AUTOMATION SOFTWARE – OPC DataHub: Addressing the need for data sharing
June 14, 2007
By Jeremy Pollard
With the insatiable appetite that all companies have for fresh data, it’s no wonder that industrial Ethernet is being used on most, if not all, plant floors. However, with multiple applications trying to communicate with the PLCs that hold data, there is a real risk of having the PLCs “cough and sputter” when trying to deliver the data because they do not have the dynamic headroom that a normal PC does. For example, if you have 10 applications running that need to retrieve the plant efficiency rate in real time, you will want the applications to go to an all-knowing place to get the data because a single point of reference will reduce the bandwidth and display the results faster. This all-knowing place could be the OPC DataHub from Software Toolbox.
In the above example, the 10 applications would request the data from the hub, not the PLC. But this data restaurant can serve up more than this.
As usual, I installed the software and looked at the Help file, which is context sensitive and very thorough. I had a short demo of the software, so I knew my way around. The software’s front end is really easy to navigate because the back end is where the power is.
For instance, say you have 10 Rockwell PLCs and 10 GE PLCs. You still need a device OPC server to get the data from the PLC to the DataHub. Once the data is exposed to the DataHub from the OPC device server, it is available in many forms, including web server, direct via OPC and database formats.
The floor applications and remote devices can now access the data directly from the DataHub without bothering the source PLCs. The DataHub can perform dynamic data exchange (DDE) and act as an OPC data server. This means that the DataHub can consolidate data from multiple sources, but present a single interface to remote applications.
For example, if you were running Wonderware’s Intouch, the OPC server would be the DataHub. An Excel spreadsheet could use the DDE server information to tabularize your data. It is easy and supports NetDDE as well.
You may also want to consider tunnelling and bridging. Bridging allows two OPC servers to share data, which may be useful in remote locations where you need to get data from a remote PLC that is being accessed by a separate OPC device server.
Tunnelling works like an Internet connection, where the data resides at the data server end and access to that data is on the network. Local plant employees can access the data from anywhere, as can anyone with access to the Intranet. The only issue here is that a license of the OPC DataHub is required for each location, which can be expensive. Therefore, bridging may be the better solution.
Using the exposed application programming interface, you can write custom applications that circumvent the licensing of each client. The OPC Extender application, also from Software Toolbox, can provide this functionality in an easy-to-use form.
Using a web browser has long been a desire of all industrial applications, but most of the HMI vendors still require you to have a server and client component. The DataHub needs a server component, but the client pages are code generated, so a normal browser can be used.
Once you connect to the web services on the DataHub data server, the WebPages fly onto the screen with live data. Most of the configuration for these HTML pages is done with code. There is no HTML front end to aid you in creating these pages.
The licensing for the web server is not cheap at more than $3,000 US, but running as many clients as you need (using the ASP/AJAX software model), regardless of where they are, may be attractive to you. The update time is as fast as your Internet connection.
The product can also act as a data logger, writing data points based on a wide array of conditions, and writing associated data with the trigger point data as well.
An additional feature is the ability to generate a short message service (SMS) e-mail when certain conditions occur. While you cannot have predefined lists of e-mail recipients, you can send the message to various e-mail addresses.
The product lacks the ability to create data groups within itself. Instead, it relies on the OPC device server to provide that organization.
DataHub takes the strain away from the communication processors in the PLCs and moves it to the PC in which the DataHub is located. It uses the resources of a low-cost device, which leaves the PLC to do the work it is supposed to do.
While I believe that the licensing costs are too heavy, the OPC DataHub may allow you to do some things that you otherwise may not have been able to. It is worth a look.
Name: OPC DataHub
Vendor: Software Toolbox
Application: Data sharing
Price: $995 US
Jeremy Pollard is a 25-year veteran of the industrial automation industry. He has worked as a systems integrator, consultant and an educator in the field. Jeremy can be reached at email@example.com.