Guralp Systems CMG-DM24 - Manual (Page 101)

Operator's guide
Triggering several Güralp instruments simultaneously
A common use of the external triggering feature is to ensure that all
instruments in an array trigger at the same time. This can be achieved
with the wiring layout below. With this arrangement, any instrument
can generate a trigger, which will be passed on to all the instruments
in the array.
For each instrument:
•
pin A is connected to a common ground;
•
pin B is connected to the instrument's power supply as normal
and also to pin E through a diode (an IN4001 is suitable);
•
pins F and H are connected to each other and to a common
trigger line; and
•
the remaining data pins are connected to your recording
equipment as normal.
The diode at pin E is important, because if two instruments generate a
trigger simultaneously, their power supplies will both be connected
via the internal relay contacts to the common trigger line on pins H,
and hence connected together. This can cause considerable current
flow with consequent risk of fire, as well as severe damage to
equipment and cables.
In the case where a single power supply is used to power all of the
equipment, this is not an issue and pin E should be connected directly
to pin B on all units. Pin B should then also be connected to the
power supply's positive terminal.
The more common case, where each unit has it's own power supply, is
shown below. Power supply wiring is omitted for the sake of clarity
but note that all the power supply's ground terminals will be
connected together via the links between pin A on each unit. The
power supplies must, therefore, have floating outputs or grounded
negative terminals.
October 2009 101