Data collector

Data collector IO The Data collector I/O is used when performing streaming measurements. During streaming measurements, data arrives in consecutive chunks with a size equal to the instrument's record length. To form a continuous stream of data, these chunks must be appended to each other. The data collector does this job. It will fill its data with the arriving chunks of data, see the picture below.

Data collector example

When a Data collector is used in combination with other I/Os which process the data, there are two ways to connect them to each other, each with its own advantage and disadvantage:

  • first process the data with the I/Os and then collect the data
    The I/Os only have (relative) small chunks of data to process, which can be done relatively fast. The Data collector only has to collect the already processed data. The disadvantage is that the original data is not collected this way; when later turns out that the data was wrongly processed, the measurement will have to be done again.
  • first collect the data and then process the data with the I/Os
    The I/Os will have to process the full data size of the Data collector, even if it's only partly filled yet. This can create a very heavy load on the computer, even causing the streaming measurement to be stopped because the computer cannot keep up anymore. The advantage is that the original data is kept, making it possible to change the data processing in a later stage.

The first method is preferred in most situations. When the original data is important, it is always possible to create a second Data collector to collect the original, unprocessed data.

When a graph contains a Data collector, it is possible, while the Data collector is being filled, to zoom in on the latest data and have the graph automatically keep the latest data visible. Choose the appropriate zoom factor in the graph and right-click the time base axis and select Follow source from the popup menu. This will show a sub menu with the possible sources to follow and an option not to follow a source.

When streaming data needs to be stored on disk, use a Disk writer sink which can store streaming data directly. Do not store streaming data that is collected in a Data collector I/O using a Disk writer. Each time the Data collector receives new data, this will be signaled to the Disk writer, which will then add the complete Data collector content to the file, not just the new data.

Properties and actions

To control the behavior of the Data collector I/O, several properties are available. These can be accessed through a popup menu which is shown when the I/O is right clicked.

Data size

The Data size property sets the size of the output block (the "record length") of the Data collector. Several default values are available, as well as a user defined setting. The size of the collected data can be set to a maximum of 20 million samples.

Fill Mode

The Fill mode property sets how the data collector is filled with data.

  • From left to right: new data is appended starting from the left
  • From right to left: existing data is shifted to left, new data is appended at the right

When full

The When full property determines what action the Data collector performs when the output data block is full.

  • Continue: the oldest data is shifted out at the left, while new data is appended to the right
  • Stop: data collecting is stopped when full. (The measurement is NOT stopped.)
  • Clear: the output data is cleared and the filling starts over again
  • Overwrite: existing data in the output array is overwritten by the new data (roll mode)

Clear

The Data collector I/O can be manually cleared with the Clear action.

Common properties and actions