Triggering, Clocks, and Timing Systems
A shared timing system tells every diagnostic when to start and provides the common clock that makes cross-channel comparison meaningful.
Why timing is central
In a pulsed experiment, dozens of instruments must capture the same event window and record samples that can be aligned to a fraction of the fastest phenomenon. This requires two things: a trigger that starts acquisition, and a clock that all channels count against.
Triggers
A trigger is an event that starts or gates acquisition. Triggers may be a scheduled shot start, a threshold crossing on a monitored signal, or a software command. Pre-trigger buffering lets a system keep samples from just before the trigger, so the onset of a fast event is not lost.
- Hard trigger: an electrical pulse distributed to all digitizers.
- Software trigger: a command issued over the control network.
- Level trigger: fires when a signal crosses a set threshold.
- Gated acquisition: records only while a condition holds.
Distributing a clock
A single oscillator is fanned out so every digitizer counts the same ticks. Because cable lengths differ, systems calibrate and compensate propagation delay so that timestamp zero means the same instant everywhere. Protocols such as IEEE 1588 (Precision Time Protocol) synchronize distributed clocks over a network to sub-microsecond accuracy.
Jitter and drift
Jitter is short-term random variation in when an edge arrives; drift is slow change in clock rate, often with temperature. Both blur alignment. Good timing design minimizes jitter in the trigger fan-out and disciplines the master clock against a stable reference.
Sample alignment
Even with a shared clock, channels sampled at different rates need resampling to a common grid before they are compared. This is a transformation step in the pipeline, and it must record the interpolation method so the operation is reproducible. Accurate timing is the foundation that lets a density measurement be causally linked to a magnetic one.