High-speed detection of rolling contact fatigue in railway rails

Eddy current and associated electromagnetic methods have long been used for the detection of surface defects on a variety of products. With the ever-increasing use of computer technology coupled with the availability of inexpensive memory, the trends have been toward software implementation of the detection process. The analogue/digital boundary has been pushed ever forward towards the defect detector. There is more use of computer techniques to enhance the presentation of results while ignoring the basic analogue detection function. Whilst this option is well-suited to many applications, there is a need to take the boundary a little further away from the defect detector for specific applications. Even with modern high-speed processors there is merit in the early stages of detection being analogue, both on cost and performance grounds. Here, one analogue method of implementing a high-speed sensitive and selective detection system for small defects is discussed.