1

Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment 1

Aim: Conversion of Galvanometer into Ammeter and Voltmeter.

Materials required:

Galvanometer

Cell

Rheostat

Ammeter of desired range

Resistance wire

Key

Screw gauge

Lab Procedure:

The shunt resistance required to convert the galvanometer into ammeter of range I is

calculated using the formula,

G-the resistance of the galvanometer.

I- the range of desired ammeter

Ig = nk, the current required for full scale deflection in the galvanometer,

where, n- total number of divisions in the galvanometer

k- the figure of merit of the galvanometer.

Then, the length of the wire required for shunt can be calculated using the formula,

2

Where, ρ- the resistivity of material of the wire

r- the radius of the wire, which can be measured using a screw gauge.

Cut the resistance wire at a length of (l+2) cm.

Make two marks near the ends of the wire so that the distance between the marks is

exactly l cm.

The wire is now connected to the terminals of the galvanometer so that the marks are just

outside the terminals of the galvanometer.

The galvanometer with the shunt connected across its terminals is the converted ammeter

of the desired range.

Connections are made as shown in the circuit diagram.

The galvanometer with shunt resistance is connected in series to a battery through an ammeter, key

and rheostat.

Insert the key.

Adjust the rheostat and set the current reading I of the given ammeter at a particular value.

The reading of the galvanometer Ig’ is noted. Now, the current through the converted ammeter is

calculated using the relation,

The error of the converted ammeter is calculated as I – I’.

Repeat the experiment by changing the rheostat resistance.

A graph can be drawn with (I – I’) along Y-axis and I’ along X-axis. This is called the

correction graph.

Thus, the converted ammeter is verified with an ammeter of the same range and a

correction graph is obtained.

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Observations:

Resistance of the galvanometer, G = ............ohms

Figure of merit of the galvanometer, k = ............... amp./div.

Number of divisions in the galvanometer scale, n = ................

Current for full scale deflection, Ig = nk =............amp.

Desired range of the converted ammeter (I) ---------mA

Shunt resistance,

Calculations:

Shunt resistance,

Radius of the wire, r = --------cm = ------- X 10-2 m.

Resistivity of the material of the wire, ρ = --------------Ωm

Length of the wire required for shunt can be calculated using the formula,

Result:The given galvanometer is converted into an ammeter of range 0 to ………….A by

connecting a shunt resistance of …………ohms

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTAND INSTRUMENTATION

LAB

Subject Code: 1621308

Experiment 2

Calibration of Ammeter, Voltmeter and Wattmeter.

Objective:

Calibration of voltmeter using DC potentiometer

Calibration of Ammeter using DC potentiometer

Apparatus Required:

1. Calibration of voltmeters and ammeter by Potentiometer

2. Potentiometer

3. Sliding jockey

4. Mains cord

5. Patch cords

Theory:

A potentiometer instrument for measuring the potential (or voltage) in a circuit taps off a fraction

of a known voltage from a resistive slide wire and compares it with the unknown voltage by

means of a galvanometer. The potentiometer method is the usual basis for the calibration of

voltmeters, ammeters, and wattmeters. Since the potentiometer is a DC measurement device, the

instrument to be calibrated must be of the DC or electrodynamometer type. One of the first

requirements in this calibration procedure is that a suitable, stable DC supply be available, since

any variation in the supply voltage causes a corresponding change in the voltmeter calibration

voltage.

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Diagram of Callibration of Voltmeter:

Diagram of Callibration of Ammeter:

Procedure:

1. Connect the mains cord to the Trainer kit and switch On Mains Supply.

3. Note the output of standard DC supply (Vdc) by connecting terminal 32 to digital voltmeter

V1’s positive terminal and ground terminal 6 to negative of V1.

4. Once voltage is noted from V1, disconnect them and connect the negative terminal of

galvanometer G1 to positive terminal 32 of DC supply.

5. Connect positive terminal of G1 to jokey.

6. Connect terminal 3 and 4 to digital ammeter A1 polarity wise.

7. Connect DC potentiometer between terminal 5 and 6. Connect 5 to X and 6 to Z terminal. 8.

Vary VR2 knob to set the current in A1 (say 30 mA).

9. Touch jokey to X and then to Z terminals of potentiometer and see the reading of

galvanometer. Compare both reading of galvanometer.

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10. Now slide the jokey on potentiometer wire and the find null point i.e., the point where

galvanometer G1 shows zero reading.

11Connect the circuit according to the provided circuit Diagram.

12. Set the voltage in analog DC Voltmeter (V) to some value (say 1 V) with the help of VR1

knob.

13. Touch jokey to X and then to Z terminals of potentiometer and see the reading of

galvanometer. Compare both reading of galvanometer.

14. Now slide the jokey on potentiometer wire and the find null point.

15. Now measure distance D (in cm) moved from terminal Z to null point.

Observation Table:

For Voltmeter Calibration

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For Ammeter Calibration

Distance L (in cm) moved from terminal Z to null point is

L = [(n-1)*100 + r] cm.

n= number of wire from the Z terminal, for odd line of wire take reading from lower scale and

for even line wire take reading from upper scale.

C=Vdc /L VDC = DC Supply Voltage.

L= Distance

C= Voltage drop per cm.

Precaution:

1. Handle all the equipments with care

2. Make connections according to circuit diagram

3. Take the readings carefully& the connections should be tight

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION

LAB

Subject Code: 1621308

Experiment 3

Determination of Inductance, Capacitance using AC bridges.

Object:- Measurement of the unknown inductance by using Hay’s bridge method

Apparatus:-Multimeter ,LCR meter, Hay’s bridge kit, Patch cords.

Theory:-

The hays bridge is the modification of the Maxwell Bridge. This bridge uses a resistance in

series with the standard capacitor. The bridge has four resistive arms in which the arms one is

consists of the resister R1, Lx .The arm 2 is consists of the variable resistance R3.The low value

of the resistance is obtain by the low resistive arms of the bridge. The value of R4 and C4 is the

standard value of the capacitor and resistance. By using the unknown inductance having a

resistanceR1. R2, R3,R4-is the known non-inductive resistance and C4 is standard value of the

capacitor. The unknown value of inductance and Quality factor of the Bridge is obtained by

formula.

Lx = (R2R3C4) /(1+ 2R42C4 )

2) Quality factor (Q)=(1/ 2R42C42)

Basic AC bridges consist of four arms, source excitation and a balanced detector. Commonly

used detectors for AC bridges are:

(1)Head phones

(2)Vibration galvanometers

(3)Tunable amplifier detectors Vibration galvanometer is extremely useful at power and low

audio frequency ranges. Vibration galvanometers are manufactured to work at various frequency

ranging from 5 KHZ to 1 KHZ. But one most commonly used between 200HZ

Advantage-1) This Bridge gives very simple expression for unknown for High Q coil.

2) This bridge also gives a simple expression for Q factor.

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Disadvantage-1)The hays bridge is suited for the measurement of the High Q inductor.

2)It is used to find the inductor having the q value of the smaller then 10.

Procedure:

1)Study the circuit provided on the front panel of the kit.

2)Connect unknown inductance LX1 in the circuit. Make all connections to complete the bridge.

3)Put the supply ON

4)Set the null point of galvanometer by adjusting variable resistance R3.

5)Note value of R2, R3, and C4 by removing connection by patch cords.

6)Calculate theoretical value of LX1 using L=R2R3C4

7)Measure value of LX2 by LCR meter and compare it.

8)Repeat process for LX2.

Circuit Diagram:-

Figure 1. Diagram of a bridge for measuring

inductance: (U) current source; (G) galvanometer;

(R3), (R2), and (R3) ohmic resistances; (Cx,)

standard capacitance; (Lx) inductance being

measured

Result:- The unknown is inductance measured

using Hay’s bridge and is found to be___

Precautions :

1.connections should be tight.

2.Instrument should be handled carefully

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENT AND INSTRUMENTATION

LAB

Subject Code: 1621308

Experiment :3A

Aim:-Measurement of the unknown inductance by using Maxwell bridge method.

Apparatus Required:

Transformer 230/15v

Bread board

Resistors

Variable Resistor

Inductors

Digital Multimeter

Theory:

This bridge circuit measures an inductance by comparison with a variable standard selfinductance.

Let, L1 = unknown inductance of resistance R1,

L2 = variable inductance of fixed resistance R2,

R2 = variable resistance connected in series with inductor L2,

R3, R4 = known non-inductive resistances

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At balance, L1 = R3L2/R4 , R1= R3(R2+r2)/R4.

Procedure:

1. Connect the circuit as shown in the figure.

2. Connect the unknown inductance in L1.

3. Connect the multimeter between ground and output of imbalance amplifier.

4. Vary R2, from minimum position, in clockwise direction.

5. If the selection of R2 is correct the balance point can be obtained at minimum position.

6. Vary R2 for fine balance adjustment.

Observation:

Sl No. R2 R3 C1 L1=R3L2/R4 True Value of

L1

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Result: Actual and practical values of Inductances are found to be nearly equal.

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENT AND INSTRUMENTATION

LAB

Subject Code: 1621308

Experiment :3B

Objective:

To determine the unknown value of inductance by comparing with a standard variable

capacitance using Maxwell’s Inductance Capacitance bridge.

Apparatus:

Transformer 230/15v

Bread board

Resistors

Variable Resistor

Inductors

Capacitor

Digital Multimeter

Theory:

This bridge circuit measures an inductance by comparison with a standard variable capacitance . The

connections and the phasor diagrams for balance conditions are shown below.

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Let, L1 = unknown inductance of resistance R1,

R2, R3, R4 = known non-inductive resistances

L2 = variable inductance of fixed resistance R2,

C4 = variable standard capacitance.

Writing the equation for balance

(R1+jωL1)(R4/1+jωC4R4) = R2R3

Separating the real and imaginary terms, we have

R1 = R2R3/R4 and L1 = R2R3C4

Procedure:

1. Connect the circuit as shown in the figure.

2. Select the value of R2.

3. Vary R3 from minimum position in clockwise direction.

4. If the selection of R2 is correct, the balance point is observed at minimum voltage, for a

particular R1 and then increases by varying R3 in the same clockwise direction.

If that is not the case,select another value of R2.

5. Vary R3 for fine balance adjustment.

6. Observe the balance of bridge either using loud speaker or digital multimeter.

7. Connect the digital multimeter at the output of the detector. Alternately, adjust R3 and proper

selection of R2.

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Sl No. R2 R3 C1 L1=R3L2/R4 True Value of

L1

16

Re

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Result:Actual and practical values of Inductances are found to be nearly equal.

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENT AND INSTRUMENTATION

LAB

Subject Code: 1621308

Experiment :3C

Objective:

To determine the unknown value of capacitance using Desauty’s bridge.

Apparatus:

Transformer 230/15v

Bread board

Resistors

Variable Resistor

Capacitors

Digital Multimeter

Theory:

The bridge is the simplest of comparing two capacitances. The connections and the phasor

diagram of this bridge are shown below. Let

C1 = Capacitor whose capacitance is to be measured.

C2 = A standard capacitor R3,

R4 = Non-inductive resistors.

The balance can be obtained by varying either R3 or R4. Resistors R1 and R2 are connected in

series with C1 and C2 respectively. r1 and r2 are small resistances representing the loss

component of the two capacitors.

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At balance, (R1+ r1+ 1/jωC1) R4 = (R2+ r2+1/jωC2) R3

From which we have C1/C2 = R4/R3 . Figure b shows the phasor diagram of the bridge under

balance conditions. The angles δ1 and δ2 are the phase angles of capacitors C1and C2

respectively.

Dissipation factor for the capacitors are D1 = tan δ1 =ω C1r1 and D2 = tan δ2 =ω C2R2

D2 – D1 = ω C2(R1R4/R3 – R2)

Therefore, if the dissipation factor of one of the capacitors is known, the dissipation factor for the

other can be determined.

Procedure:

1. Connect the circuit as shown in the figure.

2. Connect the unknown capacitor in C1.

3. Select any value of R3.

4. Connect the multimeter between ground and output of imbalance amplifier.

5. Vary R2, from minimum position, in clockwise direction.

6. If the selection of R3 is correct the balance point can be obtained at minimum position.

7. If that is not the case,select another R3.

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8. Since, the unknown capacitance whose resistive effect would be made for capacitive form and

R2 is adjusted for minimum output.

Observation:

Sl. No. R3 R2 C2 C1=R2C2/R3 True Value of C1

Result: The unknown capacitance is determined using the Desauty’s bridge.

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENT AND INSTRUMENTATION

LAB

Subject Code: 1621308

Experiment :4

Use of AC potentiometer, chokes, resistance model

Objective: Use of AC potentiometer

Theory:

The Potentiometer is an instrument which measures unknown voltage by balancing it with a

known voltage. The known source may be DC or AC. The working phenomenon of DC

potentiometer and AC potentiometer is same. But there is one major difference between their

measurements, DC potentiometer only measures the magnitude of the unknown voltage. Where

as,ACpotentiometer measures both the magnitude and phase of unknown voltage by comparing

it with known reference. There are two types of AC potentiometers:

1. Polar type potentiometer.

2. Coordinate type potentiometer.

Polar type Potentiometer

In such type of instruments, two separate scales are used to measure magnitude and phase angle

on some reference of the unknown e.m.f. There is a provision on the scale that it could read

phase angle up to 3600. It has electrodynamometer type ammeter along with DC potentiometer

and phase-shifting transformer which is operated by single phase supply. In phase-shifting

transformer, there is a combination of two ring-shaped laminated steel stators connected

perpendicularly to each other as shown in the figure. One is directly connected to power supply

and the other one is connected in series with variable resistance and capacitor. The function of

the series components is to maintain constant AC supply in the potentiometer by doing small

adjustments in it.

Between the stators, there is laminated rotor having slots and winding which supplies voltage to

the slide-wire circuit of the potentiometer. When current start flowing from stators, the rotating

field is developed around the rotor and due to it e.m.f. is induced in the rotor winding. The phase

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displacement of the rotor emf is equal to rotor movement angle from its original position and it is

related to stator supply voltage. The whole arrangement of winding are done in such a way that

the magnitude of the induced emf in the rotor may change but it does not affect the phase angle

and it can be read on the scale fixed on the top of the instrument.

The induced emf in rotor winding by stator winding 1 can be expressed as

The induced emf in the rotor winding by the stator winding 2,

From equation (1) and (2), we get

Therefore, resultant induced emf in the rotor winding due to two stator winding

Where, Ø gives the phase angle.

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Coordinate type Potentiometer:

In coordinate AC potentiometer, two separate potentiometers are caged in one circuit as shown

in the figure. The first one is named as the in-phase potentiometer which is used to measure the

in-phase factor of an unknown e.m.f. and the other one is named as quadrature potentiometer

which measures quadrature part of the unknown e.m.f. the sliding contact AA’ in the in-phase

potentiometer and BB’ in quadrature potentiometer are used for obtaining the desired current in

the circuit. By adjusting rheostat R and R’ and sliding contacts, the current in the quadrature

potentiometer becomes equal to the current in the in-phase potentiometer and a variable

galvanometer shows the null value. S1 and S2 are signs changing switches which are used to

change the polarity of the test voltage if it is required for balancing the potentiometer. There are

two step-down transformers T1 and T2 which isolate potentiometer from the line and give an

earthed screens protection between the winding. It also supplies 6 volts to potentiometers. Now

to measure unknown e.m.f. its terminals are connected across sliding contacts AA’ using selector

switch S3. By doing some adjustments in sliding contacts and rheostat, the whole circuit gets

balanced and galvanometer reads zero at the balanced condition. Now the in-phase component

VA of the unknown e.m.f. is obtained from the in-phase potentiometer and quadrature component

VB is obtained from quadrature potentiometer.

Thus, the resultant voltage of the coordinate AC potentiometer is

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And the phase angle is given by

Applications of AC Potentiometer:

1. Measurement of self-inductance.

2. Calibration of voltmeter.

3. Calibration of Ammeter.

4. Calibration of watt meter.

For application of AC Potentiometer check the experiment no. 2 .

Objective: Use of AC choke:

In electronics, a choke is an inductor used to block higher-frequency alternating current (AC) in

an electrical circuit, while passing lower-frequency or direct current (DC). A choke usually

consists of a coil of insulated wire often wound on a magnetic core, although some consist of a

doughnut-shaped "bead" of ferrite material strung on a wire. The choke's impedance increases

with frequency. Its low electrical resistance passes both AC and DC with little power loss, but it

can limit the amount of AC due to its reactance.

The name comes from blocking—"choking"—high frequencies while passing low frequencies. It

is a functional name; the name "choke" is used if an inductor is used for blocking or decoupling

higher frequencies, but is simply called an "inductor" if used in electronic filters or tuned

circuits. Inductors designed for use as chokes are usually distinguished by not having the low-

loss construction (high Q factor) required in inductors used in tuned circuits and filtering

applications.

A choke, with two 20 mH windings and rated to handle 2 A

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Types & Construction:

Chokes are divided into two broad classes:

Audio frequency chokes (AFC) – designed to block audio and power line frequencies while

allowing DC to pass

Radio frequency chokes (RFC) – designed to block radio frequencies while allowing audio

and DC to pass.

Audio frequency chokes:

Audio frequency chokes (AFC) usually have ferromagnetic cores to increase their inductance.

They are often constructed similarly to transformers, with laminated iron cores and an air gap. A

major use in the past was in power rectifiers and direct current motor controllers to produce

direct current (DC), where they were used in conjunction with large electrolytic capacitors to

remove the voltage ripple (AC) at the output DC. A rectifier circuit designed for a choke-output

filter may produce too much DC output voltage and subject the rectifier and filter capacitors to

excessive in-rush and ripple currents if the inductor is removed. However, modern electrolytic

capacitors with high ripple current ratings, and voltage regulators that remove more power

supply ripple than chokes could, have eliminated heavy, bulky chokes from mains frequency

power supplies. Smaller chokes are used in switching power supplies to remove the higher-

frequency switching transients from the output and sometimes from feeding back into the mains

input. They often have toroidal ferrite cores.

Some DIY car audio hobbyists use choke coils with car audio systems (specifically in the wiring

for a subwoofer, to remove high frequencies from the amplified signal).

Radio frequency chokes:

Radio frequency chokes (RFC) often have iron powder or ferrite cores. They are often wound in

complex patterns (basket winding) to reduce self-capacitance and proximity effect losses.

Chokes for even higher frequencies have non-magnetic cores and low inductance.

A modern form of choke used for eliminating digital RF noise from lines is the ferrite bead, a

cylindrical or torus-shaped core of ferrite slipped over a wire. These are often seen on computer

cables. A typical RF choke value could be 2 millihenries.

An MF or HF radio choke for tenths of an ampere, and a ferrite bead VHFchoke for several

amperes

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A ferrite "bead" choke, consisting of a cylinder of ferrite encircling a computer power cord to

block electronic noise.

Common-mode (CM) chokes:

The common-mode choke, where two coils are wound on a single core, is useful for suppression

of electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for

prevention of malfunctioning of power electronics device. It passes differential currents (equal but opposite),

while blocking common-mode currents.[2] The magnetic flux produced by differential-mode (DM) currents in the

core tend to cancel each other out since the windings are negative coupled. Thus, the choke presents little

inductance or impedance to DM currents. Normally this also means that the core will not saturate for large DM

currents and the maximum current rating is instead determined by the heating effect of the winding resistance.

The CM currents, however, see a high impedance due to the combined inductance of the positive coupled

windings.

A typical common-mode choke configuration. The common mode currents, I1 and I2, flowing in the

same direction through each of the choke windings, creates equal and in-phase magnetic fields

which add together. This results in the choke presenting a high impedance to the common mode

signal

Near magnetic field emission reduction

When the CM choke is conducting CM current, most of the magnetic flux generated by the windings is confined with the inductor core due to its high permeability. In this case, the leakage flux, which is also the near magnetic field emission of the CM choke is low. However, the DM current flowing through the windings will generate high emitted near magnetic field since the windings are negative coupled in this case. To reduce the near magnetic field emission, a twisted winding structure can be applied to the CM choke.

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A balanced twisted windings CM choke

The prototype of the balanced twisted winding CM choke

CM choke with DM current

The difference between the balanced twisted windings CM choke and conventional balanced two winding CM choke is that the windings interact in the center of the core open window. When it is conducting CM current, the balanced twisted winding CM inductor can provide identical CM inductance as the conventional CM inductor. When it is conducting DM current, the equivalent current loops will generate inversed direction magnetic fields in space so that they tend to cancel each other.

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The equivalent current loops and the magnetic fields generated

Measurement for near magnetic field emission

We need to conduct a current to a certain inductor. And then, use a probe to measure the near field emission. First of all, a signal generator is connected to an amplifier, serving as a voltage source. The output of the amplifier is then connected to the measured inductor. To monitor and control the current flowing through the inductor, a current clamp is used to clamp the conducting wire. An oscilloscope is connected to the current clamp to show the current waveform. A probe is then used to measure the flux in the air. A spectrum analyzer is connected to it to collect the data

29

Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment :5

Aim: To observe the loading effect of a multi-meter while measuring voltage across a low

resistance and high resistance.

Equipment/Components Required:

Digital multimeter (DMM)

Volt-ohm-milliammeter (VOM)

Variable DC power supply

Breadboard

Resistors : 4.7 W, 47 W, 3.9 kW, 5.6 kW, 3.9 MW, 5.6 MW

Theory:

When we use a voltmeter to measure the voltage in a circuit, we always assume its input

impedance is very large that it does not load the circuit and it will always indicate the correct

voltage in a circuit. Unfortunately this is not always the case.

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In order for any instrument to provide a measurement, it must take a small amount of energy

from the circuit under test, and use this energy to obtain a reading. While the amount of

energy taken from most circuits is virtually undetectable, this is not always so. Consider the

circuit as shown in Figure 1. Ideally, the internal resistance of a voltmeter is infinitely large,

resulting in no circuit current. The voltage appearing across the voltmeter will be 10 V

which means that the voltmeter provides a correct reading of 10.0 V.

However, all voltmeters have some internal resistance. If the internal resistance of the

voltmeter was equal to the series resistance, 5.6 MW, then the voltage appearing across the

voltmeter would be half of the supply voltage, resulting in a reading of 5.0 V. If the internal

resistance of the voltmeter is even smaller, the voltmeter’s reading will be smaller too. The

degree to which a meter loads a circuit under test is called the loading effect and is

determined mathematically as:

In order to know whether the internal resistance of the meters is comparable with the circuit

under test, you must know the meter’s internal resistance. The internal resistance of the

DMM and VOM for its ammeter operation can be found in their operation manual.

PROCEDURES:

1. Voltmeter Loading Effect

1.1 Refer to the manual of the DMM, obtain the internal resistance of the voltmeter and

record this value.

Rint = ______________Ω

1.2 The internal resistance of an analog meter is generally dependent on the voltage range

used. In order to determine the internal resistance, the manufacturer provides a specification

called the sensitivity, S which has units of kW/V. The internal resistance is then determined as

the product of sensitivity and the voltage range of the meter as:

Refer to the manual of the VOM, obtain the sensitivity of the meter. Determine the

correct range that we would use to measure a voltage of 10 V. Calculate and record

the internal resistance of meter on this range.

Vrange

S

Rint

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1.3 Connect the circuit of Figure 3. Place the DMM voltmeter directly across the terminals

of the voltage source and adjust the voltage source for exactly 10 V which is the

unloaded voltage between terminals A and B.

VAB (unloaded) = ___________________V

1.4 Remove the DMM and connect it between terminals A and B. Measure the voltage

appearing between these terminals.

VAB (measured) = ___________________V

1.5 Calculate the loading effect of the DMM.

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

1.6 Replace the DMM with a VOM. Set the Vrange of the VOM to appropriate range to

measure 10 V. Measure the voltage appearing between these terminals.

VAB (measured) = ___________________V

1.7 Calculate the loading effect of the VOM.

____________________________________________________________

_____________________________________________________________

___________________________________________________________

____________________________________________________________

____________________________________________________________

1.8 Based on the test circuit, calculate the internal resistance of the VOM.

____________________________________________________________

____________________________________________________________

____________________________________________________________

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1.9 Refer to Figure 4. Calculate the voltage across each of the resistors using the voltage

divider rule.

V1(unloaded)

V2(loaded)

1.10 Connect the circuit of Figure 4 and measure the voltages V1 and V2 with both the

DMM and VOM voltmeters.

Reading V1 V2

DMM

VOM

1.11 Calculate the corresponding loading effect of the DMM and the VOM

1.12 Replace the resistors 5.6 kW and 3.9 kW with 5.6 MW and 3.9 MW in Figure 4.

Calculate the voltage across each of the resistors and measure the voltage across each of

the resistors with DMM and VOM.

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1.13 Calculate the corresponding loading effect of the DMM and the VOM.

3. Ammeter Loading Effect:

Use a DMM ohmmeter to measure the actual resistance of a 4.7 W resistor. Use a

DMM voltmeter to adjust the voltage source to 0.3 V. Calculate the unloaded current of

the circuit in Figure 5.

Actual resistance of the 4.7 W

resistor = ____________W

Unloaded current , I = _______________A

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Connect the circuit of Figure 5. Use the DMM as ammeter first and record the meter’s

reading. Repeat with a VOM ammeter. (Ensure that the ammeter is on the correct range

and polarity to measure the current).

Calculate the loading effect of the two ammeters

2.4 Calculate the internal resistance of each of the ammeters

2.5 Replace the 4.7 W resistor with a 47 W resistor and adjust the voltage of the DC supply to

3 V. Measure the current of the circuit with the DMM and VOM ammeters and

calculate the corresponding loading effect.

35

Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment :6

Aim:Measurement of voltage, frequency, time period and phase angle using Cathode Ray

Oscilloscope (CRO).

Apparatus: CRO, Function generator, Digital Voltmeter, Connecting Wires

Circuit Diagram:

An oscilloscope is a measuring device used commonly for measurement of voltage, current, frequency, phase difference and time intervals. The heart of the oscilloscope is the cathode ray tube, which generates the electron beam, accelerates the beam to high velocity, deflects the beam to create the image, and contains the phosphor screen where the electron beam eventually becomes visible. To accomplish these tasks, various electrical signals and voltages are required. The power supply block provides the voltages required by the cathode ray tube to generate and accelerate the electron beam, as well as to supply the required operating voltages for the other circuits of the oscilloscope. Relatively high voltages are required by the cathode tubes, on the order of a few thousand volts, for acceleration, as well as a low voltage for the heater of the electron gun, which emits the electrons. Supply voltages for the other circuits are various values usually not more than few hundred volts.

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The oscilloscope has a time base, which generates the correct voltage to supply the cathode ray tube to deflect this part at a constant time dependent rate. The signal to be view is fed to you vertical amplifier, which increases the potential of the input signal to a level that will provide a usable deflection of the electron beam. To synchronize the that the horizontal deflection starts at the same point of the input vertical signal each time it sweeps, a synchronizing or triggering circuit is used. This circuit is the link between the vertical input and the horizontal time base. Procedure: Phase Measurement using Lissajous Patterns (X-Y Mode):

To Measure the phase difference of two sine waves their frequencies must be equal.

1. Connect a 1Volt peak-peak, 1KHz sine wave signal from the function generator to the

horizontal input of the CRO.

2. Connect the output of phase shift network to the vertical input as shown in figure.

3. Adjust the vertical and horizontal gains properly for good display.

4. Observe Lissajous Patterns for different combinations of R and C values.

Calculate the phase angle as

Sine θ = A/B

A: Distance between the points where the ellipse crosses the y-axis and the origin. B: Distance between the origin and the y – co-ordinate of the maxima of the ellipse. Calculate theoretical phase difference as

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! = tan-1 (f1/f2)

Where f2 = 1/2"RC f1 = input signal frequency.

LISSAJOUS’ FIGURES

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment :7

Aim: Measurement of time period, frequency,

Theory:

There are many methods for measurements of frequency or time. In our experiment only a few of

them are used: analog methods based on measurement of time with the oscilloscope, and direct

method based on of measurement frequency and time with the multifunction digital counter.

Oscilloscope method used in the experiments are extremely simple - they implement either

internal (linear) time base, or external reference signal (Lissajous method). Having known the

time base speed time/div (a value which may be read from oscilloscope’s screen), all we need to

do is to measure the length of one or more cycles of the observed signal.. This method is fast but

not very precise.

Sinusoidal (external) time-base method (The Lissajous method).

An other analog frequency measurement method involving the oscilloscope rely on using the

oscilloscope as a kind of null indicator for comparison of a sine signal with unknown frequency

with a reference sine signal whose frequency should be well defined and easily varied. One of

the signals is fed to the Y channel of the oscilloscope, the second one to the X channel. An

interaction of these two signals produces on the display more or less complicated snaky loops,

whose form allows for determining the unknown frequency. A typical Lissajous figure is shown

in Fig. 1

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Fig. 1 Frequency measurement with the Lissajous method a) measurement diagram, b) Lissajous

figure and frequency determination.

If we assume that fy is the unknown frequency signal connected to the Y channel and fx is the

reference signal connected to the X channel then we have

where nx, ny denote number of intersections of the Lissajous curve with horizontal and vertical

axes, respectively, and dφ/dt is the rate of phase change (the trace rotation speed). The reference

signal should be adjusted until the displayed figure is possibly stable (dφ/dt ≈ 0). It is sometimes

attainable with difficulty, and needs both signal sources involved having adequate frequency

stability. The method's error is roughly equal to relative calibration error of the reference source.

Due to the mentioned stability problems, usefulness of the method is limited to rather low

frequency applications.

Digital counter method.

Digital counter methods rely on continuing number of events (in this case – the number of

cycles) with the counter open during precisely determined window. The periodic input signal of

any shape, including sine waveform, is formed in an input shaper block to have standard form of

possibly short pulses that are fed to the counter controlled by an accurate and stable quartz

oscillator (see Fig.2).

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If the counter is opened for e.g. 1 second, then the number of pulses counted during this time

directly gives the measured frequency. If we denote open gate time as τ, input signal period as

Tx, and number of cycles counted as N, then

and the unknown frequency is equal to

It is intuitively obvious that the accuracy of this method mainly depends on the accuracy of gate

timing. It may be shown that the limiting error of direct frequency measurement method is equal

to

where δgfref is the limiting error of quartz oscillator frequency.5gfk is the limiting.

In conclusion, one may see that the limiting error of direct frequency measurement method decreases

- as the number N increases, i.e. measured frequency rises,

- gating time τ is longer.

Laboratory module description

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Fig. 1. Module F01. G1 – sinusoidal waveform output, G2 – rectangular waveform output, PF –

phase shifter

Measurements and tasks

Table 1. Measurement functions of 53220A Keysight digital frequency counter

Table 2. Measurement functions of 1052 Rigol oscilloscope

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Note: Before the measurements:

- connect power supply to the F01 Module.

- set a frequency counter impedance to 50 Ω for inputs 1 and 2:

Measurements of time parameters of sinusoidal signals

1.1 Use the DFC 53220A (Digital Frequency Counter) to measure time parameters (period and

frequency) of sine signal from generator G1 output in F01 module

Measure appropriate parameters using following functions

a) PERIOD – measure the period of the signal with gating time of 1 s. If selected gating

time is longer than measured period, the DFC measures an average period.

b) FREQ – measure the frequency of the signal with gating time of 1 s. In this case, the

frequency is measured with the indirect method.

c) TOTALIZE:GATED – counting the number of pulses during 1 s of Gate Time. This case

realizes the direct frequency measurement method (using frequency definition – counting of

phenomena occurrences during reference time interval).

Compare and comment obtained results from PERIOD, FREQ and TOTALIZE:GATED

measurement method

1.2 Use the oscilloscope to measure time parameters (period and frequency) of sine signal from

generator G1 output in F01 module.

Take measurements of the period and frequency with the use the manual procedure (length

measurements) and the automatic measurement functions. Set the oscilloscope to minimize

measurements errors.

Insert the oscillograms into the report. Write down Cx constant and measurement results.

Estimate the limiting error of both measurements.

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Compare and comment obtained results of period and frequency measurements with the

corresponding values obtained in point 1.1a and 1.1b. Assume the DFC as a reference

instrument.

Measurements of time parameters of rectangular signals.

2.1 Use the DFC 53220A (Digital Frequency Counter) to measure time parameters (period and

frequency) of sine signal from generator G2 output in F01 module.

Prior to the measurements assess the stability of the G2 generator and adjust the resolution of the

frequency counter. To do this, set the number of digits displayed on the frequency counter

display in a way to achieve observed instability of the result on the least significant digit

.

a) Measure the period and frequency using the PERIOD and FREQ functions respectively. Set

the gating time of 1 s.

Compare and comment on the results

b) Measure the pulse width of rectangular waveform (Width: Pos) and time interval between

pulses (Width: Neg).

c) Determine duty cycle of the signal based on the parameters obtained in point a) and b).

d) Measure the duty cycle of the signal using automatic function in the DFC (DutyCycle: Pos).

Compare and comment results obtained in points c) and d).

2.2 Use the oscilloscope to measure time parameters (period and frequency) of sine signal from

generator G2 output in F01 module

a) Take measurements of the period and frequency with the use the manual procedure (length

measurements) and the automatic measurement functions. Set the oscilloscope to minimize

measurements errors.

Insert the oscillograms into the report. Write down Cx constant and measurement results.

Estimate the limiting error of both measurements

Compare obtained results of period and frequency measurements with the corresponding values

obtained in point 2.1a. Assume the DFC as a reference instrument.

point 3.1.

Compare obtained results of period and frequency measurements with the corresponding values

obtained in point 2.1a. Assume the DFC as a reference instrument.

b) Take measurements of the pulse width and time interval with the use the manual procedure

and the automatic measurement functions (WIDTH+ and WIDTH-).

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Insert the oscillograms into the report. Estimate the limiting error of the measurements.

c) Based on results in point a) and b), determine value of the duty cycle and estimate the limiting

error of both results.

d) Take measurements of the duty cycle with the use of automatic function +DUTY.

Compare values of duty cycle obtained in points 2.1c and 2.1d. Assume the DFC as a reference

instrument

Measurements of phase shift of sinusoidal signals

3.1 Connect the output of the G1 generator to the input of the phase shifter PF in F01 module.

Use the DFC to measure the phase shift between signals on the input and output of the PF

module.

To gain measurement result in range of 0 - 360ºset option:

3.2 Use the oscilloscope to measure phase shift between signals on the input and output of the PF

module. Use the sine signal from G1 as an input signal for the phase shifter (PS).

Take measurements with the use the manual procedure (length measurements. Set the

oscilloscope to minimize measurements errors. Insert the oscillogram into the report and mark all

sectors used for ε calculation.

Estimate the limiting error of phase shift measurement.

Compare and comment obtained result of phase shift measurement with the corresponding value

of phase shift obtained in point 3.1.

Conclusion::

In conclusion, one may see that the limiting error of direct frequency measurement method

decreases

- as the number N increases, i.e. measured frequency rises,

- gating time τ is longer

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment :8

Aim: Measurement of rise, fall and delay times using a Cathode Ray Oscilloscope

Theory:

Rise Time

In the digital world, rise time measurements are critical. Rise time may be a more appropriate

performance consideration when you expect to measure digital signals, such as pulses and steps.

our oscilloscope must have sufficient rise time to accurately capture the details of rapid

transitions. Rise time describes the useful frequency range of an oscilloscope.

To calculate the oscilloscope rise time required for our signal type, use the following equation:

This basis for oscilloscope rise time selection is similar to that for bandwidth. As in the case of

bandwidth, achieving this rule of thumb may not always be possible given the extreme speeds of

today’s signals. Always remember that an oscilloscope with faster rise time will more accurately

capture the critical details of fast transitions. In some applications, we may know only the rise

time of a signal. A constant allows we to relate the bandwidth and rise time of the oscilloscope,

using the equation:

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Rise time is the amount of time a pulse takes to go from a low to high voltage. By convention,

the rise time is measured from 10% to 90% of the full voltage of the pulse. This eliminates any

irregularities at the pulse’s transition corners. Pulse width is the amount of time the pulse takes to

go from low to high and back to low again. By convention, the pulse width is measured at 50%

of full voltage. Figure 69 illustrates these measurement points.

For rise time and fall time measurements, the 10% and 90% amplitude points are used as starting

and ending reference points.

Procedure:

1. Apply a signal to the INPUT jack. Set the vertical MODE to the channel to be used. Use the VOLTS/DIV and VARIABLE to adjust the waveform peak-to-peak height to five divisions. 2. Using the vertical POSITION control and the other controls, adjust the display sich that the wavedoem is centered vertically in the display. Set the SWEEP TIME/DIV to as fast a setting as possible consistent with observation of both the 10% and 90% points. Set the SWEEP VARIABLE control to CAL position. 3. Use the horizontal POSITION control to adjust the 10% point to coincide with a vertical graduation line and measure the distance in divisions between the 10% and 90% points on the waveform. Multiply this by the SWEEP TIME/DIV and also by 1/10 if "X10MAG" mode was used. . NOTE: The graticule on the CRT includes the 0, 10, 90, and 100 % lines assuming that 5 divisions correspond to 100 %. Use them as a reference for accurate measurements. Using the formula: Risetime = Horizontal distance (div) X (SWEEP TIME/DIV setting) / "X10 MAG" value.

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Example For the example, the horizontal distance is 3.3 divisions. The SWEEP TIME/DIV is 2 (us/div) Substituting the given value Risetime = 3.3 (div) X 2 (us/div) = 6.6 us Rise time and fall time can be measured by making use of the alternate step 3 as described below as well. 4. Use the Horizontal POSITION control to set the 10% point to coincide with the center vertical graduation line and measure the horizontal distance to the point of the intersection of the waveform with the center horizontal line. Let this distance be D1. Next adjust the waveform position such that the 90% point coincides with the vertical centerline and measure the distance from that line to the intersection of the waveform with the horizontal centerline. This distance is D2 and the total horizontal distance is then D1 plus D2 for use in the above relationship in calculating the rise time or fall time. Using the formula: Risetime = (D1 + D2) (div) X (SWEEP TIME/DIV setting) / "X10 MAG" value.

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Example

For the example, the measured D1 is 1.6 divisions while D2 is 1.4 divisions. If SWEEP

TIME/DIV is 2 us/div we use the following relationship

Substituting the given value:

Rise time = (1.6 + 1.4) (div) X 2 (us/div) = 6 us

Conclusion:

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Government Polytechnic, Muzaffarpur

ELECTRONIC MEASUREMENTANDINSTRUMENTATION LAB

Subject Code: 1621308

Experiment :9

Aim: Measurement of R, L and C using a LCR bridge/Universal bridge.

Apparatus Required:

LCR meter ,connecting chords

Theory:

LCR meters are measuring instruments that measure a physical property known as impedance.

Impedance, which is expressed using the quantifier Z, indicates resistance to the flow of an AC

current. It can be calculated from the current I flowing to the measurement target and the voltage

V across the target’s terminals. Since impedance is expressed as a vector on a complex plane,

LCR meters measure not only the ratio of current and voltage RMS values, but also the phase

difference between current and voltage waveforms.

LCR meter measurement circuit: Two-terminal method

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Typical equations for LCR meters

Equivalent circuit mode

Open correction and short correction

The test fixture used when measuring a target has residual components and can be expressed

using an equivalent circuit such as that shown in the figure below. Consequently, the measured

value Zm is expressed using an equation that contains these residual components, as shown

below. To calculate the true value Zx, it is necessary to calculate the open residual component

and short residual component and then correct the measured value. These correction processes

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are known as open correction and short correction, respectively, and LCR meters include

functionality for performing both.

Zm: Measured value

Zs:

Short residual impedance (Rs: residual resistance; Ls: residual inductance)

Yo:

Open residual admittance (Go: residual conductance; Co: stray capacitance)

Zx:

True value (measurement target’s impedance)

Measurement signal level

The measurement signal output from the LCR meter is voltage-divided between the output

impedance R and the measurement target Zx. Thus the set measurement signal level V is not

applied as-is to the measurement target Zx. LCR meters have three measurement signal modes.

Open-voltage (V) mode:

The user sets the measurement signal level V in the figure. This value is the voltage when the

measurement terminals are in the open state.

Constant-voltage (CV) mode:

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The user sets the value Vx in the figure (the voltage between the measurement target Zx’s

terminals). This mode is used when measuring targets that exhibit voltage dependence, for

example MLCCs with a high dielectric constant.

Constant-current (CC) mode:

The user sets the value I in the figure (the current that flows to the measurement target Zx). This

mode is used when measuring measurement targets that exhibit current dependence, for example

inductors with cores.

Obsevation:

Conclusion: