French to English Tech/Engineering Electronics / Elect Eng x-ray scanning

I'm translating a document explaining how an x-ray machine with a conveyor that supplies the items, sends its results to a PC monitor. But I'm not sure what "AU" means here. All I can think of is the chemical symbol for gold, but I don't see how that can be relevant. It can't be "at/to the" if followed by a preposition, right? Here are some examples:

Les messages de défauts majeurs s’affichent sur le XXX dans la fenêtre de défaut. La liste des messages possibles est la suivante :
• AU sur la ligne générale
• AU machine contrôle RX

And some examples I assumed were just "au=at the" but they could be different because it's all in caps:

Les entrées TOR utilisées sont :
GSK AU LIGNE GENERAL
PUPITRE AU PUPITRE DE COMMANDE
CONVOYEUR RX AU MACHINE XRAY
CARTER AU FACE AVANT MACHINE.

It's mostly the "AU sur" that's confusing me; and an error message saying simply "at the x-ray inspection machine". The rest most likely make sense if it's "at the". Thanks in advance!!