Concatenate strings should work or just use one string constant with multiple lines. The problem you're having could be that the instrument requires some sort of delay but without details on the instrument, only you or the vendor can answer that. Some instruments will have a queue and others won't. The other possiblity is that you need some kind of termination character between commands. This might be a carriage return for a serial instrument or the ; character for a GPIB one. Check the instrument manual or provide the make and model and maybe someone here has some experience with it.
