Dakota Ultrasonics CMX - Manual (Page 69)

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CHAPTER EIGHT
THRU PAINT MEASUREMENT TECHNIQUE
8.1 Introduction to Thru Paint Measurement
The principle behind thru paint measurement is by measuring the time between two
backwall echoes returning from the test material. Since both of these backwall
echoes travel the same path through the paint or coating, the thickness of the coating
is subtracted out of the measurement so that only the actual material thickness can
be measured. This feature saves the user a great deal of time scraping and
removing the coating from tanks and pipes during the inspection process.
The primary purpose of thru paint measurement is to determine actual or overall
material thickness by eliminating the coating thickness. Thru paint mode cannot be
used for flaw or pit detection. Therefore, inspectors may need to use echo-echo thru
paint mode in conjunction with the standard pulse-echo flaw detection mode for some
applications. Chassis tubing inspectors and sanctioning bodies will use the echo -
echo mode for tubing with powder coatings, and pulse-echo mode for tubing without
coating. The combination of using both modes is ideal for the advanced inspectors
needs.
8.2 Using Thru Paint Mode
The first thing to note in this section, is that by selecting the transducer type from the
list of probes stored in the CMX, a basic echo-echo thru paint configuration is
recalled from memory. Each of the transducers in the list contains pre-configured
echo-echo settings. The standard transducer that will be used for common steel
applications ¼” 5MHz high damped transducer (1/4IN – 5.0MHZ HD). This is the
recommended transducer for this industry and should be used for thru paint
applications. Any of the auto recognition coating transducers are also high damped
transducers and will work in echo-echo mode as well.
Note: When a transducer is selected for use, all of the measurement modes
available for use with this transducer can easily be determined by pressing the multi-
mode button on the keypad. The CMX has been programmed to identify the modes
available to a specific transducer.
Once the transducer type has been selected and the appropriate calibration
procedure completed, the CMX can toggle between pulse-echo (flaws & pits), and
echo-echo (thru paint) modes by simply pressing the MULTI MODE key located on
the keypad. Refer to page 38 for additional information.
The CMX can also be configured for thru paint applications by selecting a factory
setup stored in the list of setups in the CMX. Refer to page 86 for information on
recalling a setup. Once either the transducer type or setup has been selected, the
inspector is ready to begin making measurements.