LabVIEW
Event Case
Solved!
Events are primarily for user interactions, not for indicator changes (except for writing to values signaling properties, which would not be useful here because writing to one fires the event even if the value has not changed.)
All you probably need is a "last value" tunnel, e.g. as follows:
(And if you are really only interested in whole milliseconds, a simple tick count would not require any multiplication.)
An event triggers if the value is changed by the user.
(A special case is writing to a signaling value property of the control assigned to the value changed event. In that case, the event fires unconditionally. This is intentional. You can always compare old vs new value from the event data node and execute something else (e.g. an empty case inside the event structure) if the are equal.)
Event structures require some basic knowledge to avoid problems. (There are a lot of landmines if you don't know what you are doing so start reading here but be aware that I don't agree with some of the statements). LabVIEW is primarily a dataflow language and event structures came much later, Still, they are one of the best tools for UI design if used correctly.
Hi Zuc
You are right the Event structure will not be "triggered" by the FileGlobals Variable.
The Event structure was mainly design to trigger events from the user interface, like change values, mouse clicks, etc. When using the event structure on a Queue message handler template for example, there are 2 looks one looking for any User interface interaction and a second loop as the executor of the actions triggered by the other loop. This way you avoid having 2 loops running continuously consuming machine time.
Check this example to learn more about the template.
Now, going back to your problem, if you are looking to trigger something from HW input in order to trigger an action (in your example, a digital output), then you will have to continuously read the source of your input.
The Value (signaling) may be used to generate an event programmatically, by reading a hw input an then assigning that to a Control, that control will then generate the event. I don't know how much benefit will this bring rather than watching the HW input directly to trigger some action.
@LVNinja wrote:
The Value (signaling) may be used to generate an event programmatically, by reading a hw input an then assigning that to a Control, that control will then generate the event. I don't know how much benefit will this bring rather than watching the HW input directly to trigger some action.
Careful there! As already mentioned, writing to a signaling value property of a control linked to a "value change" event will fire the event 100%, even if the value did not change (i.e. new=old).
We do have "is value changed", "boolean crossing", and other useful tools.
If you are spinning the loop to poll a value anyway, an event structure is completely pointless!
