LabVIEW Wiki - User contributions [en]

Database Access

2007-06-13T14:40:43Z

Lui:

'''Database Access''' means to connect to a [[Database]] (better Database_Management_System and the related set of data) and store, retrieve or otherwise manage data. 
There are different ways to access databases from LabVIEW. 
* '''National Instruments''' (NI) provides the '''Database Connectivity Toolset''' as an Add-On to LabVIEW. This is a set of tools to access local and remotes Databases and to operate them with or without structured query language (SQL) programming. 
''My personal impression'' was that this Toolset is way too complicated for just a single or very few projects.
* In the '''LabVIEW Technical Ressorce''' Volume 12, Number 3, Anthony Lukindo of Advanced Measurements Inc.published a paper named "Simplified LabVIEW Database Access: A Single VI Solution for Connecting, Reading and Writing to Your Database". This article was accompanied by a VI named "SQL Exe as LV2 Global.vi", which maintains all required data in [Shift Registers] and allows to perform allmost all database access by some simple calls to the above mentioned VI. If one knows some basics about SQL, this VI is IMHO much easier to use.
To use this tool one only needs an ODBC datasource file *.dsn to provide the database connection parameter. As this is ODBC-related, this VI is limitted to Windows only ;-((

Database Access

2007-06-13T14:34:19Z

Lui:

Database Access

2007-06-13T14:33:36Z

Lui: New page: '''Database Access''' means to connect to a Database (better Database_Management_System and the related set of data) and store, retrieve or otherwise manage data. There are...

'''Database Access''' means to connect to a [[Database]] (better Database_Management_System and the related set of data) and store, retrieve or otherwise manage data. 
There are different ways to access databases from LabVIEW. 
* '''National Instruments''' (NI) provides the '''Database Connectivity Toolset''' as an Add-On to LabVIEW. This is a set of tools to access local and remotes Databases and to operate them with ior without structured query language (SQL) programming. 
''My personal impression'' was that this Toolset is way too complicated for just a single or very few projects.
* In the '''LabVIEW Technical Ressorce''' Volume 12, Number 3, Anthony Lukindo of Advanced Measurements Inc.published a paper named "Simplified LabVIEW Database Access: A Single VI Solution for Connecting, Reading and Writing to Your Database". This article was accompanied by a VI named "SQL Exe as LV2 Global.vi", which maintains all required data in [Shift Registers] and allows to perform allmost all database access by some simple calls to the above mentioned VI. If one knows some basics about SQL, this VI is IMHO much easier to use.

StrictType Definition

2007-06-13T13:42:35Z

Lui: Redirecting to Strict Type Definition

#REDIRECT [[Strict Type Definition]]

Invoke Node

2007-06-13T13:38:06Z

Lui:

The '''Invoke Node''' is used to perform a method on a VI using [[VI Server]], very similar to the [[Call By Reference]] Node. '''Invoke Node''', however, does not need a strictly typed reference and as such is not bound to the VI's connector pane and is free to call '''any VI'''. On the other hand, as the connector pane of the callee is unknown at editing time, one must use several calls to '''Invoke Node''' in order to set control values, run the VI and retrieve its results. 
When using the '''Invoke Node''' it is very common to stumble upon an error:
== VI is not in appropriate state for the invoke node ==
This is a known behaviour, but I wouldn't call it an error. It's just how LabVIEW works. A lot of the methods for a VI reference can not be executed for VIs which are either in a reserved state or already running. When a VI is running is rather obvious but a reserved state means that the VI is either part of a running hierarchy of VIs (usually your application) or a strict typedefed VI reference is open to it. The reasons for this are not so simple but it comes down to protecting the VI from influences from different caller types. The Run method of the '''Invoke Node''' (amongst others) is asynchronous as it starts the VI but not necessarily waits for termination of the VI. An implicit reference to the VI as an icon in your block diagram or an explicit one in the form of a strict typedef to be used with the Call by Reference Node are synchronous as far as the caller is concerned.

If you are unable to resolve that error message, you may eventually try to use the Call by Reference Node instead. If you need for whatever reasons to use the Run method you MUST make sure that the VI is not an explicit part of your application by not adding its icon anywhere in your app (and not opening a strict typedefed reference to it either).

[[Category:Uncategorized]]

Call By Reference

2007-06-13T12:49:10Z

Lui: New page: The '''Call By Reference''' Node is used to call VIs with a specified connector pane, but without to exactly specify the VI ''at edit time''. It can be used to provide a plug-in architectu...

The '''Call By Reference''' Node is used to call VIs with a specified connector pane, but without to exactly specify the VI ''at edit time''. It can be used to provide a plug-in architecture within an application, where the actual plug-in can be choosen ''at runtime''. The number of and the specific plug-ins can be changed at any time after the calling application has been finished. 
The [[VI Reference]] used with Call By Reference must be a strictly typed reference, which can be obtained using the Open VI Reference Node. 
Aside of the [[VI Reference]] and the [[Error Cluster]] flow-through connectors, there is a specific connector pane that relates to the strictly typed VI Reference, both with the connector pane and with their data types. You can wire to these terminals just as you would to a normal subVI. 
Be aware that calling a VI with the '''Call By Reference''' Node involves a small overhead compared with a normal SubVI call, due to validating the [[VI reference]] and some other bookkeeping. This is, however, insignificant with all but very small VIs when used on local machines. It can become a problem with frequent calls to remote machines.

VI reference

2007-06-13T12:20:19Z

Lui: Redirecting to VI Reference

#REDIRECT [[VI Reference]]

VI Reference

2007-06-13T12:14:24Z

Lui: New page: A '''VI Reference''' [VI-Ref] is a reference to a VI, that is 'somewhere' loaded into the memory of a computer. This VI-Ref can than be used to access and possibly modify this VI, its comp...

A '''VI Reference''' [VI-Ref] is a reference to a VI, that is 'somewhere' loaded into the memory of a computer. This VI-Ref can than be used to access and possibly modify this VI, its components and data by means of [[VI Server]]. 
In order to open a VI-Ref one needs to specify the VI Server to work on, the [[Application Reference]] [Appref]. This defaults to the local machine, but can be any active machine that can be reached via TCP/IP connection. Use the ''Open Application Reference'' node in the Application Control palette. The LabVIEW Help states:
<blockquote>
The ''Open Application Reference'' Node returns a reference to a VI Server Application that runs on the specified computer. If no computer is specified, it defaults to the local machine. 
The returned application reference can be used in conjunction with the Property and Invoke Nodes to get or set properties and invoke methods on the application, including opening a VI Reference. 
The AppRef should be closed with the ''Close Reference'' function, if it is no longer required, allthough LabVIEW will close it as soon as no instance uses it any longer (usually when the top-level VI of the calling chain to this AppRef goes idle). </blockquote>
With an AppRef one opens a VI-Ref using the ''Open VI Reference'' node in the very same palette. Again the LabVIEW Help states:
<blockquote>
This function returns a reference to a VI, custom control, or global variable as specified by its name or path to its file location on disk. VI-Refs should as well explicitely be closed when no longer needed; allthough LabVIEW closes them under the same conditions as for AppRefs. 
A VI-Ref can be counted as similar to function pointers in other programming languages, but LabVIEW can handle such function pointers across the network.
</blockquote>
Having obtained the VI-Ref, one can (recursively) access all of its properties and components and can as well call the VI or perform some actions with it.
The former is done using [[Property Node]]s. The VI can be called using the [[Call By Reference]] node, while the methods for the VI are accessibel using the [[Invoke Node]]. Amoung the methods are [[Front Panel]] specific ones like open/close/move/scale etc, operation methods like setting or retrieving control data or running or aborting the VI and printing methods.

==See Also==
* [[VI Server]]
* [[Application Reference]]
* [[Call By Reference]] node
* [[Invoke Node]]
* [[Property Node]]

VI Server

2007-06-13T12:12:57Z

Lui:

The VI Server is a means to programmatically control front panel objects, VIs, and even LabVIEW itself, and to dynamically load, edit, run and document VIs. And all this functionality is provided on the local machine as well as across the network - whereever the remote machine is located. 
In order to create a VI Server session, one has to open an [[Application Reference]] to remote computers and a [[VI Reference]] [VI-Ref] on the desired computer.
With that VI-Ref one can perform actions with the VI like setting or retrieving control values, running it or setting and retrieving the VIs properties.

Application reference

2007-06-13T12:11:40Z

Lui: New page: An '''Applcation Reference''' [AppRef] is a reference to a VI Server, which can operate on the local machine or somewhere on the (global) network. The ''Open Application Referen...

An '''Applcation Reference''' [AppRef] is a reference to a [[VI Server]], which can operate on the local machine or somewhere on the (global) network. 
The ''Open Application Reference'' Node on the ''Application Control'' Palette returns a reference to a VI Server Application that runs on the specified computer. If no computer is specified, it defaults to the local machine. 
The returned application reference can be used in conjunction with the Property and Invoke Nodes to get or set properties and invoke methods on the application, including opening a VI Reference. 
The AppRef should be closed with the ''Close Reference'' function, if it is no longer required, allthough LabVIEW will close it as soon as no instance uses it any longer (usually when the top-level VI of the calling chain to this AppRef goes idle).
An AppRef is also used to open a VI-Ref using the ''Open VI Reference'' node in the very same palette.

==See Also==
* [[VI Server]]
* [[VI Reference]]

VI Server

2007-06-13T11:14:47Z

Lui: New page: The VI Server is a means to programmatically control front panel objects, VIs, and even LabVIEW itself, and to dynamically load, edit, run and document VIs. And all this functionality is p...

The VI Server is a means to programmatically control front panel objects, VIs, and even LabVIEW itself, and to dynamically load, edit, run and document VIs. And all this functionality is provided on the local machine as well as across the network - whereever the remote machine is located. 
In order to create a VI Server session, one has to open an [[Application reference]] to remote computers and a [[VI Reference]] [VI-Ref] on the desired computer.
With that VI-Ref one can perform actions with the VI like setting or retrieving control values, running it or setting and retrieving the VIs properties.

VIT File Extension

2007-06-13T09:16:10Z

Lui: New page: 'Vit' is the acronyme and file type for LabVIEW Templates. Templates are patterns or models, used as starting points to create a new instance (copy) of that template. This new instance can...

'Vit' is the acronyme and file type for LabVIEW Templates. Templates are patterns or models, used as starting points to create a new instance (copy) of that template. This new instance can either be used to perform some work in several instances (Think of communication using different channels or driving different devices.) or can be modified in order to not start on scratch but with some similar code. 
The latter use case is availabel with the 'File/New' command. This offers to create a new VI from one of several templates. There are templates for Data Acquisition [ [[DAQ]] ], several Frameworks and Design Patterns and some Tutorial templates.

CTL File Extension

2007-06-13T08:31:36Z

Lui: New page: 'Ctl' is the file type of LabVIEW controls. Controls are stored either ''in'' their parent vi or in dedicated files. The latter helps to define similar controls on different VIs. You...

'Ctl' is the file type of LabVIEW controls. Controls are stored either ''in'' their parent vi or in dedicated files. The latter helps to define similar controls on different VIs.
 You define user-specific controls by right-clicking a control and choosing ''Advanced/Customize''. This opens the [[control editor]], where you can change the control. '''Attention!''' Creating a control on a VI's [[Frontpanel]] [FP] from a specified *.ctl file copies this control into the FP, but does not maintain a link to the *.ctl file. Any changes applied to the *.ctl afterwards are not propagated to the VIs FP. Use [[Type Definition]]s instead if you need to maintain consistancy between different control instances.

==See Also==
* [[Type Definition]]
* [[StrictType Definition]]
* [[control editor]]

Strict Type Definition

2007-06-13T07:25:30Z

Lui:

A strict type definition [STD] is like a [[Type Definition|type definition]] with well-defined appearance. This means that all instances of STD's share the appearance of that STD, e.g. their properties cannot be changed (except of label, caption and enable-state). This iis handy whenever the size, color etc. needs to be fixed. Think of sophisticated screen designes or stacked STDs. 
STDs are created by saving as this type of control - similar to 'simple' type definitions.

==See Also==
* [[Type Definition]]

==External Links==
* Creating Type Definitions and Strict Type Definitions[http://zone.ni.com/reference/en-XX/help/371361B-01/lvhowto/creating_type_defs/]

[[Category:User Interface]]

Type Definition

2007-06-13T07:22:59Z

Lui:

A type definition [TD] is a custom control (CTL) file that has been marked as a type definition. Instances of the TD are linked to their definition. You cannot edit functional properties of TD's instances, but only optical properties. To change functional properties you have to edit their TD. All changes in a TD are propagated to all of its instances, when you save the TD or choose to 'apply changes'. 
Type definitions can be stacked, e.g. can contain other TDs as well. You use this to define clusters of different data, which are defined as well and as such can be accessed on different levels. Review the properties of, say, a waveform chart, using a property node. You'll fiond a property 'Bounds' for the chart itself as well as for its caption, label, scales, even the scales' markers and so on.

==See Also==
* [[Strict Type Definition]]

==External Links==
* [http://zone.ni.com/reference/en-XX/help/371361B-01/lvhowto/creating_type_defs/ Creating Type Definitions and Strict Type Definitions]

[[Category:User Interface]]

Strict Type Definition

2007-06-13T07:04:35Z

Lui:

A strict type definition [STD] is like a [[Type Definition|type definition]] with well-defined appearance. This means that all instances of STD's share the appearance of that STD, e.g. their properties cannot be changed (except of label, caption and enable-state). This iis handy whenever the size, color etc. needs to be fixed. Think of sophisticated screen designes or stacked STDs.

==See Also==
* [[Type Definition]]

==External Links==
* Creating Type Definitions and Strict Type Definitions[http://zone.ni.com/reference/en-XX/help/371361B-01/lvhowto/creating_type_defs/]

[[Category:User Interface]]