Department of Mechanical Engineering

MMM

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 pressured area.

through a

PROCEDURE: 1. The pressure transducer is installed in the suitable chamber. 2. The pressure transducer is connected to the front of the instrument’s display unit using the 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 from digital meter are compared with that of the analog pressure gauge & error if any is determined. RESULT:

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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

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Calculation : Error = AR- IR = IR- AR = --------------------- = ------------- Kgf / cm2

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

= error/IR * 100 = ---------------

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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. 2. 3. 4. 5. 6.

The instrument is set for full bridge. The internal calibration adjustment is made as stated above. The pan in the set up is loaded with a load in increments of 100gms each. The strain indicated is recorded from the strain indicator for corresponding loads. Now the instrument is set for half bridge and the above procedure is repeated. The readings are tabulated & the graph of stress Vs strain is plotted.

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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.

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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:

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STRAIN GAUGE FULL BRIDGE

Sl. No.

Dead weight in Kg gms

Kg

Bending Moment σb N mm

Bending stress  N/

mm2

Indicated strain

Actual strain

Youngs modulus E N/ mm2

N

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MMM

HALF BRIDGE:

Sl. No.

Dead weight in Kg

gms

Kg

Bending Moment

Bending stress 

σb N mm

N/ mm2

Indicated strain

Actual strain

Youngs modulus E N/ mm2

N

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Department of Mechanical Engineering

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QUARTER BRIDGE Bending Sl. Dead weight Moment No. in Kg σb N mm

Bending Actual Indicated stress  strain strain N/ mm2

Youngs modulus E N/ mm2

gms Kg N

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Experiment no Load cell

AIM:

date :

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 instead of using the total deflection as a measure of load. The strain gauge measures load in 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 . 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 excess load 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 9.81 6. The readings are tabulated and checked for errors if any.

RESULT:

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Department of Mechanical Engineering

MMM

Observation: Compression (+ve) Sl. No.

Actual reading ( N )

Indicator reading ( N )

%Error

1

2

3

4

5

6

7

8

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Department of Mechanical Engineering

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Tensile (- ve)

Sl. No.

Actual reading ( Kg )

Indicator reading ( N )

%Error

1

2

3

4

5

6

7

8

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Department of Mechanical Engineering

MMM

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 junctions i.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.

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3. Thermometer is inserted in the beaker & fixed in position in such a way that its reading can be noted down with out difficulty. 4. The supply for the thermocouple indicator is switch ON. 5. The temperature of the water is noted down by thermometer as well as thermocouple indicator for every 50C rise in temperature under steady state condition and the readings are tabulated. 6. Heating is stopped & water is allowed to cool. The temperature from thermometer and thermocouple indicator is noted for 50C fall in temperature. 7. Percentage error is calculated from the formula % error = Thermometer reading --- Thermocouple indicator reading

x 100

Thermometer reading.

GRAPH: 1.Thermometer reading Vs thermocouple indicator reading. 2. Indicator reading Vs % of error.

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Department of Mechanical Engineering

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Observation : K-TYPE: Sl no

Thermometer reading 50 C rise

50 C fall

Thermocouple indicator reading 50 C rise

50 C fall

%Error Rise

Fall

J-TYPE: Sl no

Thermometer reading 50 C rise

50 C fall

HKBK College of Engineering, Bengaluru

Thermocouple indicator reading 50 C rise

50 C fall

%Error Rise

Fall

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Department of Mechanical Engineering

MMM

PT-TYPE:

Sl no

Thermometer reading

Thermocouple indicator reading

%Error

50 C rise

50 C rise

Rise

50 C fall

HKBK College of Engineering, Bengaluru

50 C fall

Fall

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Department of Mechanical Engineering

Experiment No.:5

ANGULAR MEASUREMENT SINE BAR

MMM

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:

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OBSERVATIONS:

Sl no

Height of the slip

Tapered Angle

Theoretical Value

gauge ‘h’

Sin θ = h/L

Tan θ = h1 – h2

%Error

Specimen ( mm )

l

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

HKBK College of Engineering, Bengaluru

=

mm

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Department of Mechanical Engineering

MMM

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)

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Department of Mechanical Engineering

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RESULTS: Observation and tabulation SINE CENTER Distance between the axis of the roller of sine center (L) = 300 mm The length of the specimen ----------------------------- ( l ) = mm

Sl No

specime n

Larger diamete r d1. mm

Smaller diamete r d2, mm

Length of the specime n

Height differenc e b/w slip gauges

Angle of the taper using

L (mm)

‘ H’ mm

sin=h/L

Angle of the taper Tan  = (d1-d2)/2L

%Erro r

Sine center: - Tan  = ( d1-d2) 2xL  = Semi taper angle L = Length of specimen Sin  = H / L

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Department of Mechanical Engineering

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

RESULTS:

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Department of Mechanical Engineering

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OBSERVATION&TABULATIONS:

Sl No .

Specimen

Larger Diameter

Smaller Diameter

HKBK College of Engineering, Bengaluru

Angle of the Angle of the Taper Taper using Bevel using formula Protractor

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Department of Mechanical Engineering

MMM

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

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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:

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OBSERVATION & TABULATION Theoretical Sl. No. Specimen Width in mm Depth in mm

HKBK College of Engineering, Bengaluru

%Error

Width Depth Width Depth

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Department of Mechanical Engineering

MMM

Experiment No.: 9 TOOL MAKERS MICROSCOPE Date :-

AIM:-To measure the thread profile (major dia, minor dia, depth of thread, pitch thread angle) using tool makers microscope or tool room

and

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:

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Department of Mechanical Engineering

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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

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Department of Mechanical Engineering

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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:

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Department of Mechanical Engineering

MMM

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 = 2. Minor dia =

R1 ~ R4 R2 ~ R3

3. Depth of thread =

R1 ~ R2

4. Pitch of thread =

R5 ~ R6

5. Angle of thread =

R7~ R8

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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 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 sticking the 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.

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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:-

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OBSERVATION & CALCULATIONS:

Effective dia .Sl Wire dia (d) in mm No.

Micrometer reading in M mm

Q constant

E=M–Q

in mm 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=

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Experiment No.: 12 SURFACE TEXTURE MEASUREMENT Date :

AIM: To measure the surface finish (parameters) of the given specimen using measuring instruments.

stylus type

APPARATUS:-Test specimen, instruments.

measuring

standard

specimen,

surface

texture

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 value is 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.

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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 of force are measured.

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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:

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Department of Mechanical Engineering

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OBSERVATION: Feed and depth are constant. Speed N Sl No in rpm

Cutting speed v m/s

HKBK College of Engineering, Bengaluru

FR FH

FV

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Department of Mechanical Engineering

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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 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

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Department of Mechanical Engineering

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Result:

OBSERVATION:

Vertical feed constant :

Speed N Sl No

Dia.of Drill d

FV

T

in rpm

HKBK College of Engineering, Bengaluru

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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.

HKBK College of Engineering, Bengaluru

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Department of Mechanical Engineering

MMM

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.

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Department of Mechanical Engineering

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OBSERVATION & TABULATION Trail no

Indicated reading

Actual reading

Absolute error

% error based IR

% error based AR

(AR- IR) Left right

Left

right

HKBK College of Engineering, Bengaluru

Left

right

Left

right

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Department of Mechanical Engineering

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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 for the slightly wrong readings. Even the screw of a new micrometer is sometimes subjected to progressive and periodic errors.

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Department of Mechanical Engineering

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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.

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Department of Mechanical Engineering

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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 . 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.

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Department of Mechanical Engineering

MMM

OBSERVATION

1. Least count of the vernier (Thimble ) = Lcth = ------------mm. 2. Least count of the barrel

Lcbar = ---------- mm

PROGRESSIVE ERROR:-

Sl no

Nominal size of slip gauge

Micrometer reading in.

Progressive error

in, (mm)

(mm)

in, (mm)

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Department of Mechanical Engineering

HKBK College of Engineering, Bengaluru

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