Configuring the Horizontal Settings

NI High-Speed Digitizers Help (NI-SCOPE)

Edition Date: January 2017

Part Number: 370592AB-01

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The horizontal timing parameters apply to all enabled channels of the digitizer, which means that both channels of a two-channel digitizer sample the same amount of data at the same rate. Some digitizers support acquiring multirecords. multirecord acquisitions allow you to acquire multiple, triggered waveforms very quickly. Because the triggering and timing are done in hardware, multirecord acquisitions eliminate the possibility of the operating system interrupting your program and causing the digitizer to miss triggers. To find out if your digitizer supports multirecord acquisitions, refer to Features Supported by Device. The horizontal settings include the num records, sample rate, min record length, and reference position parameters.

Num Records

The num records parameter in the Configure Horizontal Timing function allows you to configure a multirecord acquisition. For a single record acquisition, set this parameter to 1.

Sample Rate

The sample rate parameter is the frequency at which digitized samples are stored, expressed in samples per second. This parameter is rounded up to the next legal sampling rate that your device supports. If the enforce realtime parameter is set to TRUE, the sampling rate must be set lower than the maximum real-time sampling rate of the digitizer, so data can be digitized at the requested rate. If you set the enforce realtime parameter to FALSE, NI-SCOPE allows you to specify sampling rates higher than the maximum real-time sampling rate of the digitizer. When you do this, NI-SCOPE enters random interleaved sampling (RIS) mode, where it acquires multiple waveforms at the maximum real-time sampling rate and reconstructs a periodic waveform.

Min Record Length

The min record length parameter is the minimum number of samples to store for each record in the acquisition. This parameter can also be rounded up. NI-SCOPE maintains a constant time per record, which is the min record length divided by the requested sampling rate. Because the sampling rate is rounded up to a legal value, the min record length can also be rounded up. You can fetch this resulting actual record length by calling Actual Record Length. Similarly, you can call Sample Rate to find the true sample rate used or Actual Sample Mode to determine if NI-SCOPE is using RIS or real-time sampling.

Reference Position

The reference position parameter determines the number of pretrigger versus posttrigger points that are stored. Reference position is expressed as a percent of the record, from 0 to 100. For example, a 0% reference position means that you have the actual record length points stored after the trigger occurs, while 100% reference position means that all the samples are stored before the trigger.

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Configuring the Vertical Settings


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