The students will be able to explain characteristic of ...mitpolytechnic.ac.in/.../MAC/Unit5MiscMeasurement.pdf · The students will be able to explain characteristic of sound and

Course Outcome:

The students will be able to explain characteristic of sound and

Measurement of sound intensity, measure shaft power, describe

contact and non contact type of speed measuring instruments &

explain working & suitable application of strain gauges.

Acoustic Measurement

• Acoustic Waves/ Sound Waves

Vibrations that consists of rapid variations in air pressure of small magnitude

• Classification of Sound Waves

Infrared Waves: Less than 20Hz

Audible Sound: 20 Hz – 20 KHz

Ultrasound : Greater than 20 KHz

• Acoustic is a branch of physics that deals with the design, generation, detection & propagation of sound waves.

MAC 17528 MAEER's MIT Polytechnic, Pune 3

Sound Characteristics

• Sound is characterized by following quantities

1. Intensity ( W/m2 ) or pressure ( μbar )

2. Frequency ( Hz )

3. Nature of Noise ( Continuous / Impulsive)

4. Loudness

5. Noise Rating ( Annoyance Rating ): Based on sound pressure level & frequency



• Intensity or Loudness

Energy flowing per second per unit area held normal to the direction of the propagation of sound wave.

It is expressed in W/m2 or J/Sec.m2

Intensity of sound wave, I = Q / t.A where Q= Sound Energy

l = P / A As Power P = Q / t

• Loudness is the degree of sensation produced in our ears

It’s a subjective term thus difficult to measure

L α Log I

Weber ( Fechner ) Law: Loudness is directly proportional to the logarithm of the sound intensity



• Measurement of Intensity of Sound Waves

Absolute intensity is expressed in W/m2 .

Standard intensity of sound is I0 = 10-16 W cm -2 or 10-12 W m -2

Intensity of sound waves is a way of stating the ratio of its intensity relative to the standard intensity.

Relative Intensity or Intensity Level of Sound Wave is given by

β = log10 ( I / I0)

Unit of intensity level is bel

As bel is a large unit another unit known as decibel ( dB ) is used

1 bel = 10 decibel

Ear can detect sounds having intensity level 0-120 dB

120dB is known as threshold of feeling



• Frequency or Pitch

Frequency is defined as number of vibrations per second

Greater the frequency higher will be the pitch.

• Pressure or Sound Pressure Level

SPL is defined as 20 times the logarithmic ratio in base 10 of the sound pressure of a sound to a reference pressure.

SPL = 20 log 10 ( P / P ref) dB

• Power or Sound Power Level

Sound Power is defined as total energy radiated per unit time by a sound source PWL = 10 log 10 ( W / W ref) dB

Wref is reference acoustic power = 10-12 W

Thus PWL = 10.log10 W + 120 dB


• Working Principle

Faraday’s Law of Electromagnetism

• Construction & Working

A conical diaphragm

A small lightweight coil attached to diaphragm

Coil moves in & out of space between N & S poles of magnet

Sound pressure waves force diaphragm in & out

With diaphragm coil also moves & induce emf across coil terminals

Emf generated is result of motion of coil which directly depends on force of waves


Acoustic Measurement Electrodynamic Microphone



• Advantages

Low Cost

Doesn’t require battery ( Active Transducer)

Small & Lightweight

• Limitation

Isolation is needed from A.C. fields to avoid hum

Output is low thus amplifier is required




Change in resistance


A thin moving diaphragm

A capsule contains carbon granules

Sound waves compress the diaphragm

Change in air space changes resistance

Passive Transducer

Change in Ω Change in Current

Output Current is function of sound pressure


Acoustic Measurement Carbon Microphone

• Advantages

Low Cost & Rugged

Relatively high output compared with other microphones

Small & Lightweight


Acoustic Measurement Carbon Microphone

• Limitation

Passive transducer

More distortion of sound compared to other microphones


Change in output voltage


A thin moving diaphragm (thickness: 0.002 mm)

Diaphragm placed in front of stationary rigid plate

Diaphragm & back plate constitute a capacitor

Charge to this capacitor maintained is constant

Sound waves displaces the diaphragm,

Change in distance between two plates changes o/p voltage. o/p voltage, E = Q.t (Q: Charge, t: distance)


Acoustic Measurement Capacitive Microphone


Change of energy


A thin moving diaphragm & Piezo crystal

Piezo Crystals: Rochelle Salt, Lead Zinconate, Barium Titanate

Diaphragm mechanically coupled / cemented on to crystal

Movement of diaphragm due to sound exerts pressure on crystal

Change in force on crystal generates electrical potential


Acoustic Measurement Piezo-electric Crystal Microphone

• Advantages

Good dynamic range

Fair frequency response

Linearity


Acoustic Measurement Piezo-electric Crystal Microphone

• Limitation

Poor sensitivity

Sensitive to vibrations

Humidity Measurement

• Humidity is amount of water vapor present in air

Moisture content in air expressed in Kg/Kg of air or in %.

Industries where humidity is important

Air Conditioning Process

Food Process Industry

Paper Industry

Textile Industry

Chemical Processing Plant

Fertilizer Industry

Psychrometry is the study of behavior of air & water vapor mixture


Psychrometric Properties • Dry Air Mixture of N( 77 % ) & O2 ( 23 % ) neglecting water vapor & other gases

• Moist Air Mixture of dry air & water vapor. Amount of water vapor depends on absolute pressure & temperature of air

• Saturated Air Condition when the air contains max. amount of water vapor that it can hold

• Dry Bulb Temperature Temperature of air recorded by ordinary thermometer

• Wet Bulb Temperature Temperature of air recorded by thermometer when its bulb is covered by wet cloth

• Dew Point Temperature Temperature at which dew formation starts when air is cooled at constant temp. MAC 17528 MAEER's MIT Polytechnic, Pune 17

Psychrometric Properties


• Construction & Working It consists of two thermometer mounted on frame One thermometer is open; other’s bulb is covered with wet cloth ( Wick ) One thermometer is for dry bulb temp. whereas other is for wet bulb temp. Frame is provided with handle for rotation of thermometer Frame is rotated for air circulation


Humidity Measurement Sling Psychrometer


MAC 17528 20 MAEER's MIT Polytechnic, Pune

• Advantages Simplest & cheapest device to measure humidity Excellent accuracy

• Disadvantages Psychrometric chart is required to know the humidity No continuous reading

• Application Routine instrument for meteorological department For calibration of other humidity measuring devices In refrigeration industry for study of processes MAC 17528 MAEER's MIT Polytechnic, Pune 21


Psychrometric Properties


Relative Humidity

• Construction & Working Materials sensitive to humidity

are human hair, animal membrane, wood & paper

Change in linear dimension due to absorption of moisture

Human hair becomes longer as humidity is increased & vice versa

Such property of material can be used to operate pointer of instrument

The indicator scale is calibrated to give indication of humidity


Humidity Measurement Hair Hygrometer

• Construction & Working Strands of hair is used for better mechanical strength to transducer Hair strands arranged parallel to each other & spaced Spring is provided for light tension to maintain proper balance in system

• Advantages Inexpensive Convenient pocket size shape Continuous reading

• Disadvantages Less accurate Limitation of temp ( 5-35 C) & humidity ( 40-95 %) Calibration has to be checked periodically

• Application Industries where high precision is not required MAC 17528 MAEER's MIT Polytechnic, Pune 24




Level Measurement


• Level Determination of position of existing interface between two media

• Need Safety Boiler Economy Inventory Control, Wastage, Overflow Monitoring Process Control

• Oil & Natural Gas Industry Tank Inventories Protect Equipments ( Turbine, Pump etc) Protect employees from injuries Protect environment

Level Measurement


• Direct Sight Glass Float Bob & Tape

• Indirect Hydrostatic Pressure Type Pressure Gauge Air Bellow Air Purge Liquid Purge Electrical Methods Capacitance Radiation

• Classification Mechanical Electrical Pneumatic Nucleonic Ultrasonic

• Selection of instrument Cost Liquid level range Nature of liquid Operating Pressure

Level Measurement



• Construction & Working Simplest method for visual reading Open End / Differential Mounted vertically adjacent to the container Pressurized container, inflammable, volatile liquids gauge is connected both way Valves are provided for maintenance For inert liquid gauge is open to atm. Pressure @ ( top of gauge = top of liquid ) Scale in engraved / itched on tube Magnetic floats can also be used

Level Measurement Sight Glass


• Advantages Simple in construction Low Cost

• Disadvantages Has to be mounted only in vertical position Accuracy depends on cleanliness of liquid

Level Measurement Sight Glass


• Construction & Working Works on buoyancy method Provides continues reading Float rests on surface of liquid & follows its level Float is attached to pointer by mechanism Float is hollow sphere ( Metallic, Plastic) Float connected to balance weight by cable cable wound over a pulley & pulley carries pointer Float ↑ Cable ↑ Pulley ↑ Pointer Cable wound over a pulley & cable carries pointer Float ↑ Cable ↑ Pointer

Level Measurement Float Gauge


• Advantages Simple in construction Low Cost Useful even for underground tanks

• Disadvantages Design should be according to tank geometry

Level Measurement Float Gauge


• Construction & Working Works on buoyancy method Provides continues reading Float rests on surface of liquid & follows its level Float is attached to pointer by some mechanism Float is hollow sphere ( Metallic, Plastic) Float connected to shaft & shaft is connected to pointer For signal magnification gear arrangement can be used Float ↑ Shaft ↑ Gear ↑ Pointer

Level Measurement Float & Shaft Gauge


• Construction & Working Works on Hydrostatic pressure measurement principle Allow bubbles of air below the water surface & measure air pressure Air pressure have direct relation with hydrostatic pressures Parts: Hollow Tube, Pressure Gauge, Regulating Valve Hollow tube is immersed in water Two connections are provided to hollow tube One to pressure gauge Other to Air tank via regulator Tank Empty, Gauge Pressure will be zero As the level increases there will be resistance to air flow Level ↑ Resistance ↑ Gauge Pressure↑ Pointer

Level Measurement Bubbler / Purge System


• Advantages Simple in construction Useful for corrosive liquids

• Disadvantages Requires pneumatic lines Can not be used for pressurized vessels

Level Measurement Bubbler / Purge System


Level Measurement Capacitive Gauge

A

q

d

.A.

d

.AC or


• Construction & Working Non Contact Method A source of gamma ray at the bottom of tank A sensor of gamma rays ( Geiger Muller Tube ) at the top of tank Sensor placed diagonally opposite & outside Gamma rays can penetrate tank Intensity of gamma rays received by sensor depends on level of liquid Higher level, More absorption of rays by liquid Less intensity of received rays & vice versa O/p of GM tube is in the form of pulses Counter is calibrated in terms of level • Advantages & Disadvantage Corrosive material, Molten Metal, Accuracy, Fast Response High Cost

Level Measurement Gamma Ray Level Gauge


• Construction & Working Non Contact Method Works on Sonar Principle A ultrasonic transmitter mounted on the top of tank Level of liquid as well as solid can be measured Transmitted wave reflected by fluid surface Receiver takes the reflected beam Time required to travel depends on level

• Advantages & Disadvantage Corrosive material, Molten Metal, Accuracy, Fast Response High Cost

Level Measurement Ultrasonic Level Gauge

Force Measurement Mechanical Tool Dynamometer


• Need of force measurement Power requirement for metal cutting Tool wear & tool life estimation Selection of tool material Design, control machining process

• Analysis of Forces Ff : Feed or Axial Force Fr: Radial Force or Thrust Fc / Ft : Cutting or Tangential Force R = {(Ff )

2+ (Fr) 2 + (Ft)

2 }1/2

• Force & Deflection Cutting force produces deflection Tool deflects elastically

tool deflection α Cutting Force

Treating tool as cantilever beam Measurement of Deflection Mechanically by dial gauge Electrically by using several transducers ( Pot, Capacitive, Inductive) LVDT



3EI

L.Fδ

3

c



• Construction & Working Simplest type of dynamo Dial indicator for force measurement Dial indicator calibrated for forces Dial indicator is used to measure dimensions Deflection produced by forces is sensed

Deflection α Force

Dial consists of graduated circular scale, plunger, gear pinion

Force Measurement Mechanical Tool Dynamometer ( Dial Gauge )




Shaft Power Measurement Eddy Current Dynamometer


• Working Principle When a conductor moves through a magnetic flux, voltage is induced & current flows • Construction A non magnetic metallic toothed rotor Rotor mounted on Engine shaft Rotor rotates inside a CI stator Stator is excited by DC supply Rotor rotates in magnetic field of stator Rotor cuts magnetic flux induces eddy

current in stator Stator is cradled ( free to rotate ) A spring balance is attached to stator

Shaft Power Measurement Eddy Current Dynamometer


• Advantages Compact compared to other dynamometer Can measure high output at all speeds Torque developed is smooth & continuous Absorption power can be changed by changing DC current

• Disadvantages Produce small torque at low speed

Torsional Shear stress – When a machine member is subjected to

the action of two equal and opposite couple acting in parallel

plane (torque or twisting) then the machine component is

subjected to torsion and the stress developed in element is

torsional shear stress.

L

G

rJ

T

T = Torque or twisting moment in N-mm

J = Polar moment of inertia in mm4

=Torsional shear stress

r = Radius of shaft in mm

G = modulus of rigidity in N/mm2

L = length of shaft in mm.

=angle of twist in radians

4

32dJ

Shaft Power Measurement Strain Gauge Transmission Dynamometer

MAC 17528 46 MAEER's MIT Polytechnic, Pune


• Construction Inline rotating torque sensor Metal shaft fitted with strain gauge Gauges fitted at 45 to shaft axis 2 strain gauges for tensile stress 2 strain gauges for compressive stress Gauges 1 & 3 diametrically opposite Gauges 2 & 4 diametrically opposite Gauges are connected to Wheatstone Bridge O/p of bridge is proportional to torsion Torque applied is proportional to power




• Advantages High sensitivity & accuracy Gives instantaneous result

• Disadvantages Expensive Initial setting requires skill & time consuming Slip rings wear out

Speed Measurement


• Tachometer Mechanical Revolution Counter & Timer Hand Speed Indicator Centrifugal Force Tachometer Slipping Clutch Tachometer

Electrical ( Non Contact ) Inductive Pick Up Capacitive Pick Up Photoelectric Tachometer Stroboscope

Electrical ( Contact ) Drag Cup Tachometer Cumulated Capacitor Tachometer Tachogenerator


• Construction & Working Consists of worm & worm wheel Shaft connected to worm With shaft worm rotates Motion is transferred to worm wheel RPM of worm wheel depends on Velocity Ratio Pointer is mounted on worm wheel Pointer gives rpm of shaft within prescribed time From total rpm in given time average speed is known

• Advantages & Disadvantages Simple construction, operation, Low cost Limited to low speed No instantaneous speed (average speed)

Speed Measurement Revolution Counter & Timer


• Construction & Working Working Principle: Ccentrifugal force 2 weights attached to pivoted arm Pivoted arm rotates with tachometer shaft Speed ↑ Centrifugal force ↑ & vice versa Weights moves outwards Lower collar rises upward Lower collar attached to pointer Pointer moves over a calibrated scale

Speed Measurement Centrifugal Force ( Fly Ball) Tachometer


Speed Measurement Hand Held ( Portable )Tachometer

• Construction & Working Working Principle: Ccentrifugal force 2 weights attached to pivoted arm Pivoted arm rotates with tachometer shaft Speed ↑ Centrifugal force ↑ & vice versa Weights moves outwards Lower collar rises upward Lower collar attached to pointer Pointer moves over a calibrated scale A small rubber covered wheel & tips Fit appropriate tip or wheel Hold against rotating shaft


Speed Measurement Hand Held ( Portable )Tachometer


• Construction & Working Consists of clutch & spring assembly Driving shaft is connected to indicating shaft with clutch Pointer attached to indicator shaft moves over a calibrated scale Pointer position gives rpm of driving shaft

• Advantages & Disadvantages Simple construction, operation, Low cost Limited to low speed Accuracy depends on spring

Speed Measurement Slipping Clutch Tachometer


Speed Measurement Mechanical Tachometer

Disadvantages Impose load on driving shaft whose rpm is to be measured, thus absorbs power Thus can’t be used for small power appn as loading effect reduce speed of shaft Speed indicated will be erroneous Hence mech tachoes used for heavy machinery Tachoes are hand held or permanently attached to driving shaft Because of inertia mech tachoes not able to follow variation in speed Speed of response is low, thus can’t be used for instantaneous speed measurement • Mech tachoes normally have two instruments used in tandem A counter for number of events & a stop watch Speed is calculated from the readings of these two instruments This can result in error.


• Construction & Working Driving shaft connected to permanent magnet A non magnetic cup ( Al ) provided very close to magnet Cup connected to pointer through spring Rotation of magnet sets eddy current in cup Pointer is mounted on the shaft of cup Spring is provided for proper balance

• Types Mechanically coupled magnet Stationary Magnet

Speed Measurement Drag Cup / Eddy Current Tachometer


• Advantages Rugged in construction, inexpensive Almost maintenance free Linear characteristic between o/p voltage & speed of shaft



• Disadvantages At very high speed linear characteristic changes Calibration is time consuming



• Construction & Working Consists of armature, permanent magnet Armature connected to driving shaft Armature rotates in magnetic field

Emf generated α Magnetic Flux & RPM

Generated Emf measured by voltmeter Voltmeter is calibrate in terms of rpm

Speed Measurement DC Tachogenerator


• Advantages Rugged in construction, inexpensive Almost maintenance free Linear characteristic between o/p voltage & speed of shaft

• Disadvantages At very high speed linear characteristic changes Calibration is time consuming

Speed Measurement DC Tachogenerator


• Construction & Working Consists of armature, permanent magnet Armature connected to driving shaft Armature rotates in magnetic field

Emf generated α Magnetic Flux & RPM

Generated Emf measured by voltmeter Voltmeter is calibrate in terms of rpm

Speed Measurement AC Tachogenerator


• Advantages Problems due to contact are eliminated Almost maintenance free Linear characteristic between o/p voltage & speed of shaft

• Disadvantages At low speed difficult to measure frequency At very high speed linear characteristic changes

Speed Measurement AC Tachogenerator


• Construction & Working Small permanent magnet with a coil wound around it This magnetic pick up is placed near a metallic toothed rotor As the shaft rotates, teeth passes by pick up & change magnetic flux Inductive voltage generates & disappears Frequency of pulses depends on no. of teeth & rpm of shaft No. of teeth is known & RPM can be found

• Speed N = Pulse per second / No. of teeth………….. rps N = 60.P / T…………………………………………………..rpm

Non Contact Speed Measurement Inductive Pick Up Tachometer


Non Contact Speed Measurement Inductive Pick Up Tachometer

• Advantages & Disadvantages Simple construction Output in digital form Less maintenance Easy to calibrate No loading effect High accuracy High Cost


• Construction & Working Vane attached to driving shaft Capacitor plates placed on either side

of vane Rotation of vane alternately changes

capacitance

Frequency of change α rpm of vane

• Advantages & Disadvantages High sensitivity, High accuracy Small loading effect Electronics circuit is complex

Non Contact Speed Measurement Capacitive Pick Up Tachometer


• Construction & Working An opaque disc mounted on rotating shaft Disc has no. of equidistant holes on its periphery One side light source & opposite light sensor O/p generated when hole comes between source & receiver Otherwise no output as light is reflected back Frequency of o/p depends on RPM & no. of holes No. of holes are known thus rpm can be calculated Pulse rate can be measured by electronic counter Electronic counter is calibrated in terms of rpm

Non Contact Speed Measurement Photoelectric Tachometer


Non Contact Speed Measurement Photoelectric Tachometer



Non Contact Speed Measurement Stroboscopic Motion


Non Contact Speed Measurement Stroboscopic Motion

Human sense of vision is slow to react to light Image remains on retina for few millisecond Can’t separate images if time is less than 0.1 sec


• Construction & Working Stroboscope is portable light source of variable frequency A disc mounted on rotating shaft Disc has no. of equidistant holes on its periphery Disc has a mark itched on its periphery Frequency of emitted light can be varied with potentiometer Frequency is varied until the mark on disc appears stationary For this condition frequency of light & shaft is same Frequency is doubled to see if one can get two stationary images N = { fm. F1. ( m – 1 ) } / ( fm – f1 )

Non Contact Speed Measurement Stroboscope



Non Contact Speed Measurement Stroboscope


Strain Measurement Fundamentals

• Force, Pressure & Stress σ = Force / Area

• Strain ε = Change in length / Original length

• Modulus of Elasticity Young’s Modulus = Simple Stress / Simple Strain

• Poisson’s Ratio ν = ε2 / ε1 ….............For most material ν = 0.3


Strain Measurement Fundamentals


Strain Measurement Strain Gauge

• Working Principle Resistance α strain R = ρ.l / A Δ R / R = GF. ε GF = (Δ R / R ) / ε

Structure A grid-shaped sensing element of thin metallic resistive foil (3 to 6μm thick) is put on a base of thin plastic film (15 to 16μm thick) and is laminated with a thin film



• Requirement of strain gauge Should be small in size with negligible mass Highly sensitive, Linear, No hysteresis, High gauge factor ( high GF means large change in resistance ) Easily attachable to specimen High speed of response with minimum lag Should be able to indicate static, transient & dynamic strain Capable of remote indication & recording Non sensitive to change in ambient conditions Should be inexpensive, reliable & easily available Resistance should be higher Should have low temperature coefficient



• Grid Material High specific resistance, High gauge factor, High electrical stability, Low hysteresis, Good solder ability & weld ability Isoelastic: ( 36 Ni+8Cu+4Mn,Si,Mo+52Fe ) GF: 3.5 Advance: ( 55Cu+45Ni) GF: 2.0. Nichrome: Ni + Cr GF: 2.0 Manganin: GF = 1.9 Monel: Gf: 1.9 Nickel: GF: -12


Strain Measurement Strain Gauge Classification

• Unbonded Strain Gauge • Bonded Strain Gauge Wire Type Foil Type Semiconductor Type


Strain Measurement Unbonded Strain Gauge

• Construction Consists of fixed & moving frame / armature Movable frame attached to shaft which is able to move due to force Strain gauge’s one end attached to movable frame & other to fixed frame Four strain gauges having equal resistance are used All gauges form a Wheatstone Bridge



• Working If movable arm is in neutral position o/p voltage is zero When o/p voltage is zero bridge is ‘balanced’ & Voltmeter reading is also zero As movable arm changes position, gauges are strained & Ω changes Voltmeter measures change in voltage But Voltmeter is calibrated in terms of force / pressure Thus one directly get the value of force / pressure





• Advantages & Disadvantages Simple Construction Low Cost Higher accuracy compared to cost Hysteresis could be an issue Change in temperature affects accuracy Lead wire reduces accuracy

• Application Measurement of force, pressure, displacement & strain


Strain Measurement Bonded Strain Gauge

• Construction & Working Consists of base, metallic sensing element & laminate film Made by using printed circuit process, conductive alloys rolled to a thin foil Conductive alloys are heat treated to optimize mech strength & temp. coeffi Gauge resistance range from 30 to 3000 Ω but 120 Ω to 350 Ω commonly used Gauge lengths from 0.008 inch to 4 inches are commercially available A grid configuration allows higher value of GF but keeps gauge length lower But Voltmeter is calibrated in terms of force / pressure Thus one directly get the value of force / pressure



• Backing Material Minimum thickness, High mechanical strength, High dielectric strength,

Minimum temperature restriction, Non hygroscopic Strong Paper ( 80-93 C), Bakelite ( up to 175 C), epoxy plastic films

• Binding Material High mechanical strength, High dielectric strength, High creep strength,

Minimum temperature restriction, Good adherence, Fast Drying Thermo plastic cement (Celluloid dissolved in acetone below 80 C), Thermo setting cement ( phenol resins up to 150 C ), Special ceramic cement ( above 200 C)




Strain Measurement Errors in Strain Gauge

• Temperature Variation Temperature changes volume as well as resistance

Differential expansion between the strain gauge & test surface

• Humidity Variation Resistance have direct relationship with the humidity It also causes electro chemical corrosion of gauge material

• Small Errors Due To Thermoelectric Effect • Errors Due To Zero Drift, Hysteresis Effect Etc • Magneto Resistive Errors In Ferromagnetic Substance


Strain Measurement Temperature Compensation in Strain Gauge

• Temperature Variation Temperature changes volume as well as resistance

Differential expansion between the strain gauge & test surface

• Humidity Variation Resistance have direct relationship with the humidity It also causes electro chemical corrosion of gauge material

• Small Errors Due To Thermoelectric Effect • Errors Due To Zero Drift, Hysteresis Effect Etc • Magneto Resistive Errors In Ferromagnetic Substance






Strain Measurement Strain Gauge Installation


Strain Measurement Strain Gauge Installation


Strain Measurement Load Cell

• Types Mechanical Load Cell

Hydraulic Load Cell

Pneumatic Load Cell Strain Gauge Load Cell


Strain Measurement Load Cell

• Types Mechanical Load Cell

Hydraulic Load Cell

Pneumatic Load Cell Strain Gauge Load Cell


Strain Measurement Strain Gauge Load Cell

• Principal Construction Working Application of wire/foil type bounded strain gauge

Works on principle of elasticity Shaft contracts or elongates Four wire type bonded strain gauges are used 2 in horizontal position & other in vertical Resistance are equal of all the gauges Gauges form Wheatstone bridge circuit No force bridge is balanced thus no output When force acts vertical gauges are strained Resistance of horizontal gauges are unaffected Force, Strain & output voltage is directly proportional Output is directly calibrated in terms of applied force



• Advantages & Disadvantages & Application Compact, Accurate, Good Sensitivity & Low Hysteresis, Low Cost

Performance affected by non-axial forces Requires temperature compensation network No overloading arrangement Suspension Bridge, Flow rate in Kg, Unsteady Force








Strain Measurement Strain Gauge Rosettes

Application of wire/foil type bounded strain gauge

Biaxial stress field Force acts in two different directions Rosettes are available in different combinations Rosette is combination of separate strain gauges Rosettes have two or more separate grids with different orientation Rosettes can be mounted without considering their orientations


Strain Measurement Strain Gauge Rosettes


Strain Measurement Application Strain Gauge








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The students will be able to explain characteristic of ...mitpolytechnic.ac.in/.../MAC/Unit5MiscMeasurement.pdf · The students will be able to explain characteristic of sound and