1 Software Redundancy

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1 1 Software Redundancy Within WinCC, the software redundancy feature makes it possible to monitor critical sections of a plant by using a redundant connection to several PLCs. WinCC (Tag Management) Tag 1 Tag 2.. Tag n Redundant Tags T 1 T 2 T 3 Logical Connections Non-redundant Connection to PLC 1 Redundant Connection Non-redundant Connection to PLC 2 PLC 1 PLC 2 Redundant PLC Section Software redundancy considerably improves reliability when critical plant sections are to be monitored. For example, a redundant connection to two PLCs means that one PLC takes over if the other PLC fails. Using software redundancy does not mean that you can only establish redundant connections to the PLCs configured. It is still possible to connect any PLC in a nonredundant layout. The switchover between redundant PLCs is performed automatically in the event of a malfunction. However, a manual switchover is also possible by specifying a tag (@ForceConnectionState). Note Establishing a redundant connection requires two PLCs. 1-1

The computer properties must be set to the following values: Step 2 Within the Alarm Logging system, the "short-term archive" must be activated: If the

2 Software Redundancy Setting up software redundancy: In order to use software redundancy under WinCC, the following settings are required in the Control Center: Step 1 The computer properties must be set to the following values: Step 2 Within the Alarm Logging system, the "short-term archive" must be activated: If the "short-term archive" has not yet been activated, proceed as follows: In the navigation window, open the pop-up menu of the "Archives" object and select the "Add/Remove" menu item. Within the "Assign Storage Parameters" dialog box, activate the "Short-Term Archive Active" check box. 1-2

In the "WinCC system messages" dialog box, activate the "Create New System Messages Only"

3 Step 3 Within the Alarm Logging, the system messages must be retrieved; select the "Options" and "WinCC System Messages" menu items for this purpose. In the "WinCC system messages" dialog box, activate the "Create New System Messages Only" option and press the "Create" button. This procedure retrieves the system messages associated with software redundancy. 1-3

$This integration procedure requires the following steps: In the Windows Explorer, start the "C:\Siemens\WinCC\bin\DynWizEdit.exe" program. Select the "German" language in the toolbar.$

4 Software Redundancy Step 4 By means of the "DynWizEdit.exe" program, integrate the Dynamic Wizard for software redundancy into the WinCC system (Graphics Designer). This integration procedure requires the following steps: In the Windows Explorer, start the "C:\Siemens\WinCC\bin\DynWizEdit.exe" program. Select the "German" language in the toolbar. Retrieve the "C:\Siemens\WinCC\wscripts\wscripts.deu\SW_Redundanz.wnf" script by selecting the "Dynamic Wizard" and "Retrieve Wizard Script" menu items. The compilation progress is shown in the output window. After the compilation has been completed successfully, the new entry "Establish Redundant Connection" appears in the "Dynamic Wizard" window. Step 5 Integrate the "SIMATIC S7 PROTOCOL SUITE" communications driver within the tag management. Step 6 Within the required bus type (e.g. MPI), create a logical connection in the "SIMATIC S7 PROTOCOL SUITE" communications driver. Give an expressive name to this connection. Step 7 Open an existing picture in the Graphics Designer. Within the Dynamic- Wizard (in the "System Functions" tab), start the "Establish Redundant Connection" program by double-clicking. 1-4

5 Step 8 Press the "More" button in the welcome screen. Step 9 Select the main connection in the "Set Options" dialog box. Then press the "More" button. 1-5

6 Software Redundancy Step 10 Edit the settings for the back-up connection in the "Set Options" dialog box. Then press the "More" button. The "Automatic Switchover" check box must be active (default setting). The settings for the back-up connection (S7 network address) can be found in the "Connection" tab. Access this tab via the connection properties dialog box for the connection. 1-6

Step 11 The settings you specified are displayed in the final "Finished" dialog box. By pressing the "Finish" button, connection-specific internal tags are created in a tag group.

7 Step 11 The settings you specified are displayed in the final "Finished" dialog box. By pressing the "Finish" button, connection-specific internal tags are created in a tag group. This tag group is stored within the tag management under "SIMATIC S7 PROTOCOL SUITE" and the associated channel unit. Note By pressing the "Back"u button, you can go back one step and make any necessary changes. 1-7

8 Software Redundancy Connection-specific Internal Tags Connection control is accomplished by means of connection-specific internal tags. The connection-specific internal tags are created by a wizard. The name of a connection-specific internal tag is composed of the name of the associated connection and an identifier. The connection name is provided with a '@' prefix to identify it as a system tag. Example: "@connection name@identifier". All connection-specific internal tags are assembled to form a "@connection name" tag group. Note Only if the associated connection is ready for operation does the WinCC data manager permit access to connection-specific tags. However, it is possible to have read and write access to connection-specific internal tags independently of the connection status. The following system tags are available for SIMATIC S7 PROTOCOL SUITE software Meaning: Type: Default: connection status DWORD read 0 = "faulty" The current connection status can be determined by means of the 'ConnectionState' tag. 0 = connection faulty 1 = connection ready for Meaning: Type: Default: error cause DWORD read 0 = "no error" The tag contains an error cause describing the reason why the connection was interrupted. Default = 0, i.e. connection not yet established or without error. When establishing a connection, the tag is loaded with 0 (no error) again. The error code is interpreted in a channel-specific manner. The S7 channel stores the S7 DOS error code here. 0 = no error <> 0 = S7 DOS error code 1-8

9 @ConnectionErrorString Meaning: error cause as string Type: TEXT8 [128] read Default: "" = "no error" The tag contains the error cause in the format of a string describing the reason why the connection was interrupted. The string is put out in the language currently selected. Default = "", i.e. connection not yet established or without error. The following texts are entered in the S7 channel in English, without regard to the selected language. "No Error" "Error hhhh" = No error = hhhh error occurred (hhhh = S7 DOS hexadecimal error Meaning: communication error counter Type: DWORD read Default: 0 = "no error" The value of this tag is incremented by 1 each time a connection is interrupted. In the event of an overflow the count starts again with Meaning: connect mode Type: DWORD write Default: 1 = "automatic" This tag enables you to specify a connection to be established automatically. The S7 channel then attempts to reestablish a failed connection at intervals of approx. 4 seconds. If a value = 0 is entered in this tag, the connection will not be reestablished automatically at intervals of 4 seconds, but remains interrupted. Writing tag takes the following effect: 0 = manual connecting mode -> deactivate automatic connecting <> 0 = automatic connect mode -> activate automatic connecting 1-9

10 Software Redundancy Meaning: preferred connection status Type: DOWRD write Default: 1 = "established" This tag can be used to notify the channel of the preferred connection status. Usually this tag has the value 1, i.e. the channel attempts to establish the connection (at regular intervals of approx. 4 seconds, if applicable). If the value 0 is written to this tag, the channel interrupts the connection. Writing to this tag takes the following effect: 0 = preferred connection status: connection interrupted -> if connection established -> cause connection to be interrupted 1 = preferred connection status: connection established -> if connection interrupted -> cause connection to be Meaning: selecting the connection address Type: DWORD write Default: 0 = "configured" This tag specifies which of the connection addresses is to be used for establishing the connection. Writing to this tag takes the following effect: 0 = connection via configured connection parameters -> previously 1 -> cause connection to be interrupted 1 = connection via alternative connection parameters -> previously 0 -> cause connection to be interrupted -> If connect mode is set to "automatic", the connection is automatically established with the corresponding address. 1-10

11 @AlternateConnectionAdress Meaning: Alternative connection address Type: TEXT8 [255] write Default: "..." = "configured" The alternative connection address string can be entered in this tag. This is the same string as the one which is displayed as connection parameter in the WinCC Control Center. The string is channelspecific. On system start-up (runtime), the configured address is entered here as default for the S7 channel. If an address has not been configured yet, the text "Illegal Address" is entered for the S7 channel. Example of an address specified for an S7 PLC with station address 3 via MPI: MPI,3 0,,0,0,02 Writing to this tag takes the following effect: -> If the address is changed by the write process, the "Connection via alternative connection parameters" setting causes the connection to be interrupted. -> If the "automatic" connect mode has been set, the connection is established automatically, using the address just previously written. 1-11

12 Software Redundancy Master-Reserve Change-over on the S7 When the Dynamics Wizard has finished setting up the redundant-backup link, you can extend the script by adding the Master-Reserve Change-over option. To do so, you open the script under Global Script -> Actions -> Global Actions. If your selected connection is called CPU_3 as in the illustrations above, Control Center- (Projekt.MCP) Projekt Variablenhaushalt Editoren Global Script Aktionen Globale Aktionen CPU_3.pas CPU_4.pas CPU_5.pas Having opened it, you then insert the sequence printed in bold type and highlighted in gray. Here too it is assumed that your connection is called CPU_3. If you have used a different name, replace each occurrence of CPU_3 with the name you have used. The bit variable SWR.Standby is the bit Reserve from the status word (DW 9.1) from the instance DB of the call for FB101 SWR_ZYK. If you have used a different name for this, replace the name accordingly.... { } MSRTStopMsgService ( ServiceID, &Error ); If ( GetTagDWordWait( "@CPU_3@ConnectionState" ) == 0 ) { SetTagDWord( "@CPU_3@ForceConnectionState", 1 ); } else { if ( GetTagBitWait( "SWR.Standby" ) == TRUE ) { SetTagDWord( "@CPU_3@ForceConnectionState", 0 ); } } return 1; } } 2-12

13 Note: you can add the Standby bit to the structure for the redundant software backup screen block (see section in the user documentation for the redundant-backup software blocks) as follows: Name Data type Offset Bit WORD Status WORD 0 0 BIT MasterSwitch BIT 2 0 BIT RedTurnOn BIT 2 9 BIT RedTurnOff BIT 2 8 BIT Standby BIT

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