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Experiment 3

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Title: Experiment 3


1
Experiment 3
  • Part A Making an Inductor
  • Part B Measurement of Inductance
  • Part C Simulation of a Transformer
  • Part D Making a Transformer

2
Review RLC and Resonance
  • How can the transfer function be greater than 1?
  • At resonance, impedance value is a minimum
  • At resonance, impedance of inductor and capacitor
    cancel each other out (equal in magnitude, phase
    is opposite)
  • So circuit is purely resistive at resonance
  • H depends on the position of Vout

http//ecow.engr.wisc.edu/cgi-bin/getbig/ece/271/a
llie/labmanuals/1271l1sp03.doc
3
Review RLC and Resonance
http//ecow.engr.wisc.edu/cgi-bin/getbig/ece/271/a
llie/labmanuals/1271l1sp03.doc
4
Inductors Transformers
  • How do transformers work?
  • How to make an inductor?
  • How to measure inductance?
  • How to make a transformer?

?
5
Part A
  • Inductors Review
  • Calculating Inductance
  • Calculating Resistance

6
Inductors-Review
  • General form of I-V relationship
  • For steady-state sine wave excitation

7
Determining Inductance
  • Calculate it from dimensions and material
    properties
  • Measure using commercial bridge (expensive
    device)
  • Infer inductance from response of a circuit. This
    latter approach is the cheapest and usually the
    simplest to apply. Most of the time, we can
    determine circuit parameters from circuit
    performance.

8
Making an Inductor
  • For a simple cylindrical inductor (called a
    solenoid), we wind N turns of wire around a
    cylindrical form. The inductance is ideally given
    by
  • where this expression only holds when the
    length d is very much greater than the diameter
    2rc

9
Making an Inductor
  • Note that the constant ?o 4? x 10-7 H/m is
    required to have inductance in Henries (named
    after Joseph Henry of Albany)
  • For magnetic materials, we use ? instead, which
    can typically be 105 times larger for materials
    like iron
  • ? is called the permeability

10
Some Typical Permeabilities
  • Air 1.257x10-6 H/m
  • Ferrite U M33 9.42x10-4 H/m
  • Nickel 7.54x10-4 H/m
  • Iron 6.28x10-3 H/m
  • Ferrite T38 1.26x10-2 H/m
  • Silicon GO steel 5.03x10-2 H/m
  • supermalloy 1.26 H/m

11
Making an Inductor
  • If the coil length is much smaller than the
    diameter (rw is the wire radius)
  • Such a coil is used in the
  • metal detector at the right

Form Diameter 2rc
Coil Length (d)
12
Calculating Resistance
  • All wires have some finite resistance. Much of
    the time, this resistance is negligible when
    compared with other circuit components.
  • Resistance of a wire is given by
  • l is the wire length
  • A is the wire cross sectional area (prw2)
  • s is the wire conductivity

13
Some Typical Conductivities
  • Silver 6.17x107 Siemens/m
  • Copper 5.8x107 S/m
  • Aluminum 3.72x107 S/m
  • Iron 1x107 S/m
  • Sea Water 5 S/m
  • Fresh Water 25x10-6 S/m
  • Teflon 1x10-20 S/m
  • Siemen 1/ohm

14
Wire Resistance
  • Using the Megaconverter at http//www.megaconverte
    r.com/Mega2/
  • (see course website)

15
Part B Measuring Inductance with a Circuit
  • For this circuit, a resonance should occur for
    the parallel combination of the unknown inductor
    and the known capacitor. If we find this
    frequency, we can find the inductance.

16
In Class Problem 1
Vout
Vin
  • What is ZLC (assuming R2 is very small)?
  • What does R2 represent?
  • What is its transfer function (equation)?
  • What is H at low and high frequencies?
  • What is H at the resonant frequency, ?0?

17
Determining Inductance
Vout
Vin
  • ReminderThe parallel combination of L and C goes
    to infinity at resonance. (Assuming R2 is small.)

18
Determining Inductance
19
(No Transcript)
20
  • Even 1 ohm of resistance in the coil can spoil
    this response somewhat

Coil resistance small
Coil resistance of a few Ohms
21
Part C
  • Examples of Transformers
  • Transformer Equations

22
Transformers
  • Cylinders (solenoids)
  • Toroids

23
Transformer Equations
Symbol for transformer
24
Deriving Transformer Equations
  • Note that a transformer has two inductors. One is
    the primary (source end) and one is the secondary
    (load end) LS LL
  • The inductors work as expected, but they also
    couple to one another through their mutual
    inductance M2k2 LS LL

25
Transformers
  • Assumption 1 Both Inductor Coils must have
    similar properties same coil radius, same core
    material, and same length.

26
Transformers
IS
IL
Note Current Direction
  • Let the current through the primary be
  • Let the current through the secondary be
  • The voltage across the primary inductor is
  • The voltage across the secondary inductor is

27
Transformers
  • Sum of primary voltages must equal the source
  • Sum of secondary voltages must equal zero

28
Transformers
  • Assumption 2 The transformer is designed such
    that the impedances are much
    larger than any resistance in the circuit. Then,
    from the second loop equation

29
Transformers
  • k is the coupling coefficient
  • If k1, there is perfect coupling.
  • k is usually a little less than 1 in a good
    transformer.
  • Assumption 3 Assume perfect coupling (k1)
  • We know M2k2 LS LL LS LL and
  • Therefore,

30
Transformers
  • The input impedance of the primary winding
    reflects the load impedance.
  • It can be determined from the loop equations
  • 1
  • 2
  • Divide by 1 IS. Substitute 2 and M into 1

31
Transformers
  • Find a common denominator and simplify
  • By Assumption 2, RL is small compared to the
    impedance of the transformer, so

32
Transformers
  • It can also be shown that the voltages across the
    primary and secondary terminals of the
    transformer are related by
  • Note that the coil with more turns has the
    larger voltage.
  • Detailed derivation of transformer equations
  • http//hibp.ecse.rpi.edu/connor/education/transfo
    rmer_notes.pdf

33
Transformer Equations
34
In Class Problem 2
NsNL
VGEN120V RL20 O NL1 NS12
Vs
VL
VGEN
  • 1. Find VL if RS0
  • Find VL if Rs 1 k O
  • Hint Is VGEN VS? Under what conditions is this
    not true? How would you find VS? Need Zin

Is
Vs
VL
Zin
35
Part D
  • Step-up and Step-down transformers
  • Build a transformer

36
Step-up and Step-down Transformers
  • Step-up Transformer

Step-down Transformer
Note that power (PVI) is conserved in both
cases.
37
Build a Transformer
  • Wind secondary coil directly over primary coil
  • Try for half the number of turns
  • At what frequencies does it work as expected with
    respect to voltage? When is ?L gtgt R?

38
Some Interesting Inductors
  • Induction Heating

39
Some Interesting Inductors
  • Induction Heating in Aerospace

40
Some Interesting Inductors
  • Induction Forming

41
Some Interesting Inductors
  • Coin Flipper
  • Flash camera circuits charge 6 capacitors
  • Large current in primary coil
  • Large current induced in coin (larger by ratio of
    turns)
  • Current in coin creates electromagnet of opposite
    polarity (Repel!)

42
Some Interesting Inductors
  • GE Genura Light

43
Some Interesting Transformers
  • A huge range in sizes

44
Household Power
  • 7200V transformed to 240V for household use

45
Wall Warts
Transformer
46
In Class Problem 1
Vout
Vin
  • What is ZLC (assuming R2 is very small)?
  • What does R2 represent?
  • What is its transfer function (equation)?
  • What is H at low and high frequencies?
  • What is H at the resonant frequency, ?0?

47
In Class Problem 1
Vout
Vin
48
In Class Problem 1
Vout
Vin
49
In Class Problem 1
  • What is H at low frequencies?
  • This can be determined from the magnitude so
  • Remember these steps!
  • Take the lowest power in the numerator and
    denominator of the equation
  • Write down x1, y1, x2, and y2 (can do this in
    your head)
  • Use the magnitude equation (square and square
    root numerator and denominator)
  • Simplify (this is the answer if approaching 0)
  • Take limit as it approaches 0 (this is the answer
    at 0)

50
In Class Problem 1
  • What is H at low frequencies?
  • Step 1 Take lowest power in numerator and
    denominator
  • Step 2 Find x1, y1, x2, y2

51
In Class Problem 1
  • What is H at low frequencies?
  • Step 3 Use the magnitude equation
  • Step 4 Simplify
  • Step 5 Take limit as ? approaches 0
  • Answer is that it becomes very small or 0

52
In Class Problem 1
  • What is H at high frequencies?
  • This can be determined from the magnitude so
  • Remember these steps!
  • Take the highest power in the numerator and
    denominator of the equation
  • Write down x1, y1, x2, and y2 (can do this in
    your head)
  • Use the magnitude equation (square and square
    root numerator and denominator)
  • Simplify (this is the answer if approaching 8)
  • Take limit as it approaches 0 (this is the answer
    at 8)

53
In Class Problem 1
  • What is H at high frequencies?
  • Step 1 Take highest power in numerator and
    denominator
  • Step 2 Find x1, y1, x2, y2

54
In Class Problem 1
  • What is H at high frequencies?
  • Step 3 Use the magnitude equation
  • Step 4 Simplify
  • Step 5 Take limit as ? approaches 8
  • Answer is that it becomes very small or 0

55
In Class Problem 1
  • What is H at the resonant frequency, ?0?

56
In Class Problem 2
57
In Class Problem 2
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