By Dan Hebert, PE, Senior Technical Editor
We covered open systems between controllers and I/O in this column late last year, and last month we discussed open systems between controllers and HMIs. This month we move one level up and examine open systems between HMIs and higher-level computing systems like MES and ERP platforms.
Ethernet is a prime mover in standardizing connections between controllers and I/O and between controllers and HMIs. For connections between HMIs and higher-level computing systems, Ethernet is one part of the equation along with myriad other standards. For this discussion, we define HMI as a computer that hosts packaged software and runs on a Microsoft or a Linux operating system.
We can divide HMI/higher-level computing system connectivity standards into three levels. First, there are physical hardware connection standards, nowadays almost always Ethernet. Second, there is the particular Ethernet software protocol, typically TCP/IP at this level.
The third set of connectivity standards defines data formats and naming conventions. Leading standards in this area include OPC, ODBC, Web services and others.
OPC can be used to directly link HMIs to upper-level computing platforms. Most every vendor of packaged HMI software supports OPC. Many upper-level computing-system vendors also support OPC directly or indirectly.
“We needed to link into our Oracle-based ERP system, and we wanted to use OPC,” says Dan Cox, director of engineering at AOC Resins in Collierville, Tenn. AOC Resins is not a machine builder, but its connectivity task is similar to that faced by any machine builder linking an OPC-compliant HMI to a database or an ERP system.
“We used a Matrikon tool called the Generic Database Access that turns user-defined Oracle variables into OPC parameters, and this greatly simplified data exchange,” explains Cox. “If there were no OPC, we would have needed to develop custom .Net programming to link the data.” Unlike the OPC link, this connection would have been beyond their internal expertise.
This is a theme that runs throughout many connectivity applications. The custom programming that was required to link HMIs with higher-level computing systems was simply beyond the capability of most control system professionals. But standards have simplified connectivity to the point where it is now feasible for a typical control system professional to create, implement and maintain these links.
Alan Cannon, a process/automation SCADA engineer at Plastic Omnium in Paris, France, used standards to link the InduSoft HMI platform to SAP via an intermediate SQL-compliant database. Plastic Omnium manufactures automotive components.
“Understanding SAP was my biggest challenge, as I am an automation/controls engineer with no SAP experience,” relates Cannon. “But once I read a 75-page manual on integration with SAP, I was able to create every tool necessary to make the connections in less than an hour. Without standards, and without the interfaces and output windows supplied from InduSoft, my debugging time would have increased tenfold.”
Web services are another industry standard used for connectivity between HMIs and upper-level computing platforms. “You can create a Web service on any kind of platform,” says Chris Jones, vice president of business solutions at system integrator Maverick Technologies in Columbia, Ill. “The Web service establishes the structure of how to create an object and what the data elements of the object will look like. It also handles security, messaging and transactions. Microsoft has been a big proponent of Web Services, but IBM and the open-source community is going along with it.”
Using Web services, Jones says he can connect a Microsoft network to an open-source network to an IBM proprietary network or a Sun Solaris environment. “It’s breaking down barriers that once required all applications to be on a similar network and architecture in order to communicate,” concludes Jones.
The bottom line is that it’s now often feasible for a machine or robot builder OEM to offer its customers connectivity between the machine or robot and higher-level computing systems via an HMI. This is a big change from the daunting connectivity complexity that existed just a few years ago.