Hello,
you could use an if - then construct and test the existance of the channel with the cno() Function.
Cno("Speed") will giv you the number of the speed channel - if it exists. Otherwise the function will return 0.
If you do not know the channel name and would like to check for the number, use the variable globusedchn to find out how many channels are allocated at the moment.
regards
Ingo Schumacher
Systems Engineering Manager CEERNational Instruments Germany