I want to know how to go about interfacing an off the shelf PLC with a vendor PLC like Honeywell, Siemens, Rockwell etc and collect the displayed data into my PLC and transmit it to a remote location. What do i need to do to achieve this?.
It isn't clear why you need an additional PLC to collect data from existing PLCs for re-transmission to a remote site. What is the data used for at the remote location? Real-time control ? Data storage (history) ?
The task of data collection from PLCs is frequently done by OPC servers, which can be purchased with a variety of drivers that talk directly to the PLC(s).
An OPC client, typically a background component of HMI software, is used to store data or to write it out to other devices. HMI software, by definition is used to display data. Nowadays, a common platform is a Windows box that runs the HMI software and an OPC server. The Windows haters on this forum will be sure to tell you how to accomplish it with other operating system platforms.
In fact, the nature of your question indicates that the tasks involved are not very clear to you, so I'd suggest that you locate a 'systems integrator' who does these sorts of things. Otherwise the learning curve can be very, very steep and implementation time very, very long.
I suggest using a gateway that can communicate to all the PLC's that you have at present and to your remote location. Try www.fieldserver.com for a list of drivers and the hardware.
Typically patience and money, both in large measure. I'm not sure what you mean by OTS and vendor, but with with few exceptions the vendor uses an OTS plc. The problem is going to be that you will most likely need to add to the program to communicate with another plc even if they are the same brand. And between brands it can range from doable to nearly impossible, by intent. If you need to ask this question, I think you will find it far more difficult than it should be.
PROFINET provides an easily configurable method for PLC-to-PLC communication across different brands of PLC. This method is called Component Based Automation (CBA). A good starting point for additional information is http://www.us.profibus.com/wordpress/?s=cba
