The thing you need first is a way for your computer to speak RS485. NI has a variety of boards and boxes that can handle that. The next thing you need is some description of how the Yokogawa controller is controlled. The PC Link, ladder, and MODBUS refer to protocols on the serial RS485 connection. I am familiar with Modbus on Eurotherm controllers, so that might be my first choice for this situation, but it really comes down to getting the commands and responses from Yokogawa. The command syntax will tell you what strings to send from LabVIEW (using VISA) and the responses will tell you what the response string you will have to parse will look like. As a general statement, you will format a string with temperature setpoints and send that with VISA Write, and then you will send some command to have the controller respond with current process value, current setpoint, or whatever you want to know. You will use VISA Read to get that string, and you will have to parse or convert that string into something meaningful to display or log. The Yokogawa manual should also tell you what to set up for parameters on the RS485 link such as 2 wire or 4 wire mode, baud rate, and so on. That stuff goes into the setup of the computers 485 device in MAX and the parameters for the VISA Open command that gets the serial port ready for use. This is all pretty plain vanilla for LabVIEW, if you can get the right info from Yokogawa.
Bart
