Eddy current testing machine is a kind of flaw detection method which uses the principle of electromagnetic induction to detect the surface and near surface defects of conductive components. The principle is that the eddy current is generated in the conductive component by magnetic coil, and the change of eddy current is measured by detecting coil, so as to obtain the relevant information of component defects.
In eddy current testing machine, in order to adapt to different testing purposes, testing coils can be divided into three categories: feed-through coil, inside pass coil and put-in coil according to the relationship between testing coils and tested components.
If the workpiece needs to be inserted and pass through the coil, the feed-through coil is used.
When inspecting the pipe fittings, sometimes the coil must be put into the pipe for inspection, then the inside pass coil is used.
When t-type (point type) coil is used, the coil should be placed on the surface of the workpiece to examine.
This kind of coil, with magnetic core inside, is small in size and high in sensitivity and probability, which makes it suitable for large components, plates, strips and other surface crack inspections. According to the use of detection coil, it can be divided into absolute coil, standard comparison coil and self comparison coil.
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The use method that only adopts one detection coil is called absolute coil type, and two detection coils connected into differential form are called standard comparison coil type. Using two coils placed in different parts of the same component to be tested as a comparison standard coil is called self comparison coil, which is a special case of standard comparison coil. The basic circuit consists of oscillator, detection coil signal output circuit, amplifier, signal processor, display and power supply.