Many measurement applications require the acquisition of bursts of data following an independent, index synchronization pulse. This is true for sector data stored on a disk drive, mechanical analysis of rotating machines and engines, and read/write operations to multiplexed memory. In each case, the underlying operation involves a cyclic process with synchronization sources associated with each individual event within the cycle, as well as a once per cycle index pulse.
A good example of this type of process is the organization of data sectors on a disk drive. In Figure 1 the upper trace (Channel 3) shows read data from a group of sectors. Each sector has an associated sector pulse, shown in the middle trace (Channel 1), and the synchronization point for the entire track is the index pulse shown in the bottom trace (Channel 2).
The Qualified First SMART® Trigger permits a single cycle synchronizing pulse, such as the index pulse of the disk drive, to initiate multiple segment acquisitions, each triggered by an individual sector pulse. It keeps the sequence mode acquisition synchronous with the cyclic process. The setup for the Qualified First trigger is shown in the dialog box in the lower half of Figure 1.
The user specifies the qualification source, slope, and threshold voltage, as well as the trigger source. If desired, holdoff by time or events can be invoked to trigger on a selected trigger event such as a specific sector. In this example, holdoff (wait) has been arbitrarily set for 3 trigger events (sector pulses). The checkbox titled “Qualify first segment only” must be checked to select this trigger mode.
Note that Qualified First Trigger mode requires that the scope be set up for sequence mode acquisition. In this mode each segment of the sequence mode acquisition is triggered by the sector pulse after the index pulse occurs. If sequence mode is not used, the trigger defaults to a normal qualified trigger.
As in any sequence mode acquisition, the display type can be selected to show individual segments or multiple segments arranged in five different patterns.
Qualified First Trigger is an extremely useful tool for the study of cyclical phenomena using segmented memory and is available on selected models of LeCroy oscilloscopes.