Alarms and Events

You can use the Alarms and Events pages of the Recording Options tab to specify conditions under which LabVIEW SignalExpress records an alarm or an event in a logged signal.

Alarms

An alarm is a notification of a signal state. You can configure alarms to activate when a signal is greater than a specified value, less than a specified value, or within or outside of a specified range of values. For Boolean signals, you can configure an alarm to activate when the signal becomes TRUE or FALSE.

LabVIEW SignalExpress automatically records changes in the alarm state, or when an alarm activates or deactivates, in the log file. When you drag a logged signal to the Data View tab, the graph displays markers at the locations where the alarm state changes during the logging operation. You also can configure actions for LabVIEW SignalExpress to take when an alarm state changes. For example, you can generate a sound, display a message to the user, generate a software trigger, create a snapshot, or execute a command to run a program.

Events

An event is an occurrence at a specific point in time. You can configure LabVIEW SignalExpress to acknowledge keystroke or signal-based events. For keystroke events, LabVIEW SignalExpress records an event in the log when a user presses the key or combination of keys you specify. For signal-based events, LabVIEW SignalExpress records an event in the log when a source signal shows a rising slope, a falling slope, or when the signal enters or leaves a window of values you specify. Use events when you want to note an occurrence during logging. For example, if you are logging sound pressure in an area with outside noise, you can configure a keystroke event so that a user can press the key each time a noise occurs that is not relevant to the signal you are recording.

LabVIEW SignalExpress automatically records events in the log file, and you can specify an annotation to display on the graph on the Data View tab when the event occurs. You also can prompt the user to enter an annotation at the time a keystroke event occurs.

Viewing Alarms and Events

LabVIEW SignalExpress displays alarm state changes and events on the graph of a logged signal, but alarm state changes and events might be difficult to locate in long logs. You can use the Event Viewer to navigate to and zoom in on alarm state changes and events. Right-click a graph on the Data View tab and select Visible Items»Event Viewer from the shortcut menu to display the Event Viewer. The Event Viewer displays similar information to the Event Log tab, and lists each alarm state change and event that occurred, as well as errors, warning, data loss notifications, and informational messages. Double-click an alarm state change or event in the Event Viewer to zoom in on the portion of the graph where the alarm state change or event occurred. You also can use the Preview graph to zoom in on a portion of a logged signal and view a specific alarm state change or event.

If you want to see a list of alarm state changes and events that you can export to a text file, right-click a logged signal in the Logged Data window and select Show Alarms and Events from the shortcut menu. Click the Export button in the window that appears to save the list as a text file.