DAKOTA ULTRASONICS DX-2 User manual

OPERATION MANUAL
DAKOTA ULTRASONICS MODEL DX-2 ULTRASONIC MICROMETER
P/N P-101-0002
Revision 1.2, June 1998

Copyright 1997 Dakota Ultrasonics. All rights reserved.
No part of this publication may be reproduced, translated into another
language, stored in a retrieval system, or transmitted in any form or by any
means; electronic, mechanical, photocopying, recording, or otherwise,
without the prior written consent of Dakota Ultrasonics.
Every precaution has been taken in the preparation of this publication.
Dakota Ultrasonics assumes no responsibility for errors or omissions.
Neither is any liability assumed for damages resulting from the use of
information contained herein.
Any brand or product names mentioned herein are used for identification
purposes only, and are trademarks or registered trademarks of their
respective holders.
300 El Pueblo Road, #100 Scotts Valley, CA 95066
Tel [phone] Fax [phone]
http://www.dakotaultrasonics.com

DX-2 Ultrasonic Micrometer
CONTENTS
INTRODUCTION
OPERATION
THE KEYPAD
THE DISPLAY
THE TRANSDUCER
MAKING MEASUREMENTS
CONDITION AND PREPARATION OF SURFACES
PROBE ZERO
CALIBRATION
SCAN MODE, ALARM MODE, DIFF MODE, RS232 PORT
TRANSDUCER SELECTION
APPENDIX A: PRODUCT SPECIFICATIONS
APPENDIX B: APPLICATION NOTES
APPENDIX C: SOUND VELOCITIES OF COMMON MATERIALS
WARRANTY INFORMATION
1
3
3
7
9
10
12
13
14
18
23
27
29
33
35
DISCLAIMER
Inherent in ultrasonic thickness measurement is the possibility that the
instrument will use the second rather than the first echo from the back
surface of the material being measured. This may result in a thickness
reading that is TWICE what it should be. Responsibility for proper use of
the instrument and recognition of this phenomenon rests solely with the
user of the instrument.

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INTRODUCTION
The Dakota Ultrasonics model DX-2 is a precision Ultrasonic
Micrometer. Based on the same operating principles as SONAR, the DX-2
is capable of measuring the thickness of various materials with accuracy as
high as ±0.001 inches, or ±0.01 millimeters. The principle advantage of
ultrasonic measurement over traditional methods is that ultrasonic
measurements can be performed with access to only one side of the
material being measured.
This manual is presented in three sections. The first section covers
operation of theDX-2, and explains the keypad controls and display. The
second section provides guidelines in selecting a transducer for a specific
application. The last section provides application notes and a table of
sound velocity values for various materials.
Dakota Ultrasonics maintains a customer support resource in order to
assist users with questions or difficulties not covered in this manual.
Customer support may be reached at any of the following:
•Dakota Ultrasonics, 300 El Pueblo Rd, #100
Scotts Valley, California 95066 USA
•Telephone: [phone]
•Facsimile: [phone]
•http://www.dakotainst.com

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OPERATION
The DX-2 interacts with the operator through the membrane keypad
and the LCD display. The functions of the various keys on the keypad are
detailed below, followed by an explanation of the display and its various
symbols. The Keypad
This key is used to turn the DX-2 on and off. When the tool is turned
ON, it will first perform a brief display test by illuminating all of the
segments in the display. After one second, the tool will display the internal
software version number. After displaying the version number, the display
will show "0.000" (or "0.00" if using metric units), indicating the tool is ready
for use.
The DX-2 is turned OFF by pressing theON/OFF key. The tool has a
special memory that retains all of its settings even when the power is off.
The tool also features an auto-powerdown mode designed to conserve
battery life. If the tool is idle for 5 minutes, it will turn itself off.

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The PRB-0 key is used to "zero" theDX-2 in much the same way that a
mechanical micrometer is zeroed. If the tool is not zeroed correctly, all of
the measurements that the tool makes may be in error by some fixed value.
Refer to page 133 for an explanation of this important procedure.
The CAL key is used to enter and exit the DX-2's calibration mode.
This mode is used to adjust the sound-velocity value that the DX-2 will use
when calculating thickness. The tool will either calculate the sound-velocity
from a sample of the material being measured, or allow a known velocity
value to be entered directly. Refer to page 144 for an explanation of the
two CAL functions available.
The IN/MM key is used to switch back and forth between English and
metric units. This key may be used at any time, whether the tool is
displaying a thickness (IN orMM) or a velocity value (IN/µsorM/s).

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The UP arrow key has two functions. When the DX-2 is in calibration
mode, this key is used to increase numeric values on the display. An auto-
repeat function is built in, so that when the key is held down, numeric
values will increment at an increasing rate. When the DX-2 is not in
calibration mode, the UP arrow key switches the SCAN measurement
mode on and off. Refer to page188 for an explanation of theSCAN
measurement mode.
The DOWN arrow key has two functions. When the DX-2 is in the CAL
mode, this key is used to decrease numeric values on the display. An
auto-repeat function is built in, so that when the key is held down, numeric
values will decrement at an increasing rate. When the DX-2 is not in
calibration mode, the DOWN arrow key switches the display backlight
between three available settings. OFF will be displayed when the backlight
is switched off. AUTO will be displayed when the backlight is set to
automatic mode, and ON will be displayed when the backlight is set to stay
on. In the AUTO setting, the backlight will illuminate while theDX-2 is
making a measurement and turn off after several seconds to conserve
battery life.

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The ALRM key has two functions. By holding down the ALRM key
when powering up the DX-2, the audible beeper will be turned on or off
accordingly. After the unit has been turned on, pressing the ALRM key will
toggle the alarm mode to the on/off positions and allow the user to enter a
nominal thickness value. Refer to page 19 for details on how to use the
alarm feature.
The DIFF key is used to enable or disable the Differential mode and
allow the user to enter a nominal value as a comparison against actual
thickness measurements. Refer to page 20 for a complete explanation of
this feature.
The SEND key is used to send the currently displayed thickness
measurement to an external storage device via the DX-2's RS232 port.
Refer to page 21 for an explanation of how to use this feature.

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The Display
The numeric portion of the display consists of 4 complete digits
preceded by a leading "1", and is used to display numeric values, as well
as occasional simple words, to indicate the status of various settings.
When the DX-2 is displaying thickness measurements, the display will hold
the last value measured, until a new measurement is made. Additionally,
when the battery voltage is low, the entire display will begin to flash. When
this occurs, the batteries should be replaced.
These eight vertical bars form the Stability Indicator. When the DX-2 is
idle, only the left-most bar and the underline will be on. While the gauge is
taking a measurement, six or seven of the bars should be on. If fewer than
five bars are on, theDX-2 is having difficulty achieving a stable
measurement, and the thickness value displayed will most likely be
erroneous.

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When the IN symbol is on, theDX-2 is displaying a thickness value in
inches. The maximum thickness that can be displayed is 19.999 inches.
When the MM symbol is on, the DX-2 is displaying a thickness value in
millimeters. If the displayed thickness exceeds 199.99 millimeters, the
decimal point will shift automatically to the right, allowing values up to
1999.9 millimeters to be displayed.
When the IN symbol is on, in conjunction with the/µssymbol, the DX-2
is displaying a sound-velocity value in inches-per-microsecond.
When theMsymbol is on, in conjunction with the/s symbol, the DX-2
is displaying a sound-velocity value in meters-per-second.

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The Transducer
The transducer is the "business end" of the DX-2. It transmits and
receives ultrasonic sound waves that theDX-2 uses to calculate the
thickness of the material being measured. The transducer connects to the
DX-2 via the attached cable, and two coaxial connectors. When using
transducers manufactured by Dakota Ultrasonics, the orientation of the
dual coaxial connectors is not critical: either plug may be fitted to either
socket in the DX-2.
The transducer must be used correctly in order for theDX-2 to produce
accurate, reliable measurements. Below is a short description of the
transducer, followed by instructions for its use.
This is a bottom view of a typical transducer. The two semicircles of the
wearface are visible, as is the barrier separating them. One of the
semicircles is responsible for conducting ultrasonic sound into the material
being measured, and the other semicircle is responsible for conducting the
echoed sound back into the transducer. When the transducer is placed
against the material being measured, it is the area directly beneath the
center of the wearface that is being measured.

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This is a top view of a typical transducer. Press against the top with the
thumb or index finger to hold the transducer in place. Moderate pressure is
sufficient, as it is only necessary to keep the transducer stationary, and the
wearface seated flat against the surface of the material being measured.
Making Measurements
In order for the transducer to do its job, there must be no air gaps
between the wear-face and the surface of the material being measured.
This is accomplished with the use of a "coupling" fluid, commonly called
"couplant". This fluid serves to "couple", or transfer, the ultrasonic sound
waves from the transducer, into the material, and back again. Before
attempting to make a measurement, a small amount of couplant should be
applied to the surface of the material being measured. Typically, a single
droplet of couplant is sufficient.
After applying couplant, press the transducer (wearface down) firmly
against the area to be measured. The Stability Indicator should have six or
seven bars darkened, and a number should appear in the display. If the
DX-2 has been properly "zeroed" (see page133) and set to the correct
sound velocity (see page144), the number in the display will indicate the
actual thickness of the material directly beneath the transducer.

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If the Stability Indicator has fewer than five bars darkened, or the
numbers on the display seem erratic, first check to make sure that there is
an adequate film of couplant beneath the transducer, and that the
transducer is seated flat against the material. If the condition persists, it
may be necessary to select a different transducer (size or frequency) for
the material being measured. See page 23 for information on transducer
selection.
While the transducer is in contact with the material that is being
measured, the DX-2 will perform four measurements every second,
updating its display as it does so. When the transducer is removed from
the surface, the display will hold the last measurement made.
IMPORTANT
Occasionally, a small film of couplant will be drawn out between the
transducer and the surface as the transducer is removed. When this
happens, the DX-2 may perform a measurement through this couplant film,
resulting in a measurement that is larger or smaller than it should be. This
phenomenon is obvious when one thickness value is observed while the
transducer is in place, and another value is observed after the transducer is
removed.

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Condition and Preparation of Surfaces
In any ultrasonic measurement scenario, the shape and roughness of
the test surface are of paramount importance. Rough, uneven surfaces
may limit the penetration of ultrasound through the material, and result in
unstable, and therefore unreliable, measurements. The surface being
measured should be clean, and free of any small particulate matter, rust, or
scale. The presence of such obstructions will prevent the transducer from
seating properly against the surface. Often, a wire brush or scraper will be
helpful in cleaning surfaces. In more extreme cases, rotary sanders or
grinding wheels may be used, though care must be taken to prevent
surface gouging, which will inhibit proper transducer coupling.
Extremely rough surfaces, such as the pebble-like finish of some cast
iron, will prove most difficult to measure. These kinds of surfaces act on
the sound beam like frosted glass on light:, the beam becomes diffused
and scattered in all directions.
In addition to posing obstacles to measurement, rough surfaces
contribute to excessive wear of the transducer, particularly in situations
where the transducer is "scrubbed" along the surface. Transducers should
be inspected on a regular basis, for signs of uneven wear of the wearface.
If the wearface is worn on one side more than another, the sound beam
penetrating the test material may no longer be perpendicular to the material
surface. In this case, it will be difficult to exactly locate tiny irregularities in
the material being measured, as the focus of the soundbeam no longer lies
directly beneath the transducer.

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Probe Zero
Setting the Zero Point of the DX-2 is important for the same reason that
setting the zero on a mechanical micrometer is important. If the tool is not
"zeroed" correctly, all of the measurements the tool makes will be in error
by some fixed number. When theDX-2 is "zeroed", this fixed error value is
measured and automatically corrected for in all subsequent measurements.
The DX-2 may be "zeroed" by performing the following procedure:
Performing a Probe-Zero
1) Make sure the DX-2 is on.
2) Plug the transducer into the DX-2. Make sure that the connectors
are fully engaged. Check that the wearface of the transducer is
clean and free of any debris.
3) The metal probe-disc is on the top end of the DX-2. Apply a single
droplet of ultrasonic couplant to the face of this disc.
4) Press the transducer against the probe-disc, making sure that the
transducer sits flat against the surface. The display should show
some thickness value, and the Stability Indicator should have
nearly all its bars illuminated.
5) While the transducer is firmly coupled to the probe-disc, press the
PRB-0 key on the keypad. TheDX-2 will display "Prb0" while it is
calculating its zero point. Upon completion, the tool will display
0.250 inches (6.35 millimeters), assuming the velocity is set at
.2330 in/µsec (mild steel).
6) Remove the transducer from the probe-disc.

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At this point, the DX-2 has successfully calculated it's internal error
factor, and will compensate for this value in any subsequent
measurements. When performing a "probe-zero", the DX-2 will always use
the sound-velocity value of the built-in probe-disc, even if some other
velocity value has been entered for making actual measurements. Though
the DX-2 will remember the last "probe-zero" performed, it is generally a
good idea to perform a "probe-zero" whenever the tool is turned on, as well
as any time a different transducer is used. This will ensure that the
instrument is always correctly zeroed.
Calibration
In order for the DX-2 to make accurate measurements, it must be set to
the correct sound-velocity for the material being measured. Different types
of material have different inherent sound-velocities. For example, the
velocity of sound through steel is about 0.233 inches-per-microsecond,
versus that of aluminum, which is about 0.248 inches-per-microsecond. If
the tool is not set to the correct sound-velocity, all of the measurements the
tool makes will be erroneous by some fixed percentage. The one point
calibration is the simplest and most commonly used calibration procedure -
optimizing linearity over large ranges. The two point calibration allows for
greater accuracy over small ranges by calculating the probe zero and
velocity. The DX-2 provides three simple methods for setting the sound-
velocity, described in the following pages.

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Calibration to a known thickness
NOTE: This procedure requires a sample piece of the specific
material to be measured, the exact thickness of which is known,
e.g. from having been measured by some other means.
1) Make sure the DX-2 is on.
2) Perform a Probe-Zero (refer to page133)
3) Apply couplant to the sample piece.
4) Press the transducer against the sample piece, making sure that
the transducer sits flat against the surface of the sample. The
display should show some (probably incorrect) thickness value,
and the Stability Indicator should have nearly all its bars on.
5) Having achieved a stable reading, remove the transducer. If the
displayed thickness changes from the value shown while the
transducer was coupled, repeat step 4.
6) Press the CAL key. The IN (or MM) symbol should begin flashing.
7) Use the UP and DOWN arrow keys to adjust the displayed
thickness up or down, until it matches the thickness of the sample
piece.
8) Press the CAL key again. The IN/µs(or M/s) symbols should
begin flashing. The DX-2 is now displaying the sound velocity
value it has calculated based on the thickness value that was
entered in step 7.
9) Press the CAL key once more to exit the calibration mode. The
DX-2 is now ready to perform measurements.

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Calibration to a known velocity
NOTE: This procedure requires that the operator know the sound-
velocity of the material to be measured. A table of common
materials and their sound-velocities can be found in Appendix C.
1) Make sure the DX-2 is on.
2) Press the CAL key to enter calibration mode. If the IN (or MM)
symbol is flashing, press theCAL key again, so that the IN/µs(or
M/s) symbols are flashing.
3) Use the UP and DOWN arrow keys to adjust the displayed velocity
up or down, until it matches the sound-velocity of the material to be
measured.
4) Press the CAL key once more to exit the calibration mode. The
DX-2 is now ready to perform measurements.
NOTE: At any time during the calibration procedure (IN,MM,IN/µs,or
M/s flashing in the display), pressing thePRB-0 key will restore the tool to
the factory default sound-velocity for steel (0.233 IN/µs).
To achieve the most accurate measurements possible, it is generally
advisable to always calibrate the DX-2 to a sample piece of known
thickness. Material composition (and thus, its sound-velocity) sometimes
varies from lot to lot and from manufacturer to manufacturer. Calibration to
a sample of known thickness will ensure that the tool is set as closely as
possible to the sound velocity of the material to be measured.