Q.3 State different errors in analog Measurement instrument.

Error: It is defined as the difference between measured value and true value of the quantity.
i) Gross errors: These errors occurring due to human mistakes in reading and calculating
measurement results are known as gross errors.
ii) Systematic errors: The Errors that remain constant or change according to a definite law on repeated
measurement of a given quantity is known as systematic errors.
A) Instrumental errors: These errors are caused due to the mechanical structure of
Measuring instrument such as:
a) Inherent shortcomings of instruments: Instrument may read too low or too high.
b) Improper use of instruments: Improper handling e.g. overloading, overheating,
failure to adjust zero, use of high resistance leads.
c) Loading effect: Cause distortion in original signal.
B) Environmental errors: These are because of surrounding conditions such as
temperature, pressure, humidity, dust, vibrations, or external magnetic fields or
electrostatic fields.
C) Observational errors: Parallax errors arise on account of pointer and scale not being on same plane,
In other words, it is incurred when the line of vision of the observer is not exactly above the pointer.
iii) Random errors: These errors are due to multitude of small factors which change or fluctuate from one
measurement to another. These persist even after gross and systematic errors are removed.
Q.4 Give Classification of Instruments
1) Absolute Instrument: These are the instrument which read quantity under measurement indirectly.
i.e. In terms of deflection, degrees & Meter constant.
e.g. Tangent Galvanometer.
2) Secondary Instruments: These give reading directly of the quantity at the time of measurement.
a) Indicating Instruments: These indicate the magnitude of quantity to be measured. The indication is
generally in the form of scale (dial) & Pointer arrangement.
e.g. Ammeter, Voltmeter, Wattmeter
b) Recording Instruments: The Recording instruments give a continuous record of the variations of the
quantity being measured.
e.g. Temperature variation in furnace, supply voltage variation in substation.
c) Integrating Instruments: The Integrating instrument integrated the quantity under measurement
over a period of time. i.e. it totalize the event over a period of time.
e.g. Ampere hour meter, watt-hour meter, energy meter in which power is measured over a period of
time which gives measurement of energy.
Q.5 List Differences between absolute and secondary instrument.
Absolute instruments Secondary instruments
It gives magnitude of quantity in terms physical It gives reading of the quantity directly on the
Constants of instrument Scale at the time of measurement
Calibration is not required Calibration with absolute instrument is required
Time to time as per requirements.
Measurement is of time consuming. Measurement is quick because of direct
Measurement.
Very rarely used in practical applications Very widely used in practical applications.
Absolute instruments are used in laboratories as Secondary instruments are used in day to day
Standardizing instruments. work.
Examples: Tangent Galvanometer Examples: Ammeter, Voltmeter
Q.7 Compare Analog Instruments to Digital Instruments:
SR.NO. Analog instrument Digital instrument
1 The accuracy of analog instrument is less. The accuracy of digital instrument is more.
2 The analog instruments required more The digital instruments required less power.
power.
3 Sensitivity of analog instrument is less. Sensitivity of digital instrument is more.
4 The analog instrument is economical. The digital instruments are expensive.
5 The analog instruments should be used in The digital instruments are portable, hence
specific position. can be used in any position.
6 The resolution of analog instruments is The resolution instruments are more. of
less. digital
7 These are somewhat less precise. These are more precise
Q.8 Name the different torque & their function in Measuring Instrument.
a) Deflecting torque: The torque which causes the moving system (and hence the pointer attached to it) to
move from zero position to indicate the electrical quantity being measured.
b) Controlling Torque: It produces an equal torque in opposite direction to deflecting torque. Thus the
deflection is proportional to quantity under measurement.
It brings back to pointer to zero position when deflecting torque becomes zero.
Methods of Providing Controlling Torque
1) Spring Control
2) Gravity Control
c) Damping Torque: The damping torque is necessary for a better response of Instrument.
The damping torque damps these oscillations and brings the pointer to final steady state position in least
possible time.
Methods of Providing Damping
1) Air Friction Damping
2) Fluid Friction Damping
3) Eddy current Damping
Q.22 List classification of Resistance along with their measuring devices used for
measurement of resistance value
1) Low Resistances: Resistance up to 1 Ohm Magnitude is known as Low Resistance.
Examples-Resistance of Transformer Winding, DC and AC Machine Armature winding,
Ammeter Coil, Wattmeter Current Coil, Earthing Grid.
Methods of Measuring Resistance
1. Kelvin’s double bridge method.
2. Potentiometer method
2) Medium Resistances: Range of Resistance above 1 Ohm up to 0.1 Mohm Falls in the
Category of medium Resistance.
Examples- Resistance of shunt field winding, voltmeter coil, Wattmeter Pressure Coil,
Heater Coil, Bulb Filament.
Methods of Measuring Resistance
1. Ammeter voltmeter method
2. Substitution Method
3. Wheatstone bridge method.
3) High Resistances: Resistance above 0.1 Mega ohm termed as high resistance.
Examples- Insulation Resistance of cable, Insulator, Oil, Dielectric Medium.
Methods of Measuring Resistance
1. Megger
2. Loss of Charge Method
Q.12 With neat sketch of PMMC instrument explain its working briefly
Working principal of PMMC Analog Instrument:
When current carrying conductor is placed in a magnetic field, it experiences
mechanical force.
In PMMC instrument, when current flows through a coil placed in the gap between
the poles, force is produced on the coil. The coil rotates and pointer attached to the coil shows deflection
proportional to the current magnitude.
Construction:
Working:
A Coil is wound on aluminium former
which is supported by spindle the two
ends of spindle are supported by jewel
bearings.
When the instrument is connected in
the circuit to measure current or
voltage, the operating current flows
through the coil.
The coil is carrying current and is placed
in the magnetic field of the permanent
magnet, mechanical torque acts on it.
The pointer attached to the moving system moves in a clockwise direction over the graduated
scale to indicate the value of current or voltage being measured.
If the current in the coil is reversed, the deflecting torque will also be reversed as a direction
of field is same hence the pointer will move in opposite direction, so these instruments work
only when current in the circuit is passing through in desired direction only. Hence, they are
used for DC measurements and not for AC measurements.
Controlling torque is achieved with spring and damping torque is provided with the help of
aluminium former.
The deflecting torque is directly proportional to current hence scale is uniform.
Advantages of PMMC Meter
1. Scale is uniform.
2. Power consumption is very low.
3. Can be used as ammeter or voltmeter of different ranges with the help of shunt and
multiplier.
4. More sensitive as compared with MI / dynamometer type instruments.
5. The torque to weight ratio is high which gives a high accuracy.
6. Most accurate instrument for measurement of DC quantities.
7. Effective eddy current damping.
8. Errors due to stray magnetic fields are small, due to strong operating magnetic field.
Disadvantages of PMMC Meter
1) Suitable for DC Measurement only
2) Cost is higher than moving iron instrument
3) Delicate construction so to be used with care
Q.1 State & Explain the construction & working of
Dynamometer type Wattmeter.
Construction:
It consists of the two fixed coils and one moving coil.
The fixed coils are placed close together and parallel
to each other. Moving coil is pivoted in between the
two fixed coils. The Moving Coil is connected in
parallel to the supply and it carries current
proportional to the supply voltage. The moving coil
is attached to the moving system so that under the
action of deflecting torque, the pointer moves over
the scale. Controlling torque is provided by springs
and damping torque is provided by air friction damping.
Working:
When the instrument is connected in the circuit, operating current flow through the coils. The interaction
between the magnetic fields produced by the coils produces mechanical force on the moving coil. The
result is that moving coil moves the pointer over the scale to give reading. Since fixed coil current is
proportional to the load current and the moving coil current is proportional to the voltage; the deflecting
torque is proportional to the product of voltage and current i.e. power. When direction of current reverses,
then it reverses the direction of current of fixed as well as moving coil so that the direction of deflecting
torque remains unchanged. Hence these instruments can be used for measurement of A.C. & D.C power.
Q.2 Compare current coil and potential coil of wattmeter.
Q.5 A single phase wattmeter
rated for 500 V; 5A is having full
scale deflection of 1000 watt.
What is multiplying factor of the
wattmeter?

Q.15 Describe Errors are introduced in single phase induction type energy meter and their compensation
1) Phase error
Energy meter read correctly when the shunt magnetic flux lag’s the applied voltage by 900. Practically,
pressure coil circuit has some resistance, due to this, the current taken by the pressure coil circuit does not
lag’s the applied voltage by 900, thus the error is introduced in energy meter and is called as phase error.
Due to phase error, energy meter will not read accurately.
2) Friction error
When the aluminium disc rotates, then there is friction at the spindle bearing and registering mechanism.
Due to this, the torque is developed which opposes the driving torque. Due to this, error is introduced in
the meter reading called as frictional error. Frictional error is serious at light load.
3) Speed error
Sometimes, the speed of the disc of energy meter is less or more than the rated speed,
due to this the meter gives error in the reading called as speed error.
4) Creeping error -
Due to excessive voltage across the pressure coil and incorrect friction compensation, the disc of energy
meter makes slow but continuous rotation when only the pressure coil is excited but there is no current
flowing through the current coil (or through the load), this error is called as Creeping error. Due to creeping
error, the energy meter records some energy consumption when load is OFF.
5) Temperature error
An increase in temperature causes increase in resistance of metal part’s this result into a small decrease in
the pressure coil flux, thus resistance of the coil increases. Due to this, the angle between voltage across
the pressure coil and pressure coil current changes. Also, resistance of the eddy current path in the
aluminium disc is increased. Therefore, the error is introduced called as temperature error. Magnitude of
temperature error is small and can be neutralize by other effects.
6) Frequency error
Energy meters are designed to operate for a particular frequency generally 50 Hz. If supply frequency
changes, the reactance of the coil changes. Due to this, small error may be introduced in meter reading.
7) Overload error
When the current coil of the energy meter carries a current greater than the rated current of the full load
current. This causes the saturation of the series magnet. Due to this, the energy meter runs slow at high
load current.
Q.16 State the Advantages of Electronic Energy Meter
1) Low cost.
2) High accuracy.
3) More flexibility.
4) High sensitivity
5) No frictional losses.
6) Less loading effect.
7) High frequency range.
8) Power consumption is less.
9) High resolution.
10) No requirement for external adjustment.
11) Low load, full load, power factor and creeping adjustments are not required.
Errors occurring in single phase electronic energy meter.
1) Error due to wrong sensor operation.
2) Error due to temperature.
3) Error due to wrong CT operation.
4) Error due to wrong PT operation.
5) Error due to wrong operation of scaling network.
6) Error due to wrong ADC operation.
7) Error due to wrong Display.
Q.1 State difference between Analog & Digital Instruments.

Q.2 List Application of Digital Multimeter

1) AC voltage measurement
2) DC voltage measurement
3) AC current measurement
4) DC current measurement
5) Measurement of frequency
Q.3 Explain working of Clamp on Meter
What is Clamp on Meter- Basically it is a
current transformer device to measure
the high values of currents without
disturbing the circuit.
Working of Clamp-on-meter:
Clip on meters are used to measure the
high current flowing through bus bar,
cable or fuse Holders carrying currents.
They consist of split core current
transformer who’s secondary winding is connected to rectifier type moving coil instrument. The primary
becomes conductor; whose current is to be measured. The split core gets aligned by the force of a spring
tension. The core is covered with insulating material. Hence higher current through conductors can be
measured. A selector switch is provided to select secondary number of turns which ultimately changes the
current range. For measuring current, the core is opened by pressing trigger shown and then clipped over
the conductor carrying current. The dial will record the current directly.
Q.12 Draw neat labelled diagram showing the controls available on front panel of general purpose CRO

Q.14 State any eight applications of CRO

1) Frequency and Time Measurement
2) Phase Difference Measurement
3) Amplitude Measurement
4) Delay Time Measurement
5) Pulse width Measurement
Q.2 Difference between Sensor & Transducer
Sr. No Transducer Sensor
1 Device which converts energy from one form to Element which responds to the physical
another phenomenon
2 It is conversion element It is sensing element
3 Sometime may not directly come in contact with Directly come in contact with measurand
measurand
4 e.g. strain Gauge e.g. Diaphragm
Q.12 State working Principle of Piezoelectric Transducer with Diagram. State its application.
Operating Principle
When force or pressure is applied to the piezoelectric material like quartz crystal or barium titanate, then
an emf is generated across the material or vice versa.
Construction & Working
Piezoelectric transducer is an active device, whose operation based on piezoelectric effect.
This effect state that, "when a pressure or force or vibration applied to the crystalline material like quartz
crystal or crystalline substances then an emf. is generated across the material or vice versa.
Fig shows the piezoelectric crystal. Two electrodes are connected across the crystal through which we get
the output e.m.f.
The construction is done in such a way so as to get capacitive action. The piezoelectric element used for
converting mechanical movement into electrical Signals.
The mechanical deformation generates a charge and this charge appears as a voltage across the electrodes.
The voltage is given by,
V= Q/C
Were,
V=emf across electrode
Q= Charges
C= capacitance
Some materials exhibit a significant and useful
piezoelectric effect; these materials are classified as
Follows.
a) Natural Crystal- Quartz Crystal, Rochelle Salt
b) Synthetic Crystals: Barium Titanate, Lithium sulphate
Applications
1. Piezoelectric transducers are used in high frequency accelerometer.
2. Piezoelectric materials are used in industrial cleansing apparatus.
3. It is used in under water detection system i.e. SONAR.
4. These are used in measurement of surface roughness in accelerometers and vibration pickups.
Q.1 Define Flow & State its Units.
Flow- Flow is defined as fluid in motion. Flow may be of gas or liquids.
Unit of Flow-Gallons/min or Gallons/sec, Liters/unit time
Q.2 State Laminar and Turbulent Flow.
1) Laminar Flow- Laminar flow occurs when the fluid flows in infinitesimal parallel layers with no
disruption between them. For laminar flow Reynolds number Re < 2100.
2) Turbulent Flow- Turbulent flow occurs when the fluid does not flow in parallel layers, the lateral
mixing is very high, and there is a disruption between the layers. Re > 2100
Q.5 Draw venturi meter and write steps to measure flow rate.
Construction & Working
Venturi meter consists of three sections
that is converging section, throat
section and diverging section.
The flow is introduced to the meter
through the inlet with diameter ‘D’. The
inclined angle of the
converging section is α1 which may be
between 19o to 23o.
The flow is then passed through the throat section which have the diameter ‘d’.
Two pressure taps (one at inlet section and second is at middle of throat section) are provided to measure
the Pressure difference by using U-tube manometer as shown in figure.
The diversion section has inclined angle α2 which may be between 5o to 15o.
Flow rate is proportional to the square root of the differential pressure.
Flow rate α √P1 – P2.
Q.11 Explain the working of electromagnetic flow meter with neat sketch.
Working
• An electromagnetic flow meter is a device that measures the flow rate of a conductive liquid by detecting
the voltage difference across the liquid as it flows through a magnetic field. The voltage difference, also
known as the electromotive force (EMF), is generated by the movement of the conductive liquid through
the magnetic field.
• Principle of Electromagnetic Flow Meter Based on Faraday’s Law
• The electro-magnetic flow meter works based upon Faraday’s Law. The law states that whenever a
conductor cuts lines of magnetic field, an induced voltage is generated and the magnitude of this induced
voltage is proportional to the rate at which these lines are cut and the voltage is perpendicular to the plane
of conductor and the magnetic field. The direction of the induced voltage is given by the Fleming’s right
hand rule.
Advantages
1. It can handle slurries and greasy materials.
2. It can handle corrosive fluids.
3. It has very low pressure drop.
4. It is totally obstruction less.
5. It is available in large pipe sizes and capacity
as well as in sever construction materials.
6. It is capable of handling low and very high-
volume flow
7. It can be used as bidirectional meter.
Disadvantage
1. It is relatively expensive.
2. It works only with fluids which are adequate electrical conductors.
3. It is relatively heavy, especially in larger sizes.
4. It must be full at all times.
5. It must be explosion proof when installed in hazardous electrical areas.
Q.22 State working principle of Thermistor.
A thermistor is a type of thermal resistor whose electrical resistance increase or decrease with change in
temperature. Thus, the thermistor is a thermally sensitive resistance whose resistance changes with change
in the thermistor body temperature.
Q.25 Classify thermistors based on Size & Shapes of thermistors
1) Disc Type 2) Bead Type 3) Rod Type
4) Probe Type 5) Washer Type