DeFelsko PosiTector UTG Quick Manual page 4

Ultrasonic Thickness Probes –
PosiTector UTG probes transmit an ultrasonic pulse into the material
to be measured. This pulse travels through the material towards the
other side. When it encounters an interface such as air (back wall) or
another material, the pulse is reflected back to the probe. The time
required for the pulse to propagate through the material is measured
by the gage, represented as t1 and t2 below.
All PosiTector UTG probes determine thickness by measuring t1
(uncoated) or t2 (coated), dividing it by two and then multiplying by
the velocity of sound for that material (steel). [UTG M and UTG P
single-echo
For uncoated materials
When a material is coated the propagation time is increased and
is shown above as
Coatings such as paint have a slower velocity of sound than that
of metal. Thus the single-echo technique will produce a thickness
result greater than the actual combined coating
Theory of Operation
mode only] See Figure 1.
t
Probe
1
t
relates directly to material thickness.
1
t
.
2
Figure 1
3
t
Probe
2
t t
>
2 1
+
metal thickness.