You would have to be more specific, as it would depend on the instrument and control applications. Broadly speaking, instrument cables are usually for extra low voltage (24v) for analogue/digital I/O, and often shielded: used for analytical, flow or level measurement. Control cables can be any voltage and used for equipment outputs (stop or start) and status monitoring (faults, running, etc). This is all in the context of a MCC or PLC. As I said, you would need to be more specific.