Acquisition Sub-System

CVI/LabWindows IVI Class Driver

Acquisition Sub-System

The acquisition sub-system configures the size of the waveform record, the length of time that corresponds to the overall waveform record, and the acquisition start time. The configurable acquisition sub-system attributes include:

You specify the minimum number of points they require the oscilloscope to acquire with the IVISCOPE_ATTR_HORZ_MIN_NUM_PTS attribute. The IVISCOPE_ATTR_HORZ_TIME_PER_RECORD attribute specifies the length of time that corresponds to the overall waveform record. You specify the length of time from the trigger event to the first point in the waveform record with the IVISCOPE_ATTR_ACQUISITION_START_TIME. If the value is positive, the first point in the waveform record occurs after the trigger event.

All of the acquisition attributes can be set individually or they can be set as a group with the IviScope_ConfigureAcquisitionRecord function.

In addition, the acquisition subsystem includes two read-only attributes:

The IVISCOPE_ATTR_HORZ_RECORD_LENGTH attribute returns the actual number of points in the waveform record. The IVISCOPE_ATTR_HORZ_SAMPLE_RATE attribute returns the effective sample rate of the oscilloscope.

The IviScope class driver defines separate attributes for the minimum record size you request and the actual record length. Typically, oscilloscopes change the record length dynamically when the acquisition type changes. For example, when you change the acquisition type from normal to envelope, many oscilloscopes reduce the record length by half. When you change the acquisition type, the instrument driver uses the value held in the IVISCOPE_ATTR_HORZ_MIN_NUM_PTS attribute to check that the new record length is equal to or greater than the minimum record length you require.