Richard,
i suppose you want to seperate alpha-chars from others.
Find attached file that may serve your task.
Maybe you have to modify it.
It's not clear to me what means "find the 3 first letters"
I found basics of this program in a book, that says:
"Jeff Kodowsky - founder of LabVIEW - suggested something
like this at a fair".
Happy WireWorks
Manfred