Unit 1 SA.pptx

❖Concept of Sensor
❖Concept of Transducer
❖Comparison between Sensors and Transducers
❖Role of Sensors in Automation
❖Broad Classification of Sensors and Transducers
❖Role of Transducer in measurement Systems
❖Block Diagram of Measurement system
SNJB’s LATE SAU. K. B. JAIN COLLEGE OF ENGINEERING | DEPT OF E&TC | PROF. D. J. PAWAR
Contents

❖Study of Static and Dynamic Characteristics of Measurement
Systems: Accuracy, Precision, Reproducibility, Linearity,
repeatability, resolution, Sensitivity, Range, Span, Dead Zone,
Hysteresis, Backlash, Dynamic Characteristics: Fidelity, Time
response and frequency response, Classification of errors – Error
analysis.
❖Concept and Basic Principle of working of Resistive Capacitive
and Inductive sensors.
Contents

❖ A sensor is a device that detects and responds to some type of
input from the physical environment. The specific input could be
light, heat, motion, moisture, pressure, or any one of a great
number of other environmental phenomena. The output is
generally a signal that is converted to human-readable display at
the sensor location or transmitted electronically over a network for
reading or further processing.
Concept of Sensor

❖ Here are a few examples of the many different types of sensors:
❖ In a mercury-based glass thermometer, the input is temperature.
The liquid contained expands and contracts in response, causing
the level to be higher or lower on the marked gauge, which is
human-readable.
❖ An oxygen sensor in a car's emission control system detects the
gasoline/oxygen ratio, usually through a chemical reaction that
generates a voltage. A computer in the engine reads the voltage
and, if the mixture is not optimal, readjusts the balance.
Concept of Sensor

❖ Motion sensors in various systems including home security lights,
automatic doors and bathroom fixtures typically send out some
type of energy, such as microwaves, ultrasonic waves or light
beams and detect when the flow of energy is interrupted by
something entering its path.
❖ A photo sensor detects the presence of visible light, infrared
transmission (IR), and/or ultraviolet (UV) energy.
Concept of Sensor

❖ A device which converts a physical quantity into the proportional
electrical signal is called a transducer. The electrical signal
produced may be a voltage, current or frequency. A transducer uses
many effects to produce such conversion. The process of
transforming signal from one form to other is called transduction. A
transducer is also called pick up. The transduction element
transforms the output of the sensor to an electrical output, as
shown in the Fig.
Concept of Transducer

Concept of Transducer
Sensing
Element
Transduction
Element
Sensor
Response
Non-
Electrical
Quantity
Electrical
Quantity
● A transducer will have basically two main components. They are
● 1. Sensing Element: The physical quantity or its rate of change is sensed and
responded to by this part of the transistor.
● 2. Transduction Element The output of the sensing element is passed on to the
transduction element. This element is responsible for converting the non-
electrical signal into its proportional electrical signal.
● There may be cases when the transduction element performs the action of
both transduction and sensing. The best example of such a transducer is a
thermocouple. A thermocouple is used to generate a voltage corresponding to
the heat that is generated at the junction of two dissimilar metals.

Comparison between Sensors & Transducer

Comparison between Sensors & Transducer
Transducer Sensor
● It helps in converting one form of energy into
another form.
● It senses physical quantities and converts into
signals which are read by an instrument.
● It converts electricity to electromagnetic waves. ● It senses physical quantity and converts into
analog quantity.
● The antenna is one type of transducer.
Microphones and loudspeakers are also of one
type.
● One type of Sensor is LED. Sensors used in
automobiles to detect touch and activate the
siren.
● It converts the measured quantity into a
standard electrical signal like -10 to +10V DC
● It is used to measure voltage, capacitance,
inductance, ohmic resistance.
● Examples: Strain gauge, piezoelectric
transducer, linear transducer, and microphone.
● Examples: Temperature sensor, thermistor,
proximity sensor, and pressure switch.

Role of Sensors in Automation
Sensors used in automation
● The industry 4.0 revolution has been through a lot of technical
progress. It has seen many sensing technologies in the past. But the
current technology can accurately respond to the needs of the
modern manufacturing process.
● It has increased the production capacity with wireless and cloud-
based connectivity. It has made possible the use of robotics and new
IIoT devices across smart manufacturing facilities.
● There are a vast number of automation sensors being used such as
tilt sensing, warehouse inventory management to vibration sensing
and analysis of moving parts, and thermal detection

Role of Sensors in Automation
● Although there are numerous sensors used today still there are some
more often and useful. The below-mentioned automation sensors are
some of the most common.
● Presence Detection Sensors
● Photo-optical Sensors
● Monitoring Sensors
● Proximity measuring sensors
● Data Sensors

Broad Classification of Sensors and Transducers
Several criteria are adopted for the classification of sensors. Some of
these include
● Based on the principle of operation (transduction principle)
● Based on energy requirements
● Based on material and technology used
● Application-based classification
● Property-based classification

Based on transduction principles
● The transduction principle is the basic criteria that should be
followed for a systematic approach to classification.
● This classification is based on the method used in the process of
converting measurand into usable output.

Active/Passive Transducers
● Based on the energy requirements of a transducer, they are
classified as active transducers and passive transducers.
● Active transducers do not need any external power supply to operate
and hence it is also called self-generating transducers.
● Eg: Thermocouple
● Transducers that require an external power source to operate is
called Passive transducers.
● Eg: LVDT

Sensor Image Sensor Motion detectors Bio Sensors Accelerometers
Technology CMOS Based IR, ultrasonic,
microwave,radar
Electrochemical MEMS based
Applications Traffic and security
surveillance
Video conferencing
Blindspot detection
Biometrics
Consumer electronics
Obstruction detection
Llight activation
Security detection
Toilet activation
Food testing
Water testing
Medical care device
Biological warfare agent
detection
Patient monitoring
Vehicle dynamic
system
Based on material and technology
Another classification is based on the material and technology
that have acquired more importance lately. The following table
shows the emerging sensor technologies with its applications.

Application based classification
Application based classification of sensors are represented as

Property based classification
● A much more elaborate classification is based on the properties
like pressure, displacement, temperature …etc.
● It is subdivided in technology scale. Pressure property is used in
technologies such as manometer and piezoelectricity.
● Semiconductors and thermal conductance use gas and
chemical properties

Something OFF the Topic

● System of measurement refers to the process of associating
numbers with physical quantities and phenomena.
● It is more like a collection of units of measurement and rules
relating them to each other. The whole world revolves around
measuring things! Everything is measured: the milk you buy, the
gas you fill for the vehicle, the steps you walk.
● Even our productivity is measured in terms of productivity
indexes on how productively we work. System of measurement
is very important and define and express the different quantities
of length, area, volume, weight, in our day-to-day
communications.
● The system of measurement is based on two important
foundation pillars of defining the basic unit of measurement, and
the measure of conversion from the basic unit to other related
units.
Measurement Systems

Measurement Systems

● In the old days, we used body parts for informal measurement
systems like foot length, cubit, handspan, etc. which were not so
accurate and vary from person to person.
● So, there was a need to regularize the measurements. A system
of measurement like the International System of Units called the
SI units ( the modern form of the metric system), Imperial
system, and US customary units were standardized across the
world.
Measurement Systems

● This term measurement system includes all components in a
chain of hardware and software that leads from the measured
variable to processed data.
● In a modern automobile there are as many as 40 – 50 sensors
(measuring devices) used in implementing various functions
necessary to the operation of the car.
● Knowledge of the instruments available for various
measurements, how they operate, and how they interface with
other parts of the system is essential for every engineer.
● Modern engineering systems rely heavily on a multitude of
sensors for monitoring and control to achieve optimum
operation.
Measurement Systems

● Every application of measurement, including those not yet
invented, can be put into one of these three categories or some
combination of them:
– Monitoring of processes and operations
– Control of processes and operations
– Experimental engineering analysis
Types of Applications of Measurement Instrumentation

Monitoring of Processes and Operations
● Here the measuring device is being used to keep track of some
quantity
● Certain applications of measuring instruments may be
characterized as having essentially a monitoring function
● e.g., thermometers, barometers, and water, gas, and electric
meters, automotive speedometer and fuel gage, and compass.

Control of Processes and Operations
● One of the most important classes of measurement application.
● Sensors are used in feedback-control systems and many
measurement systems themselves use feedback principles
in their operation.
● Sensors are used in feedback systems and feedback systems are
used in sensors. So an instrument can serve as a component of a
control system.
● To control any variable in a feedback control system, it is first
necessary to measure it. Every feedback-control system will have at
least one measuring device as a vital component.
● A single control system may require information from many
measuring instruments, e.g., industrial machine and process
controllers, aircraft control systems, automotive control systems
(speed control, antilock braking, coolant temperature regulating, air
conditioning, engine pollution, etc.).

Feedback Control System

Experimental Engineering Analysis
● In solving engineering problems, two general methods are available:
theoretical and experimental. Many problems require the application of
both methods and theory and experiment should be thought of as
complimenting each other.
Features of Theoretical Methods
● Often gives results that are of general use rather than for restricted
application.
● Invariably require the application of simplifying assumptions. The
theoretically predicted behavior is always different from the real
behavior, as a simplified physical/mathematical model is studied rather
than the actual physical system.
● In some cases, may lead to complicated mathematical problems.
● Require only pencil, paper, computers, etc. Extensive laboratory facilities
are not required.

Block Diagram of Measurement System
Measured
Medium
Primary
Sensing
Element
Variable
Conversion
Element
Variable
Manipulation
Element
Data
Transmission
Element
Data
Presentation
Element
Observer
Data
Storage /
Playback
Element
● Note: These elements are functional, not physical.

Primary Sensing Element
● This is the element that first receives energy from the measured
medium and produces an output depending in some way on the
measured quantity (measurand). The output is some physical variable,
e.g., displacement or voltage.
● An instrument always extracts some energy from the measured
medium. The measured quantity is always disturbed by the act of
measurement, which makes a perfect measurement theoretically
impossible. Good instruments are designed to minimize this loading
effect.
Variable-Conversion Element
● It may be necessary to convert the output signal of the primary
sensing element to another more suitable variable while preserving
the information content of the original signal. This element performs
this function.

Variable-Manipulation Element
● An instrument may require that a signal represented by some physical
variable be manipulated in some way. By manipulation we mean
specifically a change in numerical value according to some definite
rule but a preservation of the physical nature of the variable. This
element performs such a function.
Data-Transmission Element
● When functional elements of an instrument are actually physically
separated, it becomes necessary to transmit the data from one to
another. This element performs this function.

Data-Presentation Element
● If the information about the measured quantity is to be communicated
to a human being for monitoring, control, or analysis purposes, it must
be put into a form recognizable by one of the human senses.
● This element performs this “translation” function.
Data Storage/Playback Element
● Some applications require a distinct data storage/playback which can
easily recreate the stored data upon command

1. Accuracy:
● Accuracy is the closeness with which an instrument reading
approaches the true value of the quantity being measured.
● Thus accuracy of a measurement means conformity to truth. The
accuracy of an instrument may be expressed in many ways.
● The accuracy may be expressed as point accuracy, percent of true
value or percent of scale range.
● Point accuracy is stated for one or more points in the range, for
example, the scale of length may be read with in 0.2 mm.
● Another common way is to specify that the instrument is accurate
to within x percent of instrument span at all points on the scale.
● Another way of expressing accuracy is based upon instrument
range
Static Characteristics of Measurement Systems

2. Precision:
● Precision is the degree of exactness for which the instrument is
designed.
● It composed of two characteristics: conformity and significant
figures.
● More significant figures, estimated precision is more. For example
two resistors for values of 1792 ohms and 1710 ohms. A person even
repeated measurement it indicates 1.7 K ohms. The reader can not
read the true value from the scale.
● He estimates from the scale reading consistently yield a value of 1.5
M ohms. This is as close to the true scale as he can read the scale by
estimation although there are no deviations from the observed
value, the error created by the limitation of the error is called
precision error.

3. Reproducibility & Repeatability:
● Repeatability is the degree of closeness with which a given value may
be repeatedly measured.
● It is the closeness of output readings when the same input is applied
repetitively over a short period of time.
● The measurement is made on the same instrument, at the same
location, by the same observer and under the same measurement
conditions. It may be specified in terms of units for a given period of
time.
● Reproducibility relates to the closeness of output readings for the
same input when there are changes in the method of measurement,
observer, measuring instrument location, conditions of use and time of
measurement.
● Perfect reproducibility means that the instrument has no drift. Drift
means that with a given input the measured values vary with time.

4. Linearity:
● When the input-output points of the
instrument are plotted on the
calibration curve and resulting curve
may not be linear.
● This would be only if the output is
proportional to input. Linearity is the
measure of maximum deviation of
these points from the straight line
(Fig.).
● The departure from the straight line
relationship is non-linearity, but it is
expressed as linearity of the
instrument.

4. Linearity:
● Linearity is expressed in many different ways:
i) Independent Linearity: It is the maximum deviation from the straight
line so placed as to minimize the maximum deviation (Fig.).
ii) Zero based linearity: It is the maximum deviation from the straight
line joining the origin and so placed as to minimize the maximum
deviation.
iii) Terminal based linearity: It is the maximum deviation from the
straight line joining both the end points of the curve.

5. Resolution:
● It is the smallest quantity being measured which can be detected with
certainty by an instrument.
● If a non zero input quantity is slowly increased, the output reading
won’t increase until some minimum change in the input takes place.
The minimum change which causes the change in output is termed
resolution.

6. Sensitivity:
● Sensitivity can also be derived as for the smallest changes in the
measured variable for which the instrument responds.
● Sensitivity can be defined as the ratio of a change in output to change
in input which causes it, in steady-state conditions.
● The usage of this term is generally limited to linear devices, where the
plot of output to input magnitude is straight.
● Sensitivity = Change in output / Change in input
● Sensitivity can also be derived as for smallest changes in the measured
variable instrument responds.
● The term sensitivity is some times used to describe the maximum
change in an input signal that will not initiate on the output.
● Note: The sensitivity of the instrument should be high.

7. Range & Span
● In an analogue indicating instrument, the measured value of a variable is
indicated on a scale by a pointer.
● The choice of proper range of instruments is important in measurement. The
region between the limits within which an instrument is designed to operate
for measuring, indicating or recording a physical quantity is called the range
of the instruments.
● The Scale Range of an instrument is thus defined as the difference between
the largest and the smallest reading of the instrument. Supposing the highest
point of calibration is Xmax units while the lowest is Xmin units and the
calibration is continuous between the two points, then the instrument range
is between Xmin and Xmax .
● Many times it is also said that the instrument range is Xmax. The instrument
span is the difference between highest and the lowest point of calibration.
Thus Span = Xmax - Xmin

8. Dead Zone
Dead Zone: for the largest range of values
of a measured variable, to which the
instrument does not respond.
● The dead zone occurs more often due
to static friction in indicating an
instrument.
● A practical example is: Due to static
friction, a Control valve does not open
even for a large opening signals from
the controller.

9. Hysteresis
● Hysteresis: Hysteresis: Hysteresis is a
phenomenon that illustrates the different
output effects when loading and
unloading.
● Many times, for the increasing values of
input an instrument, may indicate one set
of output values. For the decreasing values
of the input, the same instrument may
indicate its different set of output values.
When output values are plotted against
input the following kind of graph is
obtained.

1. Fidelity
● Fidelity of a system is defined as the ability of the system to reproduce
the output in the same form as the input.
● It is the degree to which a measurement system indicates changes in
the measured quantity without any dynamic error.
● Supposing if a linearly varying quantity is applied to a system and if the
output is also a linearly varying quantity the system is said to have 100
percent fidelity.
● Ideally a system should have 100 percent fidelity and the output should
appear in the same form as that of input and there is no distortion
produced in the signal by the system.
● In the definition of fidelity any time lag or phase difference between
output and input is not included.
Dynamic Characteristics of Measurement Systems

2. Time Response & Frequency Response
● Speed(Freq.) of Response is defined as the rapidity with which an
instrument or measurement system responds to changes in measured
quantity.
● Response Time is the time required by instrument or system to settle to its
final steady position after the application of the input.
● For a step input function, the response time may be defined as the time
taken by the instrument to settle to a specified percentage of the quantity
being measured, after the application of the input.
● This percentage may be 90 to 99 percent depending upon the instrument.
For portable instruments it is the time taken by the pointer to come to rest
within +-0.3 percent of final scale length and for switch board (panel) type
of instruments it is the time taken by the pointer to come to rest within 1
percent of its final scale length.

3. Dynamic Error
● The dynamic error is the difference between the true value of the quantity
changing with time and the value indicated by the instrument if no static error
is assumed.
● However, the total dynamic error of the instrument is the combination of its
fidelity and the time lag or phase difference between input and output of the
system.
● Overshoot- Moving parts of instruments have mass and thus possess inertia.
When an input is applied to instruments, the pointer does not immediately
come to rest at its steady state (or final deflected) position but goes beyond it
or in other words overshoots its steady position. The overshoot is evaluated as
the maximum amount by which moving system moves beyond the steady
state position. In many instruments, especially galvanometers it is desirable to
have a little overshoot but an excessive overshoot is undesirable.

3. Dynamic Error
● Fidelity: It is defined as the degree to which a measuring instrument
is capable of faithfully reproducing the changes in input, without
any dynamic error.
● Lag: Every system takes at least some time to respond, whatever
time it may be to the changes in the measured variable.
● For Example Lag occurs in temperature measurement by
temperature sensors such as Thermocouple or RTD or dial
thermometer due to scale formation on thermowell due to process
liquid.
● Retardation lag: the response of the measurement begins
immediately after the change in measured quantity has occurred.
● Time delay lag: in this case after the application of input, the
response of the measurement system begins with some dead times.

What is a Sensor?

Concept and Basic Principle of working of Resistive,
Capacitive and Inductive sensors.
1. HOW RESISTIVE SENSORS WORK:
● A resistive sensor is a transducer or
electromechanical device that converts a
mechanical change such as displacement into an
electrical signal that can be monitored after
conditioning.
● Thermistors, photoresistors, and potentiometers
are some examples of common resistive sensors.
FACTORS AFFECTING RESISTANCE
The resistance of a material depends on four factors:
● Cross-sectional area or thickness
● Length
● Temperature
● Conductivity

● R is the resistance of the conductor,
● A is the area of the conductor,
● l is the conductor’s length, and
● ρ(rho) is the resistivity of the conductor.

Examples of some basic resistive sensors:
Light dependent
resistors
(photoresistors)
Thermistors NTC Thermistor Photoresistor

2. HOW CAPACITIVE SENSORS WORK:
● What is a capacitive sensor?
● A capacitive sensor is an electronic
device that can detect solid or
liquid targets without physical
contact.
● To detect these targets, capacitive
sensors emit an electrical field from
the sensing end of the sensor. Any
target that can disrupt this
electrical field can be detected by a
capacitive sensor.

● Types of materials capacitive sensors can detect:

● Capacitive sensor main parts
Sensor’s Body Indicator LED Sensing Range

3. HOW INDUCTIVE SENSORS WORK:
● An inductive sensor is an electronic
device that can detect ferrous
metal targets without physical
contact.
● Inductive sensors will also detect
non-ferrous metal targets like
aluminum, brass, and copper. But
using non-ferrous metal targets
decreases an inductive sensor’s
sensing range.

Sensing range
● The sensing range of an inductive sensor is the distance from the sensor’s
face to the maximum distance the sensor can detect a metal target.
● The sensing distance can be found on the sensor’s datasheet.
● The datasheet will also show some correction factors when you want to
detect a non-ferrous metal.
● Non-ferrous metal is a type of metal that does not have a significant amount
of iron in it. Brass, aluminum, and copper are examples of non-ferrous metals.
This means these metals do not have a significant amount of iron within
them.
● Here for this inductive sensor, the datasheet shows the sensing distance as 12
mm. This works only when the object is steel which has a significant amount
of iron in it.

INDUCTIVE sensor main parts
Sensor’s Body Indicator LED Cable End

Unit 1 SA.pptx

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