Command line interface
The digitiser compresses data without loss, so compression is most effective when
the data contain relatively little information. During large or local seismic events,
the digitiser normally needs to decrease the compression level.
bits
can be one of
8BIT
,
16BIT
and
32BIT
.
8BIT
(the default) is the maximum
amount of compression;
32BIT
denotes no compression.
size
determines the maximum number of four-byte records in a GCF block. This
must be between 20 and 250; the default is 250. Each record can represent 1, 2 or 4
samples, depending on the compression level.
GCF blocks must be a whole number of seconds long. If you set
size
to a value so
small that packets would contain data for less than one second, the digitiser will
ignore the exact value of
size
and simply output one block every second (per
stream).
Thus, if you issue
32BIT 20 COMPRESSION
, streams with a sample rate of 20
samples/s and higher will output one block per second, whilst lower rate streams
will output 20-sample blocks: every 5 seconds for 4 samples/s data etc. The special
command
MINIMUM COMPRESSION
is a shorthand for this.
Another special command,
NORMAL COMPRESSION
, returns these settings to their
default values, equivalent to
8BIT 250 COMPRESSION
.
6.6.5 LOWLATENCY
Syntax:
LOWLATENCY
This is a special mode for applications requiring lower sample rate data in as close to
real time as possible. In this mode, the digitiser takes a 200 samples/s stream and
passes it through low-pass and decimation filters internally, before exposing it as a
20 samples/s stream at an increased rate of 1 block per second.
To enable low latency mode on all three components, first use
SAMPLES/SEC
to set
Tap 0 to 200 samples/s, then issue the following commands:
NORMAL
COMPRESSION
0 7
CONTINUOUS
0 1
BANDPASS
LOWLATENCY
7
TRIGGERS
If you want to enable low latency mode on some components only, replace the 7s
above with another value (
e.g.
1 =
Z
, 2 =
N
, 4 =
E
).
To disable low latency mode, issue
0 1
BANDPASS
0
TRIGGERS
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Issue U - December, 2021