Introduction The need for locating the q = 2 or q = 3/2 rational magnetic flux surface position in real time for NTM stabilisation experiments in ASDEX Upgrade [1] has driven the development of a dedicated data acquisition system to achieve this goal. Measurements of integrated magnetic field from magnetic probes and flux loops and measurements of the currents flowing in the poloidal and toroidal field coils of ASDEX Upgrade make up the set of 100 measurements used with the CLISTE tokamak equilibrium code. This code reconstructs the magnetic flux surfaces in ASDEX Upgrade [2] and cannot be presently carried out in real time. For the real time control system, a function parameterisation algorithm is used to calculate the magnetic equilibrium [3]. This statistical analysis of randomly chosen equilibrium states generates 2 sets of matrix coefficients. The calculation of 95 equilibrium parameters and the magnetic flux surfaces on a 39x69 grid is reduced to the product of these matrices and a vector of 153 elements consisting of a second degree polynomial in the leading 16 principal components of a vector of 58 measurements. For NTM stabilisation, the mirror is steered to the position required to deposit ECCD power on the rational flux surface. This position will be calculated in real time by the control system from the spatial co-ordinates of the relevant rational magnetic flux surface provided by this dedicated data acquisition system [4]. A schematic diagram of these features is shown in Fig. 1.