This month Software Toolbox, Cogent's technical and sales partner for North America and other parts of the world including South Africa, will be presenting "OPC DataHub: The 'Must Know' Tool for System Integrators" at the Wonderware SI Conference 2009 near Pretoria and Johannesburg, South Africa. They will be holding an OPC DataHub technical training session there as well.

"Manufacturers and system integrators are facing big challenges with the worldwide expansion in communications and new power generation technologies," said John Weber, President of Software Toolbox. "The OPC DataHub is a key tool for adapting to these changing needs, and meeting the data integration challenges of the coming decade."

A recent shopping trend is the superstore or hypermarket, where you can buy just about anything you need, including groceries, all at one place. As you walk down the aisles, you can fill your cart with clothing, hardware, and electronics, along with bread, milk, and carrots. The products come from many sources, near and far, but as far as the store is concerned, everything is just merchandise.

The OPC DataHub is a real-time data superstore. The data can arrive from any source--different OPC servers, remote locations, spreadsheets, databases, web applications, custom programs, and so on. What does the DataHub client see? A single, unified data set. You can bridge between any data sources, tunnel any of the data across a network, or log data from different sources into the same row of a database. It's all just data.

One valuable feature of OPC is that it tells you the quality of each connection. Knowing the quality of the data from the OPC tags is critically important to the functioning of most systems. This vital information is maintained in the OPC DataHub with each DataHub point. Tracking the quality of a DataHub point as it changes from "Good" to "Not Connected" or "Bad" can be used to trigger data logging, send emails, or do high-level control of a system. Managers using MES and ERP tools can derive a lot of useful information by monitoring point quality, or failures to change values.

While an operator or manager can visually monitor point quality in an HMI or the DataHub Data Browser, the following scripts automate tracking and monitoring, so you can get the most out of your OPC tag quality:

• QualityTrack.g - writes the quality of an input point as the value of another, synthetic, output point. You can then use the value of the output point to trigger data logging or send emails.
• TagMonitor.g - also creates synthetic DataHub points, and watches them for changes in quality, as well as a failure to change value within a specified time period. Other watch conditions can be added, too. Email and database events can then be triggered from the synthetic points.
• FixQuality.g - changes point quality for OPC clients that treat "Bad" quality as a disconnection. With this script running, those OPC clients will receive a value of -1 for the point, but the quality of the connection will remain "Good", and the client won't disconnect when a tag quality changes to "Bad".