DAKOTA ULTRASONICS PX-7 User manual

OPERATION MANUAL
DAKOTA ULTRASONICS MODEL PX-7 PRECISION THICKNESS GAUGE
P/N P
-
129
-
0002
Rev
1.
60
January
200
8
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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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PX-7 Ultrasonic Thickness Gauge
CONTENTS
INTRODUCTION
OPERATION
THE KEYPAD
THE DISPLAY
THE TRANSDUCER
MAKING MEASUREMENTS
CONDITION AND PREPARATION OF SURFACES
SELECTING MEASUREMENT MODE &THE LOCK MODE
CALIBRATION
SCAN MODE,ALARM MODE,DIFF MODE,RS232 PORT
TRANSDUCER SELECTION
APPENDIX A:PRODUCTSPECIFICATIONS
APPENDIX B:APPLICATION NOTES
APPENDIX C:SOUND VELOCITIES OF COMMON MATERIALS
WARRANTY INFORMATION
1
3
3
7
9
10
12
13
14
17
22
25
27
29
31
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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PX-7 Ultrasonic Thickness Gauge
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INTRODUCTION
The Dakota Ultrasonics model PX-7is a precision Ultrasonic
Micrometer. Based on the same operating principles as SONAR, the PX-7
is capable of measuring the thickness of various materials with accuracy as
high as ±0.0001 inches, or ±0.001 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 thePX-7, 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
The PX-7interacts 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 PX-7on 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 "0.0000" (or "0.000" if using metric units), indicating the tool is
ready for use.
The PX-7is 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 CAL key is used to enter and exit the PX-7's calibration mode.
This mode is used to adjust the sound-velocity value that the PX-7will 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 page14 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).
The UP arrow key has two functions. When thePX-7is 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 PX-7is in
measurement mode, this key is used to select between three different
modes of measurement ( echo-echo, interface-echo, or auto ). Refer to
page14 for an explanation of the calibration procedure and page13 to
review the various measurement modes.
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The SCAN key switches the SCAN measurement mode on and off.
Refer to page 17 for an explanation of theSCAN measurement mode.
The DOWN arrow key has three functions. When thePX-7is 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 PX-7is 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 the PX-7is
making a measurement and turn off after several seconds to conserve
battery life. Finally, if the DOWN arrow key is pressed and held down while
powering the PX-7on, a LOC mode will be toggled on/off.
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The ALRM key has two functions. By holding down theALRM key
when powering up the PX-7, 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 18 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 page19 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 PX-7's RS232 port.
Refer to page 20 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 PX-7is 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 PX-7is
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, thePX-7is 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, thePX-7is displaying a thickness value in
inches. The maximum thickness that can be displayed is 1.0000 inches.
When the MM symbol is on, the PX-7is displaying a thickness value in
millimeters. If the displayed thickness exceeds 20.00 millimeters, the
decimal point will shift automatically to the right, allowing values up to 25.40
millimeters to be displayed.
When the IN symbol is on, in conjunction with the/µssymbol, the PX-7
is displaying a sound-velocity value in inches-per-microsecond.
When theMsymbol is on, in conjunction with the/s symbol, the PX-7
is displaying a sound-velocity value in meters-per-second.
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The Transducer
The transducer is the "business end" of thePX-7. It transmits and
receives ultrasonic sound waves that thePX-7uses to calculate the
thickness of the material being measured. The transducer connects to the
PX-7via the attached cable, and one coaxial connector.
The transducer must be used correctly in order for thePX-7to produce
accurate, reliable measurements. Below is a short description of the
transducer, followed by instructions for its use.
The diagram above is a side view of a typical single element delay line
transducer. This delay line is fastened to the transducer with a retainer
ring. A drop of couplant is applied between the delay line and
transducer body. The transducer body contains one crystal element that
is responsible for conducting ultrasonic sound into and back from the
material being measured. When the transducer is placed against the
material being measured, it is the area directly beneath the delay line that
is being measured.
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When measuring, press against the top of the transducer 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
delay line seated flat against the surface of the material being measured.
Making Measurements
In order forthe 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
PX-7has been set to the correct sound velocity (see page14), 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 22 for information on transducer
selection.
While the transducer is in contact with the material that is being
measured, the PX-7will 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 PX-7may 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.
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Selecting Measurement Mode
The PX-7 is equipped with four measurement mode options (echo-
echo, interface-echo, auto, or plas). In echo-echo mode, the gauge has the
ability to read thin metals down to .006 inches (.15 millimeters). The echo-
echo mode also allows the user to measure the thickness of metals that
have been previously coated or painted on the surface. This enables the
user to determine the thickness of the metal without having to remove the
paint. In interface-echo mode, the gauge has the ability to read plastics
and thicker materials. The PX-7's auto mode will automatically switch
between echo-echo and interface-echo according to the different materials
being measured. Finally, the plas mod can be used to measure thin plastics
using a special graphite tip. The following section outlines how to switch
between measurement modes:
Measurement Modes
1) Make sure the PX-7is on.
2) Press the UP arrow key to toggle between measurement modes.
The gauge will display GatE followed by I-E, E-E, Auto, or PLAS
depending on which mode the PX-7 was last used in.
3) Repeat step 2 until the desired mode has been displayed.
Note: Once the mode has been selected, the user can use the built-in
LOC feature to prevent additional users from accidentally changing
the mode. When thePX-7is in LOC mode, all features (with the
exception of the calibration and units), are locked and cannot be
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altered by the user. Press and hold the DOWN arrow key while
powering up the PX-7to toggle the LOC feature on/off. Repeat
procedure to toggle on/off status.
Calibration
In order for the PX-7to 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 PX-7providestwo 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 PX-7is on.
2) Apply couplant to the sample piece.
3) 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.
4) Having achieved a stable reading, remove the transducer. If the
displayed thickness changes from the value shown while the
transducer was coupled, repeat step 3.
5) Press the CAL key. The IN (or MM) symbol should begin flashing.
6) Use the UP and DOWN arrow keys to adjust the displayed
thickness up or down, until it matches the thickness of the sample
piece.
7) Press the CAL key again. The IN/µs(orM/s) symbols should
begin flashing. The PX-7is now displaying the sound velocity
value it has calculated based on the thickness value that was
entered in step 6.
8) Press the CAL key once more to exit the calibration mode. The
PX-7is 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 PX-7is on.
2) Press the CAL key to enter calibration mode. If theIN (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
PX-7is 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 theSCAN key will restore the tool to
the factory default sound-velocity for steel (0.233IN/µs).
To achieve the most accurate measurements possible, it is generally
advisable to always calibrate the PX-7to 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.
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PX-7 Modes
Scan Mode
While thePX-7excels at making single point measurements, it is
sometimes desirable to examine a larger region, searching for the thinnest
point. The PX-7includes a feature, called Scan Mode, which allows it to do
just that.
In normal operation, the PX-7performs and displays four
measurements every second, which is quite adequate for single
measurements. In Scan Mode, however, the tool performs eight
measurementsevery second, but does not display them. While the
transducer is in contact with the material being measured, the PX-7is
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 PX-7will display the smallest measurement it found.
When the PX-7is not in calibration mode, press the SCAN 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, thePX-7will (after a brief
pause) display the smallest measurement it found.
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Alarm Mode
The Alarm Mode feature of the PX-7 allows the user to set an audible
and visual Hi / Lo parameter when taking measurements. If the
measurement falls below or above the Hi / Lo limits, set by the user, a red
light will be illuminated on the front panel of the gauge and the beeper
sounded. This improves the speed and efficiency of the inspection process
by eliminating constant viewing of the actual reading displayed. The
following pages outline howto enable and set up this feature:
Using the Beeper
1) While the unit is off, press and hold down theALRM key.
2) PressON/OFF key to power up the unit.
3) Release the ALRM key -BEEP ON or BEEP OFF will be displayed
enabling or disabling the beeper.
4) Repeat steps 1 through 3 to toggle between BEEP ON or BEEP
OFF.
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