A sensor system (100) includes a reader (150) with a sensor unit (155, 156) and an accommodation Space (151) for an exchangeable cartridge (110). The cartridge (110) is held in the accommodation space (151) by at least one contact element (111) which has an increased thermal resistance and/or a contact area of reduced size. Thus a more homogenous temperature distribution can be achieved within the cartridge (110), reducing distortions which might adversely affect optical measurements.