ABEM Terraloc Pro 2
49
TTL
Falling Edge
The instrument is triggered when the TTL signal on
the digital trig input goes from high to low
Channel
The instrument is triggered when the signal on any
channel input, including the reference channels,
exceeds the trig input level. If you use Channel
triggering, you should check and/or set the trig input
level.
Manual only The instrument will only trigger manually from the
keyboard (internal or external)
Trig input
level
-
The trig input level can be set from 0 to 100%.
Increasing the trigger input level increases the sensitivity, which
means that a lower signal level is needed to trig the Terraloc Pro 2.
Decreasing the trigger input level on the other hand decreases the
sensitivity, which means that a higher signal level is needed to trig
the Terraloc Pro 2. Sensitivity level needs to be high enough to
ensure triggering by the trigger signal, but not so high that spurious
signals will trigger in advance of the actual shot impulse. For
example, when a geophone is used as the source of the trigger
signal, a time delay will always be present between the shot instant
and the triggering time. There are two main causes for this:
1.
The propagation delay from the shot point to the geophone
2.
The rise time of the geophone output signal to the triggering level
Figure 43 illustrates the relationship between trigger sensitivity and
the rise time of the receiver output signal to the triggering level.
Figure 43 Trig signal from a geophone and the trig event
To reduce the propagation delay the only way is to move the
geophone closer to the shot point. This cannot always be done due
to physical limitations in which case you will have to accept the
delay.
The rise effect is another matter, because it is influenced by a
number of conflicting requirements. If the trigger sensitivity is
