DeFelsko PosiTector UTG v.2.2 - Manual (Page 3)

3
In multiple-echo mode the Gage determines
thickness by measuring the time between at least
three consecutive back wall echoes.
steel
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 material. 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).
Probe
1
t
2
t
3
t
1
t
2
t
3
t
Coating
Figure 2
Operation Overview Operation Overview
1. Turn the Gage ON (see Power-Up - pg. 5)
2. Verify accuracy (see Verification - pg. 9)
3. Select the correct velocity of sound (see pg. 10)
4. Measure the part (see How to Measure - pg. 5)
Probe
sound than that of metal. Thus the single-echo tech-
nique will produce a thickness result greater than the
actual combined coating+metal thickness.