OPC Toolbox 2.1.4

Logging OPC Data

This example demonstrates how to configure and execute a logging session, and how to retrieve data from that logging session.

Contents

Step 1: Create the OPC Toolbox™ Object Hierarchy

This example creates a hierarchy of OPC Toolbox™ objects for the Matrikon™ Simulation Server. To run this example on your system, you must have the Matrikon Simulation Server installed. Alternatively, you can replace the values used in the creation of the objects with values for a server you can access.

da = opcda('localhost','Matrikon.OPC.Simulation.1');
connect(da);
grp = addgroup(da,'CallbackTest');
itm1 = additem(grp,'Random.Real8');
itm2 = additem(grp,'Random.UInt2');
itm3 = additem(grp,'Random.Real4');

Step 2: Configure the Logging Duration

This example sets the UpdateRate value to 0.2 seconds, and the RecordsToAcquire property to 40.

set(grp,'UpdateRate',0.2);
set(grp,'RecordsToAcquire',40);

Step 3: Configure the Logging Destination

In this example, data is logged to disk and memory. The disk file name is LoggingExample.olf. If the file name exists, the Toolbox engine must overwrite the file.

set(grp,'LoggingMode', 'disk&memory');
set(grp,'LogFileName', 'LoggingExample.olf');
set(grp,'LogToDiskMode','overwrite');

Step 4: Start the Logging Task

Start the group object. Wait two seconds and show the last acquired value. Then wait for the logging task to complete.

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

sPeek =
    LocalEventTime: [2006 11 21 8 18 20.2180]
             Items: [3x1 struct]

Display the item ID and values

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

    'Random.Real4'    'Random.UInt2'    'Random.Real8'
    [ 8.5855e+003]    [       23256]    [ 4.6293e+003]

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

wait(grp, inf)

Step 5: Retrieve the Data

You can retrieve data in structure format, or into separate arrays. This example retrieves the first 20 records into a structure array.

sFirst = getdata(grp, 20);

The getdata function removes the records from the OPC Toolbox engine. You can examine the available records using the RecordsAvailable property of the group

recAvail = grp.RecordsAvailable

recAvail =
    20

This example retrieves the balance of the records into separate arrays. All values are converted 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               252  cell
  exQual         20x3              5760  cell
  exTStamp       20x3               480  double
  exVal          20x3               480  double

You can retrieving data from disk for a specific item, using the 'itemids' filter.

sReal8Disk = opcread('LoggingExample.olf', 'itemids', 'Random.Real8')

sReal8Disk =
40x1 struct array with fields:
    LocalEventTime
    Items

Examine the first record.

sReal8Disk(1).Items

ans =
       ItemID: 'Random.Real8'
        Value: 1.4230e+004
      Quality: 'Good: Non-specific'
    TimeStamp: [2006 11 21 8 18 19.1390]

Step 6: Clean Up

Always remove OPC Toolbox objects from memory, and the variables that reference them, when you no longer need them. Deleting the client object deletes the group and item objects also.

disconnect(da)
delete(da)
clear da grp itm1 itm2 itm3