I can’t tell you how many times over the years I’ve had someone ask me what the “best” protocol is. That’s like asking me who has the best pancakes, what’s the best car of 2015 and the best Christmas movie of all time (Pancake Place in Green Bay, Wisconsin; 2015 Nissan Maxima; It’s a Wonderful Life).
The truth, of course, on the question of factory floor protocols is simply “it depends.” Do you want to move I/O data or information? How fast do you need to move your data? How much do you need to move? How many devices? There is no end to the questions I could ask you.
But most of the time, what drives your choice of protocol comes down to what PLC is used in your building, or by what the majority of your customers want. If you’ve got Siemens, I’ll tell you Profibus DP or ProfiNet IO is your best bet. If you’re using a Rockwell ControlLogix or CompactLogix, EtherNet/IP (or sometimes DeviceNet) is your best choice.
There are other advantages to EtherNet/IP:
1.Ethernet/IP uses all the transport and control protocols used in traditional Ethernet including the Transport Control Protocol (TCP), the Internet Protocol (IP), and the media access and signaling technologies found in off-the-shelf Ethernet interface cards.
2.Ethernet/IP is a certifiable standard. Devices are required to be certified by approved EtherNet/IP test labs to ensure the consistency and quality of field devices.
3.The core of EtherNet/IP is the Control and Information Protocol (CIP) that is also used in ControlNet, DeviceNet, and CompoNet. This standard organizes networked devices as a collection of objects. It defines the access, object behavior, and extensions, which allow widely disparate devices to be accessed using a common mechanism.
4.EtherNet/IP is a very widely implemented standard with a massive amount of vendor support in everything from tiny photoeyes to massive chiller systems.
5.I/O data moves reasonably fast in an EtherNet/IP system, generally at 10 ms cycle times. In some applications that cycle time can be pushed to 1 ms.
6.There’s a multitude of support tools, training, and documentation about how to design and integrate an EtherNet/IP system with Rockwell controllers.
7.Rockwell provides the Add On Profile (AOP) program, which improves how a vendor’s device integrates with a Logix PLC. (Read the whitepaper on the Add On Profile program).
8.There isn’t an industry that doesn’t use EtherNet/IP to some extent.
EtherNet/IP isn’t perfect. Here’s what the detractors have to say:
1.It has limited bandwidth. Rockwell PLCs can only move packet sizes of around 500 bytes. That’s sometimes a huge hurdle.
2.EtherNet/IP is an application layer protocol that is transferred inside a TCP/IP Packet. A lot of processor bandwidth goes to the processing of the TCP/IP layers.
3.There’s no real information modeling. You can create objects with attributes but can’t link objects together into any sort of hierarchy.
4.The EtherNet/IP motion extension, CIP Motion, isn’t nearly as widely accepted as EtherCAT and SERCOS.
5.There is limited functionality to EtherNet/IP with Rockwell controllers that are not part of the Logix family.
6.The sweet spot for EtherNet/IP is discrete control. You can make it work in process control, but that’s like using your Cadillac to haul rocks for your wife’s rock garden.
7.There are really no generic diagnostics built into all EtherNet/IP devices. Devices have to design and implement their own, custom diagnostics.
8.There is no EtherNet/IP standard for device replacement. Replacing a device can be as difficult as the initial configuration of the device.
So, is EtherNet/IP the “best protocol”? My answer is yes, no, and maybe. Your application requirements and current infrastructure really drive the answer to that.
If you need help to understand what might be the best technology to use, simply CONTACT ME and I will be glad to discuss your requirements and what RTA can do to assist you.For more information on EtherNet/IP, get my EtherNet/IP overview.