DeltaV OPC Mirror Redundancy with a mixed of Redundant and Non-redundant 3rd Party OPC Server

I want to understand how the redundancy of the DeltaV OPC Mirror works.

Let say we have the following:

DV_APPSTN_P = Primary DV Application Station

DV_OPC_P = Primary DV OPC Server

DV_OPCM_P = Primary DV OPC Mirror

3rd_Party1_OPC_P = Primary 1st 3rd Party OPC Server

 

DV_APPSTN_S = Secondary DV Application Station

DV_OPC_S = Secondary DV OPC Server

DV_OPCM_S = Secondary DV OPC Mirror

3rd_Party1_OPC_S = Secondary 1st 3rd Party OPC Server

 

3rd_Party2_OPC = 2nd 3rd Party OPC Server (Non-redundant)

 

Question: What will happen to the OPC communication with regards to 1st 3rd Party OPC Server (Active) if the 2nd 3rd Party OPC Server fails? Or is this above configuration possible?

15 Replies

  • Hello Alec,

    I think the above configuration will work.

    In case a watchdog or a heartbeat mechanism is not configured then the 1st 3rd Party OPC Server (Active) will see the last value that it received before the 2nd 3rd Party OPC Server fails. The values will not change unless communication is restored and the 2nd 3rd Party OPC Server sends new different values.

    In case there is no configured checking mechanism in sending OPC parameter values, the 1st 3rd Party OPC Server (Active) will think that it will still be able to send values to the failed 2nd 3rd Party OPC Server. The 1st 3rd Party OPC Server (Active) does not have any idea that the 2nd 3rd Party OPC Server has failed. However, the OPC Mirror connection list would show that the OPC write fails.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    Thanks Neil.
    The 1st 3rd Party OPC Server I am referring is redundant (with Active & Standby) while the 2nd 3rd party OPC Server is not redundant (Active or Not Active nor Standby).
    So, the 1st 3rd Party OPC Server has nothing to do with the 2nd 3rd Party OPC Server.
    And since both 3rd Party OPC Servers are connected to the Redundant OPC emersonexchange365.com/.../6130, if the non-redundant 3rd Party OPC Server fails, what will happen to the redundant 3rd Party OPC Server (Active)?
    Are you saying that it will hold the last value until the non-redundant 3rd Party OPC Server becomes Active or backs online?
  • In reply to Rein:

    Hello Alec,

    I am aware that the 1st 3rd Party OPC Server is redundant and the 2nd 3rd party OPC Server is simplex.

    Nothing will happen to the redundant 3rd Party OPC Server (Active) when the 2nd 3rd party OPC Server fails in case there is no custom configured watchdog/heartbeat and transmit checking mechanism.

    The OPC Mirror whether redundant or simplex acts as a bridge. In your case when the 2nd 3rd party OPC Server fails the OPC Mirror is the only one that detects the failure. The 3rd Party OPC Server (Active) is still connected to the OPC Mirror so it thinks it is connected.

    Yes the last value will be held on the OPC Mirror (this is what the 3rd party OPC servers are looking at) unless configured otherwise or if there is a custom watchdog/heartbeat that checks if the 2nd 3rd party OPC Server is still OK.

    Hope this helps.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    Hello Neil,
    1. How is the connection done? Do I have to use 2 ports of the Simplex 3rd Party OPC Server and assign them different IP addresses and connect them to DeltaV OPC Servers (Active & Standby), respectively? Or I'll just use 1 port and use a switch to split the ethernet connection to both Active and Standby DeltaV OPC Servers?
    2. What will happen if the ACTIVE DeltaV OPC Server fails?
  • In reply to Rein:

    Hello Alec,

    Following are my replies.

    1. Both would work but the usual way is to use a switch. OPC communication works as long as there is a connection and the proper credentials/privileges are set. Remember that OPC originated from Microsoft (OLE).

    2. Normally the redundant OPC server will perform a redundancy switchover when its active node fails. The standby node would become the new active and continue the communication.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    To conclude, for this to work:
    I have to configure a custom watchdog/heartbeat that checks if the Deltav OPC Servers (Active and Standby) and the 1st 3rd Party OPC Server (Active and Standby) are OK or not. But I will not configure a custom watchdog/lifebeat that checks if the 2nd(or Simplex) 3rd Party OPC Server is still OK. If the Simple 3rd Party OPC Server fails, no switching will occur. Is that correct?
  • In reply to Rein:

    Hello Alec,

    Configuring a custom watchdog/lifebeat or write check depends on the requirement. Normally health checking is required since it is important for the process or customer to know if the data value is good or valid. In some rare cases the customer does not want a watchdog/lifebeat or write check and in my experience at least one customer has this because they have alternate way in detecting if the nodes are at fault.

    Yes you are correct, by default no redundancy switchover of the redundant OPC server or redundant OPC Mirror when the failure is not local to itself (redundant node). In this case the failure is the Simple 3rd Party OPC Server not the 1st 3rd Party OPC Server (Active and Standby). There will be no redundancy switchover since the 1st 3rd Party OPC Server (Active and Standby) is still in good condition.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    To Alec and Neil,
    Please note when you implement your watchdog logic in OPC mirror that the watchdog should be the last pipe of each respective device. My experience is old so I'm not sure it is still valid, but it is important. We were communicating over OPC mirror with multiple PLCs. We added more points to our plant-wide PI database and went over our OPC license. When this happened, the registers in the last pipe of the last device stopped updating. We were no longer receiving new information on the analog registers of a PLC controlling a vacuum pump. The heartbeat was implemented in an earlier pipe and it was updating correctly. Our "heartbeat" was fine, but our analog data was stale. I do not remember seeing an OPC error in OPC Mirror when our analog data in the last pipe stopped updating.
    This might not be a problem for you, but it would be better to anticipate this and plan for it in advance than to be surprised by it.

  • In reply to Neil Castro:

    Hello Neil,
    In the OPC Server Monitor Configuration, there are 2 options for Enabling the OPC Mirror Redundancy Monitoring. One is "Failure on ANY Server" and the other is "Failure of ALL Servers. The " Failure on ANY Server" is selected because we have an existing redundant 3rd party OPC Server.
    What do you mean by this? Does this overwrites the logic on the watchdog?

    Or do I need to install Simplex OPC Mirror on the simplex 3rd  Party OPC Server?

    If yes, will there be any conflict with the other OPC Mirror installed in the redundant DeltaV OPC Server?

    Regards,

  • In reply to Rein:

    Hello Alec,

    The server monitoring of the OPC Mirror is disabled by default. This dictates the switchover behavior of the redundant OPC Mirror node with respect to the OPC servers it is bridging/connecting.

    I think this setting does not affect a custom watchdog.

    There is no need to install a simplex OPC Mirror on the simplex 3rd Party OPC Server. Unless it is used to bridge 2 or more OPC servers.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    Hello again Neil,
    Yes, by default, the server monitoring is disabled. But it's enabled because we have other redundant 3rd party OPC servers connected. Therefore, connecting other simplex 3rd party OPC server to both the Active and Standby OPC Mirror is not ok.
    Regards.

  • In reply to Rein:

    Hello Alec,

    I do not understand what you mean by connecting other simplex 3rd party OPC server to both the Active and Standby OPC Mirror. The redundant OPC Mirror is configured on the current active OPC Mirror node and this configuration is automatically replicated to the standby OPC Mirror node. It is possible to connect a simplex OPC server to a redundant OPC Mirror.

    Connecting a non-DeltaV redundant OPC server to an OPC Mirror (redundant or simplex) is the tricky part since each OPC vendor handles redundancy in different ways. So you would need to consult the provider of the non-DeltaV redundant OPC server on how redundancy is being handled on their side and on how redundant OPC connection is being handled.

    DeltaV redundant OPC server is straight forward. It is possible to connect an OPC client to the active or standby DeltaV OPC server individually but this is not the normal way. DeltaV provides an OPC proxy server for their redundant OPC server. Instead of OPC clients connecting to individual active and standby DeltaV OPC server the client connects to the proxy server. In this way the OPC client does not need to determine which OPC server is the current active. The proxy server ensures the client connects to the current active DeltaV OPC server all the time and this is true when the DeltaV OPC server performs a redundancy switchover.

    There are some people who already did redundant OPC server connection including me. They might be able to help you on the detailed configuration if they know the requirements and information of the 3rd party OPC servers.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    What I mean is that the simplex 3rd party OPC Server which is a non-Deltav is connected physically to the Active Deltav OPC Server and to Standby Deltav OPC Server using 2 cat5e cables. To illustrate it properly, from simplex 3rd party OPC Server to a switch is cat5e. Then from switch to Active Deltav OPC Server is cat5e. Then, from switch again to Standby Deltav OPC Server is another cat5e. Only the cat5e is redundant and not the 3rd party OPC Server.
    I hope you understand now.
  • In reply to Rein:

    Hello Alec,

    There is no issue in your case, connecting simplex 3rd party OPC Servers to a redundant DeltaV OPC server via redundant OPC Mirror.

    Cheers,
    Neil Castro
  • In reply to Neil Castro:

    It's been a while Neil.
    Just an update.
    The OPC Server Monitor Configuration is set to "Failure of ALL Servers will switch-over the OPC Mirror from Active to Stand-by".
    This will also overrides the watchdog.
    To summarize, it is just ok to connect a simplex 3rd party OPC Server to a redundant OPC Mirror. Watchdog is not necessary at all for the simplex OPC Server as it has of no use since if it fails, all data will be lost from this simplex 3rd party OPC Server.

    Mod, please mark this thread as answered. Thanks.