Whether or not to bring a magnetic cylinder how to distinguish?

What is the difference between the cylinder with or without magnetic? If there is a magnetic, so what is the advantage? A: do you want with magnetic cylinder, the main is to see whether the actual need. If is magnetic, the piston in the cylinder with a magnetic ring. At this time, can be installed outside the cylinder a magnetic switch, so that the cylinder during movement, can be achieved by magnetic induction electrical signals are given, which can make the PLC control.