Ehternet V Controlnet

What are peoples opinions here on using either Ethernet or Controlnet to link seperate Control Logix chassis, HMI etc.

Everyone seems to use Controlnet but then you need extra software and PCMK card etc but with Ethernet you dont need it.

From what I have been told and have learned so far ethernet is a better choice.

TimeFluxCap said:

What are peoples opinions here on using either Ethernet or Controlnet to link seperate Control Logix chassis, HMI etc.

Everyone seems to use Controlnet but then you need extra software and PCMK card etc but with Ethernet you dont need it.

From what I have been told and have learned so far ethernet is a better choice.

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Ethernet can pose some setup headaches. You can't run the cables in conduit for long distances (you get signal degridation).

Ethernet still has a lot of advantages (as I'm sure you're aware)

All the machines I design are pretty tightly coupled physically. I don't have to go 200 feet with anything so noise control isn't as much of an issue for me.

With that disclaimer out of the way, I use Ethernet whenever possible to HMI's and have started moving to Ethernet I/P for I/O and drives. I like Ethernet because it seems to provide all ease of setup of ControlNet on the Logix5K side without the added requirement of RSNetworx. The physical media is easier to work with and the physical layout CAN be easier to handle (in some cases). And raw speed can certainly be your friend. While Ethernet doesn't have the strict control of scheduled messages versus unshceduled messages the raw speed of the link plays to your favor.

Keith

ControlNet is deterministic and features built in redundacy (don't have to use it) so there are some advantages if devices on the network have to receive/write data at precise intervals.

For I/O control I would use ControlNet only.
ControlNet is 100% deterministic, reliable and in reality is less expensive than Ethernet.
For Ethernet I/O add cost of:
- Separate cable infrastructure from IT networks
- Expensive Industrial Switches
- Addtional cost of making networks noise immune

But Ethernet is prefered for HMI and data collection.

I am in 100% agreement with Contr_Conn.

ControlNet is hands down better for I/O.

Determinism being key to reliable control quite often.

The raw speed and connectivity of 100mbt Ethernet makes it the winner for HMI and Data Collection.

It can be argued that Ethernet can be quite deterministic if a dedicated network is used for I/O and I/O only. This is true and it does become somewhat deterministic. The traffic is still 1st come 1st serve though, and the higher cost of multiple Ethernets rules it out for I/O IMHO.

RSL and Contr_Conn

Due you classify IO as chassis to chassis? I think you do but want to know for sure.

I am referring to actual I/O data from another chassis and I/O related Produced/Consumed tags from another chassis.

Information that is event triggered or not time sensitive should still be messaged on demand. I think either network can handle messages, although Ethernet has a lot more bandwidth and is faster.

No, it is not as cut and dry as chassis to chassis. It all depends on the nature of the data and it's use to me.

In a lot of applications you could select either and never have a problem. You will eventually have a disapointing integration if you choose at random without considering all the variables.

How is that for muddy water?

RSL said:

I am referring to actual I/O data from another chassis and I/O related Produced/Consumed tags from another chassis.

Information that is event triggered or not time sensitive should still be messaged on demand. I think either network can handle messages, although Ethernet has a lot more bandwidth and is faster.

No, it is not as cut and dry as chassis to chassis. It all depends on the nature of the data and it's use to me.

In a lot of applications you could select either and never have a problem. You will eventually have a disapointing integration if you choose at random without considering all the variables.

How is that for muddy water?

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Fair points. Your right, must consider the application.

Heres a question I pose then.

Basically ControlNet is better for faster time critical applications ie bottling plant, while Ethernet is sufficient for non time critical applications. Most of the plant I work at is controlled by DCS which takes around a second for changed to be registered on the SCADA. Using this as a guide I think Ethernet is ok for our applications. Chassis to chassis communications will be in the same cabinet.

I have seen both used on large scale projects with success.

The main advantage of Ethernet is that currently it does not need scheduling. The next advantage is that all devices can be on the same subnet.

Disadvantages...not cheap to do properly and LOTS of cable running back to your switches. Plus performance is pretty much determined by the switches and how well they are set up.

Controlnet is just one cable. The rules are very straightforward and performance is strictly determined by how you schedule it. Media redundacy is very straightforward.

Disadvantages...need to schedule any new devices.

Overall I vote with the others. ControlNet for IO unless some significant consideration compels an Ethernet solution only.

Actually on one job I used ControlNet for the HMI as well with perfect success. The spec demanded redundant media for the HMI network and it turned out MUCH cheaper to get a couple of 1784-PCIC cards than implement all the palaver necessary to get a true Layer 3 redundant switches setup.

I ust want to add example to other comments that transferring 1 byte information throw ControlNet is much faster solution than using 100Mb Ethernet.
There is huge differnt if packet sizes.

m2c

ControlNet for I/O and ethernet for HMI. This will insure the IT people stay out of the process. Sometimes they think they own ethernet and its components.

RSL and Contr_Conn
Due you classify IO as chassis to chassis? I think you do but want to know for sure.

Click to expand...

I classify I/O as scheduled connection, no matter if it is a real Input/Output or internal data (Prduced/Consumed)

This will insure the IT people stay out of the process

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This is very important to keep IT as far as possible: as soon as IT sees CAT5 cables and switches they want to take control of it.

I understand, that scheduling of the ControlNet looks scary, but if you did it few times - you definately change your mind.

One thing to remember: You can't add any CNET I/O witout taking whole network and all controllers down!

I find the fact that you have to put all the controllers in program mode and shut down the system in order to re-schedule it to be THE MOST annoying part of ControlNet. If you could reschedule on the fly with a few disclaimers about dropped connections etc. it would be wonderful.

I don't see that happening, or it already would have.

I agree once you schedule a network 3 or 4 times it really is no big deal.

Rescheduling is also required if you add or change any produced/consumed tags and I agree that this is the biggest drawback with ControlNet. On the positive side, however, I like the fact that bandwidth is always reserved for non-scheduled (ie SCADA) communications regardless of the amount of scheduled traffic.