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DSC Module - Libraries, Processes, Database, Shared Variables, Alarms, Traces

OK, I need some general knowledge of the DSC module and in particular, processes.  First off, I am reading shared variables from a remote PC.  I have figured out how to programmatically create a database.  Now I realize if I want to record a shared variable to my database I must first open a trace.  Fine. To use the "Open a Trace" VI I must give it a process name. OK. Now the "Open a Trace" gives me a "Trace Reference" which I then use to "write trace" which I call "begin logging".  Now to later view this logged data I can use the "Read Trace".  So now what if I wanted to log alarms I would first do a "read alarm" and pipe in the shared variable.  Now that I have read the alarms, how do I log them to a database created on this pc.  I see there is an "Enable alarm logging on a process". OK. I think the way the Hierarchy works is:

Database --> Process (or library) --> Trace (or shared variable)

So if I can enable alarm logging on a process which is a part of a database then how can I set the HI and Lo values from this PC and not the other one?  I think that I am missing information on how all of these work together.  My project eventually will be to read shared variables from a device that won't be a PC and won't have the Labview capabilities.  I think I need a good explanation of how all of this works.

 

Thanks

Matt

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OK, Sorry for the babbling.  Here is a more straight forward question: In the DSC Module: Can someone please explain how Libraries, Processes, Database, Shared Variables, Alarms, Traces all relate to each other or at least point to some material that would better explain it.

 

Thanks

Matt

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Hi Matt,

 

I think you might find this whitepaper useful: Logging Data with National Instruments Citadel.  It provides a good overview of how the citadel database logs data and alarms.

 

Libraries that use the shared variable engine are called processes, and can be monitored using the Distributed System Manager (Tools >> Distributed System Manager).  You can modify the logging and alarming properties of the shared variables in the properties of that specific variable, or you can use the Multiple Variable Editor (right click on the library or when selecting multiple variables) to modify multiple variable properties at one time.  In the properties is where you can set the Hi and Lo alarm values.

 

That database is what stores the data from the shared variables.  This historical data is called a trace.  A trace contains data type, data values, timestamps, and qualities of the shared variable.  You can view this trace information that has been stored in the database by using the Measurement and Automation Explorer (on the left, under Historical Data >> Citadel 5 Universe, navigate to the library, then select View Data button above the navigation area).  Alarm information is actually stored to a SQL Server.  This is explained under the Historical Alarm and Event Data section of the link above.

 

You can use a computer that does not have LabVIEW on it to run an application created in the LabVIEW development environment.  You will need the LabVIEW Run-Time Engine (free) as well as the DSC Run-Time Engine (needs to be purchased).

 

You might also find the examples provided in LabVIEW helpful.  You can find them by going to Help >> Find Examples.  You will then want to look under "Toolkits and Modules" and "Datalogging and Supervisory Control" for examples.

 

Finally, here some other links you may find useful.  Enhanced System Security with the LabVIEW Datalogging and Supervisory Control Module and Using the LabVIEW Shared Variable.

 

Regards,

 

Elizabeth K. 

National Instruments | Applications Engineer | www.ni.com/support 

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