software redundancy

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03.98 Software Redundancy

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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.

PLC 1 PLC 2

WinCC (Tag Management)

Tag 1

Tag 2

Tag n

.

.

T 1 T 2 T 3

RedundantPLC Section

RedundantConnection

RedundantTags

LogicalConnections

Non-redundantConnection to PLC 1

Non-redundantConnection to PLC 2

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 non-

redundant 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.


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Software Redundancy 03.98

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Setting up software redundancy:

In order to use software redundancy under WinCC, the following settings are

required in the Control Center:

Step 1The 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.


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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.


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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.


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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.


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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 channelunit.

Note

By pressing the "Back"u button, you can go back one step and make any

necessary changes.


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1.1 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 associatedconnection 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 S7PROTOCOL SUITE

software redundancy:

@ConnectionState

Meaning: connection status

Type: DWORD

Access: read

Default: 0 = "faulty"

The current connection status can be determined by means of the

'ConnectionState' tag.

0 = connection faulty

1 = connection ready for operation

@ConnectionError

Meaning: error cause

Type: DWORD

Access: read

Default: 0 = "no error"

The tag contains an error cause describing the reason why the

connection was interrupted. Default = 0, i.e. connection not yetestablished 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


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@ConnectionErrorString

Meaning: error cause as string

Type: TEXT8 [128]

Access: 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" = No error

"Error hhhh" = hhhh error occurred

(hhhh = S7 DOS hexadecimal error code)

@ConnectionErrorCount

Meaning: communication error counter

Type: DWORD

Access: 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 0.

@ConnectionEstablishMode

Meaning: connect mode

Type: DWORDAccess: 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 the @ConnectionEstablishMode tag takes the following effect:

0 = manual connecting mode-> deactivate automatic connecting

0 = automatic connect mode

-> activate automatic connecting


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@ForceConnectionState

Meaning: preferred connection status

Type: DOWRD

Access: 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 established

@ForceConnectionAdress

Meaning: selecting the connection address

Type: DWORD

Access: write

Default: 0 = "configured"

This tag specifies which of the connection addresses is to be used for

establishing the connection.


0 = connection via configured connection parameters

-> if @ForceConnectionAddress previously 1


1 = connection via alternative connection parameters

-> if @ForceConnectionAddress previously 0


-> If connect mode is set to "automatic", the connection is

automatically established with the corresponding address.


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@AlternateConnectionAdress

Meaning: Alternative connection address

Type: TEXT8 [255]

Access: 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 channel-

specific. 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


-> 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.


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2 Master-Reserve Change-over on the S7When 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, open @CPU_3.pas.

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 ingray. 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;

}}


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Note: you can add the Standby bit to the structure for the redundant software backup

screen block (see section 7.2.2 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 0 9

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