Create the OPC Object Hierarchy

Create a hierarchy of objects.

da = opcda('localhost','Matrikon.OPC.Simulation.1');
connect(da);
grp = addgroup(da,'CallbackTest');
additem(grp,'Random.Real8');
additem(grp,'Random.UInt2');
additem(grp,'Random.Real4');

Configure the Logging Duration

Set the group's UpdateRate value to 0.2 seconds, and the RecordsToAcquire property to 40.

grp.UpdateRate = 0.2;
grp.RecordsToAcquire = 40;

Configure the Logging Destination

Configure the group to log data to disk and memory. Use a file in a temporary folder.

logFileName = fullfile(tempdir,'LoggingExample.olf');
grp.LoggingMode = 'disk&memory';
grp.LogFileName = logFileName;
grp.LogToDiskMode = 'overwrite';

The disk file name is LoggingExample.olf. If the file name exists, the toolbox engine overwrites the file.

Start the Logging Task

Start the logging task on the group object. Wait two seconds and show the last acquired value.

start(grp)
pause(2)
sPeek = peekdata(grp,1)

sPeek = 

    LocalEventTime: [2016 4 12 13 49 24.9080]
             Items: [3×1 struct]

Display the item ID and values

disp({sPeek.Items.ItemID;sPeek.Items.Value});

    'Random.Real8'    'Random.UInt2'    'Random.Real4'
    [  8.5714e+03]    [        9961]    [  1.9025e+04]

Wait for the object to complete logging before continuing with the example.

wait(grp)

Retrieve the Data

Retrieve the first 20 acquired records into a structure.

sFirst = getdata(grp,20);

The getdata function removes the records from the toolbox engine. Examine the available records using the RecordsAvailable property of the group.

recAvail = grp.RecordsAvailable

recAvail =

    20

Retrieve the balance of the records into separate arrays, converting all values to double-precision floating point numbers.

[exItmId,exVal,exQual,exTStamp,exEvtTime] = getdata(grp, ...
    recAvail,'double');

Examine the contents of the workspace.

whos ex*

  Name            Size            Bytes  Class     Attributes

  exEvtTime      20x1               160  double              
  exItmId         1x3               408  cell                
  exQual         20x3              8880  cell                
  exTStamp       20x3               480  double              
  exVal          20x3               480  double              

Retrieve data from disk for a specific item, using the 'itemids' filter.

sReal8Disk = opcread(logFileName,'itemids','Random.Real8')

sReal8Disk = 

40×1 struct array with fields:

    LocalEventTime
    Items

Examine the second record.

sReal8Disk(2).Items

ans = 

       ItemID: 'Random.Real8'
        Value: 1.4955e+04
      Quality: 'Good: Non-specific'
    TimeStamp: [2016 4 12 13 49 24.3890]

Clean Up

Disconnect and delete OPC objects from the toolbox engine.

disconnect(da)
delete(da)
delete(logFileName)

Deleting the client object also deletes the group and item objects.