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1 Electronic Instrumentation Experiment 9 •Part A: Simulation of a Transformer •Part B: Making an Inductor •Part C: Measurement of Inductance •Part D: Making a Transformer Inductors & Transformers How do transformers work? How to make an inductor? How to measure inductance? How to make a transformer? 18 October 2003 Electronic Instrumentation ? 2 Some Interesting Inductors Induction Heating 18 October 2003 Electronic Instrumentation 3 Some Interesting Inductors Induction Heating in Aerospace 18 October 2003 Electronic Instrumentation 4 Some Interesting Inductors Induction Forming 18 October 2003 Electronic Instrumentation 5 Some Interesting Inductors Primary Coil Secondary Coil Coin Flipper 18 October 2003 Electronic Instrumentation 6 Some Interesting Inductors GE Genura Light 18 October 2003 Electronic Instrumentation 7 Some Interesting Transformers A huge range in sizes 18 October 2003 Electronic Instrumentation 8 Wall Warts 18 October 2003 Electronic Instrumentation 9 Some Interesting Transformers High Temperature Superconducting Transformer 18 October 2003 Electronic Instrumentation 10 Household Power 7200V transformed to 240V for household use 18 October 2003 Electronic Instrumentation 11 Inductors-Review General form of I-V relationship dI V L dt For steady-state sine wave excitation Z L jL 18 October 2003 V jLI Electronic Instrumentation 12 Inductors-Review R1 R2 50 1k V V1 V VOFF = 0 VAMPL = 1 FREQ = 1k L1 1mH 0 Simple R-L Filter • High Pass Filter • Corner Frequency 18 October 2003 1 R f 167kHz 2 L Electronic Instrumentation 13 Inductors-Review 1.0V 0.8V 0.6V 0.4V 0.2V 0V 1.0Hz 10Hz V(R1:2) 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz V(L1:1) Frequency 18 October 2003 Electronic Instrumentation 14 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 ( 0 N rc ) L Henries d 2 2 where this expression only holds when the length d is very much greater than the diameter 2rc 18 October 2003 Electronic Instrumentation 15 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 18 October 2003 Electronic Instrumentation 16 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 18 October 2003 Electronic Instrumentation 17 Making an Inductor If the coil length is much small than the diameter (rw is the wire radius) 8rc L N rc {ln( ) 2} rw 2 Such a coil is used in the metal detector at the right 18 October 2003 Electronic Instrumentation 18 Making an Inductor All wires have some finite resistance. Much of the time, this resistance is negligible when compared with other circuit components. l Resistance of a wire is given by R s A l is the wire length A is the wire cross sectional area (rw2) s is the wire conductivity 18 October 2003 Electronic Instrumentation 19 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 18 October 2003 Electronic Instrumentation 20 Wire Resistance Using the Megaconverter at http://www.megaconverter.com/Mega2/ (see course website) 18 October 2003 Electronic Instrumentation 21 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 18 October 2003 Electronic Instrumentation 22 Transformers IS IL Note Current Direction Let the current through the primary be I S Let the current through the secondary be I L The voltage across the primary inductor is jLI S jMI L The voltage across the secondary inductor is jLI L jMI S 18 October 2003 Electronic Instrumentation 23 Transformers Sum of primary voltages must equal the source VS RS I S jLS I S jMI L Sum of secondary voltages must equal zero 0 RL I L jLL I L jMI S 18 October 2003 Electronic Instrumentation 24 Transformers Note the following simplifying information for cylindrical or toroidal inductors 2 2 ( 0 N rc ) L Henries d NL 2 a LL a LS N S For k 1 M LS LL a LS 18 October 2003 Electronic Instrumentation 2 2 L L 2 a2 25 Transformers Cylinders (solenoids) Toroids 18 October 2003 Electronic Instrumentation 26 18 October 2003 Electronic Instrumentation 27 Transformers Transformers are designed so that the inductive impedances Z L jL are much larger than any resistance in the circuit. Then, from the second loop equation 0 RL I L jLL I L jMI S jLL I L jMI S 18 October 2003 N L IL N S IS Electronic Instrumentation 28 Transformers The voltages across the primary and secondary terminals of the transformer are related by N S VL N LVS Note that the coil with more turns has the larger voltage 18 October 2003 Electronic Instrumentation 29 Transformers The input impedance of the primary winding reflects the load impedance. It can be determined from the loop equations Z IN V S L L S L RS jLS IS RL jLL 2 2 Z IN N S N RL L 18 October 2003 Electronic Instrumentation 30 Transformer Rectifier R1 V1 TX1 5 V VOFF = 0 VAMPL = 120 FREQ = 60 D1 D1N4148 D4 D1N4148 D3 D1N4148 D2 33uF R2 1k D1N4148 0 V C2 0 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. 18 October 2003 Electronic Instrumentation 31 Transformer Rectifier 120V Filtered 80V 40V -0V Unfiltered -40V -80V -120V 10.000s 10.005s V(R1:2) V(R3:2) 10.010s V(D2:2) 10.015s 10.020s 10.025s 10.030s 10.035s 10.040s 10.045s 10.050s V(R4:1) Time 18 October 2003 Electronic Instrumentation 32 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. 18 October 2003 Electronic Instrumentation 33 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. 18 October 2003 Electronic Instrumentation 34 Determining Inductance 0 1 LC f0 1 2 LC Reminder—The parallel combination of L and C goes to infinity at resonance. jL 1 jC jL Z|| 2 jL 1 jC 1 LC 18 October 2003 Electronic Instrumentation 35 L1 R1 100uH 50 V V1 VOFF = 0 VAMPL = 1 FREQ = 1k C1 .68uF V R2 50 0 1.0V 0.8V 0.6V 0.4V 0.2V 0V 1.0KHz V(C1:1) 3.0KHz 10KHz 30KHz 100KHz 300KHz 1.0MHz V(C1:2) Frequency 18 October 2003 Electronic Instrumentation 36 Even 1 ohm of resistance in the coil can spoil this response somewhat 1.0V 0.5V SEL>> 0V V(R3:2) V(R4:1) 1.0V 0.5V 0V 1.0KHz V(C1:1) 3.0KHz 10KHz 30KHz 100KHz 300KHz 1.0MHz V(C1:2) Frequency 18 October 2003 Electronic Instrumentation 37 Project 3: Beakman’s Motor The coil in this motor can be characterized in the same way 18 October 2003 Electronic Instrumentation 38 Optional Project: Paperclip Launcher A small disposable flash camera can be used to build a magnetic paperclip launcher 18 October 2003 Electronic Instrumentation 39