Ultrasonic Thickness Gage

1WMPD4003292F

About this manual

No part of this publication may be reproduced, transmitted,
transcribed, or translated into any language in any form by anymeans without the written permission of A&D Company, Limited.
The contents of this manual and the specifications of the
instrument covered by this manual are subject to change for
improvement without any notice and obligation on the part of the
manufacturer.
2017

ULTRAGEL II , HIGH Z
of Magnaflux.

All rights reserved.

and SONO

are registered trademarks

1.

Contents

Safety Information .................................................................. 4
1-1-1. Meaning of Alert Indications ................................................ 4
1-1-2. Cautions Concerning Safety Indications .............................. 4
1-1-3. Cautions Concerning Performance ..................................... 52.
Introduction............................................................................. 6
2-1.
Features ............................................................................... 6
3.
Overview "Unpacking, Names, Operation & Response" ....................... 8
3-1.
Unpacking............................................................................. 8
3-2.
Names .................................................................................. 9
3-3.
Operation and Response .................................................... 10
4.
Measurements ...................................................................... 13
4-1.
Preparation ......................................................................... 13
4-2.
Basic Measurement ............................................................ 14
4-2-1. Primary Operation ............................................................. 14
4-2-2. Probe - Zero Function ...................................................... 15
4-2-3. Switching the Display Resolution ...................................... 16
4-2-4. Switching Measurement Modes ........................................ 16
4-3.
Sound Velocity Calibration .................................................. 17
4-3-1. Use of Sound Velocity Calibration ..................................... 18
4-3-2. Calibration of Known Sound Velocities .............................. 18
4-3-3. Calibration of Unknown Sound Velocities .......................... 19
4-3-4. Two point calibration for Sound Velocities ......................... 20
4-3-5. Initialization of Sound Velocities ........................................ 21
4-3-6. Pre-installed Sound Velocities .......................................... 21
5.
Information and Cautions...................................................... 23
5-1.
Battery ................................................................................ 23
5-2.
Transducer.......................................................................... 23
5-3.
Measurement of the Tube & Pipe........................................ 26
5-4.
Couplant ............................................................................. 28
5-5.
Measurement Principle ....................................................... 29
5-6.
Reference Data of Sound Velocities ................................... 30
6.
Specifications ....................................................................... 31－ 3 －1. Safety Information

This section describes information to use the AD-3255 safely andto prevent injury.

1-1-1. Meaning of Alert Indications
All safety messages are identified by the following of ANSI Z535.4.
Each alert indication has the following meaning.

Warning Definitions

A potentially hazardous situation which, if not avoided,

Warning could result in death or serious injury.
CautionA potentially hazardous situation which, if not avoided,
may result in minor or moderate injury or damage to the
instrument.
This is a hazard alert mark.
Operation is prohibited.

OthersCaution An important description for proper use of the instrument.
Note

The information that helps users operate the instrument.

1-1-2. Cautions Concerning Safety Indications
CautionRepair Only authorized individuals may open the case and repair the
AD-3255. Loss of data or malfunctions may result from
opening the case. Contact your local dealer or our service
department to resolve the issue.
Failure Should the AD-3255 experience a malfunction, stop usage
immediately, post a notice indicating "Out of Order" on the AD3255 and move it to place where it will not be used by mistake.
Continued usage of it in this state is very dangerous. Contact
your local dealer for repair.
－ 4 －1-1-3. Cautions Concerning Performance
Gently use the AD-3255 because of the precision instrument.
Strong impacts could result in a malfunction.
Use the accessory carrying case for transport.
The main unit and transducer are calibrated as pair in the factory.
Failure to use an authorized transducer may result in incorrect
thickness measurements. Always keep the main unit and transducer
as pair when asking for a repair.
The AD-3255 is not waterproof. Avoid water, moisture, oil anddust. Avoid an extreme temperature change or impact. Do not
immerse the transducer in water or oil.
Avoid contaminating the transducer connector with water, oil and dust.
Use the accessory strap as needed.
Example: Tie the strap to the main unit to avoid losing the test piece.
Tie the strap to the main unit to prevent the set frombeing stored in a piecemeal fashion.
Do not pull excessively on or sharply bend the transducer cable.
Clean the main unit using a lint free cloth that is moistened withwater and neutral detergent. Clean the connectors and electricalterminals using a dry lint free cloth.
Operating temperature range: 0 [°C] to 50 [°C]
Remove the batteries from the main unit when the AD-3255 is not
used for a long time.

－ 5 －2. Introduction

Congratulations on purchasing an ultrasonic thickness gage AD3255 of A&D Company,Ltd. We recommend that you read throughthis manual carefully before using the AD-3255 for the first time.
Keep the manual nearby for reference.

2-1. Features
The AD-3255 can measure the thickness of various materials usinga principle similar to sonar, displays the thickness value in 0.1 [mm]or 0.01 [mm] units, and is equipped with a multimode feature.
The multimode feature
Pulse - Echo ModeUse this mode for basic measurements or detection of flaws,
cracks and pits.
Echo - Echo Mode
When measuring the thickness, use this mode to eliminate
errors concerned with measuring coating and paintthicknesses. Use the optional transducer, AD-3255-04.
The sampling mode
Single Point Mode
This mode can measure single point thickness where thetransducer is placed.
Sampling rate: 7 [times/ second]
Scan Mode
This mode can display a minimum value from thickness inareas where the transducer has been moved.
Sampling rate: 16 [times/ second]－ 6 －Probe-Zero Function
The AD-3255 is equipped with a probe-zero function to calibrate
the zero point of the transducer in the pulse - echo mode.
The sound velocity can be calibrated with a single point calibration,
two point calibration or numerical input.
The coupling state symbol
indicates the state of the transducer
contacting the material surface.
The AD-3255 can store user settings and calibration data.
The battery indicator

indicates the battery power.

The AD-3255 is equipped with an automatic power-off function:
When no operation is performed for approximately 5 minutes, thedisplay blinks for 20 seconds and then the power is turned off.
The AD-3255 can measure the thickness of metal, plastic, ceramics,
epoxy resin, glass and a variety of other materials.
The range of sound velocity:
1000 to 9999 [m/s],
The range of thickness:
0.8 to 200 [mm],Using the accessory transducer.

－ 7 －3. Overview "Unpacking, Names, Operation & Response"
3-1. Unpacking

Upon receiving the product, inspect the main unit and accessories
contained in the package. Should anything be missing or
damaged, contact and consult your local dealer.
Use the carrying case for transport.
Packing list is as follows:
Main unit .......................................................................................................................... 1
Test piece "is equivalent to the thickness of 4.00 mm" AD-3255-01 .... 1
Transducer for the pulse - echo mode
AD-3255-02 .... 1
Carrying case ............................................................................................................... 1
Empty bottle for the couplant .............................................................................. 1
Strap .................................................................................................................................. 1
Instruction manual "This manual" ........................................................................ 1
Main unit

Test piece

BottleStrap

Transducer for thepulse - echo mode

Carrying case－ 8 －This manual

3-2. Names
Transducer connector "Transmitter"
Transducer connector "Receiver"
References
Battery indicator
Units
Measurement mode
Coupling state
Display :Thickness data andsettings are displayed.
Switches :When pressed,
the buzzer sounds.
Strap holes
Battery coverwhich covers the battery
box in which twoalkaline batteries, "LR6,AA" can be installed.

Transducer forthe pulse - echo mode
Plugs

－ 9 －

3-3. Operation and Response

Switches

Turns the AD-3255 on/off.
(Hold down the switch to turn off.)
Turns the backlight on/off.
Changes the display resolution to 0.1 [mm] or 0.01 [mm].
With the main unit turned off, press theswitch whilepressing and holding theswitch.
Enters the sound velocity settings from the measurement.
Returns the measurement from the sound velocity settings.
Starts the probe - zero function from the measurement.
Specifies a connected transducer in the probe - zerofunction.

Increases the parameter in the setting mode.
Selects a measurement mode in the measurement.
Single point mode
Indication
Measures the thickness in the space where the transduceris placed on the material surface.
Sampling rate: 7 [times/sec.]
Scan mode............................................. Indication
Displays a minimum thickness from the measured data inareas where the transducer has been moved.
Sampling rate: 16 [times/sec.]
Decreases the parameter in the setting mode.
Selects the measurement mode.
Pulse - echo mode ....................... Hide + , Indication
This mode is for basic measurements and can be used todetect flaws, cracks or pits.
Echo - echo mode....................... Show +, Indication
This mode can measure the thickness while eliminating
errors concerned with measuring coating and paintthicknesses.
－ 10 －

Cautions
Use the optional AD-3255-04 transducer if a thickness ismeasured using the echo - echo mode.
The backlight consumes the battery power.
The AD-3255 cannot perform in other modes while the current
mode is active or busy. For example:
During sound velocity calibrations, the probe-zero function
cannot be performed.
During thickness measurements, numerical input is unavailable.
While setting information is displayed, switches cannot be
operated.

Coupling Indication

The AD-3255 can indicate the coupling state between thetransducer and material surface. The coupling state symbol
indicates stable and measurable contact. The blinking symbol
indicates unstable and weak contact.

Units

The units of thickness [mm] or sound velocity [m/s] are displayed.
The unit [in] is not displayed.

Battery Indicator

The blocks indicate the state of the battery.
Adequate battery power.
Blocks indicate changes in battery power levels.
The battery power has been consumed.
Replace with two new alkaline batteries, "LR6, AA".

－ 11 －

Buzzer

Different buzzer sound types indicate the following:___ _Turning on the AD-3255.
pitt pitt
pii___ __ _ _pitt pitt pitt pitt

Turning off the AD-3255.
Initializing sound velocity or when changing
display resolution.

pitt

Switch response

pitt

Measuring thickness.

Error CodeBattery power has been consumed.

Contact your local dealer for any error other than the one
displayed above.

－ 12 －

4. Measurements
4-1. Preparation

Step 1. Install "or Replace" Batteries.
Open the battery cover.
Install two new alkaline batteries
matching polarities "+ and -" withthose of the electrical terminals.
Close the battery cover.

Step 2. Connect Plugs of the Transducer.
Connect the plugs of the transducer to theconnectors on the main unit.
The connector can connect either thetransmitter plug or receiver plug.
Clean the surface of the transducer if dust
is present.

Step 3. Prepare the Couplant.

Prepare the couplant using the bottle.

Step 4. Prepare the Test Piece.
Prepare the accessory test piece withan equivalent thickness of 4.00 mm.
Apply couplant to the surface of thetest piece.

Step 5. Prepare a Material Sample Piece.
Prepare a sample piece to measure the thickness.
Apply couplant to the surface of the material.
－ 13 －

4-2. Basic Measurement

4-2-1. Primary Operation
Step 1. Turn on the Main Unit.

Press theswitch to turn on the main unit.
The buzzer sounds "pitt pitt".
Theof the pulse - echo mode is displayed.
Theof "the initial" sound velocity is displayed.

Step 2. Confirm the Sound Velocity "if necessary".
Press theswitch.
Confirm theof the sound velocity forthe test piece. Select it using theswitchfrom pre-installed values "or using theswitch or
switch", if necessary.
Press theswitch to store the sound velocity.

Step 3. Specify the Transducer "if necessary".
Press theswitch to display the current
transducer. Specify theusing theswitch or
switch.

Step 4. Calibrate the Zero Point.
Contact the transducer to the surface ofthe test piece coated with couplant.
During calibration, the coupling state
symboland the processing indicatorare displayed. The calibration isfinished when 4.00 [mm] is measured andthe buzzer sounds "pitt".

－ 14 －

Step 5. Measure the Material.

Contact the transducer to the surface ofthe material coated with couplant. The
coupling state symbol
is displayed
and the thickness is measured.

Step 6. Turn off the Main Unit.

Hold down theswitch to turn off themain unit. The buzzer sounds "pii".

4-2-2. Probe - Zero Function
Use this function to calibrate the zero point concerning the pulse echo mode. This function cannot be used for the echo - echo mode.

Step 1. Confirm the Sound Velocity "if necessary".
Press theswitch in the measurement mode.
Confirm theof the sound velocity
for the test piece. Select it using theswitch from pre-installed values "or using
theswitch or
switch", if necessary.
Press theswitch to store the soundvelocity.

Step 2. Specify the Transducer.
Press theSpecify theswitch to display the current transducer.
using theswitch or
switch.

AD-3255-02
AD-3255-03
AD-3255-04
AD-3255-05
Not used

Accessory
OptionOptionOption－ 15 －

Step 3. Calibrate the Zero Point.

Contact the transducer to the surface of thetest piece coated with couplant.
During calibration, the coupling state symbol
and the processing indicatorare displayed. The calibration isfinished when 4.00 [mm] is measured andthe buzzer sounds "pitt".

4-2-3. Switching the Display Resolution
With the main unit turned off, press theswitchwhile pressing and holding theswitch to turnon the main unit. The display resolution is switched
to 0.1 [mm] or 0.01 [mm].
Example:4-2-4.

Switching Measurement Modes

The following modes in the measurement can be selected.
Single Point ModeThe
are displayed when theswitch ispressed in the measurement mode. This mode can measuresingle point thickness where the transducer is placed.
Sampling rate : 7 [times/sec.]
Scan ModeThe
are displayed when theswitch is pressedin the measurement mode. This mode can display a minimum
value from the thickness in the area where the transducer has
been moved. Sampling rate : 16 [times/sec.]－ 16 －

In this mode, any brief interruptions "example: a week contact, no
couplant area" of less than 2 seconds in the signal will be ignored.
When the blinking symbol
is displayed, and the contact of
the transducer is lost for 2 seconds or more, the AD-3255 will
display the smallest measurement data.
The measurement value blinks when a minimum value isdisplayed. Blinking continues until the scan mode is turned off.
To measure further, continue as it is.
The AD-3255 doesn't store the scan mode settings. The single
point mode will run when restarting the AD-3255.

4-3. Sound Velocity Calibration
Cautions
Confirm the[m/s] of the sound velocity when calibrating
the sound velocity using the accessory test piece. The settings are
not needed if the sound velocity has not changed.
Sample piece whose coating or paint has removed is required forboth the single point and the two point calibrations. If the sample
piece's coating or paint is not removed, a correct thickness value
cannot be displayed.
In order to keep the accuracy of the measurement, use sample
pieces of known thickness.
Both in the single point and the two point calibrations, measuring thesample thickness is required. Or the calibrations are not performed.
Under the situation, only numerical value input is possible.

－ 17 －

4-3-1. Use of Sound Velocity Calibration"The single point calibration" is the simplest and is commonly used as
the calibration procedure that can optimize the linearity in a wide range.
The method to input the sound velocity using numerical switches.
Refer to "4-3-2. Calibration of Known Sound Velocities".
The method to calculate the sound velocity based on known
thickness of sample piece.
Refer to "4-3-3. Calibration of Unknown Sound Velocities".
"The two point calibration" allows for greater accuracy over a small range
by calculating the probe-zero function and sound velocity calibration.
Refer to "4-3-4. Two point calibration for Sound Velocities".
The method to restore to the sound velocity of the test piece.
Refer to "4-3-5. Initialization of Sound Velocities".
The method to select a sound velocity from pre-installed values.
Refer to "4-3-6. Pre-installed Sound Velocities".

4-3-2. Calibration of Known Sound Velocities
Step 1. Numerical Input of the Sound Velocity.
Press theswitch in the measurement mode.
Display the sound velocity using theswitch from pre-installed values"or using theswitch or
switch".
Press theswitch to store the sound velocity.
Refer to "5-6.Reference Data of Sound"
Velocities" concerning principal sound velocities.

－ 18 －

4-3-3. Calibration of Unknown Sound Velocities
Prepare a sample piece that the thickness is known.

Step １. Perform the Probe-Zero Function.
Perform the "4-2-2. Probe - Zero Function".

Step ２. Measure the Thickness of Sample Piece.
Apply couplant to the surface of thesample piece. Press the transducer against
it. The thickness value is displayed.
Remove the transducer from thesurface after the measurement.

Step ３. Input the Thickness Value.
Press theswitch. The mm blinks.
Input the thickness value using theswitch or
switch.
Press theswitch to store.
The sound velocity is calculated.
Press theswitch to return tothe measurement.

－ 19 －

4-3-4. Two point calibration for Sound Velocities
Prepare two sample pieces or a sample piece with two points
whose thicknesses are known.

Step １. Perform the Probe-Zero Function.
Perform the "4-2-2. Probe - Zero Function".

Step 2. Measure the Thickness of the First Point.
Apply couplant to the first point of thesample piece. Press the transducer
against it. The thickness value of thefirst point is displayed.
Remove the transducer from thesurface after the measurement.

Step 3. Input the Value of the First Point.
Press theswitch. The mm blinks.
Input the value of the first point using
theswitch or
switch.
Press theswitch to display.

Step 4. Measure the Thickness of the Second Point.
Apply couplant to the second point of
the sample piece. Press the transducer
against it. The thickness value of thesecond point is displayed.
Remove the transducer from thesurface after the measurement.

－ 20 －

Step 5. Input the Value of the Second Point.
Input the value of the second point
using theswitch or
switch.
Press theswitch to store and to
display an updated sound velocity.
Press theswitch again so as toexit the calibration mode and performthe measurement with this range.

4-3-5. Initialization of Sound Velocities
With the main unit turned off, press theswitch while pressing andholding theswitch to turn on the main unit.
Release theswitch when the sound velocity is displayed.
The 5920 [m/s] is set to the sound velocity after initialization.

4-3-6. Pre-installed Sound Velocities
The pre-installed sound velocities are as follows:
Refer to the "5-6.Reference Data of Sound". The sound velocity
varies in accordance with the temperature and characteristics ofthe substance.
5920 [m/s]6260 [m/s][m/s]
2720 [m/s]4300 [m/s]
4700 [m/s]5630 [m/s]5740 [m/s]Iron, Accessory test piece
Aluminum
The latest sound velocity that is input
Acrylic resin
Brass
CopperNickelStainless steel

The sound velocity values are sorted in ascending order in the table.
－ 21 －

Therefore, the location of the latest input value varies depending on
the magnitude.

Step 1. Select the Sound Velocity.

Press theswitch in the measurement mode.
Select a sound velocity using theswitch.
Press theswitch to store the new soundvelocity.

－ 22 －

5. Information and Cautions
5-1. Battery

Cautions
Use the specified battery. Install and replace with new batteries.
Install two new alkaline batteries matching polarities "+ and -" withthose of the electrical terminals. Incorrect polarities may result in
malfunctions or damage.
Do not charge the battery. Do not short the terminals of the battery.
Do not disassemble the battery. Do not throw the battery into the fire.
Doing so may cause an explosion of the battery or a leakage from thebattery.
Dispose of the battery properly in accordance with the local
regulations concerning environmental protection.
Keep the battery out of reach of babies or young children.

5-2. Transducer

Probe - Zero Function
We recommend performing this function to maintain the accuracy of
the thickness whenever measuring.
Appropriate Transducer
It is an important to select the appropriate transducer for highly
accurate or highly reliable measurements. Different type oftransducers may be required on the material used. The strength ofultrasonic wave passed through the material is influenced by thefollowing conditions.
The Input Strength of the Ultrasonic Signal
The stronger the inputted ultrasonic wave is, the stronger the received
echo will be. The strength of the input signal is mainly influenced by－ 23 －

the size of the emitter of the transducer. Large emitters can transmit
stronger energy to the material more than small ones.
Absorption and Scattering
Ultrasonic waves are capable of traveling through any material but are
partially absorbed by them. If the signal of the ultrasonic wave ispassed through air bubbles etc. included in the material, the soundwave is scattered. This phenomenon reduces the signal and reduces
the performance of the thickness gage that detects the signal. The
higher ultrasonic wave frequencies are absorbed and are scattered
more than those of lower frequencies. Lower frequencies have
weaker directivity than higher ones. The transducer of higher
frequency is the better choice to detect the exact location of flaws,
cracks or pits.
The State, Roughness and Unevenness of a Surface
Material shape and the roughness of its surface are causes ofmeasurement failure. It is difficult for ultrasonic waves to penetrateuneven surfaces and will result in unstable measurements or poor
reliability. The surface whose thickness is to be measured should beclean and free of any small particulate matter, rust, or dirt. Make themeasurement surface clean and free from particles, rust or dirt. If anyof these obstructions are present, the transducer cannot make proper
contact. In general, clean the surface using a wire brush or sandpaper.
In special cases, clean the surface using a rotary sander or grinder.
Excessive scraping is not necessary. Measuring the very roughsurface like an uneven cast-iron surface is the most difficult. Thisrough surface affects to the sound wave such that the light passes
through the frosted glass. The sound wave is absorbed and scatteredin all directions. Not only does the rough surface result inmeasurement failure, but it also causes excessive transducer wear.
The transducer should be inspected periodically for signs of unevensurface wear. If the surface of the transducer is worn on one side－ 24 －

more than another, the sound wave traveling through the material may
no longer be perpendicular to the material surface. In this case, anaccurate measurement cannot be made.
Holding the Transducer
Press the top of the transducer using thumb or index finger whenmeasuring. Press the transducer properly and keep the position sothat the transducer maintains contact with the surface.
Propagation of Ultrasonic Wave
The sound velocity is easily influenced by the temperature, state ofstress and other physical properties. There are some materials whosesound velocities vary based on the kind of ultrasonic wave and the
direction of travel.
Shape of the Transducer
The appropriate transducer should be selected in accordance with thegeometric shape of the measurement area. In this case, it isnecessary to select the size of the transducer. Connect the transmitterplug and the receiver plug to the coaxial connectors on the main unit.
The plugs can be connected to either the transmitter connector or
receiver connector.
Principle of the "Probe - Zero Function" and Error
Because there is a distance between the coupling surface and thetransmitter element of the transducer, the input position of the coupling
surface and the position of the transmitter element does not match.
Therefore, an error of the delay time will occur. If the "probe - zerofunction" is not performed correctly, an error to the thickness
measurement will occur. If the "probe - zero function" is performed
correctly, the constant error is eliminated and the correct thickness
value will be obtained automatically.
Error Due to Paint or Coating
If paint or coating on the material is very thick, the thickness of thepaint or coating may be included for the measurement.
－ 25 －

Gap of the Transducer
There is an acoustic barrier "gap" between two hemi-circles inside of
the transducer. The ultrasonic wave is transmitted from one of thehemi-circles, its echo is received at the other hemi-circles. Put thematerial under the center of two hemi-circles.
Plug

Top

Gap

5-3. Measurement of the Tube & Pipe

Measurement of Pipe and Tube
The direction of the transducer is important when measuring the wall
thickness of a pipe. If the diameter of the pipe is more thanapproximately 10 cm, it is necessary to match the direction of theacoustic barrier "gap" of the transducer to the perpendicular direction"right angle" of the long axis direction. The measurement of narrow
pipes uses two direction measurements. One of the directions isperpendicular to the long axis direction, and the other is parallel. The
thickness is the smaller of the two values.
The Direction of the Acoustic
Barrier "Gap" of the Transducer
NG, The direction of "gap" is tilted.
OK, The direction of "gap" is parallel.
OK, The direction of "gap" isperpendicular.

－ 26 －

Measuring Laminated Material
In general, there is a difference in the density "sound velocity"
between non-laminated and laminated materials "taping, covering or
painted with epoxy, polyethylene and adhesive, etc.". Multi-laminatedmaterials may even exhibit noticeable changes in the sound velocity
across a single surface. In this case, it is necessary to perform acalibration procedure on a sample piece of known thickness. Ideally,
the sample piece should be the same material being measured, or atleast from the same lamination lot. Individual sound velocity errors canbe minimized by doing so. When measuring laminates, an additional
important consideration is that any included air gaps or pockets willcause premature reflection of the ultrasonic wave. If these effects
exist, the thickness value would be less than the actual thickness. On
the other hand, should air gaps or pockets exist in the material, their
existence would be obvious as obtaining the correct measurement
value will not be possible.
Measurement through Paint and Coating
The sound velocity is remarkably different when a coating exists.
For example: A case that the surface of the steel pipe has a coating ofapproximately 0.6 [mm] thickness. The sound velocity of the steel pipe
is 5920 [m/s]. The sound velocity of the coating is 2300 [m/s].
If the thickness is measured on the coated steel pipe after the soundvelocity is set to the value of the steel pipe, the measured value would
be 2.5 times that of the correct thickness. In this case, the error can beeliminated by the echo - echo mode. The echo - echo mode canmeasure the thickness by excluding the coating thickness completely.
When measuring through a coating, required conditions are as follows :Thickness of a coating ........................................ thinner than 1 mm
Thickness ratio of the material to a coating ....... more than 8-times
The status of a coating may be cause of measurement failure.
The thickness of a coating cannot be measured.
－ 27 －

Suitability of Materials
The measurement of the thickness gage depends upon the soundwave passing through the material. All materials do not allow soundwaves to penetrate. Ultrasonic thickness measurement can be used
for metal, plastic, glass and multifarious materials. but it cannot be
used for some cast iron, concrete, wood, fiberglass "fiber-reinforced
plastic" or some rubber.
Reflection Wave
In measuring of ultrasonic wave thickness in the standard pulse echo mode, not the first reflected wave from the bottom face of themeasured object but the second reflected wave may be measured.
In this case, the thickness value is 2 times that of the correct
thickness. Fully understand these phenomena when using thisthickness gage.

5-4. Couplant

Function of the Couplant
In order to couple the ultrasonic wave between the transducer and thematerial, it is necessary to fill the surface with couplant"Incompressible fluid." Typical couplants are machine oil, glycerin,water, and commercial couplant.
Suitable Quantity of the Couplant
In general, apply approximately one drop of the couplant to thesurface. Applying too much couplant may result in measurement
errors.

Error Related to the Couplant
Should the couplant form a bridge-like thread when removing thetransducer from the surface, the measurement value would be
different between the value of placing the transducer on the surface
and the value removing the transducer from the surface.
－ 28 －Example of Couplants on the Market.
Company name
Magnaflux
Registered trademark
ULTRAGEL II , HIGH Z , SONO

5-5. Measurement Principle
When the ultrasonic wave is transmitted from the transmitter elementof the transducer, the ultrasonic wave pulse "T pulse" is inputted into
the material, and the ultrasonic wave pulse "Echo B" is reflected at thebottom, and is received at the receiver element which is then amplified
as an electric signal. The ultrasonic thickness gage measures the time
length between "T pulse" and "Echo B", and deducts a delay time ofthe delay material, and allows the thickness to be converted anddisplayed. The calculation formulas are as follows:
H : The thickness of the materialv : The sound velocity of the materialt : The time between inputting the ultrasonic wave andreflecting it at the bottom and receiving it as a echo.

H=

vxt
2

Acoustic barrier "Gap"

Transmitter element

Receiver element

Delay material

Transducer

Pulse T

Echo B

Material

Thickness H－ 29 －

5-6. Reference Data of Sound Velocities
Caution The sound velocity of the substance varies in accordance withtemperature and the characteristics of the substance.
Sound velocity [m/s]
1480
1550
1900
2170
2300
2500
to
2800
2720
3230
3240
3500
to
5600
3600
4170
4700
4700
5570
5630
5710
5750
5790
5870
to
5950
5920
5990
6260

Substance

Water 20 [°C]
Natural rubber, Soft rubber
Polyethylene
Lead
Vinyl chloride
Epoxy resin
Acrylic resin
Tin
GoldCast iron
SilverZinc
Brass
CopperQuartz glass
NickelTeflonCrystalStainless steel, SUS304
Steel
Iron
Titanium
Aluminum－ 30 －

6. Specifications

Measurements

Measurement method ............................. Ultrasonic pulse echo technique
Unit ........................................................................................................................ mm, m/s
Sampling rate
Single point mode ........................................................................... 07 times/sec.
Scan mode ....................................................................................... 16 times/sec.

Measurement range
Pulse - echo mode
7 MHz transducer
5 MHz transducer

AD-3255-02 ......................... 0.8 to 200.0 mm
Accessory and optionAD-3255-03 ......................... 1.0 to 300.0 mm
OptionAD-3255-04 ......................... 2.0 to 300.0 mm
Option2.5 MHz transducer AD-3255-05 ......................... 3.0 to 300.0 mm
Option5 MHz transducer

Echo - echo mode
5 MHz transducer

AD-3255-04 ......................... 4.0 to
Option30.0 mm

Measurement accuracy
Range 00.8 to 50.0 mm ...................................... ±0.1 mm ±0.5 %50.1 to 300.0 mm ...................................... ±0.1 mm ±1.5 %The operation temperature range .................................................. 5 to 40 °C

The range of the sound velocity .................................. 1000 to 9999 m/s
Display digits ............................................................................. 4-1/2 digit display
Display range ............................................................................ 0.65 to 600.0 mm
Display resolution .............................................................................. 0.1 / 0.01 mm
The accuracy depends upon the measurement conditions
and the surface of the material.

－ 31 －

General

Display .............................................................. 4.5 digits LCD with EL backlight
Power source ................................................ 2 alkaline batteries "LR6 or AA"
Operation environment .............................. 0 to 50 °C, less than 85 %R.H.
Storage environment ............................ -10 to 55 °C, less than 85 %R.H.
Size of the main unit ..................... 73 mm(W) x 143 mm(H) x 32 mm(D)Mass of the main unit .......... Approximately 160 g "excluding batteries"
Battery life
Approximately 30 hours or more with backlight off, 25 °C andmeasuring 4 mm thickness continuously.
Battery indicator
The battery indicator blinks when the battery power has been consumed.
Automatic power off function
When left idle for approximately 5 minutes, the display blinks for 20
seconds and then the power is turned off.
Accessories
7 MHz transducer ...................................................................................... 1 piece
Test piece "is equivalent to the thickness of 4.00 mm" .................... 1 piece
Carrying case ............................................................................................... 1 piece
Empty bottle for the couplant ............................................................. 1 piece
Strap .................................................................................................................. 1 piece
Instruction manual "This manual" ........................................................... 1 book

Options and Accessories
AD-3255-01
AD-3255-02
AD-3255-03
AD-3255-04

AD-3255-05

Test piece "is equivalent to the thickness of 4.00 mm"(the same as accessory)
7 MHz transducer, φ6 mm, (the same as accessory)
Pulse - echo mode ............................. 0.8 to 200.0 mm
5 MHz transducer, φ10 mm,
Pulse - echo mode ............................. 1.0 to 300.0 mm
5 MHz transducer, φ10 mm,
Pulse - echo mode ............................. 2.0 to 300.0 mm
Echo - echo mode ............................... 4.0 to 30.0 mm
2.5 MHz transducer, φ14 mm,
Pulse - echo mode ............................. 3.0 to 300.0 mm－ 32 －

List of the Transducer
Type
Display symbol
Frequency
Transducer element
Range
Cable
Use

Minimum diameter
Wall thickness
Type
Display symbol
Frequency
Transducer element
Range
Cable
Use
Minimum diameter
Wall thickness
Type
Display symbol
Frequency
Transducer element
Range
Cable
Use
Minimum diameter
Wall thickness

AD-3255-02

Accessory & Option

7 MHz
φ6 mm
Pulse - echo mode
0.8 to 200.0 mm (Steel)Approx. 85 cm
Thin object, wall thickness of pipe, gradualcurved surface
φ15 mmx 2.0 mmAD-3255-03

Option5 MHz
φ10 mmPulse - echo mode
Approx. 85 cm
Thick object
φ20 mmx 3.0 mmAD-3255-04

1.0 to 300.0 mm (Steel)

Option5 MHz
φ10 mmPulse - echo mode
Echo - echo mode
Approx. 115 cm
Thick object, through paint
φ20 mmx 4.0 mm

－ 33 －

2.0 to 300.0 mm
4.0 to 030.0 mm
1Type
Display symbol
Frequency
Transducer element
Range
Cable
Use
Minimum diameter
Wall thickness
Display symbol

AD-3255-05

Option2.5 MHz
φ14 mmPulse - echo mode
3.0 to 300.0 mm
Approx. 85 cm
Thick object, attenuating & scattering object
2
φ30 mmx 4.0 mm
The following symbols are not used.

Note
1 The conditions of the measurement through the paint are that"paint thickness is 1 mm or thinner" and that thickness ratio of"paint" and "measurement object" is 1 : 8 or more at least. The
thickness cannot measure in some case. Paint thickness cannot
measure.
2 In case of a cast iron (such as FC200), measurement range is 3.0
to 40.0 mm.

－ 34 －

MEMO－ 35 －

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