User's Manual

2-76
1010NFM-3JSection 2
To adjust the Tn mark position press the <3> key on the keypad to bring up the [TnSet] command.
Pressing the <+> or <-> keys will cause the Tn marker to move later or earlier, respectively. The
change from the default value (in samples) will appear in the number to the right of the command. As
you adjust the Tn marker, both Tn and Vs (liquid sound velocity) will change accordingly. To exit this
mode, press the <0> key on the keypad.
Zero Crossover Adjustment: (Hot Key 4)
Observe the small “X” mark located on the zero crossing line near the middle of the receive signal in
the Graph Screen above. This “X” indicates the central crossover which the 1010 is using to measure
the transit-time delta. This crossover will generally be close to the peak of the receive signal with at
least one well formed (non-aberrated) receive cycle on each side of the crossover. If it appears that the
placement of this crossover is unsatisfactory then it can be adjusted by pressing the <4> key on the
keypad, which will invoke the [ZCOSet] command. The crossover point can then be moved in either
direction on the waveform using the <+> or <-> keys. The change from the default value (in receive
cycles) will appear in the number to the right of the command. To exit this mode, press the <0> key.
Envelope Threshold Adjustment: (Hot Key 5 & 6)
Pressing the <=> key causes the graph to toggle between the default signal waveform screen and the
signal envelope screen (see example below). This envelope screen can aid in the diagnosis of Tn
errors caused by unusual receive waveform distortion. Signal distortion is sometimes caused by poor
transducer selection or poor pipe wall conditions, which may result in an incorrectly measured fluid
sound velocity. To improve the automatic measurement of Tn, the envelope threshold limit can be
adjusted to exclude portions of the envelope, which may be causing the Tn detection problem.
F 0.73
VS 1469.73
[ ] 1691:1929 476
D 4:4 4
Tn 55.06 55.06
dT 3.11
S 72 1
SN 124:1
CQ 17:1
Envelope Signal
TN marker
Crossover Marker
Command Line appears here
Envelope Threshold
91
3
HiSet
If it appears that the default placement of the Tn marker is incorrect or unstable, it can be adjusted by
pressing the <5> key on the keypad to invoke the [EnvSet] command (while viewing the envelope
screen). A horizontal line representing the envelope threshold level will appear along with a number
indicating the percentage level. The High and Low thresholds can then be moved either up or down on
the envelope using the <+> or <-> keys. While viewing the Tn marker position, adjust the thresholds so
that they are well above the baseline “noise” level but below the first major peak. To exit this mode,
press the <0> key.