Continuing from the previous article, this time I will describe the common types of triggers typically provided by point-measurement spectrometers.
Point-measurement spectrometers generally offer one or two kinds of triggers. The first, which is provided by most devices, is the “line trigger.” The second, which is not always offered, is the “frame trigger.”
Line Trigger
The line trigger is the same type of trigger commonly referenced in imaging industries. (For details about triggers in general, please refer to the earlier article.) The name “line trigger” comes from the fact that the detector used in the spectrometer is a line-scan detector and the acquired data are one-dimensional arrays (lines). When a line-trigger signal is input, the spectrometer acquires one unit of data (one line) per trigger, as shown below.
Figure 1. Operation of a line trigger
Frame Trigger
A frame trigger is used in environments where a fixed number of data lines are repeatedly acquired; it indicates the start of a frame or the period from start to end of acquisition. Frame triggers can be either edge-type or level-type signals.
Edge-type frame trigger example:
If you configure the number of line data that compose a frame in advance (for example, 4 lines), then input a frame-trigger signal at the start and subsequently input line triggers, the device will group the four line-triggered data following the frame trigger into a single frame and deliver it as such. Any subsequent line triggers after those four lines are ignored until the next frame trigger is received.
Figure 2. Trigger environment using edge frame trigger
Level-type frame trigger example:
If you use a level signal for the frame trigger, then after the frame trigger is asserted, the spectrometer treats incoming line triggers as valid until the frame-trigger level changes; the collected line triggers during that period are grouped into a single frame and delivered. Subsequent line triggers after the frame are ignored until the next frame trigger is asserted.
Figure 3. Line trigger environment using level frame trigger
Summary / Caution
The above explains the general trigger modes to help readers understand typical behavior. However, because spectrometer and detector manufacturers vary, actual operation may differ between products. Please verify the exact behavior required for your intended use before operating the spectrometer.
