Log data in a distributed environment

You can use the InTouch distributed history system to retrieve historical data from any InTouch application on the network. This system also allows for remote retrieval of data from multiple history databases simultaneously. These databases are called history providers.

Only one InTouch node can log to a distributed history file. However, an unlimited number of InTouch nodes can view the contents of the file.

A remote node retrieving data from a history file may not see data for the last hour of data (based on the logger node's time). Remote trends can only view data that has been written to the logging node's disk.

Data for each tag checked for 'Log Data' is automatically written to disk after 22 samples for that tag have been collected. If the HTUpdateToCurrentTime() function is called, data is written to disk regardless of the number of samples collected. By default, data is written to disk once an hour. You can change this interval by adding the following line to the INTOUCH.ini file:

ForceLogging=X;

Where X is minutes and can be set to any interval between 5 and 120.

Note: The NetDDE Helper service must be running when you use the distributed history system.

The following figure shows the configuration of a typical distributed history system using Network Application Development (NAD) to distribute the application.

Nodes 1 and 2 contain copies of the same InTouch application; however, the application is configured to allow only Node 1 to log to a local history file, whereas either node can retrieve from the local history file or the remote history file. Node 3 is also logging to and retrieving from the remote history file location. Node 3, the history provider, is assigned the name HistPrv1. Node 1 is both a development and run-time station, while Node 2 is just a run-time station.

Create this type of application

1. Create a history provider list. See Configure remote history providers.

2. Create and configure a historical trend object. For more information, see Trending tag data in AVEVA™ InTouch HMI Application Development.

3. Configure the application for distributed logging. See Configure distributed historical logging.

4. Distribute the application. See Configure an InTouch application for NAD.

You can distribute your application manually or by using NAD. When you distribute your application, the historical provider list file is distributed as part of the application.

After you have distributed your application, you can run the View nodes and retrieve both local tags and tags from a remote history provider. While the application runs on all the View nodes, only the logging node logs to the historical log file; other nodes can only read from it.