Ultrasonic Thickness Gage

1WMPD4003292A

Note
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

All rights reserved.

ULTRAGEL II , HIGH Z and SONOof the Magnaflux company.

are registered trademarks

Contents
1.

Safety Information ....................................................................2
1-1-1. Meaning of Alert Indications ................................................2
1-1-2. Cautions Concerning Safety Indications..............................2
1-1-3. Cautions Concerning Performance .....................................32.
Introduction ..............................................................................4
2-1. Features .................................................................................43.
Overview "Unpacking, Names, Operation & Response".........................6
3-1. Unpacking ..............................................................................6
3-2. Names ....................................................................................7
3-3. Operation and Response........................................................84.
Measurements........................................................................ 11
4-1. Preparation........................................................................... 11
4-2. Basic Measurement..............................................................124-2-1. Primary Operation.............................................................124-2-2. Probe - Zero Function ......................................................14
4-2-3. Switching the Display Resolution ......................................15
4-2-4. Switching Measurement Modes ........................................15
4-3. Sound Velocity Calibration....................................................16
4-3-1. Use of Sound Velocity Calibration .....................................16
4-3-2. Calibration of Known Sound Velocities..............................17
4-3-3. Calibration of Unknown Sound Velocities..........................17
4-3-4. Two point calibration for Sound Velocities .........................18
4-3-5. Initialization of Sound Velocities ........................................19
4-3-6. Pre-installed Sound Velocities..........................................20
5.
Information and Cautions .......................................................215-1. Battery..................................................................................21
5-2. Transducer ...........................................................................21
5-3. Measurement of the Tube & Pipe .........................................24
5-4. Couplant ...............................................................................26
5-5. Measurement Principle .........................................................27
5-6. Reference Data of Sound Velocities .....................................28
6.
Specifications .........................................................................29－ 1 －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
AD-3255 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.
－ 2 －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 and dust.
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 moistened with waterand 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.

－ 3 －2. Introduction
Congratulations on purchasing an ultrasonic thickness gage
AD-3255 of. We recommend that you readthrough this manual carefully before using the AD-3255 for the firsttime. 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 paint thickness.
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]－ 4 －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 other metal, plastic,
ceramics, composite materials, epoxy resin, glass and a variety ofother materials.
The range of sound velocity:
1000 to 9999 [m/s],
The range of thickness:
0.8 to 200 [mm],Using the accessory transducer.

－ 5 －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－ 6 －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

－ 7 －

3-3. Operation and Response

Switches

Turns the AD-3255 on/off.
Turns the backlight on/off.
Changes the display resolution to 0.1 [mm] or 0.01 [mm].
switch while pressing and holding thePress theswitch after turning off the main unit.
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 thetransducer is placed on the material surface.
Sampling rate : 7 [times/sec.]
Scan mode ............................................ Indication
Displays a minimum thickness from the measured datain the area 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 major measurements and can be used
to detect a flaw or pit.
Echo - echo mode ....................... Show +, Indication
This mode can be measure the thickness that iseliminated errors concerned with measuring coating
and paint thickness.
－ 8 －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 can not perform in other modes while the current
mode is active or busy. For example :During sound velocity calibrations, the probe-zero function can
not 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 symbol
indicates stable
and measurable contact. The blinking symbol
indicates
unstable and weak contact. When the measurement is complete,
the buzzer sounds.

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 to 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".

－ 9 －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 error code
displayed above.

－ 10 －

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.

Battery coverLR6 or AA
batteries
Battery box

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 plug if couplant is present.

Step 3. Prepare the Couplant.

Plug
Connector

BottlePrepare the couplant using the bottle.
Couplant

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

Test piece
Couplant

Step 5. Prepare a Material Sample Piece.
Prepare a sample piece to measure the thickness.
Apply couplant to the surface of the material.
－ 11 －

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 twice.
Confirm theof the sound velocity forthe test piece. Select it using theswitchfrom pre-installed values "or using theswitch andswitch", if necessary.
Press theswitch to store it.

Twice
SelectStep 3. Specify the Transducer "if necessary".
Press theswitch to display the current
transducer. Specify theusing theswitch andswitch.

or

Step 4. Calibrate the Zero Point.
Contact the transducer to the surface ofthe test piece coated with couplant.
The calibration is finished when theindicator
is displayed, 4.00 [mm] ismeasured and the buzzer sounds "pitt".

－ 12 －

Test piece

Couplant
ResultStep 5. Measure the Material.
Contact the transducer to the surface ofthe material. The indicatorisdisplayed and the thickness ismeasured.

Transducer
Material
Thickness

Step 6. Turn off the Main Unit.
Press theswitch to turn off the main
unit. The buzzer sounds "pii".

－ 13 －

VersionTurn off4-2-2. Probe - Zero Function
Use this function to calibrate the zero point concerning the pulse echo mode. Don't use this function for the echo - echo mode.

Step 1. Confirm the Sound Velocity "if necessary".
Press theswitch twice in themeasurement mode.
Confirm theof the soundvelocity for the test piece. Select it using
theswitch from pre-installedvalues "or using theswitch andswitch", if necessary.
Press theswitch to store it.

Twice
or

SelectStep 2. Specify the Transducer.
Press theSpecify theswitch to display the current transducer.
using theswitch andswitch.

AD-3255-02

Accessory

AD-3255-03

OptionAD-3255-04

Optionor

Not usedTransducer

Step 3. Calibrate the Zero Point.
Contact the transducer to the surface of thetest piece coated with couplant.
The calibration is finished when the indicatoris displayed, 4.00 [mm] is measured andthe buzzer sounds "pitt".

－ 14 －

Couplant

Test piece4-2-3. Switching the Display Resolution
Press theswitch to turn on the main unit whilepressing and holding theswitch after turning
off the main unit. The display resolution is switched
to 0.1 [mm] or 0.01 [mm].

Turning off

Example:The display resolution has been exchanged from 0.01 [mm] to 0.1 [mm].

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.]
In this mode, any brief interruptions "example: a week contact,no couplant area, etc." less than 2 seconds in the signal will beignored.
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 5 times when a minimum value
is displayed.
The AD-3255 doesn't store the scan mode settings. The single
point mode will run when restarting the AD-3255.
－ 15 －

4-3. Sound Velocity Calibration
Cautions
Confirm the[m/s] to 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
can not be displayed.
In order to keep the accuracy of the measurement, use sample
pieces of known thickness.

4-3-1. Use of Sound Velocity Calibration"The single point calibration" is the simplest and is commonlyused as the calibration procedure that can optimize the linearity ina 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 select a sound velocity from pre-installed values.
Refer to "4-3-6. Pre-installed Sound Velocities".
－ 16 －

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

Twice
or

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 the sample Measure it and remove the transducer
piece. Press the transducer against it. The
thickness value is displayed.
Couplant
Remove the transducer from the surface
Sample pieceafter the measurement.

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

Calculated velocity

Thickness

4-3-4. Two point calibration for Sound Velocities
Prepare a sample piece "or two pieces" whose thickness 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.

Measure it and remove the transducer

Couplant
Sample piece
Measured value

Step 3. Input the Value of the First Point.
Press theswitch. The mm blinks.
Input the value of the first point using
theswitch andswitch.
Press theswitch to displayof next step.

orCorrected value

Proceed next step

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.

－ 18 －

Measure it and remove the transducer

Measured value

Step 5. Input the Value of the Second Point.
Input the value of the second point
using theswitch andswitch.
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.

orUpdated velocity

Thickness

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

－ 19 －

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

Step 1. Select the Sound Velocity.
Press theswitch twice in the measurement.
Select a sound velocity using theswitch.
Press theswitch to store a new sound velocity.

Twice
Selection

Storage－ 20 －

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.

－ 21 －

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
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 in－ 22 －

measurement 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 morethan another, the sound wave traveling through the material may nolonger 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
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.
－ 23 －

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.
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.
－ 24 －

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 theother 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.

－ 25 －

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 can not use
for a part kind of cast iron, concrete, wood, fiberglass "fibre-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 this thickness gage.

5-4. Couplant
Function of the Couplant
In order to couple the ultrasonic wave between the transducer andthe material, 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.
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.
－ 26 －Example of Couplants on the Market.
Company name
Magnaflux company
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
to convert the electric signal toan ultrasonic wave.

Receiver element
to convert the ultrasonic wave toan electric signal.

Delay material

Transducer

Pulse T

Echo B

Material

Thickness H－ 27 －

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－ 28 －

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
5 MHz transducer
Echo - echo mode
5 MHz transducer

AD-3255-02 ......................... 0.8 to 200.0 mm
AD-3255-03 ......................... 1.0 to 300.0 mm
AD-3255-04 ......................... 2.0 to 300.0 mm
AD-3255-04 ......................... 4.0 to

30.0 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 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.

－ 29 －

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
Approx. 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

Test piece "is equivalent to the thickness of 4.00 mm"

AD-3255-02

7 MHz transducer, 6 mm,
Pulse - echo mode .............................. 0.8 to 200.0 mm

AD-3255-03

5 MHz transducer, 10 mm,
Pulse - echo mode .............................. 1.0 to 300.0 mm

AD-3255-04

5 MHz transducer, 10 mm,
Pulse - echo mode .............................. 2.0 to 300.0 mm
Echo - echo mode ............................... 4.0 to 30.0 mm－ 30 －

List of the Transducer
Type ............................................. AD-3255-02
Accessory.....................
Display symbol
Frequency ............................... 7 MHz
Transducer element .......... 6 mm
Range ........................................ 0.8 to 200.0 mm (Steel)
Cable .......................................... Approximately 85 cm
Use ............................................... Thin object, wall thickness of pipe, gradualcurved surface, pulse - echo mode
Minimum diameter ........ 15 mm
Wall thickness .................. x 2.0 mm

OptionType ............................................. AD-3255-03
Display symbol .....................
Frequency ............................... 5 MHz
Transducer element .......... 10 mm
Range ........................................ 1.0 to 300.0 mm (Steel)
Cable .......................................... Approximately 85 cm
Use ............................................... Thick object, pulse - echo mode
Minimum diameter ........ 20 mm
Wall thickness .................. x 3.0 mm
Type ............................................. AD-3255-04
Display symbol .....................
Frequency ............................... 5 MHz
Transducer element .......... 10 mm
Range
Pulse - echo mode ........ 2.0 to 300.0 mm
Echo - echo mode ......... 4.0 to 030.0 mm
Cable .......................................... Approximately 115 cm
Use ............................................... Thick object
Minimum diameter ........ 20 mm
Wall thickness .................. x 3.0 mm

OptionThe following symbols are not used.
Display symbol .....................
,－ 31 －

MEMO－ 32 －

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