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Signal detection circuit
In the eddy current detection, the eddy current detecting coil is usually used as a bridge wall constituting the balanced bridge. Under normal circumstances, the balance of the bridge circuit can be achieved by adjusting the variable resistor in the balanced bridge, as shown in the following figure:

When the detected impedance changes (such as a defect in the detected part of the coil), the bridge loses balance, and the output voltage is no longer zero, but a very weak signal, the size of which depends on the electromagnetic characteristics of the part being tested. .

Application of eddy current testing

1. Eddy current detecting device
The eddy current detecting device includes a detecting coil, a detecting instrument and an auxiliary device, and is also equipped with a standard sample and a comparative sample.

Detect the core part of the instrumental eddy current test. The function is to generate an alternating current supply detecting coil, amplify the detected voltage signal, suppress or eliminate the interference signal, and extract the useful signal. The test results are finally displayed. According to the object and purpose of the inspection, the eddy current testing instrument is divided into three types: eddy current testing, eddy current conductivity meter and eddy current thickness gauge. With the development of electronic technology, intelligent eddy current testing instruments have emerged.

Eddy current detector
Three types of eddy current detectors have different circuit types, but in order to reflect the impedance of the test piece through the impedance change of the detection coil, they need to perform some of the same tasks: (1) generating an excitation signal; (2) Detecting eddy current information; (3) identifying influencing factors; (4) indicating detection results

Therefore, the composition is roughly the same, consisting of an oscillator, a probe (detection coil and assembly), a signal output circuit, an amplifier, a signal processor, a display, and a power supply.

The oscillator generates oscillating currents of various frequencies through the detection coil, which produces an alternating magnetic field and induces eddy currents in the workpiece. When the test piece has defects or physical properties changes, the coil voltage changes, the coil voltage change input amplifier is amplified by the signal detection circuit, the various interference signals are eliminated by the signal processor, and finally the useful signal is input into the display to display the detection result.