Sensing

Parichay Bhattacharjee
Manager, CRM-III
Bokaro Steel Plant
Steel Authority of India Limited
Email: parichay.b@sail.in
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 Definition

✓ A sensor detects (senses) changes in the ambient conditions

or in the state of another device or a system, and forwards or
processes this information in a certain manner [1].

“A device which detects or measures a physical property and

records, indicates, or otherwise responds to it” [2].
References: ‐ Oxford Dictionary
1. http://www.businessdictionary.com/definition/sensor.html
2. https://en.oxforddictionaries.com/definition/sensor

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Sensors

✓ They perform some input functions by sensing or feeling the

physical changes in characteristics of a system in response to a
stimuli.
✓ For example heat is converted to electrical signals in a
temperature sensor, or atmospheric pressure is converted to
electrical signals in a barometer.

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Transducers

✓ Transducers convert or transduce energy of one kind into

another.
✓ For example, in a sound system, a microphone (input device)
converts sound waves into electrical signals for an amplifier to
amplify (a process), and a loudspeaker (output device)
converts these electrical signals back into sound waves.

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 Sensor vs. Transducer

✓ The word “Transducer” is the collective term used for both

Sensors which can be used to sense a wide range of different
energy forms such as movement, electrical signals, radiant
energy, thermal or magnetic energy etc., and Actuators which
can be used to switch voltages or currents [1].

References:
1. http://www.electronics‐tutorials.ws/io/io_1.html

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Sensor Features
✓ It is only sensitive to the measured property (e.g., A
temperature sensor senses the ambient temperature of a
room.)
✓ It is insensitive to any other property likely to be encountered
in its application (e.g., A temperature sensor does not bother
about light or pressure while sensing the temperature.)
✓ It does not influence the measured property (e.g., measuring
the temperature does not reduce or increase the
temperature).
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Sensor Resolution
✓ The resolution of a sensor is the smallest change it can detect
in the quantity that it is measuring.
✓ The resolution of a sensor with a digital output is usually the
smallest resolution the digital output it is capable of
processing.
✓ The more is the resolution of a sensor, the more accurate is its
precision.
✓ A sensor’s accuracy does not depend upon its resolution.

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Sensor Classes
Based on Based on
Output Data type

Analog Scalar

Vector/
Digital
Multimedia

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Analog Sensors
✓ Analog Sensors produce a continuous output signal or voltage
which is generally proportional to the quantity being measured.
✓ Physical quantities such as Temperature, Speed, Pressure,
Displacement, Strain etc. are all analog quantities as they tend to be
continuous in nature.
✓ For example, the temperature of a liquid can be measured using a
thermometer or thermocouple (e.g. in geysers) which continuously
responds to temperature changes as the liquid is heated up or
cooled down.

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Digital Sensors
✓ Digital Sensors produce discrete digital output signals or voltages
that are a digital representation of the quantity being measured.
✓ Digital sensors produce a binary output signal in the form of a logic
“1” or a logic “0”, (“ON” or “OFF”).
✓ Digital signal only produces discrete (non‐continuous) values, which
may be output as a single “bit” (serial transmission), or by
combining the bits to produce a single “byte” output (parallel
transmission).

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Scalar Sensors
✓ Scalar Sensors produce output signal or voltage which is generally
proportional to the magnitude of the quantity being measured.
✓ Physical quantities such as temperature, color, pressure, strain, etc.
are all scalar quantities as only their magnitude is sufficient to
convey an information.
✓ For example, the temperature of a room can be measured using a
thermometer or thermocouple, which responds to temperature
changes irrespective of the orientation of the sensor or its
direction.

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Vector Sensors
✓ Vector Sensors produce output signal or voltage which is generally
proportional to the magnitude, direction, as well as the orientation
of the quantity being measured.
✓ Physical quantities such as sound, image, velocity, acceleration,
orientation, etc. are all vector quantities, as only their magnitude is
not sufficient to convey the complete information.
✓ For example, the acceleration of a body can be measured using an
accelerometer, which gives the components of acceleration of the
body with respect to the x,y,z coordinate axes.

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Sensor Types
• Light Dependent resistor
Light • Photo‐diode
• Thermocouple
Temperature • Thermistor
• Strain gauge
Force • Pressure switch
• Potentiometer, Encoders
Position • Opto‐coupler
• Reflective/ Opto‐coupler
Speed • Doppler effect sensor
• Carbon Microphone
Sound • Piezoelectric Crystal
• Liquid Chemical sensor
Chemical • Gaseous chemical sensor

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 Pressure Sensor Ultrasonic Distance Sensor Tilt Sensor Infrared Motion Sensor
Source: Wikimedia Commons Source: Wikimedia Commons Source: Wikimedia Commons Source: Wikimedia Commons

Analog Temperature Sensor Camera Sensor

Source: Wikimedia Commons Source: Wikimedia Commons

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 Sensorial Deviations
✓ Since the range of the output signal is always limited, the
output signal will eventually reach a minimum or maximum,
when the measured property exceeds the limits. The full scale
range of a sensor defines the maximum and minimum values
of the measured property.
✓ The sensitivity of a sensor under real conditions may differ
from the value specified. This is called a sensitivity error.
✓ If the output signal differs from the correct value by a
constant, the sensor has an offset error or bias.
Reference: https://en.wikipedia.org/wiki/Sensor

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 Non-linearity

✓ Nonlinearity is deviation of a sensor's transfer function (TF)

from a straight line transfer function.
✓ This is defined by the amount the output differs from ideal TF
behavior over the full range of the sensor, which is denoted as
the percentage of the full range.
✓ Most sensors have linear behavior.

Reference: https://en.wikipedia.org/wiki/Sensor

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 ✓ If the output signal slowly changes independent of the
measured property, this is defined as drift. Long term drift
over months or years is caused by physical changes in the
sensor.
✓ Noise is a random deviation of the signal that varies in time.

Reference: https://en.wikipedia.org/wiki/Sensor

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 Hysteresis Error
✓ A hysteresis error causes the sensor output value to vary
depending on the sensor’s previous input values.
✓ If a sensor's output is different depending on whether a
specific input value was reached by increasing or decreasing
the input, then the sensor has a hysteresis error.
✓ The present reading depends on the past input values.
✓ Typically in analog sensors, magnetic sensors, heating of
metal strips.
Reference: https://en.wikipedia.org/wiki/Sensor

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 Other Errors
✓ If the sensor has a digital output, the output is essentially an
approximation of the measured property. This error is also called
quantization error.
✓ If the signal is monitored digitally, the sampling frequency can cause a
dynamic error, or if the input variable or added noise changes
periodically at a frequency proportional to the multiple of the
sampling rate, aliasing errors may occur.
✓ The sensor may to some extent be sensitive to properties other
than the property being measured. For example, most sensors are
influenced by the temperature of their environment.
Reference: https://en.wikipedia.org/wiki/Sensor

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 Actuation
Parichay Bhattacharjee
Manager, CRM-III
Bokaro Steel Plant
Steel Authority of India Limited
Email: parichay.b@sail.in
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Actuator

✓ An actuator is a component of a machine or system that

moves or controls the mechanism or the system.
✓ An actuator is the mechanism by which a control system acts
upon an environment
✓ An actuator requires a control signal and a source of energy.

Introduction to Internet of Things 2

✓ Upon receiving a control signal is received, the actuator
responds by converting the energy into mechanical motion.
✓ The control system can be simple (a fixed mechanical or
electronic system), software‐based (e.g. a printer driver, robot
control system), a human, or any other input.
Current Pneumatic Manual
Electric

Pressure

Mechanical

Voltage (air) Drive (e.g.

Hydraulic crankshaft) Control Signal Actuator
(fluid)

Introduction to Internet of Things 3

Actuator Types
Hydraulic

Pneumatic

Electrical

Thermal/ Magnetic

Mechanical

Introduction to Internet of Things 4

 Hydraulic Actuators

✓ A hydraulic actuator consists of a cylinder or fluid motor that

uses hydraulic power to facilitate mechanical operation.
✓ The mechanical motion is converted to linear, rotary or
oscillatory motion.
✓ Since liquids are nearly impossible to compress, a hydraulic
actuator exerts considerable force.
✓ The actuator’s limited acceleration restricts its usage.
Reference: https://en.wikipedia.org/wiki/Actuator

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Fig: An oil based hydraulic actuator
Fig: A radial engine acts as a hydraulic actuator
Source: Wikimedia Commons
File: Radial_engine.gif

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 Pneumatic Actuators
✓ A pneumatic actuator converts energy formed by vacuum or
compressed air at high pressure into either linear or rotary motion.
✓ Pneumatic rack and pinion actuators are used for valve controls of
water pipes.
✓ Pneumatic energy quickly responds to starting and stopping signals.
✓ The power source does not need to be stored in reserve for
operation.

Reference: https://en.wikipedia.org/wiki/Actuator

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✓ Pneumatic actuators enable large forces to be produced from
relatively small pressure changes (e.g., Pneumatic brakes can
are very responsive to small changes in pressure applied by
the driver).
✓ It is responsible for converting pressure into force.

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Fig: A manual linear pneumatic actuator Fig: An air pump acts as a pneumatic actuator

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 Electric Actuators

✓ An electric actuator is generally powered by a motor that

converts electrical energy into mechanical torque.
✓ The electrical energy is used to actuate equipment such as
solenoid valves which control the flow of water in pipes in
response to electrical signals.
✓ Considered as one of the cheapest, cleanest and speedy
actuator types available.
Reference: https://en.wikipedia.org/wiki/Actuator

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Fig: A motor drive‐based rotary Fig: A solenoid based electric bell ringing
actuator mechanism
Source: Wikimedia Commons
File: Electric_Bell_animation.gif

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 Thermal or Magnetic Actuators
✓ These can be actuated by applying thermal or magnetic energy.
✓ They tend to be compact, lightweight, economical and with high
power density.
✓ These actuators use shape memory materials (SMMs), such as
shape memory alloys (SMAs) or magnetic shape‐memory alloys
(MSMAs).
✓ Some popular manufacturers of these devices are Finnish Modti Inc.
and American Dynalloy.
Reference: https://en.wikipedia.org/wiki/Actuator

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 Fig: A piezo motor using SMA
Source: Wikimedia Commons
File: Piezomotor type bimorph.gif

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 Fig: A coil gun works on the principle of magnetic actuation

Source: Wikimedia Commons

File: Coilgun animation.gif

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 Mechanical Actuators

✓ A mechanical actuator converts rotary motion into linear

motion to execute some movement.
✓ It involves gears, rails, pulleys, chains and other devices to
operate.
✓ Example: rack and pinion.

Fig: A rack and pinion mechanism

Source: Wikimedia Commons
Reference: https://en.wikipedia.org/wiki/Actuator File: Rack and pinion.png

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 Fig: A crank shaft acting as a mechanical actuator
Source: Wikimedia Commons
File: Cshaft.gif

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 Soft Actuators

✓ Soft actuators (e.g. polymer based) are designed to handle

fragile objects like fruit harvesting in agriculture or
manipulating the internal organs in biomedicine.
✓ They typically address challenging tasks in robotics.
✓ Soft actuators produce flexible motion due to the integration
of microscopic changes at the molecular level into a
macroscopic deformation of the actuator materials.
Reference: https://en.wikipedia.org/wiki/Actuator

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 Shape Memory Polymers

✓ Shape memory polymer (SMP) actuators function similar to

our muscles, even providing a response to a range of stimuli
such as light, electrical, magnetic, heat, pH, and moisture
changes.
✓ SMP exhibits surprising features such a low density, high
strain recovery, biocompatibility, and biodegradability.

Reference: https://en.wikipedia.org/wiki/Actuator

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 Light Activated Polymers

✓ Photopolymer/light activated polymers (LAP) are a special

type of SMP that are activated by light stimuli.
✓ The LAP actuators have instant response.
✓ They can be controlled remotely without any physical contact,
only using the variation of light frequency or intensity.

Reference: https://en.wikipedia.org/wiki/Actuator

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