Güralp digitizers and digital instruments can be supplied with external triggering capabilities installed.
These digitizers use pins on the DATA OUT port to transmit and receive triggers. The pins are arranged for maximum flexibility. You can use them to
External trigger input and output can be enabled and disabled separately.
To understand how to connect the equipment together, it is useful to know a little about how the digitizer is organised internally.
There are two internal components related to triggering:
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 connects the two Trigger Out pins of the DATA OUT port. These are normally pins E and F.
The Trigger Out pins are only connected 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 performs an action when it detects a trigger signal: normally, by recording additional data streams. The receiver will always start recording if the trigger generator in the same digitizer produces a signal. If external trigger input has been enabled, the receiver will also act on a logic signal received on the Trigger In pin of the DATA OUT port.
Any signal between +3 and +30 V referenced to power ground (pin A) can be used: the instrument's own power supply (pin B) can be used if you wish.
The Trigger Out pins are not connected if you provide a Trigger In voltage. The instrument must trigger itself for the relay to switch. This arrangement prevents any trigger loops from occurring.
The diagrams on this page show the additional connections you will need to make. Pins A and B, and the data pins, should be connected to your power and data systems as normal.
If your equipment can trigger from 24 V DC, the simplest arrangement is to use the voltage across the sensor's power supply as a trigger.
Connect the ground pin A to your equipment's trigger return line. If your equipment does not have a separate trigger return line, consult its documentation for how to apply trigger voltages. Güralp digitizers use the power ground line as a trigger return. (The diagram above does not show the power supply to either the sensor or the triggered equipment: only the triggering system is shown.)
Because a trigger signal may last for only a short time, inserting pins E and F directly into your equipment's power circuit is not normally advisable. Ideally, the equipment should be continuously powered and listening on dedicated trigger input lines. If this is not possible, it may be enough to build a control circuit with a time-out period, which supplies your equipment with power for a suitable minimum length of time whenever pins E and F are connected.
The digitizer cannot anticipate a trigger. Pre-trigger recording is achieved using a continuously-updated buffer of the most recent data. Any external equipment must have its own buffering capabilities if you need pre-trigger data.
Connect pin B to pin E, and pin F to your equipment's trigger signal input.
Connect the remaining pins as normal.
If your equipment needs a different voltage, you will need to provide a separate voltage source for the triggering system. Be careful not to connect two power supplies together. The instrument's power supply can be protected by inserting a diode from pin B to pin E (see below.)
To trigger an instrument from an external source through a relay:
Connect a relay between pins B and H, connected to your generator so that the two pins are connected when a trigger occurs.
The relay allows you to power the external generator from any source. This includes the instrument's own power supply at pins A and B, if it is suitable.
Connect the other pins as normal.
If you prefer, you can use a separate power source for your trigger generator. However, because pin H is referenced to power ground, the external power supply must share a common ground with that of the digitizer.
Instruments in a seismic array need to trigger simultaneously whenever an event occurs. This can be achieved with a single external trigger source as above. Alternatively, you can set up the digitizers so that if any digitizer detects a trigger condition, the entire array is triggered. This is done by wiring up the instruments as shown below.
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,
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 be connected via the trigger line. If all your instruments share the same power supply, you may not need the diode.
Once your equipment is correctly connected, you can power up the system and configure the digitizer for external triggering. You do not need to reboot the digitizer to do this.
Right-click on the digitizer's icon and select Control.... Switch to the Triggering tab.
To enable external trigger input, enter TRIGGERIN ENABLE at the digitizer command line. To disable it, issue TRIGGERIN DISABLE.
To enable external trigger output, enter TRIGGEROUT ENABLE; to disable it, issue TRIGGEROUT DISABLE.
All of these commands take effect immediately.