full manual 1

MEASUREMENTS AND INSTRUMENTATION LABORATORY MANUAL

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Expt. No: 1 Date:

CHARACTERISTICS OF LVDT AND I/P CONVERTER

i) CHARACTERISTICS OF LVDT

AIM: To study the characteristics of Linear Variable Differential Transformer (LVDT).

APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2 3

LVDT Digital Displacement Indicator CRO

- - -

- - -

1 1 1

THEORY:

The most widely used inductive transformer to translate linear motion into electrical signals is LVDT. It consists of one primary winding (P) and two secondary windings (S1 & S2) , identically placed on either side of primary winding. The primary winding is connected to an AC source. A soft movable iron core is placed inside the former. Displacement to be measured is applied to soft movable iron core. The frequency of AC supply to the primary winding is 50Hz to 20 KHz. When the primary winding is excited by an AC source, an alternating magnetic field is produced which in turn induces AC voltages in two secondary windings. The output of S1 is ES1 and S2 is ES2. To convert the output from S1 and S2 into a single voltage signal, the two secondary windings S1 and S2 are connected in direct opposition. The output of the transducer is the difference of the two voltages. Differential output voltage Eo = ES1 ~ ES2 When the core is at null position, the flux linking with both the secondary windings is equal and hence the emfs are induced in them. i-e Eo = 0 V as ES1 = ES2. Now if the core is moved to the left of the null position, more flux links with windings S1 and less with windings S2. Accordingly ES1 is more than ES2. The magnitude of output voltage is thus Eo = ES1 ES2 and the output voltage is in phase with say, the primary voltage. Similarly, if the core is moved to the right of the null position, the flux linking with S2 becomes larger than that linking with S1. Thus Eo = ES2 ES1 and 180o out of phase with the primary voltage. The amount of voltage change in either secondary winding is proportional to the amount of movement of core. Hence we have an indication of amount of linear motion. By noting which output voltage is increasing or decreasing, we can determine the direction of motion.



CIRCUIT DIAGRAM: TABULATION: Sl.No.

Push Side Reading Pull Side Reading Micrometer

Reading (mm) Indicated

Reading (V) Micrometer

Reading (mm) Indicated

Reading (V)



PROCEDURE:

1. Connections are given as per the circuit diagram. 2. The LVDT jig micrometer scale is calibrated by (0 mm - 10 mm),

(10 mm - 0 mm), (20 mm 10 mm). 3. The micrometer scale arrangement is set to 10 mm and the DPM is set to

0 using zero adjust pot provided in the signal conditioning unit. 4. The micrometer scale arrangement is set to 15 mm and the pot is not

adjusted until the DPM shows 5 mm. 5. Now the LVDT trainer is calibrated and the core position is varied using

micrometer scale arrangement. The corresponding output voltage with respect the core displacement is noted and observed.

6. The graph between displacement and output voltage is plotted.



MODEL GRAPH:

Linear Range

Residual Voltage

Distance (mm)

Voltage (V)



INFERENCE:

RESULT:



SCHEMATIC OF CURRENT TO PRESSURE CONVERTER:



ii) CHARACTERISTICS OF I/P CONVERTER

AIM: To study the characteristics of current to pressure (I/P) converter.

APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2 3 4 5

I/P Converter Pressure Gauge Current Source Ammeter Air Compressor

- - -

MI -

- - - - -

1 1 1 1 1

THEORY: Current to Pressure Converter converts the current in terms of milli-ampere to its corresponding pressure. It requires constant air supply (20 PST) for the conversion. Air supply from air compressor is given to pressure regulator and the regulated air supply is given to I/P Converter. As shown in the figure, the regulated air supply enters through restriction and comes out through the nozzle. In front of the nozzle a flopper is placed. The mid point of the flopper is fixed on a pivot, so that the flopper moves freely in to and fro motion. One end of the flopper is placed near by the nozzle and the other end is placed near by the current carrying coil. This operating coil is energized by the current flowing through it. As the current in the coil is increased, one side of the flopper moves forward the coil and hence the other end moves towards the nozzle. When the flopper moves towards the nozzle, there is increase in back pressure. When the flopper moves, always there will be decrease of back pressure. So, the back pressure is directly proportional to the distance (x) between the nozzle and the flopper. This relationship is given by,

Po= ps / [1-16 )/( dx 2] Where, Po = Back pressure (PSI)

ps = Regulated pressure supply (PSI)

X = Distance between the nozzle and the flopper (mm)

D = Diameter of the restriction and the nozzle (mm)



TABULATION: Sl.No.

Input Current in mA Outlet Pressure in PSI



AIR FILTER AND REGULATOR:

Filter is made up of sintered bronze or play propylene. Filters are designed to separate condensed water, rust, dirt, scale, corrosive liquids and other debris from air lines which may cause wear and premature failure of air tools, valves, cylinder, current to pressure converter and other pneumatic equipment. Filter unit is placed upstream of the regulator. Regulators are used for maintaining delivery pressure as per the setting done independent of fluctuation in primary pressure.

Rapid response and accurate pressure air wide range of applications. Minimum delay of pressure over a wide rang of air flow. Ensuring that varying flow demand by various air operated equipment /

tools at down stream end.

PROCEDURE:

1. The Air compressor is switched on and the compressor pressure is raised to 45 PSI.

2. The output pressure is kept constant at 20 PSI by slightly adjusting the knob at the top of the regulator to maintain 20 PSI.

3. The current source is switched on. 4. The current signal to the current to pressure converter is varied and the

corresponding output pressure at the gauge is noted down. INFERENCE:

RESULT:



C1

C2

R1

a

b

c

d

E

I1

I1

I2

I2

C4 0.2 F

DCB

DCB

DRB DRB

DRB

CIRCUIT DIAGRAM:

DCB- Decade Capacitance Box DRB- Decade resistance Box



Expt. No: 2 Date:

SCHERING BRIDGE AND MAXWELLS INDUCTANCE BRIDGE

i) SCHERING BRIDGE

AIM: To measure the given unknown capacitance using Scherings Bridge. APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2 3 4 5 6 7

Decade Capacitance Box Decade Resistance Box Capacitance CRO Function Generator Bread Board Connecting Wires

- - -

Single - - -

- -

0.2 F - - -

2 2 1 1 1 1

As required THEORY: AC BRIDGE:

The figure shows a basic AC bridge. The four arms of the bridge are impedances Z1, Z2, Z3, and Zx, the conditions for balance of bridge require that there should be no current through the detector this requires that the potential difference between the points b and d should be zero this will be the case when the voltage drop from a to b equals to voltage drop from a to d, both in magnitude and phase. In complete notations we can write as.

E1 = E2

OR

Z1I1 = Z2I2 ---------------(1)

Also at balance, I1-I3 = E/Z1+Z2 and I2 = I4 = E/Z2 + Zx Substitute the value of I1 and I2 in equation (1)

Z1Zx = Z2Z3 1. Two balance equations are always obtained for an AC bridge, both

magnitude and phase relationships must be satisfied. This requires that real and imaginary terms must be separated, which give two equations to be satisfied for balance.

2. The two balance equations enable us to know two unknown quantities. The two quantities are usually a resistance and an inductance or a capacitance.

3. In order to satisfy both conditions for balance and for convenience of manipulation, the bridge must contain two variable elements in its configuration. For greatest convenience, each of the balance equations must contain one variable element and one only. The equations are then said to be independent.



4. In this bridge circuit, balance equations are independent of frequency.

TABULATION:

S.No R1 () R3 ()

SET VALUE Cx (F)

OBSERVED VALUE Cx (F)



SCHERINGS BRIDGE:

A very important bridge used for the precision measurement of capacitors and their insulating properties is the Scherings Bridge. Its basic circuit arrangement is given in fig.

For balanced condition, the general equation is Z1Zx = Z2Z3 Therefore Zx = Z2Z3 / Z1, Zx = Z2Z3Y1 Where Zx = Rx j / Cx Z2 = R2 Z3 = j / Cx Y1 = 1/R1 + j C1 As Zx = Z2Z3Y1

Therefore [Rx-j/ Cx] = R2 [-j/ Cx] * [1/R1+j/ Cx] [Rx-j/ Cx] = [R2 (-j) / R1 (Cx)] + [R2C1/C3] Equating the real and imaginary terms, we get

Rx = R2C1/C3 And Cx = (R1/R2) C3

Now if Rx and Cx are unknown and R1, R2 & R3 are known, we can find the

unknowns from the above equations.

PROCEDURE:

1. Connections are given as per the circuit diagram. 2. The unknown capacitance is connected across the terminal Rx, Cx. 3. Any one multiplier arm is selected and it is connected by the connecting

link. 4. Now the variable resistance arm R1 is varied to balance the bridge. 5. The balance condition is checked by CRO. The known resistance is

measured using multimeter. 6. The values are substituted in the formula and checked with the set values. 7. The above procedure is repeated by selecting various multiplier arm values

for various unknown Capacitance. INFERENCE: RESULT:



CIRCUIT DIAGRAM:

Cb

Rb Ra

Ld

Rd Rc



ii) MAXWELLS INDUCTANCE BRIDGE

AIM: To measure the given unknown inductance using Maxwells Inductance Bridge. APPARATUS / INSTRUMENTS USED:


VMB 03 Trainer Kit Unknown Inductance Multi meter CRO Probe

- - - - -

1 1 1 1 2

THEORY:

An AC bridge method is employed for measurement of core losses in magnetic material. The MaxwellWien Circuit or Maxwells Inductance Capacitance Bridge is used for the measurement of core loss. Ld = unknown inductance Rd = effective resistance of inductance Ra, Rb, Rc = unknown non-inductive resistance

Cb = variable standard capacitor

Thus we have two variables Ra and Cb which appear in one of the two balance

equations and hence the two equations are independent. The Q-factor can be calculated from the following expression:

bbd

d RCRLQ

In order to use this bridge circuit for the measurement of power loss, the primary of the test frame is connected in the bridge as shown.

The maximum flux density is calculated from the equation.

bbcacadbd

cabb

bdd

RCRRj RRLjRR

or RRRCj1

R)Lj(R

Z1Z4= Z2Z3

b

cad R

RRR bcad CRRL



TABULATION: Cb = F

S.No Ra () Rc ()

SET VALUE Ld (H)

OBSERVED VALUE Ld (H)



4max 10*4

NAfBE ave

Where, Eavg = average absolute value of secondary voltage

Bmax = Maximum flux density N = No. of turns in secondary winding of test frame A = cross section area of ferromagnetic specimen in square cm The test frame is represented by a series combination of inductance and resistance.

PROCEDURE:

1. Connections are given as per the circuit diagram. 2. The unknown inductance is connected. 3. Any one multiplier arm is selected and it is connected by the connecting

link. 4. Now the variable resistance arm Ra is varied to balance the bridge. 5. The balance condition is checked by CRO. The known resistance is

measured using multimeter. 6. The values are substituted in the formula and checked with the set values. 7. The above procedure is repeated by selecting various multiplier arm values

for various unknown inductances. INFERENCE:

RESULT:



CIRCUIT DIAGRAM:

V



Expt. No: 3 Date:

WHEATSTONE BRIDGE AND KELVIN DOUBLE BRIDGE

i) WHEATSTONE BRIDGE

AIM: To measure the given unknown resistance using Wheatstone Bridge. APPARATUS / INSTRUMENTS USED:


10 k Potentiometer Decade Resistance box CRO or Multi meter Bread Board Connecting wires

- - - - -

- - - - -

2 1 1 1

As required THEORY:

A bridge is the name used to denote a special class of measuring circuits. They are most often used for making measurements of resistance, capacitance, and inductance. Bridges are used for resistance measurements when a very accurate determination of a particular resistance value is required. The most well known and widely used resistance bridge is the Wheatstone bridge. It was invented by Samuel Christie but improved to the point of being a commercial product by Charles Wheatstone. It is used for accurately measuring resistance values from milliohms to mega ohms. Most commercial Wheatstone bridges are accurate to approximately 0.1 percent. Thus the values of resistance obtained from the bridge are far more accurate than the values obtained from the ohmmeter or the voltmeter ammeter method. The circuit of DC Wheatstone bridge is shown in fig, where Rx is the resistance to be measured. The bridge works on the principle that no current will flow through the very sensitive D Arsenal Galvanometer connecting nodes b and c of the bridge circuit if there is no potential difference between them. When there is no current flow in galvanometer, then bridge is said to be in balanced condition. The balanced condition is achieved if the voltage Vo is divided in path a-c-d resistors R3 and Rx. Then nodes b and c will be at the same potential. Thus the conduction of no current flow through the galvanometer implies that

R1 I1 = R3 I2 I1 = I3 and I2 = I4 I1 = I3 = V / (R1 + R2) and I2 = I4 = V/ (R3 +Rx)

Substitute the value of I1 and I2 in equation (1)

R1 V/ (R1 + R2) = R3 V/ (R3 + Rx)



R1 R3+ R1 Rx = R1 R31+ R2 R3 TABULATION:

S.No R1 () R2 ()

R3 ()

SET VALUE Rx (F)

OBSERVED VALUE Rx (F)



Now if Rx is unknown and R1, R2 and R3 are known, we can find Rx from

Rx= R2 R3 / R1 The ratio R2 / R3 can be set to 10-3, 10-2, 10-1, 1, 10,102, 103 etc. R3 is a continuously adjustable variable resistor. When a null is achieved, the resistance can be calculated from the above equation. PROCEDURE:

1. Connections are given as per the circuit diagram. 2. The unknown resistance is connected across the terminal Rx 3. Any one multiplier arm is selected and it is connected by the connecting

link. 4. Now the two variable resistance arms are varied to balance the bridge. 5. The balance condition is checked by using CRO or multi-meter. The known

resistance is measured using Multi-meter. 6. The values are substituted in the formula and checked with the set values. 7. The above procedure is repeated by selecting various multiplier arm values

for various unknown resistances. INFERENCE:

RESULT:



CIRCUIT DIAGRAM:

R p q

P Q

E

m n

r

S

S

a

b

c d



ii) KELVIN DOUBLE BRIDGE

AIM: To measure the given unknown resistance using Kelvin Double Bridge. APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2 3

VKB,02 Trainer Kit Multimeter Unknown Resistance

- - -

- - -

1 1 1

THEORY: The process in double bridge can be explained by suggesting the simple modification, that the actual resistance units of correct ratio be connected between the points m and n, the galvanometer be connected to the junction of the resistors. This is the actual Kelvin Bridge arrangement. This bridge incorporates the idea of a second set of ratio arms and the use of four terminal resistors for the low resistance arms. The second set of ratio arms p & q is used to connect the galvanometer to a point d at the appropriate potential between points m and n to eliminate the effect of connecting lead of resistance r between the known resistance R and the standard resistance S. The ratio p/q is made equal to P/Q. Under balanced conditions, there is no current through galvanometer, which means that the voltage drop between a and b, Eab is equal to the voltage drop Eamd.

Let

For zero galvanometer deflection, Eab = Eamd

rqpprRI

rqpq)r(p

qppRIE

qp with parallelin isr and seriesin are q and p Since

rqp

q)r(pSRIE and EQP

PE

amd

acacab

Vqp

p p across potential then rqp

q)r(pIV



TABULATION:

S.No P () Q ()

S ()

SET VALUE Rx (F)

OBSERVED VALUE Rx (F)



PROCEDURE:

1. Connections are given as per the circuit diagram. 2. The unknown resistance is connected across the terminal R. 3. Any one multiplier arm is selected and it is connected by the connecting

link. 4. Now the two variable resistance arms are varied to balance the bridge. 5. The balance condition is checked by using CRO or multi-meter. The known

resistance is measured using Multi-meter. 6. The values are substituted in the formula and checked with the set values. 7. The above procedure is repeated by selecting various multiplier arm values

for various unknown resistances. INFERENCE:

RESULT:

SQPR then

qp

QP If

qp

QP

rqpprS

QPR

rqpprRI

rqpq)r(pSRI

QPP



CIRCUIT DIAGRAM:

R1 = 15 k R2 = 33 k R3 = 47 k R4 = 100 k

Vo

Vo

+ 12 V

- 12 V

+ 12 V

- 12 V

+ 12 V

- 12 V

V (0-20)V MC

5 V

5 V

IC741

IC741

IC741



Expt. No: 4 Date:

INSTRUMENTATION AMPLIFIER

AIM: To study the characteristics of an instrumentation amplifier. APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2

3 4 5

IC 741 Resistors RPSU Voltmeter Bread Board

Op-Amp

Dual

15 k 47 k 100 k 33 k

(0-30) V

3 2 2 2 1 2 1 1

THEORY:

In analog instrumentation the transducers are frequently located at long distance from measurement systems. The signal level at the transducers sides is often low and their source impedance is high. A general amplifier for processing such signals called as an instrumentation amplifier. Instrumentation amplifiers should have

1. Differential inputs. 2. High input impedance and CMRR. 3. Provided with simple gain adjustments.

Op-Amp 1 and 2 are connected in noninverting input configuration. Instead of

grounding both inverting terminals they are connected to resistor R2 as shown. The noninverting terminals of Op-Amp 1 and 2 are fed by a voltage source V1

and V2 respectively. The circuit analysis gives the following equations. Vo1 = (1+R1/R2) V1-(R1/R2) V2 Vo11 = (1+R1/R2) V2-(R1/R2) V1 The differential gain of the stage connecting Op-Amp 1 and 2 is therefore (Vo11 - Vo1)/ (V2-V1 ) = 1+ (2R1/R2)



TABULATION:

S.No V1 Volts V2

Volts Vo(TH) Volts

Vo(ACTUAL) Volts



Op-Amp 3 is connected as a differential amplifier with a gain of R4/R3. The

overall gain of two stage cascaded amplifier is [1+ (2R1/R2)* R4/R3] The gain may be easily adjusted without distorting circuit symmetry by varying

the resistance R2. PROCEDURE:

1. Connections are made as shown in the circuit diagram. 2. By varying V1 and V2, V0 can be measured with the help of a voltmeter. 3. Gain can be calculated using the formula [1+ (2R1/R2)* R4/R3].

INFERENCE:

RESULT:



BLOCK DIAGRAM:

DC

N

etw

ork

Low

pas

s

Filt

er

Cal

ibra

ting

(Zer

oing

) N

etw

ork

Pow

er

Sup

ply

T

rans

duce

r B

ridge

D

C

Ex

cita

tion

S

ourc

e

Mea

sura

nd

Out

put

DC

Vo

ltage



Expt. No: 5 Date:

MEASUREMENT OF PHYSICAL QUANTITIES

TORQUE AND ANGLE

AIM: To measure the torque using strain gauge trainer and to measure the angle using a potentiometer. APPARATUS / INSTRUMENTS USED: Torque Measurement Strain Gauge Trainer Kit Load 100 g range 10 Nos. Angle Measurement Trainer Kit Multi-meter -1 No. THEORY: TORQUE MEASUREMENT:

Measurement of the torque transmitted by a shaft is based upon the angular

velocity or twist of the shaft in a calibrated length of torque tube attached to the shaft. This strain is sensed by a transducer and the same is measured. The strain measurement is then interpreted in terms of torque by proper calibration.

The strain in the shaft may be measured by means of strain gauge attached to its surface. The strain gauge should be properly mounted to give maximum sensitivity to the strain produced by the torsion. For a shaft subjected to pure torsion, the gauge will be strained in the direction of the major axis if the gauge is mounted at 450 to the axis of the shaft PROCEDURE:

1. The torque cell is connected to the interface board. 2. A voltmeter is connected across T1 and Ground and the EXCITATION

potentiometer is adjusted to get 5 V in the voltmeter (Proper input to Bridge circuit).

3. A voltmeter is connected across T2 and T3 and the OFFSET potentiometer is adjusted to get 0 V in the voltmeter (Bridge balancing).

4. 1 kg of weight is added to the starting point of the one meter cantilever beam and the GAIN Potentiometer is adjusted to get 1000 in the display of the interface board. (Calibrating the device to indicate the torque i.e. 1000 g-m)

5. The beam is loaded insteps of 100 g and the amplified bridge output and the torque in terms of Gram-meter from the display is tabulated.

6. The step 5 is repeated for various loading positions of the beam.



CIRCUIT DIAGRAM:

Inst

rum

enta

tion

Am

plifi

er

Display

Interface R1, R2, R3, R4 = Strain

Gauges 5V

Red

Green

White

Black

1 2 3 4 5

6 7 8 9



TABULATION:

S.No. Weight (gm) Amplified Bridge

Output (V) Torque (gm-m)



ANGLE MEASUREMENT: The resistance of a metal conductor is expressed by a simple equation which involves some physical quantities. The relationship is

ALR

Where R = resistance, L = Length of conductor, m A = Cross sectional area of conductor, m3 = Resistively of conductor material, -m The rotational potentiometer which works on the basis of change in the value of resistance with change in length of the conductor can be used for measurement of rotary displacement. The rotational devices are circular in shape and are used for measurement of angular displacement. The POT may be excited by dc voltage and the output voltage can be taken from the variable end of the POT. The POT is a passive transducer since it requires an external power source for its operation. Resistance at the output terminals Output Voltage= * Input Voltage Resistance at the input terminals

PROCEDURE:

1. The pointer of the potentiometer is set to minimum position and the calibration knob is adjusted to give 0 in the display.

2. The Pointer of the potentiometer is kept at 3600 and the calibration knob is adjusted to give 360 in the display.

3. Now gradually the position of the pointer is varied to different degrees and the readings are observed and tabulated.



CIRCUIT DIAGRAM: TABULATION:

Angular Displacement

(Degrees) Indicated reading

(Degrees)

Potentiometer

V +

-

2V + -

0.1

0.2

0.3

1.5



INFERENCE:

RESULT:



CIRCUIT DIAGRAM:

330

330

-5 V +5 V

-5 V

330

330

330

330

+5 V

+5V

1VRef/4

2VRef/4

3VRef/4

VRef = 4V

Vin = (0-30)V

-5 V

+ 5 V

-5 V

1 k

1 k

1 k

1 k

IC 741

IC 741

IC 741

IC 741



Expt. No: 6 Date:

A/D CONVERTER

AIM: To design and implement a flash-type analog to digital converter using IC741 and verify its output. APPARATUS / INSTRUMENTS USED:

S.NO ITEM TYPE RANGE QUANTITY 1 2

3 4 5 6 7 8

IC 741 Resistor LED IC 7404 IC 7408 IC 7432 RPSU Single Strand Wire

Op-Amp

NOT Gate AND Gate OR Gate

Dual

- 330 1 k

- - -

4 6 4 6 1 1 2 2

As Required THEORY:

This is the simplest, expensive A/D converter. The circuit consists of a resistive divider network i.e., op-amp comparator and a encoder circuit. A small amount of hysteresis is built into the comparator to resolve any problem that might occur, if both input were of equal voltage. At each node of the resistive divider a comparison voltage is available. Since all the resistors are of equal value, the voltage available at the nodes is equally divided between the reference voltages VR and the ground. The purpose of the circuit is to compare analog input with each of the node voltages. The circuit has the advantages of high speed as the conversion take place simultaneously rather than sequentially. Conversion time is limited only by the speed of the comparator and the priority encoder.

PROCEDURE:

1. Connections are given as per the circuit diagram. 2. Reference voltage is set. 3. Input voltage is varied from 0 to VR and corresponding output is noted and

verified with truth table.



TRUTH TABLE:

ANALOG I/P A B C D X Y 0-VR/4 0 0 0 1 0 0

VR/4-VR/2 0 0 1 1 0 1 VR/2-3VR/4 0 1 1 1 1 0 3VR/4-VR 1 1 1 1 1 1



INFERENCE:

RESULT:

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