ee1008- electrical and electronics measurements and instrumentation unit -1 measurement of r, l, c

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EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

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Page 1: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

EE1008- ELECTRICAL AND ELECTRONICSMEASUREMENTS AND

INSTRUMENTATION

UNIT -1Measurement of R, L, C

Page 2: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Wheatstone bridge

Page 3: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Balance Condition

Page 4: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Bridge balanced equation

Page 5: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Sensitivity

Current Sensitivity:-

Voltage Sensitivity:-

Bridge Sensitivity:-

Page 6: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Under Small Unbalance

Page 7: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Under Small Unbalance

Page 8: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Under Small Unbalance

Page 9: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Thevenin’s voltage

Page 10: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Sensitivity under unbalance

Page 11: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Kelvin’s Bridge

Page 12: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

One of the major drawback of the Wheatstone bridge is that, it can measure the resistance from few ohm to several mega ohm but to measure low resistance it gives significant error.

So, we need some modification in Wheatstone bridge itself, and the modified bridge so obtained is Kelvin bridge, which is not only suitable for measuring low value of resistance but has wide range of applications in the industrial world.

The kelvin’s bridge may be regarded as a modified of the wheatstone bridge to secure increased accuracy in the measurement of low resistance. It is used to measure resistance from few micro ohm to 1.0 ohm.

Page 13: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Bridge Balance Equation1

2

3

Page 14: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

From Equ. 1

4

5

6

7

8

Sub. Equ. 5 in 4

From 5

Sub 7 in 8

9

10

Sub. equ. 7 & 10 in equ. 3

11

12

13

Page 15: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Kelvin’s Double Bridge

Page 16: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

The kelvin’s double bridge incorporates the idea of a second set of ratio arms - hence the name double bridge- and the use of four terminal resistors for the low resistance arms.

1st R1/R2 2nd a/b

Page 17: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

1

2

3

4

5

Balance condition

Consider the path 5-1-2-6 back to 5 through the battery

Sub equ. 4 in equ. 2

Page 18: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

6

7

8

9

10

Page 19: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

11

12

Page 20: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

•Again we reaches to the same result i.e. t has no effect.•It indicates that the resistance of connecting lead has no effect on the measurement provided that the two sets of ratio arms have equal ratios.

Page 21: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Practical Kelvin’s double Bridge

Page 22: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

AC Bridges

•When the four resistive arms of the basic Wheatstone bridge are replaced by impedances and the bridge is excited by an AC source, the result is an AC Bridge. •To balance the bridge, two conditions must be satisfied, the resistive (R) and the reactive components (XC or XL). Once balanced, the AC Bridge indicates a null.•AC bridge circuits are also used for shifting phase, providing feedback paths for oscillators and amplifiers, filtering out undesired signals, and measuring the frequency of audio and radio frequency (RF) signals.

Page 23: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Bridge balance condition

In admittance form

Polar form of impedance

Sub. The polar values in balance condition

Page 24: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C
Page 25: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Maxwell's Bridge – Inductor L

Maxwell’s Inductance BridgeMaxwell’s Inductance Capacitance Bridge

Page 26: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

1

2

Maxwell’s Inductance Bridge

Page 27: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

3

4

Page 28: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Maxwell’s Inductance Capacitance Bridge

Page 29: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C
Page 30: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Quality Factor

Page 31: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Disadvantage:Maxwell bridge is that, they are unsuitable of measuring the low and high quality factor coils.

Page 32: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Anderson's Bridge•Need of Anderson's bridge though we have Maxwell bridge to measure quality factor of the circuit.

•The main disadvantage of using Maxwell bridge is that, they are unsuitable of measuring the low and high quality factor.

•However Maxwell bridge are suitable for measuring accurately medium quality factor respectively. •So, there is need of bridge which can measure low quality factor and this bridge is modified Maxwell's bridge and known as Anderson's bridge.

Page 33: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Convert star connected R2 , R4 , r into delta connected

Page 34: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Balance Equation

star to delta connection equivalent

Page 35: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Sub. R5 and R6 values in the balance equation

Page 36: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C
Page 37: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

This bridge is used to measure to the capacitance of the capacitor, dissipation factor and measurement of relative permittivity.

Schering Bridge

Page 38: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Balance equation

Page 39: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C
Page 40: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Measurement of high Resistance - Megger

• Insulation resistance quality of an electrical system degrades with time, environment condition i.e. temperature, humidity, moisture & dust particles.

• It also get impacted negatively due to the presence of electrical & mechanical stress, so it’s become very necessary to check the IR (Insulation resistance) of equipment at a constant regular interval to avoid any measure fatal or electrical shock.

Page 41: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C
Page 42: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

1) Deflecting & Control coil : Connected parallel to the generator, mounted at right angle to each other and maintain polarities in such a way to produced torque in opposite direction.

2) Permanent Magnets: Produce magnetic field to deflect pointer with North-South pole magnet.

3) Pointer : One end of the pointer connected with coil another end deflects on scale from infinity to zero.

4) Scale : A scale is provided in front-top of the megger from range ‘zero’ to ‘infinity’, enable us to read the value.

Page 43: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

5) D.C generator or Battery connection : Testing voltage is produced by hand operated D.C generator for manual operated Megger. Battery / electronic voltage charger is provided for automatic type Megger for same purpose.6) Pressure coil resistance and Current coil resistance : Protect instrument from any damage because of low external electrical resistance under test.

Page 44: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Working Principle of Megger• Voltage for testing produced by hand operated megger

by rotation of crank in case of hand operated type, a battery is used for electronic tester.

• 500 Volt DC is sufficient for performing test on equipment range up to 440 Volts.

• 1000V to 5000V is used for testing for high voltage electrical systems.

• Deflecting coil or current coil connected in series and allows flowing the electric current taken by the circuit being tested.

• The control coil also known as pressure coil is connected across the circuit.

Page 45: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

• Current limiting resistor (CCR & PCR ) connected in series with control & deflecting coil to protect damage in case of very low resistance in external circuit.• In hand operated megger electromagnetic induction effect is used to produce the test voltage i.e. armature arranges to move in permanent magnetic field or vice versa.• Where as in electronic type megger batteries are used to produce the testing voltage.• As the voltage increases in external circuit the deflection of pointer increases and deflection of pointer decreases with a increases of current.• Hence, resultant torque is directly proportional to voltage & inversely proportional to current.

Page 46: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

• When electrical circuit being tested is open, torque due to voltage coil will be maximum & pointer shows ‘infinity’ means no shorting throughout the circuit and has maximum resistance within the circuit under test.• If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance within circuit being tested.

•The deflection torque is produced with megger tester due to the magnetic field produced by voltage & current, similarly like ‘Ohm's Law’•Torque of the megger varies in ration with V/I, (Ohm's Law :- V=IR or R=V/I). Electrical resistance to be measured is connected across the generator & in series with deflecting coil.

Page 47: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Produced torque shall be in opposite direction if current supplied to the coil.1. High resistance = No current: - No current shall flow through deflecting coil, if resistance is very high i.e. infinity position of pointer2. Small resistance = High current :- If circuit measures small resistance allows a high electric current to pass through deflecting coil, i.e. produced torque make the pointer to set at ‘ZERO’.3. Intermediate resistance = varied current: - If measured resistance is intermediate, produced torque align or set the pointer between the range of ‘ZERO to INIFINITY’

Page 48: EE1008- ELECTRICAL AND ELECTRONICS MEASUREMENTS AND INSTRUMENTATION UNIT -1 Measurement of R, L, C

Loss of Charge Method

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