Abstract: The invention relates to a modular measuring system (10) comprising at least one measuring location having sensors, at least one connection module (18a, 18b, 18c), which is provided at the measuring location and which is preferably located in a housing (20) and is used to connect sensors, at least one communications port to connect sensors and at least one input/output unit (12), at least one element that is provided at the measuring location and that has an identification code for the input/output unit one electronic module that is provided in the input/output unit, that is controlled on the basis of the identification code, and that is used for the functions of the I/O elements (14, 16) of the input/output unit. Defining the functions of the input/output unit by means of the identification code provided at the measuring location largely prevents improper operation of the input/output unit.