Connecting to PLC through Internet

I'm currently trying to figure out a way to use the arduino so i can connect to a PLC through the internet. I need to go from the router to the arduino then through an RS232 cable to the PLC. I am currently using dial up modems and am wanting to eliminate that old technology. I can create a virtual com port on my computer and enter the IP address of the arduino.

First i would like to know if this is possible. I have the arduino uno and the ethernet shield. Going to buy a RS232 to TTL converter so i can connect the arduino and PLC.

If this is possible can anyone shoot me in the right direction as to how to talk to the PLC.
I have succesfully connected to the PLC using a serial ethernet sever but it is far to expensive to put in at all my locations.
Here is a link to what i have- Serial Sever

Thank you.

If the PLC has TTL inputs then an arduino with an ethernet shield might be affordable. The ESP8266 chips may be an inexpensive route to take. Banggood below has some chips that might be of interest.

http://www.banggood.com/buy/esp8266.html

I suspect, in their day, the dial-up modems cost more than that Serial Server you linked to.

If the PLCs are controlling something important and valuable maybe now is not the time for cheese-pairing.

Presumably if you connect via a dial-up modem the software at the remote end behaves much the same as if it was directly connected to the PLC (without the modem).

But sending data via the internet is very different. You will need software at the receiving end to interpret the messages and convert them into commands for the PLC. And somewhere in the scheme of things there will need to be a webserver.

Unless you are very good with programming, including web programming, I suspect this may be a job you should leave to a professional who can build and test a system that is as functional and as reliable as the present system.

My immediate inclination would be to use a RaspberryPi as the interface with the PLC - not an Arduino. But that does not in any way diminish the cautions I have already expressed.

An internet based system may also need special features to reduce the risk of damage by hackers as it will be permanently exposed to the public gaze in a way that your modem system is not.

...R

Thank you for your response. I guess maybe I am thinking this would be easier than what it actually is. I could set the com port on my PC to the arduino IP and connect to it using my ladder logic program that connects to it by COM ports. Just thought i could use the arduino as a bridge allowing me to connect to the plc.

Just not as simple as i want it to be.

Bhaan1:
I could set the com port on my PC to the arduino IP and connect to it using my ladder logic program that connects to it by COM ports.

That sounds like you want the Arduino to sit between a PC and your PLCs so the PC connects to the Arduino using the USB cable and the Arduino connects to the PLC via a serial connection.

You could certainly do that. But why not cut out the middle man and just connect direct from the PC to the PLCs with a USB-Serial cable.

I guess you need to explain more clearly exactly WHAT you want to do rather than HOW you think it could be done.

...R