fig1 shows schematically a temperature sensor means 1 according to one embodiment of the invention . the temperature sensor means comprises a thermally conducting layer 2 arranged to face the surface to be measured , a thermally insulating layer 3 attached to the thermally conducting layer 2 on the opposite side to the surface to be measured and a temperature sensor 5 provided between the thermally conducting layer 2 and the thermally insulating layer 3 and being completely surrounded on all its sides by either the thermally conducting or thermally insulating layers . the thermally conducting layer is a material with higher thermal conductivity than the thermally insulating layer . it could for example be a metal layer or a thermally conducting graphite or polymer layer . the temperature sensor 5 has a connection 7 through the thermally insulating layer to a control system . the thermally conducting layer 2 will improve the conductivity towards the surface to be measured and the thermally insulating layer 3 will decrease the influence from ambient temperature on the temperature sensor . in another embodiment of the invention the thermally conducting layer and / or the thermally insulating layer could be omitted fig2 a and 2b shows schematically two examples of a base station of a bioreactor system according to the invention comprising one and three temperature sensor means as described in relation to fig1 respectively . in fig2 a a base station 11 according to one embodiment of the invention is schematically shown . the base station to a bioreactor system comprises of course many more details but they are omitted in the description of embodiments of the present invention . in an embodiment the base station 11 comprises one temperature sensor means as described in relation to fig1 . suitably the temperature sensor means 1 is provided on an arm 21 as shown in fig3 . the arm is provided inside the base station 11 under a base station upper surface 13 . the arm 21 is provided such that the temperature sensor means can protrude up through an opening 15 in the base station upper surface 13 . this can be achieved by providing the arm 21 as a lever . the temperature sensor means 1 is then provided onto one end 22 of the lever 21 and if something pushes down onto the other end 23 of the lever 21 the temperature sensor means 1 will move upwards and protrude through the opening 15 in the base station . hereby the base station upper surface 13 also needs to be provided with another opening 16 for receiving a pushing means that will push the end of the lever opposite the temperature sensor means downwards . a tray adapted to hold a bioreactor and to be positioned onto the base station may comprise this one or more pushing means . another possible design would be to provide the temperature sensor means 1 on a resilient arm 21 which protrudes up through the opening 15 in the base station upper surface 13 but easily is pushed back if something presses on the temperature sensor means 1 from above . in fig3 an arm 21 with a temperature sensor means 1 is shown . this arm could be provided in the base station as described above either as a lever or as a resilient arm . in fig3 a communication connection 7 from the temperature sensor through the thermally insulating layer 3 is shown . in fig2 b a base station 17 according to another embodiment of the invention is schematically shown . in this embodiment three arms 21 comprising temperature sensor means are provided . hereby also three openings 19 a , 19 b , 19 c are provided in the base station upper surface . if the arms are of the lever type three openings corresponding to the opening 16 of fig2 a should also be provided . fig4 a and 4b shows schematically trays adapted to be provided on a base station according to embodiments of the present invention and the trays being adapted to hold bioreactor bags . the tray 31 of fig4 a can be used in either the base station 11 shown in fig2 a or the base station 17 shown in fig2 b . the tray 31 is adapted to hold a bioreactor bag and the tray comprises an opening 33 positioned to align with the opening 15 of the base station 11 of fig2 a and the middle opening 19 b of the base station 17 of fig2 b . suitably the opening 33 in the tray is somewhat larger than the temperature sensor means . hereby the temperature measurements will be less effected by the heaters that often are provided in the trays . when the tray 31 of fig4 a is used together with the base station 17 of fig2 b the two other temperature sensor means provided through openings 19 a , 19 c will not be protruding up through the openings because the tray 31 does not comprise corresponding pushing means for these temperature sensor means arms ( if the lever variant is used ). if resilient arms instead are used the temperature sensor means provided through the openings 19 a and 19 c will be pushed downwards by the tray 31 and not be used . the tray 41 of fig4 b can be used in the base station 17 shown in fig2 b . the tray 41 comprises two openings 43 a , 43 b to receive one temperature sensor means 1 each . in this embodiment the temperature sensor means 1 provided through the middle opening 19 b of the base station 17 will not be used and the temperature sensor means provided through the opening 19 a will protrude up through the opening 43 a of the tray 41 and the temperature sensor means provided through the opening 19 c will protrude up through the opening 43 b of the tray 41 . in this embodiment two bioreactor bags could be provided in the tray 41 . the openings in the trays 33 , 43 a , 43 b can in one embodiment be covered by a suitable thin film , for example a plastic film . this could be beneficial in order to keep any spillage in the tray . however this is not necessary . a control system of the bioreactor system comprises in one embodiment means for measuring the ambient temperature and means for compensating the bioreactor temperature measurement for different ambient temperatures . in an embodiment , the temperature sensor or sensors are provided in the base station instead of in the different trays . hereby the trays can be kept simple and without any need for calibration and electrical connections . it is beneficial to have all of these functions in the base station . this written description uses examples to disclose the invention , including the best mode , and also to enable any person skilled in the art to practice the invention , including making and using any devices or systems and performing any incorporated methods . the patentable scope of the invention is defined by the claims , and may include other examples that occur to those skilled in the art . such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims , or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims .