Check-line TI-25SX User manual

MODEL TI-25SX
ULTRASONIC THICKNESS GAUGE
Operating Manual
®

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TABLE OF CONTENTS
1.0 Introduction .......................................................................................................................... 1
1.1 Disclaimer
2.0 Keypad, Menu, Display & Connectors............................................................................... 3
2.1 ON/OFF/ENTER Key0
2.2 PRB 0 Key
2.3 VEL Key
2.4 LIGHT Key
2.5 UNITS Key
2.6 +/- INCREMENT/DECREMENT Keys
2.7 The Display
2.8 The Transducer
2.9 Top End Cap
3.0 Principals of Ultrasonic Measurement ............................................................................... 8
3.1 Time versus thickness relationship
3.2 Suitability of materials
3.3 Range of measurement and accuracy
3.4 Couplant
3.5 Temperature
3.6 Measurement modes
4.0 Selecting the measurement mode........................................................................................ 11
4.1 Which Mode and Transducer do I use for my applications?
5.0 Making measurements ......................................................................................................... 12
5.1 Probe Zero
5.2 Material Calibration
6.0 Additional features ............................................................................................................... 15
6.1 Unit
6.2 Lite
6.3 Lock
6.4 Factory Defaults
7.0 Appendix A - Velocity Table................................................................................................. 17
8.0 Appendix B- Application Notes ........................................................................................... 18
9.0 Warranty ............................................................................................................................... 20

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1.0 INTRODUCTION
The Checkline model TI-25SX is a basic dual element thickness gauge with the ability
to locate blind surface pitting and internal defects/aws in materials. Based on the same
operating principles as SONAR, the TI-25SX 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.
1.1 Disclaimer
Inherent in ultrasonic thickness measurement is the possibility that the instrument will
use the second rather than the rst 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 insufciently 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.

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2.0 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 TI-25SX 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 xed value. Refer
to section 5.1 for a further explanation of this important feature.
2.3 VEL Key
The VEL key is used to enter and exit theTI-25SX’s calibration mode. This
mode is used to adjust the sound velocity value that theTI-25SX will use for a
given material type. Enter a known velocity value for specic material type, or
manually continue adjusting the value until theTI-25SX displays the correct thickness
value using a test sample or calibration block with a known thickness. Refer to section
5.2 for information about Velocity Calibration.

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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 theTI-25SX 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 18 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 18
for an explanation of how to select the units.
2.6 +/- Increment/Decrement Key’s
The and Keys are used to increment/decrement values, navigate
menus, and select menu options.
2.7 MATL Key
The MATL Key is used to select a common basic material type from a short list
of 9 materials and 2 programmable custom materials for calibration. Refer to
5.3 for an explanation on selecting a basic material type.
2.8 The Display
The TI-25SX 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
TI series. As a result, some of
the icons and segments that are
illuminated during boot up, may
not be applicable to your specic
model, and will never be illuminated during operation. The icons and segments that will
be used with the TI-25SX are shown in the diagram above.

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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 TI-25SX
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 TI-25SX
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 TI-25SX has remaining.
F. Backlight : When this icon is illuminated, it indicates the backlight is on.
G. Small 14 Segment: The material velocity, speed the sound wave travels through a
given medium/material, is displayed in this area, informing the user what material
theTI-25SX is currently calibrated too. This area is also used for alpha messages in
the menu and edit modes.
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. 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.
J. 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.
K. Features: TheTI-25SX can be locked once calibrated, to avoid accidently changing
the calibration. When this icon is illuminated, theTI-25SX is in lock mode.
Refer to section 6.3 for an explanation on locking the TI-25SX.

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2.9 The Transducer
The transducer is the “business end” of the TI-25SX. It transmits and receives ultrasonic
sound waves that the TI-25SX uses to calculate the thickness of the material being
measured. The transducer connects to the TI-25SX via the attached cable, and two
coaxial connectors. When using transducers manufactured by Checkline, the orientation
of the dual coaxial connectors is not critical: either plug may be tted to either socket in
the TI-25SX.
The transducer must be used correctly in order for the TI-25SX to produce accurate,
reliable measurements. Below is a short description of the transducer, followed by
instructions for its use.
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
nger to hold the transducer in place. Moderate pressure is sufcient, as it is only
necessary to keep the transducer stationary, and the wear face seated at 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” uid, commonly called “couplant”. This uid 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

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be applied to the surface of the material being measured. Typically, a single droplet of
couplant is sufcient.
After applying couplant, press the transducer (wear face down) rmly 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 TI-25SX has been properly “zeroed” (see
page 14) and set to the correct sound velocity (see page 16), the number in the display
will indicate the actual thickness of the material directly beneath the transducer.
If the Stability Indicator has fewer than ve bars darkened, or the numbers on the
display seem erratic, rst check to make sure that there is an adequate lm of couplant
beneath the transducer, and that the transducer is seated at 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 section 4.1 for information on transducer selection.
While the transducer is in contact with the material that is being measured, the TI-25SX
will perform four measurements every second, updating its display as it does so. When
the transducer is removed from the surface, the display will hold the last measurement
made.
2.11 Top End Cap
The top end cap is where all connections are
made to the TI-25SX. 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 TI-25SX’s top end cap. The transducer
connectors are of type Lemo “00”.
NOTE: There is no polarity associated with connecting the transducer to the TI-25SX, 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 rm contact. Important: Be sure
the battery polarity is correct, which can be found on the back label of the TI-25SX.
NOTE: Rechargeable batteries can be used, however they must be recharged outside of
the unit in a standalone battery charger.

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3.0 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 difcult include some cast materials, concrete, wood, berglass,
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
efciently. 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 TI-25SX, the
transducers required, and the reasons for using specic modes:
Pulse-Echo (P-E) Mode:
Pulse-echo mode measures from the initial pulse (sometimes referred to as an articial
zero) to the rst echo (reection). 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 TI-25SX,
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 reection, it is the most sensitive mode for
measuring aw/defects when measuring heavily corroded metals.

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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 reection. The 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 at in order to obtain good measurements.
Dual element transducers are normally used in pulse-echo mode for nding 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.
Searching for small defects
Dual element delay line transducers are especially useful in searching for small defects.
In pulse-echo mode with high amplier gain, very small defects can be located. As a
result, this conguration is commonly used for corrosion inspections. The dual element
style transducer will nd wall deterioration, pits, cracks, and any porosity pockets
during tank and pipeline inspections.
Dual Element Transducer showing V-path
of signal

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4.0 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 aws 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
Electromatic.
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.
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.

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5.0 MAKING MEASUREMENTS
The steps involved in making measurements are detailed in this section. The following
sections outline how to setup and prepare your TI-25SX for eld use.
A manual zero must always be performed. A manual probe zero is performed using the
reference disk (battery disk) attached to the top of the instrument. The zero compensates
for variations of the transducer. Once the probe zero is completed, the sound velocity
must be determined to convert the transit time to a physical length. The sound velocity
can be selected from the material chart in the manual, or manually adjusted using a
single, or multiple, known reference point(s) until the TI-25SX correctly measuring the
reference point(s). The later will result in greater precision overall. To enter a common
velocity from a table of velocities, look up the material on the chart in the appendix
of this manual. Refer to the section below on Material Calibration for instructions on
manually adjusting the velocity using a reference point(s)/standard(s). To determine
the velocity of a single sample, refer to the Velocity Calibration section 5.2. The
TI-25SX can also be calibrated by selecting a common material type from a short list
of materials. To select a common material type to use for calibration, refer the Basic
Material Type section 5.3.
5.1 Probe zero
Setting the zero point of the TI-25SX 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 TI-25SX is not zeroed correctly, all the measurements taken may be in error by
some xed value.
The “on block” zero procedure is outlined below:
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 manual zero. “PRB0” will briey be displayed
on the screen, indicating the zero calculation is being performed.
5.2 Velocity Calibration
In order for the TI-25SX 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

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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.
If the material velocity is known, it can be manually entered into the TI-25SX. If the
exact material velocity is unknown, a common velocity can initially be entered to set the
TI-25SX close to the unknown target velocity, followed by multiple ne adjustments to
the velocity value until the target velocity is discovered.
The steps for entering/editing the velocity value are outlined below:
1. With the transducer free from contact with the material, press the key to
display the current velocity.
2. Use the and 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.
CHECK YOUR CALIBRATION! Place the transducer back on the calibration point
and verify the thickness. If the thickness is not correct, repeat the steps above.
5.3 Basic Material Type
If the material velocity is unknown, a sample thickness cannot be taken directly from
the material, but the general type of material is known, selecting a basic material type
from the common material (MATL) list in the TI-25SX would offer a reasonable
approximation of the thickness. There are 9 common materials and 2 user programmable
settings available. 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:

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Selecting a Basic Material Type
1. Press the key to access the material list. The edit icon will be illuminated
and ashing.
2. Use the and keys to scroll through the material options.
3. When the desired MATL setting is displayed, press the key to set the
material velocity and return to the measurement screen.
NOTE: Pressing the key prior to pressing the key will abort to the
measurement screen without saving any changes.
4. If USR1 or USR2 were selected, the velocity edit screen will be displayed and edit
icon illuminated and ashing.
5. Use the and keys to scroll to the desired material velocity.
NOTE: The longer these keys are held, the faster the velocity value is incremented.
6. When the desired velocity setting is displayed, press the key to set the material
velocity and return to the measurement screen.
NOTE: Pressing the key prior to pressing the key will abort to the
measurement screen without saving changes.

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6.0 ADDITIONAL FEATURES
6.1 Units
The TI-25SX will operate in both English (inches) or Metric (millimeters) units.
1. Press the key to toggle inches/millimeters (IN/MM).
6.2 Light
The TI-25SX uses a custom glass segmented display that is equipped with a backlight
for use in low light conditions. The options are on/off/auto, where the auto setting
only lights the display when the gauge is coupled to the material and receiving a
measurement.
The steps below outline how to toggle the backlite:
1. Press the key to access the menu items/features.
2. Use the and keys to toggle the status on/off/auto/
NOTE: Pressing the key prior to pressing the key will abort to the
measurement screen without saving changes.
3. When the desired LITE setting is displayed, press the key to set the status
and edit the BRT (brightness) option.
4. Use the and keys to scroll through the BRT (LO, MED,
HI options.
5. When the desired BRT setting is displayed, press the key to set the
brightness and return to the measurement screen.
6.3 Lock
The lock feature was built into the TI-25SX for the purpose of locking the operators
out of editing any of the gauge settings, for purposes of consistency between operators.
When the lock feature is enabled, the gauge calibration functionality cannot be altered,
as well as any of the individual features in the gauge. The only keys that are always
unlocked are the power and probe zero keys, as these must remain unlocked for
measurement functionality.

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The procedure to enable/disable the lock feature is outlined below:
1. With the TI-25SX powered off, press and hold down the key while
powering the TI-25SX on . The lock icon will be illuminated on the
display.
2. To unlock the TI-25SX repeat step one, but hold down the key while
powering the TI-25SX on.
6.8 Factory Defaults
The TI-25SX can be reset to factory defaults at any time to restore the original gauge
settings. This should only be used if the gauge is not functioning properly, or perhaps
multiple features have been enabled and a clean start is needed.
The procedure to reset the gauge is outlined below:
1. With the TI-25SX powered off, press and hold down the and keys
while powering the TI-25SX on.
NOTE: Once the measurement screen is displayed the keys can be released.

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Material Sound Velocity in/us Sound Velocity m/s
Aluminum 0.2510 6375
Beryllium 0.5080 12903
Brass 0.1730 4394
Bronze 0.1390 3531
Cadmium 0.1090 2769
Columbium 0.1940 4928
Copper 0.1830 4648
Glass (plate) 0.2270 5766
Glycerine 0.0760 1930
Gold 0.1280 3251
Inconel 0.2290 5817
Iron 0.2320 5893
Cast Iron 0.1800 (approx) 4572
Lead 0.0850 2159
Magnesium 0.2300 5842
Mercury 0.0570 1448
Molybdenum 0.2460 6248
Monel 0.2110 5359
Nickel 0.2220 5639
Nylon 0.1060 (approx) 2692
Platinum 0.1560 3962
Plexiglas 0.1060 2692
Polystyrene 0.0920 2337
PVC 0.0940 2388
Quartz glass 0.2260 5740
Rubber vulcanized 0.0910 2311
Silver 0.1420 3607
Steel (1020) 0.2320 5893
Steel (4340) 0.2330 5918
Teflon 0.0540 1372
Tim 0.1310 3327
Titanium 0.2400 6096
Tungsten 0.2040 5182
Uranium 0.1130 3378
Water 0.0580 1473
Zinc 0.1660 4216
Zirconium 0.1830 4648
7.0 APPENDIX A – SOUND VELOCITY TABLE

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8.0 APPENDIX B – APPLICATION NOTES
Measuring pipe and tubing
When measuring a piece of pipe to determine the thickness of the pipe wall, orientation
of the transducers is important. The transducer should be oriented so that the gap (sound
barrier) in the wear face is perpendicular (at a right angle) to the length (long axis) of the
tubing, allowing both sides of the transducer to make the same amount of contact. The
transducer orientation can either be parallel or perpendicular for large diameter piping,
as it’s much easier to ensure both sides are making similar contact.
Measuring hot surfaces
The velocity of sound through a substance is dependent on its temperature. As materials
heat up, the velocity of sound through them decreases. In most applications with surface
temperatures less than about 200°F (100°C), no special procedures must be observed.
At temperatures above this point, the change in sound velocity of the material being
measured starts to have a noticeable effect upon ultrasonic measurement.
At such elevated temperatures, it is recommended that the user perform calibration on
a sample piece of known thickness, which is at or near the temperature of the material
to be measured. This will allow the TI-25SX to correctly calculate the velocity of sound
through the hot material.
Expansion and contraction of the transducer based on temperature, and a varying
temperature gradient, will also affect the measurement in a pulse-echo (P-E)
measurement mode. It is recommended that a “transducer zero” be performed often to
account for the delay line changing length and adversely affecting the accuracy of the
measurements.
When performing measurements on hot surfaces, it may also be necessary to use a
specially constructed high-temperature transducer. These transducers are built using
materials which can withstand high temperatures. Even so, it is recommended that
the probe be left in contact with the surface for as short a time as needed (intermittent
contact) to acquire a stable measurement.

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Measuring laminated materials
Laminated materials are unique in that their density (and therefore sound-velocity)
may vary considerably from one piece to another. Some laminated materials may even
exhibit noticeable changes in sound-velocity across a single surface. The only way to
reliably measure such materials is by performing a calibration procedure on a sample
piece of known thickness. Ideally, this sample material should be a part of the same
piece being measured, or at least from the same lamination batch. By calibrating to each
test piece individually, the effects of variation of sound-velocity will be minimized.
If the variation is relatively close, averaging the sound velocities to minimize error is
another option.
An additional important consideration when measuring laminates is that many included
air gaps or pockets which will cause an early reection of the ultrasound beam. This
effect will be noticed as a sudden decrease in thickness in an otherwise regular surface.
While this may impede accurate measurement of total material thickness, it does
provide the user with positive indication of air gaps in the laminate.
Measuring through paint & coatings
Measuring through paints and coatings are also unique, in that the velocity of the paint/
coating will be signicantly different from the actual material being measured. A
perfect example of this would be a mild steel pipe with .025” of coating on the surface.
Where the velocity of the steel pipe is .2330 in/μsec, and the velocity of the paint is
.0850 in/μsec. If the user is calibrated for mild steel pipe and measures through both
materials, the actual coating thickness will appear to be approximately 3 times thicker
than it actually is, as a result of the differences in velocity.