Wikipedia definition: “An open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed (e.g. open process). There is no single definition and interpretations vary with usage.” They also provide 20 additional definitions! That proves their “no single definition” point.
PROFINET fits this definition. The specification is available to everyone for purchase from IEC (International Electrotechnical Commission). There are no further barriers to anyone developing a product just from the spec. The specification was created and has evolved in PI Working Groups. Many PI members participated in that work. PI membership is not required to develop a PROFINET product although I certainly encourage it! PI members who have their product certified are entitled to use the PROFINET logo.
Proprietary (Closed) Standards
Proprietary standards have been around a long time – DH+ for example. A proprietary standard is owned by one company and they exercise sole discretion as to who may use it and under what terms (and at what cost). There are probably many current examples. What about Emerson’s Charms? Is that a proprietary fieldbus? EtherCAT is a definite example of a proprietary fieldbus. It is owned by one company – Beckhoff. They retain ownership and have opted to make it available to everyone with only a small royalty to Beckhoff for every node.
Too Open Standards
How can a standard be “too open”? It can be so open that there is no assurance that devices will interoperate. Modbus is a good example here. It just moves bits and bytes that can represent anything you want them to. Many companies adopted their own rules for how the data should be arranged. Remember Enron Modbus? Special IO Servers had to be created to allow the user to modify packets, swap bytes, and other gyrations when unique data arrangements were encountered.
In Between Standards
What do you call a standard that you can buy from IEC, but you have to sign a contract to develop a product? I’ve called it an “in between” standard – kind of open, kind of closed. EtherNet/IP falls in this category.
Feel free to use the Comments to weigh into with other examples.