i need to capture the PLC data using the RS232 serial port and connect it to the computer.?

Question

the data that will be read from the PLC has to be stored in SQL using VB dot net interface.
after capturing the data onto the computer,will it be in ascii format? or
does PLC store data in Ascii format to be able to transfer this data directly onto the computer?

Answer 1

There are two ways togo :
1.) Cheap and slow (dev time) where you write a lot of the software and customize the PLC programs to continuously transmit ASCII data

2.) Expensive and Quick (Also the most robust) You spend thousands of dollars buying HMI/SCADA/OPC software. It will be the quickest solution to implement and be the most robust.

Method 1:
Depends somewhat on what brand of PLC you have but basically you have to have information mapped out in the PLC and write code which will transmit the mapped area.

You can write a program to monitor the serial port and receive the ASCII transmitted from the PLC. Once received you will have to break it apart back into the individual variables (DE-map it)


OR

Method 2:
You can invest in OPC software ( OLE for Process Control) (see link to ICONICS and search for OPC)

You would run an OPC server program on your PC which would Poll the PLC's connected to the PC. The OPC server software will then be able to serve out the polled data to various OPC clients such as HMI screens and Data loggers.

Answer 2

Yes, it's possible. I did it once long ago, but be advised that it is a very, very slow way to transfer data. If the computers have network cards, you could try an ethernet crossover cable instead.