By saying personal card I mean RFID card. For instance the Zipcar car-sharing service uses RFID cards for locking and unlocking cars and for member identification. So "logging in" means that the terminal identyfies a specified USER (this information is saved and sent to special software on the company's computer in order to control fuel distributed and prevent thefts, the pump power is on and you can start refueling a vehicle. Is that any understandable?
OK, thank you so much so could I say: "in order to start refueling swipe the USER card."?
Can I also say then: "The amount of fuel taken by the user is displayed in the middle of the terminal's screen."?
Since "you" don't do anything (there's a private conversation between the card and the pump), it seems to me you need something like:
"You must allow the pump to read your card before you can refuel."
"The pump has to read your card before you can refuel."