DeFelsko PosiTector UTG v.3.0 Quick Guide - Manual (Page 3)

2
To disconnect a probe from a body, power-down the
instrument and slide the plastic probe connector
horizontally (in the direction of the arrow) away from the
body. Reverse these steps to attach a new probe.
When powered-up the PosiTector automatically
determines what type of probe is attached and does a
self-check.
Probes 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 propogate through the
material is measured by the Gage, represented as t
1
and t
2
below.
PosiTector UTGC and UTGM (in single-echo mode) probes
determine thickness by measuring t
1
(uncoated) or t
2
(coated),
dividing it by two and then multiplying by the velocity of sound for
that material (steel). See Figure 1.
For uncoated materials t
1
relates directly to material thickness.
When a material is coated the propagation time is increased and
is shown above as t
2
.
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+metal thickness.
steel
coating
steel
2
t >
1
t
Figure 1
2
t
1
t
Pr
ob
e
Pr
ob
e