LabVIEW drivers - RKC CB500 controller

RKC CB500

Communication between LabVIEW and the RKC CB500 controller has proven to be quit a challenge. Difficult as it may seem, the information provided by RKC proofs to be accurate. The protocol uses common ASCII characters like 'EOT', 'ENQ' and 'NAK'. Using these characters it is possible to set up a driver with retry capability.

Principle

This driver uses a state-machine, which is a case-statement in which an executed case decides which case will be executed next.

The following cases for reading the process value can be recognized (in rkc read.vi):

• start conversation
• first request
• read first response
• check for errors
• send negative acknowledge
• send acknowledge
• read second response
• end conversation
• done

This sub-vi supports retries because it can send a 'negative acknowledge' or 'NAK'.

The following cases for writing the setpoint value can be recognized (in rkc write.vi):

• start conversation
• first request
• read first response
• check for errors
• end conversation
• done

This sub-vi does not support retries.

Downloads

rkc cb500.llb
The included rkc trial.vi both reads the process values and sets the setpoints of 2 RKC CB500 units. The process values are being displayed in two seperate graphs and the measured data can be logged to file

Remark

• The VIs have been made with LabVIEW 7.1 Professional Development System