National Instruments BridgeVIEW 用户手册

Chapter 4

Human Machine Interface

4-24

© National Instruments Corporation

9.

Save the VI as 

Monitor Product.vi

 in the 

BridgeVIEW\

Activity

 directory.

10. Run the VI. The Engine launches, unless it is running already. The tank 

level changes to reflect the changing values of the Product tag. When 
the value goes over 800, the 

in alarm

 Boolean changes from OFF to 

ON, indicating an alarm condition.

End of Activity 4-3.

How Do the Tags, and Alarms and Events VIs 

Affect Startup/Shutdown?  

When a user-defined VI runs and executes one of the Tags VIs or Alarms 
and Events VIs, that VI checks the status of the BridgeVIEW Engine. If it 
is not running, executing the VI automatically starts execution of the 
BridgeVIEW Engine. The BridgeVIEW Engine loads and executes all 
required device servers. When the VI returns, the Engine is running.

The BridgeVIEW Engine continues to run until you shut it down either 
programmatically or through the Engine Manager. As the Engine shuts 
down, first it checks to see if any application is running that requires its 
services. If so, it waits until that application halts before shutting down. 
Once it shuts down, it sends a shutdown message to the device servers.

You can monitor the status of the BridgeVIEW Engine with the shutdown 
output of any of the Tags VIs, Alarms and Events VIs, or the Get Engine 
Status VI. 

Note