DeFelsko PosiTector UTG v.3.0 Quick Guide - Manual (Page 4)

3
How to Measure How to Measure
The PosiTector UTGM in multiple-echo mode determines
thickness by measuring the time between at least three consecu-
tive back wall echoes.
steel
Pr
ob
e
1
t
2
t
3
t
1
t
2
t
3
t
Co
at
in
g
Figure 2
Pr
ob
e
In the figure above, multiple-echo mode measures only the time
between echoes. Regardless of whether the steel is coated or not,
all times between echoes are the same. In multiple-echo mode
the Gage determines thickness by measuring t
1
+t
2
+t
3
, dividing it
by six and then multiplying by the velocity of sound for that mate-
rial. The resultant thickness calculation made by the instrument is
therefore an accurate measurement of the steel thickness only,
disregarding the coating thickness.
The velocity of sound is expressed in inches per microsecond or
meters per second. It is different for all materials. For example,
sound travels through steel faster (~0.233 in/µs) than it travels
through plastic (~0.086 in/µs).
1. Remove rubber cap from probe. Couplant (glycol
gel - included) must be applied to the surface to be
tested to eliminate air gaps between the wear face
and the surface. A single drop of couplant is sufficient
when taking a spot measurement.
2. Place the probe flat on the surface. Use moderate pressure to
press against the top of the probe with the thumb or index finger.