Abt PLC

Sir,
Whether PLC needs the new hardware other than ordinary computer.I am in need of reply imme.I am doing the final year project in real time systems.So,I need this.I need a kind help from u abt the PLC's
I heard that PlC requires new hardware which costs so much.Whether we can do it in Ordinary PC with ext card or a complete new hardware for PLC.
Thanking U

Urs
Anand.E

It is possible to make automation projects in innummerable ways. You should provide some more info on what you want to do -
What is the proces or machine doing ?
How many digital/analog i/o ?
Any "special" kind of control required (apart form "standard" logical i/o and sequence controls) ?
etc.

It is possible to make a home-grown control on a PC with VB, C++, delphi etc. (I personally do NOT recommend to go this way !).
It is also possible to use a socalled "soft-PLC" that resides on the PC.

In both cases you need some means to connect to the i/o.
This can be an i/o card that resides in the PC (typical for just a few i/o points).
Or it can be a communication card that connects to dedicated i/o hardware (typical for when there are lots and lots of i/o).

But you should also consider using a standard PLC. These comes in small and large sizes. Changes are that this is both the most economical and easiest way to go.

Anand,

Who said PLCs are very costly ??
Checkout www.messung.com
Messung PLCs are Indigenous,dseigned and manufactured in India so they are cheaper than other multinational brands.Also they have the largest market share in India so learning Messung PLC programming will help you to get a decent job after you complete Engineering.
I guess Messung XMP8-10 Micro PLC will be sufficient for your Final Year Engineering project.Tell Messung that you need a PLC for Learning purpose to get a good discount.They can even give you programming software free of cost as you are a student.
You can also give them my reference as i am ex-messung Employee.

There are many factors that go into the true total prject cost for automation. Hardware for the logic is one, and there a PC may be less expensive than a PLC, although many micro-PLCs are available for a few hundred dollars. You need to add I/O to the system, and there the PLC or remote I/O comparison is close to a wash. You need programming software for the PLC, but you need the programming language for the PC as well. Depending on the brand, PLC software can be a few hundred to a few thousand dollars.

You need to add the cost for designing a system. PLCs are well documented, commonly used, and wiring is simple. For a single process or machine you don't need communications with PLCs, but you do for your PC. I always have more trouble wringing out the communications networks on my applications than I do with wiring I/O or with creating logic.

Then you need to add programming cost - i.e. time. Ladder logic is hard to beat here, whether it is in a PLC or a soft PLC running on a PC. This is particularly true when it comes to de-bugging. The PLC software has lots of built in monitoring and de-bugging functions specifically designed to make this process simpler.

You need an operator interface for most applications, for entering tuning and time delays and displaying diagnostics messages. You get the hardware for this "free" with the PC, but you have to program it all. With a PLC system an industrial HMI (Human Machine Interface) often costs more than the PLC, but configuring data entry field, data displays, and messages is usually straightforward and fast, acessing the PLC registers directly in most cases.

You have to take maintenance and service into account. By design PLCs are made to be easy to service, and ladder logic programming can be analyzed and accessed by many people. With a PC using C++ or similar any one other than the original programmer has a tough time servicing the software.

Then there is the cost of downtime - lost production or efficiency when the system fails. An office PC in an industrial environment is doomed to a short life because of vibration, heat, dust, voltage spikes, and so on. PLCs are more rugged and built for the application. You can get industrially hardened PCs, or build protective enclosures for the PC, but by then your cost advantage is gone.

In my opinion, when you take the total life cycle cost of a system PLCs win hands down.

Anand,

I am sure you have no plans of buying a PLC however cheap. I don't know about Messung plcs, but from what I know PLCs are not cheap ( the most moderate one's cost something aound 25000/-, cheap for an industry but not for a student). And then there's the overhead cost of the communication cable and the softwares.

Whether PLC needs the new hardware other than ordinary computer ---Anand

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First thing PLCs are not the same as PCs. Click on the learn PLCS link on the top of this page. I am sure you have enough time to read atleast a few pages so that you know what a PLC actually is.

Whether we can do it in Ordinary PC with ext card or a complete new hardware for PLC. --Anand

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Yes Anand you can use a PC to work as a PLC. However, for that you would need to design an interface kind of circuit and also a program that enables your PC to read and understand LADDER DIAGRAMS (Alternatively, you can leave the convention and program your PC based PLC in some other way/language). You can find some construction projects in in old editions of 'Elector electronics' and 'EFY' magzines to give you a guideline.Chek out "Pico PLC", Elektor Electronics april 2003.

Last words: Advise your juniors to take a hint from you and start working on their projects now.

Rajan, XMP8-10 are good small PLCS, however, the website do not mention their price.

Micro-PLC Costs

Anand didn't identify his project scope, so we have no way of knowing how many I/O and what kind of system size he needs. However, you can be up and running with a full micro-PLC for the cost of many DAQ or external I/O cards. Try AutomationDirec.com for example. There you can get:

DL-05 120 VAC powerd PLC with 8 24VDC in an 6 24VDC out: $99.00
Programming software (Windows) for 05 and 105 only: $99.00
Programming cable: $29.00

Hours of fun learning PLCs: Priceless

I am sure you have no plans of buying a PLC however cheap.

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Why not ?? I guess he dont have to pay for the Hardware from his own pocket as he is doing final year engineering project.He can convince his Project Guide to buy one for the college so that other students can also get some hands on PLC programming experience.We had many Engg Colleges as our customers who enjoyed special discount on price.

But from what I know PLCs are not cheap ( the most moderate one's cost something aound 25000/-, cheap for an industry but not for a student)

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I dunno from where you came up with this figure ?? Its about $500 !!
No way dude ! They are certainly cheaper specially Messung Micro PLC.
When i left Messung in 1998 Micro PLC (10 DI + 8 DO) use to cost around Rs 10000 but i heard they are very cheap nowdays because of the compitition from Mitsubishi/Allen Bradley/Siemens.

Rajan, XMP8-10 are good small PLCS, however, the website do not mention their price

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I guess its because they dont want to attach a fix price tag to their PLCs like other multinational players in the PLC market do.Pricing is very flexible and compititive for OEMs and Bulk Users.Contact Messung for Pricing.