NDT Systems TG400 User manual

OPERATOR'S MANUAL
TG400
Ultrasonic Thickness Gage
Featuring:
SplitView, SplitScan & AutoTrack
NDT Systems, Inc.
17811 Georgetown Lane
Huntington Beach, CA 92647
Phone: [phone]
FAX: [phone]
Rev. 1.0
07/06

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1. INTRODUCTION
First and foremost we at NDT Systems, Inc would like to thank you for your purchase of the NEW
TG400 full featured miniature A-Scan Precision Thickness Gage.
As you may have concluded, this manual contains a lot of various information. You do not necessarily
have to read the whole manual in order to use the TG400. Much of the information is presented in a
tutorial fashion to aid in the understanding of specific applications.
CThe Table of Contents of this manual is actually a TABLE/INDEX. Each menu item is mentioned
here for quick easy access to a description of the menu item you may have a question with.
CChapter 2 deals with the menu, structure a description of the features. This would be
recommended reading. There are a few images to help you better understand the concepts.
CChapter 3 & 4 is where the features are described in more detail through tutorials on various
methods of operation. You will also find this chapter help teach how to select the best
transducer for the application. Keep in mind that the proper transducer selection IS the heart of
the inspection, and the key to optimum performance of the TG400’s (or any other ultrasonic
instrument’s) use. The wrong transducer can be compared to putting a 2" speaker on a 100 watt
Macintosh receiver/amp in a stereo system. It may be the best system but it’s going to sound
lousy!
Again, thank you for your purchase of the TG400.

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1.1 Specifications
Display Super Twist LCD, 3.9" 240x320, transflective; backlit, contrast
adjustable, battery status and mode icons, large
thickness/soundpath display. Hollow or filled waveform, reversed
field selectable.
Display Mode RF; Positive Halfwave, Negative Halfwave, Full-wave rectified.
Graticule Graphically Generated, 10 x 10 major divisions
Receiver 0.5 to 25 MHZ Broadband, 1 Band Pass Filter
Gain 100 dB; 0.1, dB selectable steps
Pulser Broad Band Spike
Damping 8 values from 25 to 375 Ohms.
Linear Reject Linear to 90% maximum.
Delay 0 to 20 inches (3807mm) FS (steel equivalent).
Velocity 0.0500 to 0.9999 inch per microsecond
Zero Adjust 0 to 20,000 nanoseconds
Synchronization IP (Initial Pulse), IF (Interface), Delay
Transducer Modes Single or dual-element.
Display Modes RF; positive, negative, full-wave rectified.
Flaw Mode Two (2) gates selectable; positive or negative threshold. Visible and
audible alarms triggered at pulse repetition rate. Gate start variable
over entire displayed range. Gate width variable from gate start to
maximum displayed range. Gate level adjustable from 1% to 99%
full screen.
Thickness Mode Single echo or echo to echo thickness measurement. Independently
adjustable IP, IF and echo blocking gates. High and low alarms,
Large number readout low/high resolution selectable, last reading
hold.
Resolution 0.0001 or 0.001 inch (0.01mm).
Stored Setups 30 user defined setups.
Input/Output RS232; transfer setups to and from PC. Full instrument control by
PC.
Units Inches or millimeters

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Battery Pack Discharge time - Up to 20 hours, typical, depending upon display
back light usage. (3 ‘AA’ NiMH furnished)
Battery Charger 5 hours for full charge.
Transducer Cable Lemo Connectors.
Connectors
Size Top Section: 3.25"W x 7"L x 1.4"D
Weight (Including Approximately 1 pounds (0.6kg)
Battery Pack)

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1.2 Operator Qualifications.
The TG400's unique design makes it the most portable A-Scan Based Ultrasonic Thickness Gage
offered today. As a stand alone Thickness Gage, the TG400 has many features well beyond those of
conventional gages. The same can be said for the TG400’s thickness gaging capabilities; they are
unmatched by any other instrument used for thickness gaging and having an A-trace.
In order for the owner of this advanced technology instrument to fully benefit from the unique
features of TG400, the assigned operator(s) must be experienced and well-founded in the
fundamentals of ultrasonic testing. It would be helpful, though not necessary to possess the
qualifications of ultrasonic testing personnel as defined in Recommended Practice No. SNT-TC-1A,
Personnel Qualification and Certification in Nondestructive Testing, available from the American
Society for Nondestructive Testing (ASNT), 1711 Arlingate Lane, P.O. Box 38518, Columbus, OH
43228-0518, phone [phone], FAX [phone], telex 245347.
1.3 Operational Notations.
In order to simplify these instructions, certain consistent notations are used. In some cases, a
single key stroke produces a desired change; other changes may require a sequence of key strokes or
require continued key activation to "scroll" changes. The following terms and operational notations will
be used throughout. The operator is advised to become familiar with all of them.
KEYS
Sealed membrane keypad incorporating access to menus as well as direct access to specific
functions
VARIABLES
A variety of keys & menu selections are available to change continuous variables such as range,
delay, gate positions, alarm levels, and reject.
SCROLLING
When a key is continuously depressed to change a variable, the effect is referred to as "scrolling".
Scrolling produces either a visible change in the display, a digital readout of the changing value of the
variable, or both.
TOGGLING
Toggling refers to the kinds of changes made by "toggling" switches on an analog-type
instrument. Functions such as OFF/ON, SINGLE/DUAL, and other discrete, limited value operations
exemplify toggling. With The TG400, toggling requires depressing a key to change a function from
one state to another (OFF/ON, for example), and again depressing the key to further advance or
reverse the discrete function.
CURSOR
This term refers to the means for notifying the operator which menu item, function or variable can
be currently acted upon. In The TG400, the cursor location is indicated by highlighting the menu item.
Changing the location of the cursor is accomplished by using the arrow keys.
NOTE:
The TG400 is very much a type of computer in operation, relying heavily on extremely
sophisticated software for much of it’s operation. Should the unit ever seem non-responsive to the
front panel keys or if the operator would like to set the instrument in the factory default use the
following keystrokes. First, turn the TG400 off using the on/off key. If the unit won’t turn off in this
manner, open the rear panel & remove and replace the battery cap. Next, press and hold the SEL key
down and while holding this key down press the ON/Off key. When the instrument turns on let go the
SEL key. The unit is now in the factory default setting. This procedure can also be used if there were a

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complex setup where it may take more time to Change all the parameters rather than start from
scratch or default.
In these instructions, the notation used to indicate positioning the cursor on an item will be shown.
The box drawn around the menu or function item indicates that the operator should key the cursor to
that item, or that the item is already cursored by virtue of a programmed default.
1.4 Transducers and Reference Standards.
Section 3.0, Transducer Selection, contains detailed information regarding the selection and
application of ultrasonic transducers for use with The TG400. For best results, use transducers from
the OPTIMA line of transducers produced by NDT Systems, Inc. A free catalog will be sent on request
by contacting Customer Information at NDT Systems, Inc., 17188 Georgetown Lane, Huntington
Beach, CA 92647, phone [phone], FAX [phone]. In many cases, equivalent
transducers produced by other manufacturers will also yield acceptable results.
It should be kept in mind, though, that no matter how capable the ultrasonic instrument, system
performance and test results are highly dependent upon the characteristics, performance, and
appropriate selection of the transducers used. Also, The TG400 incorporates an automatic probe
recognition feature where many NDT Systems, Inc., Nova transducers will be recognized and a basic
instrument setup invoked for the specific transducer type.
Many common reference standards are also available from NDT Systems, Inc. For custom reference
standards or test blocks, contact Customer Information at the address on the cover.

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2. MENU DESCRIPTIONS
One of the significant features of the TG400 is the Direct Access Keypad. Velocity, Zero and Gain are
just a single keystroke away. There are also 2 option keys. Opt2 is predefined as A-Trace split. Opt1 is
reserved for future use.
MENU FLOW
The following represents the menu flow of the TG400. Pressing the MENU/ESC key repeatedly will
sequence through the menus as shown.
Note: The branch if menu choices is determined by the MODE selection in the MAIN menu. I.E., if
FLAW were selected in the main menu, under the MODE command then the branch would follow the
flaw mode selected to GATE1 then GATE2 then PUL/REC.

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With limited space available, some menu items are abbreviated. None-the-less, abbreviations
and acronyms represent terms familiar to qualified ultrasonic NDT personnel. TG400 is based upon a
powerful microcomputer, combining the absolute latest in high-speed digital electronics technology
and high capability ultrasonic instrument features. TG400 software has been designed with the needs
of NDT personnel foremost in mind; complex, computer-like terminology and operations have been
purposely avoided. The following is a description of each Menu item(s) and its associated sub-
functions.
2.2 MENUS
Menu items are arranged Horizontally along the bottom margin of the display as shown in Figure 2.1.
Whenever a Menu is displayed, an active A-trace is also displayed. The highlighted menu item can
either be selected (to reveal related sub-functions) or changed by appropriate keying of the arrow
keys. In some highlighted Menu items, variables can be changed without having to select sub-
functions. These items will display a Upon its selection. If an item has a sub menu selection the
display will read “ENTER TO SELECT”
MAIN MENU (MENU/ESC Keypad Selection)
The functions grouped in the MAIN menu are used to select TG400 basic setup parameters. These
items are logically among the first to be addressed during a new setup. Last setup/factory default
values are automatically displayed. Even though the defaults permit many kinds of ultrasonic tests
using many kinds of transducers to be successfully performed, highly precise flaw detection tests may
require refinements to the default variables to better match transducer/instrument characteristics.
GAIN
Used to adjust the amplitude of the A-trace display. Increasing or Decreasing the GAIN will
cause the A-trace signal to increase or decrease in amplitude. (Directly Adjustable via up or
down arrow)
ZERO ADJUST (Zero)
A fine delay function which allows for compensation of transducer wearsurfaces, coupling
membranes and angle beam wedge. Adjustment is continuous from 0 to 20,000 nanoseconds.
(Directly Adjustable via up or down arrow)
VELOCITY (VEL)
Sets the material velocity (inches/microsecond or mm/microsecond) used in calculations of
thickness. NOTE: The VELOCITY value will be decreased by approximately one-half from
reference velocity when ANGLE MODE is selected. (Directly Adjustable via up or down arrow)
DELAY (DLY)
Used to adjust the start of the A-trace display along the horizontal axis. Gates that are synchro-
nized with the A-trace will also delay accordingly. (Directly Adjustable
via up or down arrow)
RANGE (RNG)
Used to determine how much time (distance) is represented on the
horizontal axis of the A-trace display. Increasing or Decreasing the
RANGE will cause the A-trace display to expand or contract. (Directly
Adjustable via up or down arrow)
THRESHOLD (THRESH)
Allows Increase or Decrease the Measurement Threshold level. Any
echo or echo half cycle with amplitude equal to or greater than the
Thickness Gate Threshold will be measured. The threshold gate is
the bar on the left of the A-Trace frame extending to the first echo in

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the figure. (Directly Adjustable via up or down arrow)
PROBE ( to Probe Select & Adjustment Menu. See Below )
GATES ( to Gates Adjustment Menu. See Below )
DISP ( to Display Adjustment Menu. See Below )
ALARM ( to Alarm Setup Menu. See Below )
SETUP ( to Instrument Setup, Save & Recall Menu. See Below )
PROBE MENU
SING/DUAL
Used to select transducer type. Options are single or dual element.
Dual can also be used for thru transmission applications
CONTACT / DELAY MODE (CONT/DLY)
Contact or Delay style transducer. Must be in SINGLE Element Mode
for Delay Menu selection
DAMPING (DAMP)
Changes receiver damping through these values : 25, 50, 75, 100,
125, 150, 175 and 375 ohms. As each new value is switched in, the
effect on the waveform in the A-trace display can be observed. Use
Damping to visually optimize the receiver / transducer performance
AUTOMATIC GAIN CONTROL (AGC)
A unique feature of the TG400 is the Automatic Gain Control. This
control is is under hardware control and is fully automatic. The useful-
ness of this feature would be evident on material with varied attenuation properties such as
painted and non painted surfaces or corroded back surfaces. AGC may also help overall reading
accuracies due to the fact that the thickness gate will be reading to the same height on the echo
“flank” (first rising edge). It is generally not acceptable to use AGC with Dual Element Transduc-
ers used for corrosion surveys.
POLARITY
Selects thickness trigger to either Positive or Negative half wave.
HINT: Select the half cycle which exhibits the strongest first half cycle throughout the calibration
range.
RECTIFICATION (Rect)
Sets the rectification mode for the echo signal on the A-trace display. Four selectable
waveform types scan be displayed :
+HW - Positive half-wave rectified
+HW when selected, displays only the positive portion of the RF signal on the A-trace
display.
It is generally not acceptable to use AGC with Dual Element Transducers used for
corrosion surveys as sensitivity will be adjusted based on the largest returned echo. In the
case of pitting or corrosion the initial received signal will likely be somwhat smaller than
the baseline material back wall.

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- HW - Negative half-wave rectified
- HW when selected, displays only the negative portion of the RF signal on the A-trace display.
FW - Fullwave rectified
FW when selected, displays a superimposed -HW signal on a +HW signal on the A-
trace display.
RF - Non rectified radio-frequency
RF when selected, displays both the +HW and -HW signals, non-rectified, at 50%
screen height.
Thickness measurements are permitted in RF RECTIFICATION as well as +HW, -HW or FW. Polarity
bar indicator will also indicate appropriate half of the display when in RF mode.
FILLON - Fill the waveform when in +HW, -HW or FW mode
OFF - Display waveform in outline mode.
FILTER
A broadband frequency filter centered around 7MHz at 100% BW. Best used when probe is
10MHz or less
GATES MENU
IP BLOCKING GATE (IP-Blk)
Used to Increase or Decrease the length of the gate that is used to block out any unwanted
signals after the Main Bang (Initial Pulse ) . Adjustment of the IP BLOCKING GATE will allow
proper setup for IP to first back echo measurement in the thickness mode.
THRESHOLD (THRESH)
Allows Increase or Decrease the Measurement Threshold level. Any echo or echo half cycle
with amplitude equal to or greater than the Thickness Gate Threshold will be measured. The
threshold gate is the bar on the left of the A-Trace frame extending to the first echo in the figure.
(Directly Adjustable via up or down arrow)
ECHO BLOCKING GATE (ECHO-BLK)
Allows Increase or Decrease the length of the echo blocking gate that is used to block out any
unwanted signals between multiple echos in the thickness mode.
ZERO ADJUST (ZERO)
A fine delay function which allows for compensation of transducer wearsurfaces, coupling
membranes and angle beam wedge. Adjustment is continuous from 0 to 20,000 nanoseconds.
(Directly Adjustable via up or down arrow)
ECHO MULTIPLE (MULT)
Allows the selection of a multiple echo from which the thickness measurement will begin. For
instance, 1st to 2nd, 2nd to 3rd and so on. Up to the fifth multiple echo can be selected.
IF BLOCKING GATE (IF-Blk)
Used to Increase or Decrease the length of the gate that is used to block out any unwanted
signals between the first back echo (IF) and the second back echo. Proper adjustment of the IF
BLOCKING GATE will allow measurement of the first back echo to the second back echo in the
thickness mode.

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IP SUPPRESSION (IP-SUP)
Frequently transducers exhibit a broad roll off at the Initial Pulse. The IP Suppression can
frequently compensate for this thereby permitting measurements closer the initial pulse when in
Contact Mode. In many cases, a fine tuned setup will permit readings as thin as 0.020" using a 5
MHz 1/4" Transducer.
MEASUREMENT TIME (MEAS-TIM)
Measurement Time is a unique feature generally used in Delay Line
Transducer Measurements. In the figure to the left we have used a
standard NDT Systems, D11 Transducer. Currently the gage is
triggering on the 2nd delay line multiple which is of no value and could
potentially cause operator confusion when actual measurements
approach the delay end. Therefore, the MEAS-TIM control acts like a
blocking gate except but acts on the tail end of the measured zone.
The area we highlighted in the figure is an area to block out. When
this is done, any time the probe is coupled it will read over range
rather than a fixed reading to the delay end.
DISPLAY MENU
FREEZE
When activated stops any screen activity and “holds” whatever was
on the screen at the time the freeze option was selected. Activate the
function by using the ENTER key.
CONTRAST (CNTRST)
Using the up and down arrow keys, adjust the display to provide
optimal personal viewing.
BACKLIGHT (BKLT)
Turns the backlight to AUTO, ON or OFF. Auto will turn the backlight
on while making measurements. OO will turn the backlight on continuously
and OFF will leave the backlight off at all time. It is recommended to leave
the setting set to off if using the gage in high ambient light conditions. This
will conserve battery life. You will not notice any better viewing while
having the backlight on in high ambient light conditions.
The Following Features are NEW and Unique Productivity Features.
Note the figure to the left. You will note there are two traces annotated ‘A’
& ‘B’. The top trace ‘A’ is called the MAIN Trace Window. The Lower
Trace, ‘B’ is known as the Tracking Window. Also, take note of the Vertical
Cursors. The area between these Cursors is the section of the echo which
will be automatically Zoomed as well as Tracked. Meaning, as the echo
moves left and right on the Main Trace, the actual area of the echo is
Tracked to show the half cycle the gage is triggering on.
SIZEPressing the up and down arrow key will resize the ratio of the Main
Trace Window to the Tracking window. Pressing the Up Arrow in-
creases the Main Window size until there would only be one A-Trace
Screen presented, representing the Main Trace Window with no
Tracking window. Conversely, if you press the Down Arrow Key, the
Tracking window will increase in size, relative to the Main Trace. In this case the Track window
Meas-TIM Zone
MEAS-TIM Set

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will not ever exceed 90% of the Main Trace Window meaning the Main Trace window will always
be at least 10% of the Track window.
AUTOTRACK (TRACK)
With this feature you can turn the AutoTrack feature ON or OFF.
When AutoTrack is ON, the Track window will follow the echo at the point of thickness trigger.
This is where the Threshold line triggers on the echo. The Gage will automatically center the
echo in the center of the Track window regardless of the actual thickness being measured.
When AutoTrack is OFF the Track window does not follow the echo but rather defines an area of
Zoom which will not operate in a dynamic fashion. In this regard, the echo will move left or right
throughout the Track window. If the echo moves outside the area defined by the vertical cursors
there will be no echo displayed on the lower screen.
RANGE2 & DELAY2
These controls adjust the independent time base Range & Delay for the Tracking window. The
total Range for the Track window can not exceed the set Range of the Main Trace window. For
instance if the Main Trace is set to 3" the Track window can not be set to 4". Usually the Track
window is something like 20-40% of the Main Trace window. This operates with AutoTrack Mode
ON or OFF.
ALARM MENU (ALARM)
STATUS - Turns Alarms on & off
LO-THK Sets Low thickness alarm point
HI-THK Sets High thickness alarm point
STATUS MENU
ALRM OFF
No Alarms active
LO Only values at or below the low thickness setting will trigger the alarm light.
HI Only values at or above the high thickness setting will trigger the alarm light.
BOTH
Values at or below or above the low/Hi thickness setting will trigger the alarm light.
THICKNESS ALARM (TALRM)
Used to turn on pre-set HI-LO limit monitoring. If on and limits are set, any reading above or
below the limits will trigger the alarm speaker and light.
SETUP MENU
The functions grouped in the SETUP menu are used to select Factory stored and user modified
and Saved transducer setups.
PICKUse the Up & Down arrow to select transducer types. PICK recalls any ultrasonic setup stored in
the TG400's memory. This includes User setup, Factory Default setup or any of the other 30

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instrument setups. Note: If the gage is powered ON with the ENTER button depressed, the
Factory Default setup will be loaded.

1313
MODIFY
When selecting any of the NDT Setup #s the MODIFY select allows the user to modify a Factory
setup and save it as a specific “User” setup. This allows the user to start with a probe that may
be similar and then modify it to suit a specific probe or application.
UNITS
Allows selection of the basic unit of measurement for the gage. Select between INCHES or
MILLIMETERS.
SYNC
(IP) INITIAL PULSE SYNC
Causes the gage to synchronize the presentation of the A-trace to the Initial Pulse or Main Bang
echo. The Initial Pulse will initially appear at the left edge of the display.
(IF) INTERFACE SYNC
Causes the gage to synchronize the presentation of the A-trace to the first resolvable echo signal
past the initial pulse which is greater or equal to the Interface Threshold. This could represent the
interface of water to metal if using Immersion or bubbler test method or the interface of a plastic
tip to an entry surface is using a delay line transducer. The Interface Pulse will appear at the left
edge of the display.
One is the MAIN range. This is adjusted in the IP mode. Both the menu selectable range and keypad
range change values. The main range will incorporate the total range of the delay material (water,
plastic tip etc) as well as the thickness of the material under test.
The other is IF range which must fit fully into the MAIN range. Best way to set this up is to put
instrument into IP range and be sure that the flaw or back wall echo will always stay on screen. This
means that the water path to the IF will be seen as well as the IF to destination target/back wall. Be
sure this rule stays in place throughout the water path change probability.
It is OK to select a long MAIN range and a short IP. For instance, I even set 20 inches as a MAIN
range and then used a IF range of 2”. The IF range can never be longer than the MAIN range!!! We
think we rang this all out but.. if a limit we didn’t check gets through the gage would likely lock up.
1 Setup transducer/pulser parameters to optimize test as usual.
2 Be sure to start with IP mode (GATES menu)
3 You can adjust these parameters in RF , FW, HW- or HW+
4 On the GATES menu be sure to set an IP block outside the IP noise/ringdown at test sensitivity.
This should not approach the lower limit of the lowest potential Interface position or the Interface
(IF) could get blocked, i.e., If the IP block is set to 2 inches, the IF can not be below that limit or
the next echo over the threshold will be the IF start.
5 In the MAIN or GATES menu, set an IF threshold level (THRESH). User adjustable. 20% - 75%
depending on noise.
6 Set rectification HW+, HW-, RF or FW as desired.
3.0 TRANSDUCER SELECTION
The TG400 is a capable precision thickness gage. Virtually any broad band or general purpose
transducer (application dependant) used with the TG400, as can equivalent transducers produced by
other manufacturers. NDT Systems, Inc. Manufacturers a line of NOVA Series thickness gage
transducers which utilize our patented AutoProbe recognition technology. When using these probes
press PROBE ID and the instrument will recognize the attached probe and set up for a general
purpose test for that probe. The user can then adjust and save the modified setup.

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While the discussion below pertains to applications in metals, there are numerous applications to
a wide variety of engineering materials. For plastics, glasses and other more or less isotropic or
homogeneous materials, the procedures are similar to those for metals. Major differences in testing
nonmetals are in the velocity of sound and different impedance characteristics. Fiber-reinforced
composite materials are characteristically anisotropic, having different acoustical properties in
different directions, and often require specialized transducers and procedures for satisfactory
ultrasonic testing results.
In general, however, many of the transducer selection factors outlined below apply for nonmetals,
but additional experimentation may be required. NDT Systems, Inc. engineers have extensive
experience in ultrasonic testing of many materials and can provide assistance when called upon.
The following suggestions are by no means fully comprehensive or mandatory. Alternative ap-
proaches may produce essentially the same results. The operator should experiment to determine the
best transducer for given applications or contact NDT Systems, Inc. for advice.
Thickness Gaging Applications.
Thickness Ranges
Metals with Thicknesses Ranging from 0.008 inch to Approximately 0.750 inch (0.2 to 20.0
millimeters). In this range, there are overlapping considerations that will dictate which type of
transducer will produce the desired results. Foremost is the limitation of the minimum thickness
that can be resolved by different types of transducers.
Single Element, Delay Line Transducers.
Some highly damped, high frequency transducers of this type are capable of producing fully
resolved multiple back echos equivalent to as little as 0.005 inch (0.13mm) in steel having smooth
surfaces. However, such transducers will be relatively expensive and not readily attainable.
Standard inexpensive delay line transducers, highly damped, in the frequency range of 10 to 20
MHZ, will ordinarily produce good results down to approximately 0.008 inch (0.20mm). Given
smooth surfaces in metals having relatively low attenuation, like wrought steel or aluminum, such
transducers can be used to gage up to 0.75 inch (20mm), more or less, depending upon the
length of the delay line.
To determine the practical minimum thickness resolution of a delay line transducer, it is necessary
to have an array of thin shims ranging in thickness around the desired minimum to be measured.
Inexpensive sets of steel shims, used as feeler gages, can be obtained from well equipped
hardware stores, automotive parts houses or specialty tool suppliers. The nominal thickness is
typically imprinted onto each shim, often in inches and millimeters. Available sets contain as many
as 15 or 20 shims, ranging from 0.005 to 0.025 inch (0.13 to 0.64mm) thick. While we have found
that the stated thickness is nominal, subject to variation up to ±0.0004 inch (0.01mm), these shims
can be used to readily determine the minimum thickness that can be expected from a given
transducer.
Under ideal conditions, parts having very smooth, parallel surfaces can be measured to an
accuracy approaching ±0.0001 (±0.003mm). To achieve such accuracy, not only is it necessary
to have an appropriate transducer, the thickness gaging instrument must have extremely stable,
high speed electronic circuitry. TG400 fulfills this requirement admirably. For a procedure to
demonstrate this capability, see Section 4.3.2.3, below.
Single Element, Focused Immersion Transducers.
Some transducers of this type have been designed specifically for precision thickness gaging of
metals 0.010 inch (0.25mm) thick and greater. Small diameter, high frequency, short-focused
immersion transducers also can be used to measure the distance to quite small internal reflectors.

1515
This is useful, for example, in gaging remaining thickness over internal passages in turbine
blades. Procedures for using immersion transducers are outlined in Section 4.3.2.4, below.
Metals with Thicknesses Ranging from 0.030 inch (0.76mm) Upward.
Single Element Contact Transducers Hard-Faced Wear Plates.
Depending upon active element size and frequency, highly damped (broadband) transducers of
this type can seldom be used on steel or aluminum much below 0.030 inch (0.8mm). The ultimate
minimum thickness limitation must be determined experimentally.
The advantage of using this type of transducer is that much thicker sections can be gaged, and on
materials that have less than smooth surfaces or are relatively attenuative. Again, some
experimentation will indicate the limitations and advantages among transducers of the same type,
but having different sizes, frequencies and spectral characteristics.
When trying to achieve best results on relatively thin materials, the most important considerations
are frequency and spectral characteristics. Foremost is the need to use a transducer having the
greatest bandwidth, all other things being equal. Such transducers have relatively large, high
density masses bonded to the internal face of the active element. This mass minimizes the
amount of "ringing" of the active element following excitation by a short duration, high voltage
electrical pulse. This kind of high mechanical damping minimizes the length of the ultrasonic
wavetrain associated with the high energy initial pulse as well as the subsequent back-wall echos.
Also necessary to achieve best thickness resolution is the need to use the highest frequency
consistent with external factors that affect coupling efficiency, and to take material attenuation into
consideration. IF a transducer is expected to produce minimum thickness resolution and be used
over a broad range of thicknesses, test material attenuation may dictate a compromise. While
higher frequencies produce thinner thickness resolution, attenuation is more pronounced at higher
frequencies.
For relatively flat, smooth-surfaced steel or aluminum test objects, highly damped contact
transducers in the frequency range from 5 to 10 MHZ generally will produce acceptable results in
the thickness range from 0.040 inch (1.0mm) up to 5 inches (125mm) more or less. With
QFT-100, and under ideal external conditions, transducers of 5, 7.5 or 10 MHZ having active
elements of 0.25 to 0.50 inch (6.4 to 12.7mm) diameter will cover the range from 0.030 to 10
inches (0.76 to 250mm) or more.
For procedures outlining the use of broad banded contact transducers, see Section 4.3.2.1.
Single Element Contact Transducers with Membrane and Other Protective Devices.
So-called protected element transducers are used in relatively rugged applications involving
rough, abrasive test object surfaces or surfaces at elevated temperatures. Usual designs of
protected element transducers include reduced internal damping, lower frequencies and larger
diameters. As a result, their application typically ranges from a few tenths of an inch (10mm plus
or minus) upwards.
Often used on castings, forgings and mill-finished piping, protected element transducers are
infrequently used for thickness gaging -- more often used for flaw detection. However, if the
protective element is a relatively thin elastomer or flexible polymer, the procedures for thickness
gaging are similar to those for single element contact-type transducers. For thicker wear-caps or
temperature-protective delay lines, procedures are more like those for delay line transducers.
Dual Element Contact-Type Transducers.
This category of transducers is frequently used in thickness gaging applications, combining some
of the advantages of both single element contact and delay line models. They have two elements,
each with a separate delay line, mounted side-by-side in a single fixed housing. The elements are

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isolated acoustically from one another by a sound-absorbing barrier between them. They are
electrically isolated as well; one serves as a transmitter, the other as a receiver. The ultrasonic
instrument must provide the capability of isolating the pulser and receiver, as does the TG400.
Practical minimum thickness resolution from a dual element transducer optimized for thickness
gaging is approximately 0.040 inch (1.0mm). Typical frequencies for thickness gaging
applications range from 2.25 to 10 MHZ, and the elements can be semi-circular or rectangular.
While again it is only possible to generalize the applications, dual elements provide a good
balance among resolution, penetration and sensitivity.
Procedures for using dual element transducers are outlined in Section 4.3.2.5.
3.3 Transducers for Non-Metallic Test Materials.
Virtually all the techniques and applications described above can be applied to a host of
non-metallic and composite materials. It is not possible to cover the numerous applications in this
manual. Transducer selection for non-metals often is much more involved. However, The TG400’s
unique design can accommodate a huge variety of transducer types. For advice, contact our
Transducer Applications Specialists. Often a transducer can he recommended on the basis of a
description of the application. If not, it may he necessary to submit samples of the test material.
3.4 Transducers for Specialized Applications.
Ultrasonic testing techniques have applications beyond those traditionally though of regarding
flaw detection and thickness gaging. There are applications in material characterization, flaw
analysis, extensometry, bondtesting, liquid level sensing, velocity measurement, and others in
more or less limited usage. In some cases, because the application is specialized, so must be
the transducers.

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4.0 TG400 SETUP AND OPERATING PROCEDURES.
In designing the menus for the TG400, particular attention has been paid to simplifying the process of
locating items, then prompting the operator to do something intuitive in order to change control
settings.
4.2 FACTORY Setup Variables.
When the TG400 is turned on by pressing the ON/OFF control, the LOGO screen is displayed
automatically. When the gage is operated for the first time, or if FACTORY DEFAULT is selected from
memory, all the control variables "default" to specific values (After that they will display the last
previous setup parameters). For many common thickness gaging applications, it is only necessary to
"fine tune" a few variables. Some applications can be started without any adjustments. The
FACTORY setup variables have values that match or nearly match a variety of the most commonly
used transducers for thickness gaging.
With TG400’s broadband receiver and Spike pulser, it is possible to achieve high resolution,
penetration, and sensitivity by using relatively highly damped, broadband transducers for thickness
gaging. Of course, there will be instances where reduced bandwidth transducers will be preferred, but
a surprising number of applications can be satisfied with broadband transducers.
4.3 Thickness Gaging Procedures
Sample Setup procedures (A Walk Through using a 3/8" 5.0 MHZ Contact Transducer
Once the effects of variables affecting thickness gaging precision are understood, the operator can
quickly diagnose which variables should be adjusted. A good way of observing these effects, and to
become quickly familiar with TG400’s controls is to perform the following procedure:
1. Attach a highly damped, broadband transducer such as the OPTIMA CHG053 or NOVA C11 (5
MHZ, 3/8 inch element diameter) to the micro-dot connector on the ML-01 transducer cable
supplied with TG400. Insert the Lemo connector in the receptacle marked with a dot on the top
closure of TG400.
2. Obtain a steel stepped wedge with several known thickness steps. An excellent choice, and the
one upon which this procedure is based, is the OPTIMA Model TBS114. This wedge, made
from 4340 vacuum-melted steel alloy and nickel plated, has five steps precision machined to
thicknesses of 0.100, 0.200, 0.300, 0.400, 0.500 inch (2.54, 5.08, 7.62, 10.16, 12.70mm).
3. Couple the transducer to the 0.500 inch step using a drop of glycerin, light machine oil, mineral
oil, or low viscosity gel-type couplant. For this familiarization exercise, it will be convenient to
use a rubber band or a small weighted object that will hold the
transducer in place. This procedure will relieve you from having to
hold the transducer in place for an extended period during
familiarization.
4. Press the ON/OFF key. During this very brief period, TG400
undergoes a host of internal diagnostic checks. Once these checks
are complete, the LOGO screen automatically appears.
5. An A-trace will appear, along with the Main Menu items and a
thickness readout, the large numbers in the upper area of the A-
trace. This is the FACTORY setup default full-scale range of 2.00
inches (50mm). Also note the large back echo at the second major
horizontal scale division and the thin horizontal bar at 40% full-scale
(FS) amplitude. Observe that this horizontal line extends from the

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extreme left edge of the A-trace and terminates on the leading edge of the back echo. This line,
or bar, represents the thickness gate (T-gate) and shows which echo stops the gate. In this
example, since the 0.500 inch step is the one being measured and the horizontal FS range is
2.00 inches, the T-gate terminates on the first echo above 40% FS amplitude, the back echo
from the 0.500 inch step. Along the left-hand vertical axis, a signal will also be seen. Since the
FACTORY setup defaults to initial pulse synchronization (IP SYNC), this signal is the initial
pulse (IP) with its leading edge coincident with the left-hand vertical axis.
One other feature that should be noted is the presence of a dark bar extending horizontally
along the thickness gate, in this case on the MAIN A-Trace window from the left-hand axis. This
bar represents the IP blocking gate (IP-BLK gate) which serves to "block" out the string of high
amplitude echos typically accompanying the IP. In its FACTORY setup default position, the IP-
BLK gate is at 0.070" to block out the IP echos and thus prevent the T-gate from triggering in or
on the IP. Control of the IP-BLK gate is explained further in this procedure. (If an undamped or
lightly damped transducer other than those recommended for this exercise is being used, it may
be necessary to make an immediate adjustment of the IP-BLK gate in order to proceed. If
necessary, go to Step 15, below, and perform the necessary adjustment.)
9. For the transducers and stepped wedge recommended, the thickness readout (T-readout)
should be within a few thousandths of an inch from 0.500 inch plus or minus. Position of the
cursor in the Main Menu is at GAIN.
10 With the cursor at GAIN, Up & Down arrow keys increase/decrease effective gain accordingly.
11. To become familiar with the RANGE function, position the cursor at
RNG. The up arrow key will squeeze the echos on the A-trace to the
left, that is, except for the initial pulse. If multiple back echos are
present, they will move toward the left and approach each other
more closely. In our 0.500 inch steel block example, depress the UP
arrow key until the first back echo, originally at the second vertical
division of the electronic graticule moves to approximately fourth full
vertical division. The second back echo will be aligned (or nearly so)
at the 8th full division. The readout value under RNG should be
close to 1.2 inch.
However, note that T-readout did not change unless the gain was
substantially increased. With TG400’s digital electronics, it is not
necessary to use the graticule or other precise settings of range in
order to calibrate for, and to readout precise thicknesses.
13. The DELAY function also has pronounced effects on the location of signals on the A-trace. Set
the full-scale range using the RNG menu selection at about the 1" inch and position the cursor
at DELAY. Depress the UP arrow key and observe the effect. Signals move toward the left,
including that of the initial pulse, which moves off-screen to the left. Note that the distance
between multiple back echos does not change as it did when range
was increased. Continued depression of the RIGHT arrow key
moves echos toward the left until they are completely delayed off-
screen. If calibration has been performed for the material under test,
the readout under DELAY indicates how far the display has been
delayed.
14. With the RANGE at 1.00 inch cursor to Select GATES from the
MAIN Menu and select IP-BLK. The Up & Down arrow keys control
the length of the blocking gate, referred to as "IP-BLK gate", and
represented by the Thick dotted bar extending horizontally along the
thickness gate line on the A-trace from the left-hand side of the

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screen. Its purpose is to "block" the trailing edge echos associated with the initial pulse or any
spurious signals which might interfere with what is known as the true interface. This group of echos
contains ring-down echos from the transducer and "noise" accompanying stray reflections resulting
from coupling. The "noise" is minimal when both the front surface of the transducer and the surface of
the test object are smooth. This is the usual case with new, unworn transducers and with many finely-
machined test blocks or reference standards. However, actual test objects seldom have clean, smooth
surfaces. They often have rough machined or mill-finished surfaces (as-cast surfaces on castings),
sometimes corroded and sometimes painted surfaces. In these cases, the extent of coupling noise will
be greater than that returned from test blocks.
At default, the length of the blocking gate (IP-BLK gate) is about 0.200 inch equivalent in steel.
With medium to broadband transducers of 2.25 MHZ or greater, the distance is usually sufficient
to block IP echos and coupling noise from standard test blocks. Note, however, that it would not
be possible to material less than the width of the calibrated IP-BLK gate, less than 0.200 inch at
FACTORY defaults. If the total IP signal is greater, and the blocking gate must be increased,
any significant echos within the blocking gate, transducer back echos or otherwise, will be
blocked and will determine the minimum thickness that can be gaged with the correct digital
thickness readout. In such cases, it may be necessary to use a different transducer or a different
technique. With highly damped, broadband transducers of 5 or 10 MHZ, it should be possible to
shorten the IP-BLK gate to permit IP to first back echo digital readout of 0.030 inch steel or
equivalent.
15. At this point, use the Up/Dn arrow keys to change the length of the
IP-BLK gate in order to observe the effects of the control.
16. The IF-BLK (interface echo blocking) functions in a similar fashion as
the IP-BLK but when Interface Synchronization (IF) is selected. IF
Sync automatically starts the T-gate at the leading edge of the
interface echo (the echo between the delay line and the test object
surface. The delay line could be a plastic tip or a water path).
Whenever practical, if delay lines are used, interface synchronization
(IF Sync) should be selected. A complete description of IF Sync is
discussed in step 25e.
17. Before examining the function of THICKNESS THRESHOLD
(THESH),press MENU to display the MAIN Menu. At THRESH, note
that the horizontal T-gate bar is at 40%. Up or Down arrow keys change the threshold level of
the T-gate, and the actual level of the T-gate is readout in % full-scale amplitude, variable from
10% minimum to 90% maximum. The FACTORY default amplitude of generally 40% (probe
selection dependant) is a good compromise and generally effective when the first back echo
amplitude is maintained between approximately 70% full-scale and to somewhat greater than
saturation amplitude (greater than 100% full-scale).
18. Move the cursor to ALARM Menu item. Using the left or right arrow will move to the item. Press
ENTER to enter ALARM setup
19. Both LO-THK and HI-THK function in the same manner. These selections represent low
thickness alarm and high thickness alarm, respectively. They can be used to alert the operator
(through the front panel visual LED) when pre-set thickness levels, low, high or both low and
high, have been exceeded. The level sets are scrolled when the Up or Down arrow keys are
depressed. With the cursor at the STATUS position, arrow keys select the alarm system (visual
LED) on and off. In gaining familiarization with these features, note that it is not possible to
"cross" these levels. That is, the high alarm setting cannot be set lower than the low alarm
setting and vice-versa.