IviDigitizerBase Behavior Model

IVI Driver Help

Edition Date: August 2011

Part Number: 370430H-01

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The following behavior diagram illustrates the IviDigitizerBase group capability behavior.

Typically you configure the digitizer while it is in the Idle state. You can configure the digitizer by calling the high-level configure channel, configure acquisition type, configure acquisition record, configure trigger, and configure edge trigger source VIs or by directly calling the appropriate channel, acquisition, and trigger sub-system properties.

To acquire waveforms, the IviDigitizer class includes high-level read waveform VIs, as well as the low-level VIs to initiate acquisition, acquire status, fetch waveforms, and abort.

The Read Waveform VIs initiate a waveform acquisition and return the acquired waveform after the digitizer has returned to the Idle state.

You can use IviDigitizer Initiate Acquisition, IviDigitizer Abort, and the Fetch Waveform VIs for lower-level control over the measurement process. The IviDigitizer Initiate Acquisition VI initiates a waveform acquisition and moves the instrument into the Wait-For-Trigger state. Configure the trigger type with the trigger sub-system properties or with the IviDigitizer Configure Edge Trigger Source VI.

The IviDigitizer class provides multiple versions of the Read and Fetch VIs to accommodate digitizers of various native data sizes for each waveform sample. For example, you can retrieve waveforms as arrays of 8-bit, 16-bit, and 32-bit integers as well as 32-bit and 64-bit floating-point numbers.

If the trigger delay is negative, the first point in the waveform record occurs prior to the trigger event. When the trigger event occurs, the waveform record contains the amount of pre-trigger data that corresponds to the trigger delay. The digitizer leaves the Wait-for-Trigger state and acquires the remaining points in the waveform record. If the trigger delay equals zero, the first point in the waveform record occurs at the time of the trigger event. When the trigger event occurs, the digitizer leaves the Wait-for-Trigger state and acquires all the points in the waveform record.

If the acquisition start time is greater than zero, the first point in the waveform record occurs after the trigger event. When the trigger event occurs, the digitizer leaves the Wait-for-Trigger state, waits a length of time that is equal to the trigger delay, and acquires all the points in the waveform record.

If the digitizer has acquired the requested number of records, it returns to the Idle state. However, if the digitizer must acquire additional records to satisfy the specified Num Records requirement, it then moves to the Wait-For-Samples state. The digitizer then waits until the hold-off time expires before moving to the Wait-For-Trigger state.

Note that the hold-off time is measured from the moment the digitizer exits the Wait-for-Trigger state, not from the moment when the digitizer enters the Wait-for-Samples state.

After the instrument meets its acquisition complete criterion, the digitizer returns to the Idle state. This criterion is typically 95-98% of the acquisition record; there may be instrument specific properties that allow you to configure the completion criterion. You can use the Acquisition Status VI to determine if the acquisition is complete or is still in progress.

Use the Fetch Waveform VIs to return a waveform from a previously initiated measurement. The Read Waveform and Fetch Waveform VIs return the following parameters:

  • A waveform array
  • The time of the first point in the waveform array in relationship to the trigger event
  • The index of the first valid point in the waveform record
  • The number of valid points in the waveform record

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