UNIT IV OPTICAL, PRESSURE AND TEMPERATURE SENSORS

UNIT IV OPTICAL, PRESSURE AND
TEMPERATURE SENSORS
MR3491 SENSORS AND INSTRUMENTATION
Prepared by
A.R.SIVANESH
Assistant Professor
Department of Mechanical Engineering
Sri Ranganathar Institute of Engineering and
Technology, Coimbatore

SYLLABUS
Photo conductive cell, photo voltaic, Photo resistive,
LDR – Fiber optic sensors – Pressure – Diaphragm,
Bellows, Piezoelectric – Tactile sensors, Temperature –
IC, Thermistor, RTD, Thermocouple. Acoustic Sensors –
flow and level measurement, Radiation Sensors - Smart
Sensors - Film sensor, MEMS & Nano Sensors, LASER
sensors.
Prepared by A.R.Sivanesh AP/Mech

Photo conductive cell

Photo voltaic Cell

Photo resistive/
LDR

Fiber optic
sensors

Pressure Sensor–
Diaphragm,
Bellows,
Piezoelectric

Tactile Sensor

Temperature
sensors

Temperature sensors
• Temperature conveys the state of a mechanical system in
terms of expansion or contraction of solids, liquids or gases,
change in electrical resistance of conductors,
semiconductors and thermoelectric emfs
• bimetallic strips
• Thermocouples
• thermistors

Bimetallic strips

• Bimetallic strips are used as thermal switch in controlling the
temperature or heat in a manufacturing process or system
• It contains two different metal strips bonded together
• The metals have different coefficients of expansion. On heating
the strips bend into curved strips with the metal with higher
coefficient of expansion on the outside of the curve
• As the strips bend, the soft iron comes in closer proximity of
the small magnet and further touches.
• Then the electric circuit completes and generates an alarm.
• In this way bimetallic strips help to protect the desired application
from heating above the pre-set value of temperature
Bimetallic strips

Thermistors
• Thermistors follow the principle of decrease in resistance with
increasing temperature.
• The material used in thermistor is generally a semiconductor material
such as a sintered metal oxide (mixtures of metal oxides, chromium,
cobalt, iron, manganese and nickel) or doped polycrystalline ceramic
containing barium titanate (BaTiO3) and other compounds

• As the temperature of semiconductor material increases the number of electrons able to move
about increases which results in more current in the material and reduced resistance
• Thermistors are available in the form of a bead (pressed disc), probe or chip
• It has a small bead of dimension from 0.5 mm to 5 mm coated with ceramic or glass material.
The bead is connected to an electric circuit through two leads. Toprotect from the environment,
the leads are contained in a stainless steel tube.
Applications of Thermistors
• Tomonitor the coolant temperature and/or oil temperature inside the engine
• Tomonitor the temperature of an incubator
• Tocontrol the operations of consumer appliances such as toasters, coffee makers, refrigerators,
freezers, hair dryers, etc.
Thermistors

Thermocouple
• Thermocouple works on the fact that when a junction of dissimilar
metals heated, it produces an electric potential related to
temperature As per Thomas Seebeck (1821),
• when two wires composed of dissimilar metals are joined at both
ends and one of the ends is heated, then there is a continuous
current which flows in the thermoelectric circuit
• The net open circuit voltage (the Seebeck voltage) is a function of
junction temperature and composition of two metals

Thermocouple

Applications of Thermocouples
• To monitor temperatures and chemistry throughout the steel
making process
• Testing temperatures associated with process plants e.g.
chemical production and petroleum refineries
• Testing of heating appliance safety
Thermocouple

Acoustic sensors

The SAW (Surface Acoustic Wave) sensor is a new type of micro-sensor that has developed in
recent years. It is an acoustic surface wave device as a sensor element that will be measured
through the acoustic surface wave device. The speed or frequency of the wave is reflected and
converted into the sensor output by the electrical signal. Acoustic surface wave sensors can
accurately measure physical, chemical information (such as temperature, stress, gas density).
Due to the small size, the surface wave device is known as a new era of wireless and small
sensors; at the same time, it has strong compatibility with integrated circuits and has been
widely used in the field of simulated digital communication and sensing.
The SAW sensor can focus the signal on the surface of the substrate. It has a high operating
frequency, high information-sensitive accuracy. It can quickly convert the detected information
into electrical signal output, with real-time information detection characteristics. Additionally,
SAW sensors also have the advantages of miniaturization, integrated, passive, low cost, low
power, direct frequency signal output.
Acoustic sensors

There has been formed a variety of types including acoustic surface wave pressure sensors, acoustic
surface wave temperature sensors, acoustic surface wave biological genes, acoustic surface wave
chemical gas phase sensors, and intelligent sensors.
The sound surface wave is an elastic wave propagating in a solid shallow surface, with a variety of
modes. Rayleigh is the most widely used sound surface wave. Different types of sound surface
waves have different characteristics, and the sensors made of them can be applied to different
occasions detection.
The two basic configurations of the acoustic surface wave sensor are delay lines and resonators. and
Figure 1 shows the sensor structure category of delay linear and resonant type. The delayed line-type
and resonurable sound surface wave sensor is constructed by a piezoelectric substrate, a fork finger
transducer, and a transmitting gate.
Acoustic sensors

SAW sensor working principle
The SAW device typically uses piezoelectric crystals (e.g., quartz crystals, etc.) as a medium. Then
it generates sound waves by an additional positive voltage and propagating via a substrate, and then
converted into an electrical signal output. The mainly active effect of the SAW sensor is the
piezoelectric effect. Various factors need to be considered when designing: such as relative
dimensions, sensitivity, efficiency, and the like. Generally, the signal frequency range of the
wireless passive surface wave sensor ranges from 40 MHz to several GHz. Figure 2 shows the
common structure commonly seen by the sound surface wave sensor, and the main part includes a
piezoelectric substrate, an antenna, a sensitive film, IDT, and the like. The sensitive layer of the
sensor achieves a change in frequency by changing the speed of the acoustic surface wave.
Acoustic sensors

Wireless passive SAW system package: transmitter, receiver, sound surface wave device,
communication channel. The transmitter and receiver combine a single module of the transceiver
or the interpreter. Figure 3 is a sound surface wave system and its interrelated base parts. The
reader transmits the power to the sound surface wave device, which can be a continuous wave or
pulse of the transceiver input. Generally, the power size obtained by the sound surface wave
device has a limit to reducing the maximum transmit power, thereby obtaining the same average
power. According to the isotropic radiator, the received signal is typically emitted by an efficient
radiation power antenna.
Acoustic sensors

Radiation Sensor

Radiation sensor is a type of actinometer. This device is used for measuring broadband solar
irradiance as well as solar radiation flux density, which means that it measures the power of the
light and heat from the sun. When placed on a flat surface, sensor can be used for identifying solar
radiation.
Radiation sensor works by measuring the number of small units of light, known as photons that
impact a physical or chemical device located within the instrument. Solar radiation sensors are
typically not powered due to the fact that the components located in the device either are influenced
by or react to solar radiation in a direct manner.
PAR sensor that is capable of measuring photosynthetically active radiation, within the 400 to
700nm range, even achieves 3500nm. Silicon is a kind of semiconductor. Semiconductor
photoelectric sensor is the most ideal photoelectric sensor because of its small size, high sensitivity,
fast response speed and easy integration. Photon is the carrier of electromagnetic radiation, and in
quantum field theory, photon is considered as the medium of electromagnetic interaction. Like other
quanta, photon has wave-particle duality, which can show the properties of classical wave such as
refraction, interference and diffraction.
Radiation Sensor

Pyranometers are comprised of a thermopile sensor that typically has a black coating. The sensor is
designed to absorb solar radiation. Thermopile principle is absorption film irradiated by infrared ray is
a kind of thin film with low heat capacity and easy temperature rise. The lower part, immediately next
to the center of the liner, is a hollow structure designed to ensure the temperature difference between
the cold end and the temperature measuring end. Pyranometer sensor detect both direct and diffuse
radiation. The radiation that is absorbed by the sensor is converted to heat. That heat then flows
through the sensor to the device's housing. In addition, the dome helps to protect the thermopile
sensor from convection.
Radiation Sensor

Solar radiation sensor uses the principle of silicon photocell. Silicon photocells work on the basis
of the photovoltaic effect. When the semiconductor PN junction is at zero bias or reverse bias, in
their joint surface depletion region exists within a field, when a light photon will bound electron
excitation in the valence band to the conduction band, inspire the electron hole respectively under
the action of the electric field, drift to the N and P type area, when load on both ends of PN
junction add a light when current flows through the load. The level of possible measurement of a
solar radiation sensor will vary based on the position of the sun.
UV radiation sensor is also a kind of sensor, ultraviolet sensor can use photosensitive elements
through photovoltaic mode and photoconductive mode to convert ultraviolet signal into
measurable electrical signals. Ultraviolet radiation is a non-illumination source of radiation.
Ultraviolet radiation has a wavelength range of 10 to 400 nanometers. Since only ultraviolet
radiation with a wavelength greater than 100 nanometers can travel through the air, the effects
of ultraviolet radiation and their applications are usually discussed only in the range of 100nm to
400nm.
Radiation Sensor

Smart Sensor

In instrumentation systems, sensors are very essential devices. At present, most of the
types of sensors are smart. So in these sensors, the sensing elements & electronics are
integrated on the same chip. So, the integration of electronics and sensors to make an
intelligent sensor is known as a smart sensor. This sensor can make some decisions.
These sensors have many benefits like higher S/N ratio, fast signal conditioning,
auto-calibration, self-testing, high reliability, small physical size, detection &
prevention of failure.
Smart Sensor

A smart sensor is a device that uses a transducer to gather
particular data from a physical environment to perform a
predefined & programmed function on the particular type of
gathered data then it transmits the data through a networked
connection.
The features of the smart sensor are; self-identification, digital
sensor data, smart calibration & compensation, multi-sensing
capacity, sensor communication for configuration of remote &
remote monitoring, etc.
What is a Smart Sensor/Define Smart Sensors?
Smart Sensor

Smart sensors work by capturing data from physical environments & changing their physical
properties like speed, temperature, pressure, mass, or presence of humans into calculable electrical
signals. These sensors include a Digital Motion Processor (DMP). Here a DMP is one type of
microprocessor that allows the sensor to perform onboard processing of the smart sensor data like
filtering noise otherwise performing different kinds of signal conditioning.
These sensors have 4 main functions measurement, configuration, verification & communication.
• Measurements are simply taken through detecting physical signals & changing them into electrical
signals. So this will help in monitoring and measuring things like temperature, traffic, & industrial
applications.
• Configuration function is a significant feature as it allows the smart sensor to detect position
otherwise installation errors
• The verification function has different uses like nonstop supervision of sensor behavior, using a set
of supervisory circuits or equipment executed within the sensor.
• Lastly, the communication feature allows the sensor to converse to the main microcontroller/
microprocessor.
Smart Sensor Working Principle

The block diagram of the smart sensor is shown below. This block diagram includes
different blocks like sensing unit, signal conditioning, analog to digital conversion,
application algorithms, local user interface, memory, and communication unit or
transceiver.
Smart Sensor Block Diagram

Sensing Unit
This unit detects the changes in physical parameters & generates electrical signals
equivalent to it. Signal
Conditioning Unit
The signal conditioning unit controls the signal to meet the necessities of next-level
operations without losing data.
Analog to Digital Converter
ADC converts the signal from analog to digital format & sends it to the
microprocessor.
Local User Interface
The local user interface or LUI is a panel-mounted device used to allow building
operators to monitor & control system equipment.
Smart Sensor

Application Algorithm
The signals from smart sensors reach here & process the received data based on the
application programs previously loaded here & generate output signals.
Memory
It is used to store media for saving received & processed data.
Communication Unit
The output signals from the application algorithm or microprocessor are transmitted
to the main station through the communication unit. This unit also gets command
requirements from the key station to execute specific tasks.
Smart Sensor

Difference between Normal Sensor & Smart Sensor
Sensor Smart Sensor
A sensor is a device used to detect the physical changing &
chemical environment.
The part of a sensor is known as a smart sensor that is used for the
computer.
A sensor doesn’t include a DMP or digital motion processor. A smart sensor includes a DMP or Digital Motion Processor.
The normal sensor includes three components like sensor
element, packaging & connections, and also signals processing
hardware.
Smart sensors include different components like amplifiers,
transducers, analog filters, excitation control, and compensation
sensors.
The different types of normal sensors are pressure, position,
temperature, vibration, force, humidity & fluid property.
The different types of smart sensors are electric current, level,
humidity, pressure, proximity, temperature, heat, flow, etc.
Normal sensor output cannot be used directly because we should
convert it into a usable format.
The output of the smart sensor is ready to use.
Normal sensors are preferred when an engineer designing a
device that requires complete control on sensor input
Smart sensors are generally preferred over base sensors because
they include native processing capabilities.
Normal sensors are not expensive because they contain fewer
components.
Smart sensors are expensive as compared to normal sensors.

The advantages of the smart sensor include the following.
These are small in size
These sensors are very easy to use, design & maintain
The performance level is higher
Speed of communication & reliability is higher due to the direct conversion with the
processor.
These sensors can perform self-calibration & self-assessments.
These sensors can notice issues like switch failures, open coils & sensor
contamination.
These sensors optimize manufacturing processes easily that need changes.
They can store many systems’ data.
Smart Sensor

Disadvantages
The disadvantages of the smart sensor include the following.
Smart sensors’ reliability is one of the major drawbacks because if they are stolen or
get damaged then they can affect a lot of systems badly.
It needs both sensors & actuators.
Sensor calibration has to be managed by an external processor.
High complexity in wired smart sensors, so the cost is also very high
Applications
The applications of the smart sensor include the following.
These sensors play a key role in monitoring different industrial processes like data
collecting, measurement taking & transmitting the data to centralized cloud
computing platforms wherever data is collected & analyzed for different patterns.
So, this collected data can be simply monitored at any time by decision-makers.
Smart Sensor

Film sensors

Thin-film sensors are based on the same principle as strain gauges, which are grid-
type resistance structures whose geometric stretching and compression result in a
measurable resistance change due to length and thickness differences induced. For a
thin-film sensor, four resistors are arranged on a diaphragm in the form of a
Wheatstone bridge to detect the deformation of the diaphragm under pressure. In
the ‘thin-film process’, these strain gauges are attached onto a (e.g. metallic) base
element and structured (sputtering with associated photolithography and
etching).Thin film sensors are precise, stable, dependable and cheap, offering
numerous advantages over conventional sensors. Most applications of thin film
sensors take advantage of their small size and the options they provide engineers -
their distinctive housing being an especially useful feature for particular applications.
Some of the more fascinating uses of the thin film sensor technology lie within the
medical field. When medical pumps and irrigation systems are disrupted by a
blocked tube or pump breakdown, there may be devastating and potentially deadly
repercussions.
Film sensors

Medical device engineers often use ‘tube sensors’ to keep track of pressure in these pump systems.
These sensors work by gauging the pressure on a sensor which is placed against the widening walls of
polyurethane or PVC tubing. Device makers also might place a sensor behind the pump to track
pressures as the pump pushes against the sensor during operation. Thin film sensors have the shown
the necessary repeatability, durability and precision needed to be effective in these and other
applications.
Thin film pressure sensors are commonly used in industrial applications, particularly in hydraulic
equipment and vehicles, like cranes, steamrollers, forklifts and agricultural machinery. This is because
all essential functions of hydraulics require precise tracking of the hydraulic pressures.
Thick-film sensors, like thin-film sensors, use four resistors grouped to form a Wheatstone bridge. The
resistance structures are “printed” onto a base element (e.g. ceramic base) using thick-film
technology, and afterwards they are burnt-in at high temperature. The resistance change here is also
due to the deformation of the diaphragm, resulting from the geometrical change caused by the
stretching and compression of the material.
Piezoresistive sensors, in contrast to the first two principles, utilize a semiconductor (silicon)
measuring diaphragm with selectively diffused structures. They use the piezoresistive effect, which is
based on the change in electrical resistance in the semiconductor materials caused by the stretching
and compression, which affects the mobility of the electrons under the mechanical stress.
Film sensors

Nanosensors

Nanosensors are chemical or mechanical sensors that can be used to detect the
presence of chemical species and nanoparticles, or monitor physical parameters such
as temperature, on the nanoscale.They find use in medical diagnostic applications,
food and water quality sensing, and other chemicals.
How Do Nanosensors Work?
An analyte, sensor, transducer and detector are the components of a sensor system,
with feedback from the detector to the sensor. Sensitivity, specificity and ease of
execution are the main characteristics to consider when designing a sensor.
The materials used to build a nanosensor are related to its application. For example,
noble metal nanoparticles have size-dependent optical properties and are often
used in optical sensors. Popular materials for building nanoscale sensors include
carbon nanotubes and graphene.
Nanosensors typically work by monitoring electrical changes in the sensor materials.
For example, carbon nanotube-based sensors work in this way. When a molecule of
nitrogen dioxide (NO2) is present, it will strip an electron from the nanotube, which
in turn causes the nanotube to be less conductive.
Nanosensors

If ammonia (NO3) is present, it reacts with water vapor and donates an electron to
the carbon nanotube, making it more conductive. By treating the nanotubes with
various coating materials, they can be made sensitive to certain molecules and
immune to others.
Like chemical nanosensors, mechanical nanosensors also tend to measure electrical
changes. Those used in the MEMS systems that car airbags depend upon are
monitoring changes in capacitance. These systems have a minuscule weighted shaft
attached to a capacitor. The shaft bends with changes in acceleration and this is
measured as changes in capacitance.
They have also been developed to the point of measurement at the single-molecule
level.
Nanosensors

Types of nanosensors include:
• Carbon nanotubes, quantum dots, peptide or DNA-based fluorescent
nanosensors.
• Plasmon coupling–based nanosensors
• Plasmonic enhancing–/quenching–based nanosensors
• Magnetic resonance imaging-based nanosensors
• Photoacoustic-based nanosensors
• Multimodal nanosensors
Nanosensors

Nanosensor Applications
Nanosensors can be chemical sensors or mechanical sensors. They are used in a variety of
applications across a range of industries, from biomedical to environmental. Some common
applications are highlighted below:
• Detecting various chemicals in gases for pollution monitoring.
• Medical diagnosis, either as bloodborne sensors or in lab-on-a-chip type devices.
• To monitor physical parameters such as temperature, displacement and flow.
• As accelerometers in MEMS devices like airbag sensors.
• To monitor plant signaling and metabolism to understand plant biology.
• To study neurotransmitters in the brain to understand neurophysiology.
• To collect real-time measurements of soil conditions, such as pH, moisture, nutrients, and residual
pesticides for agricultural purposes.
• To detect pesticides on the surface of fruits and vegetables and to detect carcinogens in food.
• To detect pathogens in food as part of food safety and quality control measures.
• The real-time monitoring of the metabolic activity of cancer cells in response to therapeutic
intervention.
• The detection and monitoring of small-molecule metabolites.
Nanosensors

MEMS Sensor

The term MEMS stands for micro-electro-mechanical systems. These are a set of
devices, and the characterization of these devices can be done by their tiny size &
the designing mode. The designing of these sensors can be done with the 1- 100-
micrometer components. These devices can differ from small structures to very
difficult electromechanical systems with numerous moving elements beneath the
control of incorporated micro-electronics. Usually, these sensors include mechanical
micro-actuators, micro-structures, micro-electronics, and micro-sensors in one
package.
MEMS Sensor

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, after that it responds to the pressure which
is measured pressure with the help of some mechanical actions. The best examples of
this mainly include revolving of a motor for compensating the pressure change.
The MEMS IC fabrication can be done with silicon, whereby slight material layers are
placed otherwise fixed onto a Si substrate. After that selectively fixed away to leave
microscopic 3D structures like diaphragms, beams, levers, springs, and gears.
The MEMS fabrication needs many techniques which are used to construct other
semiconductor circuits like oxidation process, diffusion process, ion implantation process,
low-pressure chemical vapor deposition process, sputtering, etc. Additionally, these
sensors use a particular process like micromachining.
What is a MEMS Sensor?

Whenever the tilt is applied to the MEMS sensor, then a balanced mass makes a
difference within the electric potential. This can be measured like a change within
capacitance. Then that signal can be changed to create a stable output signal in
digital, 4-20mA or VDC.
These sensors are fine solutions to some applications which do not demand the
maximum accuracy like industrial automation, position control, roll, and pitch
measurement, and platform leveling.
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 Sensor Working Principle

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
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.

Laser sensor

A laser sensor is a type of sensor that utilizes laser technology for detection,
measurement, or sensing purposes. It uses a laser beam as the primary sensing
element to gather information about the surrounding environment or target object.
Laser sensors are known for their precision, accuracy, speed, and non-contact
nature, making them suitable for a wide range of applications. Here are some key
aspects of laser sensors:
Laser sensor

Laser Distance Sensors
Working Principle
Laser distance sensors use the time-of-flight principle. They emit a laser
beam and measure the time it takes for the beam to travel to the target
and back. This time measurement is used to calculate the distance.
Applications
Laser distance sensors are used for precision distance measurements in
industrial automation, robotics, surveying, construction, and material
handling. They are also employed in applications such as level sensing,
collision avoidance, and object detection.
Pros
High accuracy, fast response time, long-range measurement capability,
non-contact operation, and suitability for various surfaces and materials.
Cons
Limited performance in adverse environmental conditions (e.g., dust,
fog), sensitivity to reflective or transparent surfaces, and potential
interference from ambient light.
What types does a laser sensor have?

Laser Proximity Sensors
Working Principle
Laser proximity sensors emit a laser beam and detect the
interruption or reflection of the beam to determine the
presence or absence of objects within a certain range.
Applications
Laser proximity sensors are used for object detection,
position control, counting, and automation in industries
such as manufacturing, packaging, robotics, and conveyor
systems.
Pros
Non-contact operation, fast response time, high precision,
long sensing range, and immunity to environmental factors
like vibration or ambient light.
Cons
Limited performance with transparent or highly reflective
objects, sensitivity to dust or dirt on the optical
components. Prepared by A.R.Sivanesh AP/Mech

Laser Displacement Sensors
Working Principle
Laser displacement sensors analyze the reflected laser light from a
target object to determine its position or displacement. The analysis
is based on parameters like phase shift, interference, or triangulation.
Applications
Laser displacement sensors are used for precision measurements in
manufacturing, quality control, dimensional inspection, surface
profiling, and robotics. They are ideal for applications requiring
accurate position control or surface profile analysis.
Pros
High accuracy, fast response time, non-contact operation, wide
measurement range, and suitability for various materials and
surfaces.
Cons
Limited performance with highly reflective or transparent surfaces,
sensitivity to environmental factors like ambient light or temperature
variations. Prepared by A.R.Sivanesh AP/Mech

Laser Scanners
Working Principle
Laser scanners emit laser beams that sweep across an area or object
and measure the reflected or scattered light to create detailed 3D
representations.
Applications
Laser scanners are used in applications such as 3D mapping, surveying,
robotics, virtual reality, autonomous vehicles, and object recognition.
Pros
Accurate 3D imaging, high-resolution mapping, fast data acquisition,
versatility in scanning patterns, and applications in fields like
architecture, archaeology, forestry, and virtual reality.
Cons
Costly equipment, complex data processing, limited performance in
adverse environmental conditions, and potential challenges with
reflective or transparent surfaces.

Lidar Sensors
Working Principle
Lidar sensors use lasers to emit pulses of light and measure the time-of-flight or
phase shift of the reflected light to calculate distances and create 3D maps.
Applications
Lidar sensors are primarily used in autonomous vehicles, robotics, geospatial
analysis, forestry, urban planning, and environmental monitoring.
Pros
High-precision 3D mapping, long-range sensing, real-time data acquisition,
application in autonomous vehicles for navigation and object detection, and
suitability for various terrains and environments.
Cons
Costly equipment, complex data processing, potential interference from ambient
light or other lidar sensors, limited performance in adverse weather conditions (e.g.,
rain, fog), and sensitivity to reflective or transparent surfaces.

The following are the advantages of laser sensors.
• It has a very high direction of the beam and a small divergence angle of light
speed.
• It has high levels of brightness.
• The frequency width of the laser is 10 times smaller than ordinary light.
• Precise measurement of length and is 1000 times purer than even the best
monochromatic light source (krypton).
• Its range can extend up to several kilometers.
• It can be used for a wide variety of applications; ranging from measuring length to
thickness and even the angle, length, eccentricity of inner and outer diameter,
concentricity, and surface profile of a cylindrical shaped object.
• You can get digital (NPN or PNP output contact) as well as analog (0-10 V DC or 4-
20 mA) electrical output.
• They work well in dusty conditions. The bright light of the laser sensor is not
affected by other light sources. So, they can also be used even in direct sunlight.
Advantages of Laser

Level Sensors

A level sensor is a device that is designed to monitor, maintain, and measure liquid
(and sometimes solid) levels. Once the liquid level is detected, the sensor converts
the perceived data into an electric signal. Level sensors are used primarily in the
manufacturing and automotive industries, but they can be found in many household
appliances as well, such as ice makers in refrigerators.
Level sensors are useful devices that are used to detect the level of substances such
as liquids, powders and granular materials. There is a wide range of level sensors
and they are all used in different industries. Some level sensors can be used for any
fluid and others can only be used for certain substances.
Level sensors are used to measure substances that are inside a container or in their
natural state, e.g. rivers.
Level Sensors

• Oil Manufacturing Plants
• Water Treatment
• Paper and Pulp Production Divisions
• Petrochemical and Chemical Making & Refinery Units
• Waste Material Handling Industry
• Beverage and Food Manufacturing Factories
• Pharmaceutical Processes
• Power Generating Plants
Level sensors are used in the following industries:

Level Sensor Classification
Level Sensors can be broken into two classifications;
1. Point level measurement
2. Continuous level measurement
Point level measurement indicates when a product is present at a certain point and
continuous level measuring indicates the continuous level of a product as it rises and falls.
Level Sensors

The sensors for point level indication are:
Capacitance
Optical
Conductivity
Vibrating (Tuning fork)
Float Switch
The sensors for continuous level measuring are:
Ultrasonic
Radar (Microwave)
Level Sensor Classification

Point Level Measurement Sensors
1. Capacitance Level Sensors

These sensors are used to detect the liquid levels like slurries and aqueous liquids. They
are operated by using a probe for checking level changes. These level changes are
transformed into analog signals. The probes are generally made of conducting wire by
PTFE insulation. But, stainless steel probes are extremely responsive and hence they are
appropriate for measuring non-conductive substance granular or materials with low
dielectric constant. These types of sensors are very simple to use and clean as they do not
have any moving components.
Pros and Cons
Solid-state, compact, can be non-invasive, accurate
Can only be used in certain liquids, May require calibration
Applications
They are commonly used in applications like Tank level monitoring in chemical, water
treatment, food, battery industries and involving high pressure and temperature.
1. Capacitance Level Sensors

2. Optical Level Sensors

Optical level sensors are used to detect liquids including poised materials, interface
between two immiscible liquids and the occurrence of sediments. They are worked based
on the changes of transmission in infrared light emitted from an IR LED. The interference
from the produced light can be reduced by using a high energy IR diode and pulse
modulation methods.
Continuous optical level sensors, on the other hand, use the highly intense laser light that
can infuse dusty environments and notice liquid substances.
Pros and Cons
Compact, high pressure, no moving parts, and capability of temperature, can notice tiny
amounts of liquids.
Invasive as the sensor needs get in touch with the liquid needs power, certain wide
substances can reason coating on the Prism.
Applications
They are commonly used in applications like leak detection and tank level measurement
2. Optical Level Sensors

Another style of point level sensor is conductivity or resistance.
A conductivity or resistance sensor uses a probe to read conductivity. The probe has a pair
of electrodes and applies alternating current to them.
When a liquid covers the probe its electrodes form a part on an electric circuit, causing
current to flow which signals a high or low level.
The advantages of using a conductivity level sensor are:
There are no moving parts
They are low cost
Fairly easy to use
The disadvantages are:
They are invasive (meaning they must touch the product being sensed)
They only sense conductive liquids
The probe will erode over time
Appropriate use for these sensors would be for signaling high or low levels.
3. Conductivity (Resistance) Level Sensor

4. Vibrating (Tuning Fork) Level Sensor

Vibrating or tuning forks is another type of point level sensor.
They use a fork-shaped sensing element with two tines. The fork vibrates at its natural
resonant frequency. As the level changes, the frequency of the fork will change detecting
the level.
These sensors are:
Cost effective and compact
Invasive to the product, meaning they have to touch the material to sense the level
Easy to install
Essentially maintenance-free
They have unlimited uses based on the material that they can sense. Mining, food and
beverage, and chemical processing industries use these sensors for their applications.
4. Vibrating (Tuning Fork) Level Sensor

5.Float Switch

The last point level sensor that we will talk about is a float switch.
Float switches use a float, a device that will raise or lower when a product is applied or
removed, which will open or close a circuit as the level raises or lowers moving the float.
Advantages of a float switch are:
They are non powered device
They provide a direct indication
They are inexpensive
Disadvantages are:
They are invasive to the product
They have moving parts
They can be large in size
Float switches will only give an indication for a high or low level, they cannot measure a
variable level. A great use for float switches is in liquid storage tanks for high or low-level
indication.
5.Float Switch

Continuous Level Measurement Sensors
1. Ultrasonic Level Sensors

Ultrasonic level sensors are used to detect the levels of sticky liquid substances and bulkiness materials
as well. They are worked by producing audio waves at the range of frequency from 20 to 200 kHz.
These waves are then replicated back to a transducer. The ultrasonic sensor’s response is influenced by
turbulence, pressure, moisture, and temperature. In addition, the transducer is necessary to be
increased appropriately to obtain a better response.
Pros and Cons
Compact, cost-effective
Invasive, numbers of users are limited
The advantage of using this type of sensor is that:
These sensors have no moving parts
They are compact
They are reliable
Non-invasive (Non-contact)
Unaffected by the properties of the material they are sensing
Self-cleaning because of the vibrations they give off
The disadvantage of using this type of sensor is that:
They can be expensive
In some situations, the environment can have a negative effect on them
1. Ultrasonic Level Sensors

2. Microwave Optical Sensors

These types of sensors are used for applications like varying temperature, pressure, dirty and moist
environments, as microwaves can easily go through under these situations without involving air
molecules for energy transmission. Microwave Optical sensors can notice conductive water & metallic
substances. The measurements are accepted using time domain or pulse reflectometry.
Pros and Cons
No calibration required, very accurate, multiple output options
Costly, limited detection range, and can be affected by the environment.
The advantages of radar sensors are that:
They are not affected by temperature, pressure or dust
They can also measure liquids, pastes, powders, and solids
They are very accurate and require no calibration
They are non-invasive because they do not have to touch the product that it is sensing
The disadvantages of radar sensors are that:
They are expensive
They have a limited detection range
Applications
They are commonly used in applications like vaporous, Moist, and dusty environments.
They are also used in systems in which temperatures differ.
2. Microwave Optical Sensors

Flow Sensor

A flow sensor definition is a sensor that is used to measure a fluid like liquid or gas. These
sensors mainly use both electrical and mechanical subsystems to gauge changes within
the physical attributes of fluid & measure its flow. So measuring these mainly depends on
the physical attributes of fluid. A flow sensor is an electronic device that measures the
changes in liquids flow rate & gasses in tubes & pipes.
The flow sensor working principle is based on Bernoulli’s principle. This principle states
that the drop of pressure across the meter is simply proportional to the square of the rate
of flow. The most common way to determine the measurement of a flow is by using the
pressure drop across the cross-section of the pipe.
Flow Sensor

Flow Sensor Types
Flow sensors are categorized into three types like the following.
Positive displacement flow sensors.
Mass flow sensors.
Velocity flow sensors.
Flow Sensor

These types of flow sensors are very unique as compared to other types because they
measure the fluid’s volume directly when passing through the device. Other types of flow
sensors do not measure the rate of flow directly instead of measuring pressure, it is used
to derive the flow rate.
Positive Displacement Sensor

Positive Displacement Flow Sensor
In this kind of sensor, the volume of known fluid is trapped & moved throughout the
rotary parts. It turns the components & once it completes a complete revolution, then it is
guessed as the volume of known fluid supplied throughout the sensor. Counting the
revolutions which occur for each unit time setups the fluid volume supplied for each unit
time. As the flow of fluid moves the components directly, then rotating velocity is
proportional directly to the rate of flow.
These flow sensors can work over a broad range of fluid viscosities; they have less
maintenance & provide an electronic & mechanical interface. These sensors are used in
the measurement of gasoline, oils, hydraulic liquid, and water and gas meters installed at
home.

Mass Flow Sensor
A mass flow sensor measures the flow rate of fluid or the amount of fluid or gas flowing
throughout a pipe by simply determining the mass for each unit of time. These sensors are
extensively used in automobiles, wherever they are utilized to measure the air inflowing
the air intake system of an inside combustion engine. They work by simply measuring the
energy transfer from a heated surface to a flowing liquid. These sensors are also available
in two types thermal & Coriolis flowmeter.
The advantages of this sensor are; liquid flow can be measured directly with high accuracy,
applicable for an extensive range of fluids like highly viscous fluids, and flow measurement
can be done bidirectionally.

Velocity Flow Sensor
Velocity flow sensors are used for detecting the liquid flow speed by simply determining
the fluid’s velocity flowing throughout the sensor.
Mechanical Velocity Flow Sensor
In a mechanical velocity flow sensor, a rotary mechanical device like a paddle wheel is
arranged on a bearing that extends from the flow sensor & directly sits within the flow
path. When the fluid moves, the paddle wheel rotates & its rotation is simply detected by
a sensor like an infrared sensor, magnetic coil, or Hall effect. The flow sensor electronics
converts the revolutions into an o/p signal like a rectangular wave signal that can be
simply programmed to signify a specified volume output for each unit time.

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UNIT IV OPTICAL, PRESSURE AND TEMPERATURE SENSORS

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