with the reference curve shape 73 fig4 shows by way of example for the considered process of the interrelation of fuel heat flow and feed water injection 30 50 a possible determined reference signal 73 which is determined from the assumed model cf fig3 and the path parameters regarded as given as further illustrated in fig4 a dead band 76 is placed around the reference signal 73 it is thereby possible to be able to distinguish fundamental systematic deviations from measurement noise or other random fluctuations with a decoupling factor v initially assumed to be random the two extreme cases illustrated by the two curve shapes 74 75 may then occur if the decoupling factor v is initially selected as too great 75 and the decoupling circuit therefore too strong an undershoot then occurs and the curve shape 75 lies below the reference signal 73 if the decoupling factor v is too small 74 the calculated decoupling element has too low a decoupling strength and the amplitude of the actual signal characteristic 74 is greater than that of the reference signal 73 the rules determining when the decoupling factor v must be increased and when it must be reduced are then derived therefrom the real live steam temperature is outside the dead band 76 and the amount of the measured live steam temperature is greater than that of the model and the real live steam temperature and that of the model have the same sign the real.