What is the primary purpose of using two test coils in a bridge circuit?

Using two test coils in a bridge circuit primarily serves the function of determining the difference between a known standard sample and an unknown sample. In an Eddy Current Testing setup, one coil can be used as a reference, measuring the properties of a standard reference sample, while the second coil measures the unknown sample.

This configuration allows for a comparative analysis of the two samples, enhancing the diagnostic capability of the system. The bridge circuit is designed to balance out the readings from both coils, thereby isolating variations caused by the different conductive or geometry characteristics of the samples being tested. This approach improves the accuracy and sensitivity of detection of flaws or variations in material properties such as electrical conductivity, permeability, or geometric dimensions.

The correct application of this method is crucial in various non-destructive testing scenarios where precision is essential for safety and quality assurance.