Commercial Ethernet and EtherNet/IP

Hello.

Could anyone explain me what are the fundamental differences between commercial Ethernet and Industrial Ethernet (EtherNet/IP)? Our company is evaluating the possibility of adding Ethernet cards to our PLCs so we can get more info from our machines.

Thanks,
arigatuso.

This subject is very near and dear to my heart. I have been doing Ethernet based control for over 8 years. The only differences I have been able to come up with are name and price. I am watching with disgust as some vendors are trying to bastardize Ethernet much the same way the field buses have been. There is a widely accepted Ethernet standard. If you stick with it, you'll be fine. If you start following a particular vendor's approach, you may find yourself painted into a corner.

My advice, do the basics and you will have plenty of choices and diagnostic information available.

The word Ethernet has become synonymous with the TCP/IP protocol stack. EtherNet/IP is an application layer protocol that runs on top of the TCP/IP stack or Ethernet in the 7th layer.
EtherNet/IP has fast become an industry standard. It's a complex protocol with a complicated header but it is robust and reliable.
Many Companies are or have been developing products that use
this protocol. Furnishing your PLCs with EtherNet/IP capability is a smart move.

Just remember that ethernet defines a packet for carrying messages and data, and defines the adressing, error checking, etc. Just because you have ethernet on your PC and on several different PLCs, don't assume they will be able to talk to each other. The enquiry and response strings are in the data portion of the packet, and are protocol dependent. For example, ControlNet, Modbus on ethernet, and DeviceNet on ethernet reuire separate drivers in your PC and must be received by a PLC that can decode the instruction. An Allen Bradley with ethernet won't automatically be able to talk to a Modicon on ethernet, for example.

DeviceNet, ControlNet over Ethernet are called EtherNet/IP.
Modbus over Ethernet is called ModbusTCP.
Tom is right, these two protocols are incompatible.
Fortunatelly there are protocol converters on the market that will take care of this problem. In addition many new PLC's such as WAGO,
Beckhof etc. are capable of communication in both protocols.

Jiri, I can't agree with this statement.

Furnishing your PLCs with EtherNet/IP capability is a smart move.

It is very expensive and most people don't need it. I can only assume you sell Allen Bradley Hardware.

Okay, Shoeman I'll bite on that bait. And I'll apologize in advance for my tone, because your post sounds just like the trade magazines or those Linux zealots over at Control.com.

There is a widely accepted Ethernet standard

Click to expand...

Both major industrial Ethernet protocols do use "standard Ethernet" for media, and they use standard TCP and UDP for transports.

It's only the application protocols that have been customized for compatibility with various controller families. This is the Major Point that you did not address in your post.

So... what application level protocol have you been using for 8 years ? I have a feeling the answer is "raw packets" or "I made my own".

So what is it ?

I've only worked with Ethernet in an industrial setting for about 2 years now, but I'll throw in my two cents.

Industrial Ethernet components are usually much more robust than commercial components. They have higher tolerances for noise, broadcast storm protection, etc...

Obviously for the PLC you're going to buy the card from the manufacturer, but when it comes to hubs, switches, etc, the stuff off the shelf at Best Buy or CompUSA will give you fits in an industrial setting. Trust me a LinkSYS or Netgear won't cut it.

Raw Packets

I used QNX for the majority of the time, and that uses FLEET. FLEEt uses a send, recieve, reply approach and used MAC addresses to define nodes. I moved to TCP/IP in QNX and eventually to using Microsoft for HMI stations and communicating via raw TCP/IP. Your tone is understandable. Most people in the trade are comfortable using a vendor specific approach, but as Tom pointed out, there are specific drivers for different protocols that are being placed on ethernet. This offers advantages inside vendor specific applications, but puts you in a corner in the long run. Siemens, Foxboro, and AB, just to name a few, have put thier own spin on Ethernet and some even require you to use thier equipment and plan for layout. Just because someone says they support Ethernet, that doesn't mean they can talk to other equipment without drivers. Hart is a great example to use here, it is a standard to a point, but Invensys puts more on top of it, and they will not share how it is done. So in order to take advantage of thier great offering, you are forced to use a mostly Invensys system.

I worked on a Siemens S7 project where they wouldn't support the Ethernet installation unless you used thier specific equipment.

In my humble opinion, companies are capitalizing on the open base of Ethernet, but bastardizing it to build or keep market share.

Unless you require special timing or mission critical communications, Ethernet at the operating system level should be enough. Make your function calls and read requests and put them into the standard frame.

It is the same darn fight of who has the best fieldbus. MODBUS, DeviceNet, Profibus, or ASIBus.

RRobbins,
Thanks for your opinion. No I don't sell AB hardware although I do sell AB compatible products. And yes I am a big fan of AB.
Few years ago nobody needed cell phones and today you wonder how you could do without it.
Ethernet is taking over industrial networking although other networks will coexist for a long time to come.
AB is coming out with an Ethernet Micrologix.
Every major PLC has an Ethernet interface.
No, I don't think that Ethernet hardware is too expensive.
You don't need a KT card in your PC to communicate via Ethernet.
Just about every HMI is furnished with Ethernet port with no extra cost (I mean new designs).
If you buy an HMI with a specialty comm module you are going to be paying through your nose.

Just a couple of thoughts....

As Jiri stated above, the sheduled portion of Ethernet/IP is basically ControlNet on Ethernet hardware. When most people talk about Ethernet/IP the talk about how you connect your laptop to the PLC. I suspect shoeman is referring to this connection. This is a CIP message over Ethernet and is unscheduled. This is a case of 'double encapsulation' for lack of a better term. You have the data you want to send wrapped in a CIP protocol header wrapped in a TCP/IP header. The scheduled portion is time critical, the CIP unscheduled portion is not.

shoeman makes an inetersting point that has been battled here before. There is no data interface standard in the plc world. This discussion is about Ethernet but the physical media isn't the issue. It's the same issue over RS-232. AB uses DF1. Siemens uses MPI. Everyone has their own protocol that is completely independent of the physical media. It comes down to what the plc can interpret as it comes in the desired port. Then again you don't have a Microsoft standing over plc developers telling them how to talk either, which is where the PC consistancy comes from.

I kind of like it the way it is now. If no one thought there was a better way to move down the road 120 years ago we would still be riding in horse-drawn carriages today. People playing around with their own ideas is how better concepts and devices are born. Then again, as a plc end user I don't have to try and keep up with all the changing protocols either.

Keith

My hat's off to shoeman for a straightforward and professional explanation of his position.

I, too, was surprised the first tome somebody showed me their "Siemens Ethernet" card and special driver. I consider non-IP Ethernet systems to be essentially proprietary and I don't even put them in the same category as EtherNet/IP and Modbus/TCP and Opto22 Ethernet application protocols.

This is actually the first time I've heard of FLEET on QNX !

To address arigatuso's original post; "EtherNet/IP" is just a Allen-Bradley name for the application level protocol their controllers run on Ethernet media. It uses standard Ethernet twisted-pair media, and standard Ethernet switches and hubs, and standard Ethernet PC network interface cards.

The A-B specific part of EtherNet/IP is at the controller side and the PC application side; you will use RSLinx software to communicate with your controllers.

The only other issue that i will touch on is the use of the ethernet industrial switches and hubs. I've always being a little sceptical about using office grade equipment in an industrial enviroment and as such i have always used an industrial type. Hey, a lot of people might disagree, which would be an interesting digression.

Why choose Industrial Ethernet Units over office-grade equipment?

Temperature - Office-grade equipment is typically specified over a +5°C to +40°C temperature range, while industrial controllers such as programmable logic controllers (PLCs) are rated from 0° to +60°C. Ethernet equipment should have equal or better temperature ratings as the equipment to which it is connected. Many outdoor applications require that the equipment perform over a wider -40°C to +75°C range. These two ranges are beyond the capabilities of office-grade equipment, but generally are covered by the industrial unit without the use of fans which are undesirable in industrial applications.

Mounting - Control devices are usually mounted onto sub-panels, which are installed into industrial control panels. Devices are secured by mounting tabs or snapped onto DIN-rails. Industrial units can be mounted in this way. Office-grade equipment is intended for tabletop installation and seldom has provisions for secure mounting. Frequently, the units are left unmounted or attached using Velcro®, duct tape or a special shelf is fabricated at additional cost for their mounting. Office-grade equipment is out of place in an industrial control panel.
Power Supply - Industrial systems are usually powered from a common low-voltage control transformer or low-voltage DC power supply. Industrial ethernet units will generally operate over a wide-range of AC or DC voltages compliant to the needs of most any type of control application. A wide-range DC-to-DC converter, which can operate during brownout conditions utilizing a large input capacitor to ride-out spikes and dropouts that can frequently occur with factory power sources, is generally used in the power supply design. Additional connections are provided for redundant power schemes to ensure the greatest amount of uptime. Office-grade equipment is usually mains-powered or requires a wall-mounted plug-in transformer that is inconvenient in a control panel and susceptible to inadvertent disconnection, compromising the reliability of the system.

Regulatory Requirements - The movement of industry in embracing Ethernet standards does not remove the requirement to conform to various agency regulations not required in the office. Seldom does office-grade Ethernet equipment meet the unique requirements of industrial automation or even building automation. Generally Industrail Ethernet products are designed and tested to the higher electromagnetic compatibility (EMC) immunity standards required for industrial equipment. All the products are UL 508 Listed for use in industrial control panels and some are listed under UL 1604 for Class I, Division 2 hazardous locations. Still others are UL 864 recognized for smoke and fire protective applications. All the products carry the CE mark for installation in the European Union.

Extended Product Life Cycle - Original Equipment Manufacturers (OEMs) require a stable bill-of-material (BOM) without the additional expense and effort to requalify a replacement for an obsolete device. This is especially true when the OEM equipment has been qualified for agency approvals and subject to factory surveillance. This is not the case with office-grade equipment that is frequently changed without notification making it difficult to specify and procure the same item even over a short time span.

Responsive Technical Support - A decent supplier of indurtrial ethernet equipment will back there product.

FINALLY, you might want to check this thread out if you are interested in learning more about ethenet.
Indutrial Ethenet Course

Oh, and i am waiting to see if Bobb gets on and throws his comments about ethernet...(Bob, I'll catch up with u before Xmas hopefully)

Oh Sleepy, it is stil non-deterministic. I guess you expected that.

Switches are pretty good and certainly up the reliability of the system.

A red wine (or white or beer or good scotch or irish) would be great before Christmas old mate. Will have to get in touch. Dinner with the old cheeses would be even better.

At least there are no blatent advertisements here.

As I write this I am overlooking the plant floor of a major plant involving in excess of 100 nodes of Ethernet based control. There are dozens of 200kW plus sized motors on site, and 80 plus VSD's.

The system has been set up with one single layer of Ethernet so that all the nodes are available on a single subnet. It has all been set up by competent networking professionals.

The PLC has plenty of Ethernet cards each dedicated to various data channels. From the automation hardware perspective everything has been done right. BUT... all the cabling is commercial grade Cat5 STP and the switches are all commercial grade. It sucks. Far too many network errors are being reported by the Ethernet interfaces.

My observations:

1. The I/O data should have been done on a true Industrial network.

2. There is miles and miles of sodding blue Cat5 cable doing home runs back to the switches everywhere. At least 10 times more potential for interference and cross-coupling. The use of shielded cable means that the shield needs one good RF ground at one end and commercial grade switches just don't seem to do this well. It all seems a great leap backwards.

3. It surely isn't any cheaper and does not seem to add any functionality over the prior art...so why this fetish for pushing to try and make a sows ear of Ethernet to achieve Industrial strength silk purses?