Environmental Engineering Reference
In-Depth Information
Fig. 12.15
Cycle skipping in well-bonded casing. Courtesy Schlumberger
Question #12.1
Inspect the
t
curve in Fig.
12.15
. At the places where cycle skipping is most appar-
ent, estimate which peak was actually detected (1.e.,
E
3
,
E
5
, … etc.)
∆
Gating Systems
The amplitude of the
E
1
peak is detected by means of an electronic gate that opens
for a predetermined time, takes the maximum value of the received wave during the
time it is open, and records that amplitude on the log. There are two common meth-
ods of achieving the correct gate position in order to key on the
E
1
peak: (1) a fi xed
gate that opens at a fi xed time after the transmitter fi res or, (2) a fl oating gate that
only opens after
E
1
has been detected by the
ʔ
t
-measuring circuitry, which depends
on the bias level set by the operator.
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