1. The document discusses various types of instruments used for measurement of electrical quantities like current, voltage, power, energy, frequency, phase etc. It describes different working principles like magnetic, thermal, electrostatic etc. 2. Various classifications of instruments are provided based on their construction and working like moving coil, moving iron, electrodynamometer types. 3. Measurement techniques for parameters like flux density, magnetizing force, iron losses are also summarized along with types of instrument transformers. 4. Construction and working of instruments for measurements like wattmeter, energy meter, frequency meter and phase meter are highlighted in brief.

1. 1. Magnetic effect ( Eg. PMMC,PMMI)
2. Thermal Effect (Eg.Thermocouple)
3. Induction effect (Eg. Energy meter)
4. Electrostatic effect (Eg.Voltmeters)
5. Hall effect (Eg.Fluxmeters)

2.  Work as Motoring Principle.
 D’Arsonval principle – Conductor moving, Magnetic field - Permanent
 Core is cylindrical if coil is rectangular

3. Control – by spring
Damping – By eddy current

4. Deflection torque, Td = NBAI
where,
N = number of turns of coil,
A = Effective coil area in m2
I = Current passing through the coil in Amp,
B = Flux density in wb/m2
Then G = NBA (constant)
Td = G.I
Then Controlling torque is Tc α Ө
Tc = Ks Ө
Under the equilibrium condition,
Tc = Td
Ks Ө = G.I
Ө = (G/ Ks ) .I
Ө α I

5.  Uniform scale.
 Low power consumption.
 Sensitivity is high.
 Effective damping is provided (due to Eddy Current)
 Applicable to only D.C measurements,
 Cost is high.
Weakening of Permanent magnet and Springs due to Ageing.

6. Moving Iron
type
Moving iron
attraction type
Moving iron
repulsion type
Radial vane
type
Co-axial vane
type
Classification

7.  C = fixed coil.
 D = soft iron piece (movable)
 Damping system as Air friction type
 Control –Spring control
 Gravity control - Panel type
instruments
 Soft iron piece gets attracted by the magnetic field produced by fixed coils.

8.  Consist of two vanes, one is fixed and another is movable.
 When current (I) is flow through the coil, both the vanes are magnetized.
 These magnetized vanes are repulsion of unlike polarities, since the force of
repulsion between the two vanes causes movement (deflection).

9.  Consists of 2 vanes (radial strip of iron)
 Fixed vane is attached to coil.
 Movable vane is attached to spindle.
 Deflection (Ө) α Current (I2).

10.  Vanes are the sections of coaxial cylinder
 Fixed vane is attached to coil.
 Movable vane is attached to spindle.
Coaxial vane
Radial Vane

11.  Deflection (Ө) α Current (I).
 Applicable for both A.C and D.C measurements,
 Available up to several ranges.
 Power consumption is on higher side.
 Temperature dependent.
 Errors due to temperature, Hysteresis, Frequency change, stray
magnetic fields and eddy current.

13. Ammeter- Extension of ranges

15. Universal or Ayrton shunt type

16. Voltmeter- Extension of ranges

18. Potential divider Arrangements

19. Multimeter (or) Volt-ohm milli Ammeter

20. DVM
Integrating
type
Non –
integrating type
V/F converter
type
Potentiometric
type
Dual slope
integrating type
Potentiometric
type
Ramp type
Linear type
Stair case
type
Servo Potentiometric
type
Null balance type
Successive
approximation type

21. Power Measurements
Types:
1. Single phase power measurement
2. Three phase power measurement
Single phase power measurement – 1. Electrodynamometer type wattmeter
2. Ferro dynamic wattmeter
3. Thermocouple wattmeter
4. Low Power factor Wattmeter

22. Electrodynamometer type instruments
Construction:
• Fixed coils
• Moving Coil
• Controlling
• Moving System
• Damping
• Shielding
• Cases and Scales

23. Torque Equation
Let i1 = Instantaneous value of current in fixed coil
i2 = Instantaneous value of current in moving coil
L1 = Self inductance of fixed coil
L2 = self inductance of moving coil
M = Mutual inductance between fixed and moving coils

25. From the principle of conversation of energy,
Energy input = Energy stored + Mechanical energy
Mechanical energy = Energy input - Energy stored
Substraction (2) from equation (1),
Substraction (2) from equation (1),
The self inductance L1 and L2 are constant and hence dL1 and dL2 are zero.
Mechanical energy = i1 i2 dM
If Ti is the instantaneous deflecting torque and dθ is the change in the deflection then
Mechanical energy = Mechanical work done
= Ti dθ
i1 i2 d M = Ti dθ

26. D.C Operation:
For d.c current of I1 and I2,
The controlling torque is provided by springs hence
Thus the deflection is proportional to the product of the two currents and the rate of
change of mutual inductance.

27. A.C Operation:
In a.c. operation, the total deflecting torque over a cycle must be obtained by integrating Ti
over one period.
Average deflecting torque over one cycle is,
Now if two currents are sinusoidal and displaced by a phase angle then

28. where i1, i2 are the r.m.s. values of the two currents as,
Thus the deflection is decided by the product of r.m.s. values of two currents, cosine of
the phase angle (power factor) and rate of change of mutual inductance.

30. Errors in Electrodynamometer type
Instruments
1. Torque to weight ratio
2. Frequency errors
3. Eddy current errors
4. Stray magnetic field errors
5. Temperature errors

31. Single Phase Power Measurement

32. 1. By using 3- Single phase wattmeter – Three wattmeter method
2. By using 2- Single phase wattmeter – Two wattmeter method
3. By using 1- Single phase wattmeter – One wattmeter method
4. By using three phase wattmeter
Methods:

33. Three Wattmeter Method

34. Let
IR = instantaneous current flowing through R-phase in A
IY = instantaneous current flowing through Y-phase in A
IB = instantaneous current flowing through B-phase in A
VR = instantaneous Voltage across R-phase in V
VY = instantaneous Voltage across Y-phase in V
VB = instantaneous Voltage across B-phase in V
Instantaneous power consumed by the load
=
Sum of instantaneous readings of the wattmeter
PR = instantaneous reading of wattmeter 1 connected in R-phase in W
PY = instantaneous reading of wattmeter 2 connected in Y-phase in W
PB = instantaneous reading of wattmeter 3 connected in B phase in W
P = PR + PY + PB = vRIR + vyIy +vBIB

35. Two Wattmeter Method
Two cases
For Star
connected load
For Delta
connected load

36. STAR CONNECTED LOAD

38. DELTA CONNECTED LOAD

41. One Wattmeter Method
ThreePhasestarorDelta
connectedload

42. Three Phase Wattmeter
Construction
 3 phase wattmeter is an Electrodynamometer type
 Consist of two separate wattmeter, (i.e,. A set of Fixed
coil and set of moving coil)
 Same as Two wattmeter method

43. Working
R’ to eliminate the errors due to mutual inductance

44. Used to measure energy, which is the total power consumed over a specific
interval of time
Unit of Energy is Kwh (or) unit.
It is the integrating type instrument.(records the total quantity of electricity
in a given time).
Energy
meter
Single phase
energy meter
Three phase
energy meter

45.  Applicable in Single Phase circuit.
Cost is low.
More accurate.
Works on the principle of Induction.
A.C flux is produced due to A.C supply, then it produces the Eddy current in the
moving system which interacts with each other to produce the driving torque (causes the
rotation of Aluminum & record the Energy)
i. Driving system
ii. Moving system
iii. Braking system
iv. Registering system.

50.  Contains two electromagnet made up of silicon steel laminated.
 Coil 1 is excited by load (current coil) connected series to the load.
Coil 2 is excited by voltage (pressure coil (or) Voltage Coil), connected parallel
to the load (this magnet referred as shunt magnet).
 Contains aluminum disk.
 The disk is placed in the air gap between the series and shunt magnet.
 Contains Permanent magnet, positioned near the edge of the aluminum disk.
 by adjusting the position of permanent magnet, braking torque can be adjusted.
 Main function is to record continuously a number which is proportional to the
revolution made by the moving system.

51. Pointer type register Cyclo-meter register

52. Let,
V = Supply Voltage
Ip = Current through the pressure coil
I = Load current
φ = Phase angle of the load
φp = Flux produced by the pressure coil
φc = Flux produced by the Current coil
Eep= Eddy emf induced by flux φp
Eec= Eddy emf induced by flux φc
Iep= Eddy Current induced by flux φp
Iec= Eddy Current induced by flux φc
Net Driving Torque (Td) α T2-T1

56. Magnetic Measurements
• Operating characteristics of electrical apparatus
and machines – influenced by ferromagnetic
property
• Hence this measurements are necessary
• Some of them are
– Measurement of flux density, B
– Measurement of magnetizing force, H
– Determination of B-H curve
– Determination of eddy current and hysteresis loss
– Testing of permanent magnets

57. Types of Tests
• Ballistic Test : D.C –> FM Material -> To
determine B-H Curve and hysteresis losses
• A.C Tests : A.C -> FM Material -> To determine
eddy current and Hysteresis losses
• Steady State Test : To determine the steady state
flux density

58. Measurement of flux density B

59. Measurement of Magnetizing force H

60. Determination of B-H Curve
• Two methods
– Method of Reversal
– Step by step Method

61. Method of Reversal

62. Step by Step Method

63. Measurement of Iron Losses
• Wattmeter Method
– Epstein Square
– Llyod Fisher Square
• Bridge Method
• Potentiometer Method
• Oscillographic method

64. Epstein Square (or) Epstein frame
• An Epstein frame or Epstein square is a standardised measurement
device for measuring the magnetic properties of soft magnetic
materials, like electrical steel sheets and strips of any grade.
• It has two windings- primary and secondary windings and the
specimen to be tested acts as core.
• Each layer of the sample is double-lapped in corners.

65. Epstein Square

66. Llyod Fisher Square

67. Iron loss measurement - Wattmeter method

68. Total iron loss in the specimen is given by :
Weight of the specimen
Total iron loss in the specimen
Specific iron loss of the ring specimen =

69. Maxwell’s bridge method

71.  In power system the parameters like voltage, current, impedance, etc., are in
terms of high rating values (K) , it is not possible to measure the parameters
directly.
 So we move to Instrument Transformers.
Transformers used in conjunction with measuring instruments for
measurement purpose is called Instrument transformers.
 The Transformers which is used to measure Current referred as Current
Transformers (C.T)
 The Transformers which is used to measure Voltage referred as Potential
Transformers (P.T)

72.  Current Transformers are series connected to the line whose current to be
measured..
 It is a step up transformers (reduces the current and increases the voltage).
 It has primary winding, & coil of secondary winding.

73.  Turns ratio (n) = N2/N1
 N1 = number of turns of Primary Winding,
 N2 = number of turns of Secondary Winding.
 C.T,
 Let Turns ratio as 500:5
 I1 =500
 I2 =5
 N2/N1 = 500/5 =100
Hence, N2 = 100 N1 and I1 = 100 I2
Also V2= 100 V1
n
V
V
I
I
N
N

1
2
2
1
1
2 Precautions:
• Secondary Winding cannot be open
at the time of primary is exercised.
• The Secondary Winding is
always short circuited.

74.  Potential Transformers are Parallel connected to the line.
 It is a step down transformers.
 P.T,
If range of P.T is
11KV:110 then turns
ratio is given by
V2 = 110 V
V1= 11000V
n = V1/V2 = 100
Also V1= 100 V2
N1 = 100 N2
n
V
V
N
N

2
1
2
1

75. Current Transformer Potential Transformer
Step up Transformer Step Down transformer
Secondary Voltage is Higher than the
Primary Voltage
Primary Voltage is Higher than the
Secondary Voltage
Primary winding is less Secondary winding is less
Series connection of line Parallel connection of line

77. ADVANTAGES
 High Voltage & high current are directly measured in low
range of meters.
 Wide range of voltage and Current levels has been
measured.
 It can be act as protecting Devices.
DISADVANTAGE:
 Applicable only for A.C circuits

78. i. Ratio Errors
i. Phase angle Errors

79. 1. Frequency Meters
2. Phase Meters
1. Analog phase meters
2. Digital phase meters
FluxMeters

80. Analog
Frequency meters
Mechanical
Resonance type
Electrical
Resonance type
Weston type
Frequency meter

83.  Working principle:
 Thin steel strips (Reed) vibration proportional to input frequency.
 The bottom of the Reed (thin steel strips) is rigidly fixed on a laminated
iron core which acts as an electromagnet.
 Each and every reed has different weight and dimension.
 The producing a force of attraction on the reeds which is proportional to
square of ‘i’.
 Hence all the reeds will start vibrating.
 All the reeds vibrate with different force.
 Reed whose natural frequency = supply frequency will be in resonance
and it will vibrate most.

84. ADVANTAGES
 Simple in construction.
 Easy operating mechanism.
Disadvantage:
 Cannot be applicable for low voltage to find the frequency

85.  It consist of Fixed coil ( Magnetizing Coil), moving coil attached to pointer.
No controlling force

86. Inductive Load Capacitive Load Resistive Load
Td α Im cos (90+ α) Td α Im cos (90- β) Td α Im cos 90 = 0
3 cases:
1. F = Normal frequency
2. F = Above normal frequency
3. F = Below normal frequency

87.  It is a moving iron type instrument
 It consist of Two coils (Coil A & Coil B)
No controlling force
L – To reduce harmonics
in the current

88.  It may works on the principle of AND gate
A B Output
0 0 0
0 1 O
1 0 O
1 1 1
Amplifier
Schmitt
trigger
AND Gate
Circuit
f- unknown
Principle : No. of pulses counted at the output terminal for
a period of 1 sec gives the unknown frequency.

90.  It is used to measure the phase difference between the two signals
At Vr is Positive Half Cycle At Vr is Negative Half Cycle

91. At Vr is Positive Half Cycle At Vr is Negative Half Cycle

92.  It is used to measure the phase difference between the two signals, by means
of digital Counter

93. Φ0 = phase angle of signal 1
Φx= phase angle of signal 2
Φ0 – Φx = phase angle difference

94. Used to find flux ‘φ’ in the coil
φ α ‘i‘

95. dφ = change in flux linkage
dθ = change in deflection
N dφ = G dθ
dθ = (N/G) dφ
where G is displacement constant
N is number of turns in the search coil
dθ α dφ
Advantage
 High accurate
 Fast operation
Disadvantage
 Measurement of small phase difference is very difficult