Table of Contents
Advertisement
6.1 PULSE-ECHO MODE (P-E), COATING OFF
This mode measures from the initial pulse (sometimes referred to as an artificial zero) to the first
echo (reflection). This mode only requires one reflection and it is therefore the most sensitive mode
for measuring weak reflections (flaws) typically found when measuring heavily corroded metals. If
this mode is used to measure a coated sample, then the thickness of the substrate plus coating will
be measured.
6.2 PULSE-ECHO COATING MODE (PECT), COATING ON
A custom hybrid combination mode which allows you to measure both the coating thickness and
the material thicknesses at the same time, while still retaining the ability to locate flaws and pits in
materials.
When PECT mode is used, the coating thickness value cannot be viewed on the display of the
gauge - only the base material thickness is displayed. If the data logger is selected however, the
coating thickness value is stored in memory. When the readings data are downloaded to a PC, the
coating thickness measurements can be viewed, together with the A-Scan waveform which is also
stored in the file. This waveform can prove very valuable, as it provides the inspector additional
confidence that the measurement was successful.
The gauge is preset at the factory with a coating sound velocity of 2159 m/s (0.0850 in/µs). factory.
This velocity is a very close approximation of the common coating velocities found in the field. If you
want to change this value, connect the gauge to a PC and use Elcometer NDT Link software
supplied with the gauge to upload a new value - see "Data Transfer Software" on page 19.
Note: Rough surface conditions can have an effect on the overall accuracy in this mode. If the
surface condition is in question, the pulse-echo mode should be used in conjunction with performing
an off block automatic zero as the temperature gradient changes.
6.3 ECHO-ECHO MODE (E-E), THRUPAINT™
This 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).
Thrupaint™ mode cannot be used for flaw or pit detection. Therefore, inspectors may need to use
this mode in conjunction with the standard coating off (pulse-echo) flaw detection mode for some
applications. This combination of using both modes is ideal for the advanced inspectors needs.
6.4 SINGLE ELEMENT TRANSDUCER TRIPLE ECHO MODE (E-E-E)
The triple echo mode measures between three reflections and is used only when a single element
transducer is connected to the gauge. Similar to E-E mode, this technique is commonly used to
eliminate errors from surface coatings and also to make measurements in multiple layered
materials. The primary benefit of this mode, is that a comparison is made, between the second and
third echoes, to verify that a peak jump has not occurred, providing an additional level of confidence
to the measurement.
Generally the disadvantage is that three reflections are needed which requires the use of gates with
controllable thresholds to adjust for sensitivity over a given measurement range. However, the time
corrected gain feature built into this mode automatically adjusts the gain setting for each individual
echo reflection ensuring that the signal levels from each echo are equal in amplitude.
When the element in the transducer sends a pulse of sound waves, it also generates noise. Since
only one element is used to both send and receive sound waves, small defects that reflect very little
sound energy back to the transducer are lost in the reflection of this background noise. Therefore,
these transducers should only be used when general material thickness is required, and never used
for corrosion inspections. If you need to locate blind surface pitting or internal material flaws, a dual
element transducer should always be used.
10
Advertisement
Table of Contents
