m&m lab manual

7/23/2019 M&M Lab Manual

http://slidepdf.com/reader/full/mm-lab-manual 1/46

Department of Mechanical Engineering MMM

HKBK College of Engineering, Bengaluru 1of4

Experiment No.: 1

PRESSURE TRANSDUCER

Date :

AIM:- To calibrate the pressure transducer

APPARATUS: Pressure transducer, hand pump, digital display unit.

THEORY:

Pressure is usually expressed as force per unit area, the force exerted in a unit direction

perpendicular to the surface of unit area.

Thermodynamically pressure may be considered as the momentum change of molecular

bombardment on the boundaries of a system in unit time. Pressure can be define as.

1. Action of force against some opposite force.

2. A force in the nature of thrust distributed over a surface.

3. A force acting against the surface with in a closed container.

Often pressure is measured by transducing its effect to a deflection through a

pressured area.

PROCEDURE:

1. The pressure transducer is installed in the suitable chamber.

2.

The pressure transducer is connected to the front panel of the instrument’s display unit usingthe cable provided.

3. The power rated 230V & 50 Hz is supplied.4. The instrument now is first set to CAL position by using READ-CAL toggle switch in order

to calibrate.

5. Now the meter reads zero. If not, it is adjusted to zero again.6. The instrument is now ready to accept the pressure applied through the pressure transducer.

7. Analog out put proportional to pressure is available in the pressure gauge which is used as

the standard.

8. The experiment is repeated for different values of pressure & the readings are noted fromdigital meter are compared with that of the analog pressure gauge & error if any is

determined.

RESULT:





Observation :

Sl.

No. Actual reading in Pr. Gauge (AR)

Kgf / cm2

Indicated Reading

in Pr. Gauge (IR)

Kgf / cm2

%Error

based on(AR)

%Error

based on

(IR)

%Error

Kgf / cm2

1

2

3

4

5

6

7

8

9





Calculation :

Error = AR- IR

= IR- AR = --------------------- = ------------- Kgf / cm2

%Error based on (AR) = error/AR * 100 = ---------------

%Error based on (IR ) = error/IR * 100 = ---------------





Experiment No.: 2 MEASUREMENT OF STRAIN

AIM: To determine the Young’s modulus of mild steel using the cantilever beam and strain

gauge setup subjected to static load using Wheatstone bridge for full, half & quarter bridge .

APPARATUS: Strain gauge mounted on a cantilever beam made of steel, strain indicator,

screwdriver, weights & weight pan.

THEORY: If you load any elastic material it will undergo deformation that is, stress & strain

will develop. Stress is defined as internal resisting force offered by a material per unit area

against deformation due to applied force.. And it results in strain.

Strain = Change in length / Original length.

If we plot stress- Vs- strain for ductile material, with in the elastic limit, stress is proportional to

strain this is known as Hook’s law. After elastic limit, plastic deformation starts i.e. after

removing the load, deformation won’t disappear & molecular separation starts inside the

material. This state is known as Yield State.

INSTRUMENTATION CALIBRATION ADJUSTMENT:

The gauge factor dial is set for position 2 & the arm selection switches to position 4.

The select switch is kept in set position. The display reads set gauge factor value without

the decimal point i.e. 2.005 is simply displayed as 2005.

The select switch is kept in measure position. The display reads 0000 otherwise coarse &

fine adjustment is given with the help of screwdriver to set it to zero.

PROCEDURE:

1. The instrument is set for full bridge.

2.

The internal calibration adjustment is made as stated above.3. The pan in the set up is loaded with a load in increments of 100gms each.

4. The strain indicated is recorded from the strain indicator for corresponding loads.5. Now the instrument is set for half bridge and the above procedure is repeated.

6. The readings are tabulated & the graph of stress Vs strain is plotted.





FULL BRIDGE SETUP:

1. Connect the red & black wire to the terminals C & D of strain indicator.

2. Connect yellow & green wires to the terminal A & B of strain indicator.

3. Put arm select switch of strain indicator to position 4 and put cantilever switch of strain

indicator to position 4.

4. Proceed operation as per operating instruction given in procedure.

5. The gauge factor is 2.

6 Divide the reading obtained by 4 to obtain the actual strain.

HALF BRIDGE SETUP:

The external strain gauge bridge is connected between terminals A & C and

A & D. the ARM SELECT switch is put in position 2.





Observation

Width of the cantilever beam (b) = 20mm.

Thickness of the cantilever beam (t) = 1.6mm.

Distance of load application (l) = 80mm.

Specimen calculation:

Section modulus = Z = bh2/ 6

Gauge factor = 2

Bending moment Mb = load * length

Bending Stress = Mb / Z

Actual strain = Indicated Strain (Ei)/ bridge factor

Youngs modulus E = / €a

RESULT:





STRAIN GAUGE

FULL BRIDGE

Sl.

No.

Dead weight

in Kg

Bending

Moment

σb N mm

Bending

stress

N/ mm2

Indicated

strain

Actual

strainYoungs modulus

E N/ mm2

gms Kg N





HALF BRIDGE:

Sl.

No.

Dead weight

in Kg

Bending

Moment

σb N mm

Bending

stress

N/ mm2

Indicated

strain

Actual

strainYoungs modulus

E N/ mm2

gms Kg N





QUARTER BRIDGE

Sl.

No.

Dead weight

in Kg

BendingMoment

σb N mm

Bendingstress

N/ mm2

Indicated

strain

Actualstrain

Youngs

modulus

E N/ mm2

gms Kg N




HKBK College of Engineering, Bengaluru 10of

Experiment no

Load cell date :

AIM: To calibrate the given load cell using standard load.

APPARATUS: Load cell setup , weights etc

THEORY:

Strain gauges can be used to measure the forces along with elastic members instead of using the

total deflection as a measure of load. The strain gauge measures load in terms of unit strain. Such

device is called load cell, it used to measure heavy loads.

Load cells can be mounted in any elastic member used for measurement of force. For

larger loads the directs tensile – compressive member can be used. For smaller loads using

bending effect can provide strain amplification.

PROCEDURE:

1. Before connecting the indicator, the power source is verified to see whether it matches the

requirement of the indicator as mentioned on its rear panel. The indicator is then switched on

and allowed to warm up for 5 min. The load cell is checked for pre-load and tare the excessload by using the be tare button.

2. The weights are placed on the pan connected to compressive or tensile load cell in steps of

1Kg..

3. The indicator readings are noted.

4. Note down the value of force in Newton from the indicator.

5. The actual value of load is calculated by using the formula.

F = weight on pan x 9.816. The readings are tabulated and checked for errors if any.

RESULT:





Observation:

Compression (+ve)

Sl. No. Actual reading ( N ) Indicator reading ( N ) %Error

1

2

3

4

5

6

7

8





Tensile (- ve)

Sl. No. Actual reading ( Kg ) Indicator reading ( N ) %Error

1

2

3

4

5

6

7

8





Experiment No.: 4

THERMOCOUPLE

Date :-

AIM: -To calibrate thermocouple indicator

APPARARTUS: Thermocouple indicator of K – Type, J – Type, & PT – Type, beaker, gas

stove, burette stand, thermometer etc.

THEORY: -

Thermocouple is a device made of 2 dissimilar homogeneous metals. It consists of 2 junctionsi.e. hot or measuring junction & cold or reference junction.

Thermocouple works on 3 principles viz. Peltier, seebeck & Thomson effect.

Thermocouple used is made of nickel – chrome combination. A digital temperature 602

series indicator is capable to measure 19990c. This is a high performance rigged instrument

designed to meet industries & lab conditions. In this thermocouple the cold junction is at

atmospheric temperature or lab temperature & hot junction is the one immersed in water bath of

given temperature. Generally the temperature can be measured by 2 unequal temperature which

are imported at the 2 interference junctions & change in electric current flow through the loop

gives the value of temperature. But in the lab the calibration of thermocouple is done by noting

temperature of water in water bath using mercury thermometer & taking the readings directly on

four segment. LED (Light Emitting Display) indicator.

PROCEDURE:

1. The beaker containing water is placed on the gas stove & is heated.

2. The thermocouple is immersed in beaker in such a way that it will be in center of beaker &

should not touch the sides or bottom of beaker.





Observation :

K-TYPE:

Sl

no Thermometer reading

Thermocouple

indicator reading %Error

50 C rise 50 C fall 50 C rise 50 C fall Rise Fall

J-TYPE:

Sl

no Thermometer reading

Thermocouple

indicator reading %Error






PT-TYPE:

Sl

no

Thermometer readingThermocouple

indicator reading

%Error






Experiment No.:5 ANGULAR MEASUREMENT

SINE BAR Date :-

AIM: - To determine the taper angle of the given work piece using sine bar and compare

it with the theoretical value.

APPARATUS: Surface plate, sine bar, slip gauge set, vernier caliper, cleaning

agent, tapered workpiece, dry soft cloth, dial gauge etc.

THEORY:

Sine bar is a precision instrument used with slip gauges.

1) To measure the angles very accurately.

2) To locate the work to a given angle within very close limits.

It consists of a steel bar and two rollers made of high carbon, high chromium

corrosion resistant steel, suitably hardened, precision ground and stabilized. The normal distance

between the axes of the rollers is 200 mm ,+/- 0.2mm.

PROCEDURE:

1. The theoretical semi taper angle for wedge shaped work piece is measured using the bevel

protractor.2. The sine bar is placed on the surface plate & the distance between the roller centers (L) is

measured.3. The work piece whose taper is to be measured is clamped on the upper surface of the sine bar

such that the entire length of the taper is accessible to the dial gauge.4. The slip gauges are arranged below one of the roller such that the tapered surface is parallel

to the surface plate.5. The parallelism is checked by moving the dial gauge over the tapered surface ascertaining

that it shows null deflection.

6. The height of the slip gauges is noted and actual angle is calculated using the formula

= sin-1 (h/L)

The principle operation of a sine bar is based on the laws of trigonometry.i.e., sine = h/L

= sin-1 (h/L)

RESULTS:





OBSERVATIONS:

Sl

no Specimen

Height of the slip

gauge ‘h’

( mm )

Tapered Angle

Sin θ = h/L

Theoretical Value

Tan θ = h1 – h2

l

%Error

Where L = the distance between the two rollers of the Sine Bar = 200 mm.

l = the length of the specimen = mm





Experiment No.: 6

ANGULAR MEASUREMENT

SINE CENTRE Date :-

AIM: To determine the taper angle of the given work piece using sine centre and compare it

with theoretical value.

APPARATUS: Surface plate, sine centre, slip gauge set, vernier caliper, cleaning agent, tapered

work piece, dry soft cloth, dial gauge jafugi magnetic, etc.

THEORY:

Due to difficulty in mounting conical work piece on a conventional sine bar, sine centres

are used. Two blocks accommodating the dead centres can be clamped at any position on the

sine bar. The centres can also be adjusted depending on the length of the conical workpiece and

also ensure correct alignment of the work piece.

PROCEDURE:

1. The theoretical semi taper angle for a round conical work piece is calculated using the

formula = tan-1 ( d1-d2/2L )

2. The work piece is held in between the sine centres.

3. The sine centre is placed on the surface plate and the distance between the roller centres (L)

is measured.

4. The slip gauges are arranged below one of the rollers such that the tapered surface is parallel

to the surface plate.

5. The parallelism is checked by moving the dial gauge over the tapered surface ascertaining

that it shows null deflection.

6. The height of the slip gauges is noted and actual angle is calculated using the formula

= sin-1 (H/L)





RESULTS:

Observation and tabulation

SINE CENTER

Distance between the axis of the roller of sine center (L) = 300 mmThe length of the specimen ----------------------------- ( l ) = mm

Sl

Nospecime

n

Larger

diamete

r

d1. mm

Smaller

diamete

r

d2, mm

Length

of the

specime

n

L (mm)

Height

differenc

e b/w slip

gauges

‘ H’ mm

Angle of

the

taper

using

sin =h/L

Angle of the taper

Tan = (d1-d2)/2L

%Erro

r

Sine center: - Tan

= ( d1-d2)

2 x L

= Semi taper angle

L = Length of specimen

Sin = H / L





Experiment No.: 7

ANGULAR MEASUREMENT

BEVEL PROTRACTOR Date :

AIM: To measure the angle of taper of a given specimen

APPARATUS: Bevel protractor, specimen, plug gauge, ‘V’ Block caliper etc.

THEORY:

Optical Bevel protractor is a modified version of the vernier Bevel protractor. By using this

instrument, it is possible to take readings upto 2 minutes of an arc approximately.

It consists of an optical magnifying system (a lens) which is integral with the instruments.

The scale is graduated in a full circle marked 0 to 1800. The zero position corresponds to the

condition when the blade is parallel to the stock.

PROCEDURE:

1. The equipment is cleaned so as to remove grease and other impurities.

2. The given specimen whose taper angle has to be measured is kept on the working edge of the

bevel protractor.

3. The blade is set at an angle such that it is in contact with the entire length of the taper.

4. The reading noted gives the angle of taper in degrees.

RESULTS:





OBSERVATION&TABULATIONS:

Sl

No.

Specimen Larger

Diameter

Smaller

Diameter

Angle of the

Taper using BevelProtractor

Angle of the Taper

using formula





Experiment No.: 8

GEAR TOOTH VERNIER CALIPER

Date :-

AIM: To determine the gear tooth thickness at pitch line and distance from the top of a tooth to

the chord (depth).

APPARATUS: Gear tooth vernier caliper and Spur gears.

THEORY:

The popular method of measuring gear tooth thickness at pitch line is by using Gear tooth vernier

calliper. The gear tooth vernier calliper consists of two perpendicular vernier arms with vernier

scale on each. One of the arms is used to measure the thickness of the gear tooth and other for

measuring depth. The calliper is so set that it slides on the top of gear tooth under test and the

lower ends of the calliper jaws touch the sides of the tooth at pitch line. The reading thus noted

on vertical arm gives the gear depth and on the horizontal arm gives the tooth thickness. Since

the tooth calliper measures at a right angle or on chordal line. The thickness (t) is slightly less

than the distance along arc of pitch circle. The difference is generally ignored.

PROCEDURE:

1. The pitch circle radius and number of teeth on the gear are noted.

2. The gear tooth vernier caliper is set on the teeth such that the lower ends of the calliper jaws

touch the sides of the tooth at pitch line.

3. The reading on the horizontal vernier gives the value of Chordal thickness and reading on

vertical vernier arm gives the value of Chordal addendum or working depth.

4. The measured value is then compared with the theoretical value and hence the calliper is

calibrated for errors, if any.

Theoretical value is calculated using the formulae.

1) Chordal thickness

W = 2xR sin





2) Depth or addendum

h = m + Tm/2 [ 1- cos ()]

Where R = Pitch circle radius = T m/2

h = addendum or working depth

m = module

W = Chordal thickness.

T = No of teeth.

= 360/4T

RESULTS:





OBSERVATION & TABULATI ON

Sl. No.Specimen

Width in mm Depth in mmTheoretical %Error

Width Depth Width Depth





Experiment No.: 9

TOOL MAKERS MICROSCOPE

Date :-

AIM:-To measure the thread profile (major dia, minor dia, depth of thread, pitch and

thread angle) using tool makers microscope or tool room microscope.

APPARATUS:- Toolmakers microscope and screw thread.

THEORY: -

This is a versatile instrument based on optical means and it is used to determine the

geometry of a given screw thread. This instrument is used particularly when the pitch is small

and the image is to be magnified to a greater extent and it is projected on to the optical head. In

the optical head, different eyepieces can be used to find out the profile of the thread. It consists

of a worktable on which the work pieces can be placed and with the help of accurate micrometer

screws it can be moved in two mutually perpendicular directions. Measurements are made by

means of cross lines engraved on the eyepieces as references. The table can be rotated through

3600

PROCEDURE:

1. The given screw is placed on the worktable.

2. The mains and the lights are switched on.

3. The micrometer cross wire is adjusted in X & Y direction to measure major diameter, minor

diameter, pitch & depth of thread.

4. Take the reading with the corresponding micrometer and calculate the dimensions as given

below.

RESULTS:





Observation:

Least count of the longitudinal micrometer (X) = 0.01mm

Least count of the lateral micrometer (Y) = 0.01mm

Least count of the circular scale = 10/10min = 60min / 10min = 6min.

READING:

R1 = .mm

R2 = mm

R3 = .mm

R4 = mm

R5 = .mm

R6 = .mm

R7 = mm

R8 = mm

1. Major dia = R1 ~ R4

2.

Minor dia = R2 ~ R3

3. Depth of thread = R1 ~ R2

4. Pitch of thread = R5 ~ R6

5. Angle of thread = R7~ R8





xperiment No.:10

PROFILE PROJECTOR

Date :

AIM: -To determine the dimensions of a screw thread using profile projector.

APPARATUS: -Profile projector, screws etc.

THEORY:-

Profile projector is a device used to determine the geometry of a screw thread. Profile projector is particularly used when the pitch is very small and image is to be magnified to a

greater extent. The screen has a rotating transparent disc which is used to find the angle of thread

and also to adjust the horizontal scale. Also it consist of a graduated circular scale in degrees,

two micrometers for adjusting horizontal and vertical distance to determine the depth of thread,

pitch of thread, major and minor dia.

PROCEDURE:-

1. The screw is placed on the work table whose geometry is to be determined.

2. The mains and the lights are switched on to maximum.

3. By operating micrometer in X & Y direction (after initial setting), the pitch & depth of the

thread is measured.

4. By adjusting circular scale the included angle of the thread is determined.

5.

For finding the radius of the specimen the diameter using X & Y micrometers, reading is

calculated.

RESULT:





OBSERVATION:

Least count of the longitudinal micrometer (X) = 0.01mm

Least count of the lateral micrometer (Y) = 0.01mm

Least count of the circular scale = 10/30min = 60min / 30min = 2min.

READING:

R1 = .mm

R2 = .mm

R3 = mm

R4 = .mm

R5 = .mm

R6 = .mm

R7 = mm

R8 = mm

1 .Major dia = R1 ~ R4

2. Minor dia = R2 ~ R3

3.

Depth of thread = R1 ~ R2

4. Pitch of thread = R5 ~ R6

5. Angle of thread = R7~ R8





Experiment No.:- 11

MEASUREMENT OF EFFECTIVE DIAMETER

BY THREE WIRE METHOD

AIM: To determine the effective diameter of screw thread using 3-wire method.

APPARATUS: -

Measurement of effective diameter is the most important of all the experiment in perfect

fitting and in making threads on threaded fastners. There are various methods of measuring pitch

diameter or effective diameter, but the most common method of measuring pitch diameter is two

wire method and three wire method. In this methods small rods or wires are placed on the threads

& measurements are then made over & under the wires with the micrometer or any other

accurate measuring instrument. These wires are made up of hardened steel & given a high degree

of accuracy & finish to suit different pitches. For each pitch there is a best size of wire. If best

size of wire is used the wire makes contact with the flanks of thread on the pitch line & this

method ensures the alignment of micrometer angle faces parallel to the thread axis. Therefore

this method of measuring effective diameter is more accurate.

Effective diameter It is a diameter of imaginary co-axial cylinder which interact the flank

of thread such that width of the threads & width of the space between the threads are equal &

each being the half of the pitch.

PROCEDURE:

1. Three wires of equal and precise diameter are selected.

2. Out of the 3 wires in the set two are placed on one side & the third on the other side on the

screw. These wires are held in position over the threads either by applying grease or stickingthe ends of wires in wax or Vaseline.

3. The micrometer is used to measure the distance ‘M’ as shown.

4. Using the known values of pitch, thread angle and wire diameter the effective diameter of the

screw thread is determined as follows.





Effective diameter : E = M - Q

Where Q = W(1+cosec) – P/2 cot

W = Best wire size : W=(P/2) x sec(/2).

2 = Thread angle.(obtained from profile projector ortool maker’s

microscope)

P = Pitch .(obtained from profile projector ortool maker’s microscope)

M = Micrometer reading

5. These steps are repeated for different specimen.

RESULT:-





OBSERVATION & CALCULATIONS:

.Sl

No.Wire dia (d) in mm Micrometer

reading in M mm

Q constant

in mm

Effective dia

E = M – Q

in mm

SPECIMEN CALCULATION:

The constant Q = W(1+cosec ) – P/2 cot =

Where P = pitch of thread ==

Best wire size : W=(P/2) x sec( /2).

W =





Experiment No.: 12

SURFACE TEXTURE MEASUREMENT

Date :

AIM: To measure the surface finish (parameters) of the given specimen using stylus type

measuring instruments.

APPARATUS:-Test specimen, standard specimen, surface texture measuring

instruments.

THEORY:-

The surface texture of a material can be determined by methods of quantitative analysis. These

methods enable to determine the numerical value of the surface finish of any surface by using

instruments of stylus probe type operating on electrical principles.

It consists of a finely pointed probe or stylus which is moved over the surface of a work

piece. The vertical movement of the stylus caused due to irregularities in the surface texture can

be used to access the surface finish of the work piece.

PROCEDURE:-

1. The instruments is set to the standard Ra value (3.05 micrometers)2. The electrical connection are made & checked before operation.

3. The stylus is moved on the standard specimen & the gain is adjusted till the roughness valueis displayed on the instrument.

4. The required parameters Ra, Rq, Rz, Rt, Ry, Rp, tp & pc are noted by moving the stylus on

the test specimen.

5. The readings thus obtained determines the surface texture.





Experiment No.: 13

LATHE TOOL DYNAMOMETER.

Date :

Aim: To measure the cutting forces during turning process.

Instruments used: Lathe Tool Dynamometer setup in the lathe.

Theory:

Lathe Tool Dynamometer is the device used to measure the cutting forces during the

turning (machining) in the lathe. In a two dimensional orthogonal cutting process, we have two

cutting forces viz.

a) Tangential or cutting force FH

b) Vertical or feed force FV.

In a three dimensional turning process we come across three components of cutting forces, viz.

a) Tangential (horizontal) cutting force FH

b) Vertical or feed force FV and

c) Radial force FR .

These three forces are measured using a LTD where in strain gauges are fixed and using a wheat

stone bridge, the variation in resistance in the strain gauges, which are calibrated in terms of

force are measured.





Procedure:

1. LTD is fixed on the lathe bed such that the tool tip coincides with the line of center of the

work piece.

2.

The work piece is machined at different speeds keeping feed and depth of cut constant.

3. The values of FH , FV, FR are noted down.

4. These readings are noted down for different feed rates at constant speed and constant depth

of cut.

5. The following graphs are plotted _

I) Cutting speed Vs Cutting force FH

II) Cutting speed Vs feed force FV.

III)Cutting speed Vs Radial force FR .

Cutting speed = DN m/s

1000x60

Where D= Diameter of work piece in mm

N= speed of lathe in rpm

Result:





OBSERVATION:

Feed and depth are constant.

Sl NoSpeed N

in rpm

Cutting speed v

m/sFH FV

FR





Experiment No.:14

DRILL TOOL DYNAMOMETER

Date :

Aim: To measure the Torque and vertical thrust during the drilling process.

Instruments used: Drill Tool Dynamometer setup in the Radial Drilling

machine.

Theory:

Drill Tool Dynamometer is the device used to measure the Torque and vertical thrust

during the drilling process in a drilling machine.

The torque and the vertical thrust are measured using a Drill Tool Dynamometer where in strain

gauges are fixed and using a wheat stone bridge the variation in resistance which is calibrated in

terms of torque and thrust are measured.

Procedure:

1. Drill Tool Dynamometer is fixed on the radial-drilling machine.

2. The work piece is drilled at different speeds keeping the feed and diameter of drill

constant.

3. The values of FV and T are noted down.

4. The holes of different diameters are drilled with constant feed rates at different

speeds and the values of Fv and T are noted.

5. The graphs are plotted for

i) Speed Vs Thrust Force FV

ii) Speed Vs Torque T





Result:

OBSERVATION:

Vertical feed constant :

Sl No Dia.of Drill dSpeed N

in rpmFV T





Experiment No.: 15

Linear Variable Differential Transformer(LVDT)

Date:

AIM: To calibrate the given LVDT

APPARATUS: LVDT, displacement micrometer of LVDT

THEORY:

LVDT is a basically a mutual – inductance type transducer with variable coupling between

the primary and secondary coils. It is a mechanical displacement transducer.

The center coil of LVDT also knows as primary coil (1) is energized from an AC power

source of input voltage ei. The two end coils knows as secondary coil (2) are connected in phase

opposition and are used as pickup coils. LVDT has one core (3) also which is attached to the

moving object whose displacement is to be measured. The soft iron core provides the magnetic

coupling between the primary coil and secondary coils.

The core is free to move inside the coil in either direction from the null position. When

the primary coil is excited by a AC supply and the core lies in central / null position, the induced

EMF in the secondary coil are equal in magnitude. However the net output e0 is zero, because the

two secondary coils are connected together in phase opposition.

As the core moves towards left or right from the central position, the induced voltage of

one secondary coil increases while that of other decreases.

The output voltage is the difference of two service secondary are in opposition. The

output is proportional to displacement of core. It can be seen that with in limits, on either side of

the null position (N), core displacement result in proportional output. In general, the linear range

is primarily dependent on the length of secondary coils.





LVDT is widely used for measuring pressure, load, displacement, acceleration etc. LVDT also

finds application as the basic element in extensometers, electronic comparators, thickness

measuring units and level indicators.

PROCEDURE :

The various connections are made and core is adjusted to new position by adjusting

micrometer. A set of the reading are noted till the core reaches the extreme left position in “h”

cell position, the corresponding voltage is noted down at regular intervals. Similarly a set of

readings are noted when the core moves to the right of null position. The performance

characteristics curve for LVDT is plotted and linear range is determined.





OBSERVATION & TABULATION

Trail

no

Indicated

reading

Actual reading Absolute

error

(AR- IR)

% error

based IR

% error based

AR

Left right Left right Left right Left right





EXPERIMENT No: 16

CALIBRATION OF EXTERNAL MICROMETER

Date :

AIM : - To calibrate the given external micrometer screw thread for Progressive

and Periodic pitch errors by using Slip gauges as standard.

APPARATUS : Micrometer ( 0-25mm range ), Slip gauge set, clean dry soft

cloth, cleaning agent like petrolgel.

THEORY :

Since micrometers are most widely used for precision measurement in the average

workshop, their close tolerance and accuracy are of atmost importance. A common fault in a

micrometer is zero error, i.e. a reading is indicated when there is no gap between anvil and

spindle. Even allowing for the zero error, if a number of accurate Slip gauges is measured with

all due precautions by the micrometer, a very slight discrepancies between the gap width and

corresponding micrometer reading are often discovered. Should this be due to Slackness and end

float of the spindle screw, it can be easily rectified by tightening the taper nut on the outside of

the partially slotted hub nut which then contracts to fit the micrometer screw more closely. If

zero error remains after this adjustment, lt will be due to wear of the measuring faces. This can

usually be corrected, although often it is deliberately left alone and allowed for, either by

adjustment of the screw in hub nut or anvil, or by rotation of the thimble relative to the spindle,

depending on the design of the micrometer.

If there is no slackness and end float of the spindle screw, then pitch errors or eccentricity of the

thimble account for the slightly wrong readings. Even the screw of a new micrometer is

sometimes subjected to progressive and periodic errors.





PROGRESSIVE ERROR :

If the pitch of the thread is longer or shorter than its nominal value such errors are called

progressive error. This type of errors occurs when

i.

Tool – work velocity ratio is incorrect.

ii. Change in length due to hardening by error in the pitch of the lead screw.

iii. Due to fault in the saddle guide ways.

iv. Due to the use of an in correct gear train between – work and Tool.

v. The Progressive errors are – progressive in nature as the length of axis – increasing

errors almost obeys straight line path.

PERIODIC ERRORS :

Periodic errors are those which vary in magnitude along the length of the thread – and

repeats at regular intervals. If they recur – regularly in every revolution of the thread it is called

drunken thread. Errors of this type are – most frequently caused by lack of squareness in the

thrust bearing of the lead screw used to produce the thread. If the pitch of the screw being cut is

not equal to that of lead screw, this fault in the thrust bearing will cause a periodic error,

recurring at other intervals. Velocity ratio between work and the tool. Such a errors are

determined by measuring along a line parallel to helix other sources of periodic errors are

eccentric mounting of the gears, errors in the teeth of the gear etc.

As a micrometer screw rarely wears evenly in service, erratic pitch error develop

eventually and, since only about a third of the screwed length engages with the hub nut at any

time, the resulting errors of the readings are difficult to predict. The actual correction required

for any reading will be progressive, or erratic errors indicated for the particular reading.





PROCEDURE :

1. Check the micrometer for smooth running of spindle throughout its length, if necessary,

adjust the wear compensating arrangement to eliminate any backlash.

2. Clean the micrometer anvil carefully.

3. Note down the initial error in the micrometer. This can be done by taking reading with

micrometer anvil and spindle faces in contact.

4. Slip gauges are made ready ten minutes before required and these can be held with the help

of clean dry soft cloth during use.

5. For progressive error take a reading of micrometer by placing slip gauges 2.5 to 25mm in

steps of 2.5 in between spindle faces of micrometer and tabulate the readings in the tabular

column.

6. Periodic errors in micrometer is found by placing slip gauges 2.1 to 2.9 in steps of 0.1mm

and 20 to 20.5mm insteps of 0.1mm in between spindle and anvil faces of micrometer. The

readings for periodic error are taken at two positions of the spindle, one near each end of its

travel.

7. Note that while taking reading on micrometer faces by means of ratchet mechanism. (usually

two slip of ratchet while taking reading on micrometer indicates uniform pressure on faces).

8.

Plot the following graphs.

a) Progressive error Vs Nominal slip gauge used.

b) Combination error Vs Nominal slip gauge used.

c) Periodic error Vs Nominal slip gauge used.





OBSERVATION

1. Least count of the vernier (Thimble ) = Lcth = ------------mm.

2. Least count of the barrel Lc bar = ---------- mm

PROGRESSIVE ERROR:-

Sl

no

Nominal size of slip gauge

in, (mm)

Micrometer reading in.

(mm)

Progressive error

in, (mm)

m&m lab manual

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