Abstract: In an electromagnetic induction type displacement sensor, two coil patterns are formed on a substrate included in a scale. The coil patterns alternate with each other in the sensing direction of the sensor and are deviated in spatial phase from each other by a quarter pitch. An idle pattern portion is included in one or both of the two coil patterns in order to provide them with the same impedance. Even when sinusoidal voltages, which are different in phase by 90 degrees, are respectively applied to the coil patterns, the resulting magnetic fields are identical and insure accurate displacement detection.

Abstract: In an induction sensor, a plurality of positioning holes are formed through each of a scaler and a slider. The positioning holes of the scaler and slider are spaced the same distance from respective coils and are of the same size and arranged at the same interval. The gap length and azimuth angle between the scaler and the slider are maintained with accuracy.

Abstract: In an induction sensor for sensing the displacement of a movable body by electromagnetic induction, a scaler and a slider are each implemented as a hollow cylinder consisting of a plurality of conductors in the form of a coil. The conductors of each of the scaler and slider alternate with each other in a displacement sensing direction. The sensor can be assembled with a minimum of fine adjustment, eliminates wasteful areas, and provides the slider with high sensing accuracy without increasing currents to flow through the scaler.

Abstract: An ultrasonic flaw detection method in which defects in the weld zone of an electric resistance welded steel pipe are detected by projecting an ultrasonic wave (a) having a frequency range of from 25 MHz to 500 MHz at an angle of incidence of from 0.degree. to 12.degree. onto the weld zone of the pipe. In addition by projecting another ultrasonic wave (b) having a frequency of from 2 MHz to 10 MHz at an angle of incidence of from 15.degree. to 27.degree. onto the same weld zone enables discrimination between cold weld defects and other defects such as inclusions and penetrators.