5 triggering – Guralp Systems CMG-6TD User Manual

Page 88

Command-line interface

7.4.3 COMPRESSION

Syntax: bits size COMPRESSION or NORMAL COMPRESSION

Sets the maximum amount of compression to use. Greater compression

means the digitiser outputs data more efficiently, so more can be transmitted
over a link with a given bandwidth. However, compressing streams uses

processor power and can increase data latency.

The digitiser compresses data without loss, so compression is most effective

when the data contain relatively little information. In most cases, when a
seismic event occurs, the digitiser will need 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 data samples in a GCF block. This

must be between 20 and 250; the default is 250.

GCF blocks must be a whole number of seconds long. If you set size to a very

small value, so that size samples is less than one second for some streams,

the digitiser will output one block every second for those streams, ignoring
the value of size.

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 value, NORMAL COMPRESSION, returns the setting to its default

value, and is equivalent to 8BIT 250 COMPRESSION.

7.4.4 ETHER

Syntax: ETHER ENABLE | ETHER DISABLE

For units with integrated networking hardware, ETHER DISABLE turns off the
power to the embedded Lantronix networking module, which significantly

reduces power consumption if the networking support is not required. The
command ETHER ENABLE turns the networking module back on.

7.5

Triggering

7.5.1 TRIGGERS

Syntax: components TRIGGERS

Selects which component or components can generate a trigger. Only these
components will be examined by the triggering algorithm.