Table of Contents

I. Introduction

The P-wave velocity gantry measures the speed at which ultrasonic sound waves pass through materials that are placed between its transducers. The three orthogonal sets of piezoelectric transducers allow the velocity to be determined in the X-, Y-, and Z-directions (Figure 1) 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). A laser measures the position of the top of the split-core section and calculates the position at which the velocity was measured (this is recorded as Offset in the LIMS Database). For discrete sample cubes, the velocity is measured along each of the three axes separately using the PWC. Mini-cores are measured along the axis of the cylinder (X-direction) using the PWC. For discrete samples cubes and mini-cores, all sample information, including offset, is entered by the user when the sample was taken.

Method Theory

Measurement of P-wave velocity requires an estimate of the travel time and an accurate measurement of the ultrasonic P-wave path length through the sample.
Velocity is defined as follows:
velocity = pathlength/traveltime, or
v = dS/dt.
Traveltime measurement is estimated by an algorithm for graphical first arrival pick. An ultrasonic pulser generates a high-impulse voltage, which is applied to the ultrasonic transmitter and thereby induces oscillation of the crystal element within the transducer-specific frequency band. A trigger pulse from the pulser is then applied to the oscilloscope to record the waveform from the receiving transducer.
By measuring the acoustic traveltime of the waveform through a standard of known pathlength and velocity, the difference in expected travel time and actual travel time provides the instrumentation-specific time delay. Subtraction of the system delay time (+ liner material propagation time, if required) from the total traveltime gives the traveltime for the ultrasonic pulse through the sample.
Precise thickness of the sample, or path length, is derived from the readout of an Acuity AR700 laser displacement sensor. The laser offset correction is determined during the calibration process and requires that the system fully close the transducer caliper when the software is opened and activated. Therefore, do not place a core section underneath the transducers when the software is started.
The chisel (bayonet) transducers are fixed at 82.32 mm for the z-axis (downhole) and 31.70 mm for the y-axis (see figure 1). As mentioned above, the x-axis caliper separation is derived from an Acuity AR700 laser.
Traveltimes for samples are calculated as follows:
x-axis = total traveltime – x-system delay time – liner traveltime (section-halves only)
y-axis = total traveltime – y-system delay time
z-axis = total traveltime – z-system delay time
Liner traveltime is calculated as the liner thickness (typically 2.7 mm) divided by the published liner material velocity (cellulose butyrate = 2140 m/s).- Wasn't this experimentally determined?- Currently we are using 2100m/s.

T he travel times for any measurement signal is based on either a user selected location on a graphical display of the first arrival wave (manual pick), or a software auto-pick feature, which attempts to determine the first arrival of the measurement signal.  The auto-pick feature will search for the first instance of a signal stronger than a user set threshold value (milli-amps).  Next it will take the absolute value of the signal and determine where the wave-form crosses the graph's x-axis the 2nd time.  It will then subtract an assumed 1/2 of wave length, and display the pick location on the same graphical display.  This should get the travel-time of the measurement signal.  Verification of the signal and pick location by the user is critical.

II. Procedures

A. Preparing the Instrument

1. Double-click the MUT icon on the desktop (Figure 1a) and login using ship credentials. For more information on data uploading see the "Uploading Data to LIMS" section below.

2. Double-click the IMS icon (Figure 1b). IMS initializes the instrument. Once initialized, the logger is ready to measure the first section.

At launch, IMS begins an initialization process:

• Testing instrument communications

• Reloading configuration values

• Homing the caliper and bayonets. IMP: DO NOT place samples on the track before launching the software. 

After successful initialization, the IMS Control and Instruments' windows appear (Figure 2).

Open

***CAUTION: Make sure there are no samples or body parts underneath any of the sensors when starting IMS***

When first opening the program, all 3 sensors will go through a communication initiation process where they will move down and up. The program will display a warning message (Figure 3a) but will not stop the movement if nothing is detected on the rail.  If an object is detected a warning window will pop up (Figure 3b).

Open

The software home screen allows the user to modify a number of setup and acquisition parameters directly, as well as control the motion of the transducers.

The main window (Figure 4) includes:

1. Sample type and Measurement Axis selection: The user selects the type of sample, while simultaneously selecting the measurement axis via the pictured tiles, the current selection will be highlighted.

2. Graphical Display Tabs:  The RAW, RAW STACKED, RAW ZOOM  tabs will display the measurement signal without mathematical manipulation.  They also display the MANUAL PICK location as a vertical pink line.  The ABS and ABS ZOOM tabs display the absolute value and the uncorrected auto-pick location, which should be
   between the 1st and 2nd hump.  These displays are crucial for evaluating the signal quality and pick locations.

3. Requested Stack and Threshold sliders:

   1. Requested Stack: The number of measurement signals the software will add together with the intent of increasing the signal to noise ratio. Each time it is adjusted a new set of signals will begin stacking.  100 stacks is a typical value.

   2. Threshold:  Voltage level (y-axis of the graphical display mV) that the stacked signal must attain for consideration in a auto-pick.  If the threshold is too low, signal noise may be selected as the first arrival.  If the threshold is too high, the first arrival may be missed and included with the signal noise.

4. Mini Graphs: VELOCITY graph displays the running average of the last 1,000 samples and the TORQUE graph display the torque applied by the actuators to the sample.  The DISTANCE graph displays the AR700 distance readings.

5. Motion Control Buttons: These control the up-down motion of the caliper and bayonets.  The user may select to make slow, fast or automatic movements. EMERGENCY OPEN button will bring up bayonets and caliper simultaneously.

6. Pause Button: By selecting the pause button, the user will be able to make manual picks and have the velocity of that pick displayed.

7. Save Data: The save button is activated when an automatic velocity pick is within the velocity filter range or when a manual pick is made.

8. IMS Control panel (Figure 5): Provides access to utilities/editors via drop-down menus.

Open

Open

Before start measuring assure that the transducers are clean. If not, clean them with water and paper towels.

B. Instrument Calibration

The bayonets and caliper transducers must be calibrated and the system delay determined whenever a check standard is out of range, +/-2.0% of the expected velocity. There is a separate utility for each one:

• The bayonet transducers are calibrated by back-calculating the system delay from the total travel time, for the y- and z-axes, from the transducer separation value and theoretical velocity of distilled water at the temperature of the water bath.

• Calibration of the caliper requires the transducer and system delay to be calibrated concurrently. The transducer separation is measured with a displacement laser.

Caliper Calibration

The Caliper Calibration Utility calibrates the laser offset and the delay of the system at the same time.

Measurements are taken at standards with the same velocity but with different heights. The operator can choose the number of standards used and the material. A linear correction is applied to calibrate the laser offset, while the system delay and velocity is calculated from the time measurements. 

By convention a set of six acrylic standards with increasing sizes (15.07, 20.00, 30.03, 34.99, 34.90 and 45.01 mm) are used. They will be measured one by one, following next steps and the same procedure as an ordinary sample.

To open the Caliper Calibration Utility select: Stations > Caliper Calib. from the IMS panel menu (Figre 5). The Caliper Calibration window will open (Figure 6).

Open

 In the Caliper Configuration window there are 7 row of calibration data which will auto populate from the previous calibration.  You can standards by scanning in new id's and/or you can update the given thickness.  Any changes will available in subsequent calibrations. If the row already has the correct ID and thickness you do need to re-scan the id.

In Figure 6 (item 1) there are 7 round buttons on the left side of each row.  Only one can be selected at a time and the one selected will be updated constantly by values being measured.  When you are satisfied you have the correct time pick, select the next standard to measure.  The previous values are frozen while you measure the remaining samples.  If you reselect that standard the values will be overwritten with the current measurement, so choose wisely.

The button on the right-hand side (Figure 6, item 2) are selected if you want to use that value in the calibration.  Remember you need at least two for calibration but use all 6.  Keep in mind that the program is always re-calculating the calibration values (Figure 9 and Figure 10) and it is ok to select and unselect value to see the affect on the calibration values.  The same with remeasuring just make sure you apply the correct time pick to the correct sample.

Quick step by step

1. Select the standard

2. Optional only if needed

   1. Click Scan Standard 

   2. Use bar code scanner and scan label

   3. Click OK

3. Place the first standard in the caliper.

4. Click AUTO CLOSE

5. Set the threshold to pick the first arrival

6. Set you stack to at least 100 and wait for the time pick to stabilize.  Increase the stack as necessary.

7. When satisfied select the next standard

8. Click AUTO OPEN

9. Repeat steps 2 through 8 for each standard.

10. Select the standards to use in the calibration (can be done at anytime)

11. Click Accept Changes or Cancel Changes

To clear the rows, de-select the rows you want to clear (right-hand Boolean controls) and then click Clear All

Open

How to verify first arrival pick:

Verify the software is picking the first arrival wave in the Raw Stacked graph tab. You can adjust the threshold scale bar to achieve the proper pick location (Figure 8). Observe the graph to verify the system is getting a clean signal.  If you are not getting a clean signal, follow the steps in the trouble shooting section of this guide. Also, verify the auto-pick location in the Absolute Value tab  (ABS or ABS Zoom).  This pick should be at the zero crossing after the first significant wave form above noise (Figure 8). 

Open

Before you Accept

Check the standard's calculated velocity (= inverse of the slope) it should match the known material velocity as follows:

•  Acrylic velocity= 2730 m/s ± 2.0 %

• Aluminum velocity= 6295 m/s ± 2.0 %). 

To calculate the laser offset, the zero contact position offset was determined for the transducer and a small slope correction values (Figure 9).

Open

To calculate material velocity and the system delay value the pick time is measured during the calibration (Figure 10).

Open

Bayonet Calibration 

Because the distance between the bayonets is fixed, only the system time delay needs to be calculated. This is achieved by measuring the velocity in water of known temperature, the difference between the known and measured value is due to system delay.

To open the Bayonet calibration window (Figure 12), select Stations > Y-Bayonet Calib. or Z-Bayonet Calib. from the IMS panel menu (Figure 5).

Open

Open

Open

                                                                                               Figure 12. Y-bayonet and Z-bayonet Calibration windows.  Y-bayonet raw graph tab (left), Z-bayonet raw graph tab (center), Y-bayonet ABS Zoom graph tab (right).

To calibrate the bayonets:

1. Fill the bayonet calibration liner with DI water (Figure 13).  The water level must be high enough that the black transducer pads on the bayonets can be placed below the water line without touching the liner itself.  The water should be at room temperature if possible.

Open

C. Set Measurement Parameters

Configuration values should be set during initial setup and configuration by the physical properties technician.  There should be no need to change these values unless the configuration files is corrupted.  This window allows the user to view and modify the physical configuration values for the Velocity system, as well as the liner correction values and the velocity filter settings.

To open the Velocity instrument setup window (Figure 13), select Stations > Velocity Setup from the IMS panel menu (Figure 5).

1. Ensure the values in the window are set as shown in Figure 13.

   1. Caliper and Bayonet Offsets: Physical offset from the laser zero point to the center of the transducer pair for the three stations (caliper, bayonet Y, bayonet Z). This measurement will not change unless the station location is physically changed.

   2. Axis Separation: Physical distance between the bayonet transducer pairs. This measurement should never change unless the bayonets holders are physically changed.  The X-Axis is not shown because its separation is determined during calibration and measurement by the AR700 laser.

   3. Liner Correction: The liner delay value as determined experimentally based on the liner thickness and velocity measurements on the liner material.

   4. Velocity Disable "Save" Filter: When the filter is enabled, the save feature is inactive for any automatic velocity picks outside of the velocity range set.  

2. Click Ok to accept to save the changes and write them to the configuration file.  Click Cancel to revert to previous values.  NOTE: Only one configuration file exists in the IMS folder.  Every save will overwrite the config file.

Open

D. Preparing Sections & Samples

A temperature-equilibrated split core section-half  in it's liner is placed on the core track.  The user positions the section half under the sensor, places a small piece of glad wrap on top of the core, and triggers the measurement from the software control panel. The measurement is taken continuously, with the recorded result representing the average of several thousand determinations. 

On semi-lithified and lithified samples, loose material may be present on the core cut surface.  Before placing the working half in the core tray, make sure the surface is clean (lightly brush away any material with a Kimwipe or paper towel).

A barcode reader records all relevant sample information, which is used for the data upload into LIMS. A laser sensor measures the distance to the top of the section-half and determines the sampling interval from the known sensor offsets. 

Discrete measurements are discussed in the Caliper Measurement section below.  When inserting the bayonets or closing the calipers into/on a sample, the graph should be monitored for signal quality.

Caliper Measurement

• The sample is placed between 2 flat, 1 inch diameter sensors that squeeze firmly onto the specimen to ensure good contact.  De-Ionized (DI) Water is introduced between the sample and sensors to aid in signal propagation. For section-half measurements, place a small piece of Glad Wrap over the desired Caliper measurement location.  This will keep the transducers clean.

• One sensor acts as a transducer and the other as a receiver to record velocity measurements at a rate of 0.5 MHz.

• To measure discrete samples in multiple axis, the sample is rotated by the user to each axis (x, y, and z-axis) and measured separately.

Bayonet Measurement

• Two pairs of piezoelectric transducers, set at 90° to each other, are inserted into the unconsolidated or semi soft section-half sediment. The sensors (black circles) must be at least partially buried in the material.

• One of each pair of sensors acts as transducer and the other as receiver to measure velocity in two directions simultaneously.

Data Quality

Velocity data quality is affected by several variables.  The signal quality and pick locations should be consistently monitored by the user during every measurement.

• Quality of the acoustic coupling between the core material and the sensor transducers. Note: Use water to increase the quality of the contact.

• Quality of the coupling between both the transducer and the core liner and between the core liner and sample. Note: Use water to increase the quality of the contact.

• Consolidation of the sediments; non-cohesive sediments containing microcracks or gas voids cannot be measured accurately.

E. Making a Measurement

When scanning label barcodes on the gantry system, there are specific label types that work best.

For measurements with the bayonets and the caliper on a section half, user must use a section half label.  

For measurements on discrete samples we recommend label types: Mad Residue Small, PMAG Cube label (sample type must be CUBE, CYL, or OTHR), Mad Residue Large, or Sample Table labels (the large format).  Other label formats may not parse properly.  Note that the MAD label parsing expects the container number in the name field.  If the name field is populated with other text, the label parsing may fail.

For discrete samples shared between MAD and PMAG, use the PMAG Cube label or a sample table label.  Mad residue labels WILL NOT parse for shared samples.

Currently the instrument is being upgraded, some of the measurement options or sample information input are not available.

a) Caliper Measurements

The caliper can be used to measure section half and discrete cube samples. Before measuring samples, be sure the samples are properly prepared and the system is calibrated.  Retaining the correct "up" direction is critical for axis determination, and for other systems like P-mag orientation; make sure the sample has the "up" direction marked on it.

Section halves measured on the Caliper station are working half sections placed on the track with the blue end cap (top of section) toward the AR1000 laser.  The laser measures the distance to the top of the section and the software calculates the offset to the measurement based on the known section length.  

Discrete samples measured on the Caliper station are hard material that has been cut from the core as cubes, minicores, or slabs. Because the material can be measured in various orientations, the user must select the measurement axis.
Traveltime is calculated as total traveltime minus x-system delay time. Discrete sample measurements are not corrected for the core liner.  The offset recorded in LIMS is the top offset of the discrete sample.  The AR1000 laser is not used for discrete measurements. The transducer separation is measured with the displacement laser, as it is for the sample half measurement.  For discrete samples the axis of measurement is selected for each measurement.

Section Half Measurement Procedure

1. Place section half below the caliper.  Take care to not drag the core against the bayonets while placing the core on the track.

2. Place a drop of distilled water below the section on the transducer and on top of a piece of Glad Wrap on top of the section to improve contact between the caliper and section.  Note: Placing Glad Wrap is not required.  This is only to improve signal quality.

3. Select the proper instrument and measurement axis button (Caliper SHLF X-axis)

4. Close the transducer onto the core until contact is made.  Do not over close the caliper on the section half.  

5. Verify the automatic velocity pick in the Raw Stacked graph tab (Figure 4). You can adjust the threshold scale bar to achieve the proper pick location as long as the signal is not too noisy.  The user may want to verify the auto-pick location in the Absolute Value tab (ABS or ABS Zoom). This pick should be at the zero crossing after the first wave form.

6. Select Save Data.  A sample information window will appear (Figure 14).

7. Scan the section half barcode label to populate the fields of the sample information box.

8. Verify the measurement offset.  

   1. If the offset is incorrect, select CANCEL, or enter the offset manually.  The laser range finder sometimes struggles to return a proper offset if the end cap is not opaque or if the core is not flat on track. Try adding a post it note or opaque end cap to the section half if the laser returns the wrong offset.

9. Select SAVE DATA.

This procedure can also be used for whole rounds or pieces of section halves, but this is rarely used.  The software assumes that the whole round piece or section half piece is not within a core liner and will not correct for a liner velocity.  Scan the section half label when entering the sample ID information. 

Open

Discrete Sample Measurement Procedure

For each axis to be measured:

1. Place a small drop of water on the lower caliper transducer

2. Place the discrete sample on the caliper and add a drop of water to the top of the sample

3. Select the proper instrument and measurement axis button (Caliper X-Axis, Caliper Y-Axis, Caliper Z-Axis).

4. Lower the upper caliper transducer onto the specimen.  Do not apply unnecessary force on the specimen as it may fracture, or cause physical variation in the caliper system and measurement.

5. Verify the automatic velocity pick in the Raw Stacked graph tab (Figure 4). You can adjust the threshold scale bar to achieve the proper pick location, or pause the system to do a manual pick.  The user may want to verify the auto-pick location in the Absolute Value tab (ABS or ABS Zoom). This pick should be at the zero crossing after the first wave form.

6. Select Save Data.  The sample information window will open (Figure 15).  Note that the measurement offset will not be populated.  The laser range finder is not used for discrete measurements.

7. Scan the discrete sample barcode label to populate the fields of the sample information box.  The sample's top offset in the section-half will be used as the measurement location, enter it manually.

8. Select Save Data.

If the material to be measured is a whole piece removed from the liner (rarely used), select Caliper Piece X-Axis in Step 3. The measurement offset field in the sample information window is selectable.  Scan a section half label and enter the offset of your measurement from top of the core.

Open

b) Bayonet Measurements

Before measuring samples, be sure the samples are properly prepared and the system is calibrated.

1. Place section half below the bayonets.  Take care to not drag the core against the bayonets while placing the core on the track.

2. Select the proper instrument and measurement axis button (Y or Z bayonet)

3. Lower the selected bayonets into the section half until the black transducers are below the sediment surface.  A piece of glad wrap can be placed on the cut surface before inserting the bayonets, with water then added to aid in signal propagation.  The glad wrap is to prevent water from being absorbed into the material.

4. Verify the automatic velocity pick in the Raw Stacked graph tab (Figure 12). You can adjust the threshold scale bar to achieve the proper pick location, or pause the system to do a manual pick.  The user may want to verify the auto-pick location in the Absolute Value tab (ABS or ABS Zoom). This pick should be at the zero crossing after the first wave form above noise.

5. Select Save Data.  A sample information window will appear (Figure 14).

6. Scan the section half barcode label to populate the fields of the sample information box.

7. Verify the measurement offset.  

   1. If the offset is incorrect, select Cancel and select Save Data again, or insert it manually.  The laser range finder sometimes struggles to return a proper offset if the end cap is not opaque or if the core is not flat on track.  Try adding a post it note or opaque end cap to the section half if the laser returns the wrong offset.

8. Once the measurement offset is verified.

9. Select Save Data.

c) Manual Pick

In some cases, a user may wish to make a manual pick.  This usually occurs because the automatic pick is unsuccessful, often due to a noisy signal. 

Often, the Save Data option will not be available for a bad automatic velocity pick, because the values are outside of the velocity filter range. Figure 16 shows an example of a situation in which adjusting the threshold value could not overcome a large peak at the start of the measurement. Using the manual pick, the user is able to override the computers pick.  Both the automatic velocity pick and manual pick are recorded in LIMS.  This option is available for all measurements on the Velocity-Gantry track. 

IMPORTANT: It is important that all users, on both shifts, agree ahead of time on the proper manual pick location.  If they do not, each user is likely to induce a small offset in velocity due to inconsistent pick locations; the zoom tools in the lower left of the graph may help better locate the wave forms. First arrival location (Figure 17) is not as straight forward as one might assume. 

The manual pick location should be relatively obvious so anyone can see it above the noise, because noise is likely to be high when auto-pick doesn't work.  Then any necessary offset to correct can be applied in post processing.  The agreed upon manual pick location and any offset correction in first arrival should be documented in the scientists' methods section. 

To make a manual pick:

1. Place sample in the selected instrument

2. Once a signal is visible on the graphical display, select the Pause button in the lower left corner of the main window (Figure 4).

3. The manual pick tab will be displayed on the screen (Figure 16).

4. Slide the red line along the x-axis to the desired pick location.  The line should be placed at the first arrival. To help select the first arrival, the plot can be zoomed in using the graph palette zoom function in the lower left corner of the graphical display.

5. Verify the Velocity-manual value is reasonable for the material measured.

6. Select Save Data.  The sample information window will open.

7. Scan the sample barcode label and save the data to the LIMS database.

To exit the manual pick and return to the automatic velocity pick, press the Play button.

Open

Open

F. Evaluating your Measurement

Running a Standard as a QAQC Check

You can run a standard to verify if the instrument is measuring correctly. There are three materials available as a standard: Aluminum and acrylic are used on the caliper, and a core liner with D.I. water on the bayonets.

Expected velocities for each standard: 
Aluminum 6295 m/s (+/- 63 m/s)
Acrylic 2730 m/s (+/- 27 m/s)
Water 1480 m/s (+/- 7 m/s)

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.

G. IMS Utilities

a) Motion Utilities

The available motion utilities are found under the Motion menu from the IMS panel menu (Figure 5). 

The user may home each instrument separately using the Home Caliper, Home Y-Bayonet, Home Z-Bayonet options or home both bayonets and the caliper at the same time using the Home All command.

b) AR1000 Laser Utility

To open the AR1000 utility window (Figure 18), select Motion> AR1000 Utility from the IMS panel menu (Figure 5).  This utility is useful when a user is trying to determine if the laser is correctly reading the distance to the center of each instrument.

If the mean distance shown does not agree with the instrument offset in the Velocity Setup Window (Figure 13), the offsets reported in the database will be incorrect.

The utility immediately begins reading the AR1000 laser output and averaging the values collected once the utility is opened.

To check the instrument offsets, place an object in the center of the instrument in question, i.e. the caliper.  The object surface should be at the center of the instrument.  An end cap works well as long as it is opaque. A tape measure can also be used to independently verify the offset value.

Open

c) AR700 Displacement Laser Utility

To open the AR700 utility window (Figure 19), select Stations> AR700 Utility from the IMS panel menu (Figure 5). 

Use this utility to determine if the AR700 displacement laser is returning accurate distances.  The readings from this laser are used as the distance values in the velocity calculations.  Inaccurate readings from the laser will cause error in the velocity readings.  

The AR700 is mounted on the Caliper actuator.  The more the Caliper is closed, the smaller the laser distance returned.  It is recommended that the objects used for testing are similar in size to the samples being measured.

Open

d) EXLAR Utility

This utility allows to control the movement and change the parameters of the three Exlar actuators: Bayonet Z, bayonet Y and Caliper.

To open it, on the main window, go to: Motion > EXLAR Utility. TRITEX Configuration Utility window will open (Figure 20).