Chapter Eight Thru Paint Measurement Technique; Introduction To Thru Paint Measurement; Using Thru Paint Mode - DAKOTA ULTRASONICS MMX-7 Operation Manual

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
back wall echoes returning from the test material. Since both of these back wall
echoes travel the same path through the paint or coating, the thickness of the coating
is subtracted out of the measurement, measuring only the base material. This avoids
the time to remove existing coating from the test material during the inspection
process.
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. The combination of using both modes is
ideal for achieving the nominal base material thickness, as well as for finding defects
or pitting in materials.

8.2 Using Thru Paint Mode

By selecting the transducer type from the list of probes stored in the MMX-7, a basic
echo-echo thru paint configuration is recalled from memory. Each of the 'high
damped' transducers in the list contain pre-configured echo-echo settings. However,
fine adjustments may be necessary in order to be suitable for your specific
applications. These configurations are general setups only. Once the transducer
type has been selected, and the appropriate calibration procedure completed, the
MMX-7 can be toggled between pulse-echo (flaw & pits), and echo-echo (thru-
paint) modes by simply pressing the MULTI MODE key located on the keypad. The
standard transducer that will be used for common steel applications is a ¼" 5MHz
high damped transducer (1/4IN – 5.0MHZ HD). However, any of the transducers with
the HD label have been optimized for echo-echo thru paint applications.
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 MMX-7 has been programmed to identify the
modes available to a specific transducer.
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