Home Sigma Products Services Order Here News Links Contact

Sensitivity Diagram
Probe Angle Error Curve
Effect of OD Circumferential
Radius on Exit Angle
Effect of ID Circumferential Radius on Exit Angle
Axial Affect on Focus


Dual Focused Angle Beam Sensitivity

Many factors affect the sensitivity of dual focused angle beam transducers, such as frequency, chip size, and material to be inspected. However as a general rule, the 6dB amplitude curve is from 1/2 to 2 times the focal soundpath when the frequency vs. attenuation allows the peak of the focal length. (See the sensitivity diagram on this page). Therefore it is suggested when inspecting a thick speciman: select frequencies, refracted angles, and focal sound paths to cover the range required.

Another factor that must be considered when selecting a transducer for an inspection, is that dual focused angle beam transducers have a non constant angle behavior. The angle will vary with soundpath, and will appear higher for flaw distances less than the focal length and lower for flaw distances greater. (See the angle error diagram on this page). Considering this potential for errors in flaw location, it is advisable to establish a curve for a specific unit on a calibration block of the same material to be tested.

The Affect of an Axial Radius on Focus

The incident roof angle of a dual focused angle beam transducer directs a refracted beam to the focal intersection point, just as the incident angle on the wedge in the beam direction, directs a refracted beam to the correct exit angle. The normal design supposes that the inspection surface is flat. If the part under test is a pipe, and the transducer is radiused to optimize contact, the angle to the tangent from the beam center of the part radius, must be taken into account and used to modify the roof angle. (See the axial affect on focus this page).

The Affect of a Circumferential Radius on Exit Angle

When selecting an angle of inspection, it is assumed that the reflector will intercept the beam at that angle. This would be true if the inspection surface is flat. However, if the part under inspection is a pipe, and the direction of the inspection is circumferential, the actual angle of intercept is the angle between the exit beam and the radial from the center of curvature through the reflector. This angle is defined as the "EFFECTIVE ANGLE," it will be smaller on an I.D. radius and greater on an O.D. radius. In stating the angle in the part number, the actual or the effective can be listed.



© 1998 - 2002 Sigma Transducers, Inc.