Ethernet or Serial port

Which do you guys prefer to communicate with PLC's and HMI's Ethernet or serial port? At my new job that I went to several months ago I found that everything is on ethernet. totally new to me since I cut my teeth on the serial port. All the guy's made fun of me when they found that I never really used ethernet to communicate before, and they all said there was never a need for the serial port here. I found that they was wrong... I ran into a situation when I needed my serial port and it saved the day. I have to admit I really like the ethernet because I can connect to the network from home and solve issues with out going in, not to mention I am able to VNC into any of the touch panels as well, which is pretty cool. I am fairly new to programming and have really only been messing with code for about a 1 1/2 years now, and man have I came a long way. Can anyone give any examples where an ethernet connection would be useless over the serial port? I welcome another opportunity to get my own laugh... Of course the joke is always on the new guy

If you are only driving a screen off a PLC serial is more than adequate. A lot cheaper too. If you are driving several screens from a/several PLCs Ethernet is the go unless you have a prorietary network that is being used as peer to peer communications and will drive the screens. Proprietary is my preferred option over Ethernet for peer to peer.

Hey

All our panels communicate to PLC's over MPI or Profibus.

We do not have panels on ethernet. So, for downloading to a panel, we need to connect to the panel over MPI/PROFIBUS or SERIAL. And mostly I use Serial.

When you download to a new panel, and u want to use MPI/PROFIBUS to download to, then u need to enable that channel. Serial works allways and you never need to trouble shoot. Ethernet is the future, that's true, but not yet @ our plant.

we have a on a machine 4 MP277B panels and 3 PLC's, they are all connected on MPI, a little MPI network. The panels can connect to each PLC by using 'Change Connection', with ethernet we could've used the ethernet possibillty to overtake other panels, but we didn't.

Ethernet, all the way. Several reasons:

-- Standard cabling, and interface components, even from local office supply stores.
-- Easier to test
-- Much higher bandwidth, so can handle much more data.
-- Getting everything on one network allows for one cable connection from a PC to program, upload, download and backup any HMI or PLC on the network.
-- No swapping serial cables to DL and HMI change then make a PLC change.
-- Many PC's are now coming without serial ports.
-- Ethernet provides a ready means of connecting to Enterprise systems and/or simpler data collection systems
-- Ethernet allows for the connction of multiple HMI's/PLC's easily.
-- Ethernet can easily (and inexpensively) go wireless (though I don't advise that generally for control applications)
-- More and more devices are supporting ethernet capabilities

Just a few reasons off the top of my head.

I do not have a problem communicating with screens over serial from a network with my favourite brand as it has a pass through function to the screens.

I use a token ring based network - no crashes. Throughput at 2 megs is about 22ms for heaps of data plus Citect is dragging 15,000 digital and 150 word reads per second - not bad for slow speed of 2 mbaud over a twisted pair. The network is smart and additional tokens are issued if it gets busy.

I also use bluetooth serial ports. If the PLCs are networked, one can access all PLCs via the bluetooth serial port and then the network. If they are not networked (quite often with generator systems as they usually require stand alone) I can still communicate with up to 7 PLCs via bluetooth serial ports at the same time and still have the pass through function available via serial to the HMIs.

I do not need Ethernet and with bluetooth serial ports running at 115kbaud, I still have very good speed communications with the PLCs and screens without any cables. I have had 4 PLCs direct connected and another 2 that were networked connected via bluetooth and all on line to my laptop at once - a total of 6 PLCs via 5 bluetooth serial ports - and I was out in the carpark of the building where we were working - about 40 metres away from the control panels. No one knew what I was doing - I was doing plenty. BLUETOOTH ROCKS - NO CABLES!!!!

I like Ethernet, almost anything can be put on it.
My system has about 30PLC's on one network connected to a SCADA system that I/contractors can dial into. I don't like the security that I have as it isn't easy to regulate who has access from within the various contractors.
BobB with the bluetooth what security is there?

Anyone have any ideas on providing a secure site for remote access. I am running AB and Siemens PLC's. SCADA is a customised system that runs Kepware for comms.

Security is excellent. The bluetooth dongle in the laptop USB port will talk to anything. However, each bluetooth serial port is pre-programmed from the laptop serial port to be in discover mode. Each bluetooth serial port is programmed with a password. The bluetooth devices are then "discovered" and "pair locked" via the password to a com port number.

At the moment I have 5 of these things and each bluetooth serial port is pair locked via password and serial number to comm 6, 7, 8, 9 and 10. Comm 5 is reserved for the bluetooth USB dongle. Each device has the comm port number clearly marked on it so I know which comm port number is in which PLC.

These devices will only run with comms settings of 8, 1, N and can be programmed to run at any baud rate up to 230 kbaud. These comms settings are fine for Omron as their "Toolbus" protocol runs 8, 1, N @ 115kbaud maximum speed.

The other requirement is that there has to be power available on, I think, pin 9 of the serial port you plug into. This suits me as Omron have this available. Otherwise a separate 5VDC power supply is required to plug into the bluetooth serial port to drive it. I have that available also for SOME of the older Omron PLCs that do not have 5VDC on pin 9.

When programming the device, for example, on your laptop, the 5VDC is obtained from a lead that plugs into the laptop USB port to power the device.

I guess these devices will not be suitable for everyone and all PLCs but boy I am glad they suit Omron!

The main network I run peer to peer is Omron Controller Link, it is token ring based. I use it for programming, peer to peer comms and also for SCADA, mainly Citect. I believe Wonderware also have an Omron FINS driver available for use with this network and Omron FINS Gateway middle software. Ethernet also works with the same middle software and so does serial. This enables online access to the networked PLCs by the SCADA and the programming software at the same time with all devices online to both sets of software. Just put the programming software on one section of the screen and the SCADA on another, change the program and see an instant change in value on the SCADA screen.

With the bluetooth serial ports I can still access all PLCs on the network from my laptop with the SCADA still quite happily accessing all PLCs at the same time using the same network, whether it be Controller Link or Ethernet, from a different interface point.

Hope this helps but do not know if these devices will work happily with either AB or Siemens due to the 5VDC supply reqirement or the comms settings that the devices can handle.

Siemens seems to be a bit cranky and slow with respect to comms, particularly serial. The last time I used one on MPI it was pathetically slow and would only run @ 38.5kbaud max. We switched it to Ethernet to get some speed but comms performance was still much slower than I am accustomed to with Ethernet, in fact not a lot quicker than my normal serial interface when one considers the Ethernet was running @ 100 megs.

Have not tried AB for some time and certainly not Control Logix. I hear comms to these are pretty quick and one day may get to try one.

Despite my dislike for Ethernet, I sometimes have to use it. Usually to a SCADA system. I usually just use 1 Ethernet card in 1 PLC and run Controller Link as my peer to peer network. Everything is placed on the network and can be picked up in any PLC with the same address number as exists in the originating PLC. Makes it easy to then program the SCADA to pick up from the Ethernet port in the "access" PLC.