start

Start a logging task

Syntax

start(GObj)

Description

start(GObj) starts a data logging task for GObj. GObj can be a scalar dagroup object, or a vector of dagroup objects. A dagroup object must be active and contain at least one item for start to succeed.

When logging is started, GObj performs the following operations:

  1. Generates a Start event, and executes the StartFcn callback.

  2. If Subscription is 'off', sets Subscription to 'on' and issues a warning.

  3. Removes all records associated with the object from the OPC Toolbox™ software engine.

  4. Sets RecordsAcquired and RecordsAvailable to 0.

  5. Sets the Logging property to 'on'.

The Start event is logged to the EventLog.

GObj will stop logging when a stop command is issued, or when RecordsAcquired reaches RecordsToAcquire.

Examples

Configure and start a logging task for 30 seconds of data:

da = opcda('localhost','Matrikon.OPC.Simulation');
connect(da);
grp = addgroup(da,'StartEx');
itm1 = additem(grp,'Triangle Waves.Real8');
itm2 = additem(grp,'Saw-toothed Waves.UInt16');
grp.LoggingMode = 'memory';
grp.UpdateRate = 0.5;
grp.RecordsToAcquire = 60;
start(grp);

Wait for the logging task to finish, then retrieve the records into a double array and plot the data with a legend:

wait(grp);
[itmID, val, qual, tStamp] = getdata(grp, 'double');
plot(tStamp(:,1), val(:,1), tStamp(:,2), val(:,2));
legend(itmID);
datetick x keeplimits

Introduced before R2006a