Download this preconfigured object here.

 

Wonderware’s Industrial Application Server provides several methods to ensure data integrity. From having a hot standby available for processing objects with Application Engine Redundancy to local buffering of historian data in case of connection loss to Industrial SQL Server, Wonderware has made system robustness a focal point. In the pursuit of those goals, Wonderware has provided a $RedundantDIObject which allows the user to identify a primary connection to the PLC as well as a backup location - switching between those two sources is automated by the object.

 

In some cases, when migrating an InTouch application into Application Server for example, all that is required is functionality similar to the IOSetAccessName() function in InTouch where an existing PLC connection is reconfigured dynamically to look to an alternate location. This type of operation can certainly be achieved using the $DDESuiteLinkClient and extending it’s functionality with scripting. The following is one method to implement this switchover. A version of the enhanced object, $qDDESuiteLinkClient, is included with this note.

 

$qDDESuiteLinkClient

 

It is good practice to create Derived Templates from the version that is supplied during installation. This allows you to maintain independent configuration for this specific application. The $qDDESuiteLinkClient was derived from the$DDESuiteLinkClient and added the switchover functionality.

 

NOTE: The attributes that are locked will not be able to be changed when the instance is created.

 

General Settings:

• Enable the Detect Connection Alarm option.
• The Server Node, Server Name, and Communication Protocol and be adjusted at the instance level.

Topic Settings:

• Topic configuration and the Attribute listing (if required) can be configured at the instance level.

Object Information Settings:

• The Object Information is basic information about the object and can be updated at the instance level.

Scripts Tab:

There are a couple of scripts that were added to enable the automated switchover:

Name:	ConnectionAlarm_cot (Attempt Reconnect)
Script Info:
Script:	' Reset Retry Count me.FailoverRetryCount = 0;

 

Name:	ConnectionAlarm_cwt (Attempt Reconnect, Switch to alternate)
Script Info:
Script:	' Delcare variables for use in the script    dim retryCount as Integer; ' Assign initial values for the variables    retryCount = me.FailoverRetryCount; ' increment retry counter '  if less that max retries - reinitialize connection '  if max retries exceeded - switch server location, reset retry count    retryCount = retryCount + 1;    if retryCount > me.FailoverMaxRetries then       if me.ServerNode == me.ServerPrimaryLocation then          me.cmdSetToBackup = 1;       else          me.cmdSetToPrimary = 1;       endif;       retryCount = 0;    else       me.Reconnect = 1;    endif;     ' Assign script variables to Attributes    me.FailoverRetryCount = retryCount;

 

Name:	ConnectionAlarm_cot (Attempt Reconnect)
Script Info:
Script:	' Reinitialize Connection    me.Reconnect = 1;

 

Name:	cmdSetToPrimary_cwt (Switch to the Primary Server Location)
Script Info:
Script:	' Set the server location to the Primary, Reinitialize    me.ServerNode = me.ServerPrimaryLocation;    me.Reconnect = 1; ' Reset the command trigger    me.cmdSetToPrimary = 0;

 

Name:	cmdSetToBackup_cwt (Switch to the Backup Server Location)
Script Info:
Script:	' Set the server location to the Backup, Reinitialize    me.ServerNode = me.ServerBackupLocation;    me.Reconnect = 1; ' Reset the command trigger    me.cmdSetToBackup = 0;

 

Name:	InitializeObject (general object initialization)
Script Info:
Script:	' This script can be used to initialize anything in the application. This example sets a UDA on the engine that it is hosted on for other objects to reference.   myEngine.DIPrefix = me.Tagname + ".TAGNAME."; ' Set Initialized Status   me.objInitialized = 1;

 

UDAs Tab:

Here are the details around the UDAs that are added:

Name	Data Type	Category	Array	Initial Value
cmdSetToBackup	Boolean	User Writeable	No	Off/False
cmdSetToPrimary	Boolean	User Writeable	No	Off/False
FailoverEnable	Boolean	User Writeable	No	On/True
FailoverMaxRetries	Integer	User Writeable	No	3
FailoverRetryCount	Integer	User Writeable	No	0
objInitialized	Boolean	User Writeable	No	Off/False
ServerBackupLocation	String	User Writeable	No	localhost*
ServerPrimaryLocation	String	User Writeable	No	localhost*

* Server Locations should be set to computer names that are running the IO Server

Extensions Tab:

The Extensions tab can be used if you would like to Alarm or Historize any of the added UDAs. Implementing this is optional.