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CHAPTER SIX
THROUGH PAINT MEASUREMENT - MULTIMODE
6.1 Introduction
Through paint measurement is accomplished by measuring the time between two
repeat echoes from the back surface of the 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 so that only the actual material thickness is
measured. This avoids having to scrape or remove the coating from materials prior
to inspection. The primary purpose of thru paint measurement is to determine the
actual/nominal material thickness without error from the coating. Finally, this mode
will only work for typical epoxy based coatings.
6.2 Multi Mode Transducers
The multi echo measurement technique does have restrictions on the type of
transducers it can use successfully. The key requirement is that the transducers are
“high damped”, which refers to the duration of how long the transducer rings. In
order to improve the low end measurement range, being able to measure thin
materials, the cycles of ring must be limited so they don’t interfere with the internal
gating.
Since the
PZX-7
is a basic easy to operate gauge without the adjustability you’d get
using an advanced A-Scan scope, echo-echo mode is subject to limitations
depending on type and thickness of the coating, as well as the type of transducer
used.
The procedure for activating the through paint (E-E) measurement mode is outlined
as follows:
Echo-Echo Multi Mode
Note:
Be sure that a probe zero (if using a contact transducer) and “one point
calibration”, or a “two point calibration” has been performed prior to this
procedure.
Summary of Contents for PZX-7
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