The invention provides for a method of determining a cartridge type (320) with a fluid drug injection system (300). The fluid drug injection system comprises a pump (301) configured for receiving a fluid drug cartridge (100). The fluid drug cartridge comprises a barrel (102) filled with a fluid drug solution (104). The fluid drug cartridge comprises a plunger (106) within the barrel. The plunger is configured for forcing the fluid drug solution through an outlet (110) of the barrel. The pump comprises an actuator (122) for actuating the plunger to force the fluid drug solution through the outlet. The fluid drug injection system comprises a force sensor (128) for measuring force data (314). The force data is descriptive of the force applied to the plunger by the actuator. The method comprises: moving (400) the actuator to contact the plunger or move the plunger； measuring (402) the force data using the force sensor； determining (404) a feature signal (316, 700, 1102, 1300, 1500, 1700, 900) from the force data, wherein the feature signal is descriptive of a force modulation, wherein the feature signal is a characterization of any one of the following: a force modulation amplitude, a force modulation duration, a force modulation number； and assigning (406) the cartridge type to the fluid drug cartridge using the feature signal.
