DAKOTA ULTRASONICS MX-1 User manual

OPERATION MANUAL
DAKOTA ULTRASONICS MODEL MX-1 ULTRASONIC THICKNESS GAUGE
P/N P
-
139
-
0002
Rev 1.
9
0
,
January 2008
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Copyright 2008Dakota 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.
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MX-1 Ultrasonic Thickness Gauge
CONTENTS
INTRODUCTION
OPERATION
THE KEYPAD
THE DISPLAY
THE TRANSDUCER
MAKING MEASUREMENTS
CONDITION AND PREPARATION OF SURFACES
PROBE ZERO
CALIBRATION
PROGRAMMING THE MX-1’S SOUND VELOCITY
TRANSDUCER SELECTION
APPENDIX A:PRODUCTSPECIFICATIONS
APPENDIX B:APPLICATION NOTES
APPENDIX C:SOUND VELOCITIES OF COMMON MATERIALS
WARRANTY INFORMATION
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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 modelMX-1is a precision Ultrasonic
Micrometer. Based on the same operating principles as SONAR, theMX-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 theMX-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:
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OPERATION
TheMX-1interacts 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.
This key is used to turn theMX-1on 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.
TheMX-1is turned OFF by pressing the ON/OFF key. The gauge has
a special memory that retains all of its settings even when the power is off.
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-0key is used to "zero" theMX-1in 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 page11 for an explanation of this important procedure.
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 orMM) or a velocity value (IN/µsorM/s).
The BACKLIGHT 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 theAUTO
setting, the backlight will illuminate when theMX-1is 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 theMX-1is 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 theMX-1is
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, theMX-1is 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, theMX-1is displaying a thickness value in
inches. The maximum thickness that can be displayed is 19.999 inches.
When the MM symbol is on, theMX-1is 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, theMX-1
is displaying a sound-velocity value in inches-per-microsecond.
When theMsymbol is on, in conjunction with the/s symbol, theMX-1
is displaying a sound-velocity value in meters-per-second.
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The Transducer
The transducer is the "business end" of theMX-1. It transmits and
receives the ultrasonic sound waves which theMX-1uses to calculate the
thickness of the material being measured. The transducer connects to the
MX-1via the attached cable, and two coaxial connectors. When using
transducersmanufactured by Dakota Ultrasonics, the orientation of the
dual coaxial connectors is not critical: either plug may be fitted to either
socket in theMX-1.
The transducer must be used correctly in order for theMX-1to 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
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against the material being measured, it is the area directly beneath the
center of the wearface that is being measured.
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
MX-1has been properly "zeroed" (see page11) and set to the correct
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sound velocity (see page12), the number in the display will indicate the
actual thickness of the material directly beneath the transducer.
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 14 for information on transducer
selection.
While the transducer is in contact with the material being measured, the
MX-1will 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, theMX-1may 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 theMX-1is 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 theMX-1is "zeroed", this fixed error
value is measured and automatically corrected for in all subsequent
measurements. TheMX-1may be "zeroed" by performing the following
procedure:
Performing a Probe-Zero
1) Make sure theMX-1is on.
2) Plug the transducer into theMX-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 top of theMX-1, above the display, 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-0key on the keypad. TheMX-1will display "Prb0" while it is
calculating its zero point.
6) Remove the transducer from the probe-disc.
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At this point, theMX-1has successfully calculated it's internal error
factor, and will compensate for this value in any subsequent
measurements. When performing a "probe-zero", theMX-1will 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
theMX-1will 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 theMX-1to 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.
Programming the Sound Velocity
Since theMX-1is a fixed velocity gauge, the correct sound velocity for
the material being measured must be programmed into the gauge via the
serial port on the bottom of the unit. Approximate sound velocities for
common materials can be found in appendix C.
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Programming the MX-1
1) Connect the serial cable (Part No. N-306-0010) to a COM port on
a computer and to the RS232 connector located on the bottom of
theMX-1. Remove and replace the rubber plug before and after
programming.
2) Assuming that DakView2 PC software is installed and running,
select theMX-1icon from the DakView2 gauge selector icons. A
window will appear with the title “MX-1 Velocity Upload Utilty”.
3) Under the Preset Velocity heading are two options. The first
option is a test box with a velocity number displayed. The text box
is editable. To change the velocity, click in the text field and type in
the appropriate velocity number. The second option is a list box
with a material type displayed. To change the material type, click
the down arrow located to the right of the list box. Use the arrows
or slider bar to scroll through the available material types. Click on
a material to select it.
4) To select theunits (english or metric), click on the radio button
located to the left of the units title. A black dot will appear in the
button when selected.
5) Click on the Program Gauge button located in the top right of the
window. A pop up window will be display with the following
message “Turn on gauge power”. Press the ON/OFF button on the
MX-1to download the velocity. TheMX-1will display the new
velocity.
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TRANSDUCER SELECTION
TheMX-1is 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 theMX-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 strongersignal
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 MX-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.
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APPENDIX A
Product Specifications
Physical
Weight: 10 ounces
Size: 2.5W x 4.75H x 1.25D inches
(63.5W x 120.7H x 31.8D mm).
Operating Temperature: -20 to 120°F (-20 to 50 °C)
Case: Extruded aluminum body / nickel plated aluminum end
caps.
Keypad
Sealed membrane, resistant to water and petroleum products.
Power Source
Two “AA” size, 1.5 volt alkaline or 1.2 volt NiCad cells. 200 hours
typical operating time on alkaline, 120 hours on NiCad.
Display
Liquid-Crystal-Display, 4.5 digits, 0.500 inch high numerals. LED
backlight.
Measuring
Range: 0.025 to 19.999 inches (0.63 to 500 millimeters)
Resolution: 0.001 inch (0.01 millimeter)
Accuracy: ±0.001 inch (0.01 millimeter), depends on material
and conditions
Sound Velocity Range: 0.0492 to 0.3930 in/µs (1250 to 10000m/s)
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APPENDIX B
Application Notes
•Measuring pipe and tubing
When measuring a piece of pipe to determine the thickness of the pipe
wall, orientation of the transducers is important. If the diameter of the pipe
is larger than approximately 4 inches, measurements should be made with
the transducer oriented so that the gap in the wearface is perpendicular (at
right angle) to the long axis of the pipe. For smaller pipe diameters, two
measurements should be performed, one with the wearface gap
perpendicular, another with the gap parallel to the long axis of the pipe.
The smaller of the two displayed values should then be taken as the
thickness at that point.
Perpendicular Parallel
•Measuring hot surfaces
The velocity of sound through a substance is dependant upon its
temperature. As materials heat up, the velocity of sound through them
decreases. In most applications with surface temperatures less than about
200°F (100°C), no special procedures must be observed. At temperatures
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