Recording Experimental Signals > Recording Modes > External Trigger
When the Ext. Triggered mode is selected, the recording sweep is synchronised to a trigger pulse applied to the external trigger input of the laboratory interface. If the Active High option is selected, recording will be triggered by a 0V-to-5V transition on the trigger input. If the Active Low option is selected, recording will be triggered by a 5V-to-0V transition. (Note, some laboratory interfaces support only one or other of the two trigger polarities.)
Many kinds of electrophysiological signals are evoked by stimulating the cell or tissue, using an electrical stimulator. In order to record such signals, the recording sweep must be synchronised with the stimulator, ideally so that the sweeps starts shortly before the cell is stimulated. During a stimulus cycle, the stimulator sync. pulse is produced first (triggering the recording sweep) and, after a delay (settable on the stimulator front panel), the stimulus itself.