Locate and Browse OPC Historical Data Access Servers

Step 1: Browse 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 Client Object and Connect to 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: Browse Server Namespace and Select Items

Browse the graphical namespace of the server and select required items. For this example, Sawtoothed-Waves.Real4 item is selected.

ns = browseNameSpace(hdaObj)

ns =

  1×1 cell array

    {'Saw-toothed Waves.Real4'}

Step 4: Query Server Item Attributes

Examine the current normal maximum value of the selected item.

maxVal = readItemAttributes(hdaObj,ns(1),hdaObj.ItemAttributes.NORMAL_MAXIMUM,now,now)

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

maxVal = 

  struct with fields:

         ItemID: 'Saw-toothed Waves.Real4'
    AttributeID: 11
      Timestamp: 7.3960e+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 5: 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)