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Locate and Browse OPC Historical Data Access Servers

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This example shows how to browse the network for OPC Historical Data Access servers, and query the server name space for server items and their properties.

PREREQUISITES:

Step 1: Browse the Network for OPC HDA Servers

You use the opchdaserverinfo function to query a host on the network for available OPC Historical Data Access servers. This example uses the local host.

hostInfo = opchdaserverinfo('localhost')

hostInfo = 

OPC HDA Server Information object:
                 Host: localhost
             ServerID: Matrikon.OPC.Simulation.1
          Description: MatrikonOPC Server for Simulation and Testing
     HDASpecification: HDA1

Find the server info entry with a description starting with Matrikon.

hIndex = findDescription(hostInfo,'Matrikon')
hostInfo(hIndex)

hIndex =

     1


ans = 

OPC HDA Server Information object:
                 Host: localhost
             ServerID: Matrikon.OPC.Simulation.1
          Description: MatrikonOPC Server for Simulation and Testing
     HDASpecification: HDA1

Step 2: Construct a Client Object and Connect to the Server

Use the ServerInfo object returned in the previous step to construct a client object.

hdaObj = opchda(hostInfo(hIndex));

You can also specify the host name and server ID directly.

hdaObj = opchda('localhost','Matrikon.OPC.Simulation.1')

hdaObj = 

OPC HDA Client localhost/Matrikon.OPC.Simulation.1:
               Host: localhost
           ServerID: Matrikon.OPC.Simulation.1
            Timeout: 10 seconds

             Status: disconnected

         Aggregates: -- (client is disconnected)
     ItemAttributes: -- (client is disconnected)

Connect the client to the server.

connect(hdaObj);

Step 3: Retrieve the Server Name Space

Retrieve the name space of the server.

ns = getNameSpace(hdaObj)

ns = 

4×1 struct array with fields:

    Name
    FullyQualifiedID
    NodeType
    Nodes

Each element of the structure is a node in the server name space.

ns(1)

ans = 

                Name: 'Simulation Items'
    FullyQualifiedID: 'Simulation Items¥'
            NodeType: 'branch'
               Nodes: [8×1 struct]

Step 4: Find Items in the Name Space

Use the serveritems function to find all items in the name space containing the string Real.

realItems = serveritems(ns,'*Real*')

realItems = 

    'Bucket Brigade.ArrayOfReal8'
    'Bucket Brigade.Real4'
    'Bucket Brigade.Real8'
    'Random.ArrayOfReal8'
    'Random.Real4'
    'Random.Real8'
    'Read Error.ArrayOfReal8'
    'Read Error.Real4'
    'Read Error.Real8'
    'Saw-toothed Waves.Real4'
    'Saw-toothed Waves.Real8'
    'Square Waves.Real4'
    'Square Waves.Real8'
    'Triangle Waves.Real4'
    'Triangle Waves.Real8'
    'Write Error.ArrayOfReal8'
    'Write Error.Real4'
    'Write Error.Real8'
    'Write Only.ArrayOfReal8'
    'Write Only.Real4'
    'Write Only.Real8'

Step 5: Query Server Item Attributes

Examine the current normal maximum value of the tenth item found.

maxVal = readItemAttributes(hdaObj,realItems{10},hdaObj.ItemAttributes.NORMAL_MAXIMUM,now,now)

Warning: Saw-toothed Waves.Real4: No history available for attribute. 

maxVal = 

         ItemID: 'Saw-toothed Waves.Real4'
    AttributeID: 11
      Timestamp: 7.3643e+05
          Value: 100

The warning indicates that the item has not yet been stored in the historian database, but the preconfigured item attributes are being returned.

Step 6: Clean Up OPC Objects

Disconnect the client from the server and remove OPC objects from memory when you no longer need them. Deleting the client object also deletes the group and item objects.

disconnect(hdaObj)
delete(hdaObj)