Open Systems - HMIs and Beyond

March 16, 2009

We covered open systems between controllers and I/O in this column late last year, and in last months’ column we discussed open systems between controllers and HMIs. This month’s column will examine open systems at the next level up, between HMIs and higher level computing systems like MES and ERP platforms.

We covered open systems between controllers and I/O in this column late last year, and in last months’ column we discussed open systems between controllers and HMIs. This month’s column will examine open systems at the next level up, between HMIs and higher level computing systems like MES and ERP platforms.


As previously discussed, Ethernet has been 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 purposes of this discussion, an HMI is defined as a computer hosting packaged software running on a Microsoft or a Linux operating system.


HMI/higher level computing system connectivity standards can be divided 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 many 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. Click here to read more.