1. Experiment 9 Part A: Simulation of a Transformer
Part B: Making an Inductor
Part C: Measurement of Inductance
Part D: Making a Transformer

2. Inductors & Transformers
How do transformers work?
How to make an inductor?
How to measure inductance?
How to make a transformer? ?
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Electronic Instrumentation

3. Some Interesting Inductors
Induction Heating
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4. Some Interesting Inductors
Induction Heating in Aerospace
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5. Some Interesting Inductors
Induction Forming
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6. Some Interesting Inductors
Primary
Coil
Secondary
Coin Flipper
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7. Some Interesting Inductors
GE Genura Light
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8. Some Interesting Transformers
A huge range in sizes
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9. Electronic Instrumentation
Wall Warts
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10. Some Interesting Transformers
High Temperature Superconducting Transformer
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11. Electronic Instrumentation
Household Power
7200V transformed to 240V for household use
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12. Electronic Instrumentation
Inductors-Review
General form of I-V relationship
For steady-state sine wave excitation
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13. Electronic Instrumentation
Inductors-Review
Simple R-L Filter
High Pass Filter
Corner Frequency
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14. Electronic Instrumentation
Inductors-Review
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15. Electronic Instrumentation
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
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16. Electronic Instrumentation
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
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17. Some Typical Permeabilities
Air x10-6 H/m
Ferrite U M x10-4 H/m
Nickel x10-4 H/m
Iron x10-3 H/m
Ferrite T x10-2 H/m
Silicon GO steel x10-2 H/m
supermalloy 1.26 H/m
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Electronic Instrumentation

18. Electronic Instrumentation
Making an Inductor
If the coil length is much small than the diameter (rw is the wire radius)
Such a coil is used in the
metal detector at the right
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Electronic Instrumentation

19. Electronic Instrumentation
Making an Inductor
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
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20. 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
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21. Electronic Instrumentation
Wire Resistance
Using the Megaconverter at
(see course website)
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22. Electronic Instrumentation
Transformers
Symbol for transformer
Note that for a transformer, the symbol shows 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: M2=k2 LS LL
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23. Electronic Instrumentation
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
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24. Electronic Instrumentation
Transformers
Sum of primary voltages must equal the source
Sum of secondary voltages must equal zero
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25. Electronic Instrumentation
Transformers
Note the following simplifying information for cylindrical or toroidal inductors
For
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26. Electronic Instrumentation
Transformers
Cylinders (solenoids)
Toroids
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27. Electronic Instrumentation
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28. Electronic Instrumentation
Transformers
Transformers are designed so that the inductive impedances are much larger than any resistance in the circuit. Then, from the second loop equation
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29. Electronic Instrumentation
Transformers
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
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30. Electronic Instrumentation
Transformers
The input impedance of the primary winding reflects the load impedance. It can be determined from the loop equations
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31. Transformer Rectifier
Adding a full wave rectifier to the transformer makes a low voltage DC power supply, like the wall warts used on most of the electronics we buy these days.
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32. Transformer Rectifier
Filtered
Unfiltered
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33. 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.
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34. Determining Inductance
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.
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35. Determining Inductance
Reminder—The parallel combination of L and C goes to infinity at resonance.
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36. Electronic Instrumentation
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37. Electronic Instrumentation
Even 1 ohm of resistance in the coil can spoil this response somewhat
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38. Project 3: Beakman’s Motor
The coil in this motor can be characterized in the same way
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39. Optional Project: Paperclip Launcher
A small disposable flash camera can be used to build a magnetic paperclip launcher
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