If you can provide a list of people who have authorized access to your machine controls, then you are ahead of the game. If you can truly ensure that only the people on that list are accessing the machine and not sharing their credentials, then you are way ahead of the game.
Limiting access to the controls of a machine is certainly not a new concept. I see many organizations still using a mechanical key system for override or start up. According to multiple controls engineers, the main issue with that is people share, copy, and misplace these keys on a regular basis. In this case, just about everyone on the plant floor would have access to the controls of any machine.
Just about all of us carry a device that allows us to enter and exit our buildings. Whether it be a badge or a key fob, the technology is the same. RFID adds accountability to machine access control. For example: Jane, the team lead, has full authority to make changes in the control system. The production line comes to a screeching halt and needs to be restarted. In order to restart the machine, Jane has to present her RFID badge to a reader near the controls and she is then given access to make some adjustments within the machine. When Jane authenticates into the machine, the date, time, and Jane’s ID can be recorded. This adds full accountability to the controls and deters Jane from giving John her badge to let him restart the machine. If John makes unauthorized changes he makes them in Jane’s name.
Access control has become a popular solution in the last few years as machines have become more critical to operation. Like most RFID applications there are multiple ways to address this. The key is to select a vendor who has a core competency in the industrial space with knowledge of industrial control systems.