The Automation interface for IGSS provides access to the configuration’s databases and tables like:

• Object properties like unit, description, scan interval.
• Atom properties like process values, alarm limits, i/o modes.
• Alarms on single objects or the complete alarm list.
• Alarm start, acknowledgment and ending.
• System properties like configuration name and status, system time.
• Events when objects are changed, alarm changes, and configuration status changes.

The interface is available from all programs and languages which support the Microsoft Automation standard and, since the interface is dual, can call COM interfaces. This includes among others the Visual Basic (VB) and C/C++ programming languages and all products implementing Visual Basic for Applications (VBA) as a macro language, e.g. all Microsoft Office products.

For the examples mentioned here, VB/VBA is the programming environment used. You can try the examples yourself if you have either Visual Basic or any of the Microsoft Office products. Hints will be given to users of other environments when relevant.

If you want to use the interface from the built-in VBA some of the steps have already been done. Read the paper “Getting started with the built-in VBA” to get more information on this.

Attaching the Interface

In VBA, open the “Tools” menu and look through the list “Available References:” until you come to “IGSS32 v.4.00.00 Online Database Access”. Put a checkmark in the box next to it, and you’ve then attached the Automation interface.

(Image References – Project)

If the entry does not appear in the list “Available References:”, then click the button “Browse…” and search for file dc.exe containing the Type Library. DC.exe is found in the directory “gss” where IGSS has been installed.

For C/C++ programmers, the files dc.h, dc_i.c and dc_p.c in the directory “gss” may also be of interest because it contains declarations needed to access the pure COM interface. If you are using Microsoft C/C++, The MFC Class Wizard can produce C++ wrapper classes for the full interface.

Browsing the Interface

To see what is in the interface, “Object Browser” is indispensable. Here you select the IGSSonline library where you can then view all objects in the library, their methods, properties and events together with a short description and parameter declarations.

(Image of Object Browser)

Accessing the Interface

The only object in the interface that can be directly instantiated is IGSSDB. All other objects are retrieved from collections in IGSSDB or other objects. So you will always have to have at least one instance of IGSSDB to do anything at all. You can accomplish this in one of two ways:

implicitly when declaring the object variable:

Dim igss As New IGSSDB or

explicitly in the code module:

Dim igss As IGSSDB
Set igss = CreateObject(“DC.IGSSDB”)

Now the methods and properties of IGSSDB are available. One property is especially important since it indicates if a configuration is loaded and active. This is “IsConfigLoaded”. If this is not the case most of the interface cannot be used and will return errors. This is because if there is no configuration, then there is no online database to access. The following code will check this:

If igss.IsConfigLoaded Then
Do your database access
Else
you may try to start the configuration
igss.StartConfig
EndIf

Accessing an IGSS Object

Having an instance of the IGSSDB object, you can now get access to IGSS objects through the collection Objects. Let us now access the analog object q1 by:

Dim flowObject as IGSSOBJECT
Set flowObject = igss.Objects(“q1”)

Now the static properties of an IGSS object can be accessed. These are things like description, an engineering unit, and the number of decimals by:

Dim desc As String
Dim unit As String
Dim dec As Integer

desc = flowObject.Description
unit = flowObject.Unit
dec = flowObject.Decimals

All dynamic properties of the object are in the IGSSATOM objects. We can get these from the collection “Atoms” on the IGSSOBJECT by:

Dim processValue As IGSSATOM
Set processValue = flowObject.atoms(“Value”)

Now we can get the value, i/o-mode, etc. of the process value by:

Dim value as Double
Dim iomode as Integer

value = processValue.Value
iomode = processValue.IOmode

You could also avoid “flowObject” and “processValue” variables and get the value directly by:

Value = igss.Objects(“q1”).Atoms(“Value”)

If you only need the process value of atoms, there are a few shortcuts that can be used. Directly on the IGSSOBJECT two primary atoms have been predefined in ProcessIn and ProcessOut. For the analog object, these have been defined as “Value” and “Set Point” respectively. So you could also write:

value = flowObject.ProcessIn

Directly on the IGSSDB, there is also general access to any process value using the methods ReadDB and WriteDB. So you could also write:

value = igss.ReadDB(“q1!Value”)

The syntax for object and atom names are similar to the syntax in the DDE interface.

Using Events

To illustrate the use of events we will go through a little exercise. Let’s say we have two IGSS objects, “q1” and “q2”, which describe two flows somewhere in our process. We need to calculate the average and notify the user each time a change occurs.

In VBA events can only be used in class modules, so we have to make the following class module called EventDemo:

Dim igss As IGSSDB
Dim WithEvents q1 As IGSSATOM
Dim WithEvents q2 As IGSSATOM

Sub startSubscription()
Set igss = CreateObject(“DC.IGSSDB”)
Set q1 = igss.Objects(“q1”).Atoms(“Value”)
Set q2 = igss.Objects(“q2”).Atoms(“Value”)
End Sub

Sub endSubscription()
Set q1 = Nothing
Set q2 = Nothing
Set igss = Nothing
End Sub

Private Sub calculate()
Dim qsum As Double
qsum = q1.Value + q2.Value
MsgBox “Total flow changed to: ” & qsum
End Sub

Private Sub q1_AfterAtomChange()
calculate
End Sub

Private Sub q2_AfterAtomChange()
calculate
End Sub

Note: The “WithEvents” extension to the Dim statements is what’s doing all the magic.

Be careful not to spend too much time in the event procedures. failing to do so may disturb other tasks in the data collection procedure. Good programming practice is to do the small tasks in the event procedures and split up bigger tasks to be processed in e.g. timer events.

Instead of notifying the user, we may choose to update another IGSS object, let’s say “q3”. All we have to do now is to declare and initialize a new object:

Dim q3 As IGSSATOM
Set q3 = igss.Objects(“q3”).Atoms(“Value”)

Then the MsgBox statement can be substituted with:

q3.value = qsum

Of course, we have to make sure that q3 has either “out”, “in/out” or “local” as its I/O mode, otherwise, the statement will fail.

To start the show, we have to instantiate the class module. We do that from a normal module:

Dim evt As New EventDemo

Sub startTheShow()
evt.startSubscription
End Sub

Sub stopTheShow()
evt.endSubscription
End Sub

Moving from version 2 to version 3 or 4

A few things in the procedure connecting to the interface has changed from version 2 to version 3 or 4. These changes will require a few changes in your programs. The changes are made so that version 2 and version 3 or 4 of IGSS can coexist on the same PC and so that also programs interfacing the two versions can coexist.

If you are using VB/VBA you should:

• In the “References” dialogue detach the interface “IGSS Online Database Access” and attach “IGSS32 v.4.00.00 Online Database Access” instead.
• Explicit instantiation of the IGSSDB object should change from “CreateObject(“IGSSDB”)” to “CreateObject(“DC.IGSSDB”)”
• A few parameters have got new data types. The compiler will warn you about the changes needed.

If you are using C/C++ you should:

• Instead of the type library igssaut.tlb you should use the type library imbedded in dc.exe
• Instead of including the header file iigssaut.h you should include the header file dc.h and append the file dc_i.c to your project.
• A few parameters have got new data types. The compiler will warn you about the changes needed.