Addendum-01a Equipment Calibrations My ASNT Level III UT Study Notes. 2014-June

Addendum-01a 

Equipment Calibrations 

My ASNT Level III UT Study Notes. 

2014-June

http://en.wikipedia.org/wiki/Greek_alphabet

Speaker: Fion Zhang 

2014/6/19

Normal Beams Calibration Techniques

Attenuation due to Beam spread for: 

• Large Reflector 

• Small Reflector

Attenuation Due to Beam Spread: Large Reflector

Attenuation Due to Beam Spread: Small Reflector 

D1 

SH1 

D2 

SH2

Material Attenuation Determination:

Material Attenuation Determination: Actual BWE display

IF zero Material attenuation: The second BWE at twice the distance will be 

exactly 6dB less (50% less), half the 1st BWE height ( ½ FSH). However this 

is never the case!

Δ dB = total Material attenuation at twice distance travel. 

Material attenuation = 

ΔdB 

D1 

D2

Material Attenuation in 100mm = YdB-XdB-6dB 

Material attenuation in dB/mm = (YdB-XdB-6dB)/100 

YdB-XdB-6dB 

X dB 

Y dB

Construction of beam edges plot- Normal Transducer

Construction of Beam Edges:

20dB drop to find edges of beam

The other edge:

Construction of beam spread at 13mm:



Angle Beams Calibration Techniques

Perspex as Matching Layer/Wedge 

Tunsten impregnated 

epoxy resin 

θs 1 

2730m/s 

θs 2 

3250m/s

Perspex as Matching Layer/Wedge 

1. The Shear wave velocity of Perspex is 2730m/s, the shear wave velocity 

od steel is 3250m/s. The refracted angle of Perspex ϴ S1 is always smaller 

than ϴ S2 

2. Pespex is very absortive and attenuated efficiently, thus reflected 

compressional wavw will be dampen.

First/ Second Critical Angles 

V L1 = 2730m/s, 

V S2 = 3250m/s, V L2 = 5900m/s 

1 st / 2 nd critical angle 

27.56° 

57.14° 

° 

I st Critical angle= 27.56° 

2 nd Critical angle= 57.14° 

B 

33.42°

First/ Second Critical Angles 

27.56° 

57.14° 

° 

33.42°

Finding the probe index

Finding the probe index

Checking the probe Angle:

Calibration for range:

Calibration for range:

Angle Beam- Beam edges Proving (Vertical Axis) using IOW Block 

Stand Off Measurement Techniques. 

Stand-off 2 

Stand-off 1 

Stand off 2


Botoom edge.


Bottom Edge.

The IOW Block: The Institute of Welding Block

The Proofing: 

Plot out the Stand-Off1 & 2 readings on a transparent slide, superimposed the 

ploted transparent slide on IOW Block

Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block


Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block 

Scanned at 

½, 1, 1 ½Skips


Angle Beam- Beam edges Proving (Horizontal Axis) using IIW Block 

½Skip 

1 Skip 

1½ Skip

The DAC

The DAC

DAC Curve

DAC Curve

DAC Curve Plot 

1. Obtained the signal from the refernce reflector and mark on the 

graticule/traspatrent sheet with gain setting at 80% FSH. 

2. Set the gain control -6bB and marks the 50% mark. 

3. Set the gain contril to the 

4. Obtained the signal at the gain setting in item 1 and repeat the process at 

different sound paths. 

5. Plot the curves at the gain setting and -6dB. 

6. Determined the transfer correction. 

7. Scanned the work pieces at the “Gain Setting + Transfer Correction”

FLAT Bottom Holes FBH

FLAT Bottom Holes FBH

Reading on: FLAT Bottom Holes FBH 

https://www.cnde.iastate.edu/ultrasonics/grain-noise

FLAT Bottom Holes FBH 

A type of reflector commonly used in reference standards. The end (bottom) 

surface of the hole is the reflector.E 

quivalent:, the size of a flat-bottom hole which at the same range, gives an 

ultrasonic indication equal to the one from the discontinuity. This reflector is 

used in DGS curves, or many calibration blocks, or standards such as the GE 

specification.

Transfer Corection

Transfer Correction: Reference surface are smooth and scale free unlike 

the actual work pieces. These call for transfer correction to account for 

transfer loss resulting from actual scanning.







Transfer Correction:

Transfer Correction: Comparison of BWE for Compression Probe 

Test Material curve 

Reference Block curve 

Gain Setting 

Transfer correction 

at thickness 

Measured point 

Beam path

Transfer Correction: Compression Probe Method, Plot a curve of gain 

setting for FSH at different south paths for actual and reference block, the 

different in gain control at thickness is the transfer correction.

Transfer Correction: Angle Probes Methos, used 2 eaqual angle probes, 

pitch and catch in the test material ans using the reference block. The 

differences in gain setting is the transfer correction,

DGS- Distance Gain Size 

http://www.sonostarndt.com/EnProductShow.asp?ID=198

FLAT Bottom Holes FBH 

■ 

DGS/AVG 

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. This is 

known as Equivalent Reflector Size or ERS. DGS is an acronym for 

Distance/Gain/Size and is also known as AVG from its German name, 

Abstand Verstarkung Grosse. Traditionally this technique involved manually 

comparing echo amplitudes with printed curves, however contemporary 

digital flaw detectors can draw the curves following a calibration routine and 

automatically calculate the ERS of a gated peak. The generated curves are 

derived from the calculated beam spreading pattern of a given transducer, 

based on its frequency and element diameter using a single calibration point. 

Material attenuation and coupling variation in the calibration block and test 

specimen can be accounted for. 

http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/dgs-avg/

DGS is a primarily mathematical technique originally based on the ratio of a 

circular probe’s calculated beam profile and measurable material properties 

to circular disk reflectors. The technique has since been further applied to 

square element and even dual element probes, although for the latter, curve 

sets are empirically derived. It is always up to the user to determine how the 

resultant DGS calculations relate to actual flaws in real test pieces. 

An example of a typical DGS curve set is seen below. The uppermost curve 

(Curve #1) 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 (Curve #2) represent the relative amplitude of echoes from 

progressively smaller disk reflectors over the same distance scale.

(Curve #1) represents the relative amplitude of the echo from a flat plate 

reflector in decibels, plotted at various distances from the transducer

(Curve #2) represent the relative amplitude of echoes from progressively 

smaller disk reflectors over the same distance scale.

As implemented in contemporary digital flaw detectors, DGS curves are 

typically plotted based on a reference calibration off a known target such as a 

backwall reflector or a flat bottom hole at a given depth. From that one 

calibration point, an entire curve set can be drawn based on probe and 

material characteristics. Rather than plotting the entire curve set, instruments 

will typically display one curve based on a selected reflector size (registration 

level) that can be adjusted by the user. 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. The lower curve is a reference that has been plotted 6 dB lower. 

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. In the 

screen at right, a different reflector at a depth of approximately 26 mm has 

been gated. Based on its height and depth in relation to the curve the 

instrument calculated an ERS of 1.5 mm.

(Curve #2) represent the relative amplitude of echoes from progressively 

smaller disk reflectors over the same distance scale.

More reading on DGS

DGS- Different sizes of FBH at different distance

DGS 

# of near field

What is DGS 

TCG is a time-corrected DAC so that equal dimension reflectors give equal amplitude 

responses for all sound path distances. Used for PAUT Sectorial scans where it would 

be otherwise impossible to set every angle and sound path to the same sensitivity 

level using DAC's. 

ASTM E-1316: DGS (distance gain size-German AVG) distance amplitude curves 

permitting prediction of reflector size compared to the response from a back surface 

reflection. 

The probe manufacturer supplies data sheet diagams for each probe which shows the 

amplitude response curves from the backwall and a range of diameters of flat-bottom 

holes along the length of the soundfield. 

Have a look at EN 583-2:2001 Sensitivity and range setting for excellent authoritative 

descriptions of DAC/TCG and DGS. You'll have to look at AWS D1.1. for instance 

for knowledge of their sensitivity setting requirements. 

Knowledge of these techniques is desirable but will such knowledge really improve 

your inspection method? You use DAC because the Codes and standards you work to 

require you to assess indications to those DAC's. A report that a reflector was 3,5 mm 

equivalent FBH size to DGS would most probably be rejected.

DGS-If you have a signal feom a flaw at a certain depth, you can compare the 

signal of BWE from the FBH at that depth. The defect then could be sized as 

equivalent of the size of the FBH. 

Size 0.24 

Size 0.24 

2.4depth 

http://www.ndt.net/article/berke/berke_e.htm

Locating & Sizing Flaws

Locating reflectors with an angle-beam probe 

Fig. 53 Scanning a reflector using an angle beam probe 

The echo of a discontinuity on the instrument display does not now give us 

any direct information about its position in the material. The only available 

information for determination of the reflector position is the scale position and 

therefore the sound path s, this means the distance of the discontinuity from 

the index point (sound exit point) of the probe, Fig. 53. 

The mathematics of the right-angled triangle helps us to evaluate the Surface 

Distance and the Depth of a reflector which are both important for the 

ultrasonic test, Fig. 54a. We therefore now have the possibility to instantly 

mark a detected flaw's position on the surface of the test object by 

measurement of the surface distance from the sound exit point and to give 

the depth. For practical reasons, the reduced surface distance is used 

because this is measured from the front edge of the probe. The difference 

between the surface distance and the reduced surface distance corresponds 

to the x-value of the probe, this is the distance of the sound exit point to the 

front edge of the probe, Fig. 54b.

With ultrasonic instruments having digital echo evaluation these calculations 

are naturally carried out by an integrated microprocessor and immediately 

displayed so that the operator does not need to make any more timeconsuming 

calculations, Fig. 55. This is of great help with weld testing 

because with the calculation of the flaw depth an additional factor must be 

taken into account, namely: whether the sound pulses were reflected from the 

opposing wall. If this is the case then an apparent depth of the reflector is 

produced by using the depth formula which is greater than the thickness T of 

the test object. The ultrasonic operator must acertain whether a reflection 

comes from the opposite wall and then proceed with calculating the reflector 

depth, Fig. 56b.

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns

Scanning Patterns 

http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/common-test-practices/

Practice Makes Perfect 

81. The 100 mm radius in an IIW block is used to: 

(a) Calibrate sensitivity level 

(b) Check resolution 

(c) Calibrate angle beam distance 

(d) Check beam angle 

80. The 50 mm diameter hole in an IIW block is used to: 

(a) Determine the beam index point 



(d) Check beam angle

Practice Makes Perfect 

35. The 2 mm wide notch in the IIW block is used to: 

(a) Determine beam index point 



(d) Check beam angle

Addendum-01a Equipment Calibrations My ASNT Level III UT Study Notes. 2014-June

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