M1 Mechatronics.pptx

Mechatronics is an interdisciplinary area of engineering that combines mechanical
engineering electrical engineering and computer science.

Components of Mechatronics System
Mechatronics Electronics system consist of mechanical system, electrical systems and
information technology.
Servo Motor is a typical example for the mechatronics system.
Mechanical components -Rotor and Stator.
Electrical components -Field windings and rotor windings , Circuitry for power transmission.
Electronic components -Sensors such as optical encoders and controller’s circuit elements.

Other examples of mechatronics systems are
 Digital cameras
 Washing machine
 ATM
 Anti-Lock Braking System CNC machine tools
The key components of mechatronic systems
1. Information systems:
2. Mechanical systems;
3. Electrical systems
4. Computer systems:
5. Sensors and actuators;
6. Real-time interfacing

Basic Elements of Mechatronics System

1)Sensors and actuators
 Sensors and actuators mostly come under mechanical systems.
 The actuators produce motion or cause some action.
 The various actuators .used in the mechatronic system are pneumatic and
hydraulic actuators, electro-mechanical actuators, electrical motors such as DC
motors, AC motors, stepper motors, servomotors, and piezoelectric actuators.
 The sensors detect the state of the system parameters, inputs, and outputs.
 The various types of sensors used in the mechatronic system are linear arid
rotational sensors, acceleration sensors, force, torque and pressure sensors, flow
sensors, temperature sensors, proximity sensors, light sensors.

2) Signals and conditioning
The mechatronic systems deal with two types of signals and conditioning such as - input
and output. The input devices receive input signals from the mechatronic systems via
interfacing devices and sensors. Then it is sent to the control circuits for conditioning or
processing. The various input signal conditioning devices used in the mechatronic system
are discrete circuits, amplifiers, Analog-to-Digital (A/D) converters, Digital-to-Digital
(DZD) convertors.
The output signals from the system are sent to output/display devices through
interfacing devices. The various output signal conditioning devices used in the
mechatronic system are Digital-to-Analog (D/A) converters, Display Decoders (DD)
converters, amplifiers, power transistors, and power op-amps.

3)Digital logic systems
Digital logic devices control overall system operation. The various digital logic systems
used in the mechatronic system are logic circuits, microcontrollers, programmable
logic controllers, sequencing and timing controls, and control algorithms.
4)Software and data acquisition systems
The data acquisition system acquires the output signals from sensors in the form of
voltage, frequency, resistance etc. and it is inputted into the microprocessor or
computer. Software is used to control the acquisition of data through DAC board.
The data acquisition system consists of a multiplexer, amplifier, register, and control
circuitry and DAC board.

5) Computers and display devices
Computers are used to store a large number of data and process further through
software. Display devices are used to give visual feedback to the user. The various
display devices used in the mechatronic system are LEDs, CRT, LCD, digital displays, etc.

Objectives of Mechatronics
Actual activities in mechatronics are concerned with generating motions in machinery in
a controlled way. Controlling motions is necessary, for example, in industrial robots,
electrical and hydraulic servo drives, or in magnetic bearings. In addition to normal
usage, it is applicable in critical situations or on a higher level of autonomy, where the
necessary interactions with the human operator or user have to be facilitated and
structured.

System
A group of physical components combined to perform a specific function. A system can be
considered as a box has an input and an output . 1) Measurement system can be
considered as a system that is used to measure the required parameter. The quantity being
measured is given as the input and the value of the quantity is obtained as the output.
eg: Rotational speed measurement (ip-rotation of shaft, op- Numbers)
2. Control system cam be considered as a device that is used to control the output of the
system to a desired value.
eg. A domestic air-conditioning system that has the temperature required the house as
input and room temperature as output. That is we can set the required temperature on the
thermostat or controller and the compressor adjusts itself to pump the refrigerant through
the evaporator so as to produce the required temperature in the house.

Characteristics of sensors:
A sensor usually has static and dynamic characteristics.
Static characteristics are the values given when the steady state condition occurs ie the
value given when the transducer has settled down after having received some input.
Dynamic characteristics refer to the behaviour between the time that the input value
changes and the time the value given by the transducer settles down to steady state
value. The reason for dynamic characteristics is the presence of energy-storing
elements: Inertial: masses, inductances Capacitances: electrical, thermal

Dynamic characteristics are determined by analyzing the response of the sensor to a
family of variable input waveforms:

Static Characteristics:
1 Accuracy -The accuracy defines the closeness of the agreement between the actual
measurement result and a true value of the measurand. It is often expressed as a
percentage of the full range output or full–scale deflection.
2 Precision-It is defined as the closeness amoung set of values.Let Xt be the true value of
variable X and s random experiment measures X1,X2,…..Xi as the value of X1,X2,…..Xi
are precise when they are very near to each other nut not necessarily close to true value.
3 Range- The range of a sensor indicates the limits between which the input can vary. For
example, a thermocouple for the measurement of temperature might have a range of 25-
225 °C.

4 Span- The span is difference between the maximum and minimum values of the input.
Thus, the above-mentioned thermocouple will have a span of 200 °C.
5 Error- Error is the difference between the result of the measurement and the true
value of the quantity being measured. A sensor might give a displacement reading of
29.8 mm, when the actual displacement had been 30 mm, then the error is –0.2 mm.
6 Sensitivity -Sensitivity of a sensor is defined as the ratio of change in output value of a
sensor to the per unit change in input value that causes the output change.
7 Resolution -Resolution is the smallest detectable incremental change of input
parameter that can be detected in the output signal.
Eg: Resolution of voltmeter having 0-10V having 100 division is 0.1V

8 Hysteresis-It is the difference in output when input is varied in two ways, that is
increasing and decreasing. Some sensors do not return to same output when input
is increased or decreased. The width of expected error in terms of measured
quantity is known as hysteresis.

9 Nonlinearity-The nonlinearity indicates the maximum deviation of the actual
measured curve of a sensor from the ideal curve.
Nonlinearity (%) = Maximum deviation in input ⁄ Maximum full scale input .
10 Reproducibilty-It is defined as the abitliy of a sensor to produce same output when
same input is applied.
Taken over a long time interval.
Performed by different operators.
With different instruments.
In different laboratories.

11 Repeatibility- it is defined as the ability of a sensor to produce the same output every
time when same input is applied keeping all the physical condition same including
operation instrument ambient condition etc.
12 Stability -Stability is the ability of a sensor device to give same output when used to
measure a constant input over a period of time. The term ‘drift’ is used to indicate the
change in output that occurs over a period of time. It is expressed as the percentage of
full range output.
13 Dead band/time -The dead band or dead space of a transducer is the range of input
values for which there is no output. The dead time of a sensor device is the time duration
from the application of an input until the output begins to respond or change.

1 Speed of Response
Speed of Response is defined as the rapidity with which an instrument or measurement
system responds to changes in measured quantity. The speed at which the output
changes is less than the speed at which the input varies.
2 Measuring Lag
An instrument does not react to a change in input immediately. The delay in the
response of an instrument to a change in the measured quantity is known as measuring
lag.
Measuring lag is of two types :
Retardation type: In this type of measuring lag the response begins immediately after a
change in measured quantity has occurred.

Time delay type: In this type of measuring lag the response of the measurement system
begins after a dead zone after the application of the input.
3 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.
4 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.

TEMPERATURE SENSORS
.Temperature sensors such as bimetallic strips, thermocouples, thermistors are widely used in
monitoring of manufacturing processes such as casting, molding, metal cutting etc. The
construction details and principle of working of some of the temperature sensors are discussed
in following sections.
1. Bimetallic strips
Bimetallic strips are used as thermal switch in controlling the temperature or heat in a
manufacturing process or system. It contains two different metal strips bonded together. The
metals have different coefficients of expansion. On heating the strips bend into curved strips
with the metal with higher coefficient of expansion on the outside of the curve. As the strips
bend, the soft iron comes in closer proximity of the small magnet and further touches. Then the
electric circuit completes and generates an alarm. In this way bimetallic strips help to protect
the desired application from heating above the pre-set value of temperature.

2.Resistance Temperature Detectors (RTDS):
RTDs work on the principle that the electric resistance of a metal changes due to change in its
temperature. The correlation is
where Rt is the resistance at temperature T (⁰C) and R0 is the temperature at 0⁰C and α is the
constant for the metal termed as temperature coefficient of resistance. The sensor is usually
made to have a resistance of 100 Ω at 0 °C
On heating up metals, their resistance increases and follows a linear relationship as shown in
Figure. It has a resistor element connected to a Wheatstone bridge. The element and the
connection leads are insulated and protected by a sheath. A small amount of current is
continuously passing though the coil. As the temperature changes the resistance of the coil
changes which is detected at the Wheatstone bridge

Applications are:
1. Air conditioning and refrigeration servicing
2. Food Processing
3. Stoves and grills
4. Textile production
5. Plastics processing
6. Petrochemical processing
7. Micro electronics
8. Air, gas and liquid temperature
measurement in pipes and tanks
9. Exhaust gas temperature measurement

Thermistors
A thermistor is a resistance thermometer or a resistor whose resistance is dependent on
temperature .A thermistor is similar to an RTD, but a semiconductor material is used instead
of a metal .The name comes from a combination of the words.Resistance can change by
more than 1000 times. Thermistors sense minute changes in temperature undetected by
RTDs & thermocouples.
There are two types:
PTC (Positive Temperature Coefficient of Resistance). Resistance increases with increase in
temperature. Used in electric current control devices

NTC (Negative Temperature Coefficient of
Resistance)- Resistance decreases with increase in
temperature.
The most common type of Thermistors are those in
which resistance decreases as the temperature
increases (NTC).
The relationship between temperature and resistance
is given by the following equation.
Here, R is the resistance at temperature T
RR is the resistance at the reference temperature TR
is a constant

Applications of Thermistors
1. To monitor the coolant temperature and/or oil temperature inside the engine
2. To monitor the temperature of an incubator
3. Thermistors are used in modern digital thermostats
4. To monitor the temperature of battery packs while charging
5. To monitor temperature of hot ends of 3D printers
6. To maintain correct temperature in the food handling and processing industry equipment’s
7. To control the operations of consumer appliances such as toasters, coffee

Thermocouple
Thermocouples are active sensors employed for the measurement of temperature.
The thermoelectric effect is the direct conversion of temperature differences to an
electric voltage.
When two dissimilar metals are joined together to form two junctions such that one
junction (hot junction / measured junction) is at a higher temperature than the other
junction (cold junction / reference junction), a net emf is generated.

Principle of operation: Seebeck effect
If two junctions of thermo-couple are placed at different temperature, then an emf will be
produced in thermo-couple which will be proportional to the temperature difference.
𝛻𝑉12=𝛼𝛻𝑇
Where α is the seabeck coefficient

Applications of Thermocouples
1. To monitor temperatures throughout the steel making process
2. Testing temperatures associated with process plants e.g. chemical production and petroleum
refineries
3. Testing of heating appliance safety
4. Temperature profiling in ovens, furnaces and kilns
5. Temperature measurement of gas turbine and engine exhausts
6. Monitoring of temperatures throughout the production and smelting process in the steel, iron
and aluminium industry

LIQUID FLOW
Liquid flow is generally measured by applying the Bernoulli’s principle of fluid flow through a
constriction. The quantity of fluid flow is computed by using the pressure drop measured. The
fluid flow velocity is proportional to square root of pressure difference at the two ends of the
constriction. There are various types of fluid flow measurement devices being used in
manufacturing automation such as Orifice plate, Turbine meter etc.

1 Orifice Plate
When a liquid / gas, whose flow-rate is to be determined, is passed through an Orifice Meter,
there is a drop in the pressure between the Inlet section and Outlet Section of Orifice Meter.
This drop in pressure can be measured using a differential pressure measuring instrument.
Since this differential pressure is in direct proportion to the flow-rate as per the Bernoulli's
Equation hence the differential pressure instrument can be configured to display flow-rate
instead of showing differential pressure.

Turbine flow meter has an accuracy of ±0.3%. It has a multi blade rotor mounted centrally in the
pipe along which the flow is to be measured. Figure shows the typical arrangement of the rotor
and a magnetic pick up coil. The fluid flow rotates the rotor. Accordingly, the magnetic pick up
coil counts the number of magnetic pulses generated due to the distortion of magnetic field by
the rotor blades. The angular velocity is proportional to the number of pulses and fluid flow is
proportional to angular velocity

FLUID PRESSURE SENSORS
Chemical, petroleum, power industry often need to monitor fluid pressure. Various types of
instruments such as diaphragms, capsules, and bellows are used to monitor the fluid pressure.
1. Strain gauges on a diaphragm (Diaphram Pressure Gauge)
A diaphragm pressure gauge is a device that uses a diaphragm with a known pressure
to measure pressure in a fluid. A fluid in contact with a flexible membrane pushes on
that membrane, bending it. The pressure is a measure of how hard it pushes. When the
outside pressure is low, the reference pressure bends the membrane out. As the
outside pressure increases, it pushes back on the membrane, bending it back the other
way. By measuring how far the membrane bends, the gauge can detect the outside
pressure.

The pressure is measured by placing an electric resistance strain gauge over the
diaphram. An electric resistance strain gauge uses a long strip of an electric resistor--a
device that resists the flow of electricity. The resistor is attached to the diaphragm. As
the diaphragm bends, it stretches out the resistor, increasing the resistance. The
resistor has an electric current running through it. The more the diaphragm bends and
increases the resistance, the more the current drops. By measuring the electric current,
the gauge can determine how far the diaphragm has bent, and thus, how much
pressure the outside air is creating

2)Capsule and Bellow
The diaphragm is an elastic membrane that elongates when pressure is applied to it. The
diaphragm is a single sheet which elongate. Joining two diaphragm to form a capsule.
Two capsules joining to form a stacked diaphragm. Adding more capsules to the diaphragm
increases the sensitivity of the gauge.
When pressure is applied to the diaphragm, it flexes. The movement is transmitted by a link that
connects to the pointer. The pointer moves to indicate the amount of pressure applied to the
diaphragm. The diaphragm stays at the original position until a pressure is applied to it.

2) Bourden Tube pressure gauge

The bourdon tube is the ‘C’ shaped tube shown in the above figure. When a pressure is
applied to the tube, the tube stretches outwards. The tube end is attached to a pointer using a
link. The link-gear system makes the pointer moves along the scale. The circular motion of the
pinion gear drives the position of the pointer to indicate the amount of pressure applied to the
Bourdon tube.

2. Piezoelectric sensor
 The word "piezoelectric" literally means electricity caused by pressure
 There are certain materials that generate electric potential or voltage when mechanical strain
is applied to them or conversely when the voltage is applied to them, they tend to change
the dimensions along certain plane. This effect is called as the piezoelectric effect.
 When mechanical stress or forces are applied to some materials along certain planes, they
produce electric voltage.
 This electric voltage can be measured easily by the voltage measuring instruments, which can
be used to measure the stress or force.
 The voltage output obtained from these materials due to piezoelectric effect is proportional
to the applied stress or force.
 The output voltage can be calibrated against the applied stress or the force so that the

Potentiometer
A resistance with a movable contact (a potentiometer) may be used to measure linear
or rotational displacements.
A known voltage is applied to the resistor ends. The contact is attached to the moving
object of interest The output voltage at the contact is proportional to the
displacement.

CONSTRUCTION PRINCIPLES OF POTENTIOMETERS

Advantages:
Easy to use
Low cost
High-amplitude output signal
Proven technology
Rugged construction
Very high electrical efficiency
Availability in different forms, ranges and sizes
Disadvantages
Limited bang width
Frictional loading
Inertial loading
Limited life due to wear

Strain Gauge is a passive transducer that converts a mechanical displacement into change of
resistance.
The electrical resistance of a copper wire / iron wire changes when the wire is either stretched
or compressed.
He used a Wheatstone bridge circuit with a galvanometer as the indicator.
Strain gages are used to measure linear strains that occur at surface points of an object when
it responds to some actuating load.
Deformation of the surface element forces the strain gauge to change its length
The variation in length of the parallel segments of the wire-type conductor will be directly
proportional to the variation in electrical resistance of the conductor.

Strain gauges are widely used in experimental stress analysis and diagnosis on machines
and failure analysis. They are basically used for multi-axial stress fatigue testing, proof
testing, residual stress and vibration measurement, torque measurement, bending and
deflection measurement, compression and tension measurement and strain
measurement.

PROXIMITY SENSORS
1)Inductive Proximity Sensors

Inductive sensors operate on the basis of Faraday’s Law.They are are basically used for
detection of metallic objects.
An inductive proximity sensor has four components; the coil, oscillator, detection circuit and
output circuit. An alternating current is supplied to the coil which generates a magnetic
field. When, a metal object comes closer to the end of the coil, inductance of the coil
changes. This is continuously monitored by a circuit which triggers a switch when a preset
value of inductance change is occurred.

Inductive sensors can’t be used to detect plastic or cardboard or other non-metallic objects
because they do not possess inductive property. However, different metals have different
inductive properties and the type of metal being sensed will influence the sensing distance. For
instance, ferromagnetic materials like steel generally have the longest sensing distance, while
non-ferrous metals such as aluminum or copper have much shorter sensing distances. In general,
inductive proximity sensors are well suited to shorter-range applications

2) Capacitive Proximity Sensors
 Capacitive sensors use an alternating voltage which causes the charges to continually reverse
their positions.
 The moving of the charges creates an alternating electric current which is detected by the
sensor.
 The amount of current flow is determined by the capacitance.
 Capacitance is directly proportional to the surface area of the objects and the dielectric
constant of the material between them, and inversely proportional to the distance between.
 Larger and closer objects cause greater current than smaller and more distant objects.
 The capacitance is also affected by the type of nonconductive material in the gap between the
objects.

 In typical capacitive sensing applications, the probe or sensor is one of the conductive
objects; the target object is the other.
 The sizes of the sensor and the target are assumed to be constant as is the material
between them.
 Any change in capacitance is a result of a change in the distance between the probe and
the target.
 The electronics are calibrated to generate specific voltage changes for corresponding
changes in capacitance. These voltages are scaled to represent specific changes in distance.

Linear Variable Differential Transformer (LVDT)
 It is a passive type sensor
 An LVDT produces an output proportional to the displacement of a movable
core within the field of several coils.
 As the core moves from the null position, the voltage induced by the coils
change, producing an output representing the difference in induced voltage.
 It works on the mutual inductance principle
 It consists of a primary coil wound on an insulating form and two secondary
coils symmetrically spaced from the primary

 An external AC power source is applied to the primary coil and the two
secondary coils are connected together in phase opposition.
 The motion of the core varies the mutual inductance of secondary coils.
 This change in inductance determines the electrical voltage induced from
the primary coil to the secondary coil.
 If the core is centred in the middle of the two secondary windings, then the
voltage induced in both the secondary coils will be equal in magnitude but
opposite in phase, and the net output will be zero.
 An output voltage is generated when the core moves on either side of the
null position.

4. Ultrasonic sensor
Ultrasonic transducers or ultrasonic sensors are a type of acoustic sensor divided into three
broad categories: transmitters, receivers and transceivers. Transmitters convert electrical
signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers
can both transmit and receive ultrasound.
In a similar way to radar and sonar, ultrasonic transducers are used in systems which
evaluate targets by interpreting the reflected signals. For example, by measuring the time
between sending a signal and receiving an echo the distance of an object can be calculated.

Optical encoders provide digital output as a result of linear / angular displacement. These are
widely used in the Servo motors to measure the rotation of shafts.. It comprises of a disc with
three concentric tracks of equally spaced holes. Three light sensors are employed to detect the
light passing through the holes. These sensors produce electric pulses which give the angular
displacement of the mechanical element e.g. shaft on which the Optical encoder is mounted.
The inner track has just one hole which is used locate the ‘home’ position of the disc. The
holes on the middle track offset from the holes of the outer track by one-half of the width of
the hole. This arrangement provides the direction of rotation to be determined.

When the disc rotates in clockwise direction, the pulses in the outer track lead those in
the inner; in counter clockwise direction they lag behind. The resolution can be
determined by the number of holes on disc. With 100 holes in one revolution, the
resolution would be, 360⁰/100 = 3.6⁰

Pneumatic sensors are used to measure the displacement as well as to sense the proximity of
an object close to it. The displacement and proximity are transformed into change in air
pressure. Figure shows a schematic of construction and working of such a sensor. It
comprises of three ports. Low pressure air is allowed to escape through port A. In the
absence of any obstacle / object, this low pressure air escapes and in doing so, reduces the
pressure in the port B. However when an object obstructs the low pressure air (Port A), there
is rise in pressure in output port B. This rise in pressure is calibrated to measure the
displacement or to trigger a switch. These sensors are used in robotics, pneumatics and for
tooling in CNC machine tools.

Resolver
The resolver is an electromechanical device which converts mechanical motion to
electronic signal.It is a rotary transformer used for conversion of the angular position of
the shaft into Cartesian coordinates. It is an analogue device which has a digital
counterpart. The output of the transducer has two signals, one is proportional to
the sine of the angle and other is proportional to the cosine of the angle.

The resolver is a very precise electromagnetic device which consists two stators and two
rotor windings. Their construction is similar to the two phase two pole wounds induction
motor.
The two stator windings are placed in a same magnetic structure, but their axis is 90° apart
from each other. Similarly, the rotor windings are placed in the same magnetic structure
and are mutually perpendicular to each other.
The alternating voltage is applied across the stator windings which induces the alternating
magnetic flux. This flux induces the voltage in the rotor windings. The output voltage of
the rotor winding is directly proportional to the input voltage of the stator. The output
voltage of the rotor is equal to the sine and cosine angle of the stator.

Synchro
The Synchro is a type of transducer which transforms the angular position of the shaft into
an electric signal. It is used as an error detector and as a rotary position sensor. The error
occurs in the system because of the misalignment of the shaft. Their construction is similar to
the three phase alternator. The stator of the synchros is made of steel for reducing the iron
losses. The stator is slotted for housing the three phase windings. The axis of the stator winding
is kept 120º apart from each other.
The coils of the stator windings are connected in star. The rotor of the synchros is a dumbbell in
shape, and a concentric coil is wound on it. The AC voltage is applied to the rotor with the help
of slip rings.
The voltage is induced in the stator winding because of the mutual induction between the
rotor and stator flux. The flux linked in the stator winding is equal to the cosine of the angle
between the rotor and stator.

Acoustic emission is a phenomenon of sound and ultrasound wave generation by
materials that undergo deformation and fracture processes . Sources generating AE in
different materials are unique. Acoustic emission waves, generated by sources of
different nature depend directly on material properties and environmental factors.
Acoustic Emission Sensor
Crack jumps, processes related to plastic deformation development ,fracturing and de-
bonding of inclusions leaks, friction, knocks, chemical reactions, are some examples of
sources generating acoustic emission waves

The goals of acoustic emission examinations in industrial applications today, are
detection, location and assessment of flaws in structures made of metal, concrete or
composites. In these materials, fracture development in form of crack propagation is
a primary source of acoustic emission. Elementary crack jumps under static or
dynamic loads are followed by a rapid release of energy. A part of this energy is
released in form of stress waves as a result of fast redistribution of a stress field at
the crack top. The stress waves generated are elastic waves mostly but inelastic
waves can be generated also when stresses exceed yield limit. This occurs, for
example, at the plastic zone of a crack developing in a ductile metal.

Acoustic emission sensor is a device that transforms a local dynamic material displacement
produced by a stress wave to an electrical signal. AE sensors are typically piezoelectric sensors
with elements maid of special ceramic elements like lead zirconate titanate (PZT). These
elements generate electric signals when mechanically strained. Other types of sensors include
capacitive transducers, laser interferometers.
Selection of a specific sensor depends on the application, type of flaws to be revealed, noise
characteristics and other factors. Typical frequency range in AE applications varies between 20
kHz and 1 MHz

There are two qualitative types of sensors according to their frequency responds: resonant
and wideband sensors. Most AE sensors are of resonant type which means they are most
sensitive at their resonance frequency. These AE sensors may have other frequency bands
where their sensitivity is low. Another important property of AE sensors is a Curie Point, the
temperature under which piezoelectric element loses permanently its piezoelectric
properties. Curie temperature varies for different ceramics from 120 to 400C0.

A typical acoustic emission system consists of:
Sensors used to detect AE events.
Preamplifiers that amplify initial signal. Typical amplification gains are 40 or 60 dB.
Cables that transfer signals on distances up to 300m to AE devices. Cables are typically of
coaxial type.
Data acquisition device that performs analog-to-digital conversion of signals, filtration, hits
(useful signals) detection and it parameters evaluation, data analysis and charting.

It is used in petro-chemical, power, nuclear power, gas-treatment, military, aerospace,
medical, pharmaceutical and automotive industries and of course in academic and
industrial research institutions. Applications can be divided on three categories:
examination of structures, material study and control over manufacturing processes.
Acoustic emission method is used for control over manufacturing processes like monitoring
of welding, metal crystallization, forming and other.
Applications
Metal pressure vessel inspection Piping inspection

Vibration Sensors
Vibration sensor is a device that serves to detect the presence of vibration then it will be
converted into electrical signals. The electric signals are processed in the measuring
instrument then we can read the information in the measuring instrument.
Generally there are two types of vibration sensors
1)Contact type vibration sensors-Here the transducer is mounted on vibrating test piece.
i Acceleration Sensor
a)Piezoelectric Accelerometer
b)Piezoresistive Accelerometer
c) Capacitive Accelerometer
ii Strain Gauges
iii Velocity Sensors
2) Non-Contact type vibration sensors-Here probes and machines are not in direct contact.
i Microphones or Acoustic Pressures Sensors
ii Laser Displacement Sensors
Iii Eddy current and capacitive displacement sensors.

Acceleration sensors, also called G-force sensors, are devices that
measure acceleration caused by movement, vibration, collision, etc
Piezoelectric Accelerometers
An accelerometer is a sensor that generates an electrical output proportional to applied
acceleration. Accelerometers are designed to measure vibration and shock for a wide variety
of applications. They are simple to use and accurate over a wide frequency range which
makes them the recommended choice for many testing situations. The designs consist of
sensing crystals that are attached to a seismic mass. A preload ring or stud applies a force to
the sensing element assembly to make a rigid structure and insure linear behavior. Under
acceleration, the seismic mass causes stress on the sensing crystals which results in a
proportional electrical output. The output is collected on electrodes and transmitted by
wires connected to the microelectronic circuitry in accelerometers.

Piezoresistive Accelerometers
Piezoresistive Accelerometers design for high frequency, high shock measurement. A
piezoresistive accelerometer takes advantage of the resistance change of piezoresistive
materials to covert mechanical strain to a DC output voltage. Most of the Piezoresistive
designs are either MEMS type (gas damped) or bonded strain gauge type (fluid damped)
and they are suitable for impact measurements where frequency range and level are
considerably high.
It has a stable structure composed on a silicon chip created by the micromachining and
semiconductor production technology. A mass and a beam on which a set of the piezo-
resisters are created on a silicon chip. A set of electrical bridged is formed by such piezo-
resistive resisters to generate signals proportional to the applied acceleration.

Piezoresistive accelerometers are widely used in automobile safety testing including anti-lock
braking system, safety air-bags and traction control system as well as weapon testing and
seismic measurements. In addition, micromachined accelerometers are available and used in
various applications, such as submillimeter piezoresistive accelerometers in extremely small
dimensions used for biomedical applications.

Capacitive accelerometers
Capacitive accelerometers are similar in operation to piezoresistive accelerometers, in that
they measure a change in capacitance across a bridge; however, instead of measuring a
change in resistance, they measure a change in capacitance. The sensing element consists
of two parallel plate capacitors acting in a differential mode.
Capacitive accelerometers (vibration sensors) sense a change in electrical capacitance,
with respect to acceleration, to vary the output of an energized circuit. The sensing
element consists of two parallel plate capacitors acting in a differential mode.

These can be made very small in size and mass. The displacement of the spring-mass system
is converted into a change in resistance, due to strain, in four arms of a Wheatstone bridge.
The signal is then post-processed to read the acceleration.
Velocity sensors
Velocity sensors are used to measure a frequency range of 1 – 1000 Hz. The measurement
principle is based on a coil moving around a magnet, generating a voltage that is proportional
to the movement. The sensors are suitable for vibration monitoring and balancing
applications on rotating machinery. This type of sensor has a lower sensitivity for vibrations
with high frequencies than accelerometers, and is therefore less susceptible to overload.

Non Contact Vibration Sensors
Optical sensor
These devices are needed to obtain two beams, a measuring beam and a reference beam. The
measuring beam is focused on the vibrating object. Its reflection merges with the reference
beam and starts to interfere.
The generated interference pattern can be decoded by the photo detector. The range of an
optical sensor lies within few millimetres with a resolution in the region of nanometres.
Eddy-current sensor

M1 Mechatronics.pptx

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