Introduction
The P-wave velocity gantry measures the speed at which ultrasonic sound waves pass through materials that are placed between its transducers; this includes section halfs, discrete samples, and mini-cores.
The three orthogonal sets of piezoelectric transducers allow the velocity to be determined in the X-, Y-, and Z-directions on working-half split-core sections. The P-wave bayonets (PWBs) measure the velocity along the core (Z-direction) and across the split-core face (Y-direction), and a P-wave caliper (PWC) measures the velocity perpendicular to the split-core face (X-direction) (Figure 1).
For discrete sample cubes, the velocity is measured along each of the three axes separately using the PWC; whereas, mini-cores are measured along the axis of the cylinder (X-direction). For discrete samples cubes and mini-cores, all sample information, including offset, is entered by the user???.
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- Make sure the sensors are clean.
- For section halfs, place the desired measurement location underneath the desired sensor. Make sure that the section is oriented with the blue end-cap towards the laser (Figure 2).
Figure 2.- Correct core position.
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- Select the measurement type. Seven different measurement configurations are available (Figure 3). Currently measures to whole round sections are not available.
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2. Depending on measurement, insert the bayonets or close the caliper onto the sample. Click the instrument motion buttons to slowly lower the transducers to the sample (Figure 4). The autoclose button functions for either the caliper or the bayonets.
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3. The program continually updates the velocity calculation and displays the value (Average of the sets of stacks) in the Velocity-Auto box (Figure 5).
Figure 5.- Data display on Velocity-Auto box.
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It also displays a signal graph with a red vertical auto-pick location line (Figure 6), where the program's algorithm has placed the first arrival wave.
Note: Typical slide bar settings are 100 for the stack bar and10mV for the threshold bar.
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The program will automatically calculate the velocity from its auto-picked first arrival wave. It will , display the value in the "Velocity – Auto" box (see Figure 35) and display and the auto-pick location line (Figure 127). If either of these do are not look good, the following expected results, follow steps A, B , and C are suggested, in that order.
A.
For further information see the User Manual or ask the Physical Properties Technician.
Figure 7.- Raw Stacked signal display with red line indicating auto-pick location.
A) First Arrival Picking
The
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signal graph has several different displays, all accessible by clicking on different tabs at the top.
To zoom on the graph, pause the program and click on the magnifying glass in the Graph Tools box, Figure 12.
To evaluate the auto-pick velocity, you need to look at two graphs.Auto-pick location line
The signal graph has several different displays, all accessible by clicking on different tabs at the top. Tip, you can zoom by pausing the program and clicking on the magnifying glass in the Graph Tools box, Figure 12. The first graph you need to examine is the stacked raw value ("RAW STACKED" tab), (Figure 11). Here you see the stacked measurements display with a vertical red line showing the location of the programs auto-pick of the first arrival wave. If the red line appears very near the first significant deviation from 0 on the Y-Axis, then the value is very likely reliable.
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Figure 12. Raw Stacked signal display with red line indicating auto-pick location.
Uploading Data to LIMS
- Click the MUT Icon. Log in using database credentials.
- Once activated, the list of files from the C:\DATA\IN directory is displayed. Files are marked ready for upload by a green check mark (Figure 7).
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This document originated from Word document Gantry Velocity: Quick Start Guide Version 1.0; Version 372 written by A. de Loach (2017-12-16). Credits for subsequent changes to this document are given in the page history.
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P-Wave Quick Start Guide v2020
PWV_QSG_372.docx: A Word document of the Gantry Velocity: Quick Start Guide
Evaluating Your Measurement
The program will automatically calculate the velocity from its auto-picked first arrival wave. It will display the value in the "Velocity – Auto" box (see Figure 3) and display the auto-pick location line (Figure 12). If either of these do not look good, the following steps A, B, and C are suggested, in that order.
A) First Arrival Picking
The program's method of automatically picking the first arrival from the signal is a multi step process. For more information on how an auto-pick is made, see the user manual or ask the Physical Properties Technician.
To evaluate the auto-pick velocity, you need to look at two graphs.Auto-pick location line
The signal graph has several different displays, all accessible by clicking on different tabs at the top. Tip, you can zoom by pausing the program and clicking on the magnifying glass in the Graph Tools box, Figure 12. The first graph you need to examine is the stacked raw value ("RAW STACKED" tab), (Figure 11). Here you see the stacked measurements display with a vertical red line showing the location of the programs auto-pick of the first arrival wave. If the red line appears very near the first significant deviation from 0 on the Y-Axis, then the value is very likely reliable.
Figure 12. Raw Stacked signal display with red line indicating auto-pick location.
However, if the auto-pick location is off, or the velocities don't seem right, you may need to adjust the threshold voltage, which corresponds to amplitude on the Y-Axis. This will move the auto-pick location. Go to the "ABS ZOOM" display (Figure 13). Here you see a zoomed window of the absolute (ABS) signal value. Verify the auto-pick location is at the zero crossing after the first significant wave above noise levels. This wave may be very difficult to determine. If the pick line is not at the zero crossing after the first non noise peak, use the threshold slide bar on the right to adjust its location; NOTE the program must be running for changes to apply. As you move the threshold you should see a red horizontal line, indicating the threshold value, move up and down. When you change the threshold value enough to go over or under a neighboring peak, the auto-pick location will change in steps and your velocity will be recalculated. It is important to remember that in this display (ABS ZOOM), you are not trying to pick the first arrival peak, but the zero crossing after it. Because of the weakness of the first arrival peak, it is often difficult to resolve, which we can't do much about. However, we can reduce the error by picking a consistent location. Once picked, the program will then apply a standard half-waveform correction to get the first arrival location.
Figure 13. ABS Zoom display with threshold slide bar and uncorrected auto-pick location.
Once you have adjusted the threshold and got the auto-pick to the correct location, go back to the "RAW STACKED" or other raw displays and verify the red line is at the first arrival wave. If satisfied, you can now save your data. If the velocities and picks still don't look right, you have the option of manually picking the first arrival.
B) Manual pick
In order to do a manual pick, first pause the program. Now the "MANUAL PICK" display tab will be visible above the signal graph (Figure 14). Select that display; find the graph toolbox in the lower left corner of the display. If you need to zoom in, use the magnifying glass tool. Next, click on the crosshair tool on the far left side of the toolbox bar (Figure 14). Hover over the dotted yellow-green vertical pick line. When the icon changes, click and drag the pick line to the desired location and release. You will now see that the "Velocity –Manual" box has updated with the manually picked velocity. Both the auto-pick and manual pick velocities are saved simultaneously to the database when you upload.
Figure 14. Manual Pick display with yellow-green manual pick location.
C) Running a Standard as a QAQC Check
If you are not confident that the gantry system is running normally, you can run one of our standards to verify the instrument is giving the expected velocities for the material. We have three materials available as a standard. Aluminum and acrylic are for the caliper, and a core liner with D.I. water for the bayonets. The expected velocities for each are below:
Aluminum 6295 meters/sec (+/- 63 m/s)
Acrylic 2730 meters/sec (+/- 27 m/s)
Water 1480 meters/sec (+/- 7 m/s)
The typical allowable deviation is 1% for the caliper and 0.5% for the bayonets. There will also be differences based on temperature, especially for water and aluminum. If the standard values are out of this range, ask a technician to help calibrate the instrument.
Viewing Your Data
To view your data, or most data around the lab, you can use the LIMS Online Report Portal (LORE) or the LIMS data viewer (LIVE) through a Firefox web browser. It is good practice to check once per core or after each upload to check that your data has made it into the database.
With Firefox open, click on the toolbar link "LIMS Online Reports" or go to the "Download LIMS core data" link on the ship's homepage (Figure 15). Once in LORE, click through the search options and sample filters to find your data (Figure 16). You can leave the window open in the background and simply refresh next time you want to check your data.LORE gives you a fast way to download core data from most lab systems aboard the JR. You can export directly to an Excel or .csv file. 
Figure 15. Ship's Home page with links to LORE and core data. 
Figure 16. LORE, with P-Wave caliper data downloaded by hierarchy search.
Calibrating the PWV CALIPER
To begin calibration for the PWV select the "Caliper Piece X-Axis"Click on the "Stations" tab to access the drop down menu, then click on "Calibrate Calipers".Enter the Aluminum width- 30 mm, place Aluminum Standard (30mm) on the transducer.Close transducers slowlyClick "Laser Offset" tab (blue) Aluminum Standard field should be 6295.00Click "Determine System Delay" tab (purple)Adjust "threshold" till the redline on the graph is at first arrival pointThe Velocity should be very close to 6295.00. If so, then "Accept Changes".
Credits
This document originated from Word document Gantry Velocity: Quick Start Guide Version 1.0; Version 372 written by A. de Loach (2017-12-16). Credits for subsequent changes to this document are given in the page history.
Archived Versions
P-Wave Quick Start Guide (*.pdf)
PWV_QSG_372.docx: A Word document of the Gantry Velocity: Quick Start Guide