IOT SENSORS

IOT SENSORS
(PE674EC)
Module 2
Types of Sensors
S. RAVIKUMAR, MVSREC
What you will learn:
1. Types of Sensors
2. Resistive Sensors
3. Temperature Sensors
4. Capacitive Sensors
5. MEMS Sensors
6. SAW Sensors
7. Smart Sensors

Types of Sensors
Based on the energy requirement:
Passive sensors: A passive sensor does not need any additional energy
source and directly generates an electric signal in response to an
external stimulus; that is, the input stimulus energy is converted by the
sensor into the output signal.
The examples are a thermocouple, a photodiode, and a piezoelectric
sensor.
Active sensors: The active sensors require external power for their
operation, which is called an excitation signal. That signal is modified by
the sensor to produce the output signal.
Example: Ultrasonic sensor
Example of an active sensor is a resistive strain gauge in which
electrical resistance relates to a strain. To measure the resistance of a
sensor, electric current must be applied to it from an external power
source.

Types of Sensors
Based on the reference:
Absolute sensors: An absolute sensor detects a stimulus in reference to
an absolute physical scale that is independent on the measurement
conditions. An example of an absolute sensor is a thermistor: a
temperature-sensitive resistor. Its electrical resistance directly relates
to the absolute temperature scale of Kelvin.
Relative sensors: A relative sensor produces a signal that relates to
some special case. thermocouple—is a relative sensor. It produces an
electric voltage that is function of a temperature gradient(difference)
across the thermocouple wires.

Types of Sensors
Based on the working principle:
i. Resistive sensors
ii. Temperature sensors
iii. Strain gauge sensors
iv. Pressure sensors
v. Capacitive sensor
vi. Piezoelectric sensor
vii. Force sensor
viii.Velocity sensor
ix. Acceleration sensor
x. Flow sensor
xi. Ultrasonic sensors
xii. Infrared sensors
xiii.Surface Acoustic Wave (SAW) sensors
xiv.MEMS sensors
xv. Smart sensors

Resistive Sensors
• A resistive sensor is a resistor whose resistance changes according
to some physical change in the environment of observation.
• Examples: Potentiometer, Photoresistor, Thermistor

Resistive Sensors
Potentiometer
• The resistance varies with physical movement.
• A resistive potentiometer (pot) consists of a resistance element
provided with a sliding contact, called a wiper.
• The motion of the sliding contact may be translatory or rotational.
• Translatory resistive elements are linear (straight) devices.
• Rotational resistive devices are circular and are used for the
measurement of angular displacement

Resistive Sensors
Photoresistor
• A photoresistor (also known as light dependent resistor-LDR) is a
passive component that decreases resistance with respect to
receiving luminosity(light) on the components sensitive surface.

Resistive Sensors
Thermistor
• Resistance varies with heat.
• Thermistors are devices whose electrical resistance varies with
change in temperature.

Resistive Sensors
Thermistor
There are two types of thermistors:
Negative Temperature Coefficient (NTC) Thermistor: In an NTC
thermistor, when the temperature increases, resistance decreases. And
when temperature decreases, resistance increases. Hence in an NTC
thermistor temperature and resistance are inversely proportional.
These are the most common type of thermistor.
Positive Temperature Coefficient (PTC) Thermistor: When temperature
increases, the resistance increases. And when temperature decreases,
resistance decreases.

Resistive Sensors

Resistive Sensors
Thermistor Applications
• Digital thermometers (thermostats)
• Automotive applications (to measure oil and coolant temperatures in
cars & trucks)
• Household appliances (like microwaves, fridges, and ovens)
• Circuit protection (i.e. surge protection)
• Rechargeable batteries (ensure the correct battery temperature is
maintained)
• To measure the thermal conductivity of electrical materials
• Useful in many basic electronic circuits (e.g., as part of a beginner
Arduino starter kit)
• Temperature compensation (i.e. maintain resistance to compensate
for effects caused by changes in temperature in another part of the
circuit)
• Used in Wheatstone bridge circuits

Temperature Sensors
Thermocouple
• It is a type of temperature sensor, which is made by joining two
dissimilar metals at one end. The joined end is referred to as the HOT
JUNCTION. The other end of these dissimilar metals is referred to as
the COLD END or COLD JUNCTION.
• The cold junction is formed at the last point of thermocouple
material. If there is a difference in temperature between the hot
junction and cold junction, a small voltage is created. This voltage is
referred to as an EMF (electro-motive force) and can be measured
and in turn used to indicate temperature.

Temperature Sensors

Temperature Sensors
Resistance Temperature Detectors (RTD):
- The RTD is a temperature-sensing device whose resistance changes
with temperature.
- An RTD is a temperature sensor which measures temperature using
the principle that the resistance of a metal changes with
temperature. In practice, an electrical current is transmitted through
a piece of metal (the RTD element or resistor) located in proximity to
the area where temperature is to be measured. The resistance value
of the RTD element is then measured by an instrument. This
resistance value is then correlated to temperature based upon the
known resistance characteristics of the RTD element.

Temperature Sensors
Resistance Temperature Detectors (RTD):
- Typically built from platinum, though devices made from nickel or
copper are not uncommon, RTDs can take many different shapes like
wire wound, thin film.
- To measure the resistance across an RTD, apply a constant current,
measure the resulting voltage, and determine the RTD resistance.
RTDs exhibit fairly linear resistance to temperature curves over
their operating regions
- RTD’s are commonly used in sensing air and liquid temperatures in
pipes and ducts, and as room temperature sensors. The resistance
of RTD elements varies as a function of temperature. Some elements
exhibit large resistance changes, linear changes, or both over wide
temperature ranges.

Temperature Sensors
Applications of temperature sensors:
- Monitoring:
Portable equipment
CPU temperature
Battery temperature
Ambient temperature
- Compensation:
Oscillator drift in cellular phones
Thermocouple cold junction compensation
- Control:
Battery charging
Process control

Strain Gauge Sensors
• A Strain gauge (sometimes referred to as 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.
• Strain is defined as the amount of deformation experienced by the body in the direction of
force applied, divided by initial dimensions of the body.

• Strain is defined as the amount of
deformation experienced by the
body in the direction of force
applied, divided by initial
dimensions of the body.

• Each strain gauge is composed of a metal foil insulated by a flexible
substrate, as shown in the figure. The two leads pass a current
through the gauge, and as the surface of the object being measured
stretches or contracts, the change in resistance is measured. This
change in resistance is proportional to the change in length on the
surface of the object being tested, as shown in the equation below.
Strain gauges work by measuring the change in electrical resistance
across a thin conductive foil. The gauge factor (or “gage factor”) is the
sensitivity of the strain gauge (usually 2). It converts the change in
resistance to the change in length.

• Each strain gauge is composed of a metal foil
insulated by a flexible substrate, as shown in the
figure. The two leads pass a current through the
gauge, and as the surface of the object being
measured stretches or contracts, the change in
resistance is measured. This change in resistance
is proportional to the change in length on the
surface of the object being tested, as shown in the
equation below. Strain gauges work by measuring
the change in electrical resistance across a thin
conductive foil. The gauge factor (or “gage factor”)
is the sensitivity of the strain gauge (usually 2). It
converts the change in resistance to the change in
length.

Load testing of aircraft wing

Weight measurement

Cable bridge colomn
monitoring

Strain gauge
• The metallic strain gage consists of a very fine wire or, more commonly, metallic foil
arranged in a grid pattern.
• The grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel
direction.
• The grid is bonded to a thin backing called the carrier, which is attached directly to the test
specimen.
• Therefore, the strain experienced by the test specimen is transferred directly to the strain
gage, which responds with a linear change in electrical resistance.

Strain Gauge measurement

Capacitive Sensors
• A capacitive sensor uses the characteristics of a capacitor and its electrical field to form a
sensor.
• When a voltage is applied across the plates, a charge accumulates on each plate, creating an
electric field across the plates.
• The amount of charge a capacitor can store, known as the capacitance, depends on the size of
the plates, the distance between them and the dielectric constant of the material between
them.

Capacitive Sensors
• The capacitance (C) of a parallel plate capacitor with plate area (A) separated by distance (d) is given as
below.
C = ƐoƐrA / d
• The capacitance can be varied by varying the following:
Area of plate
Separation between the plates
Changing the dielectric material between the plates.

Capacitive Sensors
Based on variation of area of plate:
• capacitance of parallel plate capacitor is
directly proportional to the area of plate,
therefore, this property can be employed to
measure the displacement.
• For the measurement of displacement using
capacitive sensor, one plate of parallel plate
capacitor is kept fixed while the other plate
is allowed to displace.

Capacitive Sensors
Sensors Using Change in Distance between the
Plates:
• A Capacitive sensor can also be designed to
respond to linear displacement by attaching
one of the plates of capacitor to the moving
object and keeping the other plate fixed.
• When the object moves, the distance
between the plate changes and hence the
capacitance changes.
• The capacitance varies with separation
between the plates because capacitance is
inversely proportional to the distance
between the plates.

Capacitive Sensors
Plates:
• Applications
• Position sensing
• Microscope focusing
• Lens alignment
• Thickness measurements(Semiconductor
wafers, Sheet metal thickness)

Capacitive Sensors
Plates:
• Accelerometer
• Capacitive accelerometers, also known as
vibration sensors, rely on a change in
electrical capacitance in response to
acceleration.
• Accelerometers utilize the properties of an
opposed plate capacitor for which the
distance between the plates varies
proportionally to applied acceleration, thus
altering capacitance. This variable is used in
a circuit to ultimately deliver a voltage signal
that is proportional to acceleration.

Capacitive Sensors
Sensor using change in dielectric constant:
• The capacitance of parallel plate capacitor is
directly proportional to dielectric constant
(Ɛ) for a given plate area and separation.
• This principle is also utilized in capacitive
sensor for the measurement of linear
displacement.

Capacitive Sensors
Sensor using change in dielectric constant:
• The capacitance of parallel plate capacitor is
directly proportional to dielectric constant
(Ɛ) for a given plate area and separation.
• Di-electric constant of
• Apple juice : 78.2
• Vacuum : 1.0
• Air : 1.0006
• Water : 80
• Automotive oil : 2.1

Capacitive Sensors
Advantages of capacitive sensors:
• The capacitive sensors require small
physical stimuli to operate. So they can be
used in small systems.
• They are very sensitive. They are accurate
up to 0.005 %.
• The loading effect is minimum in this sensor
because of high input impedance.
• The power requirement for capacitive
sensors is very less.

Capacitive Sensors
Disadvantages:
• Metallic parts of the sensors must be well
insulated to avoid stray capacitance.
• The capacitive sensors show non-linear
behavior at the edges.
• The capacitance may change due to dust
moisture etc.
• They are temperature sensitive.

Capacitive Sensors
Applications of capacitive sensors:
• Measurement of liner and angular
displacement.
• Measurement of force and pressure.
• Humidity, liquid level etc.
• Mobile touch screens and other input
devices.

Ultrasonic Sensors
• An ultrasonic sensor can convert electrical
energy into acoustic waves and vice versa.
• The acoustic wave signal is an ultrasonic
wave traveling at a frequency above 18kHz.

MEMS Sensors
• The term MEMS stands for micro-electro-
mechanical systems.
• MEMS are low-cost, and high accuracy inertial
sensors and these are used to serve an
extensive range of industrial applications.
• This sensor uses a chip-based technology
namely micro-electro-mechanical-system.
• These sensors are used to detect as well as
measure the external stimulus like pressure.
• MEMS are microscopic integrated devices that
are a combination of electronics, electrical and
mechanical elements, all working together for a
single functional requirement.

MEMS Sensors

MEMS Sensors
• MEMS is an integration of both active and passive
components into a single silicon substrate with
the help of advanced IC manufacturing
technology.
• The active components are the Sensors and
Actuators while the passive components are the
passive electronic systems and passive
mechanical systems.

MEMS Sensors
Types of MEMS
The common types of MEMS sensors are obtainable
within the market are
MEMS accelerometers
MEMS gyroscopes
MEMS pressure sensors
MEMS magnetic field sensors

MEMS Sensors
MEMS accelerometers
• MEMS accelerometer is a micro-electromechanical device that is used to measure acceleration and
force.
• There are many types of accelerometer present in the market; they can be divided according to the
force that is to be measured.
• MEMS-based accelerometer with capacitors is typically a structure that uses two capacitors formed
by a moveable plate held between two fixed plates. Under zero net force the two capacitors are equal
but a change in force will cause the moveable plate to shift closer to one of the fixed plates,
increasing the capacitance, and further away from the other fixed reducing that capacitance. This
difference in capacitance is detected and amplified to produce a voltage proportional to the
acceleration. The dimensions of the structure are of the order of microns.

MEMS Sensors
MEMS accelerometers
• MEMS-based accelerometer with capacitors
is typically a structure that uses two
capacitors formed by a moveable plate held
between two fixed plates. Under zero net
force the two capacitors are equal but a
change in force will cause the moveable
plate to shift closer to one of the fixed plates,
increasing the capacitance, and further away
from the other fixed reducing that
capacitance. This difference in capacitance is
detected and amplified to produce a voltage
proportional to the acceleration. The
dimensions of the structure are of the order
of microns.

MEMS Sensors
MEMS accelerometers applications
• These MEMS sensors have different applications such as
• gravity sensor,
• digital compass,
• GPS tracking, and
• smartphones for various controls like switch between landscape and portrait modes and to
switch between the taps or pocket mode operations, used for anti-blur capture,
• gaming joysticks as step counters, used for stability of images in camcorders, the 3D
accelerometer is used in Nokia 5500 for tap gestures for example; you can change MP3’s by
tapping on the phone when it is inside the pocket.

MEMS Sensors
MEMS gyroscopes
• MEMS gyroscopes or MEMS angular rate sensors is a micro-electromechanical device
which is small, with inexpensive sensors which are used to measure angular velocity or
rotational motion or displacement.
• The unit of angular velocity is measured in revolutions per second (RPS) or degrees per
second. It simply measures the speed of rotation.
• Mechanically, Gyroscopes is a spinning wheel or disc mounted on an axle and the axle is
free to assume directions.
• They rely on the same principle that is vibrating objects undergoing rotation.

MEMS Sensors
MEMS gyroscopes
• Every MEMS gyroscopes have some form of the oscillating component from where
acceleration can be detected.
• There are three types of Vibratory Gyroscopes: Vibrating Beam, Vibrating Disk, and
Vibrating Shell.
• MEMS gyroscopes are used for vehicle stability control and in image stabilization, airbag
systems, Industrial robotics, Photography, automotive roll-over prevention, Car navigation
systems, and many other potential applications.

MEMS Sensors
MEMS magnetic field sensors
• MEMS magnetic field sensors are small-scale microelectromechanical systems that help in
detecting and measuring magnetic fields.
• Sensors detect changes in force so that voltage frequency can be easily measured
electronically. It can be placed close to the measurement location and thereby achieve
higher spatial resolution.
• It combines integrated bulk Hall cell technology and instrumentation circuitry to minimize
temperature-related lot associated with silicon Hall cell characteristics.
• MEMS magnetic field sensors are used for the linear angle, speed, rotational speed, linear
position and position measurements in industrial, consumer applications, and automotive.

MEMS Sensors
MEMS Advantages
The advantages of MEMS sensor include the following.
• The manufacturing of MEMS is semiconductor IC manufacturing like low-cost mass
invention, consistency is also essential to MEMS devices.
• The size of sensor sub-components will be within 1 to 100 micrometers range as well as the
MEMS device size will determine 20 micro-meter to a millimeter range.
• Power consumption is very low.
• Simple to incorporate into systems or change
• The thermal constant is small
• These can be highly opposed to shock, radiation, and vibration.
• Better thermal development tolerance
• Parallelism

MEMS Sensors
Applications of MEMS
• MEMS sensors are used in different domains which include automotive, consumer,
industrial, military, biotechnology, space exploration, and commercial purposes which
include inkjet printers, accelerometers within modern cars, consumer electronics, in
personal computers, etc.
• The best examples of MEMS devices mainly include adaptive optics, optical cross-connects,
airbag accelerometers, mirror arrays for TVs & displays, steerable micromirrors, RF MEMS
devices, not reusable medical devices, etc.

Surface Acoustic Wave (SAW) Sensors
• Surface acoustic wave sensors are a class of microelectromechanical systems (MEMS) which rely on
the modulation of surface acoustic waves to sense a physical phenomenon.
• An acoustic wave sensor uses mechanical (acoustic) waves to sense multiple phenomena from the
device's environment, which are registered as changes in the wave's phase, amplitude, and/or
frequency relative to some reference.

For surface acoustic wave (SAW) sensors, the device operation itself is fairly simple:
1.An electromagnetic impulse signal is sent to the device via wired connection or wireless antenna
2.The electromagnetic signal is transduced into a surface acoustic wave by an interdigital transducer (IDT)
3.The surface acoustic wave propagates along the surface of the substrate
4.The acoustic impulse response wave is transduced back into an electromagnetic signal
5.The electromagnetic response signal is transmitted for processing

Basic device components
The basic components of a SAW sensor are:
• A piezoelectric substrate which generates electrical charges from mechanical force, and vice versa
• At least one interdigital transducer (IDT) to convert electromagnetic waves to acoustic waves, and vice versa
• An area of propagation, in some cases conceived as a delay line (see below), through which the acoustic wave propagates

Applications
• mass
• temperature
• pressure
• stress, strain, and torque
• acceleration
• friction
• humidity and dewpoint
• UV radiation
• magnetic fields
• viscosity

Smart Sensors
What is a smart sensor?
A smart sensor is a device that takes input from the physical environment and uses built-in compute
resources to perform predefined functions upon detection of specific input and then process data before
passing it on.

Smart Sensors
• Smart sensors enable more accurate and automated collection of environmental data with less
erroneous noise amongst the accurately recorded information.
• These devices are used for monitoring and control mechanisms in a wide variety of environments
including smart grids, battlefield reconnaissance, exploration and many science applications.

Smart Sensors
• Compute resources are typically provided by low-power mobile microprocessors.
• At a minimum, a smart sensor is made of a sensor, a microprocessor and communication technology of
some kind. The compute resources must be an integral part of the physical design -- a sensor that just
sends its data along for remote processing isn't considered a smart sensor.

Smart Sensors
Properties of a smart sensor?
• Low cost, so they can be economically deployed in large numbers
• Physically small, to “disappear” unobtrusively into any environment
• Wireless, as a wired connection is typically not possible
• Self-identification and self-validation
• Very low power, so it can survive for years without a battery change, or manage with energy
harvesting
• Robust, to minimize or eliminate maintenance
• Self-diagnostic and self-healing
• Self-calibrating, or accepts calibration commands via wireless link
• Data pre-processing, to reduce load on gateways, PLCs, and cloud resource

Smart Sensors
Types of smart sensor?
• Level sensors. A level sensor is used to measure the volume of space taken up in a container. A
vehicle's fuel gauge might be connected to a level sensor that monitors the level of fuel in the tank.
• Temperature sensors. A temperature sensor is a sensor that can monitor a component's temperature
so a corrective action can be taken if necessary. In an industrial setting for example, a temperature
sensor can be used to make sure machinery is not overheating.
• Pressure sensor. Pressure sensors are often used to monitor the pressure of gasses or fluids in a
pipeline. A sudden drop in pressure might indicate a leak or a flow control issue.
• Infrared sensors. Some infrared sensors, such as those used in thermal imaging cameras or
noncontact infrared thermometers are used for temperature monitoring. Other infrared sensors are
optical sensors tuned to a frequency that enables them to see light in the infrared spectrum. These
types of sensors are used in medical equipment, such as pulse oximetry devices, and in electronic
devices designed to be operated by remote control.
• Proximity sensors. A proximity sensor is used to detect the location of a person or object with relation
to the sensor. In retail environments, proximity sensors can track customer movements throughout the
store.

Smart Sensors
Applications of smart sensors
Industrial:
In industries machines and equipment are monitored and controlled for pressure, temperature,
humidity level, and also for vibrations. A Smart Sensor can monitor all these parameters at one go
and also connects to the network without any other hardware assistance. This helps to maintain
machinery and also ensure safety for employees handling the machinery.
Finger Recognition:
A fingerprint sensor scans and captures a digital image of the fingerprint pattern. The image
captured is called live scan. Using that live scan a biometric template will be created and stored for
matching.
Pattern Recognition:
When the sensor detects the contours of an object, it compares with them and also with models in
a reference image.

Smart Sensors
Telecommunication:
A smart card similar to SIM card, called a Wireless Identity Module (WIM), Using this card e-
commerce transaction can be done with 100 percent security using encryption and digital signature.
Smart Dust:
Smart dust is a hypothetical wireless network of tiny microelectromechanical (MEMS) sensors,
robots, or devices, which can detect (for example) light, temperature, or vibration. The devices will
eventually be the size of a grain of sand, or even a dust particle, with each mote having self-contained
sensing, computation, communication, and power.
Biomedical Applications:
Many smart sensors for biomedical applications have also been developed by using chip
technology., biochips Cyto-sensor micro-physio-meter: biological applications of silicon technology.

Smart Sensors
MEMS and Process Control:
MEMS (Micro-Electro-Mechanical Systems) are very small physical systems. MEMS sensors are
a combination of electrical and mechanical components. MEMS uses a modified integrated circuit
(computer chip) fabrication techniques and materials to create these very small mechanical devices.
Defence Applications:
Smart cameras can detect objects, perform crowd pattern analysis, secure zone intrusion
detection and so on by using advanced software analytics and report alarms using IP network
facilities in them. Smart Sensors are also used in monitoring EMI fatigue loading, thermal cycling
vibration and shock levels, corrosive environments.

THANQ YOU

IOT SENSORS

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