Guralp Systems CMG-CD24 - Manual (Page 88)

CMG-CD24
7.2 Appendix B - Setting up external triggering
Güralp digitisers and digital instruments can be supplied with external
triggering capabilities installed. The external trigger system is
designed for maximum flexibility: you can trigger other digitisers or
your own equipment using built-in relays and any equipment may be
used as a trigger source, using the built-in opto-isolator. In addition, a
trigger circuit can link together any number of digitisers so that they
trigger simultaneously when they receive a signal.
7.2.1 Overview
The digitiser or digital instrument has two internal components related
to triggering: the trigger generator and the trigger receiver.
The trigger generator runs the triggering algorithm and determines
whether a trigger has occurred. If external trigger output has been
enabled, the trigger generator also operates a relay which disconnects
the Trigger Out Common pin (on the POWER/DATA/GPS port) from the
Trigger Out Normally Closed pin and connects it to the Trigger Out
Normally Open pin. See section 7.3.1.1 on page 96 for connector
details.
The relay is only activated whilst the generator is active. This does not
include any pre-trigger or post-trigger period, which is dealt with by
the trigger receiver. A trigger signal may be as short as one second.
The trigger receiver acts upon trigger signals: normally, by recording or
transmitting additional data streams. The receiver will always enable
these extra streams if the trigger generator determines that a trigger has
occurred. If the external trigger input has been enabled, the receiver
will also act on a logic signal received on the Trigger In pin of the
POWER/DATA/GPS port.
Any signal between +3 and +40 V can be used - the trigger input pins
drive an opto-isolator protected by a constant-current circuit.
88 Issue C