Making Multirecord Acquisitions

NI-HSDIO supports multirecord acquisitions, which allow you to capture multiple, triggered waveforms without software intervention. NI-HSDIO stores each record in separate memory locations on the NI device.

The main benefit of multirecord acquisitions is that you can quickly acquire numerous triggered waveforms. Multirecord acquisitions allow hardware rearming of the NI device before the data is fetched. Therefore, the rearm time, or the time when the NI device is not ready for a trigger, is extremely small, often from 1 to 100 µs, depending on the record length and the device. This short rearm time allows you to capture data whether the triggers occur microseconds or many days apart.

Fetching Multirecord Acquisitions

You use the same fetch functions for retrieving multirecord acquisitions as you do for single-record acquisitions. However, you must also specify the starting record and the number of records to fetch.

Fetching multiple records with a single fetch function requires understanding the order of the returned waveforms. If you are using a C-based language, the waveforms are packed into a one-dimensional array. For LabVIEW users, the waveforms are returned as a two-dimensional array (where rows represent records and columns represent samples). You can use the Index Array VI to extract the waveform of interest.

You can also fetch each record individually using the following procedure:

1. Set the number of records to fetch to 1.
2. Use a loop to set the starting record as the zero-based index of the record you want to fetch.
3. Call one of the fetch functions/VIs.