Beginner question: PLC suitable for this project?

Hi,

I don't know a lot about PLCs but need a controller capable of switching 6 outputs to a closed state for a variable specified time period based on output from a pc RS232 port.

Is a PLC is appropriate for such a task (with the right programming of course)?

We have an existing relay & interface board we designed and built for this purpose but it costs us too much to manufacture in small quantities and I am sure there is some sort of mass-produced controller out there able to perform such a simple task.

Can PLCs be programmed from a pc directly or is additional specialist equipment required?

Any advice would be greatly appreciated.

TIA

Owen.

It looks not so difficult for a PLC to fulfill your task. But please describe in detail.
Of course you can program you PLC from PC, what you need is only a communication cable and certain software.

Hope can help.

Basically I want to send an ID # (1-6) and a two-digit time in minutes (1-99) to the PLC and have it latch the matching output (1-6) to a closed state for the specified time.

Also, is it possible to supply input data to a PLC via USB or RS232?

Ok, sir.
Then I am sure that a very simple PLC can meet your request. And the program will not cost you so much time.

For the other question, I know that you can input data via RS232 for most of the PLCs. But for USB connection, I am sorry I don't know.
Can anybody tell us if there is some PLCs can use USB communication interface?

Excellent, thanks for your help.

Can you by any chance recommend a PLC that would cover these requirements?
Obviously I'll have to do some research now but if you have any idea of where to start that would be great.

Hi, friends.
It depends on your choose. In my country, we use SIEMENS, OMRON and AB a lot. Since your request is the very basic request for a PLC, believe me, almost all types of PLC can fit you.
So just find a vendor with strong support in your place, the support always can give you a good suggestion.

A PLC could do your job, but there may be alternatives that are better suited to your needs.
By the look of it, you already have a program that works on your PC, and you just need the IO.
Possibilities are:
USB port - See
http://www.jaycar.com.au/productView.asp?ID=KV3600&CATID=&keywords=usb&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

or go to http://www.jaycar.com.au/ and look up cat number KV3600

Another option that used to be common is an interface to a parallel printer port.

You could also try using Modbus, which is an RS 232 protocol and purchase an IO interface compatible with this protocol. Modicon has these, generally known as "Momentums", but other manufacturers supply these as well. See http://www.modbus.org/ for more info.

A final option could be to move your logic entirely to a PLC and remove it from the PC altogether. Since I don't know what you are actually doing, I don't know if this is feasible.

Just found this, an Aussie site too:

http://www.ar.com.au/~softmark/page32.html

yeah ,any PLC can suffice ur request...so choose a cheap one..good luck!
by the way,yfcarer,r u from tianjin?nice to meet u

How much is too much for the manufacture of your existing solution ?

Simon: because we are a small operation, sales come in small volumes and we can't afford to manufacture a large quantity in advance. I think a single unit costs us in excess of AU$500.
If it turns out to be cheaper it gives us the option of expanding the capabilities in the future and also lets me play around and learn to program these things

This project was not my own, but I agreed to look into a better solution and I've heard a bit about the capabilities of PLCs and having worked with simpler ready-made controller devices I thought I'd explore this option.

Doug: thanks for those links, checking them out now. The purpose of the system is to control solarium beds from a point-of-sale and appointment book system. Ideally the timing should be done outside the pc (our existing device does this). It is important that the relay stays closed for the specified time even if the pc locks up or is rebooted (the machine is running windows and not dedicated to this task alone).

Are the solarium beds controlled independently? Sounds like you could use a simple programmable relay and some switches, rather than delve into RS232 control from a PC. Programmable relays are suitable for the sort of small IO count, low flexibility requirement you have.

From a quick google, here is some general information about Telemechanique's range of programmable relays (available from Schneider Australia). These particular types are programmable from the keypad, no special software required.

Thanks, those sound like they might do the job as they have a timer capability, I'll check them out.
The beds are controlled independantly yes, all 6 can be running at once for different times.

Actually, this seems to be an application that might be perfectly suited to a very cheap micro, like Parallax http://www.parallax.com/html_pages/products/basicstamps/basic_stamps.asp

What are the implications of plc failure ?