Extreamly new to PLCs 1

[Todd15]

Hi I am a brand new chemical engineer, I graduated 4 months ago. I need some help with getting my head straight about PLCs. I work for a very small company and we are designing our first new unit (the current unit is 15 years old). One of my tasks is figuring out what type of control system to use.

The system needs to display several temperature, flow, pressure, conductivity,level and pH measurements (about 35 in total). The unit does not require a lot of automation, there will be level control on three tanks (on/off solenoids) a few control valves for flow, temperature control through 3 heat exchangers (control valves). Some of the process is manually controlled.

My confusion comes in selecting a control system. I have looked at Honeywell, ABB, Siemens, Omron and Redlion. Redlion has the ability to connect to the internet via a cell phone network (which is extremely important) but I'm confused about if Redlion's system is considered a "PLC". It offers an HMI (touch screen also important for me) and a modular control system that has I/O, PID and digital modules which seems like all I would need for our process. Do I need to buy a PLC (not even 100% sure what a PLC is for) from another company or is the Redlion control modular system enough for our requirements.

 

[danw2]

Go for it.

It sounds like it does what you need it to do. It sounds like it has the I/O, control, HMI and connectivity you need. What do think a 'PLC' is going to add to what you've already listed?

What you haven't mentioned is whether the Redlion device will log data that you can get access to. Historical process data is usually important at some point or another in a project or operation.

Dan

 

[Todd15]

Looking through the Red Lion spec sheets it said it can be connected to a PLC and it listed all the supported drivers for PLCs made by other manufacturers. It got me wondering if I needed a PLC on top of the RedLion modular control unit and HMI. My boss told me we should go with a PLC or a DCS but I'm starting to wonder if I really need one or perhaps the Redlion system is considered a PLC (or perhaps I'm just confused).

I guess a question that might solve my confusion would be, what is the difference between the RedLion process control

http://www.redlion.net/Products/ProcessControl/ModularController.html

and a PLC controller such as the SYSMAC CS series

http://www.ia.omron.com/product/family/9/index_fea.html

or the siemens S7 PLC controller?

 

[itsmoked]

Very hard for us to say for you...

I have no knowledge about the Red Lion controls but they look pretty impressive.

Twer me, I'd get a sales rep in for the RL stuff and try to learn more.

I think you have a good start and should now be able to start looking at how to do your project with a PLC and with a RL unit.

Let me back up.. As an engineer you need to look around and see what's out there that might do your task. Once you have gathered enough knowledge to think X or Y might work for you, you need to start thinking about how EXACTLY you would do the job with X or Y. You want to note each different type of issue you will be required to handle, then look at X and Y to see how to implement it in each controller.

An example would be the PIDs. How exactly would you do one in X and Y. How would the constants be adjusted?

Going thru this methodology you will come to obstacles. You then need to ask users/sales how to hurtle those obstacles.

Going thru this process gives you confidence that there won't be any surprise show stoppers, as you will have looked at all the major functions you need to handle.

Often, half way thru you may hit a brick wall. It's better to do it now before you own a bunch of very expensive hardware..

You also have to weigh your boss's "get a PLC" comment. If you run out and get the RL without a high level of confidence, reached thru the aforementioned process, and have a surprise, or worse a show stopper, you could be looking like mud.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rfischer85]

A PLC (or Programmable Logic Controller) is just a computer. They have their own programming language. And are basically the direct replacement for large numbers of physical relays, timers, coils, etc.
As itsmoked mentioned, you'll want to talk to the sales reps. to get a full breakdown of it's capabilities. But another good bet would be a local automation company. They should be able to look at your requirements and recommend the best solution. They will also be able to assist with programming issues. If you can't find one, talk to local electrical supply distributors. They most likely have a client in that field.

 

[FrancisL]

Finding a local automation company is a good idea, try searching here

http://www.controlsys.org/index.htm

And here

http://www.controlsys.org/find/search.htm

Or search for control systems integrators
They will provide some free advice before they start to charge.
Francis

 

[Kiljoy]

Be cautious when a vendor says that you can connect to a PLC via cell phone. We’ve been investigating this for several months. There are often hidden carrier fees, and not everyone is setup to do it. You also need third party software to make the connection. I’ve seen the red lion stuff. Make them come in and prove that they can connect via cell phone. Chances are they can transmit statistical information, but you will not be able to go on line and make changes to your PLC program via the cell network.

Also, red lion is kind of new to the PLC world. You may want to try some of the old standbys like AB, Siemens, and Omron.

 

[amptramp]

I would offer specifying a control system is not a basic task. Choosing a PLC adequate for the control system design requires experience. No disrespect intended but I am not sure a young Chem E has the skillset required to design a control system - let alone choosing a PLC. Get some appropriate help!

 

[jeezlouise]

Yeah, what amptramp said. Unless of course, you have time and money to burn. It's no disgrace to get appropriate help but it's just plain dumb to forge ahead hoping for the best. It always seems that there is never enough time and money to do it right the first time, but there is always time and money to do it over!

 

[PLCMentor]

Todd,
First realize that no control system ever goes in as initially conceived. You may not think there is much control, but as you move further into defining your system you may find otherwise. Your fist step should be to put together a document that defines what the system is supposed to do. Pass it around and let everyone involved chew it up. At the end of that process you will have a pretty good idea of what the system is really supposed to do.

Second if you don't have an existing control system to go off of then you need to do a little research. If you have existing controls then you need to have a good reason to be looking at something else that will cause your maintenance and other associated people to have to train on a new system. You need to take into account that Allen Bradley owns the US PLC market - Siemens owns the international market. That is important. Find out what the support level is in your area for different systems. Your local support will be very important. Not just the sales team, but local integrators and engineers that are familiar with the systems.

Third, Red Lion makes a great HMI. I dont even know if they have a PLC, but that is not their strength. It sounds like to me that you need a SCADA system to allow for proper data logging of your variables.

Finally, find someone to help you on your first project. You will not find a book or be able to train up to the point of putting together a quality system. It takes time to understand all the little things that go together to make a good control system. Lots of people can make it work, but will it interface with other systems as needed or will it be expandable, or will it be maintainable?

Russell White

Russell White, P.E.
Automation Technologies, Inc.

http://www.AutomationNC.com

Automation Help

http://www.PLCMentor.com

 

[jdenison]

Hey take a look at some modular Allen bradley PLC's and do some reading it sounds to me you could benefit here. These will also offer room for future expansion. Modicon can also offer you some expansion and do what you need. I dont want to push any product but these have been very useful for us.

 

[CcanDo]

The application may allow for using a programable relay. Or, subject to future expansion options, more than one programable and an inexpensive processor that could ultimately be used for data storage, partial or full control and etc.

Also, a modulized method allows for creating competitive vendors, programing, training and marketing. Your flow chart (mission) will change from time to time. Economics for changing a complex system/program vs. a module system can defeat the complex system due to over budget resources, time and effected periphials. Then comes debugging !!