Trigger

LabVIEW SignalExpress

previous page next page

Trigger

Extracts a section of a continuous signal based on a specified trigger. This steps waits until a signal meets a trigger condition and returns a section of the signal that starts at the trigger point, or before the trigger point if you specify Pre-trigger samples. This step returns a triggered signal that always is the same size as the input signal before the trigger, so the input signal must provide enough data after the trigger occurs for the step to return a signal of that size. If the input signal does not provide enough data, this step times out.

Details  

ParameterDescription
Input SignalDisplays the input signal.
  • Displayed signal—Specifies the signal(s) to display in the preview graph(s). This option appears only when you select a group of signals for the input.
    Note  If the input signals include scalar values that depend on the values of input waveform signals, you cannot specify to display all signals in the preview graph(s).
Output SignalDisplays the output signal.
InputContains the following option:
  • Input signal—Specifies the input value.
ConfigurationContains the following options:
  • Trigger mode—Specifies which condition the specified signal must meet for LabVIEW SignalExpress to begin extracting the signal.
    • Positive Edge—Specifies for the trigger to occur when a signal crosses the specified Level with a positive slope.
    • Negative Edge—Specifies for the trigger to occur when a signal crosses the specified Level with a negative slope.
    • Entering Window—Specifies for the trigger to occur when a signal enters the window between the specified High level and Low level values.
    • Leaving Window—Specifies for the trigger to occur when a signal exits the window between the specified High level and Low level values.
  • Level—Specifies the level that the signal must meet to trigger the input signal.
  • High level—Specifies the higher limit of the range to trigger the specified signal.
  • Low level—Specifies the lower limit of the range to trigger the specified signal.
  • Hysteresis—Specifies the amount above and below Trigger level through which the specified signal must pass before a trigger level crossing is detected. The default is 0. Use trigger hysteresis to prevent noise from causing a false trigger.
  • Trigger signal—Specifies the channel to use to search for the trigger when the input is a grouped signal. The default is the first channel in the group.
  • Pre-trigger samples—Specifies the number of pre-trigger samples per channel to acquire before the reference trigger point. Devices that NI-DAQmx supports require Pre-trigger samples to have a minimum value of 2. Post-trigger samples equal Samples to read – Pre-trigger samples. The default is 2.
  • Timeout (s)—Specifies the hardware timeout value in seconds. The default is 10.
  • Trigger found—Returns TRUE if a trigger has been found in the input signal. Returns FALSE if no trigger is found.

Trigger Details

This step can return a timeout error under the following conditions:

  • You specify a trigger Level that the input signal does not meet.
  • A trigger occurs but the input signal does not provide enough data after the trigger occurs for the step to return a signal of the same size as the input signal.
previous page start next page