DAKOTA ULTRASONICS PR-9 User manual

OPERATION MANUAL
DAKOTA ULTRASONICS
P
PR R- -9 9
Sonic Thickness Tester - Racing
P/N P-309-0002 Rev 1.11, November 2019

CONTENTS
CHAPTER ONE INTRODUCTION ...................................................................... 1
1.1 DISCLAIMER ......................................................................................................................... 1
CHAPTER TWO KEYPAD, MENU, DISPLAY & CONNECTORS ..................... 2
2.1 ON/OFF/ENTER KEY… ..................................................................................................... 2
2.2 PRB 0 KEY… ....................................................................................................................... 2
2.3 CAL KEY…. ......................................................................................................................... 3
2.4 LIGHT KEY…. ..................................................................................................................... 3
2.5 UNITS KEY…. ..................................................................................................................... 3
2.6 +/- INCREMENT/DECREMENT KEY’S…. .................................................................................. 3
2.7 SCAN KEY…. ...................................................................................................................... 3
2.8 THE DISPLAY ....................................................................................................................... 3
2.9 THE TRANSDUCER ................................................................................................................ 5
2.10 TOP END CAP .................................................................................................................... 7
CHAPTER THREE PRINCIPALS OF ULTRASONIC MEASUREMENT ........... 8
3.1 TIME VERSUS THICKNESS RELATIONSHIP ............................................................................... 8
3.2 SUITABILITY OF MATERIALS ................................................................................................... 8
3.3 RANGE OF MEASUREMENT AND ACCURACY ............................................................................ 8
3.4 COUPLANT ........................................................................................................................... 8
3.5 TEMPERATURE ..................................................................................................................... 9
3.6 MEASUREMENT MODES ........................................................................................................ 9
CHAPTER FOUR SELECTING THE MEASUREMENT MODE ....................... 11
4.1 WHICH MODE & TRANSDUCER DO I USE FOR MY APPLICATION? ............................................ 11
CHAPTER FIVE MAKING MEASUREMENTS ................................................. 13
5.1 PROBE ZERO ...................................................................................................................... 13
5.2 MATERIAL CALIBRATION ..................................................................................................... 14
CHAPTER SIX ADDITIONAL FEATURES ....................................................... 20
6.1 HIGH SPEED SCAN ............................................................................................................. 20
6.2 UNITS ................................................................................................................................ 20
6.3 LIGHT ................................................................................................................................ 20
6.4 LOCK ................................................................................................................................. 21
6.5 FACTORY DEFAULTS .......................................................................................................... 22
APPENDIX A - VELOCITY TABLE .................................................................. 24

APPENDIX B- APPLICATION NOTES ........................................................... 26

1
CHAPTER ONE
INTRODUCTION
The Dakota Ultrasonics model PR-9 is a basic dual element sonic tester with the
ability to locate blind surface pitting and internal defects/flaws in materials. Based on
the same operating principles as SONAR, the PR-9 is capable of measuring the
thickness of various materials with accuracy as high as  0.001 inches, or  0.01
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
Tel: [phone]
Fax: [phone]
www.dakotaultrasonics.com
1.1 Disclaimer
Inherent in ultrasonic thickness measurement is the possibility that the instrument will
use the second rather than the first echo from the back surface of the material being
measured. This may result in a thickness reading that is TWICE what it should be.
Responsibility for proper use of the instrument and recognition of this phenomenon
rest solely with the user of the instrument. Other errors may occur from measuring
coated materials where the coating is insufficiently bonded to the material surface.
Irregular and inaccurate readings may result. Again, the user is responsible for
proper use and interpretation of the measurements acquired.

2
CHAPTER TWO
KEYPAD, MENU, DISPLAY & CONNECTORS
The Keypad
2.1 ON/OFF/ENTER Key
The ON/OFF/ENTER key powers the unit ON or OFF. Since the same key is also
used as an ENTER key, the gauge is powered off by pressing and holding down the
key until the unit powers off.
Once the gauge is initially powered on, this key will function as the ENTER key,
similar to a computer keyboard. This key will be used to select or set a menu option.
Note: Unit will automatically power off when idle for 5 minutes. All current settings
are automatically saved prior to powering off.
2.2 PRB 0 Key
The PRB 0 key is used to “zero” the PR-9 in much the same way that a mechanical
micrometer is zeroed. If the gauge is not zeroed correctly, all of the measurements
that the gauge makes may be in error by some fixed value. Refer to page 13 for a
further explanation of this important feature.

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2.3 CAL Key
The CAL key is used to enter and exit the PR-9's calibration mode. This mode is
used to adjust the sound velocity value that the PR-9 will use when calculating
thickness. The tool will either calculate the sound-velocity from a sample of the
material being measured, or allow a known velocity value to be entered directly. This
provides increased linearity between transducers. Refer to page 14 for an
explanation on the various calibration options.
2.4 LIGHT Key
The LIGHT key accesses the backlight setting of the LCD display. The backlight has
three setting options; ON, OFF, AUTO. The auto option will only illuminate the
display when the PR-9 is measuring, or receiving an echo. If either ON or AUTO are
selected, there are three brightness options, LO, MED, HI, to select a preferred
overall brightness of the display. Refer to page 20 for an explanation on how to
enable and set the brightness.
2.5 UNITS Key
The UNITS key is used to select either English or Metric units. Refer to page 20 for
an explanation of how to select the units.
2.6 +/- Increment/Decrement Key’s
The +/- Keys are used to increment/decrement values, navigate menus, and select
menu options.
2.7 SCAN Key
The PR-9 offers a high speed scan feature. This feature allows for scanning larger
areas on a given test material, while still offering reasonable representation of
thickness over the area scanned. Refer to page 20 for an explanation on the scan
feature.
2.8 The Display

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The PR-9 uses a custom glass LCD backlit low temperature display for use in a
variety of climate conditions. It contains graphic icons, as well as both 7 and 14
segment display areas. Let’s take a closer look and what all these things are telling
us:
Note: This display is used for multiple gauge models in the ZX &PZX series. As a
result, some of the icons and segments that are illuminated during boot up, may not
be applicable to your specific model, and will never be illuminated during operation.
The icons and segments that will be used with the PR-9 are shown in the diagram
above.
A. Edit: This icon will be displayed, and blinking, to let a user know when they
are in an edit mode to change a value or setting.
B. Large 7 segment: The thickness measurement, velocity or alpha message
will be displayed in this area.
C. Measurement Modes: This icon indicates the measurement mode. The PR-
9 operates exclusively in pulse-echo (P-E) mode only.
D. Stability/Repeatability Indicator: This is used in conjunction with the
thickness measurement as a reference for the validity of the measurement.
The PR-9 takes multiple measurements per second, and when all the vertical
bars are illuminated, it’s a reference that the same thickness value is reliably
being measured multiple times per second.
E. Battery: Indicates the amount of battery life the PR-9 has remaining.
F. Backlight : When this icon is illuminated, it indicates the backlight is on.
G. Small 7 Segment: The material velocity, speed the sound wave travels
through a given medium/material, is displayed in this area, informing the user
what material the PR-9 is currently calibrated too. This area is also used for
alpha messages in the menu and edit modes.

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H. Units: This combination of icons are illuminated in different sequences to
inform the user what measurement units are currently being displayed in the
small 7 segment area.
I. Small 14 Segment: Displays the current gain setting of the PR-9 which will
always display medium (MED).
J. Units: This combination of icons are illuminated in different sequences to
inform the user what measurement units are currently being displayed in the
large 7 segment area.
K. Small 14 Segment: The material type is displayed in this area. If it is set to a
value of one of the materials in our material list, it will be displayed in alpha
characters indicating the material type. Otherwise it will be set to CUST,
indicating custom material type.
L. Features: The icons illuminated in this row across the bottom of the LCD
display which features are currently enabled. For a complete list refer to page
20. The PR-9 can be locked once calibrated, to avoid accidently changing the
calibration. When this icon is illuminated, the PR-9 is in lock mode. Refer to
page 21 for an explanation on locking the PR-9.
2.9 The Transducer
The Transducer is the “business end” of the PR-9. It transmits and receives
ultrasonic sound waves that the PR-9 uses to calculate the thickness of the material
being measured. The transducer connects to the PR-9 via the attached cable, and
two coaxial connectors. When using transducers manufactured by Dakota
Ultrasonics, the orientation of the dual coaxial connectors is not critical: either plug
may be fitted to either socket in the PR-9.
The transducer must be used correctly in order for the PR-9 to produce accurate,
reliable measurements. Below is a short description of the transducer, followed by
instructions for its use.

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This is a bottom view of a typical transducer. The two semicircles of the wear face
are visible, as is the barrier separating them. One of the semicircles is responsible
for conducting ultrasonic sound into the material being measured, and the other
semicircle is responsible for conducting the echoed sound back into the transducer.
When the transducer is placed against the material being measured, it is the area
directly beneath the center of the wear face that is being measured.
This is a top view of a typical transducer. Press against the top with the thumb or
index finger to hold the transducer in place. Moderate pressure is sufficient, as it is
only necessary to keep the transducer stationary, and the wear face seated flat
against the surface of the material being measured.
Measuring
In order for the transducer to do its job, there must be no air gaps between the wear-
face and the surface of the material being measured. This is accomplished with the
use of a "coupling" fluid, commonly called "couplant". This fluid serves to "couple", or
transfer, the ultrasonic sound waves from the transducer, into the material, and back
again. Before attempting to make a measurement, a small amount of couplant
should be applied to the surface of the material being measured. Typically, a single
droplet of couplant is sufficient.
After applying couplant, press the transducer (wear face down) firmly against the
area to be measured. The Stability Indicator should have six or seven bars
darkened, and a number should appear in the display. If the PR-9 has been properly
"zeroed" (see page 13) and set to the correct sound velocity (see page 14), the
number in the display will indicate the actual thickness of the material directly
beneath the transducer.
If the Stability Indicator has fewer than five bars darkened, or the numbers on the
display seem erratic, first check to make sure that there is an adequate film of
couplant beneath the transducer, and that the transducer is seated flat against the
material. If the condition persists, it may be necessary to select a different transducer
(size or frequency) for the material being measured. See page 11 for information on
transducer selection.
While the transducer is in contact with the material that is being measured, the PR-9
will perform four measurements every second, updating its display as it does so.

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When the transducer is removed from the surface, the display will hold the last
measurement made.
2.10 Top End Cap
The top end cap is where all connections are made to the PR-9. The diagram above
shows the layout and description of the connectors:
Transducer Connectors
Refer to Diagram: The transducer connectors and battery cover/probe zero disk are
located on the PR-9’s top end cap. The transducer connectors are of type Lemo
“00”.
Note: There is no polarity associated with connecting the transducer to the PR-9, it
can be plugged into the gauge in either direction.
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 reference disk. Simply remove
the cover when replacing the batteries (2 AA cells). When performing a manual
probe zero function, simply place the transducer on disk making firm contact.
Important: Be sure the battery polarity is correct, which can be found on the back
label of the PR-9.
Note: Rechargeable batteries can be used, however they must be recharged outside
of the unit in a standalone battery charger.

8
CHAPTER THREE
PRINCIPALS OF ULTRASONIC MEASUREMENT
3.1 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.
3.2 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.
3.3 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
type and surface, as well as the technique being used and the type of transducer.
The range will vary depending on the type of material being measured.
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 the material. For
example, the velocity in steel is typically within 0.5% while the velocity in cast iron
can vary by 4%.
3.4 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
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.

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3.5 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 sound 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 250F.
High temperature measurements
Special transducers and couplants are available for temperatures above 250F up to
1000F with intermittent contact. It is necessary to cool the transducer by
submerging it in water between measurements.
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 pulse-echo mode has larger errors due to changes in the temperature of the
transducer. However, multi-echo techniques offer temperature compensation help to
minimize these errors.
3.6 Measurement Modes
This section will cover the different measurements modes of the PR-9, the
transducers required, and the reasons for using specific modes:
Pulse-Echo (P-E) Mode:
Pulse-echo mode measures from the initial pulse (sometimes referred to as an
artificial zero) to the first echo (reflection). In this mode, either an automatic or
manual zero can be performed depending on the zero probe setting. If the manual
mode has been selected, the transducer is placed on the reference disk located on
top of the PR-9, and the PRB 0 key pressed to establish a zero point for the
transducer connected. If the Auto Zero feature is enabled, simply pressing the PRB
0 key will perform an electronic zero to establish the same zero point.
In pulse-echo mode, errors can result from surface coatings and temperature
variations. Since pulse-echo only requires one reflection, it is the most sensitive
mode for measuring flaw/defects when measuring heavily corroded metals.
V-Path Correction
Dual element delay line transducers have two piezoelectric elements focused
towards one another at a slight angle, mounted on a delay line. One element is used
for transmitting sound, while the other element receives the sound reflection. The

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two elements and their delay lines are packaged in a single housing but acoustically
isolated from each other with an insulated sound barrier. This allows the transducer
the ability to achieve very high sensitivity for detecting small defects. Also, the
surface of the test material does not have to be as flat in order to obtain good
measurements.
Dual element transducers are normally used in pulse-echo mode for finding defects,
and in echo-echo mode for through coating measurements.
Dual element delay line transducers are have a usable range of 0.025” and up,
depending on the material, frequency, and diameter.
A limitation of dual element delay-line transducers is the V shaped sound path.
Because the sound travels from one element to another, the time versus thickness
relationship is non-linear. Therefore, a correction table in the instruments software is
used to compensate for this error.
Dual Element Transducer showing V-path of signal
Searching for small defects
Dual element delay line transducers are especially useful in searching for small
defects. In pulse-echo mode with high amplifier gain, very small defects can be
located. As a result, this configuration is commonly used for corrosion inspections.
The dual element style transducer will find wall deterioration, pits, cracks, and any
porosity pockets during tank and pipeline inspections.

11
CHAPTER FOUR
SELECTING THE MEASUREMENT MODE
4.1 Which mode & transducer do I use for my application?
High penetration plastics and castings
The most common mode for these types of applications is pulse-echo. Cast iron
applications require 1 - 5MHz frequencies, and cast aluminum requires a 7 - 10MHz
frequency depending on the thickness. Plastics typically require lower frequencies
depending on the thickness and make-up of the material as well. Larger diameters
offer greater penetration power based on the size of the crystal.
Corrosion & Pit Detection in steel and cast materials
Pulse-echo mode is commonly used for locating pits and defects. Typically a 5MHz
transducer, or higher, will be used for these types of applications. Use low
frequencies for greater penetration and use higher frequencies for better resolution.
Measuring Material & Coatings
The pulse-echo coating mode should be used when both material and coating
thickness are required, while still requiring the ability to detect flaws and pits. A
special coating style transducer is required for use in this mode. There are a variety
of coating transducers in various frequencies available from Dakota.
Thru Paint & Coatings
Often times, users will be faced with applications where the material will be coated
with paint or some other type of epoxy material. Since the velocity of the coating is
approximately 3 times slower than that of steel, pulse-echo mode will result in an
error if the coating or paint is not completely removed.
Thin materials
Pulse echo mode and a high frequency transducer is commonly used for these types
of applications. The most common transducers are the 7.5MHz and 10MHz models
with extra resolution. The higher frequencies provide greater resolution and a lower
minimum thickness rating overall.
High temperature
Special 5 MHz High temperature transducers are available for these types of
applications. Both pulse-echo and echo-echo modes will also work for these
applications. However, echo-echo mode will eliminate error caused by temperature
variations in the transducer.

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Noisy Material
Materials such as titanium, stainless steel, and aluminum may have inherent surface
noise issues or mirroring effect. Higher frequency transducers 7 – 10MHz offer
improved resolution to avoid erroneous measurements.
Restricted access
Measuring materials with extreme curvatures or restricted access are best suited for
higher frequencies and smaller diameter transducers.

13
CHAPTER FIVE
MAKING MEASUREMENTS
The steps involved in making measurements are detailed in this section. The
following sections outline how to setup and prepare your PR-9 for field use.
An automatic or manual zero must always be performed. The auto zero is an ‘off
block’ electronic zero that does not require a zero reference standard. This will most
always be the zero option of choice, as it makes the zeroing process very easy and
convenient to perform. However, the manual zero option offers better accuracy in
terms of a reference point. If the manual zero option is enabled, the probe zero must
be measured on the reference disk (battery disk) attached to the top of the
instrument. The zero compensates for variations in the transducer. In either mode
the sound velocity must be determined, and is used to convert the transit time to a
physical length. The sound velocity can be selected from a material chart in the
manual, selected from a short list of common materials in the PR-9, or for greater
precision determined from a sample of the test material that has been mechanically
measured. To enter the velocity from a table, look up the material on the chart in the
appendix of this manual and refer to the section below on Calibration to a Known
Velocity. To determine the velocity of a single sample, refer to the Material
Calibration section on page 14.
When measuring curved materials, it’s more accurate to calibrate from two test
points, one at the minimum limit of the target thickness and one at the maximum limit.
In this case the reference disk mounted to the PR-9 is not used. This is called two-
point calibration and is described on page 17.
5.1 Probe zero
Setting the zero point of the PR-9 is important for the same reason that setting the
zero on a mechanical micrometer is important. It must be done prior to calibration,
and should be done throughout the day to account for any temperature changes in
the probe. If the PR-9 is not zeroed correctly, all the measurements taken may be in
error by some fixed value.
The procedure is outlined below as follows:
Performing a Probe Zero

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1) Apply a drop of couplant on the transducer and place the transducer in
steady contact with the disk (battery cover) located at the top of the unit to
obtain a measurement.
2) Be sure all six repeatability/stability bars in the top left corner of the display
are fully illuminated and stable, and last digit of the measurement is toggling
only +/- .001” (.01mm).
3) Press the key to perform the zero. “PRB0” will briefly be displayed on
the screen, indicating the zero calculation was performed.
5.2 Material Calibration
In order for the PR-9 to make accurate measurements, it must be set to the correct
sound velocity of the material being measured. Different types of materials have
different inherent sound velocities. For example, the velocity of sound through steel
is about 0.233 inches per microsecond, versus that of aluminum, which is about
0.248 inches per microsecond. If the gauge is not set to the correct sound velocity,
all of the measurements the gauge makes will be erroneous by some amount.
The One Point calibration is the simplest and most commonly used calibration
method - optimizing linearity over large ranges. The Two Point calibration allows for
greater accuracy over small ranges by calculating both the probe zero, as well as the
material velocity. The PR-9 provides three simple methods for setting the sound-
velocity outlined below:
Known Velocity
If the material velocity is known, it can be manually entered into the PR-9, rather than
have the PR-9 calculate the velocity value using a known thickness of the same
material type. The steps for entering the velocity are outlined below:
Using a Known Material Velocity

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1) With the transducer free from contact with the material, press the key
to display the current velocity.
2) Use the keys to scroll the velocity to the known target
value.
Note: The longer the keys are pressed and held, the faster the value will
increment/decrement.
Note: Pressing the key prior to pressing the key will abort the cal
routine without saving any changes.
3) Press the key to set the velocity value and return to the measurement
screen. The new velocity value will be shown at the top of the display.
Known Thickness
Often times the exact sound velocity of a material is unknown. However, a sample
with one or two known thicknesses can be used to determine the sound velocity. As
previously discussed, the PR-9 has a one or two point calibration option. The one
point calibration option is most suited for linearity over large ranges. When using the
one point option, the calibration should be perform on the thickest side of the
measurement range for the best linearity for that range. For example, if the
measurement range is .100” (2.54mm) to 1.0” (25.4mm), the user should calibrate on
a known thickness sample close to 1.0” (25.4mm). Note: It’s always handy to carry
a set of mechanical calipers to use in conjunction with the PR-9 for calibration of
various materials in the field:
One Point Calibration
Note: Be sure that a probe zero has been performed prior to performing this
calibration procedure.

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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.
Note: A sample or location on the test piece should be used as close to the
maximum thickness of the test range to minimize error.
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.
3) Press the key to enter the calibration edit screen displaying the current
measurement value.
4) Use the keys to scroll to the known thickness value.
Note: The longer the keys are pressed and held, the faster the value will
increment/decrement.
Note: Pressing the key prior to pressing the key will abort the cal
routine without saving any changes.
5) Once the known thickness value is being displayed, press the key to
display the calculated material velocity edit screen.
Note: The calculated velocity can be edited, if needed, by pressing the
keys to scroll and edit the velocity value.
6) Press the key to set the calculated material velocity and return to the
measurement screen.