An Injection Device Adapted to Detect Air in a Cartridge

A drug delivery device (100) for estimating the amount of free air in a cartridge (1) comprising a cartridge receiving portion (not shown) adapted to receive a cartridge (1), the cartridge (1) comprising a body portion (6), an axially displaceable piston (5), and a distal outlet portion (4), an expelling assembly comprising an axially displaceable piston drive member (10) adapted to interface with the proximal piston (5) portion of a received cartridge (1), the piston drive member (10) is adapted to be moveable in a distal direction, and to thereby pressurize the drug in a received cartridge. The drug delivery device further comprises means for measuring and acquiring a property relating to a fluid pres-sure of the drug in a received cartridge (1), and where the property depends on the amount of free air (7) contained in the cartridge (1). The drug delivery device further comprises means (20) for measuring and acquiring the position of the piston rod drive member (10), and means (40) for measuring and acquiring the time. The drug delivery device further comprises means (30) for storing, and means (31) for processing the acquired measurements. The processing means are configured for estimating the amount of air (7) in the cartridge (1).