DAKOTA ULTRASONICS DX-1 User manual

DX-1 Ultrasonic Micrometer
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INTRODUCTION
The Dakota Ultrasonics model DX-1 is a precision Ultrasonic
Micrometer. Based on the same operating principles as SONAR, the DX-1
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 the DX-1, 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, 155-A DuBois Street
Santa Cruz, California 95060 USA
•Telephone: [phone]
•Facsimile: [phone]
•http://www.dakotainst.com

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OPERATION
The DX-1 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-1 on and off. When the gauge is turned
ON, it will first perform a brief display test by illuminating all of the
segments in the display. After one second, the gauge 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
gauge is ready for use.
When the DX-1 is turned OFF the gauge has a special memory that
retains all of its settings even when the batteries are removed. The gauge
also features an auto-powerdown mode designed to conserve battery life.
If the gauge is idle for 5 minutes, it will turn itself off.

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The PRB-0 key is used to "zero" the DX-1 in much the same way that a
mechanical micrometer is zeroed. If the gauge is not zeroed correctly, all
of the measurements that the gauge makes may be in error by some fixed
value. Refer to page 12 for an explanation of this important procedure.
The CAL key is used to enter and exit the DX-1's calibration mode.
This mode is used to adjust the sound-velocity value that the DX-1 will use
when calculating thickness. The gauge 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 13 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 gauge is
displaying a thickness (IN or MM) or a velocity value (IN/µ
µµ
µsor M/s).

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The UP arrow key has two functions. When the DX-1 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-1 is not in
calibration mode, the UP arrow key switches the SCAN measurement
mode on and off. Refer to page 17 for an explanation of the SCAN
measurement mode.
The DOWN arrow key has two functions. When the DX-1 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-1 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 when the DX-1 is
actually making a measurement.

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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-1 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-1 is
idle, only the left-most bar and the underline will be on. When the gauge is
making a measurement, six or seven of the bars should be on. If fewer
than five bars are on, the DX-1 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, the DX-1 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-1 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 /µ
µµ
µssymbol, the DX-1
is displaying a sound-velocity value in inches-per-microsecond.
When the Msymbol is on, in conjunction with the /s symbol, the DX-1
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-1. It transmits and
receives the ultrasonic sound waves which the DX-1 uses to calculate the
thickness of the material being measured. The transducer connects to the
DX-1 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-1.
The transducer must be used correctly in order for the DX-1 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 transmit, 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-1 has been properly "zeroed" (see page 12) and set to the correct
sound velocity (see page 13), 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 18 for information on transducer
selection.
While the transducer is in contact with the material being measured, the
DX-1 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-1 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
irons, 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-1 is important for the same reason that
setting the zero on a mechanical micrometer is important. If the gauge is
not "zeroed" correctly, all of the measurements the gauge makes will be in
error by some fixed number. When the DX-1 is "zeroed", this fixed error
value is measured and automatically corrected for in all subsequent
measurements. The DX-1 may be "zeroed" by performing the following
procedure:
Performing a Probe-Zero
1) Turn the DX-1 on.
2) Plug the transducer into the DX-1. Make sure that the connectors
are fully engaged. Check that the wearface of the transducer is
clean and free of any debris.
3) On the face of the DX-1, below the keypad, is the metal probe-disc.
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 of the probe-disc. 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. The DX-1 will display "Prb0" while it is
calculating its zero point.
6) Remove the transducer from the probe-disc.

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At this point, the DX-1 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-1 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-1 will remember the last "probe-zero" performed, it is generally a
good idea to perform a "probe-zero" whenever the gauge 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-1 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 gauge is not set to the correct sound-velocity, all of the measurements
the gauge 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-1 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-1 is on.
2) Perform a Probe-Zero (refer to page 12)
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/µ
µµ
µs(or M/s) symbols should
begin flashing. The DX-1 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-1 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-1 is on.
2) Press the CAL key to enter calibration mode. If the IN (or MM)
symbol is flashing, press the CAL key again, so that the IN/µ
µµ
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-1 is now ready to perform measurements.
NOTE: At any time during the calibration procedure (IN,MM,IN/µ
µµ
µs,or
M/s flashing in the display), pressing the PRB-0 key will restore the gauge
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-1 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 gauge is set as closely as
possible to the sound velocity of the material to be measured.

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Two Point Calibration
NOTE: This procedure requires that the operator has two known
thickness points on the test piece that are representative of the
range to be measured.
1) Make sure the DX-1 is on.
2) Perform a Probe-Zero (refer to page 12)
3) Apply couplant to the sample piece.
4) Press the transducer against the sample piece, at the first/second
calibration point, 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 Probe key. The display will flash 1OF2. Repeat steps 3
through 7 on the second calibration point. The DX-1 will now
display the sound velocity value it has calculated based on the
thickness values that were entered in step 7.
9) The DX-1 is now ready to perform measurements.

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Scan Mode
While the DX-1 excels at making single point measurements, it is
sometimes desirable to examine a larger region, searching for the thinnest
point. The DX-1 includes a feature, called Scan Mode, which allows it to do
just that.
In normal operation, the DX-1 performs and displays four
measurements every second, which is quite adequate for single
measurements. In Scan Mode, however, the gauge performs sixteen
measurements every second, but does not display them. While the
transducer is in contact with the material being measured, the DX-1 is
keeping track of the lowest measurement it finds. The transducer may be
"scrubbed" across a surface, and any brief interruptions in the signal will be
ignored. When the transducer loses contact with the surface for more than
a second, the DX-1 will display the smallest measurement it found.
When the DX-1 is not in calibration mode, press the UP arrow key to
turn Scan Mode on and off. A brief message will appear in the display
confirming the operation. While scanning, the display will show a moving
series of dashes instead of a thickness value. When the transducer is
removed from the material being scanned, the DX-1 will (after a brief
pause) display the smallest measurement it found.

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TRANSDUCER SELECTION
The DX-1 is inherently capable of performing measurements on a wide
range of materials, from various metals to glass and plastics. Different
types of material, however, will require the use of different transducers.
Choosing the correct transducer for a job is critical to being able to easily
perform accurate and reliable measurements. The following paragraphs
highlight the important properties of transducers, which should be
considered when selecting a transducer for a specific job.
Generally speaking, the best transducer for a job is one that sends
sufficient ultrasonic energy into the material being measured such that a
strong, stable echo is received by the DX-1. Several factors affect the
strength of ultrasound as it travels. These are outlined below:
•Initial Signal Strength
The stronger a signal is to begin with, the stronger its return echo
will be. Initial signal strength is largely a factor of the size of the
ultrasound emitter in the transducer. A large emitting area will send
more energy into the material being measured than a small emitting
area. Thus, a so-called "1/2-inch" transducer will emit a stronger signal
than a "1/4-inch" transducer.
•Absorption and Scattering
As ultrasound travels through any material, it is partly absorbed. If
the material through which it travels has any grain structure, the sound
waves will also experience scattering. Both of these effects reduce the

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strength of the waves, and thus, the DX-1's ability to detect the
returning echo.
Higher frequency ultrasound is absorbed and scattered more than
ultrasound of a lower frequency. While it may seem that using a lower
frequency transducer might be better in every instance, low frequencies
are less directional than high frequencies. Thus, a higher frequency
transducer would be a better choice for detecting the exact location of
small pits or flaws in the material being measured.
•Geometry of the Transducer
The physical constraints of the measuring environment sometimes
determine a transducer's suitability for a given job. Some transducers
may simply be too large to be used in tightly confined areas. Also, the
surface area available for contacting with the transducer may be limited,
requiring the use of a transducer with a small wearface. Measuring on
a curved surface, such as an engine cylinder wall, may require the use
of a transducer with a matching curved wearface.
•Temperature of the Material
When it is necessary to measure on surfaces that are exceedingly
hot, high temperature transducers must be used. These transducers
are built using special materials and techniques that allow them to
withstand high temperatures without damage. Additionally, care must
be taken when performing a "Probe-Zero" or "Calibration to Known
Thickness" with a high temperature transducer. See Appendix B for
more information on measuring materials with a high temperature
transducer.

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Selection of the proper transducer is often a matter of tradeoffs between
various characteristics. It may be necessary to experiment with a variety of
transducers in order to find one that works well for a given job. Dakota
Ultrasonics can provide assistance in choosing a transducer, and offers a
broad selection of transducers for evaluation in specialized applications.