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Ultrasonic Testing (UT)

A-scan

Alternative: A-scan display, A-scan presentation,

Related Entries:logarithmic amplifier, RF display, B-scan, C-scan, D-scan, F-scan presentation, P-Scan, display,

Exhibitors Keywords:TNO Science & Indust..

Articles Selected:

- Recent Advances in the Ultrasonic Inspection Recording and Reporting Instrumentation: Part 1 (2003-09-01)

- Simulation of an Ultrasonic Inspection (1996-11-01)

Articles Keywords:A-Scan55

Description:

A display in which the received pulse amplitude is represented as a displacement along one axis (usually the y-axis)and the travel time of the ultrasonic pulse is represented as a displacement along the other axis (usually the x-axis). In a linear amplification system the vertical excursion is proportional to the amplitude of the signal. With the

use of logarithmic scale amplifiers the y-axis presents a logarithmic scale.

A-scan principle

There are different kinds of single presentations possible:

1. both half waves unrectified (RF),2. positive half wave,3. negative half wave4. rectified and unfiltered,

5. rectified and filtered (smoothing).

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A-scan RF echo display

An RF display is necessary for investigation of the signal phase shift (e.g., boundaries). Other presentations areuseful for simplifying the result and its interpretation. A-scan displays are more complex because it is the principlesthat are displayed, so multiplied signals ( skips of back wall, waterpath) and wave conversion need carefulinterpretation.With digital instruments the A-scan evaluation is supported by functions like maximum hold, averaging, echofiltering and frozen A-scan.

A-scan practical application

Further Information:

Examples of Echo Signals

The examples picks up common situations of Echo Signal conditions and displays them with their RF Signal, as it willappear at an Oscilloscope or an Ultrasonic System screen as a so called "one shoot". The conditions will be mostlybased on plastic pipes and will relate to in-line wall thickness measurement.The principles are also adaptable toother materials and to flaw detection contitions.

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Definition and Introduction to Echo Signals Display

For evaluation of Echoes it is important to analyse them for both of the half-waves (RF). For Wall Thickness

Measurement it is common to use the time of flight (TOF) method within the Interface and Backwall Echo. Therelease (trigger), for the Start and Stop Function, is due to a threshold exceeding of the echo half-wave. Thethresholds are adjustable for both echoes separately. The adjust of the position, that means where (distance), theecho is expected. The of the amplitude, that means according to the certain echo amplitude and noise level. Thefirst wavephase that will exceeds the threshold, will release the time measurement function.

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Reference:Ultrasonic Testing in Pipe Extrusion by Rolf Diederichs

Rolf Diederichscreated: 1999-12-11

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Ultrasonic Testing (UT)

acoustic impedance

Related: impedance,

Description:

Often used as the equivalent of characteristic acoustic impedance, a material propertydefined as the product of sound velocity and density of the material. The relative transmission

and reflection at an interface are governed in part by the acoustic impedances of thematerials on each side of the interface. The letter Z is used for the impedance and isexpressed in [kg/s m] = 1 Rayl. For water Z = 1.49 MRayls.

Illustrations:

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acoustic impedance

Rolf Diederichscreated: 1999-12-11

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