Triggering can mean three different things in chart recording / data acquisition instruments:
1) Sweep triggering for synchronizing the trace on an oscilloscope-type device.
2) Chart on/off or change of chart speed on a recorder.
3) or starting the data acquisition capture on a recording device.
Most are familiar with the oscilloscope trigger: It really has nothing to do with the other two. The second type of trigger can be found on WindoGrafs. It allows an amplitude level to start or stop the chart or flip-flop the chart from one pre-set speed to another. The third type is the most popular in Data Acquisition: Triggering the start of an acquisition to memory. Most Gould recording products have this Feature or Option which allows the User to set a level at which the data will begin to store. Trigger Levels can use a variety of criteria: The digital Event Marker, or the signal "Above Level", "Below Level", or "Window". A Window trigger level is both an Above and Below combined to create a "band" that allows the trigger to fire when exceeded. Real-Time (time of day) can also be used to trigger an acquisition on most models.
Pre-Trigger is very helpful in that it allows the acquisition to store data that happened before the actual trigger. When a TA's Trigger is Armed via the Front Panel button or through a PC interface, the unit begins storing. But a data file will not actually be created until the trigger occurs. So a Pre-Trigger setting of "50%" will capture an Acquisition where the first half of the signal data is from before the trigger, the rest after the trigger. Pre-Trig. can be set in increments of 1% up to 100% to show the entire length of stored data before the actual trigger. Pre-Trigger and Trigger allow the Customer to save great quantities of paper: The chart need not be run to capture the desired event. When the recorder is setup and Armed, it will wait for the trigger until dis-armed or power is removed. Once the trigger has fired and the data is stored for the desired time, the unit can either playback the data immediately and go back to normal real-time printing, or simply rest. The AUTO RE-ARM feature allows the recorder to automatically re-arm after a trigger-store-playback-sequence has occurred, so the unit is ready to capture the next event.