A-scan

A Scan at 7mm depth B Scan at 10mm depth C Scan at 13mm depth Fig. 11 Tomography scans of an internal shrinkage at different depths (A B C)... 

Simulations of that kind result in a wide variety of A-scans and wavefront snapshots. The first screening of this material reveals, that the simulations in which the transducer is coupling partly to the V-butt weld and partly to the steel exhibit quite a number of pulses in the A-scans because the coupling at the interface of the weld results — due to the anisotropic behavior of the weld — in a complicated splitting of the transmitted wavefront. The different parts of the splitted wavefront are reflected and diffracted by the backwall, the interface, and — if present — by the notch and, therefore, many small signals are received by the transducer, which can only be separated and interpreted with great difficultie.s. 

Only the simulations in which the transducer is coupling either to the V-butt weld or to the surrounding steel can be analyzed in a simple and intuitive way, which means that the different pulses in the A-scan signals can be related uniquely to the reflection or diffraction of the wavefront at the weld, the backwall, and/or the notch. 

Travel time The larger group velocity for herringbone grain orientation (see Fig. 6(b)) explains the shorter travel time (see A-scans in Fig. 7 and 8). 

The upi-SO screen display ( Figure 7 ) shows the A-scan signal (top) and the resulting B-scan image (bottom) for the tandem arrangement of Figure 6. The flaw reflection is seen on the left. 

To evaluate the VIGRAL method, we scanned steel blocks with simulated flaws using a Flexilrak and a upi-50 instrument. This system allows for rapid and accurate acquisition of the desired data, including the A-scan, B-scan, and C-scan data, and serves to evaluate, offline, the V-scan image (Figure 8). 

Fig. 4.3 Left A-scan of the field variation above the test sample. Right Test sample with different sawcuts. Right below line scan at positions indicated by white arrows.

Fig.l shows the layout of the SPATE 9000 system. It basically consists of a scan unit connected to a signal amplifier. The signals are then correlated with a reference signal derived from a load transducer (e.g. strain gauge, load cell, accelerometer, or function generator). 

The second example shows results obtained with an angle beam probe for transverse waves in coarse grained grey cast iron. Two commercially available probes are compared the composite design SWK 60-2 and the standard design SWB 60-2. The reflector in this example is a side-drilled hole of 5 mm diameter. The A-scans displayed below in Fig. 5 and 6 show that the composite probe has a higher sensitivity by 12 dB and that the signal to noise ratio is improved by more than 6 dB. 

A-scans with a visual evaluation by the tester to be of little significance. New measuring-data-evaluation-procedures were needed to place additional information at the testers disposal. 

Figure 4 presents such a crack indication in the A-Scan-image. The respective A-Scan for a flawless blade is shown in figure 5. In every case the echo from the comer serves as an indication of a good coupling. 

The figures 9 and 10 show the A-Scans of these two steps. Figure 9 presents the velocity measurement of the longitudinal wave parallel to the surface in the first step and figure 10 presents the A-Scan of the thickness measurement in the second step. 

The signal display area contains windows for both the A-scan signal and the Coverage diagram. These windows can be sized by the user, and can be viewed individually or simultaneously. 

The Display area contains the controls to alter A-scan presentation. 

Signal/Coupling. The channel to be displayed in the A-scan window is selected with the appropriate button. 

Rectified/Unrectified. The format of the A-scan signal displayed is selected using the appropriate button. The coupling channel signal is only available as a rectified signal. 

Range Start and Width. Define the start position and extent, in millimetres, of the A-Scan display window. 

Material Veloeity. Defines the velocity, in metres/sec, of ultrasound in the material of the test piece used to convert A-scan signal time to distances within the test piece. 

Sample Frequency. Defines the sampling frequency, in MHz, to be used in the digitisation of the A-scan signal. 

The system should support all the inspection types available in the PSP-3 P-scan, T-scan and Through Transmission, TOFD and A-scan. It should be possible to record data for all the inspection types simultaneously. The developments in computer hardware, in particular disk storage, during the last years have made it feasable to increase the emphasis on the A-scan recording modes. It has also been feasible to extend the P-scan format to include P-scan image storage in a full 3D format, that allows cross-section views to be generated off-line. 

The data are transmitted from the front end processor to the computer in digital form over an ethemet link. The data consist of ultrasonic data, either raw RF A-scans or data processed by the digital signal processor in the PSP-4. In addition to the ultrasonic data, scanner coordinates are transmitted over the ethemet link. 

Figure 5 shows the display in the measure mode. It consists of a detailed A-scan window and a number of smaller windows for display parameters and inspection parameters. The A-scan display may be used as a stand-alone tool or as a tool for measuring parameters required for a specific inspection, e.g. probe parameters, reference echoes, and depth compensation with automatic transfer to the data set. 

The scan mode display is divided into a number of windows, that display the data recorded from the active inspections. In addition, the A-scan data from the ultrasonic probes can be displayed in probe monitor windows, for monitoring the signal quality. Figure 7 shows the scan mode display for simultaneous recording of two P-scan inspections (displayed in the same presentation window) and a T-scan inspection together with 3 probe monitor windows. 

The analyze mode display is similar to the scan mode display used online. Analyze mode includes functions for evaluation of data, e. g. markers, measure functions, zoom function and selection of cross-section views. In addition, A-scan data can be reconstructed into images and displayed. 

Figure 9 P-scan and T-scan images reconstructed from recorded A-scans...

We are confident that any user of this combined evaluation technique, as well as the development of future test standards for manual ultrasonic testing will benefit from this result, because it allows a greater flexibility in the applicable method without loosing reliability. Often an expensive production of a reference block can be avoided and therefore testing costs are reduced. Since all calculations are performed by a PC, the operator can fully concentrate on his most important duty scanning the workpiece and observing the A-scan. Additional time will be saved for the test documentation, since all testing results are stored in the instrument s memory (the PC s hard drive) with full link to the Software World (Microsoft Word, Excel, etc.). 

The system can also numerize the A-scan from the back-wall echo of the specific target, giving the central frequency, relative bandwidth and sensitivity of the 160 apertures. 

In order to get an extremely high resolution and a small dead zone" (after the transmitter pulse) single amplifier states must have a bandwidth up to 90 MHz ( ), and a total bandwidth of 35 MHz (-3 dB) can be reached (HILL-SCAN 3010HF). High- and low-pass filters can be combined to band-passes and provide optimal A-scans. All parameters are controlled by software. 

Fig. 4 presents an A-scan of a 0,15 mm thick steel plate. The RF-A-.scan (sampled with 400 MHz) clearly separates the backwall echoes and demonstrates the high resolution of the HILL-SCAN 3010HF with a 50 MHz transducer. 

Fig. 5, also an A-scan, shows the possibility of the echo-technique for concrete. The interface and backwall-echo of a 20 cm thick concrete specimen are displayed (RF-display). A HILL-SCAN 3041NF board and a broadband transducer (40mm element 0) are used which enable optimal pulse parameters in a range of 50 to 150 kHz. Remarkable for concrete inspections is the high signal-to-noise ratio of about 18 dB. 

The HILL-SCAN 30XX boards enable ultrasonic inspections from 50 kHz (concrete inspections) to 35 MHz (inspection of thin layers) with a signal to noise ratio up to 60 dB. The gain setting range of the receiver is 106 dB. High- and low pass filters in the receiver can be combined to band-passes, so that optimal A-scans are displayed. 

Fig. 4 A-scan of a 0.5 mm steel plate (RF-recording) with 400 MHz sample frequency (HILL-SCAN 3010HF), 0.1 V/div. and lOOns/div.

AIR-1 and PS-4 are used on-site for recording of A-scan data during the on-site inspection. UltraSIM is used for initial ultrasonic simulation, scan path generation and robot simulation (together with the ROBCAD robot simulation software), online control and monitoring of the real AIR-1 robot and finally for 3D reconstruction of ultrasonic A-scan data. 

Online control of the AlR-1 robot is done from within the UltraSIM/UlScan generic scanner control module. With a scanning program as input, the control application is able to calculate and perform cartesian motion for any usual robot manipulator having an inverse solution. The planned robot motion can be simulated off-line before online execution regarding joint and robot position, speed and acceleration. During robot inspection the 3D virtual inspection environment is updated real-time according to the actual robot motion. 

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