Using the DM24
4.1.1 Triggering
The DM24 has a flexible triggering system. When the digitiser triggers, it can
optionally output (or store – see
DUAL
mode in section 4.3 on page 22) additional
data. Any combination of tap and component can be output as the result of a trigger.
In the example above, you might configure the sensor to output Tap 2 data (at 10
samples/s) continuously, but when a trigger is declared, to output Tap 0 data (at 500
samples/s) as well.
Using triggering helps you to use limited storage capacity or bandwidth more
effectively.
The digitiser can look at the data from any tap to decide if a trigger has occurred,
including taps which it does not output. Which tap you choose depends on the
frequencies you want the trigger system to be most sensitive to.
There are four types of trigger.
•
A
LEVEL trigger
occurs when the absolute sample values exceed a configured
value.
The commands
GTRIGGERS
,
MICROG
, and
HIGHPASS
control
LEVEL
triggering.
•
An
STA/LTA trigger
occurs when the ratio of a short-term average to a long-
term average for recent data exceeds a configured value.
The commands
TRIGGERS
,
TRIGGERED
,
STA
,
LTA
,
RATIOS
, and
BANDPASS
control
STA/LTA
triggering.
•
A
software trigger
occurs when you issue the command
S/WTRIGGER
.
•
An
external trigger
occurs when external equipment signals electrically to
the DM24. See section 5.1.6 on page 46 for details.
The DM24 can output data streams for a period of time before the trigger starts, and
after the trigger ends. The commands
PRE-TRIG
and
POST-TRIG
set these time
periods.
Triggering options can also be configured through Scream!.
4.2 Streams
The DM24 organizes the data it produces into streams. Each stream has a 6-
character identifier. The first four characters are taken from the
Serial Number
of the
digitiser. (Although this setting is called
Serial Number
, you can change it to a
different string if you wish, using Scream! or a terminal command.)
The next character denotes the component or output type:
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Issue U - December, 2021
