Dakota PVX User Manual

OPERATION MANUAL

DAKOTA ULTRASONICS

PPVVXX

Precision A / B Scan Thickness Gauge

P/N P-157-0002 Rev 1. 10, January 2008

Dakota Ultrasonics

CHAPTER ONE INTRODUCTION.......................................................................1

CHAPTER TWO QUICK STARTUP GUIDE........................................................2

CHAPTER THREE KEYBOA RD, MENU, & CONNECTOR REFERENCE.......12

CHAPTER FOUR PRINCIPALS OF ULTRASONIC ME ASUREMENT .............22

CHAPTER FIVE SELECTING THE MEASUREMENT MODE..........................27

CHAPTER SIX MAKING MEASURE MENTS.....................................................30

CHAPTER SEVEN USING THE A-SCAN & B-SCAN DISPLAYS.....................42

CHAPTER EIGHT THRU PAINT MEASUREMENT TECHNIQUE....................68

CHAPTER NINE ADDITIO NAL FEATURES OF THE PVX...............................71

CHAPTER TEN DATA STORAGE – SETUP, EDIT, & VIEW GRIDS...............81

CHAPTER ELEVEN SETUPS – CREATE, STORE, EDIT, & RECALL............99

CHAPTER TWELVE USING THE UTILITY SOFTWARE................................106

APPENDIX A - VELOCITY TABLE ...................................................................107

APPENDIX B - SETUP LIBRARY.....................................................................109

CHAPTER ONE
INTRODUCTION

The Dakota Ultrasonics model PVX is a visual precision A / B scan ultrasonic
thickness gauge. Based on the same operating principles as SONAR, the PVX is
capable of measuring the thickness of various materials with accuracy as high as ±

0.0001 inches, or ± 0.001 millimeters. The principle advantage of ultrasonic
measurement over traditional methods is that ultrasonic measurements can be

performed with access to only one side of the material being measured.
Dakota Ultrasonics maintains a customer support resource in order to assist users

with questions or difficulties not covered in this manual. Customer support may be
reached at any of the following:

• Dakota Ultrasonics Corporation,
1500 Green Hills Road, #107 Scotts Valley, CA
95066 USA

• Telephone: [phone]

• Facsimile: [phone]

• www.dakotaultrasonics.com

1.1 Disclaimer

The PVX is a full-featured scope that allows a great deal of control over the
functionality and electronic performance of the instrument. However, as this provides
the user greater control and versatility for a variety of applications, it also requires
that the user be comfortable with operation and waveform interpretation of the
instrument. It is strongly recommended that the contents of this manual be read in its
entirety. It is also recommended that a sufficient amount of time be allocated to
working with the instrument in a test environment prior to use in the field.
Responsibility for proper use of the instrument and recognition of this phenomenon
rest solely with the user of the instrument.

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CHAPTER TWO
QUICK STARTUP GUIDE

Turn the PVX on and off using the swit ch located on the bottom right corner of the
keypad. When PVX is initially turned on, a flash logo and blinking lights will be
displayed prior to entering into the main measurement screen. Note: This section is
primarily written as a basic startup guide only.

2.1 Selecting The Transducer Type

The first step in using the PVX is to select the transducer type stored in a setup.
There are 14 factory setups containing different transducer types that can be loaded,
modified and stored in a new setup location. By selecting the transducer type from a
predefined setup list, the PVX can recall specific properties about the transducer,
setup the display area and predefined scope settings. Note: Once the transducer
has been selected, the PVX will store and recall th is setup, containing the transducer
type, every time the PVX is powered on/off. This setup will only change if the user
physically selects another setup from the list. Therefore, if you have previously gone
through this section and selected the appropriate setup, proceed to the next section.
Use the following steps to select your setup (transducer type):

Selecting a Setup for use with a specific Transducer Type

1) Press the MULTI MODE key once to activate the load setup list containing
the transducer types and settings.

2) Use the UP and DOWN arrow keys to scroll through the setup list until the

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target setup is highlighted.

PVX Precision Visual Thickness Gauge

3) Press the ENTER key to display the confirmation screen.

4) Press the OK key to select the setup and return to the measure screen, or

ESC to cancel the selecting a setup.

2.2 Calibration

The next step is to calibrate the PVX to the material and transducer being used. If a
sound velocity is not known, the PVX can be calibrated to a known thickness sample.
This demo will briefly explain each of possible calibration techniques. Read through
the various calibration techniques and select one of the following:

Known Velocity

If the material velocity is known, the user may wish to simply enter the velocity
number into the PVX, rather than have the PVX calculate the velocity value using a
know thickness. The steps for entering the velocity are outlined below:

Using a Known Material Velocity

1) Press the MENU key once to activate the menu items tab. Press the MENU
key multiple times to tab right and the ESC key multiple times to tab left until
the CAL menu is highlighted and displaying the submenu items.

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2) Use the UP and DOWN arrow keys to scroll through the sub menu items
until VELOCITY is highlighted.

3) Press the ENTER key to display the Digits Edit Box.

4) Press the UP and DOWN arrow keys to scroll the highlighted value.

5) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

6) Repeat steps 4 & 5 until the velocity number is correctly displayed.

7) Press the OK key to set the velocity and return to the menu screen, or ESC
to cancel entering the velocity.

8) Finally, press the MEAS key to return to the measurement screen and begin
taking readings.

Known Thickness

Sometimes the sound velocity of a material is not known. In this case a sample with
a known thickness can be used to determine the sound velocity. It would be very
handy to carry a set of mechanical calipers to use in conjunction with the PVX for
calibration in the field:

Using a Known Thickness

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PVX Precision Visual Thickness Gauge

1) Physically measure an exact sample of the material or a location directly on
the material to be measured using a set of calipers or a digital micrometer.

2) Apply a drop of couplant on the transducer and place the transducer in
steady contact with the sample or actual test material. Be sure that the
reading is stable and the repeatability indicator, in the top left corner of the
display, is fully lit and stable. Press the MENU key once to activate the
menu items tab. Press the MENU key multiple times to tab right and the
ESC key multiple times to tab left until the CAL menu is highlighted and
displaying the submenu items.

3) Use the UP and DOWN arrow keys to scroll through the sub menu items
until ONE POINT is highlighted.

4) Press the ENTER key to display the Digits Edit Box.

5) Press the UP and DOWN arrow keys to scroll the highlighted value.

6) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

7) Repeat steps 5 & 6 until the known thickness value is correctly displayed.

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8) Press the OK key to calculate the velocity and return to the menu screen, or
ESC to cancel entering the velocity.

9) Finally, press the MEAS key to return to the measurement screen and begin
taking readings.

Note: CHECK YOUR CALIBRATION! Place the transducer back on the
calibration point. The thickness reading should now match the known
thickness. If the thickness is not correct, repeat the steps above.

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PVX Precision Visual Thickness Gauge

Basic Material Type

If the material velocity is unknown, and a sample thickness cannot be taken from the
material, the user may opt to choose a basic material type from a list with
approximate velocity numbers. It’s important to note that these velocities will not
always be an exact representation of the material being tested. Use these values
only if a close approximation is acceptable. Follow the steps below to select a basic
material type:

Selecting a Basic Material Type

1) Press the MENU key once to activate the menu items tab. Press the MENU
key multiple times to tab right and the ESC key multiple times to tab left until
the CAL menu is highlighted and displaying the submenu items.

2) Use the UP and DOWN arrow keys to scroll through the sub menu items
until MATERIAL is highlighted.

3) Press the ENTER key to display the list of material types.

4) Press the UP and DOWN arrow keys to scroll through the material list until
the appropriate material is highlighted.

5) Press the ENTER key to display the confirmation screen.

6) Press the OK key to select the material and return to the menu screen, or
ESC to cancel the material selection.

7) Finally, press the MEAS key to return to the measurement screen and begin
taking readings.

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2.3 Measure

The PVX is now ready to measure. There are four different measurement view
options, each with a specific purpose. The steps below outline how to toggle
between the different view mode options:

Selecting the Measurement View Option

1) Press the MENU key once to activate the menu items tab. Press the MENU
key multiple times to tab right and the ESC key multiple times to tab left until
the DISP menu is highlighted and displaying the submenu items.

2) Use the UP and DOWN arrow keys to scroll through the sub menu items

until VIEW is highlighted.

3) Use the LEFT and RIGHT arrow keys to scroll the view options.

4) Once the view is displayed, press the MEAS key to return to measurement

mode.

RF: Is useful to see exactly what the signal looks like directly around the detect
point. This view is the preferred view for precision measurements, as it allows the
user to view smaller ranges (zoomed in) around the detection point (displayed as a
vertical dashed line). This can be done manually by adjusting the delay and width
settings. It also provides the user with the ability to view and select either the positive
or negative polarity option.

RECTIFIED (RECT): Displays the entire range being scanned. This screen is useful
to “get the big picture” when viewing wide ranges (zoomed out). The point which is

triggering the digital thickness reading (called the detect) is displayed as a vertical
dashed line.

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PVX Precision Visual Thickness Gauge

BSCAN: The Time Based B-Scan provides the user with a cross sectional view of
the mat erial being tested. This mode is useful when there is concern regarding the
profile of the blind surface.

DIGITS: Displays the digital thickness value using a larger font size. This view is
useful when the PVX is being used as a basic precision thickness gauge following

the initial setup using the scope.
Once the view has been selected according to the application requirements, the

delay and width of the screen will potentially need to be adjusted, if the view has
been set to RF, RECT, or BSCAN. Use the following steps to adjust these settings

directly from the measurement screen as follows:

Adjusting the Delay & Width

1) Press the MEAS key once to activate the measure menu items. Press the

MEAS key multiple times to move right and the ESC key multiple times to

move left, until the either the DELAY or WIDTH cell is highlighted.

2) Use the UP, DOWN, LEFT, or RIGHT arrow keys to scroll the DELAY and

WIDTH values.

3) Repeat steps 1 & 2 until the range is correctly being displayed.

Alternatively, the DELAY and WIDTH values can be changed using the Digit
Edit Box as follows:

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1) Press the MEAS key once to activate measure menu items. Press the

MEAS key multiple times to move right and the ESC key multiple times to
move left, until the either the DELAY or WIDTH cell is highlighted.

2) Press the ENTER key to display the digits edit box.

3) Press the UP and DOWN arrow keys to scroll the highlighted value.

4) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

5) Repeat steps 3 & 4 until the DELAY or WIDTH value is correctly displayed.

6) Press the OK key to set the DELAY and WIDTH value and return to the
measure screen, or ESC to cancel entering the DELAY or WIDTH value.

7) Finally, press the MEAS key to return to the measurement screen and begin

taking readings.

Note: The DELAY & WIDTH can also be adjusted from the menu tab items.
However, using the hot menu keys is the easiest method.

RF RECTIFIED

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PVX Precision Visual Thickness Gauge

B-SCAN DIGITS

In the upper left corner of each of the mode photos above, is the repeatability
indicator. The repeatability indicator is represented by six vertical bars and
represents how repeatable the measurements are. In regular measurement mode,
the PVX makes 4 measurements a second. In scan mode, the PVX makes 32
measurements a second. When the PVX is idle, only the left vertical bar and the
underline will be displayed. However, when the PVX is making a measurement, five
or six of the bars should be displayed on the repeatability indicator. If fewer than five
bars are showing, the PVX is having difficulty achieving a stable measurement and
the thickness value displayed is potentially be unstable. Another thing to note is the
vertical broken line in the RF and RECTIFIED photos above. This line represents the

actual point of detection. The PVX uses a zero crossing or flank detection method,
and presents the actual point of measurement on the display.

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CHAPTER THREE
KEYBOARD, MENU, & CONNECTOR REFERENCE

3.1 Menu Key (Operation & Sub Menus )

The Menu key activates the primary menu structure containing 9 menu tab groups.
These tab groups then contain sub menu items, or functions. The sub menu items
have been organized in tab groups according to how closely they are related to the
individual tab group names. Let’s first get familiar with how to move around in these
tabs before continuing on to the sub menu functions. This procedure is outlined
below:

Activating and Getting Around in the Menu Items

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PVX Precision Visual Thickness Gauge

1) Press the MENU key once to activate the menu items tab. Press the MENU

key multiple times to tab right, and the ESC key multiple times to tab left
until the desired tab group is highlighted and displaying the submenu items.

Now that your familiar with activating and moving amongst the tab groups, let’s have
a look at how to move around in the sub menu items as follows:

Getting Around in the Sub Menu Items

1) Use the UP and DOWN arrow keys to scroll through the sub menu items
until the desired function is highlighted.

2) Depending on which function is highlighted, use the LEFT, RIGHT, and
Enter keys to scroll the options or activate the Digit Edit and List Box

options.

The sections to follow will provide the user with an explanation of the sub menu
functions:

3.2 Probe – Menu

Zero: The PVX is zeroed in much the same way that a mechanical micrometer is
zeroed. If the PVX is not zeroed correctly, all of the measurements made using the

PVX may be in error by some fixed value. Refer to the section on page 33, for an
explanation of this important procedure.

Note: This function is only used when using a contact style transducer with a pulse­echo contact setup selected. All the other transducer types use multiple echo

modes, and the zero function is not needed.
Pulse: The PVX has an adjustable pulse width for both high penetration and
resolution applications. The pulse width refers to the duration of time the pulser is

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on. The options are Spike, Thin, and Wide. Refer to page 71 for a further
explanation.

3.3 CAL – Menu

Units: Toggle between English or Metric units and low and hi resolutions. The

readout will change from inches to millimeters (IN, IN HR, MM, MM HR). The high
resolution options are indicated with HR following the units, and offer an additional
decimal place of overall resolution (i.e. IN = .001” and IN HR = .0001”).

Velocity: Function to calibrate the PVX by setting the velocity to a known material
velocity. Refer to page 35 for further info.

One Point: Performs a single point calibration. This option allows the user to
automatically calculate the velocity by entering a known sample thickness. Refer to
page 37 for further info.

Two Point: Performs a two-point calibration. This option allows the user to
automatically calculate the velocity by entering a second known sample thickness.
Refer to page 38 for further info.

Material: Select the material velocity from a chart of basic material types, when a
known sample thickness, or material velocity cannot be obtained. Refer to page 41
for further info.

3.4 DISP (display) – Menu

View: Selectable RF wave, RECT (rectified) wave, BSCAN (cross section), and

DIGITS (large digits) views. Refer to page 43 for further info.
Backlight: Selectable OFF, ON, AUTO, or INVERT backlight option. The INVERT

option is actually a screen inversion that toggles background and foreground colors.

Contrast: Adjustable display contrast for variable light conditions.
Delay: Provides the user the ability to change where the left side of the display

window starts according to thickness, in inches or millimeters. Refer to page 53 for
further info.

Width: Provides the user the ability to change the overall size of the viewable
measurement area. It functions a lot like a zoom on a camera. Refer to page 50 for
further info.

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PVX Precision Visual Thickness Gauge

3.5 TUNE – Menu

Gain: Increases or decreases the overall amplitude of the signal. Much like turning

the volume up or down on a stereo receiver. Refer to page 55 for further info.
AGC: The PVX is equipped with an automatic gain control when operating in

interface-echo and echo-echo modes only. This is much like turning the volume up
or down on a stereo receiver. However, the PVX will automatically control how much
the volume is turned up or down. Alternatively, the AGC can be manually controlled
using the same procedures as GAIN described above. Refer to page 55 for further
info.

Threshold: Enables the user to set the sensitivity level of the PVX. The amplitude
of the signal must reach and exceed the threshold level before a measurement is
detected. Refer to page 58 for further info.

Polarity: The PVX operates on a zero crossing detection principle. This feature
toggles which stroke of the cycle the crossing detection uses, either positive or

negative. Refer to page 76 for further info.
Rect Waveform: This option provides the user an outlined or filled view option when
the display setting is in RECT (rectified) wave mode only. Refer to page 78 for

further info.

3.6 GATE – Menu

Measure Mode: Used to select the measurement mode for different application

requirements. The modes are P-E (pulse-echo), P-E GT(pulse-echo w/gate), and E­E(echo-echo). Note: I-E or Interface echo mode is also a multiple echo mode that

uses two gates like E-E mode(echo-echo). Refer to page 23 for further info.
Gate 1: Gates allow the user to view areas or sections of the waveform and ignore

others. Gate 1 can be used in both pulse-echo and echo-echo measurement modes.
Refer to page 61 for further info.

Gate 2: Gates allow the user to view areas or sections of the waveform and ignore
others. Gate 2 is only used in echo-echo (interface-echo) measurement modes.
Refer to page 65 for further info.

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3.7 SETUP – Menu

Open: Displays a list of factory and user defined setups currently stored in memory.
These setups can be recalled and used at any time. Refer to page 99 for further info.
Save: Provides the user with the ability to save a custom setup that has been

modified or created by the user. Refer to page 101 for further info.
Default Setup: Loads a basic default setup. Use only as a last resort when the

setups in the PVX have been corrupted and a computer is not accessible. Refer to
page 104 for further info.

Language: Provides the user with three different language options: English,
German, and Spanish.

3.8 DATA – Menu

New: Allows the user the ability to create a new alpha numeric grid with custom

parameters, rows, and columns depending on their application reporting
requirements. Refer to page 81 for further info.

Edit: Gives the user the ability to change parameters of grid that have been
previously saved. Note: Pre-defined coordinates cannot be changed once they have
been created. Refer to page 94 for further info.

Open: This function provides the user with the ability to recall grids that currently
exist in memory from a list of grids. Refer to page 96 for further info.

Delete One Grid: This function provides the user with the ability to delete one
individual grid from a list of multiple grids previously saved in memory. Refer to page
92 for further info.

Delete All Grids: This function provides the user with the ability to delete all grids
currently stored in memory. Refer to page 92 for further info.

3.9 UTIL (utilities) – Menu

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PVX Precision Visual Thickness Gauge

Auto Find: Automatically locates the detection point if the measurement is out of the
viewable display area. Refer to page 72 for further info.
Scan Mode: This function enables a hi speed scan mode that increases the overall
sample rate from the standard 4 measurements a second to 32 measurements a

second. Refer to page 73 for further info.

Alarm Status: Toggles alarm mode on or off. Refer to page 74 for further info.
Alarm LO Limit: Gives the user the ability to set the LO limit parameter. If the

measurement falls below this value, a red light will illuminate and sound the internal
beeper. Refer to page 75 for further info.

Alarm HI Limit: Gives the user the ability to set the HI limit parameter. If the
measurement exceeds this value, a red light will illuminate and sound the internal
beeper. Refer to page 76 for further info.

3.10 XFER (transfer) – Menu

Backup Setups: Enables the user the ability to backup the setups currently stored
in the PVX to a PC via RS232 port. Refer the help section of the DakView 3 or
PVXview software for a complete elect ronic manual.

Restore Setups: Enables the user the ability to restore the setups currently saved
on a PC to an PVX via RS232 port. Refer the help section of the DakView 3 or
PVXview software for a complete electronic manual.

Backup Grid: Enables the user the ability to backup grids currently stored in the

PVX to a PC via RS232 port. Refer the help section of the DakView 3 or PVXview
software for a complete electronic manual.

Restore Grid: Enables the user the ability to restore grids currently saved on a PC
to an PVX via RS232 port. Refer the help section of the DakView 3 or PVXview
software for a complete electronic manual.

About: Provides the user with Dakota Ultrasonics contact information and the PVX
software version. Refer the help section of the DakView 3 or PVXview software for a

complete electronic manual.

3.11 CLR (clear) Key

The primary functions of the CLR key, is to clear a measurement from a grid cell
location or set obstruct, and backspace in an Alpha Edit Box. If a user has already

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saved a measurement and waveform to a cell location, use this key to clear the
measurement at any time.

3.12 MEAS (measurement mode) Key

The MEAS key puts the PVX into it’s primary mode of operation. In this mode, the
user has a complete view of the LCD, as well as control of the Hot Menu Functions.
These hot functions provide the user with the ability to make crucial adjustments to
the display, waveform settings, and grid storage locations without having to search
through the menu and sub menu items. It’s important to first get familiar with moving
around in the hot functions as follows:

Getting Around in the Hot Menus

1) Press the MEAS key at any time to return to the primarily measurement

mode.

2) Press the MEAS key multiple times to tab right through the menu fields, and

the ESC key multiple times to tab left through the menu fields, until the
desired hot function is highlighted.

Now that you’re familiar with activating and moving amongst the hot function fields,
let’s have a look at how to adjust or change the values of these fields:

Adjusting the Values of the Hot Menus

1) Use the UP, DOWN, LEFT, and RIGHT arrow keys to increase and
decrease the values of the hot function fields.

2) Repeat step 1 until the desired value has been achieved.

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PVX Precision Visual Thickness Gauge

Alternatively, the delay, width, gain, and threshold hot function fields can be
changed using the Digit Edit Box as follows:

1) Press the ENTER key to display the Digits Edit Box.

2) Press the UP and DOWN arrow keys to scroll the highlighted value.

3) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

4) Repeat steps 2 & 3 until the delay, width, gain, or threshold number is
correctly displayed.

5) Press the OK key to set and return to the measure screen, or ESC to cancel
entering the delay, width, gain, or threshold value.

3.13 OK Key

The primary function of the OK key is confirmation of a change or selection. Also
toggles display views (Rect, RF, Digits, B-Scan) while in a highlighted grid location.

3.14 ESC Key

The ESC key is used in the MENU, MEAS, and EDIT functions as a back or escape
function. Also toggles display views (RECT, RF, DIGITS, or B-SCAN) while in a

highlighted grid location. Note: If a B-SCAN was originally saved in grid location,
only DIGITS view can be toggled in conjunction with the B-SCAN.

3.15 Arrow Keys

The Arrow Keys are used to navigate through the menus, increase/decrease values,
and toggle specific function keys.

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3.16 ENTER key

The ENTER key is used in the overall menu selection process, to activate list and
edit boxes, and save measurements to grid locations.

3.17 MULTI MODE Key

The MULTI MODE key activates the Load Setup List to select a factory or
previously saved user setup for a variety of different transducer types and scope
settings. This is a quick and efficient way to change modes and transducer types
without having to manually adjust PVX. The factory setups serve as the perfect
starting point for immediate use or further fine-tuning.

3.18 ON/OFF Key

The ON/OFF key simply powers the unit either ON or OFF. Note: Unit will
automatically power off when idle for 5 minutes. All current settings are saved prior
to powering off.

3.19 Top & Bottom End Caps

The top & bottom end panels are where all connections are made to the PVX. The
diagram above shows the layout and description of the conn ectors:

Transducer Connectors

Refer to Diagram: The transducer connector and battery cover/probe zero disk are
located on the PVX’s top end cap. The transducer connector is of type Lemo “00”.

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PVX Precision Visual Thickness Gauge

Probe Zero Disk & Battery Cover
Refer to Diagram: The Battery cover is the large round disk shown in the diagram.

Note: This same disk is also used as a probe zero disk. Simply remove the cover

when replacing the batteries (3 AA cells). When performing a probe zero function,
simply place the transducer on the disk making firm contact.

Important: Be sure to follow the polarity labels located on the back label of the PVX.
Note: Rechargeable batteries can be used, however they must be recharged outside

of the unit in a stand alone battery charger.

RS-232 Connector
Refer to Diagram: The RS-232 connector, located on the bottom end cap, is a 2 pin

female Lemo connector. It is designed to connect directly from the PVX to a
standard AT serial port on a PC. The cable supplied with the PVX is a Lemo to 9 pin
serial cable. Note: This connector is also used to upgrade the PVX with the latest
version of firmware.

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CHAPTER FOUR
PRINCIPALS OF ULTRASONIC MEASUREMENT

4.1 Time versus thickness relationship

Ultrasonic thickness measurements depend on measuring the length of time it takes
for sound to travel through the material being tested. The ratio of the thickness
versus the time is known as the sound velocity. In order to make accurate
measurements, a sound velocity must be determined and entered into the
instrument.

The accuracy of a thickness measurement therefore depends on having a consistent
sound velocity. Some materials are not as consistent as others and accuracy will be
marginal. For example, some cast materials are very granular and porous and as a
result have inconsistent sound velocities.

While there are many different ultrasonic techniques to measure thickness, which will
be discussed below, all of them rely on using the sound velocity to convert from time
to thickness.

4.2 Suitability of materials

Ultrasonic thickness measurements rely on passing a sound wave through the
material being measured. Not all materials are good at transmitting sound.
Ultrasonic thickness measurement is practical in a wide variety of materials including
metals, plastics, and glass. Materials that are difficult include some cast materials,
concrete, wood, fiberglass, and some rubber.

4.3 Range of measurement and accuracy

The overall measurement capabilities, based on the wide variety of materials, is
determined by the consistency of the material being measured

The range of thickness that can be measured ultrasonically depends on the material
as well as the technique being used and the type of transducer. Thickness
measurements can be made from a minimum of 0.010 inch to 9.999” in steel.
However, the maximum attainable thickness is much less for more attenuative
materials (materials that absorb sound).

Accuracy, is determined by how consistent the sound velocity is through the sound
path being measured and, is a function of the overall thickness of th e material. For
example, the velocity in steel is typically within 0.5% while the velocity in cast iron
can vary by 4%.

4.4 Couplant

All ultrasonic applications require some medium to couple the sound from the
transducer to the test piece. Typically a high viscosity liquid is used as the medium.
The sound frequencies used in ultrasonic thickness measurement do not travel

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PVX Precision Visual Thickness Gauge

through air efficiently. By using a liquid couplant between the transducer and test
piece the amount of ultrasound entering the test piece is much greater.

4.5 Temperature

Temperature has an effect on sound velocity. The higher the temperature, the slower
sound travels in a material. High temperatures can also damage transducers and
present a problem for various liquid couplants.

Since the sou nd velocity varies with temperature it is important to calibrate at the
same temperature as the material being measured.

Normal temperature range

Most standard transducers will operate from 0°F to 180°F.

High temperature measurements

Special transducers and couplants are available for temperatures above 180°F up to
650°F with intermittent contact. It is necessary to cool the transducer, by submerging
the transducer in water between readings, when measuring high temperatures.

Modes and temperature errors

In addition to errors caused by velocity changing with temperature, some modes
(measurement techniques) are affected more than others. For example, dual
element mode has larger errors due to changes in temperature of the delay line.
However, multi-echo tec hniques help to minimize these errors. The PVX operates in
multi-echo modes for a variety of transducer types.

4.6 Measurement Modes

In this section we will discuss the different measurements modes the PVX is capable
of operating in, the transducers required, and the reasons for using specific modes:

Pulse-Echo Mode (flaws & pits)

Pulse-echo mode measures from the initial pulse (sometimes referred to as an
artificial zero) to the first echo (reflection). In this mode, the transducer is placed on a
reference disk, located on top of the PVX, and a key is pressed to establish a zero
point for the particular transducer.

In pulse-echo mode errors result from surface coatings and temperature variations.
Since pulse-echo only requires one reflection, it is the most sensitive mode for

measuring weak reflections (flaws) typically found when measuring heavily corroded
metals.

Echo-Echo (Interface-Echo) Modes

The echo-echo modes measure between two reflections. This technique is
commonly used to eliminate errors from surface coatings in echo-echo mode, as well
as make measurements in multiple layered materials. The disadvantage is that two

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echoes are needed which requires a much stronger echo (reflection). In interface­echo mode, it moves the interface further out in time eliminating any noise that’s
close to the initial pulse.

Important: The primary difference between interface-echo and echo-echo mode, is
interface-echo mode measures from the end of an interface (delay line), to the first

return reflection of the test material. However, in echo-mode, the measurement is
made between two return reflections (echoes). Although both modes use two gates
and virtually look the same on the scope, they are measuring in different ways and
are used to accomplish different application tasks. The diagrams below will offer an
additional explanation of the differences in these modes as follows:

Delay Line Single Element Transducer in Interface-Echo mode

Diagram 1

Refer to diagram 1. This diagram illustrates the sound path being measured in

interface-echo mode. (A) is the transducer. Point (B) is the piezoelectric crystal that
emits the sound wave. (C) is the delay line, most commonly made of acrylic or
graphite. The delay tip will act as the interface and the measurement will be made
starting from the difference of the reflection off the end of the delay tip (E). The
sound will also travel through the delay tip (C) and test material (F), and reflect back
to the piezoelectric crystal off the back wall of the test material. The measurement
will be made from the reflection off the end of the delay tip and back wall of the test
material.

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PVX Precision Visual Thickness Gauge

Diagram 2

Refer to diagram 2. Referring to (Idle), you’ll notice that when the PVX is in

interface-echo mode a waveform from the end of the delay line will always be
displayed and active on the screen when idle (A). Since the gates are also used in
interface-echo mode, they will be displayed (B). When measuring, two detects will be
displayed between two waveforms at (C) & (F). The measurement starts at (C), the
end of the delay line, and measures to the back wall of the test material at (F). Point
(D) represents the gate 1 start position, and (E) the gate 2 hold-off. Notice that the
start position of the gate 2 hold-off (E) has been adjusted to the right of the delay line
waveform. This is done to avoid potential detection on the ring down of the delay line
interface, and allow a detection to occur on the back wall of the test material at (F).

Diagram 2

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Dakota Ultrasonics

Refer to diagram 3. The above diagram illustrates a typical view of echo-echo mode
using a delay line style transducer. The end of the interface or delay line is displayed
at (B). However, unlike interface echo mode the measurement is occurring between
two return reflections (A) and (B). Recall that in interface echo mode, the
measurements occurred between the interface (B) and the first return reflection (A).
This is the primary difference between the two modes. An important thing to note is
that the ring down cycles from the transducer are much less than in interface echo
mode. This allows the PVX to see much closer to the first return reflection making it
possible to measure very thin materials. This mode is also used for thru-paint
measurements. By measuring between two echoes, the thickness of paint &
coatings will be eliminated completely. Therefore, any paint or coating on the surface
of the test material will not be added to actual thickness of the test material.

4.7 Glossary of terms

Repetition Rate & Display Update

The repetition rate is how often the PVX generates a burst of ultrasound.
The PVX has a fixed repetition rate of 1 kHz, or 1000 times per second. The PVX

updates the display 4 times per second in regular measurement mode and 32 times a
second in hi speed scan mode. Therefore, the scan mode is most suitable for fast
scans of a test piece at a lower resolution.

Variable Pulser Width

Transducers have a center frequency where they are most efficient at transmitting
sound (i.e. they are resonant). The PVX has a variable width pulser with three
setting options (spike, thin, wide). These settings determine the period of time the
pulser turned is on. High frequency applications, where resolution is a requirement,
may require the spike or thin settings to achieve optimal results. Low frequency
applications, where more penetration is a needed, may require the thin or wide
settings, offering increased penetration. The variety of transducer frequencies and
diameters used in conjunction with the pulser settings, enable users to fine tune the
PVX for their application needs.

Gates

Gates control the time measurement process. They enable the user to select
measurement regions and threshold levels (sensitivity). The PVX is equipped with
two gates. In pulse-echo mode a single gate can be used to eliminate noise. In
echo-echo (interface-echo) mode both gates are used. In this mode the second gate
starts automatically after a signal is detected during the gates region, and after a user
adjustable delay, sometimes called a hold-off.

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