Manual No. OM5000
Jan X/04 Ver 1.40
15
The most important function for a gate in ultrasonic thickness gaging is to select (and indicate) the
thickness echo period across which the instrument is to compute the thickness. Figure 10(b) shows
such a "thickness gate" set to automatically trigger across the IP-first back surface echo period.
Thickness gates can be used to trigger between virtually any two echos.
A relatively common situation occurring during the desired setting of a thickness gate is irrelevant
echos (noise) between the start echo and stop echo representing the thickness period. The noise
will cause the automatic thickness gate to erroneously stop or "hang-up". Such noise can be
"blocked" from interfering with the setting of the thickness gate by simultaneously using another
adjustable gate, called a blocking gate. Figure 10(c) shows how a blocking gate can be adjusted so
its width is long enough to block the IP noise - which would otherwise prevent the thickness gate from
properly triggering between the IP and first back echo shown in Figure 10(c). A similar blocking gate
is used to block the noise in front of the IF echo during immersion or delay line transducer gaging.
A dual trace scope conveniently permits the gates to be selectively displayed (one at a time),
although they are always operational (when turned on) whether or not being displayed.
Figure 10... Gate Examples
