Which PLC?

[Bill Simpson]

stupidav,

Sure would be interested in seeing a recent market share breakdown such as the one you mentioned.. Didn't have any luck searching for it however.... Any chance you could post a url for the mag or article??

 

[mwiskow]

Have you looked at Allen-Bradley ControlLogix processors?
They support multiple communication platforms on the same backplane,
as well as multiple processors. Communication between networked processors is easily accomplished.

With that being said, I agree with others who have responded to your inquest: Be sure that you have local support before chosing your hardware. Without it your control system is too vulnerable to downtime.

 

[stupidav]

I want to say it was automation world or control engineering, I haven't had any luck finding the artical yet but I will keep looking.

www.automationworld.com
www.controleng.com

Again I could be wrong but these are the two that I normally read.

 

[Jim Dungar]

More third party reviews

Here are some more world-wide "unbiased" reviews.

http://www.iainsider.co.uk/IAIOCT03.PDF
http://www.jimpinto.com/enews/sep11-2003.html#3

 

[tguclu]

It's getting clear

First of ally , i want to thank all of you for your answers.As JesperMp said , tunel auotmatin has several subsytems like ventilation , trafic contrl ,vms systems ,fire , telecontrol , SCADA , ligthning .

My comapny never wroked with PLC's . Firms like Koyo ,ControlLogic etc. dont give local support in Turkey so I have to by pass them.

From your posts i got that " stay away from S5 series" is taht right ? S7-400 series seems more useful .

About redundancy , I have a question. I thought that a redundant system gives hot back-up service .But JesperM's post has raides some questions in my mind ?

And what is " level of redundancy" ?

When I talk about redundant system I mean of to master PLC's.one is the actual performer and other is stand-by module.

When sth happens to master one ,stand-by takes the control without affecting the whole system.
And other " slave" PLC's don't have to know who is teh master ? Am I right?

Another question is ,ModBus depends of RS-232/485 connection.Through that , seems hard to make " a network" .

How about profibus ?

 

[Jim Dungar]

Modbus is a protocol. Networks can be created on many different mediums.

Now speaking for Modbus, the popular networks are:
RS232 over copper wires is limited in length to about 16 meters. RS232 over fiber optic or radios can be run for extremely longer lengths. RS232 can only have one initiating device (master) active at a time and up to 126 responding devices (slaves). This is not a prefered medium for redundant communications.

RS485 over copper wires is often limited to about 600 meters (some systems can be longer). In other respects RS485 is similar to RS232 except it is limited to 32 total devices.

TCP/IP can use commercially available network components for worldwide distances. TCP/IP can have multiple intiating devices active at a time. The number of responding devices is only dependent on the network bandwith. TCP/IP is the current preferred medium for redundancy.

I have had experience with Schneider (Modicon) Quantum processors in several systems requiring redundancy. One of the larger ones is a local power generating plant. There are 5 locations with hot-standby processors, all PLC racks have redundant power supplies. The communications network is Modbus TCP on a self healing fiber optic ring. The SCADA system has 8 computers running Wonderware software. The intial startup was done with the PLC hot-standby IP address swapping done in the SCADA system. At the first available shut down the IP address swapping was moved to the local network interface modules.

 

[JesperMP]

tguclu,

redundancy can cover several areas of the automation project.
Typically there are:
Control (the CPUs).
Supervision (HMI and their associated networks).
Actuation and sensing (IO and its associated networks).
Power supply (segmented into the above for Control, Supervision, Actuation and sensing).

The CPU redundancy will work as you have described yourself.

From your previous posting, I am guessing that you are searching for sub-suppliers for the control project:
Then what you have to do is to write a specification for the sub-supplier that he must provide a safe system according to international or turkish standards.
It is the supplier that must engineer the solution, including safety issues like redundancy.
The supplier must present to you HOW he will establish a safe system. The "only" thing you must do is to be able to understand what he presents to you.

 

[undercontrol]

Well, like I always say : Go for Unity Quantum Hot Standby, give u "more than 20 years hot standby experience".
What else?? Modbus, checked. Modbus Plus, checked. Profibus, hmmm checked too.

 

[parky]

Hi, Having been in the business for many years & programmed all sorts of plc's & Scada's I would not recomend any particular type but suggest you go for one of the main brands like Siemens, AB or Mitsubishi.
If your engineers are not very conversant with plc's I suggest make it all AB, the ethernet on the logix family is easy & if you use RSView (providing you don't need to much of a complex scada) the scada it will talk with all the plc's with little effort, I have currently been involved with a project that has 5 SLC505's a couple of Compact Logix, a micrologix 1500 & 12 AB powermonitors running on a factory wide network, also connected to this is a Mitsubishi q series via a Beijers E700 HMI with ethernet card & dual protocol (to patch data from the "Q" to one of the SLC's, & all this on RSView + RS linx, it works well even though we are logging to 23 different databases (rsview) 3 Access ones & 2 SQL ( on a seperate server) + 7 floating clients for viewing remotely
the RSlogix software is easy to understand & the rockwell site is great for sorting problems. Other Scada's are Ifix, wonderware or Factorylink (don't recommend Wincc).
Hope this helps.