EtherNet/IP, EtherCAT, Profinet and Modbus TCP: which protocol is right for you?

Anything industrial has to be better than its commercial counterpart—true story or a fallacy? Let’s see.

Ethernet communications is very pervasive in plant and machine build applications. Human-machine interfaces (HMIs), sensors and I/O blocks can all be present on the network topology. I am referring to the cable infrastructure—Cat. 6/6E cable and connectors—and this infrastructure is easily scalable and implemented. We typically have done this with our home-based networks, wired and wireless.

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The connectivity is the plumbing of the network, but the water that runs through it—aah, the water. Imagine different-colored water running through the pipes all at the same time. It creates a problem, but with an Ethernet network this analogy can happen.

The water that flows through the Ethernet cable is called a protocol. It’s data. And there are many protocols that can run on a standard Ethernet cable infrastructure. The rate at which this data is transmitted is normally not an issue since it is typically fast enough, but faster speeds will result in a better response from your system.

Modern-day Ethernet runs at 1 gigabit/second (Gbps). Legacy networks can run as slow as 10 megabit/second (10 Mbps), or 100 times slower. This would be noticeable. One bottleneck in legacy is the speed of the switches and the routers.

Your home network uses standard Ethernet protocol. It is non-deterministic, which refers to the amount of time a data packet gets to its destination, which in industrial terms means that the system cannot be “real time.”

This protocol is very well-suited for most normal data communications since we really don’t care if an email shows up in 10 milliseconds or 100 milliseconds, but in industry it could make a difference.

If a sensor were connected to a remote-I/O-networked chassis and the lag time of the sensor coupled with the transmission time to the controller was lagging, then the process may fail or just stop depending on the function of that sensor. Better real time may be helpful.

This is where industrial protocols enter the story: EtherNet/IP, ProfiNet, Modbus TCP and EtherCAT.

EtherNet/IP

EtherNet/IP was developed to assist vendors of all stripes to be able to connect their devices to an Ethernet-compatible programmable logic controller (PLC). It also allows for communication between devices, depending on what devices they are. It supports high data transfer rates over the Ethernet plumbing, which has to support all devices attached to that network. Most devices auto-negotiate the transfer speed with the connected switch or router.

EtherNet/IP supports electronic data sheets (EDSs). This allows the vendor to allow the controller of choice to integrate the device since the EDS tells the controller who and what it is. It also shares tag and/or numeric values that the programmer can access to get to the nuts and bolts of the device.

EtherNet/IP can offer real-time data rates for fast processes.

EtherCAT

One of the other discrete control protocols is EtherCAT. This protocol was based out of Europe and is maintained by an open group, the EtherCAT Technology Group (ETG), which is similar to the Open DeviceNet Vendors Association (ODVA) and its affiliation with EtherNet/IP.

While EtherNet/IP devices can talk to each other, EtherCAT devices cannot. It is a master/slave topology where the controller typically would be the master and all remote devices would be the slaves. It has high very data transfer rates, which allows it to be used in high-speed applications.

The slaves have to be able to support this protocol by virtue of an application-specific integrated circuit (ASIC) chip that must be implemented in the slave hardware, which can impact the offerings of third-party hardware.

Both protocols can run on existing physical networks, whether they be IT or OT.

Profinet

Profinet is supported by Profibus & Profinet International (PI), which was developed initially for process control and has expanded to be an all-round automation protocol offering real-time deterministic data transfer as well as non-deterministic communications. It is also a master/slave network, so all slave devices must have the ability to talk Profinet.

Cabling is specific to Profinet so, as a design effort, the cabling specifications should be adhered to.

Modbus TCP

Last but not least is Modbus TCP, which is an implementation of the Modbus serial protocol over Ethernet. It is also a master/slave network and supports many new and legacy devices.

Data rates are not as high as other protocols, but it better supports legacy devices especially with Ethernet to RS-485 devices allowing a master to see serial devices.

Modbus TCP does support real-time communications with devices that are native to the protocol, whereas the serial devices would still be limited by their serial communication rate.

It is a different world out there from even 20 years ago, when you had to use a single vendor’s devices. With multiple protocols running on the same network, multiple vendor devices can co-exist and deliver data when and where it is needed. Most if not all SCADA/HMI vendors support all of these protocols, so you can have mixed vendor data on the same screen and in real time.