Introduction

A Sequencer block for reading CDP event data from CDP Logger or LogServer and exposing it as a message-based API.

Glossary

This documentation refers to two kinds of events:

• CDP events - CDPEventManager events. For example, CDPAlarm Set, Clear and Acknowledge events. These are the events that are logged by CDP Logger, LogWriter and read by EventLogReader.
• Message events - the event inputs and outputs of sequencer blocks as defined by the IEC 61499 standard. In this document, also referred as event messages or just messages.

Usage

To set up an EventLogReader, add it to the configuration and connect it to a CDP Logger or LogServer by setting the ServerAddress and ServerPort properties.

Once connected, the EventLogReader will start continuously emitting Definition messages as new CDP event senders are discovered. The Definition message contains the Path of the CDP event sender and a list of Tags associated with it. To read logged CDP event data, send a ReqEvents message to the EventLogReader and listen for the Event messages.

The following is a block diagram of the typical usage of the EventLogReader block. See below for instructions on how to replicate the example.

Tips

• Combine the EventLogReader with RangeScanner and LogWriter to extract a part of the log to a new Datastore.
• The logs can be quite large, so it is recommended to use the Limit property to read data in batches.
• Disable the IncludeInitialValues property to prevent repeating values at batch borders when extracting data in batches (meaning the RangeEnd emitted with the last ReqDataDone is the RangeStart of the next ReqData). Otherwise, the first row of each batch always contains the initial value of every node.

Configuration

See below for a list of configuration options specific to this block.

Message Events

Reading Tags

When reading data, the associated tags can be accessed in two ways:

• Parse the semicolon-separated list in the Tags argument.
• Add each tag as a separate output argument with the tag name as the argument name. In that case, the tag value will be set to the argument value. Note each user-added argument must be listed in the Data property of the message event.

This affects the Definition and Event messages.

Arguments

CDP Event Code Flags

Common event codes used in the CDP framework (note that multiple flags can be set at the same time):

Properties

Example

Here is a minimal example using the EventLogReader. The example connects to a CDP Logger running on localhost and extracts all CDP events to a CSV file in small batches and keeps extracting as new CDP events are emitted.

To run the example, start the application and trigger manually the EventLogReader's Init message. The extracted values will be written to a "log-events.csv" file in the application's working directory.

Here is how to replicate the example:

• Create a system.
• From the Resource tree, add
  • CDPLogger.CDPLogger - the built-in logger component which by default logs all CDP events that occur in a system to CDPCompactDatastore.
  • Sequencer.RangeScanner - scans the time range by small batches.
  • CDPLogger.EventLogReader - reads CDP events from the CDPLogger component. In this minimal example, we have not set any filters, so it will read all CDP events and forward them to the LogWriter.
  • CDPLogger.LogWriter - writes the received CDP events to a new Datastore (CSVDatastore in this example).
• Optionally, add two Sequencer.DebugPrinter blocks to print any Error messages.
• Add a CDPLogger.CSVDatastore into the LogWriter block to store extracted CDP events in a CSV file.
• Because we are continuously extracting CDP events, set the RangeCriterion property of EventLogReader to Logstamp. Since an alarm reprise event contains an old timestamp (the event is old), we must use the Logstamp that is updated when the event is received to get the RangeScanner to move forward.
• Connect the blocks as shown in the image above.

Possible Improvements

Some ideas not implemented in this minimal example:

• Instead of directly extracting to LogWriter on localhost, use Retagger and LogDataAggregator to re-tag and serialize the data for uploading to a cloud service. In the cloud side, deserialize using LogDataDisaggregator before passing the data to LogWriter. This way multiple edge devices can upload data to a central cloud database.
• Replace the CSVDatastore in the LogWriter block with a time-series database such as InfluxDatastore for better performance, scalability and data analysis capabilities.