Basic Device Net Question

Hello all,
I am new to using DeviceNet and have a few questions. I understand the concept of why the protocol exists but have never actually used it yet.

1. If I install something like 1769-SDN into a new AB Compact Logix system, can I then use it to communicate to another existing master system that talks DeviceNet?

2. Could my new CLX system with the card installed be a slave system where I send and receive bits and transmit some analog data values to the master system? (while doing its normal job of controlling the local instrumentation, pumps, etc)

3. Would this be relatively simple to setup a connection between DeviceNET memory locations and PLC controller memory locations such that I can then read/write values from my ladder logic?

Thanks for any advice or thoughts!

Why would you want to do ANY of that with DeviceNet?
Use Ethernet instead. It's faster, simpler and more reliable.

I agree. It is a requirement of a project I am considering.

Whatever you are quoting for time getting the network setup, triple your time estimate for that portion. Setting up a Devicenet network ALWAYS takes a lot more time than you think it will.

Good to know! Thanks! - after I get to know the customer a little better I will probably suggest Ethernet or probably good old hard-wired signals - in truth they don't really need a lot beyond some basic handshaking.

Hi
I am not a big fan of Ethernet my self, well not when it comes to reliable controls, I have spend to many hours trouble shooting systems where the customer has chosen to use a $ 50 hub from Walmart.

You might need a few extra hours setting up devicenet "true", but when it runs it rock solid

Holmux said:

Hi
I am not a big fan of Ethernet my self, well not when it comes to reliable controls, I have spend to many hours trouble shooting systems where the customer has chosen to use a $ 50 hub from Walmart.

You might need a few extra hours setting up devicenet "true", but when it runs it rock solid

Click to expand...

Ethernet is just as reliable. If you use cheap or incorrect parts on Devicenet it won't be reliable either.

Your bad ethernet experience was due to poor choices and decisons when purchasing components. That would hold true on any media or protocol.

Your statement makes no sense.

Bit_Bucket_07 said:

Why would you want to do ANY of that with DeviceNet?
Use Ethernet instead. It's faster, simpler and more reliable.

Click to expand...

I second this! I would consider trying to convince your client to go with Ethernet instead.

I have used DeviceNet for exchanging data between ControlLogix plcs before with one as a master and the other as a slave. Ethernet was not an option as this was on a site with 2 different customers and concerns over network security between the 2 meant an alternative had to be used. The DeviceNet links work perfectly and have been up and running on 5 lines for over 6 years now.

Hi

As states above yes you can connect plcs together over device net.
One of your cards will have to be set up as slave so it will then only be able to be connected to the master card. The master will still be able to connected to other items up to a total of 62 addressees including the master.
Now as for transferring real values you could * your values and then / in the master system As I have connected plcs like this I have never passed real numbers from 1 plc to another
I like device net as much as I like Ethernet but I think it does take a bit more getting used to it and also you will need rs network for devicenet

Donnchadh

The Plc Kid said:

Ethernet is just as reliable. If you use cheap or incorrect parts on Devicenet it won't be reliable either.

Your bad ethernet experience was due to poor choices and decisons when purchasing components. That would hold true on any media or protocol.

Your statement makes no sense.

Click to expand...

Very often i find the choice of ethernet equipment out of my hands, I can come with a list as long with good idea's but it's down to the customer, I agree with you if the connection was made directly between the two PLC's.(cross over)

But if it has to be true the customers network, I would push for another solution.

Holmux said:

Very often i find the choice of ethernet equipment out of my hands, I can come with a list as long with good idea's but it's down to the customer, I agree with you if the connection was made directly between the two PLC's.(cross over)

But if it has to be true the customers network, I would push for another solution.

Click to expand...

I'd much rather be faced with a failed Ethernet switch than with a failed DeviceNet network. There are relatively fewer people with the necessary technical expertise to maintain DeviceNet and there are more opportunities for failure in a DN network, in my experience.

Holmux said:

You might need a few extra hours setting up devicenet "true", but when it runs it rock solid

Click to expand...

Not in my experience. I've had entire Devicenet networks go down just because I nudged a cable slightly. The thing is, Devicenet works well until it doesn't. And then you have to spend insane amounts of time tracing problems. The only advantage to it is that a customer can't go to Wal-Mart and buy a $50 devicenet card like they can with ethernet, but at the same time it is VERY easy to improperly install a devicenet network and not have it cause a problem until years down the road.

The only problem with ethernet is it's compatibility with off-the-shelf retail parts and the fact that some customers see it as a way of avoiding spending money.

FactoryTalktotheHand said:

Not in my experience. I've had entire Devicenet networks go down just because I nudged a cable slightly. The thing is, Devicenet works well until it doesn't. And then you have to spend insane amounts of time tracing problems. The only advantage to it is that a customer can't go to Wal-Mart and buy a $50 devicenet card like they can with ethernet, but at the same time it is VERY easy to improperly install a devicenet network and not have it cause a problem until years down the road.

The only problem with ethernet is it's compatibility with off-the-shelf retail parts and the fact that some customers see it as a way of avoiding spending money.

Click to expand...

I can't help it, maybe it's from working to many years with Devicenet, i like it, regarding damages to cables any system will go down, but at least with Devicenet you can go up in cable size to match the environment, not that easy with Ethernet.

But the biggest advances I see using anything else than Ethernet is when I work on a system that is internally connected via a bus or Device net, I can do faultfinding in the complete installation remotely, without worrying what else has been added to the network since last time I was connected and with out having to have access to areas I don't want access to.

You are right about the customer saving on Ethernet equipment, even if they start out with the right equipment, as soon they have a problem they make a quick fix with hub they find in the corner of the workshop and we are back to square one !!

You know he first name they are going to mention when the system is down is not there own, be course they used a cheep switch !!!

Holmux said:

I can't help it, maybe it's from working to many years with Devicenet, i like it, regarding damages to cables any system will go down, but at least with Devicenet you can go up in cable size to match the environment, not that easy with Ethernet.

But the biggest advances I see using anything else than Ethernet is when I work on a system that is internally connected via a bus or Device net, I can do faultfinding in the complete installation remotely, without worrying what else has been added to the network since last time I was connected and with out having to have access to areas I don't want access to.

You are right about the customer saving on Ethernet equipment, even if they start out with the right equipment, as soon they have a problem they make a quick fix with hub they find in the corner of the workshop and we are back to square one !!

You know he first name they are going to mention when the system is down is not there own, be course they used a cheep switch !!!

Click to expand...

I can see your point. There are also security concerns moving from more industrial-only type networks to something more "Standard" like ethernet. Now you have the PLC network connected directly to the office network (and the internet), even though it's talking a different protocol and could be separated physically, the connection is still there and Ethernet/IP devices usually will talk some level of TCP/IP. So then IT has to get involved a lot more often, and they don't know PLCs and don't want to know generally. There are a lot of considerations for both Devicenet and Ethernet/IP for sure. Both networks will run great if set up properly, and both will fail spectacularly if they aren't. They tell us over and over that Ethernet/IP networks should be kept physically separate from administrative networks, with only a single gateway path between them. And yet people don't do it because in order to get the infrastructure set up in the first place, they need the IT department's blessing, which can be difficult to get depending on where you work.

But improper setup is improper setup. And I'd still rather troubleshoot an Ethernet network than a Devicenet network any day of the week. At least you can point to that cheap Wal-Mart router and say "this is the problem." I've had much more "ghostly" problems with DeviceNet. You touch a cable and the whole system will go down, but other times you can sit there wiggling it all day, even unplug nodes and plug them back in, and it will be just fine. My time with Dnet I've had a lot of intermittent problems, where something will happen but you'll be unable to duplicate it. Ongoing issues can take months, even years, to figure out because they happen so sporadically. But I think Devicenet's main problem is the connector hardware, especially the screw-clamp plug-in terminals. This is a terrible design and I wish they'd never have been used. Sure, there are better connection options, but a lot of devices don't give you that choice.