1. What is non-destructive testing?
The use of noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. i.e. to inspect or measure without doing harm.

2. What is a vortex?
When the metal conductor in a magnetic field changes, or moving in a magnetic field, due to electromagnetic induction principle, resulting in the conductor swirling currents, called eddy current.

3. What is the impedance of flat panel display?

Eddy current testing is the eddy current sensor by measuring the electrical impedance changes in the value realized. Point impedance including reactance and impedance, we display resistance R (Resistance) as the abscissa, the reactance X (Reactance) for the longitudinal coordinates of the formation of Cartesian coordinates. By eddy current testing sensor impedance changes, you can use signal processing point information on the instrument (Q) to display, while the point Q is a two-dimensional vector points, it has a certain amplitude (Amplitude) and phase (Phase). And because a variety of causes eddy current signal component R, X change, making the location of point Q also change, Q-point, compared with the changes in impedance panel trajectories.

 4. What is the factors that affect the impedance?
The material conductivity, magnetic permeability, shape size, fill factor, lift-off effects, edge effects, and so on.

5. What is the lift-off effect?
When the detection coil and the relative position between the tested materials change, the detection coil will generate eddy currents. With the detection of eddy current density, the distance between coil and material increases and decreases, making the vector points Q in the display plane moved. This phenomenon is called lift-off effect. This principle can be used non-metallic coating of metal surface thickness measurement.

6. What is the fill factor?
It is the coupling between the detection probe and material level. The greater the fill factor of the probe coupled with the material as possible, the better the effect of electromagnetic induction, the the higher detection sensitivity. Fill factor can be expressed as η = (d / D) 2; D - Coil inner diameter (mm); d - the sample diameter (mm).

7. What are the edge and end effects?
When the coil to be tested pieces of the edge, due to the role of the edge of the signal, eddy current change, which is called the edge effect. When the detection coil close to the whole story ends when the specimen is often referred to as end-effectors.

8. What is the skin effect of alternating current?
Skin effect is a tendency for alternating current (AC) to flow mostly near the outer surface of a solid electrical conductor, such as metal wire, at frequencies above the audio range. The effect becomes more and more apparent as the frequency increases.

9. Classification of detection coil
1) Through the coil: the sample, which can be pipe, rod or wire, is placed through the coil. First, because the magnetic field generated by the coil is on the sample wall, so it is better to detect the outer wall defects. Meanwhile, the inner wall detection will use penetration test. In general, the sensitivity of inner wall defect detection is lower than that of the outer wall. Thick-walled tube defects can not use this method.
2) Interpolation coil; interpolation coil is placed inside the test tube coils, dedicated to check the defection of the thick wall of or hole. It is also used to check the quality of equipment in the pipe, such as heat exchanger tubes in service test.
3) Probe coil; probe coil is placed on the sample surface, which applies not only to the surface scan testing of a simple sheet, slab, billet, round billets, bars and large diameter pipe, but also to the inspection of the more complex mechanical parts. Compared with the through-type coils, probe coil is suitable for the small size of surface detection since the probe and its field scope is small.

10. What is a multi-frequency eddy current and remote field eddy current technique?
In the detection of many complex components, the component itself, will produce a strong interfering signals, which makes single-frequency eddy current difficult to accurately detect the defect. To overcome this interference and improve detection reliability, we can use several frequencies inspire coil at the same time. The coil can also be accessed through the detection of multiple sets of data, and then mixing the collected data processing to suppress interference signals, which species is called multi-frequency eddy current technique.
The remote -field vortex is a low-frequency eddy current that can penetrate the wall. It is often used in wear detection probe. The distance between the incentive coil and measuring coil is about twice of the pipe diameter. The coil is able to detect piercing the wall again an incentive to return the magnetic field signal, which can effectively detect metal tube inside and outside the wall or thinning degree.  

11. What is the leakage magnetic field?
When using the measured magnetization of ferromagnetic materials or magnetic devices, if the material of the material is continuous, uniform, then the material of the magnetic induction lines will be bound in the material, the magnetic flux is parallel to the surface, almost no magnetic field lines from the surface of falling, no external magnetic field was seized. However, when there are material defects in cutting magnetic field lines, the surface defects or organizational change of state will make a change in permeability. Due to the defects in magnetic permeability is very small, a great reluctance to make the magnetic circuit of magnetic flux occurs distortion, magnetic induction line will change the channel. In addition that part of the magnetic flux directly bypass through the internal or defects in the material, there are also part of the magnetic flux will leave the material surface, through the air to bypass the defect and then re-enter the material, then the magnetic flux leakage forms in the material surface defects.

12. Why to magnetize the magnetic flux leakage inspection?
Since the magnetization of materials, making materials, the magnetic field distribution becomes more uniform. This allows a greater flux leakage bypass the defect, and thus more conducive to the detection of defect signals to enhance sensitivity.

13. What are the factors that affect leakage magnetic field strength and why can only detect ferromagnetic material magnetic flux leakage?
The factors that affect leakage magnetic field strength: material, as well as defects in its own nature, such as defects in the shape, size, depth, direction and so on.
Magnetic flux leakage testing is only for the ferromagnetic material. Because non-ferrous magnetic permeability is about equal to 1, and the environment in which permeability is basically the same, so that the magnetic field around the defect will not change even changes in permeability, which also does not produce magnetic flux leakage.

14. Can magnetic flux leakage detect internal defects?
Magnetic flux leakage testing primarily directs at the surface and sub-surface defect detection. For internal defect detection of defects depends largely on the distance from the surface, as well as the material magnetization. If the defect in the material is deep inside the case, then it can not be accurately detected.

15. What is the magneto-mechanical effect, magnetic memory effect?
The main causes of the event of damage of Mechanical parts and metal components, is a variety of micro-and macro-mechanical stress concentration. In the stress concentration area, corrosion, fatigue and creep process develop the most intense. Mechanical stress is directly related to the self-magnetization of ferromagnetic materials and the residue magnetic. In the role of the geomagnetic conditions, permeability of defects department decreases, the leakage magnetic field of the workpiece surface increases. This feature of the ferromagnetic material is called magneto-mechanical effect. The existence of magneto-mechanical effect makes the surface of ferromagnetic metal piece magnetic field strength, which enhances the magnetic field to "remember" the parts of the defects or the location of stress concentration, which is the "magnetic memory" effect.

16. What is the main testing target for mental magnetic memory (MMM)
Metal magnetic memory testing is mainly used for prevention of early diagnosis of iron magnetic material, such as right pipes, containers, turbine blades, airframe, aircraft landing gear, oil well drill pipe and a variety of different shapes to build, welding first class. MMM testing is a rapid and convenient detection without surface treatment.