Choosing an Industrial Ethernet, a Checklist

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What should you look for when choosing an Industrial Ethernet? These things:Checklist

Is it an open standard? Can anyone build products for it?

PROFINET is an open standard. It’s part of IEC 61158. Anyone can buy the spec from IEC and build products. To build an EtherNet/IP product, you must sign a contract with ODVA, the EtherNet/IP standards organization. The benefit of an open standard: since anyone can make products there are many products available, competing products. Competition favors the buyer. Reference: Open Standards, Proprietary Standards, and in BetweenThe Importance of Open Standards.

Is the network itself open? Can any protocol coexist on the same network infrastructure?

PROFINET is an open network. (EtherNet/IP is also, but EtherCAT is not.) A major benefit of Ethernet is that multiple applications can run at the same time. (You can get email while your browser is open.) PROFINET traffic coexists with HTTP and other IT protocols plus OPC UA since PROFINET uses standard IEEE 802.3 Ethernet. PROFINET can be sharing real time messages while a web server in an Ethernet switch is examined from a web browser. OPC UA messages to HMIs and historians can share the network with PROFINET too.

Does the protocol cover discrete (factory), process, and motion control (drives)?

Most plants have some aspects of all three application spaces.

PROFINET covers all three. None of the others do. Sub-millisecond speeds for motion control and fast I/O. Multi-millisecond speeds for slower moving process variables. Each individual device can communicate at its own needed speed. As a special case, PROFINET can even achieve 31.25 microsecond updates.

Does the protocol handle functional safety?

PROFINET does, of course, as do most others. Modbus TCP being the exception. PROFINET pioneered the use of the now universally-adopted black channel approach to ensure that safety messages arrive when they are supposed to. And unlike the others, all three application spaces can participate in the same safety system: discrete I/O, drives, and even process instruments. Reference: Marketing Flyer: PROFIsafe

Can older, serial networks be integrated?

PROFINET integrates not just PROFIBUS, but also DeviceNet, Interbus, IO-Link, and many others. The integration is accomplished through proxies. Proxies are unlike gateways in that they are defined in the PROFINET specification. Another important benefit of open standards.

Is the Industrial Ethernet deterministic?

Determinism is not speed. Determinism is the ability to deliver the message when it is expected. PROFINET achieves determinism by the simple expedient of skipping the TCP/IP layers of the ISO/OSI reference model. EtherCAT is also deterministic; EtherNet/IP and Modbus TCP are not. Reference: So Is Ethernet Deterministic or Not?

Is it fault tolerant?

PROFINET can use redundant network media, redundant controllers, and redundant devices. Redundant media means that a single break in a cable will not cause downtime. PROFINET Bumpless Redundancy provides a literally zero second failover time. Redundant controllers are often called “hot standby” since if one fails the other immediately takes over. Reference: MinutePROFINET: Redundancy

How easy is it to troubleshoot?

PROFINET builds on the successful device diagnostics of PROFIBUS by using standard IT protocols like SNMP and LLDP. This allows “troubleshooting” before a problem is bad enough to cause a shutdown. Reference: PROFI Diagnostics.

Can a device be replaced without a computer?

PROFINET features Simple Device Replacement. All that’s required is to physically replace a failed device. No configuration is required. Reference: Simple Device Replacement Explained.

–Carl Henning

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