Electromagnetic Testing

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Frequency Selection In Chapter 1, it was observed that eddy currents are exponentially reduced as they penetrate the test object. In addition, a time or phase difference in these currents was observed (current lagging with penetration w.r.t surface current). The currents near the test coil happen first or lead the current that is deeper in the object. A high current density allows good detectability and a wide phase difference between near and far surfaces allows good resolution. Keypoint: Current deeper into the test object lag the surface current by β = x/δ radian. Charlie Chong/ Fion Zhang
Single Frequency Systems Unfortunately, if a low frequency is selected to provide good penetration and detectability, the phase difference between near and far surface is reduced. Selection of frequency often becomes a compromise. It is common practice in inservice inspection of thin-wall, nonferromagnetic tubing to establish a standard depth of penetration just past the midpoint of the tube wall. This permits about 25% of the available eddy current to flow at the outside surface of the htbe wall. In addition, this establishes a phase difference of about 150 degrees to 170 degrees between the inside and outside surface of the tube wall. The combination of 25% outside, or surface current and 170 degrees included phase angle provides good detectability and resolution for thin-wall tube inspection. (This is accomplished by properly selecting the driving frequency of the coil to limit the penetration) Calculation: δ = (πfσμ) -½ β = x/ δ radian = x / δ∙ 57.3º Where: x = depth below surface Charlie Chong/ Fion Zhang
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Electromagnetic Testing Study Guide
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E&P Applications Charlie Chong/ Fio
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Charlie Chong/ Fion Zhang
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乱七八糟 - 随看随记 C
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Charlie Chong/ Fion Zhang http://ww
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IVONA TTS Capable. Charlie Chong/ F
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EDDY CURRENT an Overview Descriptio
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Tangential Probe Charlie Chong/ Fio
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Electromagnetic Testing Advantages
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Factors Affecting Eddy Current Resp
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from this it can be seen that depth
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http://www.eng.morgan.edu/~hubert/I
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Robotic Charlie Chong/ Fion Zhang
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Measurement Techniques (EN!) a) Abs
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Figure 1.1 Arago’s Experiment Cha
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Oersted discovered the presence of
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Figure 1.3: Induced current electro
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Charlie Chong/ Fion Zhang http://en
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Charlie Chong/ Fion Zhang http://en
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The law of physics describing the p
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Charlie Chong/ Fion Zhang http://hy
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Magnetic Force The magnetic field B
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Generation of Eddy Currents When a
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Factors Affecting Inductance There
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COIL LENGTH: All other factors bein
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Coil Inductance L An approximation
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Note the direction of the primary c
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Generation of Eddy Current With a p
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Charlie Chong/ Fion Zhang Permeabil
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A Dual Variable inductors Figure 1:
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Figure 3: Here is another inductor
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Figure 4: The two inductors on this
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Grundig radio satellit 750 ■ http
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Figure 1.7: Phasor Diagram of Coil
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Current Density The distribution of
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Figure 1.8: Relative eddy current d
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Relative Magnetic Permeability Perm
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It should be observed at this point
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δ = (π x 100 x 10 3 x 4 x π x 0.
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Using 1.35 mm as depth x from surfa
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Standard Depth for Different Conduc
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Current (?) Lagging Voltage lagging
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σº∙πμ■δ∝∞ωΩθ√ρβ
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Figure 1.9 should be used as a rela
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Figure 1.8: Relative eddy current d
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Q.1.1 Generation of eddy currents d
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Q.1.5 Eddy current generated a test
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Q.1.9 Refer to Figure1.9 using exam
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Chapter 2 The Coil Arrangements Cha
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Probe coils and probe coil forms ca
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Encircling Coils Encircling coil, o
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Discussion Subject; Encircling Coil
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Bobbin Coils Bobbin coil, inside di
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Figure 2.5: Test coil configuration
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Differential coils Differential coi
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Figure 2.6: External reference diff
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Figure 2.7: Hybrid coil (through tr
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Additional Coil Characteristics Coi
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Q.2.1 Differential coils are usuall
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Q.2.6 An absolute coil measurement
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The Answers Charlie Chong/ Fion Zha
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As discussed earlier test coil desi
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Demonstration model of a moving iro
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Thus, the resistance of a 10 ft len
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SPECIFIC RESISTANCE OR RESISTIVITY
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Problem: What is the resistance of
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The inductance of a multilayer air
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Example: A coil whose dimensions ar
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Example: Using the 32 μH coil calc
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Impedance To explain the addition o
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Maximum transfer of power is accomp
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Rectangular Notation Because reacta
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Vectors With Polar Notations. Stand
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Rectangular Notation - Prefix “j
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Imaginary Component In “rectangul
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Imaginary Charlie Chong/ Fion Zhang
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To convert from rectangular to pola
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More Reading on Polar & Rectangular
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Eddy current coils with included im
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Permeability and Shielding Effects
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Another technique of shielding uses
Page 165 and 166: Saturation Approach Another coil de
Page 167 and 168: Figure 3.5: Magnetic bias probe Cha
Page 169 and 170: Materials must be chemically compat
Page 171 and 172: Q.3.1 A coil's resistance is determ
Page 173 and 174: Q.3.7 The Q or merit of a coil is d
Page 175 and 176: The Answers Charlie Chong/ Fion Zha
Page 177 and 178: Jackfruit Tree Charlie Chong/ Fion
Page 179 and 180: Electrical Conductivity σ In elect
Page 181 and 182: As previously discussed, conductivi
Page 183 and 184: Figure 4.1; Conductivity curve Char
Page 185 and 186: The coil's inductive reactance is r
Page 187 and 188: Effects of Heat Treatment on Conduc
Page 189 and 190: Permeability Permeability of any ma
Page 191 and 192: When increases in the magnetizing f
Page 193 and 194: Skin Effect Charlie Chong/ Fion Zha
Page 195 and 196: Discussion Subject: Response to the
Page 197 and 198: Lift Off Electromagnetic coupling b
Page 199 and 200: Fill factor will always be a number
Page 201 and 202: Figure 4.4: Fill factor ratios When
Page 203 and 204: Example: Calculate the resultant lo
Page 205 and 206: Figure 1.8 is again useful to illus
Page 207 and 208: Signal-to-Noise Ratio Signal-to-noi
Page 209 and 210: The Answers Charlie Chong/ Fion Zha
Page 211 and 212: Q.4.4 A (?) prime factor affecting
Page 213 and 214: Q.4.10 Temperature changes, vibrati
Page 215: Test Frequencies It is the responsi
Page 219 and 220: Eddy Current Density Since the sens
Page 221 and 222: Applicable Scenario Eddy Current De
Page 223 and 224: Standard Depth δ Formula The depth
Page 225 and 226: Example 1: As an example of how thi
Page 227 and 228: Frequency Selection - Ferromagnetic
Page 229 and 230: A frequency can always selected to
Page 231 and 232: Figure 5.1(a) shows the effect on p
Page 233 and 234: Figure 5.1: Effects of frequency ch
Page 235 and 236: Figure 5.2: Normalized impedance di
Page 237 and 238: Figure 5.3: Impedance variations ca
Page 239 and 240: Figure 5.4: Impedance variations ca
Page 241 and 242: Multiparameter Techniques It become
Page 243 and 244: Multiparameter Techniques - Multipl
Page 245 and 246: First, a frequency is selected to g
Page 247 and 248: More Reading on Characteristic Para
Page 249 and 250: Figure 1: Eddy Current Testing Char
Page 251 and 252: Figure 2: Types of Probes Charlie C
Page 253 and 254: Surface (Pancake) Probes Surface pr
Page 255 and 256: Encircling Probes Encircling probes
Page 257 and 258: Design of eddy current probes In mo
Page 259 and 260: In brief, probe design is usually d
Page 261 and 262: Analytical Approach (Pc & f g ) Ana
Page 263 and 264: RECENT TRENDS IN EDDY CURRENT PROBE
Page 265 and 266: Pressurized Heavy Water Reactors (P
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The Answers Charlie Chong/ Fion Zha
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Q.5.4 Calculate the limit frequency
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Q.5.7 Primary resistance is subtrac
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Q5.9 A 25% deep crack open to the n
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Chapter 6 Instrument Systems Charli
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Eddy Current Instrumentation Most o
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Figure 6.1: Internal functions of t
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Chernobyl Nuclear Power Plant Charl
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Figure 6.2: Four types of simple ed
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Figure 6.2(b) shows an impedance br
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Figure 6.2(d) illustrates a balanci
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Eddy current testing - Signal Analy
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Impedance Testing With impedance ma
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Phase Analysis Testing - Vector Poi
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Phase Analysis Testing - Ellipse As
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Figure 6.4: Cathode ray tube displa
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Figure 6.5: Screen image of a linea
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Impedance Plane Testing - Mode of O
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Figure 6.6: Null balance instrument
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Figure 6.7: Typical surface riding
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For deep subsurface crack detection
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Multiple circuits are used througho
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This type of digital instrumentatio
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Read Out Mechanisms - Audio Alarms
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An qualitative meter response could
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Figure 6.13: A qualitative analog m
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Read Out Mechanisms - Cathode Ray T
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Figure 6.14: Numerical readouts/dig
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Read Out Mechanisms - Computer Eddy
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Probe Delivery System Instead of mo
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Chapter 6 Review Questions Charlie
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Q.6.1 Signal preparation is usually
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Q.6.7 Amplitude gates provide a tec
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Chapter 7 Eddy Current Applications
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Discontinuity Detection The theoret
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Heat Exchanger Charlie Chong/ Fion
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Heat Exchanger TSP Charlie Chong/ F
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Heat Exchanger TSP Charlie Chong/ F
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Figure 7.2: Phase-to-depth calibrat
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The geometry of real discontinuitie
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Figure 7.5: A multifrequency applic
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Aerospace Applications Charlie Chon
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The reference specimen and its asso
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Dimensional Measurements Dimensiona
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Figure 7.6: A single frequency hard
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Conductivity Measurements Conductiv
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Alloy Sorting Alloy sorting can als
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In addition, it is advisable to hav
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Answers Charlie Chong/ Fion Zhang
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Q.7.4 Using multifrequency techniqu
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Q.7.7 Response to multilayer varyin
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Chapter 8 Other Electromagnetic Tec
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Some other technologies that have b
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Alternating current field measureme
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Figure 8.1 shows the basic principl
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ACFM Principle Charlie Chong/ Fion
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ACFM Z X Bx =magnetic flux componen
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The technique in its simplest form
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Magnetic Flux Leakage Testing Prima
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Figure 8.2: Equipment for magnetic
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Magnetic Flux Leakage Testing Charl
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The most commonly used inservice in
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Magnetic Saturation Charlie Chong/
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The magnetization curve is not retr
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Magnetic Flux Leakage Testing Charl
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Magnetic Flux Leakage The basic pri
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Magnetic Flux Leakage Magnetic Flux
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Special hybrid (driver/pick up) coi
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At distances in excess of two tube
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Figure 8.4: Remote field testing en
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Remote-Field Energy Zones - in remo
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Remote-Field Zone Transition Zone C
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RFT - Flux distribution in pipe (a)
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Remote Field Zone - The third defin
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Amplitude (voltage) - The remote fi
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RFT Charlie Chong/ Fion Zhang http:
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The Remote Field Technique is an el
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Remote Field Eddy Current Technique
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More Reading: RFT Remote Field Test
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These eddy currents, in turn, produ
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The Zones Direct Couple Zone The re
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RFT Probes Probes for inspection of
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RFT Signal Interpretation The signa
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RFT Reference Standards Reference s
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Q.8.4 A generally accepted definiti
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Q.8.8 The region of intense electro
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Chapter 9 Eddy Current Procedures,
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American Society for Testing and Ma
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Military Standard The United States
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EDDY CURRENT INSPECTION OF NONFERRO
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. Probe positioning and feeding sha
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3. Tube Inspection General (Refer t
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F. INSPECTION RESULTS AND DOCUMENTA
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G. REFERENCES The following documen
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Q.9.4 Military Standards are design
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Q.9.10 The system in QA3 is calibra
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More Reading http://www.allaboutcir
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Discussion Subject: discuss on the
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Inspection from the Tube OD Most AS
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Approximately 25 years ago, the AST
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One additional advantage of OD ECT
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The baseline eddy current test The
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There is no standard accept/reject
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Pulsed Eddy Currents Systems Charli
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Although still an active research f
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LOI (Lift-Off point of Intersection
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Gap Point : Similar to the LOI, the
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Driving Coil Charlie Chong/ Fion Zh
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Hall effect sensors In opposition t
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Crack Detection using Pulsed Eddy C
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Fig. 1 (a) ARMANDA - Automated scan
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Fig. 2. Images of the Eddy current
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Reading 2: 4.9.2.3 Pulsed Eddy Curr
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Good Luck Charlie Chong/ Fion Zhang
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