snt

Syllabus

Mid-1 syllabus:

Unit-1: Introduction: Functional elements of an instrument, generalized performance characteristics of instruments – static characteristics, dynamic characteristics. Zero order, first order, second order instruments – step response, ramp response and impulse response. Response of general form of instruments to periodic input and to transient input

Unit-2: Transducers for motion and dimensional measurements: Relative displacement, translation and rotational resistive potentiometers, resistance strain gauges, LVDT, Synchros, capacitance transducers, Piezo-electric transducers, electro-optical devices, nozzle – flapper transducers, digital displacement transducers, ultrasonic transducers, Gyroscopic sensors

Unit-3(1): Transducers For Force Measurement: Bonded strain gauge transducers, Photo electric transducers, variable reluctance pickup, torque measurement dynamometers. Transducers For Flow Measurement: Hot wire and hot-film anemometers, Electromagnetic flow meters, laser Doppler velocity meter

Mid-2 Syllabus:

Unit-3(2): Transducers For Pressure Measurement: Manometers, elastic transducers, liquid systems, gas systems, very high pressure transducers.

Unit-4: Transducers For Temperature Measurement: Thermal expansion methods, Thermometers (liquid in glass), pressure thermometers, Thermocouples, Materials configuration and techniques. Resistance thermometers, Thermistors, junction semiconductors, Sensors, Radiation methods, Optical pyrometers, Dynamic response of temperature sensors heat flux Sensors, Transducers for liquid level measurement, humidity, silicon and quartz sensors, fiber optic sensors.

Unit-5: Smart sensors: Introduction – Primary Sensors – Excitation – Amplification – Filters – Converters – Compensation– Information Coding/Processing - Data Communication – Standards for Smart Sensor Interface – The Automation Sensors –Applications: Introduction – On-board Automobile Sensors (Automotive Sensors)– Home Appliance Sensors – Aerospace Sensors –– Sensors for Manufacturing –Sensors for Environmental Monitoring

Text Books/ Weblinks

Books

1. Sensors and Transducers, D. PATRANABIS, PHI Learning Private Limited.

2. Mechatronics, W. Bolton, Pearson Education Limited.

3. Transducers and Instrumentation, by D.V.S. Murthy (PHI)

4. Instrumentation Measurement & Analysis, by B. C. NAKRA , K. K. CHAUDHRY (TMH)

References:

1. "Measurement systems application and design" by E. DOEBELIN and D. N. Manik, 5E,TMH, 2007.

2. A Course in Electrical and Electronic Measurements and Instrumentation, A. K. Sawhney, Puneet Sawhney,19th Edition, 2011

3. Sensors and Actuators, Patranabis, 2nd Edition, PHI, 2013

Web Links:

1. Industry 4.0 and IOT -NPTEL -Link

2. RK Academy -Link

3. Google books _ DVS Murthy -Link

4. Units 1 to 4 : Syllabus from Bundelkhand University- Page16 of PDF Link

5. Unit-5: Syllabus from BIET- page4 of PDF- Link

6. syllabus: VNRJIET, Pg31 of PDF- Link

7. syllabus: West Bengal University -Various Sensors -Link

Overview

Overview:
Unit-1: instrument, types of input, types of Response Sensors / Transducers
Unit-2: Motion, Dimension
Unit-3: Force, Flow, Pressure
Unit-4: Temperature, Liquid-level
Unit-5: Smart sensors: Characteristics, few Real-time Applications

Assignment Questions

UNIT-1

Q1,2,3- Easy;

Q4,5,6- Moderate;

Q7,8,9- Difficult;

1. Explain the functional elements of an instrument.

2. Compare static and Dynamic characteristics.

3. What is a sensor? What is a transducer? Give examples.

4. How an instrument is classified as zero-order, first-order and second-order systems? Explain.

5. What is a step signal? Explain the process of obtaining step-response of a first-order system.

6. What is a impulse signal? Explain the process of obtaining step-response of a first-order system.

7. Explain about the response of instruments to periodic input.

8. Explain about the response of instruments to transient input.

9. What is a ramp signal? Explain the process of obtaining step-response of a first-order system.

UNIT-2

Q1,2,3- Easy;

Q4,5,6- Moderate;

Q7,8,9- Difficult;

1. Explain about resistive potentiometer transducer.

2. In detail explain the usage of strain gauge transducer.

3. What is LVDT? Explain.

4. What is the basic principle behind piezo-electric crystal? Explain the working of a piezo-electric transducer.

5. What is the principle behind an ultrasonic sensor? Explain.

6. How to convert displacement to pressure using a transducer? Explain.

7. How do opto-electrical devices work? give a brief description with neat sketches.

8. How capacitive transducers work? explain.

9. What is the basic difference between LVDT and a Synchro? Explain about synchro in detail.

UNIT-3(1)

Q1- Easy;

Q2,3- Moderate;

Q4,5- Difficult;

1. Explain the working of a bonded strain gauge transducer.

2. How is a variable reluctance transducer used to obtain digital readings? Explain.

3. Explain the process of measuring torque on rotating shaft using a transducer.

4. With respect to power measurement of a shaft, give details of a similar transducer.

5. What is an anemometer? Compare Hot-wire/Hot-film anemometer with Laser-Doppler Anemometer.

UNIT-3(2)

Q1,2- Easy;

Q3,4- Moderate;

Q5,6- Difficult;

1. Explain about U-tube type manometer.

2. Compare various types of elastic pressure transdcuers.

3. Diaphragm based transducer is an example of elastic pressure transducer. Explain.

4. With neat sketch, explain the working of a Bourdon tube pressure transducer.

5. How very-high pressures are measured? Explain.

6. What are bellows? How are they used to measure pressure? Explain.

UNIT-4

Q1,2,3- Easy;

Q4,5,6- Moderate;

Q7,8,9- Difficult;

1. What are thermal expansion methods? Give details.

2. How is resistance property used to measure temperature? Explain about resistance thermometer.

3. What are thermistors? How are junction semiconductors different from thermistors? Explain.

4. Explain about heat-flux sensors.

5.Explain the measurement of humidity measuring.

6. What are various radiation methods? Explain about optical pyrometer.

7. What are laws of thermocouples? How are thermocouples used to measure temperature? With the help of any one method, explain its working.

8. Explain about fiber-optic sensors.

9. How to measure liquid-level using sensors/ transducers? Explain.

UNIT-5

Q1,2,3- Easy;

Q4,5,6- Moderate;

Q7,8,9- Difficult;

1. How to convert a sensor to a smart sensor? Explain.

2. Explain the terms (i) Primary sensors (ii) Excitation (iii) Amplification (iv) Filters (v) Converters

3. What is compensation? Why is it required in a circuit? Explain its relation to sensors/transducers.

4. Why is it necessary for the processing of information obtained from sensor? Explain.

5.Explain the significance of data communication in case of smart sensors.

6. What is Automation in sensors? Explain.

7. What are on-board automobile sensors? Explain.

Explain about Home Appliance sensors.

What are various sensors used in aerospace application? Explain.

What is automated manufacturing? How sensors used in this application? Explain.

Explain how sensors are used to monitor environmental parameters.

Quiz

UNIT-1

1. A sensor collects _____ from external environment.

(a) Energy (b) dust (c) particles (d) transducer (e) none

2. A transducer converts one form of _______ to another form of _______.

(a) dust, particles (b) dust, Energy (c) Energy, Energy (d) transducer, power (e) none

3. __________ is the closeness of measured value to the true value.

(a) threshold (b) resolution (c)sensitivity (d) Precision

4. The minimum input required to produce an output is called ______

(a) threshold (b) resolution (c)sensitivity (d) Precision

5. Maximum reading of a measurement is called ______ output

(a) minimum scale (b) infinity scale (c) full scale (d) zero scale

6.The equation (dq_o)/dt + 6q_o = 5 q_i is a _______ order equation.

(a) zero order (b) first order (c) second order (d) no order

7. In general a transient input stays for _______ period of time.

(a) larger (b) infinite (c) zero (d) limited

8. If damping ratio is greater than 1, then the system is said to be ______

(a) under damped (b) critically damped (c) over damped (d) normally damped

9. If the system has a ouput response oscillating that slowly reaches stable state, then it is ___

(a) under damped (b) normally damped (c) critically damped (d) over damped

10. A periodic signal ________ for ______ time of intervals

(a) repeats, regular (b) does not repeat, irregular (c) repeats, unpredictable (d)does not repeat, predictable

Key:

1. a 2. c 3. d 4. a 5. c 6. b 7. d 8. c 9. d 10. a

UNIT-2

1. Example of a inverse transducer is _________.

(a) piezo-electric (b) solar cell (c) capacitive (d) none

2. A resistance potentiometer is a __________ order instrument.

(a) first (b) second (c) zero (d) none

3. In a resistance potentiometer, non-linearity _______with increase of load to potentiometer resistance.

(a) increases (b) none (c) does not change (d) decreases

4. In a strain-gauge, Gauge-factor =

(a) (ΔL/R)/(ΔL/R) (b) (ΔR/R)/(ΔL/L) (c) (ΔR/L)/(ΔL/R) (d) (ΔL/L)/(ΔR/R)

5. A LVDT core is made of __________ material.

(a) weak permeable (b) non- permeable (c) high permeable (d) high permittivity

6. Capacitive transducers are used for ________ measurements.

(a) flow (b) natural (c) static (d) dynamic

7. Rochelle salt belongs to _______ group.

(a) sea-salt (b) natural (c) synthetic (d) none

8. Piezo-electric transducers are ________ transducers.

(a) Active (b) Passive (c) Inverse (d) None

9. A single free-gyro can measure rotation about ____________

(a) one axis (b) two perpendicular axes (c) Eight parallel axes (d) Four axes

10. A free-gyro angular velocity = _______; where Tf is constant friction torque, Hs is angular momentum of spinning wheel

(a) ω_d = H_s/T_f (b) ω_d = T_f*H_s (c) ω_d = T_f/H_s (d) ω_d = √(T_f*H_s)

Key:

1. a 2. c 3. d 4. b 5. c 6. d 7. b 8. a 9. b 10. c

UNIT-3(1)

1. _______ strain gauge has no moving parts.

(a) Bonded (b) unbonded (c) both a, b (d) none

2. A photo-voltaic cell converts ________energy to _________.

(a) heat, electric (b) electric, heat (c) light, electric (d) electric, light

3. ________is the opposing force acting on a inductor by itself.

(a) Conductance (b) Resistance (c) Inductance (d) Reluctance

4. transducer used to measure torque is ______

(a) dynamometer (b) tachometer (c) LDR (d) LVDT

5.In a electro-magnetic flow meter, to measure the flow, it must be ______

(a) vacuum (b) air (c) conductive liquid (d) insulating liquid

6. Hot-wire anemometer transducer used to measure _______.

(a) pressure (b) flow (c) temperature (d) force

7. Doppler effect; Assume an observer at stationary position; an object that produces a frequency of fo approaches the observer; The frequency received by the observer _____

(a) does not change (b) decreases (c) none (d) increases

8. Disadvantage of hot-wire anemometer is ________

(a) it measures flow

(b) it measures force

(d) none

Key:

1. a 2. c 3. d 4. a 5. c 6. b 7. d 8. c

UNIT-3(2)

1. Manometer is used to measure ___________

(a) pressure (b) temperature (c) distance (d) density

2. In a diaphragm type of pressure transducer, when pressure is applied, the diaphragm moves ___________

(a) downward (b)to left (c) to right (d) upward

3. Bellows are elastic transducers that are used to measure ______

(a) temperature (b) pressure (c) distance (d) density

4. In a very high-pressure transducer, bellows are filled with ____________

(a) water (b) air (c) kerosene (d) bubbles

5. Bourdon tube is a _______ of ring structure

(a) wire (b) solid tube (c) spring (d) hollow tube

6. To remove air above the ________ of elastic transducer, a vent is provided at top.

(a) diaphragm (b) bourdon tube (c) bellows (d) manometer

Key: 1-a, 2-d, 3-b, 4-c, 5-d, 6-a

UNIT-4

1. Two different metals with different temperature coefficients are bonded firmly. Now when the junction temperature changes,

(a) nothing happens

(b) bends uniformly to a circular arc

(d) bends to a triangle

2. In case of liquid-in-glass thermometers, Auxiliary thermometer is used to _______

(a) read more temperature

(b) it is just dummy

(d) increase visibility

3. Pressure thermometer uses the _______ and ________

(a) manometer, bimetallic thermometer

(b) bourdon tube, liquid-in-glass thermometer

(d) diaphragm, liquid-in-glass thermometer

4. Two different metals firmly joined. When one of the junctions kept at reference, and other junction temperature varies, Voltage is produced. This device is called ___________

(a) Thermometer (b) Pyrometer (c) Thermocouple (d) Thermistor (e) none

5. In case of Thermistors with positive temperature coefficient, if temperature increases, then resistance _________

(a) increases (b) decreases (c) remains same (d) none

6. Optical pyrometer uses the following elements:

(a) filament of lamp (b) lens (c) eye-piece (d) a, b, c (e) none

7. While using temperature sensors, _____________ can produce promising compensation

(a) specific heat (b) rugged environment (c) speed response (e) dual-sensors

8. A Gardon-gage is better than Slug-type heat-flux sensor because

(i) large heat sink (ii) lesser heat sink (iii) thermocouple connected to heat-flux

(a) i, ii (b) ii, iii (c) i, iii (d) none

9. Liquid-level measurement: If the liquid level increases, the air pressure in the pipe ____

(a) decreases (b) equals (c) increases (d) does not effect

10. A smooth finished mirror type surface collects dew drop (condensation). This

measurement, method uses __________ to measure humidity.

(a) only LEDs

(b) only photo transistors

(d) LED and photo transistor

11. Fiber-optic based pressure measurement, uses _______ and ______

(i) optical fiber cable, light source

(ii) light is passed from one end of fiber and reaches the other end

(iii) the amount of light that passes the other end decreases, when pressure applied on the

optical fiber

(a) i, ii (b) ii, iii (c) i, iii (d) ) i, ii, iii

Key: 1-b, 2-c, 3-b, 4-c, 5-a, 6-d, 7-e, 8-c, 9-c, 10-d, 11-d

UNIT-5

1. Primary sensors are different from smart sensors. Primary sensors are:

(a) sensors +supply voltage + trigger input

(b) sensors only

(d) supply voltage only

2. Power supply, trigger input (AC/DC) are called _________ which are given to a sensor

(a) excitation (b) amplification (c) filter (d) converter

3. When the input sensed by a sensor is very low, __________ is required.

(a) excitation (b) amplification (c) filter (d) converter

4. Interfacing an analog output of a sensor to a microprocessor requires _________

(a) excitation (b) amplification (c) filter (d) converter

5. Correction, compensation, linearization, processing. This is collectively called _____

(a) information coding/processing

(b) excitation

(d) none

6. HART is used for data communication. HART =

(a) Highway Addressable Remote Trigger

(b) Host Addressable Remote Transducer

(d) Highway Addressable Remote Transducer

7. Smart Sensor = Primary Sensor + _____________

(a) converter

(b) supply voltage

(d) transducer

8. Application of Sensors that are used in manufacturing industry:

(a) distance sensing

(b) pattern recognition

(d) all the options (a, b, c)

9. Application of aerospace sensors:

(a) head light control

(b) pattern recognition

(d) none

10. Application of Sensors that are used for Environmental monitoring are:

(a) pollution hazards

(b) environmental pollution

(d) all the options (a, b, c)

(e) none

11. Application of Sensors that are used in manufacturing industry:

(a) distance sensing

(b) pattern recognition

(d) all the options (a, b, c)

(e) none

12. Application of Sensors that are used for on-board automobiles:

(a) flow-rate

(b) temperature

(d) all the options (a, b, c)

(e) none

13. To reduce noise in microchips/smart sensors, one of the best techniques is ___________

(a) cross-correlation

(b) semi-correlation

(d) all the options (a, b, c)

(e) none

14. Automation uses:

(a) distance sensing

(b) Bluetooth

(d) all the options (a, b, c)

(e) none

Key: 1-b, 2-a, 3-b, 4-d, 5-a, 6-d, 7-c, 8-d, 9-c, 10-d, 11-d, 12-d, 13-a, 14-c

Class Tests

Class Test-1:

1. Explain about the functional elements of an instrument.

2. Discuss about

(i) Static sensitivity

(ii) Resolution

(iii) Hysteresis

(iv) Precision

3. What is a second order system? Explain its characteristics in general

4. Explain the response obtained from an instrument for a general periodic input.

5. Explain about a zero-order system.

Class Test-2:

1. Explain the working of LVDT.

2. What is the basic principle behind piezo-electric crystal? Explain the working of a piezo-electric transdcuer.

3. With neat sketches, give brief description and working of a strain-guage.

4. What is the principle behind an ultrasonic sensor? Explain.

5. How to convert displacement to pressure using a transducer? Explain.

Class Test-3:

1. Explain about any one type of elastic transducer

2. Explain about Manometer

Class Test-4:

1. Explain about Thermocouple.

2. What is the purpose of bourdon tube in pressure thermometer? Explain.

Previous Papers

1
2

Unit-1: Instrument, types of input, types of Response Sensors / Transducers

Syllabus: intro, elements, characteristics, responses Introduction: Functional elements of an instrument, generalized performance characteristics of instruments – static characteristics, dynamic characteristics. Zero order, first order, second order instruments – step response, ramp response and impulse response. Response of general form of instruments to periodic input and to transient input

Transducer: Energy Converter i.e., converts energy from one form to another form

Examples: Microphone, Speaker, Antenna, Strain gauge

Sensor: Sense the physical characteristic of environment in which it is placed; Response is change in its V, I, R, C, L, etc.,

Examples: Temperature sensor, Color sensor, Ultrasonic sensor, Gas sensor , Pressure sensor, etc.,

Example of a Feedback system: Home heating instrument:

A bimetallic will sense room temperature
It helps in giving input to the controlling unit
Controller will instruct the control element to maintain the temperature
Hence the temperature is maintained as per predefined value.

Primary sensing element:

receives energy --> produces some output depending on the measured quantity; Ex: Temperature varies continuously, produces frequent changes; so one cannot see a fixed temperature; A Good instrument is designed to minimize this effect.

Variable conversion element: A more suitable variable for processing Variable manipulation equipment: Ex: Amplifier output is a multiple of input

Data transmission element: if above two elements are physical (not functional), then this exists.

Data storage/playback element: For future data retrieval

Data presentation element: Translation of the variable value of previous stages; pointer moving over a scale, a recording pen moving over a chart, etc.,

Generalized performance characteristics of instruments

Static Characteristics: Measurement of quantities that are constant or vary slowly

Accuracy: It is indirectly given by error in a reading.

%Error = [ (MeasuredValue - TrueValue) / TrueValue ] x 100% or else

%Error = [(MeasuredValue - TrueValue) / FSO ] x 100%

where FSO = FullScaleOutput

Precision Value being close to the true value

Repeatability: difference of output y at a given input x (obtained in two consecutive measurements)  Static sensitivity: Ratio of incremental output to incremental input

S = Δy / Δx

Non-Linearity: deviation of i/p vs FSO

deviation from best fit straight line obtained by regression analysis.

Non-linearity consequence is distortion

Threshold: Smallest input that produces detectable output

Resolution: Smallest incremental input that produces detectable output o it increases by number of decimal digits (generally)

Hysteresis:

x is i/p, y is o/p

x vs y plot

difference in the output of the sensor when input goes this way: xmin to xmax again xmax to xmin.

Dynamic Characteristics: Measurement of quantities that vary rapidly.

Generalized mathematical model of Measurement system

nth order differential equation

Zero-order instrument

a0, b0 are non-zero; remaining all are zeros.
a0 qo = b0 qi
qo = K qi where K = b0/a0 = sensitivity
no distortion
no time-lag
Example: Potentiometer

First-order instrument

a1, a0, b0 are non-zero; remaining all are zeros.
a1 dqo/ dt + a0 qo = b0 qi
(𝜏D+1) qo = K qi
𝜏 = a1/a0 =time constant; K=b0/a0;
Example: liquid-in-glass thermometer
Step-response:

Particular Solution = qopi = K qis
Complementary Function = qocf = C e^(-t/𝜏)
qo = K qis (1- e^(-t/𝜏) )
settling time: After step input is applied, Time taken by a system to reach (+ or -tolerance) around its final value.

Ramp response:

qi = qis t
qocf = C e^(-t/𝜏)
(𝜏D+1) qo = K qis t
qo = C e^(-t/𝜏) + K qis (t- 𝜏)
qo = K qis [ 𝜏 e^(-t/𝜏) + t- 𝜏 ]

Impulse response

Impulse of strength A where lim p(t) with T-->0

(𝜏D+1) qo = K A/T
qo = ( KA/T ) (1- e^(-t/𝜏)) as T-->0
i.e., qo = ( KA/𝜏 ) e^(-t/𝜏)

Second-order instrument

a2 d^2qo/ dt^2 + a1 dqo/dt + a0 qo = b0 qi
K = b0/a0
ωn = sqrt(a0/a2) = undamped natural frequency
ζ = a1 / (2 x sqrt(a0 a2)) = damping ratio
Step-response:

input constant

Ramp response:

ramp = qis t

Impulse response:

Response for (a) Periodic input (b) Transient input:

Periodic Input: Periodic means repeats itself over a period of time

Fourier series representation

The Fourier series is a infinite series; Only first TEN harmonics (frequencies) are to be considered. Also any signal can be represented in both COSINE and SINE or as a single entity shown below.

Frequency response and phase response

Transient Input: The input has some value for a period of time t0, later always zero. That means input dies over a period of time. Fourier transform/ Laplace transform can be used for solving.

Frequency response:

Types of transients:

A general transient response with the help of FT and IFT blocks:

Unit-2: Motion and Dimension Sensors

Syllabus:

Transducers for motion and dimensional measurements: Relative displacement, translation and rotational resistive potentiometers, resistance strain gauges, LVDT, synchros, capacitance transducers, Piezo-electric transducers, electro-optical devices, nozzle – flapper transducers, digital displacement transducers, ultrasonic transducers, Gyroscopic sensors

Potentiometer:

R = ρ L/ A

R= resistance = ohms

ρ = resistivity = ohm-meter

L= length of the straight wire

A= Area of cross-section of the wire

Relative displacement:
a wire (copper-nickel alloy) is wound on an insulator
Maximum resistance between x and y position is R ohms.
the position where jockey (Gold-silver) is placed on the wire where insulation is removed. This device is called Potentiometer.
The conducting jockey position decides the resistance of the potentiometer.
if jockey at position x; the potentiometer resistance is 0 ohms
if jockey position at position below x; it varies as R/20, R/10 as the jockey moves downwards towards point y;
if jockey is at point y; the potentiometer is having maximum resistance, i.e, R ohms
There are different jockey shapes like circular, rectangular, etc.,
The smallest voltage that can be measured is △V = V/n

where V is applied voltage between x and y positions and n is number of turns (the wire wound along insulator)

The jockey size must be appropriate such that, it does not short two or more wires at a time; This effects the precision.
if the potentiometer is loaded, its linearity is effected.
A potentiometer can also have a rotary motion as shown below:

resistance between positions 1 and 3 is fixed
to use as potentiometer, use (1 and 2) OR (2 and 3)
the wiper moves in rotary motion along the resistive material;
so rotary motion is converted to resistance

Resistance Strain gauges:

Strain gauges are classified as:

1. Bonded strain gauges

2. Unbonded strain gauges

3. Semiconductor strain gauges

4. Capacitive strain gauges

type1,2 are resistive strain gauges; type-4 is a capacitive.

When we see term, resistance, we need to recollect : R = ρ L/ A L= length of unfolded wire A= area of cross section of wire ρ = resistivity of the wire used

Bonded strain gauge:

Fig(a) bonded strain gauge Fig(b) is using a strain gauge in a circuit

There are no moving parts in bonded strain gauge.
The strain-gauge is used in a bridge network which is already in a balanced state.
The four arms are such that there is no deflection in the galvanometer.
on an elastic material, a wire (thin film like) in the form of a coil/ foil/ is placed of different shapes. This is the default resistance.
When force is applied, the material deforms and the wire stretches, making a change in the default resistance.
when one of the arm resistance changes, causes the bridge unbalance. This unbalance causes deflection in galvanometer/ any other instrument which is used for calibration purpose.
Gauge-factor= (ΔR/R)/ (ΔL/L)

Unbonded Strain-gauge:

On a fixed base, there is a moving part in the middle.
at two opposite different location unbonded wires are mounted with moving part and fixed base.
When force is applied, Purple wires stretch; Black wire compress. This creates a change in resistance.
Always a strain-gauge is used in a bridge network.

LVDT:

(LINEAR VARIABLE DIFFERENTIAL TRANSFORMER)

LVDT consists of a non-magnetic hollow cylindrical chamber with two windings over it.

Primary winding - P at the middle o Secondary winding which splits into two parts as:
Secondary winding1 (S1) at one end of the chamber
Secondary winding2 (S2) which is a part at the other end

S1-P: this combination produces voltage V1
S2-P: produces voltage V2

A piston type Ferrite material based arrangement can move freely within the chamber.
When Force is applied on the top surface of the piston
Under stable condition (force not applied), piston stays at the center of the hollow chamber; This creates V1-V2= 0V;
Force applied into chamber (PUSH): piston moves in towards S2 winding; This creates a potential V2 greater than V1
Force applied out of chamber (PULL): piston moves out towards S1 winding; This creates a potential V1 greater than V2
The piston moves linearly; this movement produces potential difference of two transformer windings; hence the name LINEAR VARIABLE DIFFERENTIAL TRANSFORMER

Synchros:

linear force ==> LVDT

Rotatory force ==> Synchros

Rotor has primary winding- P; it it attached to AC supply via slip-rings.
Stator has three or more windings = Secondary Windings;
here it is three; o namely S1, S2, S3. o each winding separated from other by 120°
Primary coil (ferrite rod/core/ rotor) can be at :
S2: it has a Voltage of 120° from S1 o S3: it has a Voltage of 240° from S1 and 120° from S2
S1: no phase shift; as it is the reference location
Synchros are of two types:

Torque Type:

This is basic synchro (discussed above)

Control Type:

Two synchros are coupled
single AC supply
Windings are electrically connected

S11 to S21
S12 to S22
S13 to S23

R1 rotor rotates for a torque applied;
This moves at an angle θ1;
the rotor R1 produces a field such that, rotor R2 if not oriented with R1, makes a similar angle movement (till it attains same rotational position as R1)

Capacitance transducers:

* C= ε A/ d

* Two metallic plates separated by a distance d

* One of the plates (bottom) is fixed to ground/ object.

* Using a spring like structure Plate1 is above the bottom plate.

* When force applied on the top plate, the distance reduces and C changes.

* The capacitive transducer is used in a bridge network/ or as per requirement.

* These transducers can be of Cylindrical, Spherical, etc., shapes also.

Piezo-electric transducers:

piezo electric transducer

piezo connected to amplifier

* Mechanical deformation produces charge Q with capacitance C i.e, E= Q/C

* Pertinent constant = g33 = (e0/t ) / (fi /wl)

* Materials are Quartz, Barium Titanate, etc.,

* The Piezoelectric crystals are used in many modes likes, thickness shear, face shear, thickness expansion, Transverse expansion, etc.

* The following are the properties of the Piezoelectric Crystals.

The piezoelectric material has high stability.
It is available in various shapes and sizes.
The piezoelectric material has output insensitive to temperature and humidity.

Applications:

The piezoelectric material has high stability and hence it is used for stabilizing the electronic oscillator.
The ultrasonic generators use the piezoelectric material. This generator is used in SONAR for underwater detection and in industrials apparatus for cleaning.
It is used in microphones and speakers for converting the electric signal into sound.
The piezoelectric material is used in electric lighter.

Electro-optical devices:

* Any application contains LASER/ Light generating device and Light capturing device like photo diode/ photo transistor/ LDR/ etc.,

* Example1: LASER light is focused by a lens and depending on direct focus/ reflection, reaches the lens placed before the photo diode.

photo diode analysis

* This lens converges all rays received from multiple directions to a single photo diode point.

* Example-2: it is a LASER interferometer.

* It provides very precise motion measurement

* By counting illumination cycles, can calculate the distance between any two positions of the movable mirror.

Nozzle – flapper transducers:

* it is a displacement to pressure measurement device

* fixed restriction supply provides the pressure Ps

* there is a gap between flapper and Pipe nozzle; distance is Xi

* This decreases the pressure Po.

* as the flapper displacement reduces Xi value, then the pressure Po increases.

* Xi is 1/proportional to Po on a calibrated scale.

Digital displacement transducers:

* Slots/ holes are arranged in a binary fashion/ decimal fashion as per requirement.

* for example, for the translational digital displacement, observe the second figure.

* The black set is a movable part, where the box and brushes are fixed.

* At a fixed location,light passes through the holes and read by the photo diode/transistors/ LED... LEDs ON status indicates the displcement digitally (binary form here)

Ultrasonic transducers:

* Pulse generator produces pulses

* There is a magnetostrictive wire, within the non-magnetic chamber.

* A movable magnet 🧲 moves over the non-magnetic chamber.

* if Xi is less, the refleceted pulses are quickly received by the RX. If Xi is large, pulses received take long time/ of lower frequency.

* The magnet is the object that takes the force and produce the displacement.

Gyroscopic sensors:

figure1

figure2

* single axis gyroscope is shown in figure2

* A gyroscope of three axis has the following axes: Pitch, Roll, Yaw along x, y and z axes respectively. It is shown in figure1.

* The vehicle axes are used as reference but not the space-axes.

* The rotation theta must be small, so as to tirgger/balance even small motion.

* The rotation phi can be large.

* Depending on the object/vehicle movement, the spin wheel rotates to balance the axes motion.

Unit-3(1): Force, Flow measurement

Unit-3(1): Transducers For Force Measurement: Bonded strain gauge transducers, Photo electric transducers, variable reluctance pickup, torque measurement dynamometers. Transducers For Flow Measurement: Hot wire and hot-film anemometers, Electromagnetic flow meters, laser Doppler velocity meter.

Transducers For Force Measurement:

Bonded strain gauge transducers

* refer to strain gauge topic in unit-2 ----LINK

Photo electric transducers

1. LDR (light dependent resistor):

LDR is an acronym for Light Dependent Resistor. LDRs are tiny light-sensing devices also known as photoresistors. An LDR is a resistor whose resistance changes as the amount of light falling on it changes. The resistance of the LDR decreases with an increase in light intensity, and vice-versa. This property allows us to use them for making light sensing circuits.
The Light-dependent resistors made with photosensitive semiconductor materials like Cadmium Sulphides (CdS), lead sulfide, lead selenide, indium antimonide, or cadmium selenide and they are placed in a Zig-Zag shape as below; This shape can attract more light.
The LDR has the highest resistance in dark around 1012 Ohm and this resistance decreases with the increase in Light.

2. Photo Diode:

A photodiode is a PN-junction diode that consumes light energy to produce an electric current. They are also called a photo-detector, a light detector, and a photo-sensor.
Photodiodes are designed to work in reverse bias condition.
Typical photodiode materials are Silicon, Germanium and Indium gallium arsenide.
A photodiode is subjected to photons in the form of light which affects the generation of electron-hole pairs. If the energy of the falling photons (hv) is greater than the energy gap (Eg) of the semiconductor material, electron-hole pairs are created near the depletion region of the diode.
The electron-hole pairs created are separated from each other before recombining due to the electric field of the junction. The direction of the electric field in the diode forces the electrons to move towards the n-side and consequently the holes move towards the p-side. As a result of the increase in the number of electrons on the n-side and holes on the p-side, a rise in the electromotive force is observed.
When an external load is connected to the system, a current flow is observed through it.
Applications;

Photodiodes are used in safety electronics such as fire and smoke detectors.
Photodiodes are used in numerous medical applications. They are used in instruments that analyze samples, detectors for computed tomography and also used in blood gas monitors.
Photodiodes are used in solar cell panels.
Photodiodes are used in logic circuits.
Photodiodes are used in the detection circuits.
Photodiodes are used in character recognition circuits.
Photodiodes are used for the exact measurement of the intensity of light in science and industry.

3. Photo Transistor:

Dark Current: There is a dark current or small reverse saturation current through phototransistors even if there is no light incident on them. Dark current increases with an increase in temperature. If the voltage applied across the collector-emitter junction increases above the breakdown voltage, permanent damage occurs to the phototransistors.

A Phototransistor is a kind of transistor that is sensitive to light. It comprises of a photodiode & a transistor which is used to detect light and convert it into an electrical signal. The phototransistor was invented by John Northrup Shive in 1950 at Bell Telephone Laboratories.
Its operation is based on the concept of the photoelectric effect. That is, when light is incident on a surface, the light energy is converted into electrical energy.
Phototransistors are typically made up of a semiconductor material such as silicon or germanium, along with other materials that are used to form the various layers and junctions within the device.
Advantages:

High light sensitivity: They can detect even very small amount of light.
They have high gain.

It can be used as amplifiers: Since they are made of semiconductor material, they can act as a switch or amplifier. This means that the small current generated by the photodiode can be amplified to a larger current that can be easily measured or processed.

Very cheap and easily available.
Produce high current than photodiodes

Disadvantages:

Voltages over 1000 V cannot be handled by silicon-made phototransistors.
Sensitive to surges, electrical spikes, and electromagnetic energy.
Do not allow electrons to move freely as in other devices.
Low-frequency response.

Applications:

Remote control systems to detect signals from remote controls, such as those used in TVs, DVD players, and other electronic devices.

4. photo voltaic cell:

A photovoltaic (PV) cell, commonly called a Solar cell, is a nonmechanical device that converts sunlight directly into electricity.
Some PV cells can convert artificial light into electricity.

A photovoltaic cell is comprised of many layers of materials, each with a specific purpose. The most important layer of a photovoltaic cell is the specially treated semiconductor layer. It is comprised of two distinct layers (p-type and n-type), and is what actually converts the Sun's energy into useful electricity through a process called the photovoltaic effect.
On either side of the semiconductor is a layer of conducting material which "collects" the electricity produced. Note that the backside or shaded side of the cell can afford to be completely covered in the conductor, whereas the front or illuminated side must use the conductors sparingly to avoid blocking too much of the Sun's radiation from reaching the semiconductor.
The final layer which is applied only to the illuminated side of the cell is the anti-reflection coating. Since all semiconductors are naturally reflective, reflection loss can be significant. The solution is to use one or several layers of an anti-reflection coating (similar to those used for eyeglasses and cameras) to reduce the amount of solar radiation that is reflected off the surface of the cell.
The most common material for commercial solar cell construction is Silicon (Si), but others include Gallium Arsenide (GaAs), Cadmium Telluride (CdTe) and Copper Indium Gallium Selenide (CIGS). Solar cells can be constructed from brittle crystalline structures (Si, GaAs) or as flexible thin-film cells (Si, CdTe, CIGS).

Variable reluctance pickup

1. It is the opposing force acting on an inductor (like a wire has resistance and conductance); a coil has reluctance and inductance.

2. This transducer consists of a ferro-magnet wound by a coil which is given excitation (power supply). 3. An analog meter (usually an ammeter used to measure current) is connected in the excitation loop.

4. This ammeter will show the amount of current flowing in the coil.

5. An iron piece moves towards the ferromagnet, when force is applied.

6. The gap between the iron piece and ferro-magnet is air.

7. When the air-gap reduces (when force applied on iron piece), the reluctance reduces and hence the current increases.

8. This change in the current is calibrated for a current-to-force conversion scale.

Torque measurement dynamometers

There are different types of torque measurement techniques:

a) Absorption technique (the measured torque is not utilized properly, results in loss in the form of heat) b) Transmission technique (torque from a system is transmitted to another system; Ex: Belt type arrangement)

c) driving technique (torque from a system is driven to another system)

1. A dynamometer is used to measure torque and power.

2. A shaft rotating is fitted between, two wodden blocks through proper fitting which can be tightened or loosened.

3. Weight (W) is applied which causes wooden blocks to apply brake gradually when weight is increased.

4. Hence the name absorption type of dynamometer. The torque is wasted in the form of brake form.

5. Torque = L x W Where L =length from shaft to the position of weight (W) is placed

Transducers For Flow Measurement:

Hot wire and hot-film anemometers

Two types of measurement techniques:

a. Constant current type

b. constant temperature type

Electromagnetic flow meters

* A metallic pipe of surrounded by magnetic field passes from left to right with a velocity v

* it must be a conductive fluid.

* If a conductor moves in the presence of magnetic field, emf is induced. This is Fleming Right Hand rule.

* The emf developed may be +e or -e as per direction of flow across the pipe.

* e= Blv where B=magnetic flux density, l= length of the conductor, v=velocity of conductor

* appriximate resistance of the fluid is R, then overall voltage is e-iR where i is the current flowing in the conductor.

Laser Doppler velocity meter

wear-out of sheet due to regular velocity measurement

*when the

Laser-Doppler Velocity Meter

Higher frequency received when sheet moves faster

Lower frequency received when sheet moves slowly

Unit-3(2): Pressure measurement

Unit-3(2): Transducers For Pressure Measurement: Manometers, elastic transducers, liquid systems, gas systems, very high pressure transducers.

Transducers For Pressure Measurement:

Manometers

1. It is a U-shaped hollow tube; Hollow part named as tube-A (left side) and tube-B (right side)

2. It is filled with a fluid

3. when there is no pressure on side-A, shows a balanced level,

4. When pressure is applied on side-A, then liquid level drops and on side-B, the fluid level raises.

5. The difference in the levels of fluid between side-A and side-B is h

6. Pressure applied is, P = ρ h where ρ is fluid density

Elastic transducers (Liquid systems & gas systems)

Bourdon Tube:

1. A hollow tube of ring structure

2. one end is air inlet

3. the other end is a moving part; movement increases with pressure

4. When air pressure increases at inlet end, the moving part moves so that this arrangement is attached to a pointer that moves

Diaphragm:

1. An empty box (cuboid like) structure, in which middle layer is filled with elastic membrane.

2. at the bottom of the box is the air inlet.

3. to compensate the pressure, a small outlet is provided to remove air above the diaphragm.

4. When pressure is applied at the inlet end, the diaphragm is connected to a pointer which moves on a calibrated scale.

Bellows:

1. It is a hollow elastic membrane in a zig-zag manner at the edges.

2. It expands when pressure is increased and compresses when pressure decreased in side the bellows.

3. The top surface of the bellow is connected to a pointer, the moves on a pressure-calibrated scale.

4. When pressure is applied at the bottom end of the bellows, the bellows expand. The pointer moves on a pressure-calibrated scale showing the pressure.

5. To retract back the bellows to the normal position, springs are connected at the sides of the edges.

Very High pressure transducers

1. Instead of using hollow bellows, kerosene filled bellows are used to measure high pressure.

2. a wire is placed inside a coil; this module is placed inside the bellows (which is filled with kerosene, a high-density fluid)

3. Water is a high-density fluid, but rusts/ oxidizes with material. Petrol/ diesel are also high-density fluids which are expensive. Hence Kerosene is preferred. (kerosene is high density/ does not erode the container in which is stays, even for a long period)

4. When external pressure is applied, the bellows compress , there by the wire and the coil compress. The wire and the coil setup is connected to a wheat-stone bridge network, which becomes unbalanced in this situation.

5. The unbalanced bridge causes deflection in galvanometer which is calibrated against pressure-scale.

Unit-4: Temperature measurement

syllabus: Transducers For Temperature Measurement: Thermal expansion methods, Thermometers (liquid in glass), pressure thermometers, Thermocouples, Materials configuration and techniques. Resistance thermometers, Thermistors, junction semiconductors, Sensors, Radiation methods, Optical pyrometers, Dynamic response of temperature sensors heat flux Sensors, Transducers for liquid level measurement, humidity, silicon and quartz sensors, fiber optic sensors

1. Thermal Expansion Methods

1a. BiMetallic Thermometers
1b. Liquid-in-glass Thermometers
1c. Pressure Thermometers

2. Thermoelectric sensors (Thermocouples); Materials, Configuration and Techniques

3. Resistance thermometers

4. Thermistors

5. Junction semiconductor sensors

6. Radiation methods

6a. Optical Pyrometers

7. Dynamic response of temperature sensors

8. Heat-Flux sensors

Miscellaneous:

9. Liquid-level measurement

10. Humidity measurement

11. Micro-machined Silicon and Quartz sensors

12. Fiber-Optic sensors

Transducers For Temperature Measurement:

Thermal expansion methods

BiMetallic Thermometers:

1. Two different metals A and B

2.With different thermal-expansion coefficients α_A and α_B

3. these two different metals are firmly bonded together

4. temperature change causes differential expansion and the BiMetallic structure deforms into a uniform circular arc.

ρ =2t/3(α_A-α_B )(T2 -T1 ) where ρ is radius of curvature t is thickness of total strip thickness T2-T1 is temperature rise

Thermometers (liquid in glass)

(or) Liquid-in-glass thermometers

1. It consists of a bulb at the bottom, followed by capillary tube, later which is calibrated over a temperature scale

2. temperature sensitive fluid is filled in the bulb

3. When the bulb is placed in a hot fluid, the fluid in the bulb expands; Rises to a level 4. Two types of liquid-in-glass thermometers:

4a. Full-immersion type: In this type, there is no specific level indicated on the thermometer up to which level the thermometer is to be immersed.

4b. Partial-immersion type: In this type, there is marking on thermometer, up to which it can be immersed in a hot fluid.

5. Full-immersion type is more accurate compared to partial-immersion type thermometer.

6. Auxiliary thermometer is also based on liquid-in-glass thermometer, which is used a reference to reduce errors.

Pressure thermometers

1. A bulb filled with temperature-sensitive fluid.

2. This bulb is connected to a capillary tube

3. the capillary tube other end is connected to a bourdon tube

4. When the bulb is placed inside a hot liquid, the temperature-sensitive fluid expands, pushes the pivot of bourdon-tube, this pivot moves pointer on temperature-calibrated scale.

5. The more the temperature, the more the expansion of fluid, exerts more pressure in the bourdon tube, hence more temperature reading on the scale

Thermocouples

Watch the videos---Link1 Link2

1. Two different metals are joined firmly

2. When the junction is heated, produces voltage across (the two metal ends)

3. To reduce errors, out of two junctions available, one of the junction is used as reference whose temperature is known value.

4. junction T1, temperature to be measured (unknown), while T2 is a reference (known value of temperature). This method reduces errors.

Thermocouple Laws:

Law-1. wires connecting thermocouple, used uncovered (i.e., exposed to environment), also does not effect the produced voltage.

Law-2,Law-3. Voltage-measuring device can be inserted between junctions, to measure emf.

Law-4. Platinum used as reference metal. All possible metals can be calibrated later.

Law-5. to measure unknown temperature, temperature of one of the thermo-junctions must be known.

Types of Reference junction based thermocouples:

1. ice-bath reference junction

2. isothermal-block reference junction

Materials configuration and techniques

1. tungsten-rhenium: this combination used in jet, rocket engines upto 5000°F;

2. rhodium-iridium: used at 4000°F

3. cooled thermocouples: Liquid coolant used to to cool the chamber where thermocouple is placed. Proper scaling/calibration is needed.

4. Boron/Graphite: good sensitivity; 40uV/°C; Can be used in short times; upto 4500°F;

Resistance thermometers

*Note: Also called RTD (resistance temperature detector)

1. R= Ro (1 + a_1 T + a_2 T^2 + ....) where R = real time resistance Ro is resistance at 0°C a_0 =1; a_1, a_2,... are constants for increasing accuracy. T is operating temperature

2. Platinum, nickel, copper are mostly used.

3. Tungsten and nickel alloy also used.

4. A coil of wire is cemented to base; upper part of the coil sealed by a cover;

5. When placed on/in a hot object; the coil resistance changes as per the formular mentioned above.

6a. The resistance of the coil changes with temperature. These two leads of the resistance thermometer are connected to a bridge network.

6b. the bridge will show deflection or can be brought to null using a proper technique. These need to be calibrated on a temperature scale.

Thermistors

Thermistors / (bulk Semiconductor temperature sensors)

1. bulk Semiconductor temperature sensors are called Thermistors

2. R = Ro [ e^ β((1/T) - (1/To)) ] where T, To in Kelvin R is resistance at T°K and Ro is resistance at To °K β is characteristic of material 3. Conductors have small +ve temperature coefficient i.e., T increases, Resistance increases i.e., I (current) decreases

4. Semiconductors have large -ve temperature coefficient i.e., T increases, Resistance decreases i.e., I increases

5. Manganese, nickel, Cobalt oxides milled in proper proportions with binders are pressed into a desired shape and sintered ( solidify by heating without liquification)

6. semiconductors have nonlinear resistance. (observe point-1, its exponentially related to temperature)

7. Other semiconductor resistors are: carbon resistors and Si and Ge crystal elements.

8. Silicon (Si) with varying amounts of boron impurities can have positive OR NEGATIVE TEMPERATURE coefficients.

Junction semiconductors sensors

*1.semiconductor junction diodes and transistors are also used as temperature sensors.

2. mostly digitally used

3. After measuring a reference-junction, sends a proportional voltage to a computer which collects data.

4. the temperature measurement is corrected digitally using a software program.

5. {Advantages}: Linearity, Good sensitivity, simple circuit.

6.{Disadvantage}: upper temperature of 200°C is limited by Silicon device property.

Radiation methods & Optical pyrometers

Radiation Methods:

1. Physical bodies emit radiation (sub-atomic particles) for various reasons.

2. Every object above absolute zero, emits radiation (i.e., with some temperature, emits radiation)

3. black body will absorb all radiation that falls on it, and emit maximum amount of thermal radiation for a given temperature.

4. Wavelength lie in between visible and IR (infrared) region

Radiation methods (Radiometers): They are commonly called as radiation pyrometer, radiation thermometer, Optical Pyrometers. Various type like:

(i) Unchopped Broad Band Radiation Thermometer

(ii)Chopped Broad Band Radiation Thermometer

(iii)Chopped Selective Band Radiation Thermometers

(iv) Automatic Null Balance Radiation Thermometers

(v) optical pyrometers (Monochromatic, Two-coloured, Black body-tipped)

Optical Pyrometer:

Lens = converge rays

Aperture = to concentrate on a particular object (like Binoculars have a small opening eye piece)

Target = any object with some temperature

1. light from Target will pass through a lens, then through Aperture, Will fall on Heated Filament (lamp);

2. But still the image of target, must be visible through lens of Eye-piece lens

3. When the filament is heated, lamp brightness increases

4a. As the brightness of lamp increases, the Target starts to disappear.

4b. At a certain current/ lamp brightness, Targets completely disappears.

5. The temperature of the filament/ current supplied to filament is calibrated to temperature scale

6. In this way the brightness of lamp (which is proportional to current, which again is proportional to temperature of filament of lamp) gives the temperature of the target is obtained.

7. As this technique is manual null-balance principle, it is not usable for continuous or automatic applications.

Dynamic response of temperature sensors heat flux Sensors

1a. Dynamic characteristic of temperature sensor are related to, heat-transfer and -storage parameters. 1b. This causes the sensor, to lag from that of the measured medium.

2. Conservation of energy:

where

Tin = temperature indicated by sensor

Tact = actual temperature of surrounding fluid

τ = time constant

M =mass of sensing element

C= specific heat of sensing element

U = overall heat transfer coefficient

A= heat transfer area

3. Speed of response can be increased by:

3a. decreasing M and C OR

3b. increasing U and A

4. Dynamic response tests of temperature sensors, in the laboratory are always not accurate.

5. Errors may be present due to improper installation, relocation of insulations in probe construction etc.,

6. Dynamic compensation of temperature sensors:

6a. For a rugged environment, a sluggish response may be obtained.

6b. a dynamic-compensation device cascaded, will improve the response.

6c. compensation is for specific sensor dynamics:

6c(i) Operating conditions change ---> changes in numerical values or form of Transfer Function ---> loss of compensation

6d. increased speed of response (amplify the signal only up to a certain level) ---> overall sensitivity effected.

6e. Dual-sensors can produce promising compensation.

Heat-Flux sensors

Two types of Heat-flux sensors:-

a. Slug-type sensors

b. Steady-state sensors OR Asymptotic sensors OR Gardon Gage

Slug-type heat-flux sensor

1. slug of metal is buried (also insulated) from surface

2. Across the surface heat-transfer rate is to be measured

3. local heat transfer rate = q

where M = mass of slug C= specific heat of slug A= area of slug T =temperature of slug

4. For this sensor, front-face temperature is more compared to the rear-face temperature. But the heat transfer-rate is constant.

5. before the front-surface reaches max, rear-surface reaches steady-state. This optimum value is given by δ

where δ = k T fmax/ (1.366 q)

Gardon Gage OR Asymptotic sensors OR Steady-state sensors:

1. A thin constantan disk is connected at its edges to a large copper heat sink, while a thin copper wire is fastened at the center of the disk.

2. this forms a differential thermocouple between center and its edges.

3. Thermocouple is directly connected to heat-flux.

4. first order-type system

Transducers for liquid level measurement

Method1:

* When liquid level rises, the shallow cylinder (floating) moves up and up;

* A linkage rod connected to the cylinder moves jockey over a linear variable resistor whose resistance changes

* The wires from the linear variable resistor is connected to one of the arms of a Wheat stone bridge.

* The change in resistance is calibrated over a (liquid-level) scale.

Method-2:

*When liquid-level rises, the shallow cylinder is pushed upwards.

* This causes change in force exerted by the cylinder.

* Force is calibrated over a liquid-level scale.

Method-3:

* When the liquid in the container ,has some pressure.

* When the liquid volume increases, the pressure also increases.

* The pressure can be calibrated over liquid-level indicator scale.

* The above methods are applicable for a open vessels/ containers.

Method-4:

* For closed containers/vessels differential pressure is to be measured.

* Here the air/gaseous pressure with liquid pressure are measured.

* This difference is calibrated over a liquid-level calibrated scale.

Method-5:

* The regulator allows air into the pipe.

* Now as the liquid level raises, the pressure in the pipe increases.

* This causes the pressure sensor to show deflection over a liquid-level calibrated scale.

Transducers for humidity measurement

Method-1:

* strictly a Laboratory method.

* water vapour in air is absorbed by sample chemicals.

* it is weighed carefully. it has a systematic error of 3%

*it is called Gravimetric Hygrometer. Hygrometer is used to measure humidity This method is one time measurement, also manually to be done for repeated values.

Method-2:

*Dunmore sensor

* for continuous or control of relative humidity, electrical transducers are required.

* A plastic pipe, with dual-winding of noble-metal wires with a fixed spacing between them.

* Lithium-chloride solution is coated over it.

*Electrical resistance of this path varies with relative humidity of the surrounding air

Method-3:

*Pope Cell

*sulfonated polystyrene ion exchange device

*Non-linear resistance

* few Mega Ohms at 0% humidity to 1000 ohms at 100% humidity

* single sensor can cover complete range

Method-4:

* Dew-point measurement

* A smooth finished mirror type surface collects dew drops (condensation) at a particular temperature

* LEDs produce light and fall on the drops collected.

* Photo transistors collect the reflected light; More drops accumulated, means more reflection.

Method-5:

* it is electrolytic type of measurement

* sample gas is passed through an analyzer tube

* inside the tube is platinum wires in double-helix structure DC supply is applied at its ends

* space between wire is coated by desiccant(phosphorous pentoxide) {solids that absorb water, like silica gel in bags, bottles, etc.,}

* When moisture in sample gas is taken by P2O5, water is electrolyzed into H and O and measure the current flows Current is proportional to moisture;

Silicon and Quartz sensors

Fiber optic sensors

Light intensity modulation is measured i.e., variation of light intensity is measured. This can be attenuation, scattering, fluorescence, internal reflection.

The optical fiber here used for two applications:

(a) Pressure Measurement

(b) Temperature Measurement

Pressure Measurement

Construction:

*Elastic silica diaphragm is on top layer, into which optical fiber is embedded.

*To give it a support, is the silica base.

Working:

*light is passed from one end at the bottom and reaches the other end under normal condition

*When external pressure is applied, the fiber bends and the intensity of light that passes the other end reduces. This is because, the fiber bends and less amount of light passes through the fiber. The more pressure, the less the light passing.

*This light passing the other end is measured using photodiode, which in turn indicates the same as voltage.

Temperature Measurement

Construction:

* it is a fluorescent material + optical measurement, hence the name Fluoroptic system

* a fluorescent material shine brighter when light is focused on it, gradually its brightness decreases with time (if light focus is stopped)

* A material with exponentially decaying fluorescence (i) applied to the surface, whose temperature is to be measured (ii) or placed at the tip of the probe.

Working:

* Xenon flash sends a short-pulse of blue light (Transmission through Optical fiber)

* immediately, red color light (long-wavelength) is passed through same optic fiber.

* This long wavelength light gets reflected from the fluorescent material

* The duration of light that the fluorescent material decays, depends on the temperature at which it exists. i.e., T proportional to duration of light dimming.

* This dimming light is collected with an optical sensor ,which in turn calibrates decay of light to temperature.

Unit-5: Smart Sensors

Syllabus: Smart sensors: Introduction – Primary Sensors – Excitation – Amplification – Filters – Converters – Compensation– Information Coding/Processing - Data Communication – Standards for Smart Sensor Interface – The Automation Sensors –Applications: Introduction – On-board Automobile Sensors (Automotive Sensors)– Home Appliance Sensors – Aerospace Sensors –– Sensors for Manufacturing –Sensors for Environmental Monitoring

Rearranged Syllabus:

Smart Sensors:

1. Introduction

2. Primary Sensors

3. Excitation, Amplification, Filters

5. Converters

6. Compensation

8. Information Coding/Processing

9. Data Communication

10. The Automation

Sensors- Their Applications:

11.Introduction

12. On-board Automobile Sensors (Automotive Sensors)

13. Home Appliance Sensors

14. Aerospace Sensors

15. Sensors for manufacturing

16. Sensors for Environmental Monitoring

Smart Sensors:

Introduction

* Intelligent sensors = Smart sensors

* Smart Sensors= Sensors + compensation of non-ideal behavior + communication the host + Advanced Signal Processing Unit

* Properties:

@ Auto linearization of non-linear transfer characteristics.

@ Auto correction of offsets, time, temperature, etc., @ auto ranging and calibration

@ Self-tuning control algorithms

@ auto-acquisition, storage of calibration constants

@ signal processing, data analysis

@ communication through serial bus

*Integration features of Smart Sensors include: improved computing capability + digital communication + new sensing methods

*Single chip pressure sensor

*semiconductor thermocouple

*integrated thermopile system

Primary Sensors

* External stimuli (means inputs) such as strain/stress, thermal, optical, electric/magnetic, change the material atomic/molecular or crystalline state.

* Ignore a values from other parts of sensor

* environmental conditions to be maintained

* response/ sensitivity to environmental effects

* silicon based micro-sensor technology mostly used.

* Example: A single chip pressure sensor consists of the following:

@ it consists of a deformable silicon diaphragm with piezo resistors arranged along edges of diaphragm which form bridge circuit.

@ this unit is connected to a signal conditioning unit within the chip.

Excitation, Amplification, Filters

Excitation:

*It may be supply given to primary sensors.

*It may also include supply given to processing chips connected to primary sensors.

*Also the supply may be AC or DC. For running devices DC supply is needed. For giving inputs like pulse input to trigger devices, AC suuply of small voltage and a desired frequency must be used.

Amplification:

*Output of a sensor is small. Such voltage or current can not drive the next level devices.

*If gain is very high, noise also gets amplified; which in turns increases problems.

*stage-wise sufficient amplification with proper compensation is required.

Filters:

*conversion of values/signals at different stages require different filters.

*these are mostly analog.

*consume more time.

*consume more power also.

Converters

*internal interfacing between continuous and discrete processing.

*software can be used to range selection, etc.,

Mulitivibrator:

*These are used to produce binary values 1 and 0;

*The frequency is dependent on the input voltage. Hence the name voltage-controlled oscillator.

*Time Period= T = R C

*Frequency of oscillation = f= 1/ T

Integrated Ring oscillator:

*These contain modules like pressure sensors (like piezo-electric sensors), ADC, Capacitive

sensors, frequency-dividers, etc., all embedded within the chip.

Compensation

(a) Non-linearity

(b) noise and interference

(d) drift

(e) cross-sensitivity

Information Coding/Processing

* signal from sensor be :

# corrected

# compensated

# linearized

# digitized

# reduced from cross-sensitivity

# communication bus

# display processing

* smart sensor uses a microcontroller and memory; retrieve a set of mapped-values;

Data Communication

* it is essential in smart transmitters (which are smart sensors connected to transmitting units)

* HART (Highway Addressable Remote Transducer) protocol is used mostly.

* HDLC (high-level Data Link Control), SDLC (synchronous data link control), FIP (Factory

Instrumentation Protocol) are some other protocols.

* HART protocol can be used with digital communication with superimposed modulation

between field device and host system.

* various IEEE (Institute for Electrical and Electronic Engineers) standards are predominant

among various semiconductor devices.

Ex: Bluetooth, Wi-Fi, LAN, etc.,

The Automation

* To implement, various complex blocks are to be connected.

* these blocks to be controlled using one of the control technique:

# Hierarchical control structure system

# distributed control structure

Sensors- Their Applications:

On-board Automobile Sensors (Automotive Sensors)

* Flow-rate sensors

* Pressure sensors

* Temperature sensors

*Oxygen sensors

* Torque and Position sensors

Home Appliance Sensors

* Magnetic sensors, temperature sensing, radiation sensors, pyro-electric IR sensors,

Photodiode- LED pair, etc., can be found in home appliances

Aerospace Sensors

* Static Pressure sensors

* Temperature sensing

* Fluid velocity sensors

* sensing direction of air-flow

* Monitoring Strain, Force, Thrust, and Acceleration

Sensors for manufacturing

* sensors like distance sensing, contour tracking, Machine vision, Pattern recognition,

Machine diagnosis, Process parameter sensing

Sensors for Environmental Monitoring

* Pollution Hazards

* environmental pollution

* Ecological studies of Air

impQ

1
2