Dakota MMX-7 User Manual

OPERATION MANUAL

DAKOTA ULTRASONICS

MMMMXX--77

Data Logging Thickness Gauge

P/N P-160-0002 Rev 1. 10, January 2008

CHAPTER ONE INTRODUCTION.......................................................................1

CHAPTER TWO QUICK STARTUP GUIDE........................................................2

CHAPTER THREE KEYBOARD, M ENU, & CONNECTOR REFERENCE.......12

CHAPTER FOUR PRINCIPALS OF ULTRASONIC ME ASUREMENT .............21

CHAPTER FIVE SELECTING THE MEASUREMENT MODE..........................25

CHAPTER SIX MAKING MEASUREMENTS.....................................................28

CHAPTER SEVEN USING THE DIGITS & B-SCAN DISPLAYS ......................41

CHAPTER EIGHT THRU PAINT MEASUREMENT TECHNIQUE....................53

CHAPTER NINE ADDITIO NAL FEATURES OF THE MMX-7...........................54

CHAPTER TEN DATA STORAGE – SETUP, EDIT, & VIEW GRIDS...............58

CHAPTER ELEVEN SETUPS – CREATE, STORE, EDIT, & RECALL............75

CHAPTER TWELVE USING THE UTILITY SOFTWARE..................................81

APPENDIX A - VELOCITY TABLE .....................................................................82

APPENDIX B - SETUP LIBRARY.......................................................................84

CHAPTER ONE INTRODUCTION

The Dakota Ultrasonics model MMX-7 is a digital ultrasonic thickness gauge with a time based B-Scan and alpha numeric data logger. Based on the same operating principles as SONAR, the MMX-7 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.

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 Corporation, 1500 Green Hills Road, #107 Scotts Valley, CA 95066 USA

• Telephone: (831) 431- 9722

• Facsimile: (831) 431-9723

• www.dakotaultrasonics.com

1.1 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 rest solely with the user of the instrument.

CHAPTER TWO QUICK STARTUP GUIDE

Turn the MMX-7 on and off using the switch located on the bottom right corner of the keypad. When MMX-7 is initially turned on, a flash logo and blinking lights will be displayed prior to entering into the main measurement screen. Note: This section is primarily written as a basic startup guide only.

2.1 Selecting The Transducer Type

The first step in using the MMX-7 is to select the transducer type according to frequency and diameter. By selecting the transducer type from a predefined list, the MMX-7 can recall specific properties about the transducer. Note: Once the transducer has been selected, the MMX-7 will store and recall this transducer type every time the MMX-7 is powered on/off. The type will only change if the user physically selects another transducer type from the list, or selects a previously saved setup. Therefore, if you have previously gone through this section and selected the transducer you are using, proceed to the next section. Use the following steps to select your transducer type:

Selecting the Transducer Type

1) Press the MENU key once to activate the menu items tab. Press the MENU key multiple times to tab right and the ESC key multiple times to tab left until the PROBE menu is highlighted and displaying the submenu items.

2) Use the UP and DOWN arrow keys to scroll through the sub menu items until TYPE is highlighted.

MMX-7 Data Logging Ultrasonic Thickness Gauge

3) Press the ENTER key to display the list of transducer types.

4) Press the UP and DOWN arrow keys to scroll through the transducer list until the appropriate type is highlighted.

5) Press the ENTER key to display the confirmation screen.

6) Press the OK key to select the transducer and return to the menu screen, or

ESC to cancel the selecting the transducer.

2.2 Probe Zero & Calibration

The next step is to calibrate the MMX-7 to the material and transducer being used. If the materials sound velocity is unknown, the MMX-7 can be calibrated to a known thickness sample. This demo will briefly explain both of these techniques.

In either case, the transducer MUST be zeroed on the probe zero disk (battery cover) located on the top of the unit as follows:

Performing a Probe Zero

1) Apply a drop of couplant on the transducer and place the transducer in steady contact with the probe zero disk, and obtain a steady reading.

2) Assuming the probe menu is still displayed from the previous type selection, use the UP and DOWN arrow keys to scroll through the sub menu items

until ZERO TRANSDUCER is highlighted.

3) Press the ENTER key to display the confirmation screen.

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4) Press the OK key to complete the probe zero function, or ESC key to cancel the probe zero function.

5) Remove the transducer from the probe zero disk, and proceed to the calibration section.

Note: The value that is displayed will change depending on the current velocity setting in the MMX-7. Disregard the number that is displayed. It is not important. What is important is accurately performing the steps outlined above

to insure reliability of the probe zero calculation.

Known Velocity

If the material velocity is known, the user may wish to simply enter the velocity number into the MMX-7, rather than have the MMX-7 calculate the velocity value on using a know thickness. The steps for entering the velocity are outlined below:

Using a Known Material Velocity

1) Press the MENU key once to activate the menu items tab. Press the MENU key multiple times to tab right and the ESC key multiple times to tab left until the CAL menu is highlighted and displaying the submenu items.

MMX-7 Data Logging Ultrasonic Thickness Gauge

2) Use the UP and DOWN arrow keys to scroll through the sub menu items until VELOCITY is highlighted.

3) Press the ENTER key to display the Digits Edit Box.

4) Press the UP and DOWN arrow keys to scroll the highlighted value.

5) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

6) Repeat steps 4 & 5 until the velocity number is correctly displayed.

7) Press the OK key to set the velocity and return to the menu screen, or ESC to cancel entering the velocity.

8) Finally, press the MEAS key to return to the measurement screen and begin taking readings.

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Known Thickness

Sometimes the sound velocity of a material is unknown. In this case a sample with a known thickness can be used to determine the sound velocity. It would be very handy to carry a set of mechanical calipers to use in conjunction with the MMX-7 for calibration in the field:

Using a Known Thickness

Note: Be sure that the probe zero procedure has been performed prior to

performing this calibration procedure.

1) Physically measure an exact sample of the material or a location directly on the material to be measured using a set of calipers or a digital micrometer.

2) Apply a drop of couplant on the transducer and place the transducer in steady contact with the sample or actual test material. Be sure that the reading is stable and the repeatability indicator, in the top left corner of the display, is fully lit and stable. Press the MENU key once to activate the menu items tab. Press the MENU key multiple times to tab right and the ESC key multiple times to tab left until the CAL menu is highlighted and

displaying the submenu items.

MMX-7 Data Logging Ultrasonic Thickness Gauge

3) Use the UP and DOWN arrow keys to scroll through the sub menu items until ONE POINT is highlighted.

4) Press the ENTER key to display the Digits Edit Box.

5) Press the UP and DOWN arrow keys to scroll the highlighted value.

6) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

7) Repeat steps 5 & 6 until the known thickness value is correctly displayed.

8) Press the OK key to calculate the velocity and return to the menu screen, or ESC to cancel entering the velocity.

9) Finally, press the MEAS key to return to the measurement screen and begin taking readings.

Note: CHECK YOUR CALIBRATION! Place the transducer back on the calibration point. The thickness reading should now match the known thickness. If the thickness is incorrect, repeat the steps above.

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Basic Material Type

If the material velocity is unknown, and a sample thickness cannot be taken from the material, the user may opt to choose a basic material type from a list with approximate velocity numbers. It’s important to note that these velocities will not always be an exact representation of the material being tested. Use these values only if a close approximation is acceptable. Follow the steps below to select a basic material type:

Selecting a Basic Material Type

2) Use the UP and DOWN arrow keys to scroll through the sub menu items until MATERIAL is highlighted.

3) Press the ENTER key to display the list of material types.

4) Press the UP and DOWN arrow keys to scroll through the material list until the appropriate material is highlighted.

5) Press the ENTER key to display the confirmation screen.

6) Press the OK key to select the material and return to the menu screen, or ESC to cancel the material selection.

7) Finally, press the MEAS key to return to the measurement screen and begin taking readings.

MMX-7 Data Logging Ultrasonic Thickness Gauge

2.3 Measure

The MMX-7 is now ready to measure. There are two different measurement view options, each with a specific purpose – Digits & B-Scan. The steps below outline how to toggle between the different view mode options:

Selecting the Measurement View Option

1) Press the MENU key once to activate the menu items tab. Press the MENU key multiple times to tab right and th e ESC key multiple times to tab left until the DISP menu is highlighted and displaying the submenu items.

2) Use the UP and DOWN arrow keys to scroll through the sub menu items

until VIEW is highlighted.

3) Use the LEFT and RIGHT arrow keys to scroll the view options.

4) Once the view is displayed, press the MEAS key to return to measurement

mode.

DIGITS: Displays the digital thickness value using a larger font size. This view is useful when the MMX-7 is being used as a basic thickness gauge.

BSCAN: The Time Based B-Scan provides the user with a cross sectional view of the material being tested. This mode is useful when there is concern regarding the profile of the blind surface. This can also be a useful view when scanning for pits and flaws.

Once the view has been selected according to the application requirements, the delay and width of the screen will potentially need to be adjusted, if the view has

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been set to BSCAN. Use the following steps to adjust these settings directly from the measurement screen as follows:

Adjusting the Start (B-ST) & Depth (B-DEP)

1) Press the MEAS key once to activate the measure menu items. Press the

MEAS key multiple times to move right and the ESC key multiple times to

move left, until the either the B-ST or B-DEP cell is highlighted.

2) Use the UP, DOWN, LEFT, or RIGHT arrow keys to scroll the B-ST and B-

DEP values.

3) Repeat steps 1 & 2 until the range is correctly being displayed.

Alternatively, the B-ST and B-DEP values can be changed using the Digit Edit Box as follows:

1) Press the MEAS key once to activate measure menu items. Press the

MEAS key multiple times to move right and the ESC key multiple times to move left, until the either the B-ST or B-DEP cell is highlighted.

2) Press the ENTER key to display the digits edit box.

3) Press the UP and DOWN arrow keys to scroll the highlighted value.

MMX-7 Data Logging Ultrasonic Thickness Gauge

4) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

5) Repeat steps 3 & 4 until the B-ST or B-DEP value is correctly displayed.

6) Press the OK key to set the B-ST and B-DEP value and return to the measure screen, or ESC to cancel entering the B-ST or B-DEP value.

7) Finally, press the MEAS key to return to the measurement screen and begin

taking readings.

Note: The B-ST & B-DEP can also be adjusted from the menu tab items. However, us ing the hot menu keys is the easiest method.

DIGITS B-SCAN

In the upper left corner of each of the mode photos above, is the repeatability indicator. The repeatability indicator is represented by six vertical bars and represents how repeatable the measurements are. In regular measurement mode, the MMX-7 makes 4 measurements a second. In scan mode, the MMX-7 makes 32 measurements a second. When the MMX-7 is idle, only the left vertical bar and the underline will be displ ayed. However, when the MMX-7 is making a measurement, five or six of the bars should be displayed on the repeatability indicator. If fewer than five bars are showing, the MMX-7 is having difficulty achieving a stable measurement and the thickness value displayed is potentially be unstable.

CHAPTER THREE KEYBOARD, MENU, & CONNECTOR REFERENCE

3.1 Menu Key (Operation & Sub Menus )

The Menu key activates the primary menu structure containing 9 menu tab groups. These tab groups then contain sub menu items, or functions. The sub menu items have been organized in tab groups according to how closely they are related to the individual tab group names. Let’s first get familiar with how to move around in these tabs before continuing on to the sub menu functions. This procedure is outlined below:

Activating and Getting Around in the Menu Items

MMX-7 Data Logging Ultrasonic Thickness Gauge

1) Press the MENU key once to activate the menu items tab. Press the MENU

key multiple times to tab right, and the ESC key multiple times to tab left until the desired tab group is highlighted and displaying the submenu items.

Now that your familiar with activating and moving amongst the tab groups, let’s have a look at how to move around in the sub menu items as follows:

Getting Around in the Sub Menu Items

1) Use the UP and DOWN arrow keys to scroll through the sub menu items until the desired function is highlighted.

2) Depending on which function is highlighted, use the LEFT, RIGHT, and Enter keys to scroll the options or activate the Digit Edit and List Box

options.

The sections to follow will provide the user with an explanation of the sub menu functions:

3.2 Probe – Menu

Zero: The MMX-7 is zeroed in much the same way that a mechanical micrometer is

zeroed. If the MMX-7 is not zeroed correctly, all of the measurements made using the MMX-7 may be in error by some fixed value. Refer to the section on page 32, for an explanation of this important procedure.

Type: Enables the user to select the type of transducer being used from a chart of transducer types. This provides increased linearity between transducers. Refer to

page 28 for a further explanation. Gain: Increases or decreases the overall amplitude of the signal. Much like turning the volume up or down on a stereo receiver. Refer to page 50 for further info.

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AGC: The MMX-7 is equipped with an automatic gain control when operating in echo-echo mode only. This is much like turning the volume up or down on a stereo receiver. However, the MMX-7 will automatically control how much the volume is turned up or down. Alternatively, the AGC can be manually controlled using the same procedures as GAIN described above. Refer to page 50 for further info.

Measure Mode: Used to select the measurement mode for different application requirements. The modes are P-E (pulse-echo) and E-E(echo-echo). Refer to page 22 for further info.

3.3 CAL – Menu

Units: Toggle between English or Metric units. The readout will change from inches

to millimeters. Velocity: Function to calibrate the MMX-7 by setting the velocity to a known material velocity. Refer to page 34 for further info. One Point: Performs a single point calibration. This option allows the user to automatically calculate the velocity by entering a known sample thickness. Refer to

page 36 for further info. Two Point: Performs a two-point calibration. This option allows the user to automatically calculate the velocity by entering a second known sample thickness.

Refer to page 37 for further info. Material: Select the material velocity from a chart of basic material types, when a

known sample thickness, or material velocity cannot be obtained. Refer to page 40 for further info.

3.4 DISP (display) – Menu

View: Selectable BSCAN (cross section), and DIGITS (large digits) views. Refer to

page 42 for further info.

Backlight: Selectable OFF, ON, AUTO, or INVERT backlight option. Contrast: Adjustable display contrast for variable light conditions. B-ST: Provides the user the ability to change the start position of the B-SCAN view.

Refer to page 48 for further info.

MMX-7 Data Logging Ultrasonic Thickness Gauge

B-DEP: Provides the user the ability to change the overall depth of the viewable measurement area. It functions a lot like a zoom on a camera. Refer to page 46 for further info.

3.5 SETUP – Menu

Open: Displays a list of factory and user defined setups currently stored in memory. These setups can be recalled and used at any time. Refer to page 75 for further info.

Save: Provides the user with the ability to save a custom setup that has been

modified or created by the user. Refer to page 77 for further info. Default Setup: Loads a basic default setup. Use only as a last resort when the

setups in the MMX-7 have been corrupted and a computer is not accessible. Refer to page 79 for further info.

Language: Provides the user the ability to select different languages for the MMX-7. Refer to page 79 for further info.

3.6 DATA – Menu

New: Allows the user the ability to create a new alpha numeric grid with custom

parameters, rows, and columns depending on their application reporting requirements. Refer to page 58 for further info.

Edit: Gives the user the ability to change parameters of grid that have been previously saved. Note: Pre-defined coordinates cannot be changed once they have

been created. Refer to page 70 for further info. Open: This function provides the user with the ability to recall grids that currently

exist in memory from a list of grids. Refer to page 72 for further info. Delete One Grid: This function provides the user with the ability to delete one individual grid from a list of multiple grids previously saved in memory. Refer to page

68 for further info. Delete All Grids: This function provides the user with the ability to delete all grids

currently stored in memory. Refer to page 68 for further info.

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3.7 UTIL (utilities) – Menu

Scan Mode: This function enables a hi speed scan mode that increases the overall

sample rate from the standard 4 measurements a second to 32 measurements a second. Refer to page 54 for further info.

Alarm Status: Toggles alarm mode on or off. Refer to page 55 for further info. Alarm LO Limit: Gives the user the ability to set the LO limit parameter. If the

measurement falls below this value, a red light will illuminate and sound the internal beeper. Refer to page 56 for further info.

Alarm HI Limit: Gives the user the ability to set the HI limit parameter. If the measurement exceeds this value, a red light will illuminate and sound the internal

beeper. Refer to page 57 for further info.

3.8 XFER (transfer) – Menu

Backup Setups: Enables the user the ability to backup the setups currently stored in the MMX-7 to a PC via RS232 port. Refer the help section of the MMX- 7sonicview software for a complete electronic manual.

Restore Setups: Enables the user the ability to restore the setups currently saved on a PC to an MMX-7 via RS232 port. Refer the help section of the MMX7sonicview software for a complete electronic manual.

Backup Grid: Enables the user the ability to backup grids currently stored in the

MMX-7 to a PC via RS232 port. Refer the help section of the MMX-7sonicview software for a complete electronic manual.

Restore Grid: Enables the user the ability to restore grids currently saved on a PC to an MMX-7 via RS232 port. Refer the help section of the MMX-7sonicview software for a complete electronic manual.

About: Provides the user with Dakota Ultrasonics contact information and the MMX-7 software version. Refer the help section of the MMX-7sonicview software

for a complete electronic manual.

MMX-7 Data Logging Ultrasonic Thickness Gauge

3.9 CLR (clear) Key

The primary functions of the CLR key, is to clear a measurement from a grid cell location or set obstruct, and backspace in an Alpha Edit Box. If a user has already saved a measurement and waveform to a cell location, use this key to clear the measurement at any time.

3.10 MEAS (measurement mode) Key

The MEAS key puts the MMX-7 into it’s primary mode of operation. In this mode, the user has a complete view of the LCD, as well as control of the Hot Menu Functions. These hot functions provide the user with the ability to make crucial adjustments to the display, feature settings, and grid storage locations without having to search through the menu and sub menu items. It’s important to first get familiar with moving around in the hot functions as follows:

Getting Around in the Hot Menus

1) Press the MEAS key at any time to return to the primarily measurement

mode.

2) Press the MEAS key multiple times to tab right through the menu fields, and

the ESC key multiple times to tab left through the menu fields, until the desired hot function is highlighted.

Now that you’re familiar with activating and moving amongst the hot function fields, let’s have a look at how to adjust or change the values of these fields:

Adjusting the Values of the Hot Menus

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1) Use the UP, DOWN, LEFT, and RIGHT arrow keys to increase and decrease the values of the hot funct ion fields.

2) Repeat step 1 until the desired value has been achieved.

Alternatively, the B-ST and B-DEP hot function fields can be changed using the Digit Edit Box as follows:

1) Press the ENTER key to display the Digits Edit Box.

2) Press the UP and DOWN arrow keys to scroll the highlighted value.

3) Press the LEFT and RIGHT arrow keys to scroll the digit locations.

4) Repeat steps 2 & 3 until the delay, width, gain, or threshold number is correctly displayed.

5) Press the OK key to set and return to the measure screen, or ESC to cancel entering the B-ST or B-DEP values.

3.11 OK Key

The primary function of the OK key is confirmation of a change or selection. It also toggles the view from B -SCAN to DIGITS in previously saved grid location.

3.12 ESC Key

The ESC key is used in the MENU, MEAS, and EDIT functions as a back or escape function. It also toggles the view from B -SCAN to DIGITS in previously saved grid

location.

3.13 Arrow Keys

MMX-7 Data Logging Ultrasonic Thickness Gauge

The Arrow Keys are used to navigate through the menus, increase/decrease values, and toggle specific function keys.

3.14 ENTER key

The ENTER key is used in the overall menu selection process, to activate list and edit boxes, and save measurements to grid locations.

3.15 MULTI MODE Key

The MULTI MODE key toggles the measurement mode of the MMX-7, from pulse- echo (flaw mode), to echo-echo (thru paint) mode. This is a quick automatic preset

mode that enables the user to change modes without having to manually adjust the mode between pulse-echo and echo-echo. Both modes have been configured for use with any transducer type selected.

3.16 ON/OFF Key

The ON/OFF key simply powers the unit either ON or OFF. Note: Unit will automatically power off when idle for 5 minutes. All current settings are saved prior to powering off.

3.17 Top & Bottom End Caps

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The top & bottom end panels are where all connections are made to the MMX-7. The diagram above shows the layout and description of the connectors:

Transducer Connectors

Refer to Diagram: The transducer connectors, and battery cover/probe zero disk are located on the MMX-7’s top end cap. The transducer connectors are of type Lemo “00”. Note: There is no polarity associated with connecting the transducer to the MMX-7.

Probe Zero Disk & Battery Cover Refer to Diagram: The Battery cover is the large round disk shown in the diagram.

Note: This same disk is also used as a probe zero disk. Simply remove the cover

when replacing the batteries (3 AA cells). When performing a probe zero function, simply place the transducer on disk making firm contact. Important: Be sure to

follow the polarity labels located on the back label of the MMX-7. Note: Rechargeable batteries can be used, however they must be recharged outside of the unit in a stand alone battery charger.

RS-232 Connector Refer to Diagram: The RS-232 connector, located on the bottom end cap, is a 2 pin

female Lemo connector. It is designed to connect directly from the MMX-7 to a standard AT serial port on a PC. The cable supplied with the MMX-7 is a Lemo to 9 pin serial cable. Note: This conn ector is also used to upgrade the MMX-7 with the latest version of firmware.

CHAPTER FOUR PRINCIPALS OF ULTRASONIC MEASUREMENT

4.1 Time versus thickness relationship

Ultrasonic thickness measurements depend on measuring the length of time it takes for sound to travel through the material being tested. The ratio of the thickness versus the time is known as the sound velocity. In order to make accurate measurements, a sound velocity must be determined and entered into the instrument.

The accuracy of a thickness measurement therefore depends on having a consistent sound velocity. Some materials are not as consistent as others and accuracy will be marginal. For example, some cast materials are very granular and porous and as a result have inconsistent sound velocities.

While there are many different ultrasonic techniques to measure thickness, which will be discussed below, all of them rely on using the sound velocity to convert from time to thickness.

4.2 Suitability of materials

Ultrasonic thickness measurements rely on passing a sound wave through the material being measured. Not all materials are good at transmitting sound. Ultrasonic thickness measurement is practical in a wide variety of materials including metals, plastics, and glass. Materials that are difficult include some cast materials, concrete, wood, fiberglass, and some rubber.

4.3 Range of measurement and accuracy

The overall measurement capabilities, based on the wide variety of materials, is determined by the consistency of the material being measured

The range of thickness that can be measured ultrasonically depends on the material as well as the technique being used and the type of transducer. Thickness measurements can be made from a minimum of 0.010 inch to 9.999” in steel. However, the maximum attainabl e thickness is much less for more attenuative materials (materials that absorb sound).

Accuracy, is determined by how consistent the sound velocity is through the sound path being measured, and is a function of the overall thickness of the material. For example, the velocity in steel is typically within 0.5% while the velocity in cast iron can vary by 4%.

4.4 Couplant

All ultrasonic applications require some medium to couple the sound from the transducer to the test piece. Typically a high viscosity liquid is used as the medium. The sound frequencies used in ultrasonic thickness measurement do not travel

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through air efficiently. By using a liquid couplant between the transducer and test piece the amount of ultrasound entering the test piece is much greater.

4.5 Temperature

Temperature has an effect on sound velocity. The higher the temperature, the slower sound travels in a material. High temperatures can also damage transducers and present a problem for various liquid couplants.

Since the sound velocity varies with temperature it is important to calibrate at the same temperature as the material being measured.

Normal temperature range

Most standard transducers will operate from 0°F to 180°F.

High temperature measurements

Special transducers and couplants are available for temperatures above 180°F up to 650°F with intermittent contact. It is necessary to cool the transducer, by submerging the transducer in water between readings, when measuring high temperatures.

Modes and temperature errors

In addition to errors caused by velocity changing with temperature, some modes (measurement techniques) are affected more than others. For example, dual element mode has larger errors due to changes in temperature of the delay line. However, multi-echo techniques help to minimize these errors.

4.6 Measurement Modes

In this section we will discuss the different measurements modes the MMX-7 is capable of operating in, the transducers required, and the reasons for using specific modes:

Pulse-Echo Mode (Flaw & Pit detection)

Pulse-echo mode measures from the initial pulse (sometimes referred to as an artificial zero) to the first echo (reflection). In this mode, the transducer is placed on a reference disk, located on top of the MMX-7, and a key is pressed to establish a zero point for the particular transducer.

In this mode errors result from surface coatings and temperature variations. Since pulse-echo only requires one reflection, it is the most sensitive mode for

measuring weak reflections (flaws) typically found when measuring heavily corroded metals.

V-Path Correction

Dual element delay line transducers have two piezoelectric elements mounted at an angle on one end of the delay line. One element is used for transmitting sound, while the other element only receives sound. The two elements and their delay lines are

MMX-7 Data Logging Ultrasonic Thickness Gauge

packaged in a single housing but acoustically isolated from each other with a sound barrier. This allows the transducer the ability to achieve very high sensitivity for detecting small defects. Also, the surface of the test material does not have to be as flat in order to obtain good measurements.

Dual element transducers are normally used in pulse-echo mode for finding defects, and in echo-echo mode for through coating measurements.

Dual element delay line transducers are usable over a range of 0.025 inches to 20 inches depending on the material, frequency, and diameter.

A limitation of dual element delay-line transducers is the V shaped sound path. Because the sound travels from one element to another, the time versus thickness relationship is non-linear. Therefore, a correction table in the instruments software is used to compensate for this error.

Dual Element Transducer showing V-path of signal

Echo-Echo Mode

The echo-echo mode measures between two reflections. This technique is commonly used to eliminate errors from surface coatings and also to make measurements in multiple layered materials. The disadvantage is that two echoes are needed which requires a much stronger echo (reflection).

Dual Element Transducer in Echo to Echo mode

Searching for small defects

Dual element delay line transducers are especially useful in searching for small defects. In the pulse-echo mode with high amplifier gain, very small defects can be measured. This is very useful during corrosion inspections overall. The dual element style transducer will find wall deterioration, pits, and any porosity pockets during tank and pipeline inspections.

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