to ensure the soundness of the weld is use of DGS scales in Ultrasonic testing. order to bring the 3mm diameter disc on to curve II) then one uses the lines. Physics of NDT made clear by simulation · Ultrasonic Testing for Education · Eddy DGS (Distance Gain Size) or AVG (Abstand Verstaerkung Gröesse – in german) curves from manufacturer (Krautkrämer) are compared to simulation data for. block method the characteristic curve of the sound field is always determined before carrying out an ultrasonic test, whereas in the DGS method DGS diagrams.
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If the ranges of the backwall and the disc reflector are different, then attenuation shall be accounted for separately. Consider a probe scanning over three similar discontinuities of different sizes:. At longer beam paths, set the backwall to RE2 and add 8 dB. The generated curves are derived from the calculated beam spreading ultradonic of a given transducer, based on ultrasoniic frequency and element diameter using a single calibration point.
Traditionally this technique involved manually comparing echo amplitudes with printed curves, however contemporary digital flaw detectors can draw the curves curbe a calibration routine and automatically calculate the ERS of a gated peak. Part Two Training Courses: This is a typical scale, and the shape of the curves and reference reflectors will depend on the test range, as well as the probe diameter and frequency.
Reflectors of different size, at the same beam path distance, will have an echo height proportional to their area, assuming that the reflectors are in the far zone.
For each FBH diameter, there is a very good agreement for the FBHs echoes amplitudes in the far field where the specular echo amplitude linearly decreases with the depth on the figures, but there are discrepancies for the highest diameters at the smallest depths. DGS is a sizing technique that relates the amplitude of the echo from a reflector to that of a flat bottom hold at the same depth or distance.
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In the example below, the upper curve represents the DGS plot for a 2 mm disk reflector at depths from 10 mm to 50 mm. A 6 mm disc should have an amplitude 4 times that of a 3 mm disc. Frequency Crystal Mode Calibration flaw Calibration depth 1. This is not realistic, so the final modification to the DGS scales is to include a characteristic curve for a backwall reflection. The features of DGS are:.
The curves show a good agreement between simulated and experimental data for FBH deeper than the cuve depth.
From that one calibration point, an entire curve set can be drawn based on probe and material characteristics. In the early days of development of the DGS approach to DGS sizing, it was necessary to employ this generalised approach.
The input signal frequency is 4. The uppermost curve represents the relative amplitude of the echo from a flat plate reflector in decibels, plotted at various distances from the transducer, and the curves below represent the relative fgs of echoes from progressively smaller disk reflectors over the same distance scale.
DGS/AVG | Olympus IMS
In the general diagram the size of reflector is given as a ratio between the size of the disc and the size of the crystal. These types of scales are made specifically for a particular probe the B4S — 4 MHz, 24 mm diameter zero compression probe and shows a characteristic curve for 6 mm, 4 mm and 3 mm reflectors. The red curve shows the response of a backwall reflection.
For small FBH above the focal spot the difference is up to 6 dB. The blue curves plotted show how the amplitudes obtained from different sizes of disc shaped reflector equivalent to a FBH decrease as the distance between the probe and the reflector increases.
It can be noted than all the FBH of this experiment are deeper than the focal spot.
UT – FBH: DGS curves
This curve shows a family of characteristic curves from 2 mm to 10 mm equivalent flat bottomed hole EFBH.
These are called the reference echo curves, and are used to set the correct sensitivity from the backwall.
There are also two other curves — RE1 and RE2.
In the screen at left, the red gate marks the reflection from a 2 mm diameter flat bottom hole at approximately 20 mm depth. Since this reflector equals the selected registration level, the peak matches the curve at that depth. The information we learn from ultrqsonic helps us personalise and continually improve the service we provide through our website and other channels. This of course assumes that the reflectors are in the far zone and are smaller than the beam diameter.
The measurements have been made with the following contact probes: Roll over the probes to scan the defects. This technique has one limitation — it assumes that there is a backwall reflector available at mm. The gain to be added can be then obtained by the difference on the Y-axis between the backwall curve at the backwall range and the curve of the disc reflector of the given size at the test range.
The interaction model is the Kirchhoff model which is well suited to specular echoes. When this concept was first established, the general DGS diagram was dfs as shown below:.
Our security procedures mean that we may occasionally request proof of identity before we disclose personal information to you. It is first used with great diameter reflectorsthen with FBH of different diameters at different depths in water:.
Material attenuation and coupling variation in the calibration block and test specimen can be accounted for. Of course, we transmit the entire credit card number to the appropriate credit card company during order processing.
Ultrasonic Flaw Detection Tutorial.