Electrical B.Tech UET Peshawar Solved papers

1. Classification of instruments according to function:
1) Indicating instruments
2) Recording instruments
3) Integrating instruments
Explanation:
1) Indicating instruments: Indicating instruments indicate, generally the quantity to be measured by
means of a pointer which moves on a scale. Examples are ammeter, voltmeter, wattmeter etc.
2) Recording instruments: These instruments record continuously the variation of any electrical
quantity with respect to time. In principle, these are indicating instruments but so arranged that a
permanent continuous record of the indication is made on a chart or dial. The recording is generally
made by a pen on a graph paper which is rotated on a dice or drum at a uniform speed. The amount of
the quantity at any time (instant) may be read from the traced chart. Any variation in the quantity with
time is recorded by these instruments. Any electrical quantity like current, voltage, power etc., (which
may be measured lay the indicating instruments) may be arranged to be recorded by a suitable
recording mechanism.
3) Integrating instruments: These instruments record the consumption of the total quantity of
electricity, energy etc., during a particular period of time. That is, these instruments totalize events over
a specified period of time. No indication of the rate or variation or the amount at a particular instant are
available from them. Some widely used integrating instruments are: Ampere-hour meter: kilowatthour
(kWh) meter, kilovolt-ampere-hour
ComparisonAnalog and Digital Instruments:
Analog Digital
Analog signal is a continuous signal which
represents physical measurements
Digital signals are discrete time signals
generated by digital modulation
Display results in the form of wave signal Display results in the form of binary bit
Uses continuous range of values to
represent information
Uses discrete or discontinuous values to
represent information
Low cost and portable Cost is high and not easily portable
Analog instrument draws large power Digital instrument draws only negligible
power
Analog instruments are rarely used Digital instruments are widely used
Impedance is low Impedance is high
Analog instruments usually have a scale
which is cramped at lower end and give
considerable observational errors
Digital instruments are free from
observational errors like parallax and
approximation errors

2. Deflecting torque:
The deflecting torque is produced by making one of the
magnetic, heating, chemical, electrostatic and
electromagnetic induction effects of current or voltage
and cause the moving system of the instrument to move
on a calibrated scale from its zero position to indicate
on a graduated scale the value of electrical quantity
being measured. The method of producing this torque
depends upon the type of instrument.
Types of errors in measurements:
There are three basic types errors in measurements which given below:
1) Systematic Errors
2) Random Errors
3) Gross Errors

3. 1) Systematic Errors: Systematic errors are those that remains constant with repeated
measurements. Since they arise from inaccuracies in the manufacture of an instrument or from
improper adjustment or application of an instrument. Some of the more common systematic errors
are:
Zero Error: All readings are in error by the same amount. An example would be a voltmeter that
reads 1 V low on all readings, including zero.
Scale Error: This depends on the magnitude of the reading. An example would be a voltmeter that
reads 1 V high at 10 V, 2 V high at 20 V, and so on.
Response time error: This is due the instruments inability to follow dynamic changes in the
measured quantity.
Loading error: The instrument extracts sufficient energy from the system under measurement so
that the value of the measured parameter is changed.
2) Random Errors: Random errors are those errors due to unknown causes and are observed when
the magnitude and polarity of a measurement fluctuate in an unpredictable manner. Some of the
more common random errors are:
Rounding error: This occurs when readings are between scale graduations and the reading is
rounded up or down to the nearest graduation.
Periodic error: This occurs when an analog meter reading swings or fluctuates about the correct
reading.
Noise: The sensitivity of the instrument is changed or the reading is altered by outside
interference.
Backlash: The reading either lags or leads the correct value because of mechanical play, friction
or damping.
Ambient influences: Due to conditions external to the measuring system, such as variation in
temperature, humidity or atmospheric pressure.
Random errors cannot normally be corrected but they can be minimized by a skilled observer.
3) Gross Errors: Gross errors, as the name implies are usually quite large and can be divided into
two major categories:
Human error: This occurs when the operator makes a mistake such as reading the wrong scale or
reading.
Equipment faults: This error source can be large and sometimes erratic.
Gross errors cannot be eliminated but they can be significantly minimized by 1) careful operator
attention and cross-checking of results, and 2) frequent equipment calibration.
Parts of CRT: A CRT is electronic tube design to display electrical data.
The basic CRT consists of four major components
1) Electron gun (2) Focusing and accelerating anodes (3) Horizontal and vertical deflection
plates (4) Evacuated Glass envelope (5) Base
1) Electron gun: It is used for producing a strain of electrons.
2) Focusing and accelerating anodes: These are used for producing a narrow and sharply focus
beam of electrons
3) Horizontal and vertical deflection: These are used for controlling the path of the beam.
4) Evacuated Glass envelope: With a phosphorescent screen which produces bright spot when
struck by a high velocity electron beam. The electron gun assembly consists of an indirectly

4. heated cathode (K), a control grid (G), an accelerated anode A1, focusing anode A2 and
accelerating anode A3.
5) Base: It provides connection to external circuitry
Construction and Working Principle of CRT:
The construction of CRT is shown below, the CRT uses electrostatic focus and electrostatic
deflection, an arrangement found in most oscilloscopes.
Heater element is energized by alternating current to obtain high emission of electron from cathode
control grid is bias negative with respect to cathode it controls the density of electron beam to focus
the electron beam on the screen focusing anode is used. The focusing anode operate at a potential
of twelve hundred volt ( 1200V) and accelerating anode at 2000 V to accelerate the electron beam.
Two pairs of deflection plates provided in the CRT these deflection plates are mounted at right
angle to each other to provide electron beam deflection along vertical and horizontal axis of the
screen. The screen consists of a glass which is coated by some florescent material lying zinc
silicate. This is semitransparent phosphor substance. When high velocity electron beam struck the
phosphorescent screen the light emits from it. The property of phosphor to emit light when its atoms
are excited is called fluorescence.
Primary use of Kelvin Double Bridge:
The primary use of Kelvin Double Bridge is the precise measurement of low value resistance. The Kelvin
double bridge is the modification of the Wheatstone bridge and provides greatly increased accuracy
in measurement of low resistance.
Transducer: An electrical transducer is a device which is capable of converting the physical
quantity into a proportional electrical quantity such as voltage or electric current. Hence it
converts any quantity to be measured into usable electrical signal. This physical quantity which is
to be measured can be pressure, level, temperature, displacement etc. The output which is
obtained fromthe transducer is in the electrical form and is equivalent to the measured quantity.
For example, a temperature transducer will convert temperature to an equivalent electrical
potential. This output signal can be used to control the physical quantity ordisplay it.

5. Types of Transducer: These are the followings:
Types of Transducer based on Quantity to be measured:
• Temperature transducers (e.g. a thermocouple)
• Pressure transducers (e.g. a diaphragm)
• Displacement transducers (e.g. LVDT)
• Flow transducers
Types of Transducer based on the Principle of Operation
• Photovoltaic (e.g. a solar cell)
• Piezoelectric Transducer
• Chemical Transducer
• Inductive Transducer
• Capacitive Transducer
• Electromagnetic Transducer
• Hall Effect Transducer
• Photoconductive Transducer
Types of Transducer based on Whether an External Power Source is required or not
Active Transducer
Passive Transducers
Light sensitive Transducer:
A Light sensitive Transducer is a passive devices that convert the light energy whether visible or in the infra-
red parts of the spectrum into an electrical signal output. Light sensitive Transducer are more commonly
known as “Photoelectric Devices” or “Photo Transducers” because they convert light energy (photons) into
electricity (electrons).
Photoelectric devices can be grouped into two main categories, those which generate electricity when
illuminated, such as Photo-voltaic or Photo-emissive etc., and those which change their electrical properties in
some way such as Photo-resistors or Photo-conductors. This leads to the following classification of devices.
 Photo-emissive Cells – These are photo devices which release free electrons from a light sensitive
material such as cesium when struck by a photon of sufficient energy. The amount of energy the photons
have depends on the frequency of the light and the higher the frequency, the more energy the photons
have converting light energy into electrical energy.
 • Photo-conductive Cells – These photo devices vary their electrical resistance when subjected to light.
Photoconductivity results from light hitting a semiconductor material which controls the current flow

6. through it. Thus, more light increase the current for a given applied voltage. The most common
photoconductive material is Cadmium Sulfide used in LDR photocells.
 • Photo-voltaic Cells – These photo devices generate an emf in proportion to the radiant light energy
received and is similar in effect to photoconductivity. Light energy falls on to two semiconductor materials
sandwiched together creating a voltage of approximately 0.5V. The most common photovoltaic material
is Selenium used in solar cells.
 • Photo-junction Devices – These photo devices are mainly true semiconductor devices such as the
photodiode or phototransistor which use light to control the flow of electrons and holes across their PN-
junction. Photo junction devices are specifically designed for detector application and light penetration
with their spectral response tuned to the wavelength of incident light.
Method of measuring unknown capacitance with help of bridge:
Measurement of the unknown capacitance by Schering Bridge:
The Schering bridge one of the most important ac bridge is
used the extensively for the
measurement of capacitors.
In the Schering bridge the arm 1 now contains a parallel
combination of the
Resistor and the capacitor and standard arm contain only one
capacitor. The standard
Capacitor is usually a standard high quality mica capacitor.
In the balance condition of the bridge the sum of the phase
angles of the arms 1
And 4 is equal the sum of the phase angle of arms 2 and 3.at
the balance in condition there
is no current flow in the galvanometer.
The balance equation is derived in the usual manner, and by
substituting the
Corresponding impendence and the admittance the value of
the unknown capacitor and
The resister is finding as given below.
Cx=C3 (R1/R2).
Rx=R2 (C1/C2)
Procedure:-
1) Study the circuit provided on the front panel on the kit.
2) Connect the unknown capacitance of the position given.
3) Set the null point of galvanometer by adjusting the variable
4) Calculate the value of unknown capacitance by formula given
Result: -The values of unknown capacitance is measured by shearing bridge
Construction and Working principle of LVDT Transducer:
Construction: An LVDT is composed of seven components, not including the conditioning circuitry:
 Primary coil

7.  Secondary coil 1
 Secondary coil 2
 Ferromagnetic core
 Shaft
 Shield
 Handle
The ferromagnetic core is
the moving component
whose position within the
shaft is sensed. Around the
shaft are wound three inductors, the primary winding in the middle and the secondary windings (wound in
opposite direction) on either side of the primary. Each of the secondary should have the same number of
turns and be of the same length, otherwise the null position and linearity will be affected. A cylindrical shield
protects the windings from damage and also serves to contain the magnetic field used for sensing. The
physical component which will be measured using the LVDT is mechanically coupled to the ferromagnetic core
using a threaded (and non-ferromagnetic) handle. For some applications, a guide system and even a spring-
return (which is known as a “gage head” configuration) may be included in the assembly.
Working Principle of LVDT
LVDT works under the principle of mutual induction, and the displacement which is a non-electrical energy is
converted into an electrical energy. And the way how the energy is getting converted is described in working
of LVDT in a detailed manner.
When an AC excitation signal is applied to the Primary Coil (P), voltages are induced in the two secondary
coils (S). The MAGNETIC CORE inside the COIL WINDING ASSEMBLY provides the magnetic flux path
linking the Primary and secondary Coils. Since the two voltages are of opposite polarity, the Secondary
Coils are connected series opposing in the center, or Null Position. The output voltages are equal and
opposite in polarity and, therefore, the output voltage is zero. The Null Position of an LVDT is extremely
stable and repeatable. When the MAGNETIC CORE is displaced from the Null Position, an electromagnetic
imbalance occurs. This imbalance generates a differential AC output voltage across the Secondary Coils
which is linearly proportional to the direction and magnitude of the displacement. As shown in the figure,
when the MAGNETIC CORE is moved from the Null Position, the induced voltage in the Secondary Coil,
toward which the Core is moved, increases while the induced voltage in the opposite Secondary Coil
decreases.
Electrical Strain Gauge:
Strain Gauge is a passive transducer that converts a mechanical elongation or displacement produced due
to a force into its corresponding change in resistance R, inductance L, or capacitance C. A strain gauge is
basically used to measure the strain in a work piece. If a metal piece is subjected to a tensile stress, the

8. metal length will increase and thus will increase the electrical resistance of the material and vice versa. This
will also change the electrical resistance of the conductor. If both these stresses are limited within its elastic
limit, the metal conductor can be used to measure the amount of force given to produce the stress, through
its change in resistance.
Types
Strain gauge transducers are broadly classified into two. They are
1. Electrical Resistance Type Strain Gauge
In an electrical resistance strain gauge, the device consists of a thin wire
placed on a flexible paper tissue and is attached to a variety of materials to
measure the strain of the material. When a force is applied on the wire,
there occurs a strain (consider tensile, within the elastic limit) that increases
the length and decreases its area. Thus resistance of the wire changes, this
change in resistance is proportional to the strain and is measured using a
Wheatstone bridge. A full bridge circuit is used in applications where
complimentary pair of strain gauges is to be bounded to the test specimen.
In practice, a half bridge and full bridge circuit has more sensitivity than the
quarter bridge circuit. But since, the bonding is difficult, a quarter bridge
circuits are mostly used for strain gauge measurements. A full bridge circuit
is said to be more linear than other circuits.
An external supply is given to the bridge as shown in the diagram. Initially, when there is no application of
strain, the output measurement will be zero. Thus, the bridge is said to be balanced. With the application of a
stress to the device, the bridge will become unbalanced and produces an output voltage that is proportional to
the input stress.
2. Variable Inductance Type Strain Gauge:

9. he basic arrangement of a variable inductance strain gauge is shown below. This type of strain gauge is very
sensitive and can be used to measure small changes in length – as small as 1 millionth of an inch. Thus, it is
highly applicable as a displacement transducer.
Instruments: Instruments are devices which are used for the measurements of quantities. Electrical
measuring instruments are devices which are used for the measurement of various electrical aspects such
as the presence and amount of current, voltage, resistance and power through installation. Some electrical
measuring instruments that measure one of the electrical aspects mentioned are ammeters, voltmeter and
ohmmeters.
Types of Instruments: Different types of electrical instruments are given below:
Analogue instruments
Moving-iron instrument
The moving-coil rectifier instrument
Electronic instruments
Electro dynamic (or Dynamometer) type Instruments
Secondary Instruments:
1) Indicating instruments
2) Recording instruments
3) Integrating instruments
Permanent Magnet moving coil Instruments:
The permanent magnet moving coil instrument or PMMC type instrument uses two permanent
magnets in order to create stationary magnetic field. These types of instruments are only used for
measuring the dc quantities as if we apply ac current to these type of instruments the direction of current
will be reversed during negative half cycle and hence the direction of torque will also be reversed which
gives average value of torque zero. The pointer will not deflect due to high frequency from its mean position
showing zero reading. However it can measure the direct current very accurately.

10. Let us move towards the constructions of permanent magnet moving coil instruments. We will see the
construction of these types of instruments in
five parts and they are described below:
1) Stationary part or magnet system:
magnets are used of high field
intensities, high coercive force. The
magnets which we are using nowadays
are made up of materials like alcomax
and alnico which provide high field
strength.
2) Moving coil: The moving coil can freely
moves between the two permanent
magnets
3) Control system: The spring generally
acts as control system for PMMC
instruments.
4) Damping system: The damping force hence torque is provided by movement of aluminum
former in the magnetic field created by the permanent magnets.
5) Meter: Meter of these instruments consists of light weight pointer to have free movement and scale
which is linear or uniform and varies with angle.
Permanent Magnet moving coil Instrument used as a voltmeter:
When PMMC is used as a voltmeter, the coil is connected in series with high resistance.
Permanent Magnet moving coil Instrument used as an ammeter:
When PMMC is used as an ammeter, except for a very small current range, the moving coil is connected
across a suitable low resistance shunt, so that only small part of the main current flows through the coil.
The shunt consists of a number of thin plates made up of alloy metal, which is usually magnetic and has a low
temperature coefficient of resistance, fixed between two massive blocks of copper. A resistor of same alloy is
also placed in series with the coil to reduce errors due to temperature variation.
Essentials of an electronic instrument
As shown Figure, an electronic instrument is made up of the following three elements:

11. Transducer:It is the first sensing element
and is required only when measuring a
non-electrical quantity, say, temperature or
pressure. Its function is to convert the non-
electrical physical quantity into an
electrical signal. Of course, a transducer is
not required if the quantity being measured
is already in the electrical form.
Signal modifier: It is the second element and its function is to make the incoming signal suitable for
application to the indicating device. For example, the signal may need amplification before it can be properly
displayed. Other types of signal modifiers are: voltage dividers for reducing the amount of signal applied to the
indicating device or wave shaping circuits such as filters, rectifiers or chopper etc.
Indicating device:For general purpose instruments like voltmeters, ammeters or ohm meters, the indicating
device is usually a deflection type meter as shown in Figure. In digital readout instruments, the indicating
device is of digital design.
Measuring Standards of an electronic Instrument:
These are the followings:
 All the measuring electronic instruments are calibrated at the time of manufacture against
measurement standards.
 Its measuring error is very less and can be neglected.
 It uses low power
 The size of electronic instrument is very small
 The time it takes for the measuring is less and hence show the result quickly.
Electrical Measuring Transducers:
In exact sense of word a measuring transducer is a device which will transform the change of one size in a
change other. In terms of electronics a measuring transducer is determined usually as a device, transducers
an unelectric physical size (called a physical measurand) in an electric signal, or vice versa. Present, certainly
and exceptions from this rule
It is necessary from here, that measuring transducers are used in the electronic systems, i.e. in technical
devices p. by an electric signal, representing the result of measuring or supervisions. On the other hand, a
measuring transducer can be used on the output of the system
that, say, to generate mechanical motion depending on an
electric managing signal. The example of realization of
transducers is the system in which a microphone (entrance
transducer) converts a sound (physical measurand) into an
electric signal. The last increases, and then acts on a loud
speaker (output transducer), playback a sound substantially
more loud, than that which is perceived by a microphone.
Maxwell’s Induction Bridge:
The Maxwell's Inductance Bridge is most commonly used bridge
for measurement of inductance so f Q value below 10. A typical
Maxwell’s bridge consists of an inductance measured in
comparison with a capacitance in laboratory operations. The
input for the bridge is given through a standard 1 KHz oscillator

12. circuit which produces a 1 KHz sine wave at constant amplitude. The basic circuit diagram is as shown below.
In this bridge the arms bc and cd are purely resistive while the phase balance depends on the arms ab and ad.
Here l1 = unknown inductor of r1. l2 = variable inductor of resistance R2. r2 = variable electrical resistance. As
we have discussed in Ac Bridge according to balance condition, we have at balance point
We can vary R3 and R4 from 10 ohms to 10,000 ohms with the help of resistance box.
Piezoelectric Transducer:
Piezoelectric transducers are a type of electroacoustic transducer that converts the electrical charges
produced by some forms of solid materials into energy. The word "piezoelectric" literally means electricity
caused by pressure.
Explanation:
The piezoelectric transducers work on the principle of piezoelectric effect. When mechanical stress or forces
are applied to some materials along certain planes, they produce electric voltage. This electric voltage can be
measured easily by the voltage measuring instruments, which can be used to measure the stress or force.
The physical quantities like stress and force cannot be measured directly. In such cases the material exhibiting
piezoelectric transducers can be used. The stress or the force that has to be measured is applied along certain
planes to these materials. The voltage output obtained from these materials due to piezoelectric effect is
proportional to the applied stress or force. The output voltage can be calibrated against the applied stress or
the force so that the measured value of the output voltage directly gives the value of the applied stress or
force. In fact the scale can be marked directly in terms of stress or force to give the values directly.
The voltage output obtained from the materials due to piezoelectric effect is very small and it has high
impedance. To measure the output some amplifiers, auxiliary circuit and the connecting cables are required.
Wheatstone bridge:
We can measure unknown resistance by Wheatstone bridge using the following procedure.
1. Connect the unknown resistor, Rx, to the terminal of the
bridge.
2. Set the scale of the detector (galvanometer) to the least
sensitive range to prevent damage to the detector if the
bridge is severely unbalanced.
3. Connect the excitation source and adjust the resistor dial
until a null is obtained (zero deflection of the galvanometer).
4. If not at the most sensitive scale, increase the sensitivity of
the galvanometer and repeat step 3; otherwise, proceed to
step 5.
5. Calculate the unknown resistance with equation R1Rx = R2R3. By substituting an AC source and an
AC detector, it is possible to measure the value of a resistor at the frequency at which it will be used.
Extension range of an Instrument:
The range of an instrument can be extended by the using the following methods:

13.  In ammeter by connecting a shunt resister
 In voltmeter by connecting a series resister.
Kilowatt hour meter:
kWh meter is the electric meter that measures the amount of electrical energy in kWh that was consumed in
the house. The kWh meter has a counter display that counts units of kilowatt-hour (kWh). The energy
consumption is calculated by calculating the difference of the counter's reading in the specified period.
Kilowatt-hour is an energy unit (symbol kWh or kW·h).
One kilowatt-hour is defined as the energy consumed by power consumption of 1kW during 1 hour:
1 kWh = 1kW · 1h
The symbol of Kilowatt hour meter is .
Maximum demand indicator:
Maximum Demand Indicator (MDI) is an instrument which measures the maximum amount of electrical energy
required by a specific consumer during a given period of time.
Construction:
MDI instruments are designed in such a way that they record the base load requirement of electrical energy.
They can also measure the peak load but are unable to record sudden short circuit or High motor Starting
Currents. Its main construction parts are:
1. A Dial connected with moving system
2. A pointer on dial
3. Reset device
4. Fraction device
5. Indicating pin
Maximum demand indicator is often available as a built in feature of three phase energy meters, included in a
single case.
Maximum Demand is calculated by
Maximum Demand (KW) =
Maximum Energy Recorded (KWh)
⁄Time (hours)
Difference between primary and secondary instruments:
Primary Instruments Secondary Instruments
These instruments give the value of the electrical
quantity in terms of absolute quantities (or some
constants) of the instruments and their deflections.
They are direct reading instruments. The quantity to
be measured by these instruments can be determined
from the deflection of the instruments.

14. In this type of instruments no calibration or
comparison with other instruments is necessary.
They are often calibrated by comparing them with
either some absolute instruments or with those which
have already been calibrated.
They are generally not used in laboratories and are
seldom used in practice by electricians and engineers. These instruments are used in general for all
laboratory purposes.
Some of the examples of absolute instruments are:
* Tangent galvanometer
* Raleigh current balance
* Absolute electrometer
Some of the very widely used secondary instruments
are: ammeters, voltmeter, wattmeter, energy meter
(watt-hour meter), ampere-hour meters etc.
Various methods of supporting the moving system in an instrument:
There are two methods of supporting the moving system:
a) By pivoting
b) By thread suspension
Pivoting:
If the ends of the spindle are conical, the bearing friction will
be more. To reduce the bearing friction the bearing is slightly
rounded off to reduce the contact area which will reduce the
bearing friction but the pressure on the ends of the spindle will
exceed 80 T/m2
when the ends are very sharp. To reduce the
pressure on the ends, the pivot is slightly sounded off.
Materials used are sapphire jewels (for bearings).
Thread suspension:
Thread suspension is advantageous when the operating
forces are small compared to the weight of the system. This
type completely eliminates bearing friction. Thread suspension also provides controlling torque in addition to
supporting.
Multimeter:
A multimeter is an instrument used to measure electric current, voltage, and usually resistance, typically
over several ranges of value. A multimeter, therefore, is a
combination of several different types of meters all in one
box. At the minimum, a multimeter combines three distinct
types of meters (ammeter, voltmeter, and ohmmeter) into
a single device. A multimeter may be digital or analog.
Measurements with Multimeter:

15. The face of a digital multimeter typically includes four components:
 Display: Where measurement readouts can be viewed.
 Buttons: For selecting various functions; the options vary by model.
 Dial (or rotary switch): For selecting primary measurement values (volts, amps, ohms).
 Input jacks: Where test leads are inserted.
First of all set the dial (or rotary switch) for selecting the measurement for voltage, current or resistor.
Connect leads negative and positive from the input jacks with the given device same polarities.
Hence the required result will be shown on the display.

16. AC and DC bridges and its uses:
The D.C bridges are used to measure the resistance while the A.C bridges are used to measure the
impedances consisting capacitance and inductances. The D.C bridges use the D.C voltages as the
excitation voltage while the A.C bridges use the alternating voltage as the excitation voltage.
The two types of D.C bridges
1. Wheatstone Bridge
2. Kelvin Bridge
The various types of A.C Bridges are:
1. Capacitance Comparison Bridge
2. Inductance Comparison Bridge
3. Maxwell’s Bridge
4. Hay’s Bridge
5. Anderson Bridge
6. Schering Bridge
7. Wien Bridge
Oscilloscope:
An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic
signals. In effect, the device draws a graph of the instantaneous signal voltage as a function of time.
A typical oscilloscope can display alternating current (AC) or pulsating direct current (DC) waveforms having a
frequency as low as approximately 1 hertz (Hz) or as high as several megahertz (MHz). High-end
oscilloscopes can display signals having frequencies up to several hundred gigahertz (GHz). The display is
broken up into so-called horizontal divisions (hor div) and vertical divisions (vert div). Time is displayed from
left to right on the horizontal scale. Instantaneous voltage appears on the vertical scale, with positive values
going upward and negative values going downward.
Function of oscilloscope:
The functions of oscilloscope are the followings:
1) Displays amplitude, frequency of one or more input signals.
2) Compares amplitude, frequency, phase of two or more input signals.
3) Shows time relationship of start and stop of two or more input signals.
4) Shows time constant of input signals.
Potentiometer:
It is an instrument used for the measurement of electromotive force by balancing it against the
potential difference produced by passing the known current through a known variable resistance.

17. A variable resistor with a third adjustable terminal, the potential at the third terminal can be adjusted
to give any fraction of the potential across the ends of the resistor.
The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric
potential (voltage); the component is an implementation of the same principle, hence its name.
Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment.
Potentiometers operated by a mechanism can be used as position transducers, for example, in a joystick.
Potentiometers are rarely used to directly control significant power (more than a watt), since the power
dissipated in the potentiometer would be comparable to the power in the controlled load.
Meggars:
It is an instrument which is used for the measurement of resistance of electrical insulation.
The device enable us to measure electrical leakage in wire, results are very reliable as we shall be passing
electric current through device while we are testing. The equipment basically use for verifying the electrical
insulation level of any device such as motor, cable, generator winding, etc. This is a very poplar test being
carried out since very long back. Not necessary it shows us exact area of electrical puncture but shows the
amount of leakage current & level of moisture within electrical equipment/winding/system.