ndt laboratory no04 new usm36

7/26/2019 NDT Laboratory No04 New USM36

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Laboratory No.4

Working with USM 36 apparatus part 2Calibrating the USM 36

Calibration of the instrument

The location of a discontinuity can be instantly determined using its echo if the instrument i

correctly calibrated. Calibration means, linear display, from the zero point on the scale, of a certaidistance range of the object to be tested. The zero point on the scale corresponds to the surface of the tes

object and the 10th scale graduation the maximum distance, e.g. 100 mm steel, 10 mm aluminum, 25 mm

brass etc. When specifying the calibration range the naming of the material is also important because thdisplayed distance of the echo, sound path s, is always deduced from the time of flight t of the pulse an

the sound velocity c according to the equation:

=

2

wheres = sound path [mm]

c = sound velocity [km/s]t = transit time [ms]

This relationship is not unimportant for the ultrasonic operator but it is not required for th

sequence of calibration.

The associated sound paths correspond logically to the paths being travelled in the test object, foexample with a straight-beam probe it is the multiple of the test object's thickness t, therefore:

1st Echo = t,

2nd Echo = 2t,3rd Echo = 3t, etc.

We must now adjust 2 of these echoes on the corresponding scale graduation to the requirecalibration range. The instrument is then calibrated, i.e. by reading off the scale position T the sound pat

s (distance) of the associated reflector can be determined (location of reflectors, wall thicknes

measurement).

Calibration with a straight-beam probe

The reference piece used for calibration is called the Calibration Block, or Standar

Calibration Block, if the block used is standardized. The Standard Calibration Block1, also simpl

referred to as K1 block (according to BS 2704 - A2), has a thickness of exactly 25 mm and is made o

low-alloyed fine grained steel so that it can be used for nearly all types of calibration when similar steelare to be tested.

Fig. 1 Standard Calibration Block 1


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Calibrating the display range

Before working with the USM 36, you have to calibrate the instrument: you have to adjust the materia

velocity and display range and allow for the probe delay depending on the material and dimensions of thtest object.

To ensure a safe and proper operation of the USM 36, it is necessary that the operator be adequatel

trained in the field of ultrasonic testing technology.

Choosing the measuring point

The sound path measurement in the calibration process or in the subsequent echo evaluation proces

depends on the choice of the measuring point which can be set either to flank, tojflank or to peak in th

USM 36. In principle, the peak measurement should be preferred because the measured distances do no

depend on the echo height in that case. However, there are application cases in which the flan

measurement is either specified, or it must be applied for technical reasons, e.g. in many tests using dualelement (TR) probes.

Attention: In any case, the setting of the measuring point must always be identical for the calibration anfor the subsequent test application. Otherwise measurement errors might occur.

Calibration with straight- and angle-beam probes

Case A: With known material velocity

Calibration process

Fig. 2 Transducer with calibration block

Set the known material velocity (function group RANGE for steel the velocity value

5920 m/s).

Couple the probe to the calibration block. Set the required display range using the function RANGE. The calibration echo must b

displayed on the screen.

Position the gate on one of the calibration echoes until the sound path of the echo i

indicated in the measurement line. After this, adjust the setting of the function PROBE DELAY until the correct sound pat

for the selected calibration echo is indicated in the measurement line.

You are carrying out the calibration for the calibration range 100 mm using the calibratio

standard K1 (thickness 25 mm) which is laid down flat.

Set RANGE to 100 mm. Set the known material velocity of 5920 m/s (please see ISO 10863).


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Set the gate so that it is positioned on the first calibration echo (from 25 mm). Read the sound path in the measurement line. If this value is not equal to 25 mm, adjust th

setting of the function PROBE DELAY until it is at 25 mm.

This completes the calibration of the USM 36 to the material velocity of 5920 m/s (233 "/ms) wita calibration range of 100 mm/5" for the probe used.

Case B: With unknown material velocity

Use the semi-automatic calibration function of the USM 36 with the functions of the functio

group AUTOCAL for this calibration case.

The distances between 2 calibration echoes must be entered as default data (se

figure 3). The USM 36 will then carry out a plausibility check, calculate the materiavelocity and the probe delay, and automatically set the parameters.

Calibration process

You have to enter the distances (lines) of two calibration echoes as default settings, lik

in figure 3. The USM 36 will then carry out a plausibility check, calculate the materiavelocity and the probe delay, and set the parameters automatically if the plausibility

given. Otherwise, an error message is given.

Fig. 3

Set the required display range using the function RANGE. The two selected calibration echoe

must be displayed on the screen. Set the range so that the second calibration echo is positioned i

the right half of the screen. Switch to the function group AUTOCAL.

Enter the distances of the two calibration echoes in S-REF 1 and S-REF 2.

Position the gate on the first calibration echo. (A-START). Switch to the function RECORD and press one of the selector keys.

Press one of the selector keys again to record the first calibration echo.

Shift the gate to the second calibration echo.

Switch to the function RECORD again and press one of the selector keys to record the seconcalibration echo.

Example

Set the required display range at 100 mm, using the function RANGE(see fig. 4). Validate pressingbutton left.

The initial value for PROBE DELAYis 0 s(see fig. 4)

Set the known material velocity 5920 m/s (select velocity and pressing button left give you th

possibility to change the value of velocity and after press again button left in the function grou

RANGE, to validate the values made).

Press and switch to the function group CALand select AUTOCAL(see fig. 5).


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Enter the distances (thicknesses) of the two calibration lines S-REF1 (25 mm) and validate the valu

pressing button left. After enter the distance S-REF2 (100 mm) and validate the value pressingbutton left (see fig. 5).

Figure 4 Figure 5

Position the gate A (green line) on the first calibration echo (for gate a start, see figure 5).

Read the sound path (SA^)in the measurement line. If this value is not equal to 25 mm, adjust the settin

of the function PROBE DELAYuntil it is at 25 mm.

To made this press and switch to the function group RANGEand select PROBE DELAYpressbutton left and correct the value of SA^until it is at 25 mm (in this time the value indicated on PROB

DELAYthe value is changing and finally obtain 0.753 s) and after press left button (see fig. 6).

Press and switch to the function group CALand select AUTOCAL and after select RECORDS

REF1 and press to record the first calibration echo (see fig. 5).The recording of the first calibration echo is confirmed by change the function RECORDS-REF1 i

RECORDS-REF2(see figure 7).

Figure 6 Figure 7

Move the gate to the second calibration echo (for S-REF2 SA^= 100mm, see figure 8).

To make the positioning the gate A (green line) on the second calibration echo, press and switch t

the function group GATESand select GATE A , then press button right , after press button le

and modified the value of gate A positioning from 24.19 mm till 96.54 mm, after press button le

again.


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Press and switch to the function group CALand select AUTOCAL and after select RECORDS

REF2, and before,ensure first that the value for SA^ to be 100 mm, and after press to record th

second calibration echo (see fig. 8).The recording of the second calibration echo is confirmed and by change the function RECORD S

REF2in RECORDOFF.If the second echo is not stored, the calibration failed and ERROR MESSAGEdisplay.

The correct calibration is confirmed by the message with the message in line in video inversAUTOCAL COMPLETE (see figure 9).

Figure 8 Figure 9

If you see the message in line in video inverse AUTOCAL COMPLETE (see figure 9), also you caread the material velocity 5920 m/s and probe delay value 0.758 s (see figure 9).

The correct calibration is confirmed by the message AUTOCAL COMPLETE (see figure 9).

The USM 36 will now automatically determine the sound velocity and the probe delay and set th

corresponding functions accordingly.

Note

Each master student must repeat the example presented above

ndt laboratory no04 new usm36

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