SV Software Triggering (Analog Edge) VI

Sound and Vibration Measurement Help


Edition Date: March 2018
Part Number: 372416L-01
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Owning Palette: Common Utilities VIs

Requires: Sound and Vibration Toolkit

Implements a software trigger. When the trigger is detected on the trigger channel, all signals are triggered so that the channels stay aligned in time. This function requires that each waveform in input signals has equal dt and Y (length). Returns one triggered set of data per call.

Details  

force trigger (F) when TRUE, specifies that the VI should return a block of data without waiting for the specified trigger condition to be met and forces output ready to TRUE. When FALSE, this VI operates normally by inspecting input signals for the specified trigger condition.
restart (F = first call) clears any previously detected triggers. The default is FALSE. This VI automatically restarts on first call, or when any of the following parameters changes in input signals:
  • dt
  • t0
  • array length
  • channel info
  • number of channels
input signals specifies the input data for trigger detection and continuously acquires the data with a constant block size. Make sure that all channels have the same type of timing information for t0, dt, and number of samples. If input signals is empty, this VI will continue to inspect buffered samples for the specified trigger condition.
t0 specifies the start time of the waveform.
dt specifies the time interval in seconds between data points in the waveform.
Y specifies the data values of the waveform.
level trigger configuration specifies the analog level trigger conditions that must be met for a valid trigger.
level specifies the threshold value input signals must cross before a trigger is detected. The default is 0.
slope specifies whether a trigger is detected as input signals crosses level on a rising edge or a falling edge.

0Falling—The VI detects a trigger on the falling edge, or negative slope.
1Rising (default)—The VI detects a trigger on the rising edge, or positive slope.
hysteresis specifies the amount above or below level through which input signals must pass before a trigger level crossing is detected. The default is 0.

Use hysteresis to prevent noise from causing a false trigger. For a rising edge slope, the signal must pass below level minus hysteresis before a trigger is detected. For a falling edge slope, the signal must pass above level plus hysteresis before a trigger is detected.
trigger channel index (0) specifies which element of the input signals array will be monitored for a trigger. All input signals are returned in triggered signals.
mode (FIFO) specifies how this VI will buffer and return multiple triggers. The default is First In, First Out.

0First In, First Out (default) — Returns each triggered block in the order detected. Can lead to a backlog of triggers in the internal buffer.
1Last Available — Returns the last available triggered block. Keeps the internal buffer from growing, but can result in some previous triggers not being returned for processing.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
pretrigger samples (0) specifies the number of samples prior to the detected trigger to return in triggered signals. The maximum pretrigger samples is the block size -1 (N - 1). The default is 0, meaning that the first sample in triggered signals corresponds to the detected trigger.
triggered signals returns the triggered portion of the input signals when output ready is TRUE. triggered signals returns the same block size as input signals, including pretrigger samples.
t0 returns the trigger time of the waveform.
dt returns the time interval in seconds between data points in the waveform.
Y returns the data values of the waveform.
attributes returns the names and values of all waveform attributes. You also can use the Get Waveform Attribute VI to retrieve the names and values of all attributes or the value of a single attribute.
output ready returns TRUE when a new set of triggered signals is available for processing.
new trigger detected returns TRUE when trigger conditions were met on the trigger channel in this block iteration.
error out contains error information. This output provides standard error out functionality.

SV Software Triggering (Analog Edge) Details

Managing Buffer Size  When performing lossless trigger detection using trigger mode First In, First Out, use empty input signals to inspect the buffer for additional triggers. This may reduce the backlog of triggers in the internal buffer. When writing an application such as a real-time analyzer, use trigger mode Last Available to make sure that the latest triggered block is returned and processed. This ensures that the internal buffer will not grow in size.

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