magnetic sensor.
• The permanent magnet is attached to the tip of a
rotating shaft
• The magnetic sensor is fixed in a state where it is
mounted on a PCB board at a position where it receives
the magnetic field generated by the permanent magnet.
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Magnetic Encoder
• When the permanent magnet attached to the shaft rotates, the
direction of the magnetic field detected by the magnetic sensor
changes, as a result the encoder detects the rotational position and
speed of the motor shaft.
• A magnetic encoder is robust and resistant to dust, dirt, and
moisture. However, it may be affected by external magnetic fields
or high temperatures
34
Inductive Encoder
• An inductive encoder uses coils and metal plates to
generate electrical signals.
• The coils are attached to the stationary part and create
an alternating current that induces an electromagnetic
field.
• The metal plates are attached to the moving part and
change the impedance of the coils depending on the
position.
• The changes in impedance affect the voltage and current
in the coils and produce corresponding signals.
• An inductive encoder is durable and reliable but may
have lower resolution
35
Linear Variable Differential Transformer (LVDT)
• LVDT is inductive transducer to translate the linear motion
into electrical signals.
• It generates an AC signal whose magnitude is a function of
the displacement of a moving core.
• The numbers of turns in both the secondary windings are
equal, but they are out of phase to each other.
• A movable soft iron core slides within hollow former and
therefore affects magnetic coupling between the primary and
two secondary windings.
• The output differential voltage is proportional to the
displacement of the iron core.
• When the core is at central position of the cylinder, differential
flux is zero and this position is referred as null or zero position.
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Linear Variable Differential Transformer (LVDT)
• As the core is displaced slightly to one side or the other from this
null or zero position this the induced voltage in one of the
secondaries will be become greater than that of the other
secondary and an output will be produced.
• The polarity of the output signal depends upon the direction and
displacement of the moving core.
Eo = ES1 – ES2
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Linear Variable Differential Transformer (LVDT)
Benefits of LVDT:
1) Infinite resolution is present in LVDT
2) High output
3) LVDT gives High sensitivity
4) Very good linearity
5) Ruggedness
6) LVDT Provides Less friction
7) Low hysteresis
8) LVDT gives Low power consumption.
Applications of LVDT:
1) LVDT is used to measure displacement ranging from
fractional millimeter to centimeter.
2) Acting as a secondary transducer, LVDT can be used as a
device to measure force, weight and pressure, etc.
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Linear Variable Differential Transformer (LVDT)
E.g. An LVDT produces an rms output voltage of 2.6 V for
displacement of 0.4 μm. Calculate the sensitivity of LVDT.
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Rotary Variable Differential Transformer (RVDT)
• RVDT is an electro-mechanical transducer that provides
a variable AC output voltage that is proportional to the
angular displacement of its input shaft.
• As RVDT is an AC-controlled device, there is no
electronic component inside it.
• Also, the electrical output of RVDT is obtained by the
difference in secondary voltages of the transformer, so it
is also called a differential transformer.
• The core of this transducer is cylindrical iron core and
may be rotated between the windings by means of a
shaft.
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Rotary Variable Differential Transformer (RVDT)
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Rotary Variable Differential Transformer (RVDT)
Condition 1: When shaft is at null position, the emf induced in
both the secondary windings are equal but opposite in phase.
Therefore, the differential output potential is zero.
E1 = E2
E0 = E1 - E2 = 0
Condition 2: When the shaft moves in clockwise direction, more
portion of the core comes across the winding S1.
E1 > E2
E0 = E1 - E2 = positive
Condition 3: When shaft moves in anticlockwise direction, more
portion of the core comes across the winding S2.
E1 < E2
E0 =E1 - E2 = negative
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Accelerometer
Acceleration transducers (accelerometers) are used to measure
acceleration as well as shock and vibration.
Piezoelectric Accelerometer
Consists of a piezoelectric quartz crystal on which an accelerative
force, whose value is to be measured, is applied.
Due to the special self-generating property, the crystal produces a
voltage that is proportional to the accelerative force.
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Accelerometer: Piezoelectric Accelerometer
44
Accelerometer: Piezoresistive Accelerometer
Work by measuring the electrical resistance of a material when
mechanical stress is applied.
Instead of sensing the capacitance changes in the seismic mass, a
piezoresistive accelerometer takes advantage of the resistance
change of piezoresistive materials to covert mechanical strain to a
DC output voltage
Widely used in automobile safety testing including anti-lock
braking system, safety airbags and traction control system as well
as weapon testing and seismic measurements.
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GPS Sensor
GPS stands for Global Positioning System.
The system contains satellites and ground based control
installations. GPS sensor consists of surface mount chip which
processes signals from GPS satellites using a small rectangular
antenna, often mounted on the top of the GPS chip.
GPS module is usually small board on which GPS sensor is
mounted with additional components.
GPS receiver is a device which includes data display and other
components such as memory for data storage in addition to GPS
module .
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GPS Sensor
The GPS system consists of three segments i.e., space segment,
control segment, user segment.
Space segment contains about 31 satellites as of August 2018
which are located in the orbit about 12,500 miles above earth.
Hence each of these satellites circle two times in 24 hours.
Control segment contains command, control and monitoring
stations.
User segment consists of receiving devices (e.g. both government
and private).
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GPS Sensor Working
As shown in figure, about four satellites are needed to
determine a position on the earth in 3 dimensional space.
Each of these satellites carry multiple atomic clocks which
maintain precise time and pseudo random number
generator in the form of linear feedback shift register.
GPS receiver can distinguish signals from at least four
satellites by comparing their received pseudo random bit
sequences and can calculate receiver's distance to each of
these satellites by comparing arrival times of satellite
signals.
48
Bluetooth Sensors
The Bluetooth Low Energy is a short- range, low-power with a less-
data-rate wireless communication protocol
Its protocol stack is designed in such a way that it competently
transfers insignificant amounts of data with less consumption of
power.
Due to this, Bluetooth Low Energy is the most preferred wireless
protocol for battery-operated applications.
49
Bluetooth Sensors
Bluetooth sensor is a device that helps us connect to
GPS and IPS (Indoor Positioning System) technology.
After establishing that link, we perform tasks, such as
sending data about a vehicle’s current state outdoors or
indoors.
These sensors require no wiring for connection as the
Bluetooth technology does it on its own.
With this technology, we can connect two devices for
data transfer.
Bluetooth sensors are used in different applications.
They are easy to install, consume less energy, and ensure
reliable connectivity
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Bluetooth Beacon sensors
Bluetooth Beacon sensors are small transmitters that broadcast
signals to close portable devices using Bluetooth Low Energy
technology .
They have an action range of around 90 meters and can only
transmit data but cannot receive it. Once the sensor detects the
nearby devices, it sends digital messages to the targeted devices.
Currently, beacons are used proportionally with mobile applications.
These mobile applications obtain a unique identifier to perform
several functions, such as triggering a location-based action and
tracking customers.
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Range Sensors
52
Triangulation Method
Geometrical images to establish a distance measurement
e.g. project a well defined light pattern (e.g. point, line) onto the
environment.
reflected light is than captured by a photo-sensitive line or
53
Ultrasonic Ranging Sensor
An ultrasonic sensor is an instrument that measures the
distance to an object using ultrasonic sound waves.
An ultrasonic sensor uses a transducer to send and receive
ultrasonic pulses that relay back information about an
object's proximity.
High-frequency sound waves reflect from boundaries to
produce distinct echo patterns.
Ultrasonic sensors work by sending out a sound wave at a
frequency above the range of human hearing. The transducer
of the sensor acts as a microphone to receive and send the
ultrasonic sound.
The sensor determines the distance to a target by measuring
time lapses between the sending and receiving of the
ultrasonic pulse. 54
Working Principle of Ultrasonic Sensor
It sends an ultrasonic pulse out at 40kHz which travels through the
air and if there is an obstacle or object, it will bounce back to the
sensor.
By calculating the travel time and the speed of sound, the distance
can be calculated.
For presence detection, ultrasonic sensors detect objects regardless of
the color, surface, or material (unless the material is very soft like
wool, as it would absorb sound.)
To detect transparent and other items where optical technologies
may fail, ultrasonic sensors are a reliable choice.
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Laser Range Sensor
Laser distance sensors are designed for non-contact distance
measurements: laser gauges for measuring ranges up to 10m,
laser distance sensors for up to 270m.
These sensors are used for positioning and type classification
in machine building and handling equipment.
Here are applications for detections, measurements or
positioning. What different laser sensors have in common are
the advantages that the use of laser light provides.
A first advantage is the high light intensity, which enables
very accurate measurement, positioning or detection (down to
nanometers).
Another advantage is the measurement speed; this is very high
due to the use of light as a medium.
56
Working Principle of Laser Sensor
Laser distance sensors measure distances and allow it to take
measurements at great distances.
These distance sensors work on the basis of the Time-of-Flight (ToF)
principle, which means that the sensor emits a laser beam and
receives the reflection from it.
The time that elapses between sending and receiving the laser light
ensures that the laser distance sensor can internally determine the
distance. The distance over which the measurements can be taken
differs per series.
In signal processing, the time taken by the light to emit and the
time taken by the fight to reflect back are calculated.
The speed of Laser light emission is fixed. So, the object's distance
from the sensor can be calculated simply by using speed and time.
The sensor will generate an electrical signal according to the
distance sensed. This signal is either digital or analog.
57
Advantages and Disadvantages of Laser Sensor
Advantages
Measurements are very accurate.
Disadvantages
More expensive than analog measuring devices.
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Applications of Laser Sensors
Quality control
Aligning the railway track
Measuring wire diameter
Welding head position
Measure brake rotor thickness
Vehicle counting
Measuring the distance between two sheets
Checking wood thickness
Deviation control in the process
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Part II
Force Sensors,
Magnetic Sensors
&
Heading Sensors
60
Strain Gauge
A Strain gauge is a sensor whose resistance varies with applied
force; it converts force, pressure, tension, weight, etc., into a change
in electrical resistance which can then be measured.
The majority of strain gauges are foil types, available in a wide
choice of shapes and sizes to suit a variety of applications.
They consist of a pattern of resistive foil which is mounted on a
backing material.
They operate on the principle that as the foil is subjected to stress,
the resistance of the foil changes in a defined way.
61
Working of Strain Gauge
62
Strain Gauge Types
Based on principle of working :
Mechanical
Electrical
Piezoelectric
Based on mounting :
Bonded strain gauge
Unbonded strain gauge
Based on construction :
Foil strain gauge
Semiconductor strain gauge
Photoelectric Strain gauge
63
Strain Gauge Applications
Advantages
There is no moving part.
Disadvantages
It is non-linear.
It needs to be calibrated.
Applications
Residual stress
Vibration measurement
Torque measurement
Strain measurement
64
Load Cell
Load cell is a sensor or a transducer that converts a load or
force acting on it into an electronic signal.
There are many different kinds of load cells.
Resistive load cells work on the principle of piezo-resistivity.
When a load/force/stress is applied to the sensor, it changes its
resistance. This change in resistance leads to a change in
output voltage when a input voltage is applied.
Capacitive load cells work on the principle of change of
capacitance which is the ability of a system to hold a certain
amount of charge when a voltage is applied to it. For
common parallel plate capacitors, the capacitance is directly
proportional to the amount of overlap of the plates and the
dielectric between the plates and inversely proportional to the
gap between the plates.
65
How does a resistive load cell works
A load cell is made by using an elastic member (with very
highly repeatable deflection pattern) to which a number of
strain gauges are attached.
67
How does a resistive load cell works
During a measurement, weight acts on the load cell’s metal spring
element and causes elastic deformation.
This strain (positive or negative) is converted into an electrical
signal by a strain gauge {SG) installed on the spring element.
We use Wheatstone bridge circuit to convert this change in
strain/resistance into voltage which is proportional to the load.
The four strain gauges are configured in a Wheatstone Bridge
configuration with four separate resistors connected as shown in
what is called a Wheatstone Bridge Network.
An excitation voltage - usually 10V is applied to one set of corners
and the voltage difference is measured between the other two
corners.
At equilibrium with no applied load, the voltage output is zero or
very close to zero when the four resistors are closely matched in
value. That is why it is referred to as a balanced bridge circuit.
68
Wheatstone Bridge Circuit
69
Wheatstone Bridge Circuit
When the metallic member to which the strain gauges
are attached, is stressed by the application of a force, the
resulting strain - leads to a change in resistance in one (or
more) of the resistors.
This change in resistance results in a change in output
voltage. This small change in output voltage (usually
about 20 mV of total change in response to full load) can
be measured and digitized after careful amplification of
the small milli-volt level signals to a higher amplitude 0-
5V or 0-10V signal.
These load cells have been in use for many decades now,
and can provide very accurate readings but require many
tedious steps during the manufacturing process.
70
Magnetic Sensor
Magnetic sensors convert the change/magnitude of a
magnetic field into an electrical signal
Magnetic sensors are the solid state devices used in
A magnet brought Into close contact with a coil will Increase the magnetic flux density In
72
the coil and generate induced electromotive force and induced current.
Magneto-resistive Sensor
These sensors are used to measure electrical resistance as a
function of the applied magnetic field.
It works on the principle of AMR (Anisotropic magneto-
resistance) or MR (Magneto-resistance) or GMR (giant
magneto-resistive) or TMR (tunnel magneto-resistive) effect.
An MR sensor element is a magnetic sensor element using
the Magneto-Resistance effect (MR effect).
There are a number of MR sensor types using different
operating principles.
The following describes the basic MR effect.
The MR effect is a phenomenon where resistance changes with
changes in a magnetic field.
It is an effect that occurs in magnetic materials (for example,
iron, nickel or cobalt).
73
Hall Effect Sensors
Hall-effect sensors are the linear transducers that are used to
measure the magnitude of the magnetic field. Working on the
principle of Hall Effect, these sensors generate a Hall voltage when
a magnetic field is detected, which is used to measure the magnetic
flux density.
These sensors are also used for detecting proximity, position, speed,
etc.
74
Hall Effect Sensors
When a semi-conductor with current running through it
and a magnet is placed so that its magnetic field runs
perpendicular to this current, the magnetic field of the
current reacts to the magnetic field of the permanent
magnet, causing the electrons flowing through the
conductor to be pulled to one side of the conductor, due to
the Lorentz force.
This creates a potential difference, referred to as Hall
voltage, in the conductor.
The magnitude of the Hall voltage is proportional to the
strength of the magnetic field.
The Lorentz force is the force that a particle experiences
due to electrical and magnetic fields.
75
Current Sensors
A current sensor is a device that detects electric current
in a wire and generates a signal proportional to that
current.
The generated signal could be analog voltage or current
or a digital output.
The generated signal can be then used to display the
measured current in an ammeter, or can be stored for
further analysis in a data acquisition system, or can be
used for the purpose of control.
Types of Current Sensor
Shunt Resistor
Hall Effect Current Sensors
Current Transformer
76
Current Sensor Working Principle
Once current is supplied throughout a circuit or a wire then a
voltage drop takes place and also magnetic field will be
generated nearby the current-carrying conductor.
So, there are two kinds of current sensing direct current sensing &
indirect current sensing.
Direct sensing mainly depends on Ohm's law whereas indirect
sensing depends on Ampere's & Faraday's law.
Direct Sensing is used to measure the voltage drop associated
with the flow of current throughout passive electrical
components.
Similarly, indirect sensing is used to measure the magnetic field
nearby a current-carrying conductor. After that, magnetic field
which is produced is used for inducing proportional current or
voltage which is afterward changed to use measurement or
control purposes. 77
Heading Sensors
An earth's magnetic field sensor, a compass or its
electrical equivalent, the magnetic fluxgate, that
provides the heading information from which the
Autopilot computes steering commands.
The Heading Sensor is central to the control of your
Autopilot.
Gyroscopes and compasses are the two most widely
employed sensors for determining the heading of a
mobile robot (besides, of course, odometry).
Gyroscopes can be classified into two broad
categories:
a) Mechanical gyroscopes
b) Optical gyroscopes. 78
Compass Sensors
Compass sensor is the device whose function is to give the
right directions with respect to the North and South magnetic
poles of the earth.
The needle present on a compass always points towards the
geometric North of Earth.
This device makes use of principles of magnetism for
operation.
Digital Compass Sensor is actually a magnetometer that can
measure the Earth's magnetic field.
The resistance of the magnetic sensor present in
magnetometer changes in proportional to the magnetic field
present in a particular direction.
The magnetometer measures the magnetic field strength
and orientation. 79
Compass Sensors
There are two configurations of Compass Sensors available
based on there working principle.
They are the Magnetic Compass and Gyro Compass.
Magnetic Compass contains a magnetic element to detect
the magnetic field.
This magnetic element aligns itself with magnetic lines of
Earth's magnetic field.
Magnetic Compass points towards the magnetic pole of the
Earth, whereas Gyro compass points towards the true poles
of the earth.
Gyro compass consists of a rapidly spinning wheel.
80
Compass Sensors
Gyroscope sensor is a device that can measure and maintain the
orientation and angular velocity of an object.
These are more advanced than accelerometers. These can measure
the tilt and lateral orientation of the object whereas accelerometer
can only measure the linear motion.
Gyroscope sensors are also called as Angular Rate Sensor or
Angular Velocity Sensors. These sensors are installed in the
applications where the orientation of the object is difficult to sense
by humans.
Measured in degrees per second, angular velocity is the change in
the rotational angle of the object per unit of time.
The concept of Coriolis force is used in Gyroscope sensors.
In this sensor to measure the angular rate, the rotation rate of the
sensor is converted into an electrical signal.
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Inclinometer
An inclinometer measures angles of slope, elevation, or
depression of an object with respect to gravity's direction. It is
also known as a tilt indicator, tilt sensor, tilt meter, etc.
The resulting measurement is either given an angular
measurement (degrees, minutes, seconds etc.) or as a
percentage with reference to a level zero plane.
Inclinometers use an accelerometer to measure these angles.
They monitor the effect of gravity on a small mass suspended
in an elastic support structure so that when the device tilts,
this mass moves and causes a change of capacitance
between the mass and the support.
The tilt angle is calculated from the difference in measured
capacitance
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Inclinometer
Given two electrodes – one fixed, and one with a movable mass
suspended by springs. The fixed electrode represents a perfectly level
inclinometer in a horizontal position, where the base capacitance is
measured. If the inclinometer is tilted (represented by the movable
mass), the position relative to the horizontal position is changed,
and the capacitance is again measured at this point. The change in
capacitance when the electrode is tilted is measured and this is used
to measure the incline value.
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