Trigger and Gate Express VI

Owning Palette: Signal Manipulation Express VIs

Requires: Base Development System

Uses triggering to extract a segment out of a signal. The trigger conditions can be based on a start or stop trigger threshold or can be static. When a trigger condition is static, the trigger occurs immediately and this Express VI returns a predefined number of samples.

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Add to the block diagram

Find on the palette

Dialog Box Options

Parameter	Description
Start Trigger	Contains the following options: Threshold—Uses a threshold to indicate when to start triggering. Start sense—Specifies on what edge of the signal to start taking samples. The options are Rising edge, Rising or Falling edge, or Falling edge. This option is available only when you select Threshold. Start level—Amplitude that the signal must cross in the Start sense direction before the Express VI starts taking samples. The default is 0. This option is available only when you select Threshold. Pre samples—Specifies the number of samples that occur before the start trigger to return. The default is 0. This option is available only when you select Threshold. Immediate—Begins the triggering immediately. The start of the signal is the start trigger.
Stop Trigger	Contains the following options: Number of samples—Ends the triggering when the Express VI collects Samples. Samples—Specifies the number of samples to collect before stopping the trigger. The default is 1000. Threshold—Uses a threshold to indicate when to stop triggering. Stop sense—Specifies on what edge of the signal to stop taking samples. The options are Rising edge, Rising or Falling edge, or Falling edge. This option is available only when you select Threshold. Stop level—Amplitude that the signal must cross in the Stop sense direction before the Express VI stops taking samples. The default is 0. This option is available only when you select Threshold.
General	Contains the following options: Trigger channel—Specifies the channel to use if the dynamic data type input contains multiple signals. The default is 0. Reset after each trigger found—Resets the trigger conditions after finding each trigger. When you select this option, the Trigger and Gate Express VI does not buffer data with each iteration of a loop. Select this checkbox when you have a new data set for each iteration and you want to find data related only to the first trigger point. Deselect this checkbox when you want to pass only one set of data into a loop and then call the Trigger and Gate Express VI in a loop to get all the triggers in the data. Note  When you do not select this option, the Trigger and Gate Express VI buffers data. In this case, if the Trigger and Gate Express VI is called in a loop, it can start a backlog of data if there is new data for each loop (because one set of data can contain several trigger points). Because there is no reset, it buffers all the data from each loop so that it can find all the triggers, but all the triggers might not be found. Remain triggered after trigger found—Remains triggered after finding a trigger. This option is available only when you select the Threshold option in the Start Trigger section. Hysteresis—Specifies the amount above and below Start level or Stop level through which Signals must pass before a trigger level crossing is detected. The default is 0. Use trigger hysteresis to prevent noise from causing a false trigger. For a rising edge Start sense or Stop sense, the signal must pass below Start level or Stop level minus Hysteresis before detecting a trigger level crossing. For a falling edge Start sense or Stop sense, the signal must pass above Start level or Stop level plus Hysteresis before detecting a trigger level crossing.
Output segment size	Contains the following options: Automatic number of samples—Specifies that the Express VI returns the portion of the signal that matches the trigger criteria. Number of output samples—Specifies the number of samples to include in each output segment. This option is available only if the Automatic number of samples checkbox does not contain a checkmark.
Input Signal	Displays the input signal. If you wire data to the Express VI and run it, Input Signal displays real data. If you close and reopen the Express VI, Input Signal displays sample data until you run the Express VI again. Number of points in the data—Specifies the number of points in the data. The default is 4400.
Results Preview	Displays a preview of the measurement. The Results Preview plot indicates the value of the selected measurement with a dotted line. If you wire data to the Express VI and run the VI, Results Preview displays real data. If you close and reopen the Express VI, Results Preview displays sample data until you run the VI again. If the cutoff frequency values are invalid, Results Preview does not display valid data.

Block Diagram Inputs

Parameter	Description
Manual Trigger	Starts the trigger immediately and overrides the Start Trigger settings you configure. The default is FALSE.
Signals	Contains the input signal or signals.
Data Index	Contains the index of the detected trigger. If this Express VI is in a loop, wire Data Index to the iteration terminal of the loop.
Reset	Controls the initialization of the internal state of the VI. The default is FALSE.
error in	Describes error conditions that occur before this node runs.

Block Diagram Outputs

Parameter	Description
Triggered Signals	Returns the resulting segment between Start Trigger and Stop Trigger. If no data meets the requirements of the trigger, this output returns an empty signal.
Previous Signals	Contains the last triggered output data. If no data meets the requirements of the trigger, this output contains the most recent segment that meet the requirements of the trigger.
error out	Contains error information. This output provides standard error out functionality.
Data Available	Indicates if data is available that meets the requirements of the trigger.

This Express VI operates similarly to the following VIs and functions:

Basic Level Trigger Detection