Hello,

I want to control a Keithley 2400 with a PLC Siemens S7200 via RS232. Does somebody know what comm cable can I use to send and receive data between both devices?

 

There are 2 cables to program/communicate with the S7-200 family:
6ES7901-3CB30-0XA0 SIMATIC S7-200, PC/PPI CABLE MM MULTIMASTER, FOR CONNECTING S7-200 TO SERIAL PORT OF PC, SUPPORTS FREEPORT AND GSM MODEMS.

6ES7901-3DB30-0XA0 SIMATIC S7-200,USB/PPI CABLE MM MULTIMASTER, FOR CONNECTING S7-200 TO USB PORT OF PC, FREEPORT NOT SUPPORTED.

The first one is a RS-232 to RS485 converter, and supports Freeport; this is the one you need for RS-232 commms. The second one is a USB to RS-485 converter; since it does not support Freeport mode, you cannot use it in your application.

How do you plan to communicate with the keithley unit once you connect with the appropriate cable? I personnally know nothing of this unit, but here is a link to S7-200 tips and tricks on communications. You will find there many links to MicroWin program examples you can use to start your application:
http://www.automation.siemens.com/microset/html_76/support/tipps/tt-kommunizieren.htm

Hope this helps,
Daniel Chartier